Papers for Friday, Apr 08 2022

We present a new Keck/NIRSPEC observation of metastable helium absorption from the upper atmosphere of HD 189733b, a hot Jupiter orbiting a nearby moderately active star. We measure an average helium transit depth of $0.420 \pm 0.013$% integrated over the [-20, 20] km/s velocity range. Comparing this measurement to eight previously published transit observations with different instruments, we find that our depth is 32% (9$\sigma$) lower than the average of the three CARMENES transits, but only 16% (4.4$\sigma$) lower than the average of the five GIANO transits. We perform 1D hydrodynamical simulations of the outflow, and find that XUV variability on the order of 33%--common for this star--can change the helium absorption depth by 60%. We conclude that changes in stellar XUV flux can explain the observational variability in helium absorption. 3D models are necessary to explore other sources of variability, such as shear instability and changing stellar wind conditions.

We search for additional companions in the GJ 367 exoplanet system, and aim at better constraining its age and evolutionary status. We analyse high contrast direct imaging observations obtained with HST/NICMOS, VLT/NACO, and VLT/SPHERE. We investigate and critically discuss conflicting age indicators based on theoretical isochrones and models for Galactic dynamics. A comparison of GAIA EDR3 parallax and photometric measurements with theoretical isochrones suggest a young age $\le$60 Myr for GJ 367. The star's Galactic kinematics exclude membership to any nearby young moving group or stellar stream. Its highly eccentric Galactic orbit, however, is atypical for a young star. Age estimates considering Galactic dynamical evolution are most consistent with an age of 1 to 8 Gyr. We find no evidence for a significant mid-infrared excess in the WISE bands, suggesting the absence of warm dust in the GJ 367 system. The direct imaging data provide significantly improved detection limits compared to previous studies. At 530 mas (5 au) separation, the SPHERE data achieve a 5 sigma contrast of $2.6 \times 10^{-6}$. The data exclude the presence of a stellar companion at projected separations $\ge$0.4 au. At projected separations $\ge$5 au we can exclude substellar companions with a mass $\ge$ 1.5 M$_{\rm Jup}$ for an age of 50 Myr, and $\ge$ 20 M$_{\rm Jup}$ for an age of 5 Gyr. By applying the stellar parameters corresponding to the 50 Myr isochrone, we derive a bulk density of $\rho_{\rm planet} = 6.2$ g/cm$^3$ for GJ 367b, which is 25% smaller than a previous estimate.

Assuming a LCDM universe in a single-field inflationary scenario, we compute the three-point correlation function of the observed matter density fluctuation in the squeezed triangular configuration, accounting for all the relativistic effects at the second order in perturbations. This squeezed three-point correlation function characterizes the local-type primordial non-Gaussianity, and it has been extensively debated in literature whether there exists a prominent feature in galaxy clustering on large scales in a single-field inflationary scenario either from the primordial origin or the intrinsic nonlinearity in general relativity. First, we show that theoretical descriptions of galaxy bias are incomplete in general relativity due to ambiguities in spatial gauge choice, while those of cosmological observables are independent of spatial gauge choice. Hence a proper relativistic description of galaxy bias is needed to reach a definitive conclusion in galaxy clustering. Second, we demonstrate that the gauge-invariant calculations of the cosmological observables remain unaffected by extra coordinate transformations like CFC or large diffeomorphism like dilatation. Finally, we show that the relativistic effects associated with light propagation in observations cancel each other, and hence there exists NO non-Gaussian contribution from the so-called projection effects.

We examine the long-term evolution of accretion tori around black hole (BH) remnants of compact object mergers involving at least one neutron star, to better understand their contribution to kilonovae and the synthesis of r-process elements. To this end, we modify the unsplit magnetohydrodynamic (MHD) solver in FLASH4.5 to work in non-uniform three-dimensional spherical coordinates, enabling more efficient coverage of a large dynamic range in length scales while exploiting symmetries in the system. This modified code is used to perform BH accretion disk simulations that vary the initial magnetic field geometry and disk compactness, utilizing a physical equation of state, a neutrino leakage scheme for emission and absorption, and modeling the BH's gravity with a pseudo-Newtonian potential. Simulations run for long enough to achieve a radiatively-inefficient state in the disk. We find robust mass ejection with both poloidal and toroidal initial field geometries, and suppressed outflow at high disk compactness. With the included physics, we obtain bimodal velocity distributions that trace back to mass ejection by magnetic stresses at early times, and to thermal processes in the radiatively-inefficient state at late times. The electron fraction distribution of the disk outflow is broad in all models, and the ejecta geometry follows a characteristic hourglass shape. We test the effect of removing neutrino absorption or nuclear recombination with axisymmetric models, finding $\sim 50\%$ less mass ejection and more neutron-rich composition without neutrino absorption, and a subdominant contribution from nuclear recombination. Tests of the MHD and neutrino leakage implementations are included.

When ice on the surface of dust grains in protoplanetary disk sublimates, it adds its latent heat of water sublimation to the surrounding flow. Drawing on the analogy provided by tropical cyclones on Earth, we investigate if this energy source is sufficient to sustain or magnify anticyclonic disk vortices that would otherwise fall victim to viscous dissipation. An analytical treatment, supported by exploratory two-dimensional simulations, suggests that even modestly under-saturated flows can extend the lifetime of vortices, potentially to a degree sufficient to aid particle trapping and planetesimal formation. We expect the best conditions for this mechanism to occur will be found near the disk's water ice line if turbulent motions displace gas parcels out of thermodynamic equilibrium with the dust mid-plane.

We report the first spatially resolved measurements of gas-phase metallicity radial gradients in star-forming galaxies in overdense environments at $z\gtrsim2$. The spectroscopic data are acquired by the \mg\ survey, a Hubble Space Telescope (HST) cycle-28 medium program. This program is obtaining 45 orbits of WFC3/IR grism spectroscopy in the density peak regions of three massive galaxy protoclusters (BOSS 1244, BOSS 1542 and BOSS 1441) at $z=2-3$. Our sample in the BOSS 1244 field consists of 20 galaxies with stellar-mass ranging from $10^{9.0}$ to $10^{10.3}$ \Msun\ , star formation rate (SFR) from 10 to 240 \Msun\,yr$^{-1}$, and global gas-phase metallicity (\oh) from 8.2 to 8.6. At $1\sigma$ confidence level, 2/20 galaxies in our sample show positive (inverted) gradients -- the relative abundance of oxygen increasing with galactocentric radius, opposite the usual trend. Furthermore, 1/20 shows negative gradients and 17/20 are consistent with flat gradients. This high fraction of flat/inverted gradients is uncommon in simulations and previous observations conducted in blank fields at similar redshifts. To understand this, we investigate the correlations among various observed properties of our sample galaxies. We find an anticorrelation between metallicity gradient and global metallicity of our galaxies residing in extreme overdensities, and a marked deficiency of metallicity in our massive galaxies as compared to their coeval field counterparts. We conclude that the cold-mode gas accretion plays an active role in shaping the chemical evolution of galaxies in the protocluster environments, diluting their central chemical abundance, and flattening/inverting their metallicity gradients.

Double source lensing, with two sources lensed by the same foreground galaxy, involves the distance between each source and the lens and hence is a probe of the universe away from the observer. The double source distance ratio also reduces sensitivity to the lens model and has good complementarity with standard distance probes. We show that using this technique at high redshifts $z>1$, to be enabled by data from the Euclid satellite and other surveys, can give insights on dark energy, both in terms of $w_0$-$w_a$ and redshift binned density. We find a dark energy figure of merit of 245 from combination of 256 double source systems with moderate quality cosmic microwave background and supernova data. Using instead five redshift bins between $z=1.1$-5, we could detect the dark energy density out to $z\approx5$, or make measurements ranging between 31$\sigma$ and 2.5$\sigma$ of its values in the bins.

One of the largest uncertainties in stellar evolutionary computations is the accuracy of the considered reaction rates. The 12C(alpha,gamma)16O reaction is particularly important for the study of low- and intermediate-mass stars as it determines the final C/O ratio in the core which influences the white dwarf cooling evolution. Thus, there is a need for a study of how the computations of white dwarfs and their progenitors that are made to date may be affected by the uncertainties of the 12C(alpha,gamma)16O reaction rates. In this work we compute fully evolutionary sequences using the MESA code with initial masses in the range of 0.90 <= Mi/Msun <= 3.05. We consider different adopted reaction rates, obtained from the literature, as well as the extreme limits within their uncertainties. As expected, we find that previous to the core helium burning stage there are no changes to the evolution of the stars. However, the subsequent stages are all affected by the uncertainties of the considered reaction rate. In particular, we find differences to the convective core mass during the core helium burning stage which may affect pulsation properties of subdwarfs, the number of thermal pulses during the asymptotic giant branch and trends between final oxygen abundance in the core and the progenitor masses of the remnant white dwarfs.

Among the various oscillation modes of neutron stars, f- and g- modes are the most likely to be ultimately observed in binary neutron star mergers. The f-mode is known to correlate in normal neutron stars with their tidal deformability, moment of inertia and quadrupole moment. Using a piecewise polytropic parameterization scheme to model the uncertain hadronic high-density EOS and a constant sound-speed scheme to model pure quark matter, we refine this correlation and show that these universal relations also apply to both self-bound stars and hybrid stars containing phase transitions. We identify a novel 1-node branch of the f-mode that occurs in low-mass hybrid stars in a narrow mass range just beyond the critical mass necessary for a phase transition to appear. This 1-node branch shows the largest, but still small, deviations from the universal correlation we have found. The g-mode frequency only exists in matter with a non-barotropic equation of state involving temperature, chemical potential or composition, or a phase transition in barotropic matter. The g-mode therefore could serve as a probe for studying phase transitions in hybrid stars. In contrast with the f-mode, discontinuity g-mode frequencies depend strongly on properties of the transition (the density and the magnitude of the discontinuity) at the transition. Imposing causality and maximum mass constraints, the g-mode frequency in hybrid stars is found to have an upper bound of about 1.25 kHz. However, if the sound speed c_s in the inner core at densities above the phase transition density is restricted to c_s^2 < c^2/3, the g-mode frequencies can only reach about 0.8 kHz, which are significantly lower than f-mode frequencies, 1.3-2.8 kHz. Also, g-mode gravitational wave damping times are extremely long, >10^4 s (10^2 s) in the inner core with c_s^2< c^{2/3} (c^2), in comparison with the f-mode damping time, 0.1-1 s.

We study the 3D axis of rotation (3D spin) of 77 HI galaxies from the MIGHTEE-HI Early Science observations, and its relation to the filaments of the cosmic web. For this HI-selected sample, the alignment between the spin axis and the closest filament ($\lvert \cos \psi \rvert$) is higher for galaxies closer to the filaments, with $\langle\lvert \cos \psi \rvert\rangle= 0.66 \pm 0.04$ for galaxies $<5$ Mpc from their closest filament compared to $\langle\lvert \cos \psi \rvert\rangle= 0.37 \pm 0.08$ for galaxies at $5 < d <10$ Mpc. We find that galaxies with a low HI-to-stellar mass ratio ($\log_{10}(M_{\rm HI}/M_{\star}) < 0.11$) are more aligned with their closest filaments, with $\langle\lvert \cos \psi \rvert\rangle= 0.58 \pm 0.04$; whilst galaxies with ($\log_{10}(M_{\rm HI}/M_{\star}) > 0.11$) tend to be mis-aligned, with $\langle\lvert \cos \psi \rvert\rangle= 0.44 \pm 0.04$. We find tentative evidence that the spin axis of HI-selected galaxies tend to be aligned with associated filaments ($d<10$ Mpc), but this depends on the gas fractions. Galaxies that have accumulated more stellar mass compared to their gas mass tend towards stronger alignment. Our results suggest that those galaxies that have accrued high gas fraction with respect to their stellar mass may have had their spin axis alignment with the filament disrupted by a recent gas-rich merger, whereas the spin vector for those galaxies in which the neutral gas has not been strongly replenished through a recent merger tend to orientate towards alignment with the filament. We also investigate the spin transition between galaxies with a high HI content and a low HI content at a threshold of $M_{\mathrm{HI}}\approx 10^{9.5} M_{\odot}$ found in simulations, however we find no evidence for such a transition with the current data.

Predictions of the mean and covariance matrix of summary statistics are critical for confronting cosmological theories with observations, not least for likelihood approximations and parameter inference. The price to pay for accurate estimates is the extreme cost of running a large number of $N$-body and hydrodynamics simulations. Approximate solvers, or surrogates, greatly reduce the computational cost but can introduce significant biases, for example in the non-linear regime of cosmic structure growth. We adopt a Bayesian approach to solve the estimation problem for both the means and covariances using a combination of simulations and surrogates. Our framework allows incorporating prior information for the mean and covariance. We derive closed-form solutions for Maximum A Posteriori covariance estimates that are efficient Bayesian shrinkage estimators, guarantee positive semi-definiteness, and can optionally leverage analytical covariance approximations. We discuss choices of the prior and propose a simple procedure for obtaining optimal prior hyperparameter values with a small set of test simulations. We test our method by estimating the covariances of clustering statistics of GADGET-III $N$-body simulations at redshift $z=0.5$ using surrogates from a 100-1000$\times$ faster particle-mesh code. Taking the sample covariance from 15,000 simulations as the truth, and using an empirical Bayes prior with diagonal blocks, our estimator produces nearly identical Fisher matrix contours for $\Lambda$CDM parameters using only $15$ simulations of the non-linear dark matter power spectrum. In this case the number of simulations is so small that the sample covariance would be degenerate. We show cases where even with a na\"ive prior our method still improves the estimate. Our framework is applicable to a wide range of cosmological and astrophysical problems where fast surrogates are available.

We present the validation of a transiting low-density exoplanet orbiting the M2.5 dwarf TOI 620 discovered by the NASA TESS mission. We utilize photometric data from both TESS and ground-based follow-up observations to validate the ephemerides of the 5.09-day transiting signal and vet false positive scenarios. High-contrast imaging data are used to resolve the stellar host and exclude stellar companions at separations $\gtrsim 0.2''$. We obtain follow-up spectroscopy and corresponding precise radial velocities (RVs) with multiple PRV spectrographs to confirm the planetary nature of the transiting exoplanet. We calculate a 5$\sigma$ upper limit of $M_P < 7.1$ M$_\oplus$ and $\rho_P < 0.74$ g cm$^{-3}$, and we identify a non-transiting 17.7-day candidate. We also find evidence for a substellar (1-20 M$_{\rm J}$) companion with a projected separation $\lesssim 20$ au from a combined analysis of Gaia, AO imaging, and RVs. With the discovery of this outer companion, we carry out a detailed exploration of the possibilities that TOI 620 b might instead be a circum-secondary planet or a pair of eclipsing binary stars orbiting the host in a hierarchical triple system. We find, under scrutiny, that we can exclude both of these scenarios from the multi-wavelength transit photometry, thus validating TOI 620 b as a low-density exoplanet transiting the central star in this system. The low density of TOI 620 b makes it one of the most amenable exoplanets for atmospheric characterization, such as with JWST and Ariel, validated or confirmed by the TESS mission to date.

Axion-like particles (ALPs) can be produced by thermal processes in a stellar interior, escape from the star and, if sufficiently light, be converted into photons in the external Galactic magnetic field. Such a process could produce a detectable hard X-ray excess in the direction of the star. In this scenario, a promising class of targets is the red supergiants, massive stars which are experiencing the late part of their evolution. We report on a search for ALP-induced X-ray emission from Betelgeuse, produced via the combined processes of Bremsstrahlung, Compton and Primakoff. Using a 50 ks observation of Betelgeuse by the \emph{NuSTAR} satellite telescope, we set 95\% C.L. upper limits on the ALP-electron ($g_{ae}$) and ALP-photon ($g_{a\gamma}$) couplings. For masses ${m_{a}\leq(3.5-5.5)\times10^{-11}}$ eV, we find $g_{a\gamma} \times g_{ae}< (0.4-2.8)\times10^{-24}$ GeV$^{-1}$ (depending on the stellar model and assuming a value of the regular Galactic magnetic field in the direction transverse to Betelgeuse of $B_T$=1.4 $\mu$G). This corresponds to ${g_{ae}<(0.4-2.8) \times10^{-12}}$ for ${g_{a\gamma}>1.0\times10^{-12}}$ GeV$^{-1}$. This analysis supercedes by over an order of magnitude the limit on $g_{ae} \times g_{a\gamma}$ placed by the CAST solar axion experiment and is among the strongest constraints on these couplings.

Detailed numerical models of chromosphere and corona are required to understand the heating of the solar atmosphere. An accurate treatment of the solar chromosphere is complicated by the effects arising from Non Local Thermodynamic Equilibrium (NLTE) radiative transfer. A small number of strong, highly scattering lines dominate the cooling and heating in the chromosphere. Additionally, the recombination times of ionised hydrogen are longer than the dynamical timescales, requiring a non-equilibrium (NE) treatment of hydrogen ionisation. The MURaM code is extended to include the physical process required for accurate simulation of the solar chromosphere, as implemented in the Bifrost code. This includes a time-dependent treatment of hydrogen ionisation, a scattering multi-group radiation transfer scheme and approximations for NLTE radiative cooling. The inclusion of NE and NLTE physics has a large impact on the structure of the chromosphere; the NE treatment of hydrogen ionisation leads to a higher ionisation fraction and enhanced populations in the first excited state throughout cold inter-shock regions of the chromosphere. Additionally this prevents hydrogen ioniation from buffering energy fluctuations, leading to hotter shocks and cooler inter-shock regions. The hydrogen populations in the ground and first excited state are enhanced by $10^2-10^3$ in the upper chromosphere and up to $10^9$ near the transition region. Including the necessary NLTE physics leads to significant differences in chromospheric structure and dynamics. The thermodynamics and hydrogen populations calculated using the extended version of the MURaM code are consistent with previous non-equilibrium simulations. The electron number and temperature calculated using the non-equilibrium treatment of the chromosphere are required to accurately synthesise chromospheric spectral lines.

The FAST Ultra-Deep Survey (FUDS) is a blind survey that aims for the direct detection of HI in galaxies at redshifts $z<0.42$. The survey uses the multibeam receiver on the Five Hundred Meter Aperture Spherical Telescope (FAST) to map six regions, each of size 0.72 deg$^2$ at high sensitivity ($\sim 50 \mu$Jy) and high frequency resolution (23 kHz). The survey will enable studies of the evolution of galaxies and their HI content with an eventual sample size of $\sim 1000$. We present the science goals, observing strategy, the effects of radio frequency interference (RFI) at the FAST site, our mitigation strategies and the methods for calibration, data reduction and imaging as applied to initial data. The observations and reductions for the first field, FUDS0, are completed, with around 128 HI galaxies detected in a preliminary analysis. Example spectra are given in this paper, including a comparison with data from the overlapping GAL2577 field of Arecibo Ultra-Deep Survey (AUDS).

Future high-contrast imaging spectroscopy with a large segmented telescope will be able to detect atmospheric molecules of Earth-like planets around G- or K-type main-sequence stars. Increasing the number of target planets will require a coronagraph with a small inner working angle (IWA), and wide spectral bandwidth is required if we enhance a variety of detectable atmospheric molecules. To satisfy these requirements, in this paper, we present a coronagraphic system that provides an IWA less than 1$\lambda_0 / D$ over a moderate wavelength band, where $\lambda_0$ is the design-center wavelength and $D$ denotes the full width of the rectangular aperture included in the telescope aperture. A performance simulation shows that the proposed system approximately achieves a contrast below $10^{-10}$ at 1$\lambda_0 / D$ over the wavelengths of 650--750nm. In addition, this system has a core throughput $\geq$ 10\% at input separation angles of $\sim$ 0.7--1.4$\lambda_0 / D$; to reduce telescope time, we need prior information on the target's orbit by other observational methods to a precision higher than the width of the field of view. For some types of aberration including tilt aberration, the proposed system has a sensitivity less than ever-proposed coronagraphs that have IWAs of approximately $1\lambda_0/D$. In future observations of Earth-like planets, the proposed coronagraphic system may serve as a supplementary coronagraphic system dedicated to achieving an extremely small IWA.

The primordial Lithium Problem is intimately connected to the assumption that ${}^{7}{\rm Li}$ observed in metal-poor halo stars retains its primordial abundance, which lies significantly below the predictions of standard big-bang nucleosynthesis. Two key lines of evidence have argued that these stars have not significantly depleted their initial ${}^{7}{\rm Li}$: i) the lack of dispersion in Li abundances measured at low metallicity; and ii) the detection of the more fragile ${}^{6}{\rm Li}$ isotope in at least two halo stars. The purported ${}^{6}{\rm Li}$ detections were in good agreement with predictions from cosmic-ray nucleosynthesis which is responsible for the origin of ${}^{6}{\rm Li}$. This concordance left little room for depletion of ${}^{6}{\rm Li}$ depletion, and implied that the more robust ${}^{7}{\rm Li}$ largely evaded destruction. Recent (re)-observations of halo stars challenge the evidence against ${}^{7}{\rm Li}$ depletion: i) lithium abundances now show significant dispersion, and ii) sensitive ${}^{6}{\rm Li}$ searches now reveal only firm upper limits to the ${}^{6}{\rm Li}/{}^{7}{\rm Li}$ ratio. The tight new ${}^{6}{\rm Li}$ upper limits generally fall far below the predictions of cosmic-ray nucleosynthesis, implying that substantial ${}^{6}{\rm Li}$ depletion has occurred--by factors up to 50. We show that in stars with ${}^{6}{\rm Li}$ limits and thus lower bounds on ${}^{6}{\rm Li}$ depletion, an equal amount of ${}^{7}{\rm Li}$ depletion is more than sufficient to resolve the primordial ${}^{7}{\rm Li}$ Problem. This picture is consistent with stellar models in which ${}^{7}{\rm Li}$ is less depleted than ${}^{6}{\rm Li}$, and strengthen the case that the Lithium Problem has an astrophysical solution. We conclude by suggesting future observations that could test these ideas. (abridged)

We study the influence of a cosmological population of dense gas clouds on distant sources, with emphasis on quasar optical variability. In addition to gravitational lensing such clouds affect flux measurements via refraction in the neutral gas and via dust extinction, leading to a variety of possible light curves even in the low optical depth limit. We classify and illustrate the types of light curves that can arise. For sources as large as quasars we show that gravitational lensing and extinction are the dominant effects, with gas refraction playing only a minor role. We find that clouds with mass ~10^{-4.5+/-0.5} M_\odot can reproduce the observed distribution of quasar variation amplitudes, but only if such clouds make up a large fraction of the closure density. In that case there may also be substantial extinction of distant optical sources, which can in principle be constrained by data on "standard candles" such as type Ia supernovae. Unfortunately that extinction is essentially grey, even when the material opacity is strongly wavelength dependent, making it difficult to distinguish from the influence of the background geometry. We propose a novel statistical test of the origin of quasar variability, based on the angular structure of the variation timescale for a large number of quasars distributed all over the sky. If quasar variability is primarily due to nanolensing that angular structure is expected to include a quadrupole term of amplitude $\sim5\%$, which ought to be measurable with future data from the Gaia mission.

The observed early X-ray plateau in the afterglow lightcurves of some gamma-ray bursts (GRBs) is attributed to the dipole radiations (DRs) of a newborn magnetar. A quasi-periodic oscillation (QPO) signal in the plateau would be strong evidence of the magnetar precession motion. By making a time-frequency domain analysis for the X-ray afterglow lightcurve of GRB 180620A, we find a QPO signal of $\sim650$ seconds in its early X-ray plateau. We fit the lightcurve with a magnetar precession model by adopting the Markov chain Monte Carlo algorithm. The observed lightcurve and the QPO signal are well represented with our model. The derived magnetic field strength of the magnetar is $B_{\rm p}= (1.02^{+0.59}_{-0.61})\times10^{15}$~G. It rapidly spins down with angular velocity evolving as $\Omega_{s} \propto(1+t/\tau_{\rm sd})^{-0.96}$, where $\tau_{\rm sd}=9430$~s. Its precession velocity evolution is even faster than $\Omega_s$, i.e. $\Omega_{ p}\propto (1+t/\tau_{p})^{-2.18\pm0.11}$, where $\tau_{p}=2239\pm206$~s. The inferred braking index is $n=2.04$. We argue that the extra energy loss via the magnetospheric processes results in its rapid spin-down, a low braking index of the magnetar, and the strong precession motion.

The attenuation of very high energy (VHE) photons by the extragalactic background light (EBL) prevents the observation of high redshift flat spectrum radio quasars (FSRQs). Existing EBL models predict only a handful of FSRQs which fall above the sensitivity of the forthcoming VHE telescopes. However, recent detection of high redshift FSRQs by existing Cherenkov telescopes question the inferred opacity of the universe to VHE gamma-rays. In order to justify the VHE detection of these FSRQs, we introduce a redshift dependent correction factor to the existing opacity estimate. Using this we identify the plausible VHE FSRQ candidates by extrapolating the Fermi gamma-ray spectrum to VHE regime. Our study suggests among 744 FSRQs reported in Fermi fourth catalog-Data release 2 (4FGL-DR2), 34 FSRQs will be detectable under Alpha configuration of Cherenkov Telescope Array Observatory (CTAO) while the number will increase to 37 under Omega configuration. Considering the flux variability of blazars, doubling the average Fermi gamma-ray flux will result in additional 44 FSRQs detectable by CTAO Omega configuration.

Blue Large Amplitude Pulsators (BLAPs) are a relatively new class of blue variable stars showing periodic variations in their light curves with periods shorter than a few tens of mins and amplitudes of more than ten percent. We report nine blue variable stars identified in the OmegaWhite survey conducted using ESO's VST, which show a periodic modulation in the range 7-37 min and an amplitude in the range 0.11-0.28 mag. We have obtained a series of followup photometric and spectroscopic observations made primarily using SALT and telescopes at SAAO. We find four stars which we identify as BLAPs, one of which was previously known. One star, OW J0820--3301, appears to be a member of the V361 Hya class of pulsating stars and is spatially close to an extended nebula. One further star, OW J1819--2729, has characteristics similar to the sdAV pulsators. In contrast, OW J0815--3421 is a binary star containing an sdB and a white dwarf with an orbital period of 73.7 min, making it only one of six white dwarf-sdB binaries with an orbital period shorter than 80 min. Finally, high cadence photometry of four of the candidate BLAPs show features which we compare with notch-like features seen in the much longer period Cepheid pulsators.

We complete the survey for finite-source/point-lens (FSPL) giant-source events in 2016-2019 KMTNet microlensing data. The 30 FSPL events show a clear gap in Einstein radius, $9\,\mu{\rm as}<\theta_{\rm E} <26\,\mu{\rm as}$, which is consistent with the gap in Einstein timescales near $t_{\rm E}\sim 0.5\,$days found by Mroz et al. (2017) in an independent sample of point-source/point-lens (PSPL) events. We demonstrate that the two surveys are consistent. We estimate that the 4 events below this gap are due to a power-law distribution of free-floating planet candidates (FFPs) $dN_{\rm FFP}/d\log M = (0.4\pm 0.2)\,(M/38 M_\oplus)^{-p}$/star, with $0.9\lesssim p \lesssim 1.2$. There are substantially more FFPs than known bound planets, implying that the bound planet power-law index $\gamma=0.6$ is likely shaped by the ejection process at least as much as by formation. The mass density per decade of FFPs in the Solar neighborhood is of the same order as that of 'Oumuamua-like objects. In particular, if we assume that 'Oumuamua is part of the same process that ejected the FFPs to very wide or unbound orbits, the power-law index is $p=0.92\pm 0.06$. If the Solar System's endowment of Neptune-mass objects in Neptune-like orbits is typical, which is consistent with the results of Poleski et al. (2021), then these could account for a substantial fraction of the FFPs in the Neptune-mass range.

To understand how the evolution of grain size distribution in galaxies affects observed dust properties, we apply a post-processing dust evolution model to galaxy merger trees from the IllustrisTNG cosmological hydrodynamical simulation. Our dust model includes stellar dust production, sputtering in hot gas, dust growth by accretion and coagulation in the dense interstellar medium (ISM), and shattering in the diffuse ISM. We decompose the grain size distribution into different dust species depending on the elemental abundances and the dense ISM fraction given by the simulation. In our previous work, we focused on Milky Way (MW) analogs and reproduced the observed MW extinction curve. In this study, we compute dust spectral energy distributions (SEDs) for the MW analogues. Our simulated SEDs broadly reproduce the observed MW SED within their dispersion and so does the observational data of nearby galaxies, although they tend to underpredict the MW SED at short wavelengths where emission is dominated by polycyclic aromatic hydrocarbons (PAHs). We find that metallicity and dense gas fraction are the most critical factors for the SED shape, through their influence on coagulation and shattering.The overall success of our models in reproducing the MW SED further justifies the dust evolution processes included in the model and predicts the dispersion in the SEDs caused by the variety in the assembly history. We also show that the most significant increase in the dust SED occurs between redshifts $z\sim 3$ and 2 in the progenitors of the simulated MW-like galaxies.

The nucleosynthesis production of fluorine (F) is still a matter of debate. Asymptotic giant branch (AGB) stars are one of the main candidates for F production. However, their contribution to the total F budget is not fully known due to the lack of observations. In this paper, we report the detection of AlF line emission, one of the two main carriers of F in the gas-phase in the outflow of evolved stars, towards five nearby oxygen-rich AGB stars, $o$ Ceti, R Leo, IK Tau, R Dor, and W Hya. From spatially resolved observations, we estimated the AlF emitting region with a radius $\sim11R_{\star}$ for $o$ Ceti and $\sim9R_{\star}$ for R Leo. From population diagram analysis, we report the AlF column densities of $\sim 5.8\times10^{15}$ cm$^{-2}$ and $\sim 3\times10^{15}$ cm$^{-2}$ for $o$ Ceti and R Leo, respectively, within these regions. For $o$ Ceti, we used the C$^{18}$O ($v=0$, $J=3-2$) observations to estimate the H$_2$ column density of the emitting region. We found a fractional abundance of $f_{\rm AlF/H_2}\sim(2.5\pm1.7)\times10^{-8}$. This gives a lower limit on the F budget in $o$ Ceti and is compatible with the solar F budget $f_{\rm F/H_2}=(5\pm2)\times10^{-8}$. For R Leo, a fractional abundance $f_{\rm AlF/H_2}=(1.2\pm0.5)\times10^{-8}$ is estimated. For other sources, we cannot precisely determine the emitting region based on the available data. Assuming an emitting region with a radius of $\sim 11R_{\star}$ and the rotational temperatures derived for $o$ Ceti and R Leo, we crudely approximated the AlF column density to be $\sim(1.2-1.5)\times10^{15}$ cm$^{-2}$ in W Hya, $\sim(2.5-3.0)\times10^{14}$ cm$^{-2}$ in R Dor, and $\sim(0.6-1.0)\times10^{16}$ cm$^{-2}$ in IK Tau. These result in fractional abundances within a range of $f_{\rm AlF/H_2}\sim(0.1-4)\times10^{-8}$ in W Hya, R Dor, and IK Tau.

There is a small group of peculiar early-type stars on the main sequence that show different rotation velocities from different spectral lines. This inconsistency might be due to the binary nature of these objects. We aim to verify this hypothesis by a more detailed spectroscopic and photometric investigation of one such object: HD 183986. We obtained 151 high and medium resolution spectra that covered an anticipated long orbital period. There is clear evidence of theorbital motion of the primary component. We uncovered a very faint and broad spectrum of the secondary component. The corresponding SB2 orbital parameters, and the component spectra, were obtained by Fourier disentangling using the KOREL code. The component spectra were further modeled by iSpec code to arrive at the atmospheric quantities and the projected rotational velocities. We have proven that this object is a binary star with the period $P$ = 1268.2(11) d, eccentricity $e$ = 0.5728(20), and mass ratio $q$ = 0.655. The primary component is a slowly rotating star ($v \sin i = 27$ km.s$^{-1}$) while the cooler and less massive secondary rotates much faster ($v \sin i \sim 120$ km.s$^{-1}$). Photometric observations obtained by the TESS satellite were also investigated to shed more light on this object. A multi-period photometric variability was detected in the TESS data ranging from hours (the $\delta$ Sct-type variability) to a few days (spots/rotational variability). The physical parameters of the components and the origin of the photometric variability are discussed in more detail.

Photometric observations of occultations of transiting exoplanets can place important constraints on the thermal emission and albedos of their atmospheres. We analyse photometric measurements and derive geometric albedo ($A_\mathrm{g}$) constraints for five hot Jupiters observed with TESS in the optical: WASP-18 b, WASP-36 b, WASP-43 b, WASP-50 b and WASP-51 b. For WASP-43 b, our results are complemented by a VLT/HAWK-I observation in the near-infrared at $2.09~\mu$m. We derive the first geometric albedo constraints for WASP-50 b and WASP-51 b: $A_\mathrm{g}<0.445$ and $A_\mathrm{g}<0.368$, respectively. We find that WASP-43 b and WASP-18 b are both consistent with low geometric albedos ($A_\mathrm{g}<0.16$) even though they lie at opposite ends of the hot Jupiter temperature range with equilibrium temperatures of $\sim1400$ K and $\sim2500$ K, respectively. We report self-consistent atmospheric models which explain broadband observations for both planets from TESS, \HST, \Spitzer and VLT/HAWK-I. We find that the data of both hot Jupiters can be explained by thermal emission alone and inefficient day-night energy redistribution. The data do not require optical scattering from clouds/hazes, consistent with the low geometric albedos observed.

Our goal is to estimate the mass of the Local Group (LG) and the individual masses of its primary galaxies, the M31 and the Milky Way (MW). We do this by means of a supervised machine learning algorithm, the gradient boosted decision trees (GBDT) and using the observed distance and relative velocity of the two as input parameters. The GBDT is applied to a sample of 2148 mock LGs drawn from a set of 5 dark matter (DM)-only simulations, ran within the standard $\Lambda$CDM\ cosmological model. The selection of the mock LGs is guided by a LG model, which defines such objects. The role of the observational uncertainties of the input parameters is gauged by applying the model to an ensemble of mock LGs pairs whose observables are these input parameters perturbed by their corresponding observational errors. Finally the observational data of the actual LG is used to infer its relevant masses. Our main results are the sum and the individual masses of the MW and M31: $M_{tot} = 3.31 ^{+0.79}_{-0.67} $, $M_{MW}=1.15^{+0.25}_{-0.22}$ and $M_{M31}=2.01^{+0.65}_{-0.39} \ \ \times 10^{12}M_{\odot}$ (corresponding to the median and the 1st and 3rd quartiles). The ratio of the masses is $M_{M31}/M_{MW}=1.75^{+0.54}_{-0.28}$, where by convention the M31 is defined here to be the more massive of the two halos.

The elemental abundances in the broad-line regions of high-redshift quasars trace the chemical evolution in the nuclear regions of massive galaxies in the early universe. In this work, we study metallicity-sensitive broad emission-line flux ratios in rest-frame UV spectra of 25 high-redshift (5.8 < z < 7.5) quasars observed with the VLT/X-shooter and Gemini/GNIRS instruments, ranging over $\log(M_{\rm{BH}}/M_{\odot})= 8.4-9.8$ in black hole mass and $\log(L_{\rm{bol}}/\rm{erg\, s}^{-1})= 46.7-47.7$ in bolometric luminosity. We fit individual spectra and composites generated by binning across quasar properties: bolometric luminosity, black hole mass, and blueshift of the \civ\, line, finding no redshift evolution in the emission-line ratios by comparing our high-redshift quasars to lower-redshift (2.0 < z < 5.0) results presented in the literature. Using Cloudy-based locally optimally-emitting cloud photoionisation model relations between metallicity and emission-line flux ratios, we find the observable properties of the broad emission lines to be consistent with emission from gas clouds with metallicity that are at least 2-4 times solar. Our high-redshift measurements also confirm that the blueshift of the CIV emission line is correlated with its equivalent width, which influences line ratios normalised against CIV. When accounting for the CIV blueshift, we find that the rest-frame UV emission-line flux ratios do not correlate appreciably with the black hole mass or bolometric luminosity.

A recent work has found a tight global relation between the GRB fluence, peak flux ( based on the optimum time scale determined from the Bayesian Blocks-based analysis) and duration using data from the Fermi Gamma-Ray burst monitor, which they have dubbed as "Fundamental Plane". We quantitatively characterize the tightness of this Fundamental Plane relation using by calculating the scatter in dex. We also check for a fundamental plane using the peak flux over time scales of 64 ms, 256 ms and 1024 ms. For our analysis, we incorporate the uncertainties in the above observables and carried out both a PCA as well as regression-based analysis. We find that the scatter in the fundamental plane is 0.16-0.17 dex. This is not as as tight as some of the other well known scaling relations in Astrophysics.

We simulate the decay of isolated, spherically symmetric droplets in a cosmological phase transition. It has long been posited that such heated droplets of the metastable state could form, and they have recently been observed in 3D multi-bubble simulations. In those simulations, the droplets were associated with a reduction in the wall velocity and a decrease in the kinetic energy of the fluid, with a consequent suppression in the gravitational wave power spectrum. In the present work, we track the wall speed and kinetic energy production in isolated droplets and compare them to those found in multi-bubble collisions. The late-time wall velocities that we observe match those of the 3D simulations, though we find that the spherical simulations are a poor predictor of the kinetic energy production. This implies that spherically symmetric simulations could be used to refine baryogenesis predictions due to the formation of droplets, but not to estimate any accompanying suppression of the gravitational wave signal.

The diamagnetism of ice particles of the rings can explain their separation and the sharp edges of the rings. The existing gravitational theories of the origin of rings can't explain these observed facts. Taking into account the magnetic field of Saturn, all the particles of the rings acquire stability in the horizontal and vertical directions. The force of diamagnetic expulsion of inhomogeneous magnetic field inside the rings structure forms sharp edges and separates the particles.

Understanding the formation and evolution of the stellar-mass binary black holes discovered by LIGO and Virgo is a challenge that spans many areas of astrophysics, from stellar evolution, dynamics and accretion disks, to possible exotic early universe processes. Over the final years of their lives, stellar-mass binaries radiate gravitational waves that are first observable by space-based detectors (such as LISA) and then ground-based instruments (such as LIGO, Virgo and the next generation observatories Cosmic Explorer and the Einstein Telescope). Using state-of-the-art waveform models and parameter-estimation pipelines for both ground- and space-based observations, we show that (the expected handful of) these multiband observations will allow at least percent-level measurements of all 17 parameters that describe the binary, the possible identification of a likely host galaxy, and the forewarning of the merger days in advance allowing telescopes at multiple wavelengths to search for any electromagnetic signature associated to it. Multiband sources will therefore be a gold mine for astrophysics, but we also show that they are less useful as laboratories for fundamental tests of general relativity than has been previously suggested.

We present new room-temperature 1100 - 1800 cm^{-1} spectra of melilite silicates and 600 - 2000 cm^{-1} spectra of three randomly orientated fine-grained carbonates to determine the possible carrier(s) of a 6.9~micron absorption feature observed in a variety of dense astronomical environments including young stellar objects and molecular clouds. We focus on the low-mass post-AGB star Sakurai's Object which has been forming substantial quantities of carbonaceous dust since an eruptive event in the 1990s. Large melilite grains cannot be responsible for the 6.9-micron absorption feature because the similarly-shaped feature in the laboratory spectrum was produced by very low (0.1 per cent by mass) carbonate contamination which was not detected at other wavelengths. Due to the high band-strength of the 6.9-micron feature in carbonates, we conclude that carbonates carry the astronomical 6.9~micron feature. Replacement of melilite with carbonates in models of Sakurai's object improves fits to the 6 - 7-micron Spitzer spectra without significantly altering other conclusions of Bowey's previous models except that there is no link between the feature and the abundance of melilite in meteorites. With magnesite (MgCO3), the abundance of 25-micron-sized SiC grains is increased by 10 - 50 per cent and better constrained. The mass of carbonate dust is similar to the mass of PAH dust. Existing experiments suggest carbonates are stable below 700~K, however it is difficult to ascertain the applicability of these experiments to astronomical environments and more studies are required.

We numerically model the collapse of magnetic rotating protostellar clouds with mass of 10 $M_{sun}$. The simulations are carried out with the help of 2D MHD code Enlil. The structure of the cloud at the isothermal stage of the collapse is investigated for the cases of weak, moderate, and strong initial magnetic field. Simulations reveal the universal hierarchical structure of collapsing protostellar clouds, consisting of flattened envelope with the qausi-magnetostatc disk inside and the first core in its center. The size of the primary disk increases with the initial magnetic energy of the cloud. The magnetic braking efficiently transports the angular momentum from the primary disk into the envelope in the case, when initial magnetic energy of the cloud is more than 20 % of its gravitational energy. Intensity of the outflows launched from the region near the boundary of the first core increases with initial magnetic energy. The `dead' zone with small ionization fraction, $x<10^{-11}$, forms inside the first hydrostatic core and at the base of the outflow. Ohmic dissipation and ambipolar diffusion determine conditions for further formation of the protostellar disk in this region.

High-contrast imaging of exoplanets hinges on powerful post-processing methods to denoise the data and separate the signal of a companion from its host star, which is typically orders of magnitude brighter. Existing post-processing algorithms do not use all prior domain knowledge that is available about the problem. We propose a new method that builds on our understanding of the systematic noise and the causal structure of the data-generating process. Our algorithm is based on a modified version of half-sibling regression (HSR), a flexible denoising framework that combines ideas from the fields of machine learning and causality. We adapt the method to address the specific requirements of high-contrast exoplanet imaging data obtained in pupil tracking mode. The key idea is to estimate the systematic noise in a pixel by regressing the time series of this pixel onto a set of causally independent, signal-free predictor pixels. We use regularized linear models in this work; however, other (non-linear) models are also possible. In a second step, we demonstrate how the HSR framework allows us to incorporate observing conditions such as wind speed or air temperature as additional predictors. When we apply our method to four data sets from the VLT/NACO instrument, our algorithm provides a better false-positive fraction than PCA-based PSF subtraction, a popular baseline method in the field. Additionally, we find that the HSR-based method provides direct and accurate estimates for the contrast of the exoplanets without the need to insert artificial companions for calibration in the data sets. Finally, we present first evidence that using the observing conditions as additional predictors can improve the results. Our HSR-based method provides an alternative, flexible and promising approach to the challenge of modeling and subtracting the stellar PSF and systematic noise in exoplanet imaging data.

One "strong" magnetic cloud (MC) with the magnetic field magnitude reaching $\sim$ 40 nT at 1 au during 2012 June 16-17 is examined in association with a pre-existing magnetic flux rope (MFR) identified on the Sun. The MC is characterized by a quasi-three dimensional (3D) flux rope model based on in situ measurements from the Wind spacecraft. The magnetic flux contents and other parameters are quantified. In addition, a correlative study with the corresponding measurements of the same structure crossed by the Venus Express (VEX) spacecraft at a heliocentric distance 0.7 au and with an angular separation $\sim 6^\circ$ in longitude is performed to validate the MC modeling results. The spatial variation between the Wind and VEX magnetic field measurements is attributed to the 3D configuration of the structure as featured by a knotted bundle of flux. The comparison of the magnetic flux contents between the MC and the source region on the Sun indicates that the 3D reconnection process accompanying an M1.9 flare may correspond to the magnetic reconnection between the field lines of the pre-existing MFR rooted in the opposite polarity footpoints. Such a process reduces the amount of the axial magnetic flux in the erupted flux rope, by approximately 50\%, in this case.

Analysing a large representative sample of local galaxies (8707), we find that the variation in the shape of their dust attenuation curves is driven primarily by their structure, i.e., distribution of stars (and dust) within them. The attenuation curve for spheroid dominated galaxies, as compared to the disc dominated ones, is nearly twice as steep. Both structural types cover distinct ranges of attenuation slope values. Similar findings are reflected in the case of star-forming and passive galaxies. Spheroids and passive galaxies witness minimal attenuation in the optical compared to UV wavelengths underlining the lack of dusty birth-clouds that define complex star-dust geometry. The distinction in the attenuation properties of spheroids and discs is maintained in each stellar mass range emphasising that structure is the primal cause of variation. However, within a structural group, the attenuation curve becomes shallower with both the increase in total stellar mass and optical depth of the galaxy. Overall, with the extinction curve fixed to be the same for all galaxies, the star-dust geometry emerges to be the prime determinant of the variation in their attenuation properties.

We report on the detection of MKT J174641.0$-$321404, a new radio transient found in untargeted searches of wide-field MeerKAT radio images centred on the black hole X-ray binary H1743$-$322. MKT J174641.0$-$321404 is highly variable at 1.3 GHz and was detected three times during 11 observations of the field in late 2018, reaching a maximum flux density of 590 $\pm$ 60 $\mu$Jy. We associate this radio transient with a high proper motion, M dwarf star SCR~1746$-$3214 12 pc away from the Sun. Multiwavelength observations of this M dwarf indicate flaring activity across the electromagnetic spectrum, consistent with emission expected from dMe stars, and providing upper limits on quiescent brightness in both the radio and X-ray regimes. \textit{TESS} photometry reveals a rotational period for SCR~1746$-$3214 of $0.2292 \pm 0.0025$ days, which at its estimated radius makes the star a rapid rotator, comparable to other low mass systems. Dedicated spectroscopic follow up confirms the star as a mid-late spectral M dwarf with clear magnetic activity indicated by strong H$\alpha$ emission. This transient's serendipitous discovery by MeerKAT, along with multiwavelength characterisation, make it a prime demonstration of both the capabilities of the current generation of radio interferometers and the value of simultaneous observations by optical facilities such as MeerLICHT. Our results build upon the literature of of M dwarfs' flaring behaviour, particularly relevant to the habitability of their planetary systems.

Ultralight bosons are promising dark matter candidates and can trigger superradiant instabilities of spinning black holes (BHs), resulting in long-lived rotating "bosonic clouds" around the BHs and dissipating their energy through the emission of monochromatic gravitational waves (GWs). We focus on the scalar bosons minimally coupled with both isolated stellar-origin BHs (SBH) and their binary merger remnants, and perform Bayesian data analysis to search for the stochastic GW background from all the unstable modes that can trigger the superradiant instabilities using the data of Advanced LIGO and Advanced Virgo's first three observing runs. We find no evidence for such signal, and hence rule out the scalar bosons within the mass range $[1.5, 16]\times10^{-13}$ eV, $[1.9, 8.3]\times10^{-13}$ eV and $[1.3, 17]\times10^{-13}$ eV at $95\%$ confidence level for isolated SBHs having a uniform dimensionless spin distribution in $[0,1]$, $[0,0.5]$ and $[0.5,1]$, respectively.

The detection of GW190521 by the LIGO-Virgo collaboration revealed the existence of black holes (BHs) in the pair-instability (PI) mass gap. Here, we investigate the formation of BHs in the PI mass gap via star -- star collisions in young stellar clusters. To avoid PI, the stellar-collision product must have a relatively small core and a massive envelope. We generate our initial conditions from the outputs of a hydro-dynamical simulation of the collision between a core helium burning star ($\sim 58$ M$_\odot$) and a main-sequence star ($\sim 42$ M$_\odot$). The hydro-dynamical simulation allows us to take into account the mass lost during the collision ($\sim 12$ M$_\odot$) and to build the chemical composition profile of the post-collision star. We then evolve the collision product with the stellar evolution codes PARSEC and MESA. We find that the post-collision star evolves through all the stellar burning phases until core collapse, avoiding PI. At the onset of core collapse, the post-collision product is a blue super-giant star. We estimate a total mass loss of about 1 M$_\odot$ during the post-collision evolution, due to stellar winds and shocks induced by neutrino emission in a failed supernova. The final BH mass is $\approx{87}$ M$_\odot$. Therefore, we confirm that the collision scenario is a suitable formation channel to populate the PI mass gap.

The detection of GW190521 by the LIGO-Virgo collaboration proved the existence of black holes in the theoretically predicted pair-instability gap of their mass spectrum. Some recent studies suggest that such massive black holes could be produced by the collision of an evolved star with a carbon-oxygen core and a main sequence star. Such a post-coalescence star could end its life avoiding the pair-instability regime and with a direct collapse of its very massive envelope. It is still not clear, however, how the collision shapes the structure of the newly produced star and how much mass is actually lost in the impact. We investigated this issue by means of hydrodynamical simulations with the smoothed particle hydrodynamics code StarSmasher, finding that the collision can remove up to 12% of the initial mass of the colliding stars. This is a non-negligible percentage of the initial mass and could affect the further evolution of the stellar remnant, particularly in terms of the final mass of a possibly forming black hole, if the core avoids the pair-instability regime. We also found that the main sequence star can plunge down to the outer boundary of the carbon-oxygen core of the primary, changing the inner chemical composition of the remnant. The collision expels the outer layers of the primary, leaving a remnant with an helium-enriched envelope (reaching He fractions of about 0.4 at the surface). These more complex abundance profiles can be directly used in stellar evolution simulations of the collision product.

Aims. On Earth, plate tectonics play an integral role in driving the long-term carbon cycle; however, on tidally locked rocky exoplanets alternative tectonic mechanisms driven by tidal stress and tidal heating could serve in an analogous way. Methods. We calculate tidal stress and tidal heating rates to model the likelihood of tectonic activity maintaining stable climates suitable for surface liquid water on tidally locked rocky exoplanets with radii ${R}_{p}$ $\le$ 1.23R$_\oplus$. Results. Applying the tidal models to our sample of 767 tidally locked rocky exoplanets reveals that $\sim$10% of exoplanets, including Proxima Cen b and GJ 1061 d from the circumstellar habitable zone (CHZ), pass the tidal stress subduction threshold for mobile lid tectonic activity and reside within the optimal tidal heating zone. This subset of exoplanets could sustain tidally induced temperate mobile lid tectonic activity comparable to plate tectonics on Earth, aiding in maintaining the presence of surface liquid water. Furthermore, $\sim$40% of exoplanets from our sample located in the CHZ would be unable to maintain the tectonic activity needed to stabilise the climate and are unlikely to retain surface liquid water. When broadening our modelling to establish the overlap between tidal stress, tidal heating, and the CHZ, to discover optimal regions to target for future observations, we determine that tidally driven tectonic activity conducive to the maintenance of surface liquid water occurs predominantly around M dwarfs, and identify intersections, where both mobile lid and optimal tidal heating could be sustained on eccentric (e>0.1) Earth-sized exoplanets (${R}_{p}$ = 1.0-1.23R$_\oplus$) orbiting in the CHZ of low-mass M dwarfs.

Classical Cepheids are essential objects in the study of stellar evolution and cosmology; however, we know little about their magnetic properties. We report the detection of Stokes $V$ features interpreted as Zeeman signatures in four classical Cepheids using high-resolution spectropolarimetric observations obtained with ESPaDOnS at CFHT. Eight observations of $\eta$ Aql were acquired in 2017 covering its 7.2 d pulsation period, and single observations of Polaris, $\zeta$ Gem, $\delta$ Cep and RT Aur were obtained in 2020 as part of our ongoing systematic survey. We use mean circular polarization Stokes $V$ profiles generated using the Least-Squares Deconvolution procedure to diagnose Zeeman signatures and measure mean longitudinal field strengths $\langle B_{z}\rangle$. We detect magnetic signatures across all pulsation phases of $\eta$ Aql ($-0.89\pm0.47$ G$\,<\langle B_{z}\rangle<1.27\pm 0.40$ G), as well as in the single observations of Polaris ($0.59\pm0.16$ G), $\zeta$ Gem ($0.41\pm0.16$ G) and $\delta$ Cep ($0.43\pm0.19$ G). The Stokes $V$ profile of Polaris is detected at extremely high S/N and implies a complex magnetic field topology. It stands in stark contrast to all other detected Stokes $V$ profiles, which show unusual approximately unipolar positive circular polarization lobes analogous to those observed in some Am stars.

We present new functionality within PICASO, a state-of-the-art radiative transfer model for exoplanet and brown dwarf atmospheres, by developing a new pipeline that computes phase-resolved thermal emission (thermal phase curves) from three-dimensional (3D) models. Because PICASO is coupled to Virga, an open-source cloud code, we are able to produce cloudy phase curves with different sedimentation efficiencies ($f_{sed}$) and cloud condensate species. We present the first application of this new algorithm to hot Jupiter WASP-43b. Previous studies of the thermal emission of WASP-43b from Kataria et al. (2015) found good agreement between cloud-free models and dayside thermal emission, but an overestimation of the nightside flux, for which clouds have been suggested as a possible explanation. We use the temperature and vertical wind structure from cloud-free 3D general circulation models of Kataria et al. (2015) and post-process it using PICASO, assuming that clouds form and affect the spectra. We compare our models to results from Kataria et al. (2015), including the Hubble Space Telescope (HST) Wide-Field Camera 3 (WFC3) observations of WASP-43b from Stevenson et al. (2014). In addition, we compute phase curves for Spitzer at 3.6 and 4.5 $\mu m$ and compare them to observations from Stevenson et al. (2017). We are able to closely recover the cloud-free results, even though PICASO utilizes a coarse spatial grid. We find that cloudy phase curves provide much better agreement with the WFC3 and Spitzer nightside data, while still closely matching the dayside emission. This work provides the community with a convenient user-friendly tool to interpret phase-resolved observations of exoplanet atmospheres using 3D models.

Observations and numerical simulations have shown that outflows generally exist in the accretion process. We revisit the thermal equilibrium solutions of black hole accretion flows by including the role of outflows. Our study focuses on the comparison of the cooling rate of outflows with that of advection. Our results show that, except for the inner region, outflows can dominate over advection in a wide range of the flow, which is in good agreement with previous numerical simulations. We argue that an advection-dominated inner region together with an outflow-dominated outer region should be a general radial distribution for both super-Eddington accretion flows and optically thin flows with low accretion rates.

NGC 1068 is a nearby Active Galactic Nucleus (AGN) of type 2, meaning that its accretion disk is hidden behind a large amount of foreground extinction. Observations at several wavelengths have revealed various disk-like structures around the nucleus, all possibly part of the putative torus responsible for the obscuration of the AGN. The paper presents results based on GRAVITY/VLTI interferometric observations in the near-infrared, which provide very high angular resolution, and gives insights into the geometry of the innermost region of the torus. The 3D orientation of the structure is surprising in several aspects, as it is misaligned with other disks present around the nucleus, and leaves a clear line of sight toward the central source.

One of the key physical processes that helps prevent strong cooling flows in galaxy clusters is the continued energy input from the cluster central active galactic nucleus (AGN). However, it remains unclear how this energy is thermalized, so that it can effectively prevent global thermal instability. One possible option is that a fraction of the AGN energy is converted to cosmic rays (CR), which provide non-thermal pressure support, and can retain energy even as thermal energy is radiated away. By means of magneto-hydrodynamical simulations, we investigate how CR injected by the AGN jet influence cooling flows of a massive galaxy cluster. We conclude that converting a fraction of the AGN luminosity as low as 10\% to CR energy prevents cooling-flows on Gyr timescales, without significant changes to the structure of the multi-phase intra-cluster medium. CR-dominated jets, by contrast, lead to the formation of an extended, warm central nebula that is supported by CR pressure. We report that the presence of CR is not able to suppress the onset of thermal instability in massive galaxy clusters, but CR-dominated jets do significantly change the continued evolution of gas as it continues to cool from isobaric to isochoric. CR redistribution in the cluster is dominated by advection, rather than diffusion or streaming, but the heating by CR streaming helps maintain gas in the hot and warm phase. Observationally, self-regulating, CR-dominated jets produce a {\gamma}-ray flux in excess of current observational limits, but low CR fractions in the jet are not ruled out.

Existing star-forming/AGN classification schemes using optical emission-line diagnostics mostly fail for low-metallicity and/or highly star-forming galaxies, missing AGN in typical $z\sim0$ dwarfs. To recover AGN in dwarfs with strong emission lines, we present a classification scheme optimizing the use of existing optical diagnostics. We use SDSS emission-line catalogs overlapping the volume- and mass-limited RESOLVE and ECO surveys to determine the AGN percentage in strong emission line dwarfs. Our photoionization grids show that the [O III]/H$\beta$ versus [S II]/H$\alpha$ diagram (SII plot) and [O III]/H$\beta$ versus [O I]/H$\alpha$ diagram (OI plot) are less metallicity sensitive and more successful in identifying dwarf AGN than the popular [O III]/H$\beta$ versus [N II]/H$\alpha$ diagnostic (NII plot or "BPT diagram"). We identify a new category of "Star Forming-AGN" (SF-AGN) classified as star-forming by the NII plot but as AGN by the SII and/or OI plots. Including SF-AGN, we find the $z\sim0$ AGN percentage in dwarfs with strong emission lines to be $\sim$3-15%, far exceeding most previous optical estimates ($\sim$1%). The large range in our dwarf AGN percentage reflects differences in spectral fitting methodologies between catalogs. The highly complete nature of RESOLVE and ECO allows us to normalize strong emission-line galaxy statistics to the full galaxy population, reducing the dwarf AGN percentage to $\sim$1-2%. The newly identified SF-AGN are mostly gas-rich dwarfs with halo mass $ < 10^{11.5} M_\odot$, where highly efficient cosmic gas accretion is expected. Almost all SF-AGN also have low metallicities (Z $\lesssim 0.4$ Z$_\odot$), demonstrating the advantage of our method.

Aerosols have been found to be nearly ubiquitous in substellar atmospheres. The precise temperature at which these aerosols begin to form in exoplanets has yet to be observationally constrained. Theoretical models and observations of muted spectral features suggest that silicate clouds play an important role in exoplanets between at least 950 and 2,100 K. However, some giant planets are thought to be hot enough to avoid condensation altogether. Here, we present the near-UV transmission spectrum of an ultra-hot Jupiter, WASP-178b ($\sim$2,450~K), that exhibits significant NUV absorption. This short-wavelength absorption is among the largest spectral features ever observed in an exoplanet in terms of atmospheric scale heights. Bayesian retrievals indicate the presence of gaseous refractory species containing silicon and magnesium, which are the precursors to condensate clouds at lower temperatures. SiO in particular has not been detected in exoplanets before, but the presence of SiO in WASP-178b is consistent with theoretical expectation as the dominant Si-bearing species at high temperatures. These observations allow us to re-interpret previous observations of HAT-P-41b and WASP-121b that did not consider SiO to suggest that silicate cloud formation begins on exoplanets with equilibrium temperatures between 1,950 and 2,450~K.

General Relativity (GR) exists in different formulations. They are equivalent in pure gravity but generically lead to distinct predictions once matter is included. After a brief overview of various versions of GR, we focus on metric-affine gravity, which avoids any assumption about the vanishing of curvature, torsion or non-metricity. We use it to construct an action of a scalar field coupled non-minimally to gravity. It encompasses as special cases numerous previously studied models. Eliminating non-propagating degrees of freedom, we derive an equivalent theory in the metric formulation of GR. Finally, we give a brief outlook to implications for Higgs inflation.

The identification of the nature of dark matter is one of the most important problems confronting particle physics. Current observational constraints permit the mass of the dark matter to range from $10^{-22}$ eV - $10^{48}$ GeV. Given the weak nature of these bounds and the ease with which dark matter models can be constructed, it is clear that the problem can only be solved experimentally. In these lectures, I discuss methods to experimentally probe a wide range of dark matter candidates.

We present a new method which accounts for changes in the properties of gravitational-wave detector noise over time in the PyCBC search for gravitational waves from compact binary coalescences. We use information from LIGO data quality streams that monitor the status of each detector and its environment to model changes in the rate of noise in each detector. These data quality streams allow candidates identified in the data during periods of detector malfunctions to be more efficiently rejected as noise. This method allows data from machine learning predictions of the detector state to be included as part of the PyCBC search, increasing the the total number of detectable gravitational-wave signals by up to 5%. When both machine learning classifications and manually-generated flags are used to search data from LIGO-Virgo's third observing run, the total number of detectable gravitational-wave signals is increased by up to 20% compared to not using any data quality streams. We also show how this method is flexible enough to include information from large numbers of additional arbitrary data streams that may be able to further increase the sensitivity of the search.

The cosmological constant is not necessarily small in the early universe. If a scalar field obtains a vacuum expectation value after a phase transition (PT), a possibly large cosmological constant could present before PT. The early cosmological constant (ECC) and the PT process may be detectable from dark radiation (DR) today, such as in the cosmic axion background. We show that for a broad class of DR models, the DR density and spectrum are significantly modified by the presence of an ECC. From the density and the spectrum of the DR today, we can deduce the temperature and the strength of the PT.

We consider the Penrose process near the naked singularity in the Reissner-Nordstr\"{o}m metric. Particle 0 falls from infinity and decays to two fragments at some point $r_{0}$. We show that the energy extraction due to this process can be indefinitely large in the limit $r_{0}\rightarrow 0$. In doing so, the value of the particle charge can remain bounded, in contrast to the previously known examples of the Penrose process in the electric field with unbounded energy extraction. The effect persists even in the limit of the flat pace-time.

We investigate the decay rate of a false vacuum state in de Sitter space at high Hubble rates, using two methods: the Hawking-Moss instanton method which is fully quantum mechanical but relies on the saddle-point approximation, and the Starobinsky-Yokoyama stochastic approach which is non-perturbative but does not include quantum effects. We use the flux-over-population method to compute the Hawking-Moss decay rate at one-loop order, and demonstrate that in its domain of validity, it is reproduced by the stochastic calculation using the one-loop constraint effective potential. This suggests that the stochastic approach together with the constraint effective potential can be used to accurately describe vacuum decay beyond the saddle-point approximation.

We study the precession of perihelia in the Fisher metric. Fisher metric is the solution of the Einstein's Equations with a massless scalar field as a coupling. We find an expression for the precession of perihelia in this metric. This expression contains general relativistic term for the precession of the perihelia and also an additional term which depends on the scalar field. Also, we obtain an upper bound on scalar charge $\sigma$ by using the observational value of the precession of perihelia for the Mercury planet and the discrepancy between this value and the general relativistic value.

We present a novel relativistic density-functional approach to modeling quark matter with a mechanism to mimic confinement. The quasiparticle treatment of quarks provides their suppression due to a large quark selfenergy already at the mean-field level. We demonstrate that our approach is equivalent to a chiral quark model with medium-dependent couplings. The dynamical restoration of the chiral symmetry is ensured by construction of the density functional. Supplemented with the vector repulsion and diquark pairing the model is applied to construct a hybrid quark-hadron EoS of cold compact-star matter. We study the connection of such a hybrid EoS with the stellar mass-radius relation and tidal deformability. The model results are compared to various observational constraints including the NICER radius measurement of PSR J0740+6620 and the tidal deformability constraint from GW170817. The model is shown to be consistent with the constraints, still allowing for further improvement by adjusting the vector repulsion and diquark pairing couplings.