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Abstract We present a study of the double-lined spectroscopic binary HD 21278 that contains one of the brightest main-sequence stars in the youngαPersei open cluster. We analyzed new spectra and reanalyzed archived spectra to measure precise new radial velocity curves for the binary. We also obtained interferometric data using the CHARA Array at Mount Wilson to measure the sky positions of the two stars and the inclination of the ∼2 mas orbit. We determine that the two stars have masses of 5.381 ± 0.084M_⊙and 3.353 ± 0.064M_⊙. From isochrone fits, we find the cluster’s age to be 49  ±  7 Myr (using PARSEC models) or 49.5 ± 6 Myr (MIST models). Finally, we revisit the massive white dwarfs that are candidate escapees from theαPersei cluster to try to better characterize the massive end of the white dwarf initial–final mass relation. The implied progenitor masses challenge the idea that Chandrasekhar-mass white dwarfs are made by single stars with masses near 8M_⊙. 

Abstract W Serpentis is an eclipsing binary system and the prototype of the Serpentid class of variable stars. These are interacting binaries experiencing intense mass transfer and mass loss. However, the identities and properties of both stars in W Ser remain a mystery. Here, we present an observational analysis of high-quality, visible-band spectroscopy made with the Apache Point Observatory 3.5 m telescope and Astrophysical Research Consortium Echelle Spectrograph spectrograph plus the first near-IR, long-baseline interferometric observations obtained with the Center for High Angular Resolution Astronomy Array. We present examples of the appearance and radial velocities of the main spectral components: prominent emission lines, strong shell absorption lines, and weak absorption lines. We show that some of the weak absorption features are associated with the cool mass donor, and we present the first radial velocity curve for the donor star. The donor’s absorption lines are rotationally broadened, and we derive a ratio of donor to gainer mass of 0.36 ± 0.09 based on the assumptions that the donor fills its Roche lobe and that it rotates synchronously with the orbit. We use a fit of the All-Sky Automated Survey light curve to determine the orbital inclination and mass estimates of 2.0M_⊙and 5.7M_⊙for the donor and gainer, respectively. The partially resolved interferometric measurements of orbital motion are consistent with our derived orbital properties and the distance from Gaia EDR3. Spectroscopic evidence indicates that the gainer is enshrouded in an opaque disk that channels the mass transfer stream into an outflow through the L3 region and into a circumbinary disk. 

Abstract We report long-baseline interferometric observations with the CHARA Array that resolve six previously known double-lined spectroscopic binary systems in the Hyades cluster, with orbital periods ranging from 3 to 358 days: HD 27483, HD 283882, HD 26874, HD 27149, HD 30676, and HD 28545. We combine those observations with new and existing radial-velocity measurements, to infer the dynamical masses for the components as well as the orbital parallaxes. For most stars, the masses are determined to be better than 1%. Our work significantly increases the number of systems with mass determinations in the cluster. We find that, while current models of stellar evolution for the age and metallicity of the Hyades are able to reproduce the overall shape of the empirical mass–luminosity relation, they overestimate theV-band fluxes by about 0.1 mag between 0.5 and 1.4M_⊙. The disagreement is smaller inH, and near zero inK, and depends somewhat on the model. We also make use of the TESS light curves to estimate rotation periods for our targets, and detect numerous flares in one of them (HD 283882), estimating an average flaring rate of 0.44 events per day. 

Context.V838 Mon is a stellar merger remnant that erupted in a luminous red nova event in 2002. Although it has been well studied in the optical, near-infrared, and submillimeter regimes, its structure in the mid-infrared wavelengths remains elusive. Over the past two decades, only a handful of infrared interferometric studies have been performed, suggesting the presence of an elongated structure at multiple wavelengths. However, given the limited nature of these observations, the true morphology of the source has not yet been conclusively determined. Aims.By performing image reconstruction using observations taken at the VLTI and CHARA, we aim to map out the circumstellar environment in V838 Mon. Methods.We observed V838 Mon with the MATISSE (LMNbands) and GRAVITY (Kband) instruments at the VLTI as well as the MIRCX/MYSTIC (HKbands) instruments at the CHARA array. We geometrically modelled the squared visibilities and the closure phases in each of the bands to obtain the constraints on the physical parameters. Furthermore, we constructed high-resolution images of V838 Mon in theHKbands using the MIRA and SQUEEZE algorithms to study the immediate surroundings of the star. Lastly, we also modelled the spectral features seen in theKandMbands at various temperatures. Results.The image reconstructions show a bipolar structure that surrounds the central star in the post-merger remnant. In theKband, the super-resolved images show an extended structure (uniform disk diameter ~1.94 mas) with a clumpy morphology that is aligned along a north-west position angle (PA) of −40°. On the other hand, in theHband, the extended structure (uniform disk diameter ~1.18 mas) lies roughly along the same PA. Yet the northern lobe is slightly misaligned with respect to the southern lobe, which results in the closure phase deviations. Conclusions.The VLTI and CHARA imaging results show that V838 Mon is surrounded by features resembling jets that are intrinsically asymmetric. This is further confirmed by the closure phase modelling. Further observations with VLTI can help to determine whether this structure shows any variations over time and also if such bi-polar structures are commonly formed in other stellar merger remnants. 

Abstract The 30 yr orbit of the Cepheid Polaris has been followed with observations by the Center for High Angular Resolution Astronomy (CHARA) Array from 2016 through 2021. An additional measurement has been made with speckle interferometry at the Apache Point Observatory. Detection of the companion is complicated by its comparative faintness—an extreme flux ratio. Angular diameter measurements appear to show some variation with pulsation phase. Astrometric positions of the companion were measured with a custom grid-based model-fitting procedure and confirmed with the CANDID software. These positions were combined with the extensive radial velocities (RVs) discussed by Torres to fit an orbit. Because of the imbalance of the sizes of the astrometry and RV data sets, several methods of weighting are discussed. The resulting mass of the Cepheid is 5.13 ± 0.28M_⊙. Because of the comparatively large eccentricity of the orbit (0.63), the mass derived is sensitive to the value found for the eccentricity. The mass combined with the distance shows that the Cepheid is more luminous than predicted for this mass from evolutionary tracks. The identification of surface spots is discussed. This would give credence to the identification of a radial velocity variation with a period of approximately 120 days as a rotation period. Polaris has some unusual properties (rapid period change, a phase jump, variable amplitude, and unusual polarization). However, a pulsation scenario involving pulsation mode, orbital periastron passage, and low pulsation amplitude can explain these characteristics within the framework of pulsation seen in Cepheids. 

Abstract Rapid rotation and nonradial pulsations enable Be stars to build decretion disks, where the characteristic line emission forms. A major but unconstrained fraction of Be stars owe their rapid rotation to mass and angular momentum transfer in a binary. The faint, stripped companions can be helium-burning subdwarf OB-type stars (sdOBs), white dwarfs (WDs), or neutron stars. We present optical/near-infrared Center for High Angular Resolution Astronomy (CHARA) interferometry of 37 Be stars selected for spectroscopic indications of low-mass companions. From multiepochH- and/orK-band interferometry plus radial velocities and parallaxes collected elsewhere, we constructed 3D orbits and derived flux ratios and absolute dynamical masses of both components for six objects, quadrupling the number of anchor points for evolutionary models. In addition, a new wider companion was identified for the known Be + sdO binary 59 Cyg, while auxiliary Very Large Telescope Interferometer/GRAVITY spectrointerferometry confirmed circumstellar matter around the sdO companion to HR 2142. On the other hand, we failed to detect any companion to the six Be stars withγCas–like X-ray emission, with sdOB and main-sequence companions of the expected spectroscopic mass being ruled out for the X-ray-prototypical starsγCas andπAqr, leaving elusive WDs as the most likely companions, as well as a likely explanation of the X-rays. No low-mass main-sequence close companions were identified for the other stars. 

ABSTRACT We report near-infrared long-baseline interferometric observations of the Hyades multiple system HD 284163, made with the Center for High Angular Resolution Astronomy array, as well as almost 43 yr of high-resolution spectroscopic monitoring at the Center for Astrophysics. Both types of observations resolve the 2.39 d inner binary, and also an outer companion in a 43.1 yr orbit. Our observations, combined with others from the literature, allow us to solve for the 3D inner and outer orbits, which are found to be at nearly right angles to each other. We determine the dynamical masses of the three stars (good to better than 1.4 per cent for the inner pair), as well as the orbital parallax. The secondary component (0.5245 ± 0.0047 M⊙) is now the lowest mass star with a dynamical mass measurement in the cluster. A comparison of these measurements with current stellar evolution models for the age and metallicity of the Hyades shows good agreement. All three stars display significant levels of chromospheric activity, consistent with the classification of HD 284163 as an RS CVn object. We present evidence that a more distant fourth star is physically associated, making this a hierarchical quadruple system.