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GEMINI near-infrared spectroscopic observations of young massive stars embedded in molecular clouds
K-band spectra of young stellar candidates in four Southern hemisphereclusters have been obtained with the Gemini Near-Infrared Spectrographin Gemini South. The clusters are associated with IRAS sources that havecolours characteristic of ultracompact HII regions. Spectral types wereobtained by comparison of the observed spectra with those of anear-infrared (NIR) library; the results include the spectralclassification of nine massive stars and seven objects confirmed asbackground late-type stars. Two of the studied sources have K-bandspectra compatible with those characteristic of very hot stars, asinferred from the presence of CIV, NIII and NV emission lines at 2.078,2.116 and 2.100 ?m, respectively. One of them, I16177_IRS1, has aK-band spectrum similar to that of Cyg OB2 7, an O3If* supergiant star.The nebular K-band spectrum of the associated Ultra-Compact (UC) HIIregion shows the s-process [KrIII] and [SeIV] high excitation emissionlines, previously identified only in planetary nebula. One young stellarobject was found in each cluster, associated with either the main IRASsource 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 andpreviously determined JHK magnitudes; they agree well with the valuesobtained from the kinematic method, except in the case of IRAS15408-5356, for which the spectroscopic distance is about a factor of 2smaller than the kinematic value.
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| The VELA star cloud. III - The B8 to A0 stars and interstellar reddening
The present discussion of intermediate band and H-beta observations of360 HD stars B8-A0 in Vela, and all of the CPD stars in a small adjacentregion, notes that the interstellar absorption in both cases can beunderstood as a combination of three absorbing clouds of 1 kpc-A(V) =1.5, 0.5, and 0.17. The major difference in the two environments is thepresence of numerous T Tauri stars in Taurus. Several clusters in theVela region are discussed.
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