The envelope of IRC +10216 reflecting the galactic light

Free access article

Issue		A&A Volume 401, Number 3, April III 2003


Page(s)		985 - 996
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20030127

A&A 401, 985-996 (2003)
DOI: 10.1051/0004-6361:20030127

UBV surface brightness photometry and interpretation

N. Mauron¹, P. de Laverny² and B. Lopez²

¹ Groupe d'Astrophysique, UMR 5024 CNRS, Case CC72, Place Bataillon, 34095 Montpellier, France
e-mail: mauron@graal.univ-montp2.fr
² Observatoire de la Côte d'Azur, Département Fresnel, UMR 6528 CNRS, BP 4229, 06304 Nice, France
e-mail: laverny@obs-nice.fr; lopez@obs-nice.fr

(Received 8 July 2002 / Accepted 27 December 2002 )

Abstract
We present and analyse new optical images of the dust envelope surrounding the high mass-loss carbon star IRC +10216. This envelope is seen due to external illumination by galactic light. Intensity profiles and colors of the nebula were obtained in the UBV bandpasses. The data are compared with the results of a radiative transfer model calculating multiple scattering of interstellar field photons by dust grains with a single radius. The data show that the observed radial shape of the nebula, especially its half maximum radius, does not depend on wavelength (within experimental errors), suggesting that grains scatter in the grey regime, and this is further supported by the plateau colors being close to those of the ISRF as given by Mattila (1980a). A grain radius of 0.16 $\mu$ m with envelope parameters as proposed by Groenewegen (1997) can reproduce this achromatism of shape and color characteristics. However, there remain substantial discrepancies between model and observations concerning the absolute intensity of the nebula and its radial shape. Some of these discrepancies disappear if one adopts a small grain size (~0.05 $\mu$ m), or if one assumes a lower dust mass loss rate for the outer layers ( $\theta \ge 20$ '', corresponding to 1000 years ago). Within the framework of our simple model, we cannot determine a "dominant" grain size. Future more sophisticated models will have to take into account grain size distribution, and also explore complicated issues like the effects of grain porosity and/or asphericity on scattering, the influence of the envelope small-scale structure on the radiative transfer, and the possibility of a field anisotropy. For the same reasons, it is not presently feasible to establish with confidence whether the interstellar radiation field in the visible is significantly different in strength at the location of IRC +10216 compared to the usually adopted one in the solar neighbourhood.

Key words: stars: AGB and post-AGB -- stars: circumstellar matter -- ISM: dust, extinction

Offprint request: N. Mauron, nicolas.mauron@graal.univ-montp2.fr

SIMBAD Objects

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.