Dufton, P. L.; Evans, C. J.; Hunter, I.; Lennon, D. J.; Schneider, F. R. N.
Bibliographical reference
Astronomy and Astrophysics, Volume 626, id.A50, 28 pp.
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6
2019
Journal
Citations
39
Refereed citations
35
Description
Spectroscopy for 247 stars towards the young cluster NGC 346 in the
Small Magellanic Cloud has been combined with that for 116 targets from
the VLT-FLAMES Survey of Massive Stars. Spectral classification yields a
sample of 47 O-type and 287 B-type spectra, while radial-velocity
variations and/or spectral multiplicity have been used to identify 45
candidate single-lined (SB1) systems, 17 double-lined (SB2) systems, and
one triple-lined (SB3) system. Atmospheric parameters (Teff
and log g) and projected rotational velocities (ve sin i)
have been estimated using TLUSTY model atmospheres; independent
estimates of ve sin i were also obtained using a Fourier
Transform method. Luminosities have been inferred from stellar apparent
magnitudes and used in conjunction with the Teff and
ve sin i estimates to constrain stellar masses and ages using
the BONNSAI package. We find that targets towards the inner region of
NGC 346 have higher median masses and projected rotational velocities,
together with smaller median ages than the rest of the sample. There
appears to be a population of very young targets with ages of less than
2 Myr, which have presumably all formed within the cluster. The more
massive targets are found to have lower projected rotational velocities
consistent with previous studies. No significant evidence is found for
differences with metallicity in the stellar rotational velocities of
early-type stars, although the targets in the Small Magellanic Cloud may
rotate faster than those in young Galactic clusters. The rotational
velocity distribution for single non-supergiant B-type stars is inferred
and implies that a significant number have low rotational velocity
(≃10% with ve < 40 km s-1), together with
a peak in the probability distribution at ve≃ 300 km
s-1. Larger projected rotational velocity estimates have been
found for our Be-type sample and imply that most have rotational
velocities between 200-450 km s-1.
Based on observations at the European Southern Observatory in programmes
171.D-0237 and 074D.0011.
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Sergio
Simón Díaz