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Register a new userCoRoT photometry and high-resolution spectroscopy of the interacting eclipsing binary AU Mon
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Analyses of very accurate CoRoT space photometry, past Johnson V photoelectric photometry and high-resolution echelle spectra led to the determination of improved and consistent fundamental stellar properties of both components of AU Mon. We derived new, accurate ephemerides for both the orbital motion (with a period of 11.113d) and the long-term, overall brightness variation (with a period of 416.9d) of this strongly interacting Be + G semi-detached binary. It is shown that this long-term variation must be due to attenuation of the total light by some variable circumbinary material. We derived the binary mass ratio $M_{rm G}/M_{rm B}$ = 0.17p0.03 based on the assumption that the G-type secondary fills its Roche lobe and rotates synchronously. Using this value of the mass ratio as well as the radial velocities of the G-star, we obtained a consistent light curve model and improved estimates of the stellar masses, radii, luminosities and effective temperatures. We demonstrate that the observed lines of the B-type primary may not be of photospheric origin. We also discover rapid and periodic light changes visible in the high-quality residual CoRoT light curves. AU Mon is put into perspective by a comparison with known binaries exhibiting long-term cyclic light changes.
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We analyze the CoRoT and V-passband ground-based light curves of the interacting close binary AU Mon, assuming that there is a geometrically and optically thick accretion disk around the hotter and more massive star, as inferred from photometric and spectroscopic characteristics of the binary. Our model fits the observations very well and provides estimates for the orbital elements and physical parameters of the components and of the accretion disk.
Studies of transiting extrasolar planets are of key importance for understanding the nature of planets outside our solar system because their masses, diameters, and bulk densities can be measured. An important part of transit-search programmes is the removal of false-positives. The critical question is how many of the candidates that passed all previous tests are false positives. For our study we selected 25 CoRoT candidates that have already been screened against false-positives using detailed analysis of the light curves and seeing-limited imaging, which has transits that are between 0.7 and 0.05% deep. We observed 20 candidates with the adaptive optics imager NaCo and 18 with the high-resolution infrared spectrograph CRIRES. We found previously unknown stars within 2 arcsec of the targets in seven of the candidates. All of these are too faint and too close to the targets to have been previously detected with seeing-limited telescopes in the optical. Our study thus leads to the surprising results that if we remove all candidates excluded by the sophisticated analysis of the light-curve, as well as carrying out deep imaging with seeing-limited telescopes, still 28-35% of the remaining candidates are found to possess companions that are bright enough to be false-positives. Given that the companion-candidates cluster around the targets and that the J-K colours are consistent with physical companions, we conclude that the companion-candidates are more likely to be physical companions rather than unrelated field stars.
Double Periodic Variables (DPV) are among the new enigmas of semi-detached eclipsing binaries. These are intermediate-mass binaries characterized by a long photometric period lasting on average 33 times the orbital period. We present a spectroscopic and photometric study of the DPV V495 Cen based on new high-resolution spectra and the ASAS V-band light curve. We have determined an improved orbital period of $33.492 pm 0.002$ d and a long period of 1283 d. We find a cool evolved star of $M_{2}=0.91pm 0.2 M_{odot}$, $T_{2}= 6000pm 250 K$ and $R_{2}=19.3 pm 0.5 R_{odot}$ and a hot companion of $M_{1}= 5.76pm 0.3 M_{odot}$, $T_{1}=16960pm 400 K$ and $R=4.5pm0.2 R_{odot}$. The mid-type B dwarf is surrounded by a concave and geometrically thick disc, of radial extension $R_{d}= 40.2pm 1.3 R_{odot}$ contributing $sim$ 11 percent to the total luminosity of the system at the V band. The system is seen under inclination $84.!!^{circ}8$ $pm$ $0.!!^{circ}6$ and it is at a distance $d= 2092 pm 104.6$ pc. The light curve analysis suggests that the mass transfer stream impacts the external edge of the disc forming a hot region 11 % hotter than the surrounding disc material. The persistent $V<R$ asymmetry of the H$alpha$ emission suggests the presence of a wind and the detection of a secondary absorption component in He I lines indicates a possible wind origin in the hotspot region.
We calculate the flux received from a binary system obscured by a circumbinary disc. The disc is modelled using two dimensional hydrodynamical simulations, and the vertical structure is derived by assuming it is isothermal. The gravitational torque from the binary creates a cavity in the discs inner parts. If the line of sight along which the system is observed has a high inclination $I$, it intersects the disc and some absorption is produced. As the system is not axisymmetric, the resulting light curve displays variability. We calculate the absorption and produce light curves for different values of the dust disc aspect ratio $H/r$ and mass of dust in the cavity $M_{rm dust}$. This model is applied to the high inclination ($I=85^{circ}$) eclipsing binary CoRoT 223992193, which shows 5-10% residual photometric variability after the eclipses and a spot model are subtracted. We find that such variations for $I sim 85^{circ}$ can be obtained for $H/r=10^{-3}$ and $M_{rm dust} ge 10^{-12}$ M$_{odot}$. For higher $H/r$, $M_{rm dust}$ would have to be close to this lower value and $I$ somewhat less than $85^{circ}$. Our results show that such variability in a system where the stars are at least 90% visible at all phases can be obtained only if absorption is produced by dust located inside the cavity. If absorption is dominated by the parts of the disc located close to or beyond the edge of the cavity, the stars are significantly obscured.
OB stars are important constituents for the ecology of the Universe, and there are only a few studies on their pulsational properties detailed enough to provide important feedback on current evolutionary models. Our goal is to analyse and interpret the behaviour present in the CoRoT light curve of the B0.5 IV star HD 51756 observed during the second long run of the space mission, and to determine the fundamental stellar parameters from ground-based spectroscopy gathered with the CORALIE and HARPS instruments after checking for signs of variability and binarity, thus making a step further in mapping the top of the Beta Cep instability strip. We compare the newly obtained high-resolution spectra with synthetic spectra of late O-type and early B-type stars computed on a grid of stellar parameters. We match the results with evolutionary tracks to estimate stellar parameters. We use various time series analysis tools to explore the nature of the variations present in the light curve. Additional calculations are carried out based on distance and historical position measurements of the components to impose constraints on the binary orbit. We find that HD 51756 is a wide binary with both a slow (v sin i approx 28 km s^-1) and a fast (v sin i approx 170 km s^-1) early-B rotator whose atmospheric parameters are similar (T_eff approx 30000 K and log g approx 3.75). We are unable to detect pulsation in any of the components, and we interpret the harmonic structure in the frequency spectrum as sign of rotational modulation, which is compatible with the observed and deduced stellar parameters of both components. The non-detection of pulsation modes provides a feedback on the theoretical treatment, given that non-adiabatic computations applied to appropriate stellar models predict the excitation of both pressure and gravity modes for the fundamental parameters of this star.
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