APEX SV projects

CO line emission as a measure of mass loss in AGB-stars

Coordinator: F.L. Schoier , M. Lindqvist , H. Olofsson

Data:
Program is available and data products can be downloaded

Scientific justification:

The large majority of stars that have left the main sequence will experience their final evolutionary stage on the asymptotic giant branch (AGB) as cool, luminous, and pulsa- tionally unstable red giants. They gradually develop an intense stellar wind that carries the results of internal nuclear processes, and hence these stars contribute to the chemical evolution of galaxies (Forestini & Charbonnel 1997, A&AS 123, 241; Schroeder & Sedlmayr 2001, A&A 366, 913). Moreover, the mass loss has a profound effect on the future evolution of the star (Bloecker 1995, A&A 297, 727; Habing 1996, A&AR 7, 97; Schroeder et al. 1999, A&A 349, 898). A detailed understanding of the circumstellar properties of these stars is crucial in the study of stellar evolution and galactic chemical evolution. We have undertaken systematic surveys and subsequent modelling of CO line emission of circumstellar 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) and carbon stars (Schoier & Olofsson 2001, A&A 368, 969) with great success. The properties of the circumstellar shells are determined from the CO data based on a detailed non-LTE radiative transfer modelling which self-consistently calculates also the kinetic temperature of the gas. We find that models and observations typically agree to within 20%, a value often stated as the absolute calibration uncertainty of millimetre line observations.

Proposed Observations
We have selected a sample of 9 AGB-stars (see Table 1) to be used in the APEX science verification. The sample consists of both well studied objects such as IRAS 151945115 and IRC10529 and other, less studied, interesting objects such as EP Aqr which has a complicated mass loss history. The predicted intensities for the CO J = 3 2 line are presented 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. Since the main-beam efficiency of the APEX telescope is not known at present, we present the intensity 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 spectral resolution of 1 km s-1 . The lines are typically around 20-40 km s-1 broad (2 × Vexp ).The observations are preferably carried out in a dual-beamswitch mode.

*Source list*
Source	RA	DEC	V (LSR)	Vexp	Tmb	Tmb dV
	(J2000)	(J2000)	(km s-1 )	(km s-1 )	(K)	(K km s-1 )
Carbon stars
IRAS 15194-5115	15:23:05.00	-51:25:58.0	-15.0	21.5	3.9	127.0
U Hya	10:37:33.27	-13:23:04.4	-31.5	7.0	1.5	14.6
W CMa	07:08:03.44	-11:55:23.8	1.0	10.5	0.26	4.3
Y Hya	09:51:03.72	-23:01:02.3	-7.0	9.0	0.4	6.0
X Vel	09:55:26.11	-41:35:12.8	-17.0	10.0	0.3	4.8
M-stars
IRC-30398	18:59 14.10	-29:50:22.0	-6.0	19.5	1.7	47.8
IRC-10529	20:10 27.50	-06:16:16.0	-18.0	16.0	1.5	31.6
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