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- ID:
- ivo://CDS.VizieR/J/MNRAS/380/1599
- Title:
- Ephemeris of V382 Cyg and TU Mus
- Short Name:
- J/MNRAS/380/1599
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Up to now, V382 Cyg and TU Mus are the only two discovered O-type overcontact binary stars with periods less than two days (P=1.8855 and 1.3873d). Both systems contain a visual companion. New eclipse times and analyses of orbital period variations of the two systems are presented. It is discovered that the periods of both binaries show cyclic oscillations with periods of 47.70 and 47.73yr, while they undergo continuous increases at rates of dP/dt=+4.4x10^-7^ and +4.0x10^-7^d/yr, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/544/A91
- Title:
- {epsilon} Aur visibility measurements
- Short Name:
- J/A+A/544/A91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The enigmatic binary, epsilon Aurigae, is yielding its parameters as a result of new methods applied to the recent eclipse, including optical spectro-interferometry with the VEGA beam combiner at the CHARA Array. VEGA/CHARA visibility measurements from 2009 to 2011 indicate the formation of emission wings of Halpha in an expanding zone almost twice the photospheric size of the F star, namely, in a stellar wind. These may be caused by shocks in the atmosphere from large scale convective or multi-periodic pulsation modes emerging from the star. During the total eclipse phase in 2010, when the disk was in the line of sight, we saw broadening of the Halpha absorption and a less steep drop of the visibility curve, consistent with the addition of neutral hydrogen in the line of sight but extended above and below the plane of the interferometrically imaged disk itself. This provides a unique constraint on the scale height of the gaseous component of the disk material, and, based on some additional assumptions, points to a mass of the central object being 2.4 to 5.5M_{sun}_ for a distance of 650pc or 3.8 to 9.1M_{sun}_ for a distance of 1050pc. These results can be tested during coming observing seasons as the star moves from eclipse phase toward quadrature.
224. EREBOS project. I.
- ID:
- ivo://CDS.VizieR/J/A+A/630/A80
- Title:
- EREBOS project. I.
- Short Name:
- J/A+A/630/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Eclipsing post-common-envelope binaries are highly important for resolving the poorly understood, very short-lived common-envelope phase of stellar evolution. Most hot subdwarfs (sdO/Bs) are the bare helium-burning cores of red giants that have lost almost all of their hydrogen envelope. This mass loss is often triggered by common-envelope interactions with close stellar or even substellar companions. Cool companions to hot subdwarf stars such as late-type stars and brown dwarfs are detectable from characteristic light-curve variations - reflection effects and often eclipses. In the recently published catalog of eclipsing binaries in the Galactic Bulge and in the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey, we discovered 125 new eclipsing systems showing a reflection effect seen by visual inspection of the light curves and using a machine-learning algorithm, in addition to the 36 systems previously discovered by the Optical Gravitational Lesing Experiment (OGLE) team. The Eclipsing Reflection Effect Binaries from Optical Surveys (EREBOS) project aims at analyzing all newly discovered eclipsing binaries of the HW Vir type (hot subdwarf + close, cool companion) based on a spectroscopic and photometric follow up to derive the mass distribution of the companions, constrain the fraction of substellar companions, and determine the minimum mass needed to strip off the red-giant envelope. To constrain the nature of the primary we derived the absolute magnitude and the reduced proper motion of all our targets with the help of the parallaxes and proper motions measured by the Gaia mission and compared those to the Gaia white-dwarf candidate catalog. It was possible to derive the nature of a subset of our targets, for which observed spectra are available, by measuring the atmospheric parameter of the primary, confirming that less than 10% of our systems are not sdO/Bs with cool companions but are white dwarfs or central stars of planetary nebula. This large sample of eclipsing hot subdwarfs with cool companions allowed us to derive a significant period distribution for hot subdwarfs with cool companions for the first time showing that the period distribution is much broader than previously thought and is ideally suited to finding the lowest-mass companions to hot subdwarf stars. The comparison with related binary populations shows that the period distribution of HW Vir systems is very similar to WD+dM systems and central stars of planetary nebula with cool companions. In the future, several new photometric surveys will be carried out, which will further increase the sample of this project, providing the potential to test many aspects of common-envelope theory and binary evolution.
225. ER Vulpeculae
- ID:
- ivo://CDS.VizieR/J/A+A/291/110
- Title:
- ER Vulpeculae
- Short Name:
- J/A+A/291/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+A/487/1129
- Title:
- Evolutionary models of binaries
- Short Name:
- J/A+A/487/1129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The observed distribution of orbital periods of Algols with a B-type primary at birth agrees fairly well with the prediction from conservative theory. Conservative evolution fails, however, to produce the rather large fraction of Algols observed with a high mass-ratio. In order to keep Algols for a longer time with a higher mass-ratio without disturbing the distribution of orbital periods too much, interacting binaries have to lose a significant fraction of their total mass without losing much angular momentum before or during Algolism. We propose a mechanism that meets both requirements. In the case of direct impact the gainer spins up: sometimes up to critical velocity. Equatorial material on the gainer is therefore less bound. A similar statement applies to material located at the edge of an accretion disc. The incoming material moreover creates a hot spot in the area of impact. The sum of the rotational and radiative energy of hot spot material depends on the mass- transfer-rate. The sum of both energies overcomes the binding energy at a well defined critical value of the mass-transfer-rate. As long as the transfer-rate is smaller than this critical value RLOF happens conservatively. But as soon as the critical rate is exceeded the gainer will acquire no more than the critical value and RLOF runs into a liberal era.
- ID:
- ivo://CDS.VizieR/J/ApJ/629/1055
- Title:
- Evolution of close binary systems
- Short Name:
- J/ApJ/629/1055
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We collect data on the masses, radii, etc., of three classes of close binary stars: low-temperature contact binaries (LTCBs), near-contact binaries (NCBs), and detached close binaries (DCBs). We restrict ourselves to systems in which (1) both components are, at least arguably, near the main sequence, (2) the periods are less than a day, and (3) there is both spectroscopic and photometric analysis leading to reasonably reliable data. We discuss the possible evolutionary connections between these three classes, emphasizing the roles played by mass loss and angular momentum loss in rapidly rotating cool stars. We describe a new mechanism, differential rotation as observed in the Sun, which can explain the remarkable efficiency of heat transport in the outer envelopes of contact binaries.
- ID:
- ivo://CDS.VizieR/J/A+A/511/A22
- Title:
- EW Ori differential uvby light curves
- Short Name:
- J/A+A/511/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent studies of inactive and active solar-type binaries suggest that chromospheric activity, and its effect on envelope convection, is likely to cause significant radius and temperature discrepancies. Accurate mass, radius, and abundance determinations from additional solar-type binaries exhibiting various levels of activity are needed for a better insight into the structure and evolution of these stars. We aim to determine absolute dimensions and abundances for the G0 V detached eclipsing binary EW Ori, and to perform a detailed comparison with results from recent stellar evolutionary models.
- ID:
- ivo://CDS.VizieR/J/MNRAS/461/1576
- Title:
- EX Hya mid-eclipse timings
- Short Name:
- J/MNRAS/461/1576
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A study on the intermediate polar EX Hya is presented, based on simultaneous photometry and high-dispersion spectroscopic observations, during four consecutive nights. The strong photometric modulation related to the 67-min spin period of the primary star is clearly present, as well as the narrow eclipses associated with the orbital modulation. Since our eclipse timings have been obtained almost 91000 cycles since the last reported observations, we present new linear ephemeris, although we cannot rule out a sinusoidal variation suggested by previous authors.
- ID:
- ivo://CDS.VizieR/J/A+A/556/A86
- Title:
- FGK dwarf stars limb darkening coefficients
- Short Name:
- J/A+A/556/A86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Limb darkening is a fundamental ingredient for interpreting observations of planetary transits, eclipsing binaries, optical/infrared interferometry and microlensing events. However, this modeling traditionally represents limb darkening by a simple law having one or two coefficients that have been derived from plane-parallel model stellar atmospheres, which has been done by many researchers. More recently, researchers have gone beyond plane-parallel models and considered other geometries. We previously studied the limb-darkening coefficients from spherically symmetric and plane-parallel model stellar atmospheres for cool giant and supergiant stars, and in this investigation we apply the same techniques to FGK dwarf stars. We present limb-darkening coefficients, gravity-darkening coefficients and interferometric angular diameter corrections from Atlas and SAtlas model stellar atmospheres. We find that sphericity is important even for dwarf model atmospheres, leading to significant differences in the predicted coefficients.
