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We surveyed 0.5 square degrees in the Bar of the LMC with ISOCAM at 4.5 and 12 μm, and with DENIS in the I, J, and Ks bands. Our goal was to build a complete sample of Thermally-Pulsing AGB stars. Here we present the first analysis of 0.14 square degrees. In total we find about 300 TP-AGB stars. Among these TP-AGB stars, 9% are obscured AGB stars (high mass-loss rates); 9 of them were detected by IRAS, and only 1 was previously identified. Their luminosities range from 2 500 to 14 000 L⊙, with a distribution very similar to the one of optical TP-AGB stars (i.e. those with low mass-loss rates). Such a luminosity distribution, as well as the percentage of obscured stars among TP-AGB stars, is in very good agreement with the evolutionary models of Vassiliadis & Wood (1993) if most of the TP-AGB stars that we find have initial masses smaller than 1.5 to 2 M⊙.

We used ISOCAM and ISOPHOT to observe the spectral energy distribution between 3.6 and 60 μm of AGB stars in the Small Magellanic Cloud detected by IRAS. CAM-CVF spectra are made which enable us to establish the carbon- or oxygen-rich nature of the stars.We are in the process of analysing this data using a radiative transfer model. This will provide us with accurate determinations of luminosity and mass loss rate. Combining the results on the SMC, LMC and Galaxy we hope to address the open question of the metallicity dependencies of the mass loss rate. This in turn is important in the ejection of matter by AGB stars into the interstellar medium.

Almost 5 billion years ago, the Sun formed in a local contraction of a cloud of molecular gas. A rotating disk of gas and dust is believed to have fed material onto the proto-Sun for the first few million years of its life, and to have formed the planets, comets and other Solar System objects. Similar disks, but with less mass, have been observed around a few main-sequence stars such as Vega1. The dust particles orbiting stars like Vega will be removed on timescales of the order of 1 Myr (Vega is about 350 Myr old), and therefore must be resupplied1, at least for a time. But earlier surveys2,3 lacked the sensitivity to determine how many nearby stars have dust disks, and to investigate how long such disks survive. Here we report infrared observations indicating that most stars younger than 300 Myr have dust disks, while most older than 400 Myr do not: ninety per cent of the disks disappear when the star is between 300 and 400 Myr old. Several events that are related to the ‘clean up’ of debris in the early history of our Solar System have a similar timescale.

We present results of a monitoring campaign of the high-mass X-ray binary system 4U 1700-37/HD 153919, carried out with XMM-Newton in February 2001. The system was observed at four orbital phase intervals, covering 37% of one 3.41-day orbit. The lightcurve includes strong flares, commonly observed in this source. We focus on three epochs in which the data are not affected by photon pile up: the eclipse, the eclipse egress and a low-flux interval in the lightcurve around orbital phase phi ~0.25. The high-energy part of the continuum is modelled as a direct plus a scattered component, each represented by a power law with identical photon index (alpha ~1.4), but with different absorption columns. We show that during the low-flux interval the continuum is strongly reduced, probably due to a reduction of the accretion rate onto the compact object. A soft excess is detected in all spectra, consistent with either another continuum component originating in the outskirts of the system or a blend of emission lines. Many fluorescence emission lines from near-neutral species and discrete recombination lines from He- and H-like species are detected during eclipse and egress. The detection of recombination lines during eclipse indicates the presence of an extended ionised region surrounding the compact object. The observed increase in strength of some emission lines corresponding to higher values of the ionisation parameter xi further substantiates this conclusion., Comment: 15 pages, 7 figures, accepted for publication in Astronomy and Astrophysics

The high level of automation in the operation of the ESA Infrared Space Observatory, together with high observing efficiency, leads to a requirement for a commensurate level of automation in the subsequent processing of the astronomical data. This inevitably means that all data for a given instrument mode have the same calibration applied, regardless of the exact details of the object being observed. Questions then arise about these 'pipeline processed' data in terms of the calibration accuracy achieved; how to control the quality of data received by the observer and how much further processing is required - or desirable - by the observer.In this paper we outline the experience of two years of operation of the long wavelength spectrometer on board ISO, detailing the improvements made in the pipeline processing during this time and the difficulties encountered in the automated processing of some instrument modes.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this poster paper we present ISOCAM1 imaging of the well known LBV AG Car and the candidate LBV G79.29+0.46. AG Car has been extensively studied in the ultraviolet, optical and infrared. The optical nebula around this star was first discussed by Thackeray, 1950. Optical imaging is discussed by Paresce and Nota, 1989. The nebula is bipolar with strong emission in the NE and SW, and a size of about 40 by 30”. Far infrared emission has been observed in the nebular ring by McGregor et al., 1988a and McGregor et al., 1988b.

We present the first results of our ISO program on High-Mass X-ray Binaries (HMXBs). Infrared photometry, obtained at different aspect angles of the systems, is used to investigate the massive star’s disrupted stellar wind and the accretion flow towards the compact X-ray source. Scenarios for massive binary evolution predict that HMXBs receive a large kick velocity during the supernova explosion of the compact star’s progenitor. One might, therefore, expect to observe wind bow shocks around these systems such as observed around many OB-runaway stars. Such a wind bow shock has recently been discovered around the system Vela X-1.

The upper part of the HR diagram is populated by massive, luminous stars that show strong stellar winds. These stellar winds have a profound effect on the evolution of the most massive stars, e.g. they lead to the formation of He-rich Wolf-Rayet (WR) stars. It was shown by Humphreys & Davidson (1979) that no red supergiants (RSG) exist with luminosity above Mbol ≈ -9.7, while there are many blue supergiants with luminosities that exceed this limit. This lack of luminous RSG can be explained if very massive stars go through a short-lived phase of extensive post-main-sequence mass loss, during which a significant fraction of the H-rich envelope is removed. The Luminous Blue Variables (LBVs) may represent this short-lived phase of very high mass loss. It has been suggested that a very brief (~ 103 yrs) phase as yellow or red supergiant precedes the LBV phase (Stothers & Chin 1996). For recent reviews see Luminous Blue Variables: massive stars in transition, eds. A. Nota & H.J.G.L.M. Lamers.

To study the final stages of the evolution of stars in the range of 1–8M ⊙ we have started a project on AGB stars in the Small Magellanic Cloud (SMC). Based on the IRAS Faint Source Catalog we have selected 29 objects with IRAS 12 and 25 micron colours indicative of red AGB stars. Ground-based near-infrared (NIR) JHK images were obtained of these fields. With ISO1 (CAM and PHT) a follow-up study is being made to get the spectral energy distribution (SED) between 3.6 and 60 microns of the AGB stars detected by IRAS. We are analysing the SEDs using a radiative transfer model which provides accurate determinations of the luminosities and mass loss rates of the objects. Combining the data on the SMC, LMC and existing data on the Galaxy will answer the open question of the metallicity dependence of mass loss in late-type stars. This in turn is important in the ejection of matter by AGB stars to the interstellar medium over the age of the Galaxy.

The status of calibration and performance of the ISO Long-Wavelength Spectrometer eleven months after launch is described. The strategy followed for the calibration observations and first results are summarized. The overall performance of the instrument essentially fulfills the expectations; certain changes in sensitivity of the detectors are reported. Some improvements in the way observations are executed, which resulted from the in-flight experience, are explained.

We discuss the infrared spectral energy distribution of Be stars, focusing on new results obtained with the Infrared Space Observatory. The 60-160 μm flux of some Be stars is higher than expected, which may be due to cold dust or an outer disk component with enhanced densities. The infrared spectrum of Be stars is dominated by numerous HI recombination lines, whose line strengths show a complex behaviour. The electron temperature in the disk of ϒ Cas was found to be about 9500 K, and evidence for an elevated temperature near the upper part of the disk is presented. Be stars may be recognized from their infrared spectrum on the basis of HI line flux ratios.