Papers for Monday, Apr 18 2022

Close encounters between neutron stars and main-sequence stars occur in globular clusters and may lead to various outcomes. Here we study encounters resulting in tidal disruption of the star. Using $N$-body models, we predict the typical stellar masses in these disruptions and the dependence of the event rate on host cluster properties. We find that tidal disruption events occur most frequently in core-collapsed globular clusters and that roughly $25\%$ of the disrupted stars are merger products (i.e., blue straggler stars). Using hydrodynamic simulations, we model the tidal disruptions themselves (over timescales of days) to determine the mass bound to the neutron star and the properties of the remnant disks formed. Depending on the impact parameter and mass of the disrupted star, we find disk masses ranging from roughly $0.1-1\,M_{\odot}$ and typical radii of $\rm{a\,few}\,\it{R}_{\odot}$. Additionally, we find that neutron stars receive impulsive kicks of up to about $20\,$km/s as a result of the asymmetry of unbound ejecta; these kicks place these neutron stars on elongated orbits within their host cluster, with apocenter distances well outside the cluster core. Finally, we model the evolution of the (hypercritical) accretion disks on longer timescales (days to years after disruption) to estimate the accretion rate onto the neutron stars and accompanying spin-up. As long as $\gtrsim1\%$ of the bound mass accretes onto the neutron star, millisecond spin periods can be attained. We argue the growing numbers of {\em isolated\/} millisecond pulsars observed in globular clusters may have formed, at least in part, through this mechanism. In the case of significant mass growth, some of these neutron stars may collapse to form low-mass ($\lesssim3\,M_{\odot}$) black holes.

The total mass of the Local Group (LG) is a fundamental quantity that enables interpreting the orbits of its constituent galaxies and placing the LG in a cosmological context. One of the few methods that allows inferring the total mass directly is the "Timing Argument," which models the relative orbit of the Milky Way (MW) and M31. However, the MW itself is not in equilibrium, a byproduct of its merger history and the recent pericentric passage of the LMC/SMC. As a result, recent work has found that the MW disk is moving with a lower bound "travel velocity" of $\sim 32~{\rm km}~{\rm s}^{-1}$ with respect to the outer stellar halo (Petersen & Pe\~{n}arrubia 2021), thus biasing past Timing Argument measurements that do not account for this motion. We measure the total LG mass using a Timing Argument model that incorporates this measured travel velocity of the MW disk using several different compilations of recent kinematic measurements of M31. We find that incorporating the measured travel velocity lowers the inferred LG mass by 10-20% compared to a static MW halo, and find an updated total mass of either $4.0^{+0.5}_{-0.3}\times 10^{12}\rm M_{\odot}$ or $4.5^{+0.8}_{-0.6}\times 10^{12}\rm M_{\odot}$ depending on the adopted dataset. Measurements of the travel velocity with more distant tracers could yield even larger values, which would further decrease the inferred LG mass. Therefore, the newly measured travel velocity directly implies a lower LG mass than from a model with a static MW halo and must be considered in future dynamical studies of the Local Volume.

We present an ALMA-Herschel joint analysis of sources detected by the ALMA Lensing Cluster Survey (ALCS) at 1.15 mm. Herschel/PACS and SPIRE data at 100-500 $\mu$m are deblended for 180 ALMA sources in 33 lensing cluster fields that are either detected securely (141 sources; in our main sample) or tentatively at S/N$\geq$4 with cross-matched HST/Spitzer counterparts, down to a delensed 1.15-mm flux density of $\sim0.02$ mJy. We performed far-infrared spectral energy distribution modeling and derived the physical properties of dusty star formation for 125 sources (109 independently) that are detected at $>2\sigma$ in at least one Herschel band. 27 secure ALCS sources are not detected in any Herschel bands, including 17 optical/near-IR-dark sources that likely reside at $z=4.2\pm1.2$. The 16-50-84 percentiles of the redshift distribution are 1.15-2.08-3.59 for ALCS sources in the main sample, suggesting an increasing fraction of $z\simeq1-2$ galaxies among fainter millimeter sources ($f_{1150}\sim 0.1$ mJy). With a median lensing magnification factor of $\mu = 2.6_{-0.8}^{+2.6}$, ALCS sources in the main sample exhibit a median intrinsic star-formation rate of $94_{-54}^{+84}\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}$, lower than that of conventional submillimeter galaxies at similar redshifts by a factor of $\sim$3. Our study suggests weak or no redshift evolution of dust temperature with $L_\mathrm{IR}<10^{12}\,\mathrm{L}_\odot$ galaxies within our sample at $z \simeq 0 - 2$. At $L_\mathrm{IR}>10^{12}\,\mathrm{L}_\odot$, the dust temperatures show no evolution across $z \simeq 1 -4$ while being lower than those in the local Universe. For the highest-redshift source in our sample ($z=6.07$), we can rule out an extreme dust temperature ($>$80 K) that was reported for MACS0416 Y1 at $z=8.31$.

The visually brightest stars in globular clusters (GCs) are the ones evolving off the asymptotic giant branch (AGB) and passing through spectral types F and A--the "yellow" post-AGB (yPAGB) stars. yPAGB stars are potentially excellent "Population II" standard candles for measuring extragalactic distances. A recent survey of the Galactic GC system, using uBVI photometry to identify stars of low surface gravities with large Balmer discontinuities, discovered a candidate luminous yPAGB star in the GC M19 (NGC 6273), designated ZNG 4. The same survey also identified a bright, hotter candidate blue PAGB star, ZNG 2, lying near the top of the white-dwarf cooling sequence. Both PAGB candidates have proper motions and parallaxes in the recent Gaia Early Data Release 3 consistent with cluster membership, but they still lacked spectroscopic verification. Here we present moderate-resolution spectra of both stars, confirming them as low-gravity objects that are extremely likely to be cluster members. Through comparison with a library of synthetic spectra, we made approximate estimates of the stars' atmospheric parameters. We find that the yPAGB star ZNG 4 has an effective temperature of Teff ~ 6500 K, a surface gravity of log g ~ 1, and a metallicity of [Fe/H] ~ -1.5, similar to that of the host cluster. The blue PAGB star ZNG 2 has Teff ~ 18000 K, log g ~ 3, and an apparently low metallicity in the range of [Fe/H] ~ -2.0 to -2.5. Both stars are bright (V=12.5 and 13.3, respectively). We urge high-dispersion spectroscopic follow-up to determine detailed atmospheric parameters and chemical compositions, and to monitor radial velocities.

Seasonal variation is significant in Titan's atmosphere due to the large change of solar insolation resulting from Titan's 26.7{\deg} axial tilt relative to the plane of Saturn's orbit. Here we present an investigation of hydrocarbon and nitrile species in Titan's upper atmosphere at 400-1200 km, which includes the mesosphere and the lower thermosphere, over more than one fourth of Titan's year (2006-2014, LS=318{\deg}-60{\deg}), using eighteen stellar occultation observations obtained by Cassini/UVIS. Vertical profiles of eight chemical species (CH4, C2H2, C2H4, C2H6, C4H2, C6H6, HCN, HC3N) and haze particles are retrieved from these observations using an instrument forward model, which considers the technical issue of pointing motion. The Markov-chain Monte Carlo (MCMC) algorithm is used to obtain the posterior probability distributions of parameters in the retrieval, which inherently tests the extent to which species profiles can be constrained. The results show that no change of the species profiles is noticeable before the equinox, while the decrease of atmospheric temperature and significant upwelling in the summer hemisphere are found five terrestrial years afterwards. Altitude of the detached haze layer decreases towards the vernal equinox then it disappears, and no reappearance is identified within the time range of our data, which is consistent with observations from Cassini/ISS. This study provides observational constraints on the seasonal change of Titan's upper atmosphere, and suggests further investigations of the atmospheric chemistry and dynamics therein.

The paper deals with the conditions required to form at least two stellar generations in globular clusters under the constraints generated by feedback from massive stars as well as radiative cooling and the metallicity of the primordial clouds. Our calculations are based on two main constraints to the star formation efficiency of the first stellar generation (1G) $\epsilon_{1G}$. First, $\epsilon_{1G}$ is restricted to warrant that stellar winds and supernovae do not disrupt the leftover gas out of which a second generation (2G) would form. Second, $\epsilon_{1G}$ is also limited such that the metallicity enhancement caused by trapped supernovae is, in agreement with the observations, not larger than $\sim$ 0.1 dex. Several central parameters define the globular clusters end result: the mass and radius of the primordial clouds, their metallicity and $\epsilon_{1G}$. The parameter space composed by models which fulfilled all constraints, is here shown to coincide remarkably well with the scattered observed anti-correlation between the fraction of first generation stars ($f_{\textrm{1G}}$) and total cluster mass. Our models also discern, in agreement with the data, between single and multiple population clusters in a metallicity versus mass (or radius) plane. Hence, our results suggest that the presence of multiple stellar populations is closely linked to the ability of proto-globular clusters to retain a fraction of leftover gas.

Mechanisms have been proposed to enhance the merger rate of stellar mass black hole binaries, such as the Von Zeipel-Lidov-Kozai mechanism (vZLK). However, high inclinations are required in order to greatly excite the eccentricity and to reduce the merger time through vZLK. Here, we propose a novel pathway through which compact binaries could merge due to eccentricity increase in general, including in a near coplanar configuration. Specifically, a compact binary migrating in an AGN disk could be captured in an evection resonance, when the precession rate of the binary equals their orbital period around the supermassive black hole. In our study we include precession to due first-order post Newtonian precession as well as that due to disk around one or both components of the binary. Eccentricity is excited when the binary sweeps through the resonance which happens only when it migrates on a timescale 10-100 times the libration timescale of the resonance. Libration timescale decreases as the mass of the disk increases. The eccentricity excitation of the binary can reduce the merger timescale by a factor up to $\sim 10^{3-5}$.

Winds play a significant role in active galactic nuclei feedback process. Previous simulations studying winds only focus on a small dynamical range. Therefore, it is unknown how far the winds can go and what the properties of the winds will be if they can move to large radii. We perform simulations to study the large scale dynamics of winds driven by line force. We find that the properties of the winds depend on both black hole mass ($M_{BH}$) and accretion disk luminosity. When the accretion disk luminosity is $0.6L_{edd}$ ($L_{edd}$ being Eddington luminosity), independent of $M_{BH}$, the winds have kinetic energy flux exceeding $1\% L_{edd}$ and can escape from the black hole potential. For the case with the accretion disk luminosity equaling 0.3$L_{edd}$, the strength of the winds decreases with the decrease of $M_{BH}$. If $M_{BH}$ decreases from $10^9$ to $10^6$ solar mass ($M_\odot$), the winds kinetic energy flux decreases from $\sim 0.01 L_{edd}$ to $ \sim 10^{-6} L_{edd}$. In case of $M_{BH}\geq 10^7 M_\odot$, winds can escape from black hole potential. In the case of $M_{BH}=10^6 M_\odot$, the winds can not escape. We find that for the ultra-fast winds observed in hard X-ray bands (\citealt{Gofford et al. 2015}), the observed dependence of the mass flux and the kinetic energy flux on accretion disk luminosity can be well produced by line force driven winds model. We also find that the properties of the ultra-fast winds observed in soft X-ray bands can be explained by the line force driven winds model.

Magnetic reconnection process in the ergosphere is investigated for a relativistic plasma around a rotating non-Kerr black hole. For a rotating non-Kerr black hole immersed in magnetic field generated by an externally material, anti-parallel magnetic field line could form in the ergosphere due to the frame dragging. Therefore, magnetic reconnection could occur in the ergosphere. Such magnetic reconnection may generate negative energy at infinity by redistributing the angular momentum during the process. The results show that, with the effect of the deformed parameter, extraction of energy from a rotating non-Kerr black hole by magnetic reconnection could be enhanced in the presence of a positive deformed parameter.

The search for radio emission from the gamma pulsar J0357+3205 in the meter wavelength range was carried out. Periodic emission was found in one of the 1,700 observation sessions. The average pulsar profile is single-component with a half-width of 20-25 ms. Estimation of the pulsar flux density is 14 mJy.

Future gravitational wave detectors, such as the Laser Interferometer Space Antenna (LISA), will be able to resolve a significant number of the ultra compact stellar-mass binaries in our own Galaxy and its neighborhood. These will be mostly double white dwarf (DWD) binaries, and their underlying population characteristics can be directly correlated to the different properties of the Galaxy. In particular, with LISA we will be able to resolve $\sim\mathcal{O}(10^4)$ binaries, while the rest will generate a confusion foreground signal. Both categories can be used to address a number of astrophysical questions. Analogously to how the total electromagnetic radiation emitted by a galaxy can be related to the underlying total stellar mass, in this work we propose a framework to infer the same quantity by investigating the spectral shape and amplitude of the confusion foreground signal. For a fixed DWD evolution model, we retrieve percentage-level relative errors on the total stellar mass, which improves for increasing values of the mass. At the same time, we find that variations in the Miky Way shape, at a fixed mass and at scale heights smaller than 500~pc, are not distinguishable based on the shape of stochastic signal alone. Finally, we utilize the catalogue of resolvable sources to probe the characteristics of the underlying population of DWD binaries. We show that the DWD frequency, coalescence time and chirp mass (up to $<0.7\,$M$_\odot$) distributions can be reconstructed from LISA data with no bias.

In this work, we use a model-independent approach to determine the Hubble constant and the spatial curvature simultaneously. We use the cosmic chronometers in combination with the time delay measurements in this method, and the cosmography method is used to reconstruct distances from cosmic chronometer observations instead of the polynomial expansion. This approach avoids the problems of the physical meaning of polynomial coefficients and the calibration of "nuisance parameter". Our results show that the measured Hubble constant $H_0=72.24^{+2.73}_{-2.52} km/s/Mpc$ is in good agreement with that derived from the local distance ladder measurement. In addition, our results show that a zero spatial curvature $\Omega_k=0.062^{+0.117}_{-0.078}$ and an accelerating expansion of the Universe $q_0=-0.645^{+0.126}_{-0.124}$ are supported by the current time delay of strong lensing system and cosmic chronometer observations. If we assume a flat universe in advance, we can infer that the $H_0=70.47^{+1.14}_{-1.15} km/s/Mpc$, falls between the SH0ES and Plank CMB observation results. Moreover, the convergence and goodness of the fourth order fitting is worse than the third order fitting case. Finally, the cosmic expansion history is reconstructed within a wide range of redshifts.

Since April 28, 2020, Insight-HXMT has implemented a dedicated observation on the magnetar SGR J1935+2154. Thanks to the wide energy band (1-250 keV) and high sensitivity of Insight-HXMT, we obtained 75 bursts from SGR J1935+2154 during a month-long activity episode after the emission of FRB 200428. Here, we report the detailed time-integrated spectral analysis of these bursts and the statistical distribution of the spectral parameters. We find that for 15%(11/75) of SGR J1935+2154 bursts, the CPL model is preferred, and most of them occurred in the latter part of this active epoch. In the cumulative fluence distribution, we find that the fluence of bursts in our sample is about an order of magnitude weaker than that of Fermi/GBM, but follows the same power law distribution. Finally, we find a burst with similar peak energy to the time-integrated spectrum of the X-ray burst associated with FRB 200428 (FRB 200428-Associated Burst), but the low energy index is harder.

We determined the differential rotation (DR) parameters $A$ and $B$ (corresponding to the equatorial rotation velocity and the gradient of the solar DR) by tracing sunspot groups in sunspot drawings of the Kanzelh\"ohe Observatory for Solar and Environmental Research (KSO; 1964-2008, for solar cycles (SC) 20-23) and KSO white-light images (2009-2016, for SC 24). We used different statistical methods and approaches to analyse cycle related variations, solar cycle phase-related variations and long-term variations of the DR. $A$ and $B$ show statistically significant periodic variability. The changes in $A$ related to solar cycle phase are in accordance with previously reported theoretical and experimental results (higher $A$ during solar minimum, lower $A$ during the maximum of activity), while changes in $B$ differ from the theoretical predictions as we observe more negative values of $B$, that is, a more pronounced DR during activity maximum. The main result of this paper for the long-term variations in $A$ is the detection of a phase shift between the activity flip (in the 1970s) and the equatorial rotation velocity flip (in the early 1990s). During this time period both $A$ and activity show a secular decreasing trend, indicating their correlation. Therefore, the theoretical model fails in the phase-shift time period that occurs after the modern Gleissberg maximum, while in the time period thereafter (after the 1990s), theoretical and experimental results are consistent. The long-term variations in $B$ in general yield an anticorrelation of $B$ and activity, as a rise of $B$ is observed during the entire time period (1964-2016) we analysed, during which activity decreased. We study for the first time the variation in solar DR and activity based on 53 years of KSO data. Our results agree well with the results related to the solar cycle phase from corona observations.

Dust production is one of the more curious phenomena observed in massive binary systems with interacting winds. The high temperatures, UV photon flux and violent shocks should destroy any dust grains that condense. However, in some extreme cases dust production yields of approximately 30% of the total mass loss rate of the stellar winds have been observed. In order to better understand this phenomenon a parameter space exploration was performed using a series of numerical models of dust producing carbon phase Wolf-Rayet (WCd) systems. These models incorporated a passive scalar dust model simulating dust growth, destruction and radiative cooling. We find that reasonable dust yields were produced by these simulations. Significant changes in the dust yield were caused by changing the mass loss rates of the stars, with a greater mass loss rate contributing to increased dust yields. Similarly, a close orbit between the stars also resulted in higher dust yields. Finally, a high velocity wind shear, which induces Kelvin-Helmholtz (KH) instabilities and wind mixing, drastically increases the dust yields.

Using the Geant4 code, we have performed a full-scale simulation of the LSD response to the neutrino burst from SN1987A. The neutrino flux parameters were chosen according to one of the models: the standard collapse model or the rotational supernova explosion model. We showed that, depending on the chosen parameters, one can either obtain the required number of pulses in the detector or reproduce their energy spectrum, but not both together. The interaction of neutrino radiation both with LSD itself and with the material of the surrounding soil was taken into account in our simulation. We also explored the hypothesis that the entire unique LSD signal at 2:52 UT was produced by neutron fluxes from the surrounding granite. However, this hypothesis was not confirmed by our simulation. The results obtained provide a rich material for possible interpretations.

This event, so far unique, beautifully confirmed the standard views on the gravitational waves produced by a merger of two neutron stars, but its electromagnetic multi-wavelenth observations disagreed with the numerous initial versions of the "standard fireball model(s)" of gamma ray bursts. Contrariwise, they provided strong evidence in favour of the "cannonball" model. Most uncontroversially, a cannonball was observed at radio wavelengths, with an overwhelming statistical significance ($>\! 17\,\sigma$), and travelling in the plane of the sky, as expected, at an apparent superluminal velocity $V_{app}\sim 4\, c$.

The pressure exerted by the ambient hot X-ray gas on cluster galaxies can lead to the presence of ram pressure stripped (RPS) galaxies, characterized by asymmetric shapes, and, in some cases, tails of blue stars and/or X-ray gas, with increased star formation. We searched for such galaxies in the cluster MS 0451.6-0305 at z~0.5, based on Hubble Space Telescope (HST) imaging covering a region of about 6x6 Mpc^2, an eight magnitude ground-based catalogue with photometric redshifts, and a spectroscopic redshift catalogue. We defined as cluster members a spectroscopic redshift sample of 359 galaxies within 4sigma_v of the mean cluster velocity, and a photometric redshift sample covering the [0.48,0.61] range. We searched for RPS galaxies and tested the error on their classification with a Zooniverse collaboration, and computed the phase space diagram for the spectroscopic sample. We ran the LePhare stellar population synthesis code to analyze and compare the properties of RPS and non-RPS galaxies. We find 56 and 273 RPS candidates in the spectroscopic and photometric redshift samples, respectively, distributed throughout the cluster and tending to avoid high density regions. The phase space diagram gives the percentages of virialized, backsplash, and infall galaxies. RPS galaxy candidates typically show rather high star formation rates, young ages, and relatively low masses. This study confirms that RPS galaxies host, on average, younger stellar populations and strongly form stars when compared with non-RPS counterparts. The fact that RPS candidates with spectroscopic and with photometric redshifts have comparable properties shows that large samples of such objects could be gathered based on multi-band photometry only, a promising result in view of future very large imaging surveys.

Short-period and low-mass water-rich planets are subject to strong irradiation from their host star, resulting in hydrospheres in supercritical state. In this context, we explore the role of irradiation on small terrestrial planets that are moderately wet in the low-mass regime (0.2--1$M_{\oplus}$). We investigate their bulk properties for water contents in the 0.01--5\% range by making use of an internal structure model that is coupled to an atmosphere model. This coupling allows us to take into account both the compression of the interior due to the weight of the hydrosphere and the possibility of atmospheric instability in the low-mass regime. We show that even for low masses and low water contents, these planets display inflated atmospheres. For extremely low planetary masses and high irradiation temperatures, we find that steam atmospheres become gravitationally unstable when the ratio $\eta$ of their scale height to planetary radius exceeds a critical value of $\sim 0.1$. This result is supported by observational data, as all currently detected exoplanets exhibit values of $\eta$ smaller than 0.013. Depending on their water content, our results show that highly irradiated and low-mass planets up to $0.9M_{\oplus}$ with significative hydrospheres are not in stable form and should loose their volatile envelope.

Using $I$-band images of 35 nearby ($z<0.1$) type 1 active galactic nuclei (AGNs) obtained with Hubble Space Telescope, selected from the 70-month Swift-BAT X-ray source catalog, we investigate the photometric properties of the host galaxies. With a careful treatment of the point-spread function (PSF) model and imaging decomposition, we robustly measure the $I$-band brightness and the effective radius of bulges in our sample. Along with black hole (BH) mass estimates from single-epoch spectroscopic data, we present the relation between BH mass and $I$-band bulge luminosity ($M_{\rm BH}-M_{I,\rm bul}$ relation) of our sample AGNs. We find that our sample lies offset from the $M_{\rm BH}-M_{I,\rm bul}$ relation of inactive galaxies by 0.4 dex, i.e., at a given bulge luminosity, the BH mass of our sample is systematically smaller than that of inactive galaxies. We also demonstrate that the zero point offset in the $M_{\rm BH}-M_{I,\rm bul}$ relation with respect to inactive galaxies is correlated with the Eddington ratio. Based on the Kormendy relation, we find that the mean surface brightness of ellipticals and classical bulges in our sample is comparable to that of normal galaxies, revealing that bulge brightness is not enhanced in our sample. As a result, we conclude that the deviation in the $M_{\rm BH}-M_{I,\rm bul}$ relation from inactive galaxies is possibly because the scaling factor in the virial BH mass estimator depends on the Eddington ratio.

The molecular gas in galaxies traces both the fuel for star formation and the processes that can either enhance or suppress star formation. Observations of the molecular gas state can thus point to when and why galaxies stop forming stars. In this study, we present ALMA observations of the molecular gas in galaxies evolving through the post-starburst phase. These galaxies have low current star formation rates, regardless of the SFR tracer used, yet their optical spectra show evidence for recent bursts of star formation that have ended within the last 600 Myr. We present CO (3--2) observations for three post-starburst galaxies, and dense gas HCN/HCO$^+$/HNC (1--0) observations for six (four new) post-starburst galaxies. The post-starbursts have low excitation as traced by the CO spectral line energy distribution (SLED) up to CO (3--2), more similar to early-type than starburst galaxies. The low excitation indicates that lower density rather than high temperatures may suppress star formation during the post-starburst phase. One galaxy displays a blueshifted molecular gas outflow traced by CO (3--2). MaNGA observations show that the ionized gas velocity is disturbed relative to the stellar velocity field, with a blueshifted component aligned with the molecular gas outflow, suggestive of a multiphase outflow. Low ratios of HCO$^+$/CO, indicating low fractions of dense molecular gas relative to the total molecular gas, are seen throughout post-starburst phase, except for the youngest post-starburst galaxy considered here.

Our local motion with respect to the cosmic frame of rest is believed to be dominantly responsible for the observed dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR). We study the effect of this motion on the sky distribution of gravitational wave (GW) sources. We determine the resulting dipole anisotropy in GW source number counts, mass weighted number counts, which we refer to as mass intensity, and mean mass per source. The mass M dependence of the number density n(M) distribution of BBH is taken directly from data. We also test the anisotropy in the observable mean mass per source along the direction of the CMB dipole

We present a spectroscopic analysis of the most rapidly rotating stars currently known, VFTS 102 ($v_{e} \sin i = 649 \pm 52$ km s$^{-1}$; O9: Vnnne+) and VFTS 285 ($v_{e} \sin i = 610 \pm 41$ km s$^{-1}$; O7.5: Vnnn), both members of the 30 Dor complex in the Large Magellanic Cloud. This study is based on high resolution ultraviolet spectra from HST/COS and optical spectra from VLT X-shooter plus archival VLT GIRAFFE spectra. We utilize numerical simulations of their photospheres, rotationally distorted shape, and gravity darkening to calculate model spectral line profiles and predicted monochromatic absolute fluxes. We use a guided grid search to investigate parameters that yield best fits for the observed features and fluxes. These fits produce estimates of the physical parameters for these stars (plus a Galactic counterpart, $\zeta$ Oph) including the equatorial rotational velocity, inclination, radius, mass, gravity, temperature, and reddening. We find that both stars appear to be radial velocity constant. VFTS 102 is rotating at critical velocity, has a modest He enrichment, and appears to share the motion of the nearby OB association LH 99. These properties suggest that the star was spun up through a close binary merger. VFTS 285 is rotating at $95\%$ of critical velocity, has a strong He enrichment, and is moving away from the R136 cluster at the center of 30 Dor. It is mostly likely a runaway star ejected by a supernova explosion that released the components of the natal binary system.

Binary systems that host a massive star and a non-accreting pulsar can be powerful non-thermal emitters. The relativistic pulsar wind and the non-relativistic stellar outflows interact along the orbit, producing ultrarelativistic particles that radiate from radio to gamma rays. To properly characterize the physics of these sources, and better understand their emission and impact on the environment, careful modelling of the outflow interactions, spanning a broad range of spatial and temporal scales, is needed. Full 3-dimensional approaches are very computationally expensive, but simpler approximate approaches, while still realistic at the semi-quantitative level, are available. We present here the results of calculations done with a quasi 3-dimensional scheme to compute the evolution of the interacting flows in a region spanning in size up to a thousand times the size of the binary. In particular, we analyze for the first time the role of different eccentricities in the large scale evolution of the shocked flows. We find that the higher the eccentricity, the closer the flows behave like a one-side outflow, which becomes rather collimated for eccentricity values $\gtrsim 0.75$. The simulations also unveil that the pulsar and the stellar winds become fully mixed within the grid for low eccentricity systems, presenting a more stochastic behavior at large scales than in the highly eccentric systems.

State transitions in black hole X-ray binaries are likely caused by gas evaporation from a thin accretion disk into a hot corona. We present a height-integrated version of this process which is suitable for analytical and numerical studies. With radius $r$ scaled to Schwarzschild units and coronal mass accretion rate $\dot{m}_c$ to Eddington units, the results of the model are independent of black hole mass. State transitions should thus be similar in X-ray binaries and AGN. The corona solution consists of two power-law segments separated at a break radius $r_b \sim10^3 \,(\alpha/0.3)^{-2}$, where $\alpha$ is the viscosity parameter. Gas evaporates from the disk to the corona for $r>r_b$, and condenses back for $r<r_b$. At $r_b$, $\dot{m}_c$ reaches its maximum, $\dot{m}_{c,{\rm max}} \approx 0.02\, (\alpha/0.3)^3$. If at $r\gg r_b$ the thin disk accretes with $\dot{m}_d < \dot{m}_{c,{\rm max}} $, then the disk evaporates fully before reaching $r_b$, giving the hard state. Otherwise, the disk survives at all radii, giving the thermal state. While the basic model considers only bremsstrahlung cooling and viscous heating, we also discuss a more realistic model which includes Compton cooling and direct coronal heating by energy transport from the disk. Solutions are again independent of black hole mass, and $r_b$ remains unchanged. This model predicts strong coronal winds for $r>r_b$, and a $T\sim 6\times 10^8\,{\rm K}$ Compton-cooled corona for $r < r_b$. Two-temperature effects are ignored, but may be important at small radii.

The anthropic explanation for the peculiarly small observed value of the cosmological constant $\Lambda_{\rm obs}$ argues that this value promotes the formation of stars, planets, and ultimately of observers such as ourselves. I show that a recent analytic model of cosmic star formation predicts that although $\Lambda_{\rm obs}$ maximises the overall efficiency of star formation in the universe, the probability of generating observers peaks at $\sim400-500 \, \Lambda_{\rm obs}$. These preliminary results suggest that an immediate connection between star formation efficiency and observers' generation is not straightforward, and highlight the subtleties involved with the application of anthropic reasoning.

Faint young Sun paradox (FYSP) is one of the unsolved problem in solar physics. The present study aims to get a possible solution for the FYSP through sun-like G stars and their exoplanetary systems. Using physical properties of exoplanetary data, an empirical relationship between the rate of mass loss ($\frac{dM}{dt}$) with stellar mass (M$_{\star}$) and age ({\em t}) is obtained. We found mass loss rate varies with stellar mass as $\propto$ $(M_{\star}/M_\odot)^{-3.788}$ and proportional to the age as $\propto$ t$^{-1.25}$, which indicates rate of mass loss is higher during early evolutionary stages. Then we applied mass loss corrections to stellar masses of G-type stars with planets and obtained their initial masses at the early evolutionary stages. Subsequently, we applied these relationships to calculate the mass loss rate and mass of Sun at the early evolutionary stage, which is found to be $\sim$ 10$^{-11}$ solar mass per year and $\sim$ (1.061$\pm$0.006) solar mass respectively. The higher solar mass can probably alleviate the problem of the faint young Sun paradox. Then the estimated initial stellar masses of the host stars are used to obtain a best power law relationship with the planetary masses that supports the hypothesis that the {\em massive stars harbour massive planets.} Finally, by using the same empirical power law, planetary mass in the vicinity of Sun is estimated to be $\sim$ (0.84$\pm$0.19) Jupiter mass, which is much higher compared to the present solar terrestrial planetary mass. Hence, this study also suggests that there is a missing planetary mass in the vicinity of the Sun, which can solve the FYSP problem.

Comets provide a valuable window into the chemical and physical conditions at the time of their formation in the young solar system. We seek insights into where and when these objects formed by comparing the range of abundances observed for nine molecules and their average values across a sample of 29 comets to the predicted midplane ice abundances from models of the protosolar nebula. Our fiducial model, where ices are inherited from the interstellar medium, can account for the observed mixing ratio ranges of each molecule considered, but no single location or time reproduces the abundances of all molecules simultaneously. This suggests that each comet consists of material processed under a range of conditions. In contrast, a model where the initial composition of disk material is `reset', wiping out any previous chemical history, cannot account for the complete range of abundances observed in comets. Using toy models that combine material processed under different thermal conditions we find that a combination of warm (CO-poor) and cold (CO-rich) material is required to account for both the average properties of the Jupiter-family and Oort cloud comets, and the individual comets we consider. This could occur by the transport (either radial or vertical) of ice-coated dust grains in the early solar system. Comparison of the models to the average Jupiter-family and Oort cloud comet compositions suggest the two families formed in overlapping regions of the disk, in agreement with the findings of A'Hearn et al. (2012) and with the predictions of the Nice model (Gomes et al. 2005, Tsiganis et al. 2005).

Primordial black holes (PBHs) can be produced by a range of mechanisms in the early universe. A particular formation channel that connects PBHs with inflationary phenomenology invokes enhanced primordial curvature perturbations at small scales. In this paper, we re-examine the impact of the growth of the primordial power spectrum on PBH formation in terms of its implications for the PBH mass function. We show that the mass function is relatively insensitive to the steepness of the growth of the power spectrum and subsequent decay, depending primarily on the peak amplitude and the presence of any plateaus that last more than an e-fold. The shape of the power spectrum can of course be constrained by other tracers, and so understanding the physical limitations on its shape remains a pertinent question. We elaborate on how rapidly the background can transition between different values of the parameters of the Hubble hierarchy, which must ultimately derive from a consistent derivative expansion for the background inflaton field. We discuss artefacts associated with matching calculations, and highlight the robustness of the steepest growth index previously found for single-field inflation with conservatively smoothed transitions and limits on how much the power spectrum can grow.

The property of adiabatic invariance is studied for the generalized potential satisfying the condition of identity of sphere's and point mass's gravity. That function contains a second term corresponding to the cosmological constant as weak-field General Relativity and enables to describe the dynamics of groups and clusters of galaxies and the Hubble tension as a result of two flows, local and global ones. Using the adiabatic invariance approach we derive the orbital parameters via Weierstrass functions, including the formula for the eccentricity which explicitly reveals the differences from the Kepler problem.

Quantum gravitational effects usually are assumed to be important on small scale (Planck scale), but actually these effects are also very significant on large (cosmological) scales. It is recognized that in curved spacetime, the existence of a minimal measurable momentum is inevitable. In this paper, we study thermodynamic properties of the late time universe in the presence of a minimal measurable momentum cutoff that encodes infra-red modification of the underlying field theory. In this regard, we consider a non-relativistic regime and show that the existence of a minimal measurable momentum in the very essence of the theory leads to accelerating expansion of the universe, which can be interpreted as an alternative to Dark Energy. The universe in this model has experienced the phantom line crossing in the near past.

We investigate the possibility of detecting the gravitational influence of dark matter (DM) on the trajectory of prospective Doppler ranging missions to Uranus and Neptune. In addition, we estimate the constraints such a mission can provide on modified and massive gravity theories via extra-precession measurements using orbiters around the ice giants. We employ Monte Carlo-Markov Chain methods to reconstruct fictitious spacecraft trajectories in a simplified solar system model with varying amounts of DM. We characterise the noise on the Doppler link by the Allan deviation $\sigma_{\rm A}$, scaled on the Cassini-era value of $\sigma^{\rm{Cass}}_{\rm A}= 3 \times 10^{-15}$. Additionally, we compare the precision of prospective extra-precession measurements of Uranus and Neptune with the expected rates from simulations, in the context of modifications to the inverse square law. We estimate that the prospective mission will be sensitive to DM densities of the order of $\rho_{\rm{DM}} \sim 9 \times 10^{-20} \, (\sigma_{\rm A}/\sigma_{\rm A}^{\rm{Cass}}) $ kg/m$^3$, while the $1\sigma$ bound on the expected galactic density of $\rho_{\rm{DM}} \sim 5 \times 10^{-22}$ kg/m$^3$ decreases as $1.0 \times 10^{-20} \, (\sigma_{\rm A}/\sigma_{\rm{Cass}})^{0.8}$ kg/m$^3$. An improvement of two to three orders of magnitude from the baseline Allan deviation would guarantee a local detection of DM. Only a moderate reduction in ranging noise is required to rule out Milgrom's interpolating function with solar system based observations, and improve constraints the graviton mass beyond current local- or gravitational wave-based measurements. Our analysis also highlights the potential of future ranging missions to improve measurements of the standard gravitational parameters in the solar system.

Galileo Galilei was a skilled writer and explored several genres, from the well-known scientific writings (often in the form of dialogs) to theater and poetry. His last published poem, "Mostro son io" (A Monster am I), is a riddle written in the form of a sonnet. We suggest that the solution to Galileo's riddle is the Zodiac.

We study the possibility of monopoles serving as dark matter when they are produced during the first-order phase transition in the dark sector. Our study shows that dark monopoles can contribute only a small piece of dark matter relic density within parameter spaces where strong gravitational waves can be probed by ET and CE, and the monopoles can contribute a sizable component of the observed dark matter relic density for fast phase transitions with short duration.