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1. The former companion of hyper-velocity star S5-HVS1

   https://doi.org/10.1093/mnras/stab459  

   Lu, Wenbin; Fuller, Jim; Raveh, Yael; Perets, Hagai B; Li, Ting S; Hosek, Matthew W; Do, Tuan (March 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT The hyper-velocity star S5-HVS1, ejected 5 Myr ago from the Galactic Centre at 1800 km s−1, was most likely produced by tidal break-up of a tight binary by the supermassive black hole SgrA*. Taking a Monte Carlo approach, we show that the former companion of S5-HVS1 was likely a main-sequence star between 1.2 and 6 M⊙ and was captured into a highly eccentric orbit with pericentre distance in the range of 1–10 au and semimajor axis about 103 au. We then explore the fate of the captured star. We find that the heat deposited by tidally excited stellar oscillation modes leads to runaway disruption if the pericentre distance is smaller than about $$3\rm \, au$$. Over the past 5 Myr, its angular momentum has been significantly modified by orbital relaxation, which may stochastically drive the pericentre inwards below $$3\rm \, au$$ and cause tidal disruption. We find an overall survival probability in the range 5 per cent to 50 per cent, depending on the local relaxation time in the close environment of the captured star, and the initial pericentre at capture. The pericentre distance of the surviving star has migrated to 10–100 au, making it potentially the most extreme member of the S-star cluster. From the ejection rate of S5-HVS1-like stars, we estimate that there may currently be a few stars in such highly eccentric orbits. They should be detectable (typically $$K_{\rm s}\lesssim 18.5\,$$ mag) by the GRAVITY instrument and by future Extremely Large Telescopes and hence provide an extraordinary probe of the spin of SgrA*. 

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2. The orbit and stellar masses of the archetype colliding-wind binary WR 140

   https://doi.org/10.1093/mnras/stab1181  

   Thomas, Joshua D; Richardson, Noel D; Eldridge, J J; Schaefer, Gail H; Monnier, John D; Sana, Hugues; Moffat, Anthony F; Williams, Peredur; Corcoran, Michael F; Stevens, Ian R; et al (May 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We present updated orbital elements for the Wolf–Rayet (WR) binary WR 140 (HD 193793; WC7pd  + O5.5fc). The new orbital elements were derived using previously published measurements along with 160 new radial velocity measurements across the 2016 periastron passage of WR 140. Additionally, four new measurements of the orbital astrometry were collected with the CHARA Array. With these measurements, we derive stellar masses of $$M_{\rm WR} = 10.31\pm 0.45 \, \mathrm{M}_\odot$$ and $$M_{\rm O} = 29.27\pm 1.14 \, \mathrm{M}_{\odot }$$. We also include a discussion of the evolutionary history of this system from the Binary Population and Spectral Synthesis model grid to show that this WR star likely formed primarily through mass-loss in the stellar winds, with only a moderate amount of mass lost or transferred through binary interactions. 

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3. Constraints on the sub-pc environment of the nearby Type Iax SN 2014dt from deep X-ray and radio observations

   https://doi.org/10.1093/mnras/stab1262  

   Stauffer, C M; Margutti, R; Linford, J D; Chomiuk, L; Coppejans, D L; Demarchi, L; Jacobson-Galán, W; Bright, J; Foley, R J; Horesh, A; et al (June 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We present X-ray and radio observations of what may be the closest Type Iax supernova (SN) to date, SN 2014dt (d = 12.3–19.3 Mpc), and provide tight constraints on the radio and X-ray emission. We infer a specific radio luminosity $$L_R\lt (1.0\!-\!2.4)\times 10^{25}\, \rm {erg\, s^{-1}\, Hz^{-1}}$$ at a frequency of 7.5 GHz and a X-ray luminosity $$L_X\lt 1.4\times 10^{38}\, \rm {erg\, s^{-1}}$$ (0.3–10 keV) at ∼38–48 d post-explosion. We interpret these limits in the context of Inverse Compton (IC) emission and synchrotron emission from a population of electrons accelerated at the forward shock of the explosion in a power-law distribution $$N_e(\gamma _e)\propto \gamma _e^{-p}$$ with p = 3. Our analysis constrains the progenitor system mass-loss rate to be $$\dot{M}\lt 5.0 \times 10^{-6} \rm {M_{\odot }\, yr^{-1}}$$ at distances $$r\lesssim 10^{16}\, \rm {cm}$$ for an assumed wind velocity $$v_w=100\, \rm {km\, s^{-1}}$$, and a fraction of post-shock energy into magnetic fields and relativistic electrons of ϵB = 0.01 and ϵe = 0.1, respectively. This result rules out some of the parameter space of symbiotic giant star companions, and it is consistent with the low mass-loss rates expected from He-star companions. Our calculations also show that the improved sensitivity of the next-generation Very Large Array (ngVLA) is needed to probe the very low-density media characteristic of He stars that are the leading model for binary stellar companions of white dwarfs giving origin to Type Iax SNe. 

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4. SHARP – VIII. J0924+0219 lens mass distribution and time-delay prediction through adaptive-optics imaging

   https://doi.org/10.1093/mnras/stac1081  

   Chen, Geoff C-F; Fassnacht, Christopher D; Suyu, Sherry H; Koopmans, Léon V; Lagattuta, David J; McKean, John P; Auger, Matt W; Vegetti, Simona; Treu, Tommaso (May 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Strongly lensed quasars can provide measurements of the Hubble constant (H0) independent of any other methods. One of the key ingredients is exquisite high-resolution imaging data, such as Hubble Space Telescope (HST) imaging and adaptive-optics (AO) imaging from ground-based telescopes, which provide strong constraints on the mass distribution of the lensing galaxy. In this work, we expand on the previous analysis of three time-delay lenses with AO imaging (RX J1131−1231, HE 0435−1223, and PG 1115+080), and perform a joint analysis of J0924+0219 by using AO imaging from the Keck telescope, obtained as part of the Strong lensing at High Angular Resolution Program (SHARP) AO effort, with HST imaging to constrain the mass distribution of the lensing galaxy. Under the assumption of a flat Λ cold dark matter (ΛCDM) model with fixed Ωm = 0.3, we show that by marginalizing over two different kinds of mass models (power-law and composite models) and their transformed mass profiles via a mass-sheet transformation, we obtain $$\Delta t_{\rm BA}=6.89\substack{+0.8\\-0.7}\, h^{-1}\hat{\sigma }_{v}^{2}$$ d, $$\Delta t_{\rm CA}=10.7\substack{+1.6\\-1.2}\, h^{-1}\hat{\sigma }_{v}^{2}$$ d, and $$\Delta t_{\rm DA}=7.70\substack{+1.0\\-0.9}\, h^{-1}\hat{\sigma }_{v}^{2}$$ d, where $$h=H_{0}/100\,\rm km\, s^{-1}\, Mpc^{-1}$$ is the dimensionless Hubble constant and $$\hat{\sigma }_{v}=\sigma ^{\rm ob}_{v}/(280\,\rm km\, s^{-1})$$ is the scaled dimensionless velocity dispersion. Future measurements of time delays with 10 per cent uncertainty and velocity dispersion with 5 per cent uncertainty would yield a H0 constraint of ∼15 per cent precision. 

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5. Distribution of Si ii λ6355 velocities of Type Ia supernovae and implications for asymmetric explosions

   https://doi.org/10.1093/mnras/staa3191  

   Zhang, Keto D; Zheng, WeiKang; de Jaeger, Thomas; Stahl, Benjamin E; Brink, Thomas G; Han, Xuhui; Kasen, Daniel; Shen, Ken J; Tang, Kevin; Filippenko, Alexei V (November 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT The ejecta velocity is a very important parameter in studying the structure and properties of Type Ia supernovae (SNe Ia) and is a candidate key parameter in improving the utility of SNe Ia for cosmological distance determinations. Here, we study the velocity distribution of a sample of 311 SNe Ia from the kaepora data base. The velocities are derived from the Si ii λ6355 absorption line in optical spectra measured at (or extrapolated to) the time of peak brightness. We statistically show that the observed velocity has a bimodal Gaussian distribution (population ratio 201:110 or 65 per cent:35 per cent) consisting of two groups of SNe Ia: Group I with a lower but narrower scatter ($$11\, 000 \pm 700\, \mathrm{km\, s}^{-1}$$), and Group II with a higher but broader scatter ($$12\, 300 \pm 1800\, \mathrm{km\, s}^{-1}$$). The true origin of the two components is unknown. Naturally, there could exist two intrinsic velocity distributions observed. However, we try to use asymmetric geometric models through statistical simulations to reproduce the observed distribution assuming that all SNe Ia share the same intrinsic distribution. In the two cases we consider, 35 per cent of SNe Ia are considered to be asymmetric in Case 1, and all SNe Ia are asymmetric in Case 2. Simulations for both cases can reproduce the observed velocity distribution but require a significantly large portion ($$\gt 35{{\ \rm per\ cent}}$$) of SNe Ia to be asymmetric. In addition, the Case 1 result is consistent with recent SNe Ia polarization observations that higher Si ii λ6355 velocities tend to be more polarized. 

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