ABSTRACT KIC 3230227 is a short period (P 7.0 days) eclipsing binary with a very eccentric orbit (e = 0.6). From combined analysis of radial velocities and Kepler light curves, this system is found ...to be composed of two A-type stars, with masses of M1 = 1.84 0.18 M , M2 = 1.73 0.17 M and radii of R1 = 2.01 0.09 R , R2 = 1.68 0.08 R for the primary and secondary, respectively. In addition to an eclipse, the binary light curve shows a brightening and dimming near periastron, making this a somewhat rare eclipsing heartbeat star system. After removing the binary light curve model, more than 10 pulsational frequencies are present in the Fourier spectrum of the residuals, and most of them are integer multiples of the orbital frequency. These pulsations are tidally driven, and both the amplitudes and phases are in agreement with predictions from linear tidal theory for l = 2, m = −2 prograde modes.
There is growing evidence that some Be stars were spun up through mass transfer in a close binary system, leaving the former mass donor star as a hot, stripped-down object. There are five known cases ...of Be stars with hot subdwarf (sdO) companions that were discovered through International Ultraviolet Explorer (IUE) spectroscopy. Here we expand the search for Be+sdO candidates using archival FUV spectra from IUE. We collected IUE spectra for 264 stars and formed cross-correlation functions with a model spectrum for a hot subdwarf. Twelve new candidate Be+sdO systems were found, and eight of these display radial velocity variations associated with orbital motion. The new plus known Be+sdO systems have Be stars with spectral subtypes of B0-B3, and the lack of later-type systems is surprising given the large number of cooler B-stars in our sample. We discuss explanations for the observed number and spectral type distribution of the Be+sdO systems, and we argue that there are probably many Be systems with stripped companions that are too faint for detection through our analysis.
We present the discovery of a gap near MG 10 in the main sequence on the Hertzsprung-Russell Diagram (HRD) based on measurements presented in Gaia Data Release 2 (DR2). Using an observational form of ...the HRD with MG representing luminosity and GBP − GRP representing temperature, the gap presents a diagonal feature that dips toward lower luminosities at redder colors. The gap is seen in samples extracted from DR2 with various distances, and is not unique to the Gaia photometry-it also appears when using near-IR (NIR) photometry (J − Ks versus ). The gap is very narrow (∼0.05 mag) and is near the luminosity-temperature regime where M dwarf stars transition from partially to fully convective, i.e., near spectral type M3.0V. This gap provides a new feature in the HRD that hints at an underlying astrophysical cause, and we propose that it is linked to the onset of full convection in M dwarfs.
The Transformative Journey of HD 93521 Gies, Douglas R.; Shepard, Katherine; Wysocki, Peter ...
The Astronomical journal,
02/2022, Letnik:
163, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
HD 93521 is a massive, rapidly rotating star that is located about 1 kpc above the Galactic disk, and the evolutionary age for its estimated mass is much less than the time of flight if it ...was ejected from the disk. Here we present a reassessment of both the evolutionary and kinematical timescales for HD 93521. We calculate a time of flight of 39 ± 3 Myr based upon the distance and proper motions from Gaia EDR3 and a summary of radial velocity measurements. We then determine the stellar luminosity using a rotational model combined with the observed spectral energy distribution and distance. A comparison with evolutionary tracks for rotating stars from Brott et al. yields an evolutionary age of about 5 ± 2 Myr. We propose that the solution to the timescale discrepancy is that HD 93521 is a stellar merger product. It was probably ejected from the Galactic disk as a close binary system of lower-mass stars that eventually merged to create the rapidly rotating and single massive star we observe today.
Abstract
The B emission-line stars are rapid rotators that were probably spun up by mass and angular momentum accretion through mass transfer in an interacting binary. Mass transfer will strip the ...donor star of its envelope to create a small and hot subdwarf remnant. Here we report on Hubble Space Telescope/STIS far-ultraviolet spectroscopy of a sample of Be stars that reveals the presence of the hot sdO companion through the calculation of cross-correlation functions of the observed and model spectra. We clearly detect the spectral signature of the sdO star in 10 of the 13 stars in the sample, and the spectral signals indicate that the sdO stars are hot, relatively faint, and slowly rotating as predicted by models. A comparison of their temperatures and radii with evolutionary tracks indicates that the sdO stars occupy the relatively long-lived, He-core burning stage. Only 1 of the 10 detections was a known binary prior to this investigation, which emphasizes the difficulty of finding such Be+sdO binaries through optical spectroscopy. However, these results and others indicate that many Be stars probably host hot subdwarf companions.
Abstract
The origin of the bright and hard X-ray emission flux among the
γ
Cas subgroup of B-emission line (Be) stars may be caused by gas accretion onto an orbiting white dwarf (WD) companion. Such ...Be+WD binaries are the predicted outcome of a second stage of mass transfer from a helium star mass donor to a rapidly rotating mass gainer star. The stripped donor stars become small and hot white dwarfs that are extremely faint compared to their Be star companions. Here we discuss model predictions about the physical and orbital properties of Be+WD binaries, and we show that current observational results on
γ
Cas systems are consistent with the expected large binary frequency, companion faintness and small mass, and relatively high mass range of the Be star hosts. We determine that the companions are probably not stripped helium stars (hot subdwarf sdO stars), because these are bright enough to detect in ultraviolet spectroscopy, yet their spectroscopic signatures are not observed in studies of
γ
Cas binaries. Interferometry of relatively nearby systems provides the means to detect very faint companions including hot subdwarf and cooler main-sequence stars. Preliminary observations of five
γ
Cas binaries with the CHARA Array interferometer show no evidence of the companion flux, leaving white dwarfs as the only viable candidates for the companions.
ABSTRACT We present a spectroscopic investigation of the Be+sdO binary system HR 2142 that is based upon large sets of ultraviolet observations from the International Ultraviolet Explorer (IUE) and ...ground-based H observations. We measured radial velocities for the Be star component from these spectra and computed a revised orbit. In order to search for the spectral signature of the hot subdwarf, we cross-correlated the short wavelength end of each IUE spectrum with a model hot star spectrum, and then we used the predicted Doppler shifts of the subdwarf to shift-and-add all the cross-correlation functions to the frame of the subdwarf. This merged function shows the weak signal from the spectral lines of the hot star, and a best fit is obtained with a mass ratio , companion temperature kK, projected rotational velocity km s−1, and a monochromatic flux ratio near 1170 of . This hot subdwarf creates a one-armed spiral, tidal wake in the disk of the Be star, and we present a circumbinary disk model that can explain the occurrence of shell absorption lines by gas enhancements that occur where gas crossing the gap created by the subdwarf strikes the disk boundaries. The faint companion of HR 2142 may be representative of a significant fraction of Be stars with undetected former mass donor companion stars.
We used archival International Ultraviolet Explorer (IUE) high-dispersion, short wavelength spectra data to search for evidence of the spectra of hot subdwarf companions of six rapidly rotating Be ...stars in binary systems. We searched for the signature of a hot companion through an analysis of the cross-correlation functions (CCFs) of observed and model spectra that were separated into primary and secondary components using a Doppler tomography algorithm and adopted spectroscopic orbital solutions. A positive detection of the flux from a hot companion was made for the reconstructed secondary CCF of just one target, 60 Cygni (B1 Ve). We estimate that the companion of the Be star in 60 Cygni has kK, mass ratio , and monochromatic flux ratio in the spectral region near 1525 Å. If the companions of the other target Be stars are also hot, then they must be faint and contribute less than of the UV flux (<0.6% in the case of γ Cas). We also discuss a shell episode of Pleione (28 Tau) recorded in the IUE spectran in an appendix.
We present the results of a speckle interferometric survey of Galactic massive stars that complements and expands upon a similar survey made over a decade ago. The speckle observations were made with ...the Kitt Peak National Observatory and Cerro Tololo Inter-American Observatory 4 m telescopes and USNO speckle camera, and they are sensitive to the detection of binaries in the angular separation regime between 003 and 5'' with relatively bright companions (V < 3). We report on the discovery of companions to 14 OB stars. In total we resolved companions of 41 of 385 O-stars (11%), 4 of 37 Wolf-Rayet stars (11%), and 89 of 139 B-stars (64%; an enriched visual binary sample that we selected for future orbital determinations). We made a statistical analysis of the binary frequency among the subsample that are listed in the Galactic O Star Catalog by compiling published data on other visual companions detected through adaptive optics studies and/or noted in the Washington Double Star Catalog and by collecting published information on radial velocities and spectroscopic binaries. We find that the binary frequency is much higher among O-stars in clusters and associations compared to the numbers for field and runaway O-stars, consistent with predictions for the ejection processes for runaway stars. We present a first orbit for the O-star d Orionis; a linear solution of the close, apparently optical, companion of the O-star i Orionis; and an improved orbit of the Be star d Scorpii. Finally, we list astrometric data for another 249 resolved and 221 unresolved targets that are lower mass stars that we observed for various other science programs.
Abstract
We present a spectroscopic analysis of the most rapidly rotating stars currently known, VFTS 102 (
v
e
sin
i
=
649
±
52
km s
−1
; O9: Vnnne+) and VFTS 285 (
v
e
sin
i
=
610
±
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 Hubble Space Telescope/Cosmic Origins Spectrograph and optical spectra from the Very Large Telescope (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,
ζ
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.
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