Studies of massive stars in the Magellanic Clouds. II - New spectral classification of OB stars in the SMC

Context. The Cygnus complex is one of the most powerful star forming regions at a close distance from the Sun (~1.4 kpc). Its richest OB association Cygnus OB2 is known to harbor many tens of O-type stars and hundreds of B-type stars, providing a large homogeneous population of OB stars that can be analyzed. Many studies of its massive population have been developed in the last decades, although the total number of OB stars is still incomplete. Aim. Our aim is to increase the sample of O and B members of Cygnus OB2 and its surroundings by spectroscopically classifying 61 candidates as possible OB-type members of Cygnus OB2, using new intermediate resolution spectroscopy. Methods. We have obtained intermediate resolution (R ~ 5000) spectra for all of the OB-type candidates between 2013 and 2017. We thus performed a spectral classification of the sample using HeI-II and metal lines rates, as well as the Marxist Ghost Buster (MGB) software for O-type stars and the IACOB standards catalog for B-type stars. Results. From the whole sample of 61 candidates, we have classified 42 stars as new massive OB-type stars, earlier than B3, in Cygnus OB2 and surroundings, including 11 O-type stars. The other candidates are discarded as they display later spectral types inconsistent with membership in the association. We have also obtained visual extinctions for all the new confirmed massive OB members, placing them in a Hertzsprung-Russell Diagram using calibrations for Teff and luminosity. Finally, we have studied the age and extinction distribution of our sample within the region. Conclusions. We have obtained new blue intermediate-resolution spectra suitable for spectral classification of 61 OB candidates in Cygnus OB2 and surroundings. The confirmation of 42 new OB massive stars (earlier than B3) in the region allows us to increase the young massive population known in the field. We have also confirmed the correlation between age and Galactic longitude previously found in the region. We conclude that many O and early B stars at B > 16 mag are still undiscovered in Cygnus.

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An atlas of cool supergiants from the Magellanic Clouds and typical interlopers

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833219 ◽

2018 ◽

Vol 618 ◽

pp. A137 ◽

Cited By ~ 5

Author(s):

Ricardo Dorda ◽

Ignacio Negueruela ◽

Carlos González-Fernández ◽

Amparo Marco

Keyword(s):

Photographic Plate ◽

Magellanic Clouds ◽

Spectral Classification ◽

Late Type ◽

Spectral Ranges ◽

Work Done

We present an atlas composed of more than 1500 spectra of late-type stars (spectral types from G to M) observed simultaneously in the optical and calcium triplet spectral ranges. These spectra were obtained as part of a survey to search for cool supergiants in the Magellanic Clouds and were taken over four epochs. We provide the spectral and luminosity classification for each spectrum (71% are supergiants, 13% are giants or luminous giants, 4% are carbon or S stars, and the remaining 12% are foreground stars of lesser luminosities). We also provide a detailed guide for the spectral classification of luminous late-type stars, the result of the extensive classification work done for the atlas. Although this guide is based on classical criteria, we have put them together and re-elaborated them for modern CCD-spectra as these criteria were scattered among many different works and mainly conceived for use with photographic plate spectra. The result is a systematic, well-tested process for identifying and classifying luminous late-type stars, illustrated with CCD spectra of standard stars and the classifications of our own catalogue.

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A search for strong magnetic fields in massive and very massive stars in the Magellanic Clouds

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937098 ◽

2020 ◽

Vol 635 ◽

pp. A163

Author(s):

S. Bagnulo ◽

G. A. Wade ◽

Y. Nazé ◽

J. H. Grunhut ◽

M. E. Shultz ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Longitudinal Magnetic Field ◽

Massive Stars ◽

Magellanic Clouds ◽

Dipolar Field ◽

Strong Magnetic Fields ◽

Ob Stars ◽

Stellar Magnetic Fields ◽

The Universe

Despite their rarity, massive stars dominate the ecology of galaxies via their strong, radiatively-driven winds throughout their lives and as supernovae in their deaths. However, their evolution and subsequent impact on their environment can be significantly affected by the presence of a magnetic field. While recent studies indicate that about 7% of OB stars in the Milky Way host strong, stable, organised (fossil) magnetic fields at their surfaces, little is known about the fields of very massive stars, nor the magnetic properties of stars outside our Galaxy. We aim to continue searching for strong magnetic fields in a diverse set of massive and very massive stars (VMS) in the Large and Small Magellanic Clouds (LMC/SMC), and we evaluate the overall capability of FORS2 to usefully search for and detect stellar magnetic fields in extra-galactic environments. We have obtained FORS2 spectropolarimetry of a sample of 41 stars, which principally consist of spectral types B, O, Of/WN, WNh, and classical WR stars in the LMC and SMC. Four of our targets are Of?p stars; one of them was just recently discovered. Each spectrum was analysed to infer the longitudinal magnetic field. No magnetic fields were formally detected in our study, although Bayesian statistical considerations suggest that the Of?p star SMC 159-2 is magnetic with a dipolar field of the order of 2.4–4.4 kG. In addition, our first constraints of magnetic fields in VMS provide interesting insights into the formation of the most massive stars in the Universe.

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Spectral classification of O and B0 supergiants in the Magellanic Clouds

The Astrophysical Journal ◽

10.1086/155334 ◽

1977 ◽

Vol 215 ◽

pp. 53 ◽

Cited By ~ 151

Author(s):

N. R. Walborn

Keyword(s):

Magellanic Clouds ◽

Spectral Classification

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Spectral classification of OB stars in both hemispheres and the absolute magnitude calibration.

The Astronomical Journal ◽

10.1086/111285 ◽

1972 ◽

Vol 77 ◽

pp. 312 ◽

Cited By ~ 260

Author(s):

N. R. Walborn

Keyword(s):

Absolute Magnitude ◽

Spectral Classification ◽

Ob Stars ◽

The Absolute

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The Complex Upper HR Diagram

Galaxies ◽

10.3390/galaxies7030075 ◽

2019 ◽

Vol 7 (3) ◽

pp. 75

Author(s):

Roberta M. Humphreys

Keyword(s):

Mass Loss ◽

Massive Stars ◽

Magellanic Clouds ◽

Historical Overview ◽

Ob Stars ◽

Luminous Blue Variables ◽

Evolved Stars ◽

Nearby Galaxies ◽

Introductory Review ◽

Hr Diagram

Several decades of observations of the most massive and most luminous stars have revealed a complex upper HR Diagram, shaped by mass loss, and inhabited by a variety of evolved stars exhibiting the consequences of their mass loss histories. This introductory review presents a brief historical overview of the HR Diagram for massive stars, highlighting some of the primary discoveries and results from their observation in nearby galaxies. The sections in this volume include reviews of our current understanding of different groups of evolved massive stars, all losing mass and in different stages of their evolution: the Luminous Blue Variables (LBVs), B[e] supergiants, the warm hypergiants, Wolf–Rayet stars, and the population of OB stars and supergiants in the Magellanic Clouds.

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