2017A&A...602A..83Z


Query : 2017A&A...602A..83Z

2017A&A...602A..83Z - Astronomy and Astrophysics, volume 602A, 83-83 (2017/6-1)

Critical study of the distribution of rotational velocities of Be stars. II: Differential rotation and some hidden effects interfering with the interpretation of the V sin i parameter.

ZOREC J., FREMAT Y., DOMICIANO DE SOUZA A., ROYER F., CIDALE L., HUBERT A.-M., SEMAAN T., MARTAYAN C., COCHETTI Y.R., ARIAS M.L., AIDELMAN Y. and STEE P.

Abstract (from CDS):

Aims. We assume that stars may undergo surface differential rotation to study its impact on the interpretation of Vsini and on the observed distribution Φ(u) of ratios of true rotational velocities u=V/Vc (Vc is the equatorial critical velocity). We discuss some phenomena affecting the formation of spectral lines and their broadening, which can obliterate the information carried by Vsini concerning the actual stellar rotation.
Methods. We studied the line broadening produced by several differential rotational laws, but adopted Maunder's expression Ω(θ)=Ω0(1+αcos2θ) as an attempt to account for all of these laws with the lowest possible number of free parameters. We studied the effect of the differential rotation parameter α on the measured Vsini parameter and on the distribution Φ(u) of ratios u=V/Vc.
Results. We conclude that the inferred Vsini is smaller than implied by the actual equatorial linear rotation velocity Veq if the stars rotate with α<0, but is larger if the stars have α>0. For a given |α| the deviations of Vsini are larger when α<0. If the studied Be stars have on average α<0, the number of rotators with Veq~=0.9Vc is larger than expected from the observed distribution Φ(u); if these stars have on average α>0, this number is lower than expected. We discuss seven phenomena that contribute either to narrow or broaden spectral lines, which blur the information on the rotation carried by Vsini and, in particular, to decide whether the Be phenomenon mostly rely on the critical rotation. We show that two-dimensional radiation transfer calculations are needed in rapid rotators to diagnose the stellar rotation more reliably.

Abstract Copyright: © ESO, 2017

Journal keyword(s): stars: emission-line, Be - stars: rotation - stars: rotation

Simbad objects: 4

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Number of rows : 4
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 HD 45910 Be* 06 30 32.9372530321 +05 52 01.205747083 6.64 7.18 6.85 6.31 5.81 B2IIIe 219 0
2 HD 52721 Ae* 07 01 49.50977 -11 18 03.3219 5.88 6.65 6.59 7.52   B2Vne 205 0
3 * mu. Lup Be* 15 18 32.02296 -47 52 30.9957 3.82         B8Ve 95 0
4 2MASS J19120273+4742364 Pu* 19 12 02.7398748040 +47 42 36.408857134           B8.3V 53 0

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2021.12.02-01:07:54

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