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1. An extreme amplitude, massive heartbeat system in the LMC characterized using ASAS-SN and TESS

   https://doi.org/10.1093/mnras/stz2460  

   Jayasinghe, T ; Stanek, K Z ; Kochanek, C S ; Thompson, Todd A ; Shappee, B J ; Fausnaugh, M ( November 2019 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Using ASAS-SN data, we find that the bright ($V\sim 13.5$ mag) variable star MACHO 80.7443.1718 (ASASSN-V J052624.38–684705.6) is the most extreme heartbeat star yet discovered. This massive binary, consisting of at least one early B-type star, has an orbital period of $P_{\rm ASAS-SN}=32.83627\pm 0.00846\, {\rm d},$ and is located towards the LH58 OB complex in the LMC. Both the ASAS-SN and TESS light curves show extreme brightness variations of ${\sim }40{{\ \rm per\ cent}}$ at periastron and variations of $ \sim 10{{\ \rm per\ cent}}$ due to tidally excited oscillations outside periastron. We fit an analytical model of the variability caused by the tidal distortions at pericentre to find orbital parameters of $\omega =-61.4^\circ$, $i=44.8^\circ$, and $e=0.566$. We also present a frequency analysis to identify the pulsation frequencies corresponding to the tidally excited oscillations.
2. Progenitor and close-in circumstellar medium of type II supernova 2020fqv from high-cadence photometry and ultra-rapid UV spectroscopy

   https://doi.org/10.1093/mnras/stab2887  

   Tinyanont, Samaporn ; Ridden-Harper, R ; Foley, R J ; Morozova, V ; Kilpatrick, C D ; Dimitriadis, G ; DeMarchi, L ; Gagliano, A ; Jacobson-Galán, W V ; Messick, A ; et al ( March 2022 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present observations of SN 2020fqv, a Virgo-cluster type II core-collapse supernova (CCSN) with a high temporal resolution light curve from the Transiting Exoplanet Survey Satellite (TESS) covering the time of explosion; ultraviolet (UV) spectroscopy from the Hubble Space Telescope (HST) starting 3.3 d post-explosion; ground-based spectroscopic observations starting 1.1 d post-explosion; along with extensive photometric observations. Massive stars have complicated mass-loss histories leading up to their death as CCSNe, creating circumstellar medium (CSM) with which the SNe interact. Observations during the first few days post-explosion can provide important information about the mass-loss rate during the late stages of stellar evolution. Model fits to the quasi-bolometric light curve of SN 2020fqv reveal  0.23 M⊙ of CSM confined within  1450 R⊙ (1014 cm) from its progenitor star. Early spectra (<4 d post-explosion), both from HST and ground-based observatories, show emission features from high-ionization metal species from the outer, optically thin part of this CSM. We find that the CSM is consistent with an eruption caused by the injection of ∼5 × 1046 erg into the stellar envelope ∼300 d pre-explosion, potentially from a nuclear burning instability at the onset of oxygen burning. Light-curve fitting, nebular spectroscopy, and pre-explosion HST imaging consistently point to a red supergiant (RSG)more »progenitor with $M_{\rm ZAMS}\approx 13.5\!-\!15 \, \mathrm{M}_{\odot }$, typical for SN II progenitor stars. This finding demonstrates that a typical RSG, like the progenitor of SN 2020fqv, has a complicated mass-loss history immediately before core collapse.« less
3. A unicorn in monoceros: the 3 M⊙ dark companion to the bright, nearby red giant V723 Mon is a non-interacting, mass-gap black hole candidate

   https://doi.org/10.1093/mnras/stab907  

   Jayasinghe, T ; Stanek, K Z ; Thompson, Todd A ; Kochanek, C S ; Rowan, D M ; Vallely, P J ; Strassmeier, K G ; Weber, M ; Hinkle, J T ; Hambsch, F-J ; et al ( May 2021 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We report the discovery of the closest known black hole candidate as a binary companion to V723 Mon. V723 Mon is a nearby ($d\sim 460\, \rm pc$), bright (V ≃ 8.3 mag), evolved (Teff, giant ≃ 4440 K, and Lgiant ≃ 173 L⊙) red giant in a high mass function, f(M) = 1.72 ± 0.01 M⊙, nearly circular binary (P = 59.9 d, e ≃ 0). V723 Mon is a known variable star, previously classified as an eclipsing binary, but its All-Sky Automated Survey, Kilodegree Extremely Little Telescope, and Transiting Exoplanet Survey Satellite light curves are those of a nearly edge-on ellipsoidal variable. Detailed models of the light curves constrained by the period, radial velocities, and stellar temperature give an inclination of $87.0^{\circ ^{+1.7^\circ }}_{-1.4^\circ }$, a mass ratio of q ≃ 0.33 ± 0.02, a companion mass of Mcomp = 3.04 ± 0.06 M⊙, a stellar radius of Rgiant = 24.9 ± 0.7 R⊙, and a giant mass of Mgiant = 1.00 ± 0.07 M⊙. We identify a likely non-stellar, diffuse veiling component with contributions in the B and V band of ${\sim }63{{\ \rm per\ cent}}$ and ${\sim }24{{\ \rm per\ cent}}$, respectively. The SED and the absence of continuum eclipses imply that the companion mass must be dominated by a compact object. We do observe eclipses of the Balmermore »lines when the dark companion passes behind the giant, but their velocity spreads are low compared to observed accretion discs. The X-ray luminosity of the system is $L_{\rm X}\simeq 7.6\times 10^{29}~\rm ergs~s^{-1}$, corresponding to L/Ledd ∼ 10−9. The simplest explanation for the massive companion is a single compact object, most likely a black hole in the ‘mass gap’.« less
4. Characterising the orbit and circumstellar environment of the high-mass binary MWC 166 A

   https://doi.org/10.1051/0004-6361/202243957  

   Zarrilli, Sebastian A. ; Kraus, Stefan ; Kreplin, Alexander ; Monnier, John D. ; Gardner, Tyler ; Mérand, Antoine ; Morrell, Sam ; Davies, Claire L. ; Labdon, Aaron ; Ennis, Jacob ; et al ( September 2022 , Astronomy & Astrophysics)

   Context. Stellar evolution models are highly dependent on accurate mass estimates, especially for highly massive stars in the early stages of stellar evolution. The most direct method for obtaining model-independent stellar masses is derivation from the orbit of close binaries. Aims. Our aim was to derive the first astrometric plus radial velocity orbit solution for the single-lined spectroscopic binary star MWC 166 A, based on near-infrared interferometry over multiple epochs and ∼100 archival radial velocity measurements, and to derive fundamental stellar parameters from this orbit. A supplementary aim was to model the circumstellar activity in the system from K band spectral lines. Methods. The data used include interferometric observations from the VLTI instruments GRAVITY and PIONIER, as well as the MIRC-X instrument at the CHARA Array. We geometrically modelled the dust continuum to derive relative astrometry at 13 epochs, determine the orbital elements, and constrain individual stellar parameters at five different age estimates. We used the continuum models as a base to examine differential phases, visibilities, and closure phases over the Br γ and He  I emission lines in order to characterise the nature of the circumstellar emission. Results. Our orbit solution suggests a period of P  = 367.7 ± 0.1 d, approximatelymore »twice as long as found with previous radial velocity orbit fits. We derive a semi-major axis of 2.61 ± 0.04 au at d  = 990 ± 50 pc, an eccentricity of 0.498 ± 0.001, and an orbital inclination of 53.6 ± 0.3°. This allowed the component masses to be constrained to M 1  = 12.2 ± 2.2  M ⊙ and M 2  = 4.9 ± 0.5  M ⊙ . The line-emitting gas was found to be localised around the primary and is spatially resolved on scales of ∼11 stellar radii, where the spatial displacement between the line wings is consistent with a rotating disc. Conclusions. The large spatial extent and stable rotation axis orientation measured for the Br γ and He  I line emission are inconsistent with an origin in magnetospheric accretion or boundary-layer accretion, but indicate an ionised inner gas disc around this Herbig Be star. We observe line variability that could be explained either with generic line variability in a Herbig star disc or V/R variations in a decretion disc scenario. We have also constrained the age of the system, with relative flux ratios suggesting an age of ∼(7 ± 2)×10 5 yr, consistent with the system being composed of a main-sequence primary and a secondary still contracting towards the main-sequence stage.« less
5. A pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 characterized with CHEOPS

   https://doi.org/10.1093/mnras/stab3799  

   Wilson, Thomas G. ; Goffo, Elisa ; Alibert, Yann ; Gandolfi, Davide ; Bonfanti, Andrea ; Persson, Carina M. ; Collier Cameron, Andrew ; Fridlund, Malcolm ; Fossati, Luca ; Korth, Judith ; et al ( January 2022 , Monthly Notices of the Royal Astronomical Society)

   We report the discovery and characterization of a pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 (TIC 79748331), initially detected in the Transiting Exoplanet Survey Satellite (TESS) photometry. To characterize the system, we performed and retrieved the CHaracterising ExOPlanets Satellite (CHEOPS), TESS, and ground-based photometry, the High Accuracy Radial velocity Planet Searcher (HARPS) high-resolution spectroscopy, and Gemini speckle imaging. We characterize the host star and determine $T_{\rm eff, \star }=4734\pm 67\,\mathrm{ K}$, $R_{\star }=0.726\pm 0.007\, \mathrm{ R}_{\odot }$, and $M_{\star }=0.748\pm 0.032\, \mathrm{ M}_{\odot }$. We present a novel detrending method based on point spread function shape-change modelling and demonstrate its suitability to correct flux variations in CHEOPS data. We confirm the planetary nature of both bodies and find that TOI-1064 b has an orbital period of Pb = 6.44387 ± 0.00003 d, a radius of Rb = 2.59 ± 0.04 R⊕, and a mass of $M_{\rm b} = 13.5_{-1.8}^{+1.7}$ M⊕, whilst TOI-1064 c has an orbital period of $P_{\rm c} = 12.22657^{+0.00005}_{-0.00004}$ d, a radius of Rc = 2.65 ± 0.04 R⊕, and a 3σ upper mass limit of 8.5 M⊕. From the high-precision photometry we obtain radius uncertainties of ∼1.6 per cent, allowing us to conduct internal structure and atmospheric escape modelling. TOI-1064 b is one of the densest, well-characterized sub-Neptunes, withmore »a tenuous atmosphere that can be explained by the loss of a primordial envelope following migration through the protoplanetary disc. It is likely that TOI-1064 c has an extended atmosphere due to the tentative low density, however further radial velocities are needed to confirm this scenario and the similar radii, different masses nature of this system. The high-precision data and modelling of TOI-1064 b are important for planets in this region of mass–radius space, and it allow us to identify a trend in bulk density–stellar metallicity for massive sub-Neptunes that may hint at the formation of this population of planets.

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