Issue |
A&A
Volume 377, Number 1, October I 2001
|
|
---|---|---|
Page(s) | 90 - 103 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20010858 | |
Published online | 15 October 2001 |
The icy side of Frosty Leo
1
Observatoire de la Côte d'Azur, Département Fresnel UMR 6528, BP 4229, 06034 Nice Cedex 4, France
2
School of Physics, University of Sydney, NSW 2006, Australia
3
NASA Goddard Space Flight Center, Infrared Astrophysics, Code 685, Greenbelt, HD 20771, USA
4
Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA 94720-7450, USA
5
Smithsonian Astrophysical Observatory, MS42, 60 Garden Street, Cambridge, MA 02138, USA
Corresponding author: B. Lopez, lopez@obs-nice.fr
Received:
31
July
2000
Accepted:
12
June
2001
An imaging study of the bipolar nebula Frosty Leo
is presented.
In particular, we have studied the effects of spatial distribution of H2O
ice on the circumstellar environment.
Using the Keck telescope with the NIRC infrared camera, we have recovered
images at a wavelength of 3.08μm within the prominent (attenuation of
about 5 mag) water-ice absorption band, and in the adjacent quasi-continuum
at 1.6μm, 2.2μm, and 3.3μm.
While the well-known bipolar structure appears quite symmetrical in all quasi-continuum
images, the Northern lobe seems to be almost totally extinguished
(by a factor of 10) compared to the Southern one in images at 3.08μm.
This suggests a much greater concentration of ice between the observer and
the Northern lobe.
The question of the physical structure of the nebula has been addressed
with the use of numerical radiative transfer simulations which have been
able to reproduce the general behavior of the images and of earlier spectral data.
From this, we deduce and/or confirm
several parameters of interest: the typical dust grain size,
the dust density distribution in the envelope, and the abundance of water ice.
Models were produced with physically symmetrical lobes in which some one-sided
extinction was produced by an effect related to
the observer's viewing angle.
However, in order to reproduce the extreme extinction observed, more complicated
scenarios, involving asymmetry with respect to the plane of the disk, were
needed.
Additional imaging observations were conducted at 2.26μm (where the
system is bright) with the intent to recover high-angular-resolution information.
Data sets consisted of one hundred of rapid-exposure data frames from which
images were recovered using a shift-and-add algorithm.
Although these images did contain structures at the diffraction limit
of the telescope (~50 milliarcsec), no evidence for binarity
as reported by Roddier et al. ([CITE]) from adaptive optical studies was found
within the dynamical range obtained.
Key words: radiative transfer / methods: numerical / methods: observational / techniques: interferometric / stars: mass loss / stars: AGB and post-AGB
© ESO, 2001
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