| Autor: |
Zorec, J., Frémat, Y., de Souza, A. Domiciano, Royer, F., Cidale, L., Hubert, A.-M., Semaan, T., Martayan, C., Cochetti, Y. R., Arias, M. L., Aidelman, Y., Stee, P. |
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| Zdroj: |
Astronomy & Astrophysics / Astronomie et Astrophysique; Jun2017, Vol. 602, p1-21, 21p |
| Abstrakt: |
Aims. We assume that stars may undergo surface differential rotation to study its impact on the interpretation of Vsin i 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 Vsin i concerning the actual stellar rotation. Methods. We studied the line broadening produced by several differential rotational laws, but adopted Maunder's expression (θ) = 0(1 + α cos² θ) 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 Φ on the measured Vsin i parameter and on the distribution Φ(u) of ratios u = V=Vc. Results. We conclude that the inferred Vsin i 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 Vsin i 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 Vsin i 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 FROM AUTHOR] |
| Databáze: |
Complementary Index |
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