1996A&A...309..155S -
Astronomy and Astrophysics, volume 309, 155-162 (1996/5-1)
Infall in Herbig Ae/Be stars: what Na D lines tell us.
SORELLI C., GRININ V.P. and NATTA A.
Abstract (from CDS):
This paper discusses the origin of the redshifted absorption components observed in the Na D lines of some Herbig Ae/Be stars. We have computed non-LTE models of the thermal and ionization structure of gas clouds of different density, column density and chemical composition, from the solar one to that typical of CI-chondrites. The redshifted absorption lines can only form in small, dense, infalling gas clumps at distances ≲10R* from the star. If the gas has solar chemical composition, then the clump size must be L∼1011cm (about R*) and the density nH>3x1012cm–3. These conditions can be produced at the base of a column of gas falling into the star from a circumstellar accretion disk along magnetic lines. In this case, an accretion rate {dot}(M)acc>3x10–7M☉ yr–1 and a stellar magnetic field of about 600 Gauss are required. As the gas metallicity increases, less dense clouds are required to fit the Na D observations. In the extreme case of a gas cloud resulting from the evaporation of CI-chondrite meteorites, it is nH> 5x108 cm–3, L∼1011 cm. The mass of the cloud is therefore of the order of 1020gr, and the parental body must have a radius of 20km at least. These results show that both scenarios, i.e, magnetospheric accretion and evaporation of star-grazing planetesimal bodies, are in principle possible.
Abstract Copyright:
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Journal keyword(s):
Herbig Ae/Be stars - circumstellar matter - stars: pre-main sequence - stars: formation
Simbad objects:
6
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