The IR-colour–mass-loss relation of carbon-rich, dust-driven superwinds and a synthetic (–, ) diagram

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

Corresponding author: K.-P. Schröder, kps@star.cpes.susx.ac.uk

Received: 19 June 2002
Accepted: 4 November 2002

Abstract

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 (J–K) , for J–K . 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. [CITE]; Wachter et al. [CITE]) and an IMF and SFR found in the local stellar population (Schröder & Sedlmayr [CITE]). The display of the tip-AGB stars in a (J–K, M_Bol) diagram could be compared directly with observations once appropriate data become available. On a basis of 1.4 million stars brighter than M_V = 4.0, our synthetic present-day sample includes 5067 giant stars with B–V , and the collective mass-loss rate is 5.0   yr^-1. There are 20 carbon-rich supergiants with an IR excess of J–K and a mass-loss rate well in excess of  yr^-1, including 10 dust-enshrouded, extreme tip-AGB stars with J–K , seen in their short-lived (≈30 000 yrs) superwind phase with  yr^-1. They produce about 50% of the collective mass-loss of the whole sample.