2008A&A...487..645R


Query : 2008A&A...487..645R

2008A&A...487..645R - Astronomy and Astrophysics, volume 487, 645-657 (2008/8-4)

On the reliability of mass-loss-rate estimates for AGB stars.

RAMSTEDT S., SCHOEIER F.L., OLOFSSON H. and LUNDGREN A.A.

Abstract (from CDS):

In the recent literature there has been some doubt as to the reliability of CO multi-transitional line observations as a mass-loss-rate estimator for AGB stars. Using new well-calibrated CO radio line observations, the main aim of the work presented here is to carefully evaluate the reliability of CO mass-loss-rate estimates for intermediate- to high-mass-loss-rate AGB stars with different photospheric chemistries.Mass-loss rates for 10 intermediate- to high-mass-loss-rate AGB stars are derived using a detailed non-LTE, non-local radiative transfer code based on the Monte-Carlo method to model the CO radio line intensities. The circumstellar envelopes are assumed to be spherically symmetric and formed by constant mass-loss rates. The energy balance is solved self-consistently and the effects of dust on the radiation field and thermal balance included. An independent estimate of the mass-loss rate is also obtained from the combination of dust radiative transfer modelling with a dynamical model of the gas and dust particles.We find that the CO radio line intensities and shapes are successfully reproduced for the majority of our objects when assuming a constant mass-loss rate. Moreover, the CO line intensities are only weakly dependent on the adopted micro-turbulent velocity, in contrast to recent claims in the literature. The two methods used in the present work to derive mass-loss rates are consistent within a factor of ∼3 for intermediate- to high-mass-loss-rate objects, indicating that this is a lower limit to the uncertainty in present mass-loss-rate estimates. We find a tentative trend with chemistry. Mass-loss rates from the dust/dynamical model are systematically higher than those from the CO model for the carbon stars and vice versa for the M-type stars. This could be ascribed to a discrepancy in the adopted CO/H2-abundance ratio, but we caution that the sample is small and systematic errors cannot be excluded.

Abstract Copyright:

Journal keyword(s): stars: AGB and post-AGB - stars: carbon - stars: late-type - stars: mass-loss

Simbad objects: 10

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Number of rows : 10
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 IRC +10011 OH* 01 06 25.9879717848 +12 35 52.896392052   20.7   18.26 14.01 M8 413 0
2 LEE 259 C* 03 26 29.5037418864 +47 31 48.551540844       10.70   N 171 0
3 V* IK Tau Mi* 03 53 28.8924743304 +11 24 21.895183368 16.99 17.03 13.39 7.29 3.20 M7-11 613 0
4 V* TX Cam Mi* 05 00 51.1627935408 +56 10 54.041462220       14.02   M9-9.5 343 0
5 V* GX Mon OH* 06 52 47.0423680104 +08 25 19.097958468   15.40 15.46 10.56   M9 115 0
6 IRC +10216 C* 09 47 57.40632 +13 16 43.5648           C9,5e 2262 0
7 V* RW LMi C* 10 16 02.2777043904 +30 34 19.045098516       15.27   C4,3e 387 0
8 IRC -10529 OH* 20 10 27.8731455576 -06 16 13.758742596         15.49 M: 136 0
9 RAFGL 3068 C* 23 19 12.60744 +17 11 33.1332           C 265 0
10 IRC +40540 C* 23 34 27.5185864392 +43 33 01.323347256     15.12     C8,3.5eJ 175 0

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2022.11.28-12:34:43

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