Aims. We report the results of an exploratory program to image the extended circumstellar envelopes of asymptotic giant branch (AGB) stars in dust-scattered galactic light. The goal is to characterize the morphology of the envelopes as a probe of the mass-loss process. Methods. The observations consist of short exposures with the VLT and longer exposures with 1-2 m telescopes, augmented with archival images from the Hubble Space Telescope. Results. We observed 12 AGB stars and detected the circumstellar envelopes in 7. The detected envelopes have mass loss rates > ∼ 5 × 10 −6 M yr −1 , and they can be seen out to distances > ∼ 1 kpc. The observations provide information on the mass loss history on time scales up to ∼10 000 yr. For the five AGB envelopes in which the circumstellar geometry is well determined by scattered light observations, all except one (OH348.2−19.7) show deviations from spherical symmetry. Two (IRC+10216 and IRC+10011) show roughly spherical envelopes at large radii but asymmetry or bipolarity close to the star; one (AFGL 2514) shows an extended, elliptical envelope, and one (AFGL 3068) shows a spiral pattern. The non-spherical structures are all consistent with the effects of binary interactions. Conclusions. Our observations are in accord with a scenario in which binary companions play a role in shaping planetary nebulae, and show that the circumstellar gas is already partly shaped on the AGB, before evolution to the proto-planetary nebula phase.

Mass loss of red supergiants (RSG) is important for the evolution of massive stars, but is not fully explained. Several empirical prescriptions have been proposed, trying to express the mass-loss rate (Ṁ) as a function of fundamental stellar parameters (mass, luminosity, effective temperature). Our goal is to test whether the de Jager et al. (1988, A&AS, 72, 259) prescription, which is used in some stellar evolution models, is still valid in view of more recent mass-loss determinations. By considering 40 Galactic RSGs with an infrared excess and an IRAS 60-μm flux larger than 2 Jy, and assuming a gas-to-dust mass ratio of 200, we find that the de Jager rate agrees within a factor 4 with mostṀ estimates based on the 60-μm signal. It also agrees with six of the only eight Galactic RSGs for whichṀ can be measured more directly through observations of the circumstellar gas. The two objects that do not follow the de Jager prescription (by an order of magnitude) are μ Cep and NML Cyg. We also considered the RSGs of the Magellanic Clouds. Thanks to the results of previous research, we find that the RSGs of the Small Magellanic Cloud have mass-loss rates consistent with the de Jager rate scaled by (Z/Z ) α , where Z is the metallicity and α is 0.7. The situation is less clear for the RSGs of the Large Magellanic Cloud. In particular, for L > 1.6 × 10 5 L , one finds numerous RSGs (except WOH-G64) withṀ significantly smaller than the de Jager rate and indicating thatṀ would no longer increase with L. Before this odd situation is confirmed through further analyses of LMC RSGs, we suggest to keep the de Jager prescription unchanged at solar metallicity in the stellar evolutionary models and to apply a (Z/Z ) 0.7 dependence.

Abstract. We present the first results of a new survey for finding cool N-type carbon (C) stars in the halo of the Galaxy. Candidates were first selected in the 2MASS Second Incremental Release database with JHK s colours typical of red AGB C stars and K s < 13, and subsequently checked through medium resolution slit spectroscopy. We discovered 27 new C stars plus one known previously and two similar objects in the Fornax and Sculptor dwarf galaxies. We determine and discuss the properties of our sample, including optical and near-infrared colours, radial velocities, as well as Hα emission and variability that are frequent, all these characteristics being compatible with an AGB C-type classification. Surprisingly, of the 30 studied objects, 8 were found to have small but measurable proper motions (µ) in the USNO-B1.0 catalogue, ranging over 8 < µ < 21 mas yrand opening the possibility that some objects could perhaps be dwarf carbon stars. Yet, a detailed analysis based on comparison with the sample of known carbon dwarfs leads us to consider these µ as incompatible with the broader picture suggested by the other data taken as a whole. So, we adopt the view that all objects are of AGB type, i.e. luminous and distant. Because the stream of Sagittarius dwarf galaxy is known to be the dominant source of luminous C stars in the halo, we chose to determine distances for our sample by scaling them on the 26 known AGB C stars of the Sgr galaxy itself, which are found to be, in the K s -band, ∼0.5 mag less luminous than the average LMC C stars for a given J − K s colour. The obtained distances of our halo stars range from 8 to 80 kpc from the Sun. Then, examination of position and radial velocities show that about half belong to the Sgr stream. Our findings suggest that numerous AGB C stars remain to be discovered in the halo. Long term K s -band monitoring would be of great value to ascertain distance estimates through the period-luminosity relation, because a large fraction of our sample is probably made of Mira variables.

We report the results of a search for gas phase atomic metals in the circumstellar envelope of the asymptotic giant branch carbon star IRC+10216. The search was made using high resolution (λ/Δλ = 50 000) optical absorption spectroscopy of a background star that probes the envelope on a line of sight 35 from the center. The metal species that we detect in the envelope include Na i, K i, Ca i, Ca ii, Cr i, and Fe i, with upper limits for Al i, Mn i, Ti i, Ti ii, and Sr ii. The observations are used to determine the metal abundances in the gas phase and the condensation onto grains. The metal depletions in the envelope range from a factor of 5 for Na to 300 for Ca, with some similarity to the depletion pattern in interstellar clouds. Our results directly constrain the condensation efficiency of metals in a carbon-rich circumstellar envelope and the mix of solid and gas phase metals returned by the star to the interstellar medium. The abundances of the uncondensed metal atoms that we observe are typically larger than the abundances of the metal-bearing molecules detected in the envelope. The metal atoms are therefore the major metal species in the gas phase and likely play a key role in the metal chemistry.