Abstract. We present a study of known OH/IR stars in the inner bulge, observed by the ISOGAL survey at λ = 6.8 µm and λ = 14.9 µm. Bolometric corrections and luminosities are computed, based on near and mid-infrared data. The vast majority of the sources exhibit mass-loss rates in the range: 3 × 10 −7 up to a few times 10 −5 M /year. The bolometric magnitude distribution peaks at M bol = −5.0. There is no clear evidence that the luminosity is related to the expansion velocity of the envelope for the sample in the bulge observed by ISOGAL. We find that the bulge OH/IR stars do not follow a period-luminosity (PL) law and that they are systematically less luminous than the OH/IR extension of the PL relationship for Miras.

Abstract.We investigate the evolution of oxygen-and carbon-rich AGB stars, post-AGB objects, and planetary nebulae using data collected mainly from the MSX catalogue. Magnitudes and colour indices are compared with those calculated from a grid of synthetic spectra that describe the post-AGB evolution beginning at the onset of the superwind. We find that carbon stars and OH/IR objects form two distinct sequences in the (K− [

Abstract. The ISOGAL project is an infrared survey of specific regions sampling the Galactic Plane selected to provide information on Galactic structure, stellar populations, stellar mass-loss and the recent star formation history of the inner disk and Bulge of the Galaxy. ISOGAL combines 7 and 15 µm ISOCAM observations -with a resolution of 6 at worst -with DENIS IJK s data to determine the nature of the sources and the interstellar extinction. We have observed about 16 square degrees with a sensitivity approaching 10-20 mJy, detecting ∼10 5 sources, mostly AGB stars, red giants and young stars. The main features of the ISOGAL survey and the observations are summarized in this paper, together with a brief discussion of data processing and quality. The primary ISOGAL products are described briefly (a full desciption is given in Schuller et al. 2003): viz. the images and the ISOGAL-DENIS five-wavelength point source catalogue. The main scientific results already derived or in progress are summarized. These include astrometrically calibrated 7 and 15 µm images, determining structures of resolved sources; identification and properties of interstellar dark clouds; quantification of the infrared extinction law and source dereddening; analysis of red giant and (especially) AGB stellar populations in the central Bulge, determining luminosity, presence of circumstellar dust and mass-loss rate, and source classification, supplemented in some cases by ISO/CVF spectroscopy; detection of young stellar objects of diverse types, especially in the inner Bulge with information about the present and recent star formation rate; identification of foreground sources with mid-IR excess. These results are the subject of about 25 refereed papers published or in preparation.

K-band spectra of young stellar candidates in four Southern hemisphere clusters have been obtained with the Gemini Near-Infrared Spectrograph in Gemini South. The clusters are associated with IRAS sources that have colours characteristic of ultracompact H II regions. Spectral types were obtained by comparison of the observed spectra with those of a nearinfrared (NIR) library; the results include the spectral classification of nine massive stars and seven objects confirmed as background late-type stars. Two of the studied sources have K-band spectra compatible with those characteristic of very hot stars, as inferred from the presence of C IV, N III and N V emission lines at 2.078, 2.116 and 2.100 μm, respectively. One of them, I16177 IRS1, has a K-band spectrum similar to that of Cyg OB2 7, an O3If * supergiant star. The nebular K-band spectrum of the associated Ultra-Compact (UC) H II region shows the s-process [Kr III] and [Se IV] high excitation emission lines, previously identified only in planetary nebula. One young stellar object was found in each cluster, associated with either the main IRAS source or a nearby resolved Midecourse Space eXperiment (MSX) component, confirming the results obtained from previous NIR photometric surveys. The distances to the stars were derived from their spectral types and previously determined JHK magnitudes; they agree well with the values obtained from the kinematic method, except in the case of IRAS 15408−5356, for which the spectroscopic distance is about a factor of 2 smaller than the kinematic value.

Although the majority of known binary Asymptotic Giant Branch (AGB) stars are symbiotic systems (i.e. with a WD as a secondary star), main-sequence companions of AGB stars can be more numerous, even though they are more difficult to find because the primary high luminosity hampers the detection of the companion at visual wavelengths. However, in the ultraviolet the flux emitted by a secondary with T eff > 5500 ∼ 6000 K may prevail over that of the primary, and then it can be used to search for candidates to binary AGB stars. In this work, theoretical atmosphere models are used to calculate the UV excess in the GALEX near-and far-UV bands due to a main-sequence companion. After analysing a sample of confirmed binary AGB stars, we propose as a criterium for binarity: (1) the detection of the AGB star in the GALEX far-UV band and/or (2) a GALEX near-UV observed-to-predicted flux ratio > 20. These criteria have been applied to a volume-limited sample of AGB stars within 500 pc of the Sun; 34 out of the sample of 58 AGB stars (∼60%) fulfill them, implying to have a MS companion of spectral type earlier than K0. The excess in the GALEX near-and far-UV bands cannot be attributed to a single temperature companion star, thus suggesting that the UV emission of the secondary might be absorbed by the extended atmosphere and circumstellar envelope of the primary or that UV emission is produced in accretion flows.