DG Leo is a spectroscopic triple system composed by 3 stars of late-A spectral type, one of which was suggested to be a delta Scuti star. Seven nights of observations at high spectral and high time ...resolution at the Observatoire de Haute-Provence with the ELODIE spectrograph were used to obtain the component spectra by applying a Fourier transform spectral disentangling technique. Comparing these with synthetic spectra, the stellar fundamental parameters (effective temperature, surface gravity, projected rotation velocity and chemical composition) are derived. The inner binary consists of two Am components, at least one of which is not yet rotating synchronously at the orbital period though the orbit is a circular one. The distant third component is confirmed to be a delta Scuti star with normal chemical composition.
Effective temperatures of early-type supergiants are important to test stellar atmosphere- and internal structure-models of massive and intermediate mass objects at different evolutionary phases. ...However, these Teff values are more or less discrepant depending on the method used to determine them. We aim to obtain a new calibration of the Teff parameter for early-type supergiants as a function of observational quantities that are highly sensitive to the ionization balance in the photosphere and its gas pressure, independent of the interstellar extinction, and as much as possible model-independent. The observational quantities that best address our aims are the (lambda1, D) parameters of the BCD spectrophotometric system. They describe the energy distribution around the Balmer discontinuity, which is highly sensitive to Teff and logg. We perform a calibration of the (lambda1, D) parameters into Teff using effective temperatures derived with the bolometric-flux method for 217 program stars, whose individual absolute relative uncertainties are on average 0.05. The final comparison of calculated with obtained Teff values in the (lambda1,D) calibration further show that the latter have total relative uncertainties, which on average are of the order of 0.05 for all spectral types and luminosity classes. The effective temperatures of OB supergiants derived in this work agree on average within some 2000 K with other determinations found in the literature, except those issued from wind-free non-LTE plane-parallel models of stellar atmospheres, which produce effective temperatures that can be overestimated by up to more than 5000 K near Teff = 25000 K.
High resolution synthetic stellar libraries are of fundamental importance for the preparation of the Gaia Mission. We present new sets of spectral stellar libraries covering two spectral ranges: 300 ...--1100 nm at 0.1 nm resolution, and 840 -- 890 nm at 0.001 nm resolution. These libraries span a large range in atmospheric parameters, from super-metal-rich to very metal-poor (-5.0 \(<\)Fe/H\(<\)+1.0), from cool to hot (\teff=3000--50000 K) stars, including peculiar abundance variations. The spectral resolution, spectral type coverage and number of models represent a substantial improvement over previous libraries used in population synthesis models and in atmospheric analysis.
In this paper we develop a calculation code to account for the effects carried by fast rotation on the observed spectra of early-type stars. Stars are assumed to be in rigid rotation and the grid of ...plane-parallel model atmospheres used to represent the gravitational darkening are calculated by means of a non-LTE approach. Attention is paid on the relation between the apparent and parent non-rotating counterpart stellar fundamental parameters and apparent and true vsini parameters as a function of the rotation rate Omega/Omega_c, stellar mass and inclination angle. It is shown that omission of gravitational darkening in the analysis of chemical abundances of CNO elements can produce systematic overestimation or underestimation, depending on the lines used, rotational rate and inclination angle. The proximity of Be stars to the critical rotation is re-discussed by correcting not only the vsini of 130 Be stars, but also their effective temperature and gravity to account for stellar rotationally induced geometrical distortion and for the concomitant gravitational darkening effect. We concluded that the increase of the vsini estimate is accompanied by an even higher value of the stellar equatorial critical velocity, so that the most probable average rate of angular velocity of Be stars attains Omega/Omega_c ~ 0.88.
The presence of pulsations in late-type Be stars is still a matter of controversy. It constitutes an important issue to establish the relationship between non-radial pulsations and the mass-loss ...mechanism in Be stars. To contribute to this discussion, we analyse the photometric time series of the B8IVe star HD 50209 observed by the CoRoT mission in the seismology field. We use standard Fourier techniques and linear and non-linear least squares fitting methods to analyse the CoRoT light curve. In addition, we applied detailed modelling of high-resolution spectra to obtain the fundamental physical parameters of the star. We have found four frequencies which correspond to gravity modes with azimuthal order m=0,-1,-2,-3 with the same pulsational frequency in the co-rotating frame. We also found a rotational period with a frequency of 0.679 \cd (7.754 \(\mu\)Hz). HD 50209 is a pulsating Be star as expected from its position in the HR diagram, close to the SPB instability strip.
Analyses of very accurate CoRoT space photometry, past Johnson V photoelectric photometry and high-resolution échelle 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 \(M_{\rm G}/M_{\rm B}\) = 0.17\p0.03 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.
DG Leo consists of three late A-type stars forming a hierarchic and spectroscopic triple system. Although all components have similar age and mass, in-depth spectroscopic analysis showed that the ...components nevertheless behave differently with respect to pulsation and to diffusion in their outer atmospheres. Inclusion of a speckle measure shortly after periastron passage allows to obtain a much improved orbital solution as well as a reliable dynamical parallax and systemic mass. The orbital parameters also suggest a possible coplanar configuration of both pairs. This object therefore represents a first-class opportunity to investigate the link between multiplicity, chemical composition and pulsation in a coeval system.
The GAUDI database (Ground-based Asteroseismology Uniform Database Interface,
http://sdc.laeff.esa.es/gaudi/) is a preparatory archive for the COROT
(COnvection, ROtation and planetary Transits,
...http://www.astrsp-mrs.fr/projets/corot/) mission developed at LAEFF (Laboratory
for Space Astrophysics and Theoretical Physics, http://www.laeff.esa.es). Its
intention is to make the ground-based observations obtained in the preparation
of the asteroseismology programme available in a simple and efficient way. It
contains spectroscopic and photometric data together with inferred physical
parameters for more than 1500 objects gathered since January 1998 in 6 years of
observational campaigns. In this paper, the main functionalities and
characteristics of the system are described. The observations have been
collected at ESO-La Silla, Telescopio Nazionale Galileo, Observatoire de
Haute-Provence, South African Astronomical Observatory, Tautenberg Observatory
and Sierra Nevada Observatory.
In preparation for the COROT space mission, we determined the fundamental
parameters (spectral type, temperature, gravity, vsini) of the Be stars
observable by COROT in its seismology fields (64 Be ...stars). We applied a
careful and detailed modeling of the stellar spectra, taking into account the
veiling caused by the envelope, as well as the gravitational darkening and
stellar flattening due to rapid rotation. Evolutionary tracks for fast rotators
were used to derive stellar masses and ages. The derived parameters will be
used to select Be stars as secondary targets (i.e. observed for 5 consecutive
months) and short-run targets of the COROT mission. Furthermore, we note that
the main part of our stellar sample is falling in the second half of the main
sequence life time, and that in most cases the luminosity class of Be stars is
inaccurate in characterizing their evolutionary status.
The GAUDI database (Ground-based Asteroseismology Uniform Database Interface, http://sdc.laeff.esa.es/gaudi/) is a preparatory archive for the COROT (COnvection, ROtation and planetary Transits, ...http://www.astrsp-mrs.fr/projets/corot/) mission developed at LAEFF (Laboratory for Space Astrophysics and Theoretical Physics, http://www.laeff.esa.es). Its intention is to make the ground-based observations obtained in the preparation of the asteroseismology programme available in a simple and efficient way. It contains spectroscopic and photometric data together with inferred physical parameters for more than 1500 objects gathered since January 1998 in 6 years of observational campaigns. In this paper, the main functionalities and characteristics of the system are described. The observations have been collected at ESO-La Silla, Telescopio Nazionale Galileo, Observatoire de Haute-Provence, South African Astronomical Observatory, Tautenberg Observatory and Sierra Nevada Observatory.
