EDP Sciences
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Volume 398, Number 1, January IV 2003
Page(s) 229 - 237
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20021601

A&A 398, 229-237 (2003)
DOI: 10.1051/0004-6361:20021601

The IR-colour-mass-loss relation of carbon-rich, dust-driven superwinds and a synthetic ( $\vec J$- $\vec K$, $M_{\bf Bol}$) diagram

K.-P. Schröder1, 2, A. Wachter1, 2 and J. M. Winters3, 4

1  Astronomy Centre, CPES, University of Sussex, Falmer, Brighton BN1 9QJ, UK
2  Zentrum f. Astron. u. Astrophys., Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
3  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
4  LERMA, FRE-K2460, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France

(Received 19 June 2002 / Accepted 4 November 2002)

We derive relations between mass-loss rates and IR-colours ( J- K, H- K, K- L, L- M and K-[12]) for the carbon-rich, dust-driven stellar winds of extreme tip-AGB objects by applying a maximum-likelihood procedure to a representative set of 50 self-consistent, pulsating wind models. The J- K index shows the largest mass-loss related IR excess, which is consistent with observations. All synthetic IR-colours depend, in addition, on the luminosity of the individual model star. Consequently, the superwind mass-loss rates may be determined from observation by $\log{\dot{M}} =
-8.20 + 0.156$ ( J- K) $- 0.463~{M_{\rm Bol}}$, for J- K  $\ga 4$. As a case study for the interpretation of IR photometric data, we quantify the collective and individual tip-AGB mass-loss of the solar neighbourhood stellar population by means of a matching synthetic stellar sample, its IR properties and its present-day mass-loss distribution. The synthetic stars are generated on a grid of evolution tracks with a consistent mass-loss description (see Schröder et al. 1999; Wachter et al. 2002) and an IMF and SFR found in the local stellar population (Schröder & Sedlmayr 2001). The display of the tip-AGB stars in a ( J- K, $M_{\rm Bol}$) diagram could be compared directly with observations once appropriate data become available. On a basis of 1.4 million stars brighter than MV = 4.0, our synthetic present-day sample includes 5067 giant stars with B- V > 1.4, and the collective mass-loss rate is 5.0  $\times$ $10^{-4}~M_{\odot}$ yr -1. There are 20 carbon-rich supergiants with an IR excess of J- K > 4.0 and a mass-loss rate well in excess of $10^{-6}~M_{\odot}$ yr -1, including 10 dust-enshrouded, extreme tip-AGB stars with J- K > 6.0, seen in their short-lived ( $\approx$30 000 yrs) superwind phase with $\dot{M} > 10^{-5}~M_{\odot}$ yr -1. They produce about 50% of the collective mass-loss of the whole sample.

Key words: stars: carbon -- stars: circumstellar matter -- stars: evolution -- stars: late-type -- stars: mass-loss -- infrared: stars

Offprint request: K.-P. Schröder, kps@star.cpes.susx.ac.uk

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