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An X-ray halo in the ``hot-spot'' galaxy NGC 2903
In this paper we present ROSAT PSPC and HRI observations of the``hot-spot'' galaxy NGC 2903. This isolated system strikingly reveals asoft extended X-ray feature reaching in north-west direction up to aprojected distance of 5.2 kpc from the center into the halo. Theresidual X-ray emission in the disk reveals the same extension as theHα disk. No eastern counterpart of the western X-ray haloemission has been detected. The luminosity of the extraplanar X-ray gasis several 1038 erg s-1, comparable to X-ray halosin other starburst galaxies. It has a plasma temperature of about 0.2keV. The estimated star formation rate derived from X-rays and Hαresults in 1-2 M_sun yr-1. Since galactic superwinds, giantkpc-scale galactic outflows, seem to be a common phenomenon observed ina number of edge-on galaxies, especially in the X-ray regime, and areproduced by excess star-formation activity, the existence of hot halogas as found in NGC 2903 can be attributed to events such as centralstarbursts. That such a starburst has taken place in NGC 2903 must beproven. The detection of hot gas above galaxy disks also withintermediate inclination, however, encounters the difficulty ofdiscriminating between that contribution from disk and active nuclearregion.
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
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| Takýmyýldýz: | Aslan |
| Sað Açýklýk: | 09h30m46.69s |
| Yükselim: | +21°02'14.8" |
| Görünürdeki Parlaklýk: | 8.807 |
| özdevim Sað Açýklýk: | -18.1 |
| özdevim Yükselim: | 34.3 |
| B-T magnitude: | 9.191 |
| V-T magnitude: | 8.839 |
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