A FOURIER TRANSFORM METHOD for V sin i ESTIMATIONS UNDER NONLINEAR LIMB-DARKENING LAWS

A FOURIER TRANSFORM METHOD for V sin i ESTIMATIONS UNDER NONLINEAR LIMB-DARKENING LAWS

Author Levenhagen, Ronaldo Savarino Autor UNIFESP Google Scholar
Institution Universidade Federal de São Paulo (UNIFESP)
Abstract Star rotation offers us a large horizon for the study of many important physical issues pertaining to stellar evolution. Currently, four methods are widely used to infer rotation velocities, namely those related to line width calibrations, on the fitting of synthetic spectra, interferometry, and on Fourier transforms (FTs) of line profiles. Almost all of the estimations of stellar projected rotation velocities using the Fourier method in the literature have been addressed with the use of linear limb-darkening (LD) approximations during the evaluation of rotation profiles and their cosine FTs, which in certain cases, lead to discrepant velocity estimates. in this work, we introduce new mathematical expressions of rotation profiles and their Fourier cosine transforms assuming three nonlinear LD laws-quadratic, square-root, and logarithmic-and study their applications with and without gravity-darkening (GD) and geometrical flattening (GF) effects. Through an analysis of He I models in the visible range accounting for both limb and GD, we find out that, for classical models without rotationally driven effects, all the V sin i values are too close to each other. On the other hand, taking into account GD and GF, the V sin i obtained with the linear law result in V sin i values that are systematically smaller than those obtained with the other laws. As a rule of thumb, we apply these expressions to the FT method to evaluate the projected rotation velocity of the emission B-type star Achernar (alpha Eri).
Keywords methods: observational
stars: activity
stars: atmospheres
stars: emission-line, Be
stars: fundamental parameters
stars: individual (Achernar)
stars: rotation
Language English
Sponsor Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Grant number CNPq: 307660/2011-7
CNPq: 307095/2008-8
FAPESP: 04/14256-8
FAPESP: 00/10029-6
FAPESP: 1998/10138-8
Date 2014-12-10
Published in Astrophysical Journal. Bristol: Iop Publishing Ltd, v. 797, n. 1, 10 p., 2014.
ISSN 0004-637X (Sherpa/Romeo, impact factor)
Publisher Iop Publishing Ltd
Extent 10
Origin http://dx.doi.org/10.1088/0004-637X/797/1/29
Access rights Open access Open Access
Type Article
Web of Science ID WOS:000345915000029
URI http://repositorio.unifesp.br/handle/11600/38550

Show full item record




File

Name: WOS000345915000029.pdf
Size: 655.3Kb
Format: PDF
Description:
Open file

This item appears in the following Collection(s)

Search


Browse

Statistics

My Account