Bibcode
Walborn, N. R.; Sana, H.; Simón-Díaz, S.; Maíz Apellániz, J.; Taylor, W. D.; Evans, C. J.; Markova, N.; Lennon, D. J.; de Koter, A.
Bibliographical reference
Astronomy and Astrophysics, Volume 564, id.A40, 35 pp.
Advertised on:
4
2014
Journal
Citations
95
Refereed citations
87
Description
Detailed spectral classifications are presented for 352 O-B0 stars in
the VLT-FLAMES Tarantula Survey ESO Large Programme, of which 213 O-type
are judged of sufficiently high quality for further morphological
analysis. Among them, six subcategories of special interest are
distinguished. (1) Several new examples of the earliest spectral types
O2-O3 have been found, while a previously known example has been
determined to belong to the nitrogen-rich ON2 class. (2) A group of
extremely rapidly rotating main-sequence objects has been isolated,
including the largest vsini values known, the spatial and
radial-velocity distributions of which suggest ejection from the two
principal ionizing clusters NGC 2070 and NGC 2060. (3) Several new
examples of the evolved, rapidly rotating Onfp class show similar
evidence, although at least some of them are spectroscopic binaries. (4)
No fewer than 48 members of the Vz category, hypothesized to be on or
near the zero-age main sequence, are found in this sample; in contrast
to the rapid rotators, they are strongly concentrated to the ionizing
clusters and a newly recognized region of current and recent star
formation to the north, supporting their interpretation as very young
objects, as do their relatively faint absolute magnitudes. (5) A
surprisingly large fraction of the main-sequence spectra belong to the
recently recognized V((fc)) class, with C iii emission lines of similar
strength to the usual N iii in V((f)) spectra, although a comparable
number of the latter are also present, as well as six objects with very
high-quality data but no trace of either emission feature, presenting
new challenges to physical interpretations. (6) Two mid-O Vz and three
late-O giant/supergiant spectra with morphologically enhanced nitrogen
lines have been detected. Absolute visual magnitudes have been derived
for each star with individual extinction laws, and composite
Hertzsprung-Russell diagrams provide evidence of the multiple
generations present in this field. Spectroscopic binaries, resolved
visual multiples, and possible associations with X-ray sources are
noted. Astrophysical and dynamical analyses of this unique dataset
underway will provide new insights into the evolution of massive stars
and starburst clusters.
Appendix A and Table 2 are available in electronic form at http://www.aanda.org
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Sergio
Simón Díaz