CO line emission as a measure of mass loss in AGB-stars
Coordinator: F.L. Schoier , M. Lindqvist , H. Olofsson
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The large majority of stars that have left the main sequence willexperience their finalevolutionary stage on the asymptotic giant branch (AGB) as cool,luminous, and pulsa-tionally unstable red giants. They gradually develop an intense stellarwind that carriesthe results of internal nuclear processes, and hence these starscontribute to the chemicalevolution of galaxies (Forestini & Charbonnel 1997, A&AS 123,241; Schroeder & Sedlmayr 2001, A&A 366, 913). Moreover, themass loss has a profound effect on the futureevolution of the star (Bloecker 1995, A&A 297, 727; Habing 1996,A&AR 7, 97; Schroederet al. 1999, A&A 349, 898). A detailed understanding of thecircumstellar properties ofthese stars is crucial in the study of stellar evolution and galacticchemical evolution.We have undertaken systematic surveys and subsequent modelling of COline emission ofcircumstellar envelopes (CSEs) of both M-type (O-rich) AGB stars(Olofsson et al. 2002,A&A 391, 1053; Gonzalez Delgado et al. 2003, A&A 411, 123) andcarbon stars (Schoier & Olofsson 2001, A&A 368, 969) with greatsuccess. The properties of the circumstellarshells are determined from the CO data based on a detailed non-LTEradiative transfermodelling which self-consistently calculates also the kinetictemperature of the gas. Wefind that models and observations typically agree to within 20%, avalue often stated asthe absolute calibration uncertainty of millimetre line observations.
We have selected a sample of 9 AGB-stars (see Table 1) to be used in the APEX scienceverification. The sample consists of both well studied objects such as IRAS 151945115and IRC10529 and other, less studied, interesting objects such as EP Aqr which has acomplicated mass loss history. The predicted intensities for the CO J = 3 2 line arepresented in Table 1 and based on our own previous observations at several telescopes(OSO 20m, SEST, NRAO 12m, IRAM 30m, JCMT) and a circumstellar model. Sincethe main-beam efficiency of the APEX telescope is not known at present, we present theintensity estimates in the main-beam brightness scale.
The line intensities are typically around 1 K and we aim at a S/N-ratio of 10 and a spectralresolution of 1 km s-1 . The lines are typically around 20-40 km s-1 broad (2 × Vexp ).Theobservations are preferably carried out in a dual-beamswitch mode.
|Source||RA||DEC||V (LSR)||Vexp||Tmb||Tmb dV|
|(J2000)||(J2000)||(km s-1 )||(km s-1 )||(K)||(K km s-1 )|
|R Hya||13:29 42.80||-23:16:52.8||-10.0||8.0||1.8||24.4|
|EP Aqr(broad)||21:46 31.80||-02:12:45.9||-34.0||9.0||1.5||25.7|
|EP Aqr(narrow)||21:46 31.80||-02:12:45.9||-34.0||1.0||7.3||14.3|