Revealing the Nature of the Obscured High Mass X-ray Binary IGR J16318-4848

The X-ray source IGR J16318-4848 was the first source discovered by INTEGRAL on January 29, 2003. The high energy spectrum exhibits such a high column density that the source is undetectable in X-rays below 2 keV. On February 23–25, 2003 we triggered a Target of Opportunity (ToO) Program using the EMMI and SOFI instruments on the New Technology Telescope of the European Southern Observatory (La Silla) to get optical and near-infrared (NIR) observations. We discovered the optical counterpart, and confirmed the already proposed candidate in the NIR. NIR spectroscopy revealed a large amount of emission lines, including forbidden iron lines and P-Cygni profiles, showing a strong similarity with CI Cam, another strongly absorbed source. Together with the spectral energy distribution (SED), these data point to a high luminosity, high temperature source, with an intrinsic absorption greater than the interstellar absorption, but two orders of magnitude below the X-ray absorption. All these observations show that IGR J16318-4848 is a high mass X-ray binary (HMXB) at a distance between 0.9 and 6.2 kpc, the mass donor being an early-type star, probably a sgB[e] star, surrounded by a dense and absorbing circumstellar material. This would make the second HMXB with a sgB[e] star as the mass donor after CI Cam. Other sources, discovered by INTEGRAL near IGR J16318-4848 in the direction of the Norma arm, present the same characteristics, at least in X-rays. Such sources may represent a different evolutionary state of X-ray binaries previously undetected with the lower energy space telescopes; if it is so, a new class of strongly absorbed X-ray binaries is being unveiled by INTEGRAL. Out of the 15 sources present in this region, only one might be associated with an unidentified EGRET source: IGR J16393-4643. Therefore these obscured INTEGRAL sources do not seem to be powerful high energy (E > 100 MeV) emitters. Based on observations collected at the European Southern Observatory, Chile (proposal ESO N^∘ 70.D-0340).     

The stellar composition of the star formation region CMa R1 – II. Spectroscopic and photometric observations of nine young stars

We present new high- and low-resolution spectroscopic and photometric data of nine members of the young association CMa R1. All the stars have circumstellar dust at some distance, as could be expected from their association with reflection nebulosity. Four stars (HD 52721, HD 53367, LkH α  220 and LkH α  218) show H α emission and we argue that they are Herbig Be stars with discs. Our photometric and spectroscopic observations of these stars reveal new characteristics of their variability. We present first interpretations of the variability of HD 52721, HD 53367 and the two LkH α stars in terms of a partially eclipsing binary, a magnetic activity cycle and circumstellar dust variations, respectively. The remaining five stars show no clear indications of H α emission in their spectra, although their spectral types and ages are comparable with those of HD 52721 and HD 53367. This indicates that the presence of a disc around a star in CMa R1 may depend on the environment of the star. In particular we find that all H α emission stars are located at or outside the arc-shaped border of the H  ii region, which suggests that the stars inside the arc have lost their discs through evaporation by UV photons from nearby O stars, or from the nearby (<25 pc) supernova, about 1 Myr ago.     

Properties of circumstellar silicate dust (Review)

Es wird eine Übersicht über den gegenwärtigen Stand des Wissens über die Eigenschaften des zirkumstellaren Silikatstaubes gegeben. Nach der Darstellung der Entdeckungsgeschichte werden die Objekte zusammengestellt, in deren Spektren Silikatbanden beobachtet werden. Der Zusam-menhang zwischen den optischen Eigenschaften der Silikatteilchen und der Struktur der zirkumstellaren Hüllen bei der Bestimmung der ausgesandten Infrarotstrahlung wird analysiert, und alle wichtigeren Untersuchungen von Staubhüllen mit Silikatteilchen werden zusammengetragen. Wir diskutieren die optischen Eigenschaften des zirkumstellaren Silikatstaubes, wobei die amorphe Struktur besonders betont wird. Abschließend wird auf die Bedeutung von Feinstrukturen innerhalb der 10-μm-Bande, die bei verschiedenen Objekten beobachtet wurden, eingegangen.