Classification of O stars in the yellow-green: The exciting star VES 735

Citation
Cr. Kerton et al., Classification of O stars in the yellow-green: The exciting star VES 735, ASTRONOM J, 117(5), 1999, pp. 2485-2493
Citations number
37
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Space Sciences
Journal title
ASTRONOMICAL JOURNAL
ISSN journal
0004-6256 → ACNP
Volume
117
Issue
5
Year of publication
1999
Pages
2485 - 2493
Database
ISI
SICI code
0004-6256(199905)117:5<2485:COOSIT>2.0.ZU;2-Y
Abstract
Acquiring data for spectral classification of heavily reddened stars using traditional criteria in the blue-violet region of the spectrum can be prohi bitively time consuming using small to medium sized telescopes. One such st ar is the Vatican Observatory emission-line star VES 735, which we have fou nd excites the H II region KR 140. In order to classify VES 735, we have co nstructed an atlas of stellar spectra of O stars in the yellow-green (4800- 5420 Angstrom). We calibrate spectral type versus the line ratio He I lambd a 4922:He II lambda 5411, showing that this ratio should be useful for the classification of heavily reddened O stars associated with H II regions. Application to VES 735 shows that the spectral type is O8.5. The absolute m agnitude suggests luminosity class V. Comparison of the rate of emission of ionizing photons and the bolometric luminosity of VES 735, inferred from r adio and infrared measurements of the KR 140 region, to recent stellar mode ls gives consistent evidence for a main-sequence star of mass 25 M. and age less than a few million years with a covering factor 0.4-0.5 by the nebula r material. Spectra taken in the red (6500-6700 Angstrom) show that the stellar H alpha emission is double-peaked about the systemic velocity and slightly variabl e. H beta is in absorption, so that the emission-line classification is "(e )". However, unlike the case of the more well-known O(e) star zeta Oph, the emission from VES 735 appears to be long-lived rather than episodic.