Papers for Tuesday, Jul 30 2024

In order to unravel the present situation of the PBH overproduction problem, our study emphasizes the critical role played by the equation of state (EoS) parameter $w$ within the framework of effective field theory (EFT) of non-singular bounce. Our analysis focuses on a wide range of EoS parameter values that are still optimal for explaining the latest data from the pulsar timing array (PTA). As a result of our study, the most advantageous window, $0.31 \leq w \leq 1/3$, is identified as the location of a substantial PBH abundance, $f_{\rm PBH} \in (10^{-3},1)$ with large mass PBHs, $M_{\rm PBH}\sim {\cal O}(10^{-7}-10^{-3})M_{\odot}$, in the SIGW interpretation of the PTA signal. When confronted with PTA, we find that the overproduction avoiding circumstances are between $1\sigma-2\sigma$, while the EoS parameter lies inside the narrow window, $0.31<w\leq 1/3$. We propose a regularized-renormalized-resummed (RRR) scalar power spectrum that is large enough to produce EoS dependent scalar generated gravitational waves compatible with PTA evidence, while satisfying the perturbativity, causality, and unitarity criteria, within the range of $0.88 \leq c_{s} \leq 1$.

The maximum energy of electrons in supernova remnant (SNR) shocks is typically limited by radiative losses, where the synchrotron cooling time equals the acceleration time. The low speed of shocks in a dense medium increases the acceleration time, leading to lower maximum electron energies and fainter X-ray emissions. However, in Kepler's SNR, an enhanced electron acceleration, which proceeds close to the Bohm limit, occurs in the north of its shell, where the shock is slowed by a dense circumstellar medium (CSM). To investigate whether this scenario still holds at smaller scales, we analyzed the temporal evolution of the X-ray synchrotron flux in filamentary structures, using the two deepest Chandra/ACIS X-ray observations, performed in 2006 and 2014. We examined spectra from different filaments, we measured their proper motion and calculated the acceleration to synchrotron time-scale ratios. The interaction with the turbulent and dense northern CSM induces competing effects on electron acceleration: on one hand, turbulence reduces the electron mean free path enhancing the acceleration efficiency, on the other hand, lower shock velocities increase the acceleration time-scale. In most filaments, these effects compensate each other, but in one region the acceleration time-scale exceeds the synchrotron time-scale, resulting in a significant decrease in nonthermal X-ray emission from 2006 to 2014, indicating fading synchrotron emission. Our findings provide a coherent understanding of the different regimes of electron acceleration observed in Kepler's SNR through various diagnostics.

The electromagnetic emission and the afterglow observations of the binary neutron star merger event GW 170817A confirmed the association of the merger with a short gamma-ray burst (sGRB) harboring a narrow ($5$°-$10$°) and powerful ($10^{49}$-$10^{50}~$erg) jet. Using the 1~second-long neutrino-radiation-GR-MHD simulation of coalescing neutron stars of Kiuchi et al. (2023) and following the semi-analytical estimates of Pais et al. (2023), we inject a narrow, powerful, unmagnetized jet into the post-merger phase. We explore different opening angles, luminosities, central engine durations, and times after the merger. We explore early ($0.1~$s following the merger) and late ($1~$s) jet launches; the latter is consistent with the time delay of $\approx 1.74~$s observed between GW 170817 and GRB 170817A. We demonstrate that the semi-analytical estimates correctly predict the jets' breakout and collimation conditions. When comparing our synthetic afterglow light curves to the observed radio data of GW170807, we find a good agreement for a $3 \times 10^{49}$ ergs jet launched late with an opening angle in the range $\simeq 5$°-$7$°.

LAMOST J235456.73+335625 (J2354) is a binary system hosting a $\sim 0.7~\rm M_\odot$ K dwarf and a $\sim 1.4~\rm M_\odot$ dark companion, supposedly a neutron star, in a 0.48d orbit. Here we present high- and low-resolution spectroscopy to better constrain the properties of the system. The low-resolution spectrum confirms that the luminous star is a slightly metal-poor K dwarf and strengthens the limits on any optical flux from the dimmer companion. We use the high-resolution spectra to measure atmospheric parameters ($T_{\rm eff}$, $\log g$, [Fe/H], $v_{\rm rot}\sin i$) and abundances for 8 elements for the K dwarf. We refine the mass of the compact object to $M_{\rm co} \sim 1.3~\rm M_\odot$ with a minimum mass of $M_{\rm co, min} = 1.23\pm0.04~\rm M_\odot$. The expected overabundance of intermediate-mass elements from the incident supernova ejecta is not detected in the K-dwarf atmosphere. This contrasts with known binaries hosting neutron stars where almost all companions show evidence for polluting material. Moving the neutron-star progenitor further from the K-dwarf at the time of explosion to minimize atmospheric pollution requires a finely-tuned kick to produce the current orbital separation of $\sim 3.3~\rm R_\odot$. Instead, we find that a massive white dwarf with a cooling age of $\gtrsim 3~$Gyr satisfies all observational constraints. The system likely experienced two common-envelope phases leading to its current state because the white dwarf progenitor was massive enough to ignite He-shell burning. The system will become a cataclysmic variable in the distant future when the K-dwarf evolves off of the main sequence. These short-period high-$q$ binaries represent an intriguing formation pathway for compact double white dwarf binaries and thermonuclear supernovae. An ultraviolet spectrum is the most promising avenue for directly detecting the white dwarf companion.

The chemistry of phosphorus (31P) in space is particularly significant due to the key role it plays in biochemistry on Earth. Utilising radio and infrared spectroscopic observations, several key phosphorus-containing molecules have been detected in interstellar clouds, circumstellar shells, and even extragalactic sources. Among these, phosphorus nitride (PN) was the first P-bearing molecule detected in space, and still is the species detected in the largest number of sources. Phosphorus oxide (PO) and phosphine (PH3) were also crucial species due to their role both in chemical networks and in forming biogenic compounds. The still limited high-angular resolution observations performed so far are shading light on the geometrical distribution of these molecules, which represent crucial insights on their formation processes. Observations have also highlighted the challenges and complexities associated with detecting and understanding phosphorus chemistry in space, owing to the low elemental abundance of P relative to other elements. This review article provides a state-of-art picture of the observational results obtained so far on phosphorus compounds in the interstellar medium. Special attention is given to star-forming regions, and to their implications for our understanding of prebiotic chemistry and the potential for life beyond Earth. Our knowledge of the dominant formation and destruction pathways of the most abundant species has improved, but critical questions remain open, among which: what is (are) the main phosphorus carrier(s) in space? Upcoming facilities will offer new opportunities to both detect new phosphorus-bearing molecules and enlarge the number of sources in which the chemistry of P can be studied. The synergy between observations, models, laboratory experiments, and computational works is mandatory to progress in this field.

The line intensity mapping technique involves measuring the cumulative emission from specific spectral lines emitted by galaxies and intergalactic gas. This method provides a way to study the matter distribution and the evolution of large-scale structures throughout the history of the Universe. However, modeling intensity mapping from ab-initio approaches can be challenging due to significant astrophysical uncertainties and noticeable degeneracies among astrophysical and cosmological parameters. To address these challenges, we develop a semi-empirical, data-driven framework for galaxy evolution, which features a minimal set of assumptions and parameters gauged on observations. By integrating this with stellar evolution and radiative transfer prescriptions for line emissions, we derive the cosmic [CII] intensity over an extended redshift range $0 \lesssim z \lesssim 10$. Our approach is quite general and can be easily applied to other key lines used in intensity mapping studies, such as [OIII] and the CO ladder. We then evaluate the detectability of the [CII] power spectra using current and forthcoming observational facilities. Our findings offer critical insights into the feasibility and potential contributions of intensity mapping for probing the large-scale structure of the Universe and understanding galaxy evolution.

Galactic outflows driven by star formation or active galactic nuclei are typically formed by multi-phase gas whose temperature spans over 4 orders of magnitude. Probing the different outflow components requires multi-wavelength observations and long exposure times, especially in the distant Universe. So far, most of the high-z studies have focused on a single gas phase, but this kind of analysis may potentially miss a non-negligible fraction of the total outflowing gas content. In this work, we analyze the spatially resolved rest-frame UV and optical emission from HZ4, the highest redshift main sequence star-forming galaxy having a detected [C II] outflow, which traces the neutral gas component. Our goal is to study the ionized interstellar medium in the galaxy and the properties of the ionized outflow as traced by the [O III]$\lambda$5007Å and H$\alpha$ emission lines. We exploit JWST/NIRSpec observations in the integral field spectroscopy mode to investigate the galaxy properties by making use of the brightest rest-frame optical emission lines. Their high spectral and spatial resolution allows us to trace the ionized outflow from broad line wings and spatially resolve it. We also re-analyze the [C II] ALMA data to compare the neutral atomic and ionized outflow morphologies, masses, and energetics. We find that the system consists of a galaxy merger, instead of a rotating disk as originally inferred from low-resolution [C II] observations, and hosts an extended ionized outflow. The ionized outflow is being launched from a region hosting an intense burst of star formation and extends over 4 kpc from the launch site. The neutral and ionized outflows are almost co-spatial, but the mass loading factor in the ionized gas phase is two orders of magnitude smaller than in the neutral phase, as found for other lower redshift multi-phase outflows.

JWST has recently discovered a subset of reionization era galaxies with ionized gas that is metal poor in oxygen and carbon but heavily-enriched in nitrogen. This abundance pattern is almost never seen in lower redshift galaxies but is commonly observed in globular cluster stars. We have recently demonstrated that this peculiar abundance pattern appears in a compact ($\simeq 20$ pc) metal-poor galaxy undergoing a strong burst of star formation. This galaxy was originally selected based on strong CIV emission, indicating a hard radiation field rarely seen locally. In this paper, we present JWST/NIRSpec observations of another reionization-era galaxy known to power strong CIV emission, the $z=7.04$ gravitationally-lensed galaxy A1703-zd6. The emission line spectrum reveals this is a metal poor galaxy ($12+\log(\rm O/H) = 7.47\pm0.19$) dominated by a young stellar population ($1.6^{+0.5}_{-0.4}$ Myr) that powers a very hard ionizing spectrum (CIV EW = 19.4 $\unicode{x212B}$, He II EW = 2.2 $\unicode{x212B}$). The ISM is highly-enriched in nitrogen ($\log(\rm N/O)=-0.6$) with very high electron densities ($8-19\times10^4$ cm$^{-3}$) and extreme ionization conditions rarely seen at lower redshift. We also find intense CIV emission (EW$\gtrsim20$ $\unicode{x212B}$) in two new $z\gtrsim 6$ metal poor galaxies. To put these results in context, we search for UV line emission in a sample of 737 $z\gtrsim 4$ galaxies with NIRSpec spectra, establishing that 40(30)% of systems with [OIII]+H$\beta$ EW $>2000\unicode{x212B}$ have NIV] (CIV) detections with EW$>5$ $\unicode{x212B}$ ($>10$ $\unicode{x212B}$). These results suggest high N/O ratios and hard ionizing sources appear in a brief phase following a burst of star formation in compact high density stellar complexes.

High-resolution spectrographs open a detailed window onto the atmospheres of stars and planets. As the number of systems observed with different instruments grows, it is crucial to develop a standard in analyzing spectral time series of exoplanet transits and occultations, for the benefit of reproducibility. Here, we introduce the ANTARESS workflow, a set of methods aimed at processing high-resolution spectroscopy datasets in a robust way and extracting accurate exoplanetary and stellar spectra. While a fast preliminary analysis can be run on order-merged 1D spectra and cross-correlation functions (CCFs), the workflow was optimally designed for extracted 2D echelle spectra to remain close to the original detector counts, limit the spectral resampling, and propagate the correlated noise. Input data from multiple instruments and epochs were corrected for relevant environmental and instrumental effects, processed homogeneously, and analyzed independently or jointly. In this first paper, we show how planet-occulted stellar spectra extracted along the transit chord and cleaned from planetary contamination provide a direct comparison with theoretical stellar models and enable a spectral and spatial mapping of the photosphere. We illustrate this application of the workflow to archival ESPRESSO data, using the Rossiter-McLaughlin effect Revolutions (RMR) technique to confirm the spin-orbit alignment of HD\,209458b and unveil biases in WASP-76b's published orbital architecture. Because the workflow is modular and its concepts are general, it can support new methods and be extended to additional spectrographs to find a range of applications beyond the proposed scope. In a companion paper, we will present how planet-occulted spectra can be processed further to extract and analyze planetary spectra decontaminated from the star, providing clean and direct measurements of atmospheric properties.

We introduce a unified approach that, given a strong gravitationally lensed polarised source, self-consistently infers its complex surface brightness distribution and the lens galaxy mass-density profile, magnetic field and electron density from interferometric data. The method is fully Bayesian, pixellated and three-dimensional: the source light is reconstructed in each frequency channel on a Delaunay tessellation with a magnification-adaptive resolution. We tested this technique using simulated interferometric observations with a realistic model of the lens, for two different levels of source polarisation and two different lensing configurations. For all data sets, the presence of a Faraday rotating screen in the lens is supported by the data with strong statistical significance. In the region probed by the lensed images, we can recover the Rotation Measure and the parallel component of the magnetic field with an average error between 0.6 and 11 rad m$^{-2}$ and 0.3 and 3 nG, respectively. Given our choice of model, we find the electron density is the least well-constrained component due to a degeneracy with the magnetic field and disk inclination. The background source total intensity, polarisation fraction, and polarisation angle are inferred with an error between 4 and 10 per cent, 15 and 50 per cent, and 1 to 12 degrees, respectively. Our analysis shows that both the lensing configuration and the intrinsic model degeneracies play a role in the quality of the constraints that can be obtained.

Precise spectroscopic classification of planet hosts is an important tool of exoplanet research at both the population and individual system level. In the era of large-scale surveys, data-driven methods offer an efficient approach to spectroscopic classification that leverages the fact that a subset of stars in any given survey has stellar properties that are known with high fidelity. Here, we use The Cannon, a data-driven framework for modeling stellar spectra, to train a generative model of spectra from the Gaia Data Release 3 Radial Velocity Spectrometer. Our model derives stellar labels with precisions of 72 K in Teff , 0.09 dex in log g, 0.06 dex in [Fe/H], 0.05 dex in [{\alpha}/Fe] and 1.9 km/s in vbroad for main-sequence stars observed by Gaia DR3 by transferring GALAH labels, and is publicly available at this https URL. We validate our model performance on planet hosts with available Gaia RVS spectra at SNR>50 by showing that our model is able to recover stellar parameters at {\geq}20% improved accuracy over the existing Gaia stellar parameter catalogs, measured by the agreement with high-fidelity labels from the Spectroscopic Observations of Cool Stars (SPOCS) survey. We also provide metrics to test for stellar activity, binarity, and reliability of our model outputs and provide instructions for interpreting these metrics. Finally, we publish updated stellar labels and metrics that flag suspected binaries and active stars for Kepler Input Catalog objects with published Gaia RVS spectra.

Context: Current exoplanet formation studies tend to overlook the birth environment of stars in clustered environments. The effect of this environment on the planet-formation process, however, is important, especially in the earliest stage. Aims: We investigate the differences in planet populations forming in star-cluster environments through pebble accretion and compare these results with the planet formation around isolated stars. We try to provide potential signatures on the young planetary systems to guide future observation. Methods: We design and present a new planet population synthesis code for clustered environments. The planet formation model is based on pebble accretion and includes migration in the circumstellar disk. The disk's gas and dust are evolved in 1D simulations considering the effects of photo-evaporation of the nearby stars. Results: Planetary systems in a clustered environment are different than those born in isolation; the environmental effects are important for a wide range of observable parameters and the eventual architecture of the planetary systems. Planetary systems born in a clustered environment lack cold Jupiters compared to isolated planetary systems. This effect is more pronounced for low-mass stars ($\lesssim$0.2 $M_\odot$). On the other hand, planetary systems born in clusters show an excess of cold Neptune around these low-mass stars. Conclusions: In future observations, finding an excess of cold Neptunes and a lack of cold Jupiters could be used to constrain the birth environments of these planetary systems. Exploring the dependence of cold Jupiter's intrinsic occurrence rate on stellar mass provides insights into the birth environment of their proto-embryos.

We present the results from an extensive follow-up campaign of the Tidal Disruption Event (TDE) ASASSN-15oi spanning $\delta t \sim 10 - 3000$ d, offering an unprecedented window into the multiwavelength properties of a TDE during its first $\approx 8$ years of evolution. ASASSN-15oi is one of the few TDEs with strong detections at X-ray, optical/UV, and radio wavelengths and featured two delayed radio flares at $\delta t \sim 180$ d and $\delta t \sim 1400$ d. Our observations at $> 1400$ d reveal an absence of thermal X-rays, a late-time variability in the non-thermal X-ray emission, and sharp declines in the non-thermal X-ray and radio emission at $\delta t \sim 2800$ d and $\sim 3000$ d, respectively. The UV emission shows no significant evolution at $>400$ d and remains above the pre-TDE level. We show that a cooling envelope model can explain the thermal emission consistently across all epochs. We also find that a scenario involving episodic ejection of material due to stream-stream collisions is conducive to explaining the first radio flare. Given the peculiar spectral and temporal evolution of the late-time emission, however, constraining the origins of the second radio flare and the non-thermal X-rays remains challenging. Our study underscores the critical role of long-term, multiwavelength follow-up.

We present the Lyman-$\alpha$ (Ly$\alpha$) and ultraviolet (UV) luminosity function (LF), in bins of redshift, of quasars selected in the Physics of the Accelerating Universe Survey (PAUS). A sample of 915 objects was selected at $2.7<z<5.3$ within an effective area of $\sim 36$ deg$^2$ observed in 40 narrow-band filters (NB; FWHM $\sim 120$ Å). We cover the intermediate-bright luminosity regime of the LF $(10^{43.5}<(L_{{\rm Ly}\alpha}/{\rm erg\,s}^{-1})<10^{45.5}$; $-29<M_{\rm UV}<-24)$. The continuous wavelength coverage of the PAUS NB set allows a very efficient target identification and precise redshift measurements. We show that our method is able to retrieve a fairly complete ($C\sim 85\%$) and pure ($P\sim 90\%$) sample of Ly$\alpha$ emitting quasars for $L_{{\rm Ly}\alpha}>10^{44}$ ${\rm erg\,s}$$^{-1}$. In order to obtain corrections for the LF estimation, and assess the accuracy of our selection method, we produced mock catalogs of $0<z<4.3$ quasars and galaxies that mimic our target population and their main contaminants. Our results show a clear evolution of the Ly$\alpha$ and UV LFs, with a declining tendency in the number density of quasars towards increasing redshifts. In addition, the faint-end power-law slope of the Ly$\alpha$ LF becomes steeper with redshift, suggesting that the number density of Ly$\alpha$-bright quasars declines faster than that of fainter emitters. By integrating the Ly$\alpha$ LF we find that the total Ly$\alpha$ emitted by bright quasars per unit volume rapidly declines with increasing redshift, being sub-dominant to that of star-forming galaxies by several orders of magnitude by $z\sim 4$. Finally, we stack the NB pseudo-spectra of a visually selected "golden sample" of 591 quasars to obtain photometric composite SEDs in bins of redshift, enabling to measure the mean IGM absorption by the Lyman-$\alpha$ forest as a function of redshift.

Strong emission from doubly ionized oxygen is a beacon for some of the most intensely star forming galaxies known. JWST enables the search for this beacon in the early universe with unprecedented sensitivity. In this work, we extend the study of faint [OIII]$_{5008}$ selected galaxies by an order of magnitude in line luminosity. We use publicly available UNCOVER DR1 JWST/NIRCam and HST imaging data of the cluster lensing field, Abell 2744, to identify strong (rest-frame EW$>500$Å) [OIII]$_{5008}$ emitters at $z\sim7$ based on excess F410M flux. We find $N=68$ $z\sim7$ [OIII] candidates, with a subset of $N=33$ that have deep HST coverage required to rule-out lower redshift interlopers (13.68 arcmin$^2$ with F814W $5\sigma$ depth $>28$ AB). Such strong emission lines can lead to very red colors that could be misinterpreted as evidence for old, massive stellar populations, but are shown to be due to emission lines where we have spectra. Using this deep HST sample and completeness simulations, which calculate the effective survey volume of the UNCOVER lensing field as a function of [OIII] luminosity, we derive a new [OIII] luminosity function (LF) extending to $41.09<\rm{log}_{10}(L/\rm{erg\,s}^{-1})<42.35$ which is an order of magnitude deeper than previous $z\sim6$ [OIII] LFs based on JWST slitless spectroscopy. This LF is well fit by a power law with a faint-end slope of $\alpha=-2.07^{+0.22}_{-0.23}$. There is little or no evolution between this LF and published [OIII] LFs at redshifts $3\lesssim z\lesssim7$, and no evidence of a turnover at faint luminosities. The sizes of these extreme [OIII] emitters are broadly similar to their low redshift counterparts, the green peas. The luminosity function of [OIII] emitters matches that of Lyman-$\alpha$ at the bright end, suggesting that many of them should be Lyman-$\alpha$ emitters.

A model of the TU Muscae binary system has been developed by a study of 23 SWP spectrophotometric images obtained with the IUE satellite telescope and downloaded from the IUE Archive. The images are well distributed in Keplerian orbital phase thereby permitting a simultaneous fitting of the C IV wind-line profile by the SEI method and the light curve for the same bandpass by means of a program similar to that of Wilson and Devinney. The result is a set of parameters characterizing the physical and geometric properties of the wind envelopes surrounding the stars. Surprisingly, there is no evidence for a P Cygni profile or strong, distinguishable shock front in the system, as has been found for similar investigations of EM Carinae and HD159176. This is probably a result of the contact nature of the binary and the high temperature environment of such a shock. That is, most of the carbon ions in the shock are more highly ionized. Based on the parameters for the SEI fit to the C IV profile, the value for the ionization fraction of C IV in the wind was calculated to be 10-4. With this value, the mass loss rate calculated from two independent equations, was found to be about 10-6 solar masses/yr. The line blanketing or metallicity was found to be erratically variable with orbital phase and time, indicating a variable amount of fast moving, dense clouds in the winds and/or a great amount of turbulence. The meaning of rotational velocities for the stars is problematic and depends on what point on the photospheres one is considering.

Some, if not all, binary neutron star (BNS) coalescences, and a fraction of neutron - star black hole (NSBH) mergers, are thought to produce sufficient mass-ejection to power Gamma-Ray Bursts (GRBs). However, this fraction, as well as the distribution of beaming angles of BNS-associated GRBs, are poorly constrained from observation. Recent work applied machine learning tools to analyze GRB light curves observed by {\textit{Fermi}}/GBM and {\it Swift}/BAT. GRBs were segregated into multiple distinct clusters, with the tantalizing possibility that one of them (BNS cluster) could be associated with BNSs and another (NSBH cluster) with NSBHs. As a proof of principle, assuming that all GRBs detected by {\it Fermi}/GBM and {\it Swift}/BAT associated with BNSs (NSBHs) lie in the BNS (NSBH) cluster, we estimate their rates ($\mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$). We compare these rates with corresponding BNS and NSBH rates estimated by the LIGO-Virgo-Kagra (LVK) collaboration from the first three observing runs (O1, O2, O3). We find that the BNS rates are consistent with LVK's rate estimates, assuming a uniform distribution of beaming fractions ($f_b \in [0.01, 0.1]$). Conversely, using the LVK's BNS rate estimates, assuming all BNS mergers produce GRBs, we are able to constrain the beaming angle distribution to $\theta_j \in [0.8^{\circ}, 38.8^{\circ}]$ at $90\%$ confidence. We similarly place a lower limit on the fraction of GRB-Bright NSBHs to $f_B \gtrsim 0.10$ ($f_B \gtrsim 0.022$) with {\it Fermi}/GBM ({\it Swift}/BAT) data.

Methyl cyanide is one of the simplest interstellar complex organic molecules, widely detected in young solar analogues, shocked regions, protoplanetary disks and comets. CH3CN can be considered a key species to explore the chemical connections between planet forming disks and comets. For such comparison to be meaningful kinetics data for the reactions leading to CH3CN formation and destruction must be updated. We focus on the destruction of methyl cyanide through collisions with He+. A combined experimental and theoretical methodology is employed to obtain cross sections (CSs) and branching ratios (BRs) as a function of collision energy, from which reaction rate coefficients $k(T)$ are calculated in the temperature range from 10 to 300 K. CSs and BRs are measured using a guided ion beam set-up. A theoretical treatment based on an analytical formulation of the potential energy surfaces (PESs) for the charge exchange process is developed. The method employs a Landau Zener model to obtain reaction probabilities at crossings between the entrance and exit PESs, and an adiabatic centrifugal sudden approximation to calculate CSs and k(T). Rates and BRs differ from those predicted from widely-used capture models. In particular, the rate coefficient at 10 K is estimated to be almost one order of magnitude smaller than what reported in the KIDA database. As for BRs, the charge exchange is completely dissociative and the most abundant fragments are HCCN+/CCNH+, HCNH+ and CH2+. Our results, combined with a revised chemical network for formation of CH3CN, support the hypothesis that methyl cyanide in protoplanetary disks could be mostly the product of gas-phase processes rather than grain chemistry, as currently proposed. These findings are expected to have implications in the comparison of the abundance ratios of N-bearing molecules observed in disks with cometary abundance ratios

In the period between 2009 and 2015, several very high-energy (VHE $> 100$ GeV) gamma-ray flaring events from the BL Lac object PKS 1424+240 were observed by the Cerenkov telescopes VERITAS and MAGIC. It had uncertain redshift ($z$) and using spectroscopical measurement, Paiano et al. (2017) found it to be $z=0.604$. Using four different extragalactic background light (EBL) models and the photohadronic model, nine independently observed VHE gamma-ray spectra of PKS 1424+240 are analyzed and a global $\chi^2$ fit is performed on all observations to estimate the best-fit value for the redshift for each EBL model. Confidence levels (CL) intervals for the redshift are also estimated using all the EBL models. This method is tested by comparing our analysis with the observed value. It is shown that the photohadronic scenario provides an excellent description of all the observed spectra. It is found that the EBL model of Domínguez et al. (2011) is the one that provides the most restrictive limits on the redshift of PKS 1424+240, but in our analysis, $z=0.604$ lies within the $3\sigma$ CL interval of the EBL model of Saldana-Lopez et al. (2021).

We investigate the centrifugal acceleration in an axisymmetric pulsar magnetosphere under the ideal-MHD approximation. We solved the field-aligned equations of motion for flows inside the current sheet with finite thickness. We find that flows coming into the vicinity of a Y-point become super fast. The centrifugal acceleration takes place efficiently, and most of the Poynting energy is converted into kinetic energy. However, the super fast flow does not provide enough centrifugal drift current to open the magnetic field. Opening of the magnetic field is possible by the plasmas that are accelerated in the azimuthal direction with a large Lorentz factor in the closed field region. We find that this acceleration takes place if the field strength increases toward the Y-point from inside. The accelerated plasma is transferred from the closed field region to the open field region by magnetic reconnection with plasmoid emission. We also estimate the Lorentz factor to be reached in the centrifugal wind.

We present deep near-infrared $K_{\rm s}$-band imaging for 35 of the 53 sources from the high-redshift ($z > 2$) radio galaxy candidate sample defined in Broderick et al. (2022). These images were obtained using the High-Acuity Widefield $K$-band Imager (HAWK-I) on the Very Large Telescope. Host galaxies are detected for 27 of the sources, with $K_{\rm s} \approx 21.6$$-$$23.0$ mag (2$''$ diameter apertures; AB). The remaining eight targets are not detected to a median $3\sigma$ depth of $K_{\rm s} \approx 23.3$ mag ($2''$ diameter apertures). We examine the radio and near-infrared flux densities of the 35 sources, comparing them to the known $z > 3$ powerful radio galaxies with 500-MHz radio luminosities $L_{500\,{\rm MHz}} > 10^{27}$ W Hz$^{-1}$. By plotting 150-MHz flux density versus $K_{\rm s}$-band flux density, we find that, similar to the sources from the literature, these new targets have large radio to near-infrared flux density ratios, but extending the distribution to fainter flux densities. Five of the eight HAWK-I deep non-detections have a median $3\sigma$ lower limit of $K_{\rm s} \gtrsim 23.8$ mag ($1.5''$ diameter apertures); these five targets, along with a further source from Broderick et al. (2022) with a deep non-detection ($K_{\rm s} \gtrsim 23.7$ mag; $3\sigma$; $2''$ diameter aperture) in the Southern H-ATLAS Regions $K_{\rm s}$-band Survey, are considered candidates to be ultra-high-redshift ($z > 5$) radio galaxies. The extreme radio to near-infrared flux density ratios ($>10^5$) for these six sources are comparable to TN J0924$-$2201, GLEAM J0856$+$0223 and TGSS J1530$+$1049, the three known powerful radio galaxies at $z > 5$. For a selection of galaxy templates with different stellar masses, we show that $z \gtrsim 4.2$ is a plausible scenario for our ultra-high-redshift candidates if the stellar mass $M_{\rm *} \gtrsim 10^{10.5}\,{\rm M}_\odot$. [abridged]

We perform a thorough analysis of the projected shapes of nearby galaxies in both observations and cosmological simulations. We implement a forward-modeling approach to overcome the limitations in previous studies which hinder accurate comparisons between observations and simulations. We measure axis ratios of $z=0$ (snapshot 99) TNG50 galaxies from their synthetic Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) images and compare them with those obtained from real HSC-SSP images of a matched galaxy sample. Remarkably, the comparison shows excellent agreement between observations and the TNG50 simulation. Specifically, for galaxies with stellar masses $10\leq \log (M_{\star}/M_{\odot}) \leq 11.5$, we find $\lesssim 0.1\sigma$ tensions between the observation and the simulation, whereas previous studies found $\gtrsim 10\sigma$ tensions due to lack of thin galaxies in simulations. We reveal that low-mass galaxies ($M_{\star}\lesssim 10^{9.5}$) in TNG50 are thicker than their observed counterparts in HSC-SSP and attribute this to the spurious dynamical heating effects that artificially puff up galaxies. We also find that despite the overall broad agreement, TNG50 galaxies are more concentrated than the HSC-SSP ones at the low- and high-mass end of the stellar mass range of $9.0\leq \log (M_{\star}/M_{\odot}) \leq 11.2$ and are less concentrated at intermediate stellar masses. But we argue that the higher concentrations of the low-mass TNG50 galaxies are not likely the cause of their thicker/rounder appearances. Our study underscores the critical importance of conducting mock observations of simulations and applying consistent measurement methodologies to facilitate proper comparison with observations.

The search for atmospheric biosignatures in Earth-like exoplanets is one of the most pressing challenges in observational astrobiology. Detecting biogenic gases in terrestrial planets requires high resolution and long integration times. In this work, we developed and tested a machine-learning general methodology, intended to classify transmission spectra with low Signal-to-Noise Ratio according to their potential to contain biosignatures. For that purpose, we trained a set of models capable of classifying noisy transmission spectra, as having methane, ozone, and/or water (multilabel classification), or simply as being interesting for follow-up observations (binary classification). The models were trained with $\sim\, 10^6$ synthetic spectra of planets similar to TRAPPIST-1 e, which were generated with the package MultiREx, especially developed for this work. The trained algorithms correctly classified test planets with transmission spectra having SNR $<$ 6 and containing methane and/or ozone at mixing ratios similar to those of modern and Proterozoic Earth. Tests on realistic synthetic spectra based on the current Earthś atmosphere show at least one of our models would classify as likely having biosignatures and using only one transit, most of the inhabited terrestrial planets observed with the JWST/NIRSpec PRISM around M-dwarfs located at distances similar or smaller than that of TRAPPIST-1 e. The implication of this result for the designing of observing programs and future surveys is enormous since machine-assisted strategies similar to those presented here could significantly optimize the usage of JWST resources for biosignature searching, while maximizing the chances of a real discovery after dedicated follow-up observations of promising candidates.

The motion of the barycenter of the Solar System (SSB), the origin of the International Celestial Reference System, causes a directional displacement known as secular aberration. The secular aberration drift caused by the galactocentric acceleration of the SSB has been modeled in the third generation of the International Celestial Reference Frame. We aim to address another secular aberration drift effect due to the change in the line-of-sight direction and study its implications for stellar proper motions. A complete formula of secular aberration drift is derived, and its influence on stellar proper motion is computed based on the astrometric data in \textit{Gaia} Data Release 3. We found that the secular aberration drift due to the change in the line-of-sight direction tends to decrease the observed proper motions for stars with galactic longitudes between $0^{\circ}$ and $180^{\circ}$, and increase the observed proper motion for stars in the remaining region. If this secular aberration drift effect is ignored, it will induce an additional proper motion of $>1\,\mathrm{mas\,yr^{-1}}$ for 84 stars and $>0.02\,\mathrm{mas\,yr^{-1}}$ for 5\,944\,879 stars, which is comparable to or several times greater than the typical formal uncertainty of the \textit{Gaia} proper motion measurements at $G<13$. The secular aberration drift due to the change in the line-of-sight direction and the acceleration of the SSB should be modeled to make the stellar reference frame consistent with the extragalactic reference frame.

The facility adaptive optics of the Subaru Telescope AO188 recently received some long-awaited upgrades: a new 3224-actuator deformable mirror (DM) from ALPAO (hence the name change to AO3000 or AO3k), an upgraded GPU-based real-time computer, a visible nonlinear curvature wavefront sensor and a near-infrared wavefront sensor (NIR WFS), closing the loop at up to 2~kHz. The wavefront sensors were added in 2023, while the DM will be installed at the beginning of 2024. With these new features, AO3k will provide extreme-AO level of correction to all the instruments on the IR Nasmyth platform: The NIR-MIR camera and spectrograph IRCS, the high-resolution Doppler spectrograph IRD, and the high-contrast instrument SCExAO. AO3k will also support laser tomography (LTAO), delivering high Strehl ratio imaging with large sky coverage. The high Strehl will especially benefit SCExAO for high-contrast imaging, both in infrared and visible. The second stage extreme AO will no longer have to chase large residual atmospheric turbulence, and will focus on truly high-contrast techniques to create and stabilize dark holes, as well as coherent differential imaging techniques. We will finally be able to leverage the several high performance coronagraphs tested in SCExAO, even in the visible. AO3k will answer crucial questions as a precursor for future adaptive optics systems for ELTs, especially as a technology demonstrator for the HCI Planetary Systems Imager on the Thirty Meter Telescope. A lot of questions are still unanswered on the on-sky behavior of high actuator counts DMs, NIR wavefront sensing, the effect of rolling shutters or persistence. We present here the first on-sky results of AO3k, before the system gets fully offered to the observers in the second half of 2024. These results give us some insight on the great scientific results we hope to achieve in the future.

This work presents the first ever broadband (0.7-25.0 keV) timing and spectral analysis of Be-HMXB 2S 1417-624 during its 2021 outburst. Using AstroSat observations, coherent pulsations at ~17.36633 s (MJD 59239.082) were detected in 0.7-7.0 keV SXT and 3.0-25.0 keV LAXPC data. The pulse profile was dual peaked at all energies, with the relative intensity of main peak increasing with energy. The peaks in the SXT profiles were broad and comprised of several mini-structures. The LAXPC profiles were relatively smooth and had higher pulsed fraction which increased with energy. The SXT+LAXPC simultaneous energy spectrum is well described by an absorbed power-law with exponential cut-off, along with ~1.6 keV black body component and 6.47 keV emission line. A model comprising of an absorbed power law with high energy cutoff plus a partial covering absorber and Gaussian emission line also fits the spectrum quite well. These results have been compared with timing and spectral features during the previous outbursts of this transient pulsar.

We report the discovery of five white dwarf + ultracool dwarf systems identified as common proper motion wide binaries in the Gaia Catalogue of Nearby Stars. The discoveries include a white dwarf + L subdwarf binary, VVV~1256-62AB, a gravitationally-bound system located 75.6(+1.9/-1.8) pc away with a projected separation of 1375(+35/-33) au. The primary is a cool DC white dwarf with a hydrogen dominated atmosphere, and has a total age of 10.5(+3.3/-2.1) Gyr, based on white dwarf model fitting. The secondary is an L subdwarf with a metallicity of [M/H] = -0.72(+0.08/-0.10) (i.e. [Fe/H] = -0.81\pm0.10) and Teff = 2298(+45/-43) K based on atmospheric model fitting of its optical to near infrared spectrum, and likely has a mass just above the stellar/substellar boundary. The subsolar metallicity of the L subdwarf and the system's total space velocity of 406 km/s indicates membership in the Galactic halo, and it has a flat eccentric Galactic orbit passing within 1~kpc of the centre of the Milky Way every ~0.4 Gyr and extending to 15-31 kpc at apogal. VVV 1256-62B is the first L subdwarf to have a well-constrained age, making it an ideal benchmark of metal-poor ultracool dwarf atmospheres and evolution.

The Universe with the cosmic anisotropy will have a preferred direction of expansion. Therefore, reconstructing the expansion history by Gaussian Process (GP) can be used to probe the cosmic anisotropy model-independently. In this paper, for the luminosity distance $d_L(z)$ reconstruction, we turn to the inverse distance ladder where the type Ia supernova (SNIa) from the Pantheon+ sample determine the relative distances and the strongly gravitationally lensed quasars from H0LiCOW sample anchor these relative distances with some absolute distance measurements. By isolating the anisotropic information maybe carried by the Hubble constant $H_0$ and obtaining the constraint on the intrinsic parameter of SNIa, the absolute magnitude $M=-19.2522^{+0.0270}_{-0.0279}$ (at $68\%$ CL), we find that $d_L(z)$ reconstructions from samples located in different region of the Galactic coordinate system are almost consistent with each other and only a very weak preference for the cosmic anisotropy is found.

The origin of atmospheric heating in the cool, magnetic white dwarf GD 356 remains unsolved nearly 40 years after its discovery. This once idiosyncratic star with $T_{\rm eff}\approx7500$ K, yet Balmer lines in Zeeman-split emission is now part of a growing class of white dwarfs exhibiting similar features, and which are tightly clustered in the HR diagram suggesting an intrinsic power source. This paper proposes that convective motions associated with an internal dynamo can power electric currents along magnetic field lines that heat the atmosphere via Ohmic dissipation. Such currents would require a dynamo driven by core $^{22}$Ne distillation, and would further corroborate magnetic field generation in white dwarfs by this process. The model predicts that the heating will be highest near the magnetic poles, and virtually absent toward the equator, in agreement with observations. This picture is also consistent with the absence of X-ray or extreme ultraviolet emission, because the resistivity would decrease by several orders of magnitude at the typical coronal temperatures. The proposed model suggests that i) DAHe stars are mergers with enhanced $^{22}$Ne that enables distillation and may result in significant cooling delays; and ii) any mergers that distill neon will generate magnetism and chromospheres. The predicted chromospheric emission is consistent with the two known massive DQe white dwarfs.

Stellar blends, where two or more stars appear blended in an image, pose a significant visualization challenge in astronomy. Traditionally, distinguishing these blends from single stars has been costly and resource-intensive, involving sophisticated equipment and extensive expert analysis. This is especially problematic for analyzing the vast data volumes from surveys, such as Legacy Survey of Space and Time (LSST), Sloan Digital Sky Survey (SDSS), Dark Energy Spectroscopic Instrument (DESI), Legacy Imaging Survey and the Zwicky Transient Facility (ZTF). To address these challenges, we apply different normalizations and data embeddings on low resolution images of single stars and stellar blends, which are passed as inputs into machine learning methods and to a computationally efficient Gaussian process model (MuyGPs). MuyGPs consistently outperforms the benchmarked models, particularly on limited training data. Moreover, MuyGPs with $r^\text{th}$ root local min-max normalization achieves 83.8% accuracy. Furthermore, MuyGPs' ability to produce confidence bands ensures that predictions with low confidence can be redirected to a specialist for efficient human-assisted labeling.

Type Ia Supernovae (SNe Ia) discovered at redshift $z\lesssim2.5$ are presumed to be produced from Population (Pop) I/II stars. {In this work, we investigate the production of SNe Ia from Pop III binaries in the cosmological framework. We derive the SN Ia rate as a function of redshift under a theoretical context for the production of first generation stars and emanate the likelihood of their detection by the James Webb Space Telescope (JWST).} {Assuming the initial stellar mass function (IMF) favors low-mass stars as from recent numerical simulations, we found Pop III stars may give rise to a considerable amount of SNe Ia at high redshift and Pop III stars may even be the dominant SN Ia producer at z $\gtrsim 6$.} {In an optimistic scenario, we expect $\sim 1(2)$ SNe Ia from Pop III stars at $z\approx 4(5)$ for a survey of area $300 \;\rm arcmin^2$ during a $3\;\rm yr$ period with JWST. The same survey may record more than $\sim 400$ SNe Ia at lower redshift ($z\lesssim 2.5$) but with only about one of them from Pop III progenitors. There will be $\sim 6$ Pop III SNe Ia in the same field of view at redshifts of $5-10$.} Observational constraints on SN Ia rates at the redshift range of $5-10$ can place crucial constraints on the IMF of Pop III stars.

After receiving an X-ray photon, an X-ray detector is not operational for a duration known as deadtime. It is detector specific and its effect on the data depends upon the luminosity of the source. It reduces the observed photon count rate in comparison to the expected one. In periodic sources such as the Crab pulsar, it can distort the folded light curve (FLC). An undistorted FLC of the Crab pulsar is required in combination with its polarization properties for studying its X-ray emission mechanism. This work derives a simple formula for the distortion of the FLC of a pulsar caused by the detector deadtime, and validates it using Crab pulsar data from the X-ray observatories {\it NICER} and {\it NUSTAR}, which have very small and relatively large detector deadtimes respectively. Then it derives a method for correcting the distorted FLC of the Crab pulsar in {\it IXPE} data, which has intermediate detector deadtime. The formula is verified after addressing several technical issues. This work ends with a discussion of why an undistorted FLC is important for studying the formation of cusps in the FLC of the Crab pulsar.

The expansion of satellite constellations poses a significant challenge to optical ground-based astronomical observations, as satellite trails degrade observational data and compromise research quality. Addressing these challenges requires developing robust detection methods to enhance data processing pipelines, creating a reliable approach for detecting and analyzing satellite trails that can be easily reproduced and applied by other observatories and data processing groups. Our method, called ASTA (Automated Satellite Tracking for Astronomy), combines deep learning and computer vision techniques for effective satellite trail detection. It employs a U-Net based deep learning network to initially detect trails, followed by a Probabilistic Hough Transform to refine the output. ASTA's U-Net model was trained on a dataset with manually labelled full-field MeerLICHT images prepared using the LABKIT annotation tool, ensuring high-quality and precise annotations. This annotation process was crucial for the model to learn and generalize the characteristics of satellite trails effectively. Furthermore, the user-friendly LABKIT tool facilitated quick and efficient data refinements, streamlining the overall model development process. ASTA's performance was evaluated on a test set of 20,000 image patches, both with and without satellite trails, to rigorously assess its precision and recall. Additionally, ASTA was applied to approximately 200,000 full-field MeerLICHT images, demonstrating its effectiveness in identifying and characterizing satellite trails. The software's results were validated by cross-referencing detected trails with known public satellite catalogs, confirming its reliability and showcasing its ability to uncover previously untracked objects.

Pulsars often display systematic variations in the position and/or intensity of the subpulses, the components that comprise each single pulse. Although the drift of these subpulses was observed in the early years of pulsar research, and their potential for understanding the elusive emission mechanism was quickly recognised, there is still no consensus on the cause of the drift. We explore the electrodynamics of two recently proposed or refined drift models: one where plasma lags behind corotation, connecting the drift with the rotational pole; and another where plasma drifts around the electric potential extremum of the polar cap. Generally, these are different locations, resulting in different drift behaviours, that can be tested with observations. In this study, however, we specifically examine these models in the axisymmetric case, where the physics is well understood. This approach seems counter-intuitive as both models then predict similar large-scale plasma drift. However, it allows us to show, by studying conditions \emph{within} the sparks for both models, that the lagging behind corotation (LBC) model is inconsistent with Faraday's law. The modified carousel (MC) model, where plasma drifts around the electric potential extremum, not only aligns with Faraday's law, but also provides a future direction for developing a comprehensive model of plasma generation in the polar cap region. Unlike previous models, which considered the drift only inside the discharging regions, the MC model reveals that the electric field \emph{between} the discharges is not completely screened, and plasma drifts there -- a paradigm shift for the drifting subpulse phenomenon.

Reionization is one of the least understood processes in the evolution history of the Universe, mostly because of the numerous astrophysical processes occurring simultaneously about which we do not have a very clear idea so far. In this article, we use the Gaussian Process Regression (GPR) method to learn the reionization history and infer the astrophysical parameters. We reconstruct the UV luminosity density function using the HFF and early JWST data. From the reconstructed history of reionization, the global differential brightness temperature fluctuation during this epoch has been computed. We perform MCMC analysis of the global 21-cm signal using the instrumental specifications of SARAS, in combination with Lyman-$\alpha$ ionization fraction data, Planck optical depth measurements and UV luminosity data. Our analysis reveals that GPR can help infer the astrophysical parameters in a model-agnostic way than conventional methods. Additionally, we analyze the 21-cm power spectrum using the reconstructed history of reionization and demonstrate how the future 21-cm mission SKA, in combination with Planck and Lyman-$\alpha$ forest data, improves the bounds on the reionization astrophysical parameters by doing a joint MCMC analysis for the astrophysical parameters plus 6 cosmological parameters for $\Lambda$CDM model. The results make the GPR-based reconstruction technique a robust learning process and the inferences on the astrophysical parameters obtained therefrom are quite reliable that can be used for future analysis.

Fuzzy dark matter (FDM) with mass around $10^{-22}$ eV is viewed as a promising paradigm in understanding the structure formation of the local universe at small scales. Recent observations, however, begin to challenge FDM in return. We focus on the arguments between the solution to CDM small-scale curiosities and recent observations on matter power spectrum, and find its implication on an earlier formation of small-scale structure. In this article, we propose a scheme of k-ULDM scalar field with a differently-evolving sound speed, thanks to the non-canonical kinetics. With the help of the Dirac-Born-Infeld (DBI) theory, we illustrate to change the behavior of the quantum pressure term countering collapse, therefore change the history of structure growth. We find that it can truly reopen the ULDM mass window closed by the Lyman-$\alpha$ problem. We will discuss such examples in this paper, while more possibilities remain to be explored.

Understanding how and when galaxies formed stars over the history of the Universe is fundamental to the study of galaxy evolution. The star formation histories (SFHs) of galaxies in the local Universe can be measured with high precision using deep imaging with space telescopes. Such resolved SFHs are based on modelling the observed color-magnitude diagram (CMD) with stellar evolution models and rely on age-sensitive features like the main sequence turn-off to measure a galaxy's star formation rate as a function of time. There are many other population-level parameters that factor into these measurements, such as the stellar initial mass function (IMF), binary fraction, and metallicity, to name a few. We present and release StarFormationHistories.jl, a modular, open-source Julia package for measuring resolved SFHs with a focus on model flexibility for these types of population parameters. The code can model unresolved photometric binaries and supports arbitrary IMFs. Random uncertainties in the SFH measurements can be quantified with Monte Carlo posterior sampling methods. We illustrate the performance of the package on JWST/NIRCAM data of the Local Group dwarf irregular galaxy WLM $\left(M_v\approx-14.2\right)$, which exhibits a complex, well-sampled CMD, and HST/ACS data of the ultra-faint Milky Way satellite dwarf galaxy Horologium I $\left(M_v\approx-3.7\right)$, which has a much simpler but sparser CMD.

We use a combination of high-redshift observables to extract the strongest constraints to date on the fraction of axion fuzzy dark matter (FDM) in the mass window $10^{-26}\,\mathrm{eV}\!\lesssim\! m_\mathrm{FDM}\!\lesssim\!10^{-23}\,\mathrm{eV}$. These observables include ultraviolet luminosity functions (UVLFs) at redshifts $4-10$ measured by the Hubble Space Telescope, a constraint on the neutral hydrogen fraction from high-redshift quasar spectroscopy, the cosmic microwave background optical depth to reionization measurement from Planck and upper bounds on the 21cm power spectrum from HERA. In order to calculate these signals for FDM cosmology, we use the 21cmFirstCLASS code to interface between AxiCLASS and 21cmFAST and consistently account for the full cosmic history from recombination to reionization. To facilitate a full Bayesian likelihood analysis, we developed a machine-learning based pipeline, which is both accurate, and enables a swift statistical inference, orders of magnitude faster than a brute force approach. We find that FDM of mass $m_\mathrm{FDM} \!= \!10^{-23} \, \mathrm{eV}$ is bound to less than $16\%$ of the total dark matter, where the constrains strengthen towards smaller masses, reaching down to $1\%$ for $m_\mathrm{FDM}\! =\! 10^{-26} \, \mathrm{eV}$, both at $95\%$ confidence level. In addition, we forecast that a future detection of the 21cm power spectrum with HERA will lower the upper bound at $m_\mathrm{FDM}\! =\! 10^{-23} \, \mathrm{eV}$ to $\lesssim\!1\%$.

We present deep, sub-arcsecond ($\sim$2000 AU) resolution ALMA 0.82 mm observations of the former high-mass prestellar core candidate G11.92-0.61 MM2, recently shown to be an $\sim$500 AU-separation protobinary. Our observations show that G11.92-0.61 MM2, located in the G11.92-0.61 protocluster, lies on a filamentary structure traced by 0.82 mm continuum and N$_2$H$^+$(4-3) emission. The N$_2$H$^+$(4-3) spectra are multi-peaked, indicative of multiple velocity components along the line of sight. To analyse the gas kinematics, we performed pixel-by-pixel Gaussian decomposition of the N$_2$H$^+$ spectra using SCOUSEPY and hierarchical clustering of the extracted velocity components using ACORNS. Seventy velocity- and position-coherent clusters (called "trees") are identified in the N$_2$H$^+$-emitting gas, with the 8 largest trees accounting for >60% of the fitted velocity components. The primary tree, with $\sim$20% of the fitted velocity components, displays a roughly north-south velocity gradient along the filamentary structure traced by the 0.82 mm continuum. Analysing a $\sim$0.17 pc-long substructure, we interpret its velocity gradient of $\sim$10.5 km s$^{-1}$pc$^{-1}$ as tracing filamentary accretion towards MM2 and estimate a mass inflow rate of $\sim$1.8$\times10^{-4}$ to 1.2$\times10^{-3}$ M$_\odot$ yr$^{-1}$. Based on the recent detection of a bipolar molecular outflow associated with MM2, accretion onto the protobinary is ongoing, likely fed by the larger-scale filamentary accretion flows. If 50% of the filamentary inflow reaches the protostars, each member of the protobinary would attain a mass of 8 M$_\odot$ within $\sim1.6\times$10$^5$ yr, comparable to the combined timescale of the 70 $\mu$m- and MIR-weak phases derived for ATLASGAL-TOP100 massive clumps using chemical clocks.

Traditional pulsar timing techniques involve averaging large numbers of single pulses to obtain a high signal-to-noise (S/N) profile, which is matched to a template to measure a time of arrival (TOA). However, the morphology of individual single pulses varies greatly due to pulse jitter. Pulses of different fluence contribute differently to the S/N of the pulse average. Our study proposes a method that accounts for these variations by identifying a range of states and timing each separately. We selected two 1-hour observations of PSR J2145-0750, each in a different frequency band with the Green Bank Telescope. We normalized the pulse amplitudes to account for scintillation effects and probed different excision algorithms to reduce radio-frequency interference. We then measured four pulse parameters (amplitude, position, width, and energy) to classify the single pulses using automated clustering algorithms. For each cluster, we calculated an average pulse profile and template and used both to obtain a TOA and TOA error. Finally, we computed the weighted average TOA and TOA error, the latter as a metric of the total timing precision for the epoch. The TOA is shifted relative to the one obtained without clustering, and we can estimate the shift with this weighting using the same data. For the 820 MHz and 1400 MHz bands, we obtained TOA uncertainties of 0.057 microseconds and 0.46 microseconds, compared to 0.066 microseconds and 0.74 microseconds when no clustering is applied. We conclude that tailoring this method could help improve the timing precision for certain bright pulsars in NANOGrav's dataset.

Traditional nanosatellite communication links rely on infrequent ground-station access windows. While this is well suited to both payload data and detailed scheduling information, the resulting long periods without contact are ill-suited for both opportunistic tasking of satellites and triggers generated by autonomous operations. Existing orbital infrastructure in the form of satellite communication (SATCOM) networks, such as Iridium and others provide a readily available and cost effective solution to this problem. While these networks continue to be utilized onboard nanosatellites, a full characterization of their utility and performance in-orbit is vital to understand the reliability and potential for high-timeliness message delivery. The SpIRIT 6U nanosatellite is a mission led by The University of Melbourne in cooperation with the Italian Space Agency and supported by the Australian Space Agency. Developed over the last four years and launched in a 510km Polar Sun Synchronous Orbit in late 2023, SpIRIT carries multiple subsystems for scientific and technology demonstration. The Mercury subsystem provides a demonstration and characterization test bed for SATCOM utilization in-orbit, while also providing the capability of rapid down-link of detection events generated by the main scientific payload of the mission, the HERMES instrument for the detection of high-energy astrophysical transients. This paper first presents a brief payload characterization experiment overview. Early in-orbit results are then presented. This work not only sheds light on the utility of these networks for autonomous operations, and on their potential impact to enable greater utilization of nanosatellites for scientific missions, but also offers insights into the practical challenges related to the design and implementation of utilizing these networks in-orbit.

We present a study connecting the physical properties of protostellar envelopes to the morphology of the envelope-scale magnetic field. We use the ALMA polarization observations of 55 young prtostars at 0.87 mm on $\sim400-3000$ au scales from the {\em B}-field Orion Protostellar Survey (BOPS) to infer the envelope-scale magnetic field and both dust and gas emission on comparable scales to measure the envelope properties. We find that the protostellar envelopes with compact polarized dust emission tend to have lower envelope masses, than the sources with more extended envelopes. We also find that protostars showing hourglass-field morphologies tend to have lower velocity dispersions in their envelopes, whereas systems with spiral-field morphologies have higher velocity dispersion. Combining with the disk properties taken from the Orion VLA/ALMA Nascent Disk and Multiplicity (VANDAM) survey, we connect envelope properties to fragmentation. Our results suggest that envelope mass may not correlate with fragmentation, whereas turbulence appears to promote fragmentation. On the other hand, we find that fragmentation is suppressed in systems with pinched magnetic fields, suggesting that the magnetic field play a role on providing additional support against gravitational collapse, and the formation of an hourglass-like field may coincide with enhanced magnetic braking that removes angular momentum and hinders the formation of embedded disks. Nevertheless, significant misalignment between magnetic field and outflow axes tends to reduce magnetic braking, leading to the formation of larger disks.

Solar active regions (ARs) are the main sources of flares and coronal mass ejections (CMEs). NOAA AR 12089, which emerged on 2014 June 10, produced two C-class flares accompanied by CMEs within five hours after its emergence. When producing the two eruptive flares, the total unsigned magnetic flux ($\Phi_{\text{AR}}$) and magnetic free energy ($E_f$) of the AR are much smaller than the common CME-producing ARs. Why can this extremely small AR produce eruptive flares so early? We compare the AR magnetic environment for the eruptive flares to that for the largest confined flare from the AR. Besides the $\Phi_{\text{AR}}$ and $E_f$, we calculate the ratio between the mean characteristic twist parameter ($\alpha_{\text{FPIL}}$) within the flaring polarity inversion line (FPIL) region and $\Phi_{\text{AR}}$, a parameter considering both background magnetic field constraint and non-potentiality of the core region, for the three flares. We find higher $\alpha_{\text{FPIL}}/{\Phi_{\text{AR}}}$ values during the eruptive flares than during the confined flare. Furthermore, we compute the decay index along the polarity inversion line, revealing values of 1.69, 3.45, and 0.98 before the two eruptive and the confined flares, respectively. Finally, nonlinear force-free field extrapolation indicates that a flux rope was repeatedly formed along the FPIL before eruptive flares, which ejected out and produced CMEs. No flux rope was found before the confined flare. Our research suggests that even a newly emerged, extremely small AR can produce eruptive flares if it has sufficiently weak background field constraint and strong non-potentiality in the core region.

The negative hydrogen ion H$^-$ is, almost without exception, treated in local thermodynamic equilibrium (LTE) in modelling of F, G and K stars, where it is the dominant opacity source in the visual spectral region. This assumption in practice rests on the study by Lambert & Pagel from 1968. Since that work, knowledge of relevant atomic processes, and theoretical calculations of stellar atmospheres and their spectra, have advanced significantly, yet this question has not been reexamined. Calculations are presented for a slightly modified version of Lambert & Pagel's analytical model including H, H$_2$ and H$^-$, together with modern atomic data and a grid of 1D LTE theoretical stellar atmosphere models with stellar parameters ranging from T$_\mathrm{eff} = 4000$ to 7000~K, $\log{g} = 1$ to 5 cm/s$^2$, and [Fe/H]$=-3$ to 0. We find direct non-LTE effects on populations in spectrum forming regions, continua and spectral lines of the order of 1-2 percent in stars with higher T$_\mathrm{eff}$ and/or lower $\log g$. Effects in models for solar parameters are a factor of 10 smaller, of order 0.1-0.2 percent, and in models with lower T$_\mathrm{eff}$ and/or higher $\log g$ practically absent. These departures from LTE found in our calculations originate from radiative recombination of electrons with hydrogen to form H$^-$ exceeding photodetachment, i.e. overrecombination. Modern atomic data are not a source of significant differences compared to Lambert & Pagel's work, though detailed data for processes on H$_2$ resolved with vibrational and rotational states provide a more complete and complex picture of the role of H$_2$ in the equilibrium of H$^-$. In the context of modern studies of stellar spectra at percent level, our results suggest this question requires further attention, including a more extensive reaction network, and indirect effects due to non-LTE electron populations.

We present an analysis of a stellar occultation event caused by a near-Earth asteroid (98943) 2001 CC21, an upcoming flyby target in the Hayabusa2 extended mission, on March 5, 2023. To accurately determine the asteroid's shape from diffraction-affected light curves, we developed a novel data reduction technique named the Diffracted Occultation's United Simulator for Highly Informative Transient Explorations (DOUSHITE). Using DOUSHITE-generated synthetic models, we derived constraints on (98943) 2001 CC21's shadow shape from the single-chord occultation data. Our results suggest a significant elongation of the shadow with an axis ratio of $b/a = 0.37\pm0.09$. This shape can be crucial for planning Hayabusa2's high-speed flyby to optimise the limited imaging opportunities.

Herschel surveys have found large numbers of sources with red far-IR colours, and spectral energy distributions (SEDs) rising from 250 to 500$\mu$m: 500 risers. The nature and role of these sources is not fully understood. We here present Submillimeter Array (SMA) interferometric imaging at 200 GHz of a complete sample of five 500 risers with F500 $>$ 44 mJy selected within a 4.5 square degree region of the XMMLSS field. These observations can resolve the separate components of multiple sources and allow cross identification at other wavelengths using the extensive optical-to-IR data in this field. Of our five targets we find that two are likely gravitationally lensed, two are multiple sources, and one an isolated single source. Photometric redshifts, using optical-to-IR data and far-IR/submm data, suggest they lie at redshifts $z \sim 2.5 - 3.5$. Star formation rates and stellar masses estimated from the SEDs show that the majority of our sources lie on the star-formation rate-stellar mass `main sequence', though with outliers both above and below this relation. Of particular interest is our most multiple source which consists of three submm emitters and one submm-undetected optical companion within a 7 arcsecond region, all with photometric redshifts $\sim$ 3. One of the submm emitters in this group lies above the `main sequence', while the optical companion lies well below the relation, and has an estimated stellar mass of 3.3$\pm 1.3 \times$10$^{11}$ M$_{\odot}$. We suggest this object is a forming brightest cluster galaxy (BCG) in the process of accreting actively star forming companions.

Membership analysis is an important tool for studying star clusters. There are various approaches to membership determination, including supervised and unsupervised machine learning (ML) methods. We perform membership analysis using the supervised machine learning approach. We train and test our ML models on two sets of star cluster data: snapshots from $N$-body simulations and 21 different clusters from the Gaia Data Release 3 data. We explore five different ML models: Random Forest (RF), Decision Trees, Support Vector Machines, Feed-Forward Neural Networks, and K-Nearest Neighbors. We find that all models produce similar results, with RF showing slightly better accuracy. We find that a balance of classes in datasets is optional for successful learning. The classification accuracy depends strongly on the astrometric parameters. The addition of photometric parameters does not improve performance. We do not find a strong correlation between the classification accuracy and clusters' age, mass, and half-mass radius. At the same time, models trained on clusters with a larger number of members generally produce better results.

We present and study a new cross-pairwise estimator to extract the kinetic Sunyaev Zeldovich (kSZ) signal from galaxy clusters. The existing pairwise kSZ method involves pairing clusters with other clusters and stacking them. In the cross-pairwise method, we propose to pair clusters with galaxies from a spectroscopic survey and then do the stacking. Cross-pairing decreases the measurement, instrumentation, and statistical noise, thus boosting the signal-to-noise ratio. However, we also need data from a galaxy survey in addition to the CMB temperature maps and a cluster catalog in order to use this method. We do a Fisher matrix analysis for the optimised pairwise and cross-pairwise estimators and forecast the ability of future Cosmic Microwave Background (CMB) experiments and galaxy surveys to measure cosmological parameters with the kSZ effect when combined with primary CMB and Baryon Acoustic Oscillation (BAO) data. We show that using the cross-pairwise kSZ estimator (CMB-S4 clusters with DESI galaxies) leads to a factor of 3 improvement in the $1-\sigma$ error of the dark energy parameters $w_0$ and $w_a$ and a factor of 6 improvement for the growth rate index $\gamma$ compared to the pairwise estimator for the same CMB dataset and cluster catalog.

The end state of binary-neutron-star (BNS) mergers can manifest conditions to produce high-energy neutrinos. Inspired by the event GW170817, detected in gravitational waves and in optical/infrared emission, we investigate a scenario in which cosmic-ray (CR) particles are accelerated, in a population of BNS mergers, in the energy range from the knee to the ankle. By taking into account the measured thermal and non-thermal energy density of the photon fields in the source environment as a function of the time after the merger, we model the CR interactions and the consequent neutrino production. We propagate the escaped CR and neutrino fluxes through the extragalactic space and compare the expected diffuse fluxes to the experimental data and current limits. Depending on the accelerated CR mass composition and on the contribution of this possible source class to the sub-ankle CR flux, we provide indications on the rate of BNS merger events and the amount of baryons present in the source site.

The afterglows of gamma-ray bursts are non-thermal electron synchrotron emissions from relativistic shocks. The origin of strong magnetic field in the emission region remains elusive, and two field amplification mechanisms via the plasma kinetic and magnetohydrodynamic instabilities have been discussed. The polarimetric observations are a powerful probe to distinguish these two mechanisms. So far, most theoretical works have focused on the former mechanism and constructed afterglow polarization models with microscopic-scale turbulence whose coherence length is much smaller than the thickness of the blast wave. In this work, focusing on the latter mechanism, we utilize our semi-analytic model of the synchrotron polarization with large-scale turbulence whose coherence length is comparable to the thickness of the blast wave to investigate the effect of magnetic field anisotropy and the observer viewing angle. We find that the polarization in our large-scale turbulence model can exhibit both behaviors characteristic of the microscopic-scale turbulence model and those not seen in the microscopic-scale model. Then we find that the large-scale model could explain all the polarimetric observational data to date that seem to be forward shock emission. We also examine the effect of ordered-field component, and find that polarization degree and polarization angle constant in time are realized only when the energy density ratio of the ordered and fluctuated components is $\gtrsim 50$. In this case, however, the polarization degree is much higher than the observed values.

We present the abundances of magnesium (Mg) and silicon (Si) for 314 dwarf stars with spectral types in the interval K7.0-M5.5 (Teff range ~4200-3050 K) observed with the CARMENES high-resolution spectrograph at the 3.5 m telescope at the Calar Alto Observatory. Our analysis employs the BT-Settl model atmospheres, the radiative transfer code Turbospectrum, and a state-of-the-art selection of atomic and molecular data. These Mg and Si abundances are critical for understanding both the chemical evolution and assembly of the Milky Way and the formation and composition of rocky planets. Our chemical abundances show a line-to-line scatter at the level of 0.1 dex for all studied spectral types. The typical error bar of our chemical abundance measurements is +- 0.11 dex (Mg) and +- 0.16 dex (Si) for all spectral types based on the comparison of the results obtained for stellar components of multiple systems. The derived abundances are consistent with the galactic evolution trends and observed chemical abundance distribution of earlier FGK-type stars in the solar neighbourhood. Besides, our analysis provides compatible abundances for stars in multiple systems. In addition, we studied the abundances of different galactic stellar populations. In this paper, we also explore the relation of the Mg and Si abundances of stars with and without known planets.

We present preliminary findings from the photometric survey "Yes, Magellanic Clouds Again" (YMCA, PI: V. Ripepi), covering 110 square degrees in the outer regions of the Magellanic Clouds (MCs), a pair of interacting galaxies and the most massive dwarf satellites of the Milky Way. %The survey achieves a notable photometric depth, allowing us to resolve faint, old stellar populations. Among the key results, we discovered four star clusters (SCs) within the Large Magellanic Cloud (LMC) exhibiting ages within the so-called "age gap", a period deemed so far devoid of SCs. Additionally, we unveiled an ancient stellar system associated with the LMC, featuring structural properties in between the globular clusters and the ultra-faint dwarf galaxies of the Local Group. These discoveries significantly contribute to our understanding of the MCs' evolution and their complex interaction history.

This paper demonstrates the impact of state-of-the-art instrumental calibration techniques on the precision of arrival times obtained from 9.6 years of observations of millisecond pulsars using the Murriyang 64-m CSIRO Parkes Radio Telescope. Our study focuses on 21-cm observations of 25 high-priority pulsars that are regularly observed as part of the Parkes Pulsar Timing Array (PPTA) project, including those predicted to be the most susceptible to calibration errors. We employ Measurement Equation Template Matching (METM) for instrumental calibration and Matrix Template Matching (MTM) for arrival time estimation, resulting in significantly improved timing residuals with up to a sixfold reduction in white noise compared to arrival times estimated using Scalar Template Matching and conventional calibration based on the Ideal Feed Assumption. The median relative reduction in white noise is 33 percent, and the maximum absolute reduction is 4.5 microseconds. For PSR J0437-4715, METM and MTM reduce the best-fit power-law amplitude (2.7 sigma) and spectral index (1.7 sigma) of the red noise in the arrival time residuals, which can can be tentatively interpreted as mitigation of 1/f noise due to otherwise unmodeled steps in polarimetric response. These findings demonstrate the potential to directly enhance the sensitivity of pulsar timing array experiments through more accurate methods of instrumental calibration and arrival time estimation.

When the planet formation process begins in the disks surrounding young stars is still an open question. Annular substructures such as rings and gaps in disks are intertwined with planet formation, and thus their presence or absence is commonly used to investigate the onset of this process. Current observations show a limited number of disks surrounding protostars exhibiting annular substructures, all of them in the Class I stage. The lack of observed features in most of these sources may indicate a late emergence of substructures, but it could also be an artifact of these disks being optically thick. To mitigate the problem of optical depth, we investigate substructures within a very young Class 0 disk characterized by a low inclination using observations at longer wavelengths. We use 3 mm ALMA observations tracing dust emission at a resolution of 7 au to search for evidence of annular substructures in the disk around the deeply embedded Class 0 protostar Oph A SM1. The observations reveal a nearly face-on disk (i$\sim$16$^{\circ}$) extending up to 40 au. The radial intensity profile shows a clear deviation from a smooth profile near 30 au, which we interpret as the presence of either a gap at 28 au or a ring at 34 au with Gaussian widths of $\sigma=1.4^{+2.3}_{-1.2}$ au and $\sigma=3.9^{+2.0}_{-1.9}$ au, respectively. The 3 mm emission at the location of the possible gap or ring is determined to be optically thin, precluding the possibility that this feature in the intensity profile is due to the emission being optically thick. Annular substructures resembling those in the more evolved Class I and II disks could indeed be present in the Class 0 stage, earlier than previous observations suggested. Similar observations of embedded disks in which the high optical depth problem can be mitigated are clearly needed to better constrain the onset of substructures in the embedded stages.

In protoplanetary disks, small mm-cm-sized pebbles drift inwards which can aid planetary growth and influence the chemical composition of their natal disks. Gaps in protoplanetary disks can hinder the effective inward transport of pebbles by trapping the material in pressure bumps. Here we explore how multiple planets change the vapour enrichment by gap opening. For this, we extend the chemcomp code to include multiple growing planets and investigate the effect of 1, 2 & 3 planets on the water content and C/O ratio in the gas disk as well as the final composition of the planetary atmosphere. We follow planet migration over evaporation fronts and find that previously trapped pebbles evaporate relatively quickly and enrich the gas. We also find that in a multi-planet system, the atmosphere composition can be reduced in carbon and oxygen compared to the case without other planets, due to the blocking of volatile-rich pebbles by an outer planet. This effect is stronger for lower viscosities because planets migrate further at higher viscosities and eventually cross inner evaporation fronts, releasing the previously trapped pebbles. Interestingly, we find that nitrogen remains super-stellar regardless of the number of planets in the system such that super-stellar values in N/H of giant planet atmospheres may be a tracer for the importance of pebble drift and evaporation.

- Aims: We intended to quantify the impact of stellar multiplicity on the presence and properties of exoplanets. - Methods: We investigated all exoplanet host stars at less than 100 pc using the latest astrometric data from Gaia DR3 and advanced statistical methodologies. We complemented our search for common proper motion and parallax companions with data from the Washington Double Star catalogue and the literature. After excluding a number of systems based on radial velocity data, and membership in clusters and open associations, or with resolved ultracool companions, we kept 215 exoplanet host stars in 212 multiple-star systems. - Results: We found 17 new companions in the systems of 15 known exoplanet host stars, measured precise angular and projected physical separations and position angles for 236 pairs of stars, compiled key parameters for 276 planets in multiple systems, and established a comparison sample comprising 687 single stars with exoplanets. With all of this, we statistically analysed a series of hypothesis regarding planets in multiple stellar systems. Although they are only statistically significant at a 2{\sigma} level, our analysis pointed to several interesting results on the comparison in the mean number of planets in multiple versus single stellar systems and the tendency of high mass planets to be located in closer orbits in multiple systems. We confirm that planets in multiple systems tend to have orbits with larger eccentricities than those in single systems. In particular, we found a significant (> 4{\sigma}) preference for planets to exhibit high orbital eccentricities at small ratios between star-star projected physical separations and star-planet semi-major axes.

We used the dendrogram algorithm to decompose the surface density distributions of stars into hierarchical structures. These structures were tied to the multiscale structures of star clusters. A similar power-law for the mass-size relation of star clusters measured at different scales suggests a self-similar structure of star clusters. We used the minimum spanning tree method to measure the separations between clusters and gas clumps in each massive star-forming region. The separations between clusters, between clumps, and between clusters and clumps were comparable, which indicates that the evolution from clump to embedded cluster proceeds in isolation and locally, and does not affect the surrounding objects significantly. By comparing the mass functions of the ATLASGAL clumps and the identified embedded clusters, we confirm that a constant star formation efficiency of $\approx$ 0.33 can be a typical value for the ATLASGAL clumps.

The ultra high-energy (UHE) diffuse gamma-ray background holds important information on the propagation of cosmic rays in the Galaxy. However, its measurements suffer from a contamination from unresolved sources whose importance remains unclear. In this Letter, we propose a novel data-driven estimate of the contribution of unresolved leptonic sources based on the information present in the ATNF and the LHAASO catalogs. We find that in the inner Galaxy at most $\sim60\%$ of the diffuse flux measured by LHAASO at $10\,\rm{TeV}$ may originate from unresolved leptonic sources, and this fraction drops with energy to less than $20\%$ at $100\,\rm{TeV}$. In the outer Galaxy, the contribution of unresolved leptonic sources is always subdominant. It is less than $\sim 20\%$ at $10\,\rm{TeV}$ and less than $\sim 8\%$ above $\sim25\,\rm{TeV}$. We conclude that the UHE diffuse background should be dominated by photons from a hadronic origin above a few tens of $\rm{TeV}$.

The reconstruction of the polarization of a source in radio interferometry is a challenging calibration problem since the reconstruction strongly depends on the gains and leakages that need to be inferred along with the image. This is particularly true for the Event Horizon Telescope (EHT) due to its small number of antennas, small signal-to-noise ratio and large gain corruptions. To recover linear polarization, one either has to infer the leakages and gains together with the image structure, or rely completely on calibration independent closure quantities. While the first approach has been explored in Very Long Baseline Interferometry (VLBI) for a long time, the later one has been less studied for polarimetry. Closure traces are a recently proposed concept of closure quantities that, in contrast to closure phases and closure amplitudes, are independent against both gains and leakages and carry the relevant information about the polarization of the source. Here we explore, how closure traces could be directly fitted to create an image and point out an imaging pipeline that succeeds in the direct imaging from closure traces. Since closure traces have a number of inherent degeneracies, multiple local image modes that can fit the data are detected. Therefore, a multiobjective imaging technique is needed to correctly sample this multimodality. Closure traces are not constraining enough for the EHT configuration in 2017 to recover an image directly, mainly due to the small number of antennas. For planned successors of the EHT however (with a significantly larger number of antennas), this option becomes feasible and performs competitive to the imaging with residual leakages.

Context. 3D numerical simulations of radiative transfer are crucial for understanding complex astrophysical objects. For Monte Carlo radiative transfer, the spatial grid design is critical yet complex. Common grids include hierarchical octree and unstructured Voronoi grids, each with its own strengths and weaknesses. Tetrahedral grids, widely used in ray-tracing graphics, are a potential alternative. Aims. We explore the possibilities, advantages, and limitations of tetrahedral grids for Monte Carlo radiative transfer, comparing their performance with other grid structures. Method. We integrated a tetrahedral grid structure, using the TetGen library, into the SKIRT Monte Carlo radiative transfer code. Tetrahedral grids can be imported or adaptively constructed and refined within SKIRT. We implemented an efficient grid traversal method using Plücker coordinates and Plücker products. Results. We validated the tetrahedral grid construction and traversal algorithm with 2D radiative transfer benchmarks. In a simple 3D model, we compared the performance of tetrahedral, octree, and Voronoi grids. The octree grid outperformed the others in traversal speed, while the tetrahedral grid had the lowest grid quality. Overall, tetrahedral grids performed worse than octree and Voronoi grids. Conclusion. While tetrahedral grids may not be ideal for most astrophysical simulations, they offer a viable unstructured alternative to Voronoi grids for specific applications, such as post-processing hydrodynamical simulations on tetrahedral or unstructured grids.

The turbulent ionosphere causes phase shifts to incoming radio waves on a broad range of temporal and spatial scales. When an interferometer is not sufficiently calibrated for the direction-dependent ionospheric effects, the time-varying phase shifts can cause the signal to decorrelate. The ionosphere's influence over various spatiotemporal scales introduces a baseline-dependent effect on the interferometric array. We study the impact of baseline-dependent decorrelation on high-redshift observations with the Low Frequency Array (LOFAR). Datasets with a range of ionospheric corruptions are simulated using a thin-screen ionosphere model, and calibrated using the state-of-the-art LOFAR Epoch of Reionisation pipeline. For the first time ever, we show the ionospheric impact on various stages of the calibration process including an analysis of the transfer of gain errors from longer to shorter baselines using realistic end-to-end simulations. We find that direction-dependent calibration for source subtraction leaves excess power of up to two orders of magnitude above the thermal noise at the largest spectral scales in the cylindrically averaged auto-power spectrum under normal ionospheric conditions. However, we demonstrate that this excess power can be removed through Gaussian process regression, leaving no excess power above the ten per cent level for a $5~$km diffractive scale. We conclude that ionospheric errors, in the absence of interactions with other aggravating effects, do not constitute a dominant component in the excess power observed in LOFAR Epoch of Reionisation observations of the North Celestial Pole. Future work should therefore focus on less spectrally smooth effects, such as beam modelling errors.