Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998a%26a...329.1028j&link_type=abstract
Astronomy and Astrophysics, v.329, p.1028-1034 (1998)
Astronomy and Astrophysics
Astrophysics
26
Stars: Circumstellar Matter, Stars: Beta -Pictoris
Scientific paper
GHRS-EchA and G160M spectra of beta -Pictoris have been obtained in the 1400-1600 Angstroms range. A detailed analysis of the CO A-X (0-0, 1-0, 2-0) bands and of the CI lambda 1561 Angstroms multiplet is presented. A column density of the order of 2 10(15) cm(-2) is found for both species. For CO, the rotational temperature is found close to 20 K and the turbulent Doppler width is b=0.8 km.s(-1) . Including the (13) CO lines in the fit allows an estimate of the (13) CO abundance: R=(12) CO/(13) CO=20. This anomalous ratio is tentatively interpreted as being due to chemical fractionation. For the CI triplet, the absorption profile is best fitted by a combination of four velocity components matching those observed independently at the same moment from ground in the CaII H and K lines. The most intense component corresponds to zero relative velocity while the others are shifted by 3 to 10 km s(-1) . The large turbulent width of the components (4.2 km s(-1) ), the statistical population of the ground state fine structure levels and the similar column densities of CI and CO are interpreted as indicating that CI is formed by photodissociation of CO and destroyed by photoionization. The velocity structure would then indicate that part of CI is formed at large distance (S{sc im100 AU) from CO evaporating from cometary bodies while another part originates closer to the star from fast moving cometary bodies with high excentricity. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute which is operated by the Association of Universities for Research in Astronomy Inc., under NASA Contract NAS5-26555.
Feldman Paul D.
Ferlet Roger
Jolly Alison
Lagrange Anne Marie
Lecavelier Alain
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