Effects of gravitational darkening on the determination of fundamental parameters in fast-rotating B-type stars

By Y. Frémat, J. Zorec, A. Hubert, M. Floquet. 2005

208 citations recorded by the source corpus.

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 to the relation between the apparent and parent non-rotating counterpart stellar fundamental parameters and apparent, and true Vsin i parameters as a function of the rotation rate Ω/Ω c , stellar mass, and inclination angle. It is shown that omitting 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 revised while correcting not only the Vsin i 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 Vsin i increase is accompanied by an even higher value for the stellar equatorial critical velocity, so that the most probable average rate of the angular velocity of Be stars attains Ω/Ω c ≃ 0.88.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/56581116d610ce7ec46a2aa8f681853292344b9f

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In Astronomy and Astrophysics

Citations in the corpus

Rotational velocities of A-type stars - IV. Evolution of rotational velocities (2012, methodology): “The apparent v sin i of rapid rotators must then be corrected for this underestimation (Frémat et al. 2005).”
A CHARA ARRAY SURVEY OF CIRCUMSTELLAR DISKS AROUND NEARBY Be-TYPE STARS (2013, methodology): “We adopted additional constraints on some model parameters that are well defined from studies such as inclination estimates from Frémat et al. (2005) and intrinsic polarization angles from McDavid (1999) and Yudin (2001).”
A STELLAR ROTATION CENSUS OF B STARS: FROM ZAMS TO TAMS (2010, background): “On the other hand, some later studies that took the gravitational darkening effect into account (Frémat et al. 2005; Cranmer 2005) still favored relatively low Veq/Vcrit values for Be stars.”
The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters (2005, background): “…rotational velocities, vrot, of Be stars are 70%−80% of the critical breakup velocity, vcrit, although Townsend, Owocki, & Howarth (2004) and Frémat et al. (2005) showed that observed Be star rotational velocities may be systematically underestimated due to the effects of gravitational…”
Coudé-feed stellar spectral library – atmospheric parameters (2010, methodology): “Frémat et al. (2005) determined the temperature and the surface gravity, confirming that the temperature used by Kodaira & Scholz (1970) is too hot.”
Rotational velocities of A-type stars. III. Velocity distributions (2006, background): “…report that theirvsini parameters are systematically lower than those issued from classical methods by roughly 15 % among early stars up to spectral type A2, which is contrary to what is predicted by modern calculations of non-LTE rotationally broadened lines affected by GD (Frémat et al. 2005).”
The IACOB project - I. Rotational velocities in northern Galactic O- and early B-type stars revisited. The impact of other sources of line-broadening (2013, background): “– Equatorial gravity darkening will produce an obscuration of the profile wings associated with the larger velocities and thus an underestimation of the actualv sini (Townsend et al., 2004; Frémat et al., 2005).”
Classical Be stars (2013, methodology): “Meilland et al. (2012) use a similar approach, in that they determine the inclination interferometrically (using the disk as proxy), and then use v sin i and vcrit from Frémat et al. (2005) to derive W .”