Bibcode
Doran, E. I.; Crowther, P. A.; de Koter, A.; Evans, C. J.; McEvoy, C.; Walborn, N. R.; Bastian, N.; Bestenlehner, J. M.; Gräfener, G.; Herrero, A.; Köhler, K.; Maíz Apellániz, J.; Najarro, F.; Puls, J.; Sana, H.; Schneider, F. R. N.; Taylor, W. D.; van Loon, J. Th.; Vink, J. S.
Bibliographical reference
Astronomy and Astrophysics, Volume 558, id.A134, 30 pp.
Advertised on:
10
2013
Journal
Citations
125
Refereed citations
114
Description
Context. The VLT-FLAMES Tarantula Survey has an extensive view of the
copious number of massive stars in the 30 Doradus (30 Dor) star forming
region of the Large Magellanic Cloud. These stars play a crucial role in
our understanding of the stellar feedback in more distant, unresolved
star forming regions. Aims: The first comprehensive census of hot
luminous stars in 30 Dor is compiled within a 10 arcmin (150 pc) radius
of its central cluster, R136. We investigate the stellar content and
spectroscopic completeness of the early type stars. Estimates were made
for both the integrated ionising luminosity and stellar wind luminosity.
These values were used to re-assess the star formation rate (SFR) of the
region and determine the ionising photon escape fraction.
Methods: Stars were selected photometrically and combined with the
latest spectral classifications. Spectral types were estimated for stars
lacking spectroscopy and corrections were made for binary systems, where
possible. Stellar calibrations were applied to obtain their physical
parameters and wind properties. Their integrated properties were then
compared to global observations from ultraviolet (UV) to far-infrared
(FIR) imaging as well as the population synthesis code, Starburst99. Results: Our census identified 1145 candidate hot luminous stars
within 150 pc of R136 of which >700 were considered to be genuine
early type stars and contribute to feedback. We assess the survey to be
spectroscopically complete to 85% in the outer regions (>5 pc) but
only 35% complete in the region of the R136 cluster, giving a total of
500 hot luminous stars in the census which had spectroscopy. Only 31
were found to be Wolf-Rayet (W-R) or Of/WN stars, but their contribution
to the integrated ionising luminosity and wind luminosity was 40% and
50%, respectively. Similarly, stars with Minit > 100
M⊙ (mostly H-rich WN stars) also showed high
contributions to the global feedback, 25% in both cases. Such massive
stars are not accounted for by the current Starburst99 code, which was
found to underestimate the integrated ionising luminosity of R136 by a
factor 2 and the wind luminosity by a factor 9. The census inferred
a SFR for 30 Dor of 0.073 ± 0.04 M⊙
yr-1. This was generally higher than that obtained from some
popular SFR calibrations but still showed good consistency with the
far-UV luminosity tracer as well as the combined Hα and
mid-infrared tracer, but only after correcting for Hα extinction.
The global ionising output was also found to exceed that measured from
the associated gas and dust, suggesting that
{˜6+55-6}% of the ionising photons escape
the region. Conclusions: When studying the most luminous star
forming regions, it is essential to include their most massive stars if
one is to determine a reliable energy budget. Photon leakage becomes
more likely after including their large contributions to the ionising
output. If 30 Dor is typical of other massive star forming regions,
estimates of the SFR will be underpredicted if this escape fraction is
not accounted for.
Based on observations collected at the European Southern Observatory
under programme ID 182.D-0222.Appendices are available in electronic
form at http://www.aanda.orgFull
Tables D1 and D2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/558/A134
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Sergio
Simón Díaz