Engineering topics
Publications and source records attributed to Zinnecker, H..
Based on ROSAT observations and data obtained with ground-based telescopes, we have carried out an extensive study of the low-mass pre-main-sequence population in Upper Scorpius, the youngest subgroup of the Scorpius-Centaurus OB association.
We report the discovery of three proplyd-like structures in the giant HII region NGC 3603.
We present a study of the molecular cloud NGC 281 A and the associated compact and young star cluster NGC 281 (AS 179). Optical photometry leads to a new distance of 3500 pc for the star cluster which is in good agreement with the kinematical distance of the adjacent molecular cloud NGC 281 A. The exciting star HD 5005 of the optical nebulosity is a Trapezium system with O6 III as photometric spectral type for the component HD 5005 AB. For the age of the star cluster we estimated a value of about 3 x 10(exp 6) yr. The (12)CO (2 to 1), (13)CO (2 to 1), and (12)CO (3 to 2) emission shows that the molecular cloud NGC 281 A consists of two cloud fragments. The western fragment is more compact and massive than the eastern fragment and contains an NH3 core. This core is associated with the IRAS source 00494+5617, an H2O maser, and 1.3 millimeter dust continuum radiation. Both cloud fragments contain altogether 22 IRAS point sources which mostly share the properties of young stellar objects. They have luminosities between 150 and 8800 solar luminosity. The maxima of the 60 and 100 micrometers HIRES maps correspond to the maxima of the (12)CO (3 to 2) emission. The NGC 281 A region shares many properties with the Orion Trapezium-BN/KL region the main differences being a larger separation between the cluster centroid and the new site of star formation as well as a lower mass and luminosity of the molecular cloud and the infrared cluster.
We present first results of a series of pointings of the Rosat HRI at visual binaries consisting of a B-star with a later-type companion. The binaries selected for this study are very likely physical pairs. Dating of the B-type stars with respect to the zero-age main sequence, as well as spectroscopic observations of the late-type stars, provides evidence for the extreme youth of these systems with ages typically near or below 10 exp 8 yr. Surprisingly, the late-B component was in many cases detected as an X-ray source, in contrast to previous findings that X-ray emission among late-B field stars is rather uncommon.
Researchers present maps of the CO-12(1=0) line and the 100 micron and 50 micron far-infrared emission of Centaurus A, as well as measurements of the CO-12(2-1), CO-13(1-0), and the C-18O(1-0) lines at selected positions. The observations were taken with the Swedish-ESO Submillimeter Telescope (SEST) and the CPC instrument on board the Infrared Astronomy Satellite (IRAS). The millimeter data show that the bulk molecular material is closely associated with the dust lane and contained in a disk of about 180 seconds diameter and a total molecular mass of about 2 x 10 to the 8th power solar mass. The total molecular mass of the disk and bulge is of the order of 3 x 10 to the 8th power solar mass. The molecular gas in the nucleus is warm with a kinetic temperature of the order of 15 K and a number density of 10 to the 3rd power to 3 x 10 to the 4th power cm(-3). Absorption features in the CO-12 and CO-13 lines against the nuclear continuum emission indicate that the properties of giant molecular clouds are comparable to those of the Galaxy. The far-infrared data show that to a good approximation the dust temperature is constant across the dust lane at a value of about 42 K. The ratio between the far-infrared luminosity and the total molecular mass is 18 solar luminosity/solar mass and close to the mean value obtained for isolated galaxies. A comparison of the CO-12(1-0) and the far-infrared data indicates that a considerable amount of the far-infrared emission is not intimately associated with massive star formation.