Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...389..547h&link_type=abstract
Astronomy and Astrophysics, v.389, p.547-555 (2002)
Astronomy and Astrophysics
Astrophysics
31
Stars: Circumstellar Matter, Agb And Post-Agb, Stars: Individual: Hd 161796, Infrared: Ism, Ism: Lines And Bands
Scientific paper
We have modeled the complete optical to millimeter spectrum of the Post-Asymptotic Giant Branch (Post-AGB) star HD 161796 and its circumstellar dust shell. A full 2-200 mu m spectrum taken with the Infrared Space Observatory was used to constrain the dust properties. A good fit is achieved using only 4 dust components: amorphous silicates, the crystalline silicates forsterite and enstatite, and crystalline water ice, contributing respectively about 63, 4, 6 and 27% to the total dust mass. The different dust species were assumed to be co-spatial but distinct, resulting in different temperatures for the different grain populations. We find a temperature for the crystalline H_2O ice of 70 K, which is higher than thermal equilibrium calculations of pure H_2O ice would give. This implies that the ice must be formed as a mantle on top of an (amorphous) silicate core. In order to form H_2O ice mantles the mass loss rate must exceed some 5 *E-5 Msun yr-1. With a water-ice fraction of 27% a lower limit for the gas to dust mass ratio of 270 is found. At a distance of 1.2 kpc (Skinner et al. \cite{skinner_HD161796}) and adopting an outflow velocity of 15 km s-1 (Likkel et al. \cite{likkel_co_pagb}) an AGB mass loss rate of (5.1 x 10-4 Msun yr-1) is found, which lasted 900 years and ended 430 years ago. During this phase a total of 0.46 Msun was expelled. The mass loss rate was high enough to account for the presence of the H_2O ice. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA.
Barlow Michael J.
de Koter Alex
Dominik Carsten
Hoogzaad S. N.
Molster Frank J.
No associations
LandOfFree
The circumstellar dust shell of the post-AGB star HD 161796 does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The circumstellar dust shell of the post-AGB star HD 161796, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The circumstellar dust shell of the post-AGB star HD 161796 will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-958872