Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007a%26a...470..239z&link_type=abstract
Astronomy and Astrophysics, Volume 470, Issue 1, 2007, pp.239-247
Astronomy and Astrophysics
Astrophysics
10
Stars: Emission-Line, Be, Stars: Circumstellar Matter, Line:, Formation, Polarization
Scientific paper
Context: A recent analysis of visual Fe ii emission lines of 17 classic Be stars using the self-absorption curve (SAC) method revealed that these lines are optically thick and that they form in circumstellar disc (CD) regions within two stellar radii from the central star on average. Aims: The aim of this paper is to study the physical characteristics of CD regions situated close to the central star. Methods: We used the Fe ii emission line optical depths derived for a sample of the above mentioned classic Be stars that are seen either nearly pole-on or equator-on. The disc properties sought are then inferred by reproducing the average pole-on and equator-on Fe ii line optical depths using simple CD models with different density and temperature distributions. Results: We found that the CD regions near the star, which account for the average Fe ii line opacities obtained with the SAC method, have semi-height scales perpendicular to the equatorial plane h⪆0.5Ro and particle density distribution laws N(R)=N_o(R_o/R)n with n⪉1 at R⪉3Ro (Ro is the stellar radius; No is the particle density at R=R_o). Multi-scattering Monte Carlo simulations show that CD with particle density distributions N˜ R-n, where n depends on the distance R and n˜0.5 near the star, might account for the near-UV spectroplorarimetry of Be stars. CD with enhanced scale heights could explain the [ Hα, E(J-L)] correlation as they may produce about the same Hα line emission, but larger IR flux excesses than thin discs. The enlarged CD scale heights do not contradict the existing interferometric measurements and should enable us to treat more consistently Balmer line emission formation in Be stars.
Arias Maria Laura
Cidale Lydia
Ringuelet Adela E.
Zorec Jean
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