Issue |
A&A
Volume 387, Number 2, May IV 2002
|
|
---|---|---|
Page(s) | 624 - 634 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20020354 | |
Published online | 13 May 2002 |
VLT/UVES and WHT/UES absorption spectroscopy of the circumstellar envelope of
IRC + 10° 216 using background stars
First results and a search for DIBs
1
Centro de Astronomia e Astrofísica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
2
Groupe d'Astrophysique, CNRS and Université de Montpellier, Case 072, Place Bataillon, 34095 Montpellier Cedex 05, France e-mail: mauron@graal.univ-montp2.fr
3
School of Chemistry, The University of Nottingham, University Park, Nottingham, NG7 2RD, UK e-mail: June.McCombie@nottingham.ac.uk; Peter.Sarre@nottingham.ac.uk (Based on observations made with the ESO VLT 8 m telescope with UVES (program 66.C-0220), WHT/UES (La Palma) and the 1.2 m telescope of the Haute–Provence Observatory, France. )
Corresponding author: T. R. Kendall, tkendall@oal.ul.pt
Received:
7
January
2002
Accepted:
7
March
2002
A unique and novel set of observations has been undertaken to probe the
circumstellar envelope (CSE) of the nearby (130 pc) carbon star IRC +10° 216
using optical absorption spectroscopy towards background stars
lying beyond the envelope.
The primary aim of the observations is to search for diffuse band (DIB)
carriers in the CSE, for which the mass-losing envelopes of carbon
stars are a likely place of origin. Our principal target is a
star located 37´´ from IRC +10° 216 and was observed with VLT/UVES.
A detailed model atmosphere and abundance analysis shows that it is somewhat
metal-poor and has confirmed that it lies far beyond IRC +10° 216. The
circumstellar H+2H2 column density expected along the line of sight
towards this target is
relatively high, ~ cm-2, and is large compared
to that derived from the small
interstellar extinction estimated in the zone of IRC +10° 216 at
,
mag. The CSE is certainly detected in the
K i resonance lines, which are centred at the heliocentric velocity of
IRC +10° 216 and have
km s-1, consistent with twice the
terminal expansion velocity of the circumstellar gas. The data show also that
circumstellar Na i is very probably detected, as seen
towards two background stars. The strongest DIB (6284 Å) present in the UVES
wavelength coverage is detected but very probably arises in the foreground
ISM. No DIB is detected at 6614 Å, or elsewhere. Overall,
the data suggest that the DIB carriers, if present in the CSE, have a low
abundance relative to H in the C-rich envelope of IRC +10° 216, in comparison
with this ratio in the ISM.
Key words: stars: individual: IRC +10° 216 / stars: carbon / stars: circumstellar matter / ISM: lines and bands / ISM: molecules
© ESO, 2002
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