Millimeter and some near infra-red observations of short-period Miras and other AGB stars

Abstract

Millimeter observations of 48 oxygen- and 20 carbon-rich AGB Miras with periods shorter than 400 days are presented. In addition, observations of 14 O-rich and 15 C-stars with longer, or no known, periods have also been obtained. The detection statistics is as follows: in 12CO and 2-1 we observed 97 stars, and detected 66 in at least one line. We find 24 new detections in the 1-0 line, 38 new detections in the 2-1 line, and 29 stars have been detected for the first time in one or both lines. In 12CO we observed 14 stars and detected 11, with 4 new detections. In 13CO , 3-2 we observed 2 stars and had one new detection. In HCN(1-0) we observed 5 carbon stars and detected 3, one new. In SO() we observed the same 5 stars and detected none. In CS(3-2) we observed 8 carbon stars and detected 3, all new. In SiO(3-2, ) we observed 34 O-rich stars and detected 25, all new except one. Near-infrared JHK photometry is presented for seven stars. For four stars it is the first NIR data published. The luminosity and dust mass loss rate are obtained for seven very red stars with unknown pulsation period from modelling the spectral energy distribution (SED) and IRAS LRS spectra. Thereby, a new IR supergiant is confirmed (AFGL 2968). For the rest of the sample, luminosity and distance are obtained in a variety of ways: using hipparcos parallaxes, period-luminosity and period-MK-relations combined with apparent K magnitudes, and kinematic distances. The dust mass loss rate is obtained from model fitting of the SED (either from the literature, or presented in the present paper), or from the observed IRAS 60 μm flux, corrected for the photospheric contribution. The gas mass loss rate is derived from the observed CO line intensities, as presented here, combined with existing literature data, if any. This allows the derivation of the dust-to-gas ratio. Our and literature CO data has been used to calibrate the relation between mass loss rate and peak intensity of the CO(3-2) line. Diagrams showing mass loss rate, dust-to-gas ratio and expansion velocity versus pulsation period are presented. Our observations confirm the existence of an upper limit for the expansion velocity of C- and O-rich stars, and that this maximum is larger for C-stars, as predicted by the theory of radiation pressure on dust particles.