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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 In the framework of the ALOHA (Astronomical Light Optical Hybrid Analysis) project, we have implemented a fibre-linked interferometer connecting two telescopes of the CHARA (Center for High Angular Resolution Astronomy) array to the recombination beam facility using servo controlled hectometric outdoor fibres (240 m). During two consecutive nights, on-sky fringes at 810 nm were recorded on the star Vega (mag 0), with servo control of the fibre lengths. The optical path difference was set close to zero using internal fringes found before the on-sky observations. The repeatability of the delay line position offset between internal and on-sky fringes was less than 0.2 mm. The efficiency of the servo control systems has been demonstrated, leading to an enhancement of the signal-to-noise ratio from 68.9 with the servo off to 91.6 with the servo on. This result is a cornerstone for the ALOHA project goal of interferometry at 3.5 $$\mu$$m and a seminal step for the future kilometric infrared fibre-linked interferometer at CHARA. 

Abstract Massive evolved stars such as red supergiants and hypergiants are potential progenitors of Type II supernovae, and they are known for ejecting substantial amounts of matter, up to half their initial mass, during their final evolutionary phases. The rate and mechanism of this mass loss play a crucial role in determining their ultimate fate and the likelihood of their progression to supernovae. However, the exact mechanisms driving this mass ejection have long been a subject of research. Recent observations, such as the Great Dimming of Betelgeuse, have suggested that the activity of large convective cells, combined with pulsation, could be a plausible explanation for such mass-loss events. In this context, we conducted interferometric observations of the famous yellow hypergiant,ρCassiopeiae using the CHARA Array inH-andK-band wavelengths.ρCas is well known for its recurrent eruptions, characterized by periods of visual dimming (∼1.5–2 mag) followed by recovery. From our observations, we derived the diameter of the limb-darkened disk and found that this star has a radius of 1.04 ± 0.01 mas, or 564–700R_⊙. We performed image reconstructions with three different image reconstruction software packages, and they unveiled the presence of giant hot and cold spots on the stellar surface. We interpret these prominent hot spots as giant convection cells, suggesting a possible connection to mass ejections from the star’s envelope. Furthermore, we detected spectral CO emission lines in theKband (λ= 2.31–2.38μm), and the image reconstructions in these spectral lines revealed an extended circumstellar envelope with a radius of 1.45 ± 0.10 mas. 

Abstract We present measurements of the interferometrically resolved binary star system 12 Com and the single giant star 31 Com in the cluster Coma Berenices. 12 Com is a double-lined spectroscopic binary system consisting of a G7 giant and an A3 dwarf at the cluster turnoff. Using an extensive radial velocity data set and interferometric measurements from the Palomar Testbed Interferometer and the Center for High Angular Resolution Astronomy array, we measured masses M 1 = 2.64 ± 0.07 M ⊙ and M 2 = 2.10 ± 0.03 M ⊙ . Interferometry also allows us to resolve the giant and measure its size as R 1 = 9.12 ± 0.12 ± 0.01 R ⊙ . With the measured masses and radii, we find an age of 533 ± 41 ± 42 Myr. For comparison, we measure the radius of 31 Com to be 8.36 ± 0.15 R ⊙ . Based on the photometry and radius measurements, 12 Com A is likely the most evolved bright star in the cluster, large enough to be in the red giant phase, but too small to have core helium burning. Simultaneous knowledge of 12 Com A’s mass and photometry puts strong constraints on convective core overshooting during the main-sequence phase, which in turn reduces systematic uncertainties in the age. Increased precision in measuring this system also improves our knowledge of the progenitor of the cluster white dwarf WD1216+260. 

Abstract Castor is a system of six stars in which the two brighter objects, Castor A and B, revolve around each other every ∼450 yr and are both short-period spectroscopic binaries. They are attended by the more distant Castor C, which is also a binary. Here we report interferometric observations with the Center for High Angular Resolution Astronomy (CHARA) array that spatially resolve the companions in Castor A and B for the first time. We complement these observations with new radial velocity measurements of A and B spanning 30 yr, with the Hipparcos intermediate data, and with existing astrometric observations of the visual AB pair obtained over the past three centuries. We perform a joint orbital solution to solve simultaneously for the three-dimensional orbits of Castor A and B as well as the AB orbit. We find that they are far from being coplanar: the orbit of A is nearly at right angles (92°) relative to the wide orbit, and that of B is inclined about 59° compared to AB. We determine the dynamical masses of the four stars in Castor A and B to a precision better than 1%. We also determine the radii of the primary stars of both subsystems from their angular diameters measured with the CHARA array, and use them together with stellar evolution models to infer an age for the system of 290 Myr. The new knowledge of the orbits enables us to measure the slow motion of Castor C as well, which may assist future studies of the dynamical evolution of this remarkable sextuple system. 

Abstract We observe the brightest member of the Praesepe cluster, ϵ Cnc, to precisely measure the characteristics of the stars in this binary system, en route to a new measurement of the cluster’s age. We present spectroscopic radial velocity measurements and interferometric observations of the sky-projected orbit to derive the masses, which we find to be M 1 / M ⊙ = 2.420 ± 0.008 and M 2 / M ⊙ = 2.226 ± 0.004. We place limits on the color–magnitude positions of the stars by using spectroscopic and interferometric luminosity ratios while trying to reproduce the spectral energy distribution of ϵ Cnc. We reexamine the cluster membership of stars at the bright end of the color–magnitude diagram using Gaia data and literature radial velocity information. The binary star data are consistent with an age of 637 ± 19 Myr, as determined from MIST model isochrones. The masses and luminosities of the stars appear to select models with the most commonly used amount of convective core overshooting. 

The Center for High Angular Resolution Astronomy (CHARA) Array is a six-element interferometer with baselines ranging from 34 to 331 m. Three new beam combiners are entering operation: MYSTIC is a 6-telescope combiner for K-band; SPICA is a 6-telescope combiner for the visible R-band; and SILMARIL is a 3-telescope combiner for high sensitivity in H and K-bands. A seventh, portable telescope will use fiber optics for beam transport and will increase the baselines to 1 km. Observing time is available through a program funded by NSF. The programs are solicited and peer-reviewed by NSF’s National Optical Infrared Astronomy Research Laboratory. The open community access has significantly expanded the range of astronomical investigations of stars and their environments. Here we summarize the scientific work and the on-going technical advances of the CHARA Array.