An interesting candidate for isolated massive-star formation in the Small Magellanic Cloud

Selier, R.; Heydari-Malayeri, M.; Gouliermis, D. A.

doi:10.1051/0004-6361/201016100

Cited by 21 publications

(33 citation statements)

References 84 publications

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“…Our investigation is the only observational study (apart from that presented by Selier et al 2011) that approaches the issue strictly from this perspective. Based on our findings we argue that panchromatic high-resolution observations in the vicinity of apparently isolated MYSOs (and not main-sequence stars) will allow a better understanding of the conditions and the parameters that set the stage for high-mass stars to form in isolation.…”

Section: Discussionmentioning

confidence: 99%

STELLAR CLUSTERINGS AROUND “ISOLATED” MASSIVE YSOs IN THE LMC

Stephens

Gouliermis

Looney

et al. 2017

ApJ

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Observations suggest that there is a significant fraction of O-stars in the field of the Milky Way that appear to have formed in isolation or in low mass clusters (<100 M ). The existence of these high-mass stars that apparently formed in the field challenges the generally accepted paradigm, which requires star formation to occur in clustered environments. In order to understand the physical conditions for the formation of these stars, it is necessary to observe isolated high-mass stars while they are still forming. With the Hubble Space Telescope, we observe the seven most isolated massive (>8 M ) young stellar objects (MYSOs) in the Large Magellanic Cloud (LMC). The observations show that while these MYSOs are remote from other MYSOs, OB associations, and even from known giant molecular clouds, they are actually not isolated at all. Imaging reveals ∼100 to several hundred pre-main-sequence (PMS) stars in the vicinity of each MYSO. These previously undetected PMS stars form prominent compact clusters around the MYSOs, and in most cases they are also distributed sparsely across the observed regions. Contrary to what previous high-mass field star studies show, these observations suggest that high-mass stars may not be able to form in clusters with masses less than 100 M . If these MYSOs are indeed the best candidates for isolated high-mass star formation, then the lack of isolation is at odds with random sampling of the IMF. Moreover, while isolated MYSOs may not exist, we find evidence that isolated clusters containing O-stars can exist, which in itself is rare.

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Section: Discussionmentioning

confidence: 99%

STELLAR CLUSTERINGS AROUND “ISOLATED” MASSIVE YSOs IN THE LMC

Stephens

Gouliermis

Looney

et al. 2017

ApJ

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“…Because of their location and youth, these stars are good test cases to investigate whether massive stars can form in isolation (Zinnecker & Yorke 2007). Some compelling cases of likely isolated formation of massive stars have been reported in the Large (Chu & Gruendl 2008) and Small Magellanic Clouds (Selier et al 2011), and the fraction of actual isolated O stars in the Milky Way was assessed by de Wit et al (2004Wit et al ( , 2005 to be between 5% and 10%.…”

Section: Isolated O Stars In the Fieldmentioning

confidence: 99%

New members of the massive stellar population in Cygnus

Comerón¹,

Pasquali

2012

A&A

109

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Context. The Cygnus OB2 association and its surroundings display the richest collection of massive stars in our nearby Galactic environment and a wealth of signposts of the interaction between these stars and the interstellar gas. Aims. We perform a magnitude-limited, homogeneous census of O and early B-type stars with accurate spectral classifications in the blue, in a 6• × 4• region centered on Cygnus OB2 that includes most of the Cygnus X complex, a sizeable fraction of the adjacent Cygnus OB9 association, and a large area of the field surrounding these complexes. Methods. By using reddening-free indices based on BJHK magnitudes from the USNO-B and 2MASS catalogs, we are able to produce a highly complete, highly uncontaminated sample of O and early B stars, which nearly duplicates any previous census of the region for the same range of spectral types. We provide the spectral types of 60 new O and B stars, as well as a list of an additional 60 candidates pending spectroscopic confirmation. In addition, the UBV imaging of the surroundings of three apparently isolated O stars is used to investigate the possible presence of small clusters of young stars around them. Results. Early-type stars are consistent with similar distances for Cygnus OB2, OB9, and the field stars surrounding them. We confirm previous findings of an older population in Cygnus OB2 spatially offset from where the stellar density of the association peaks. Some new remarkable objects are identified, including BD+40 4210, a B0 supergiant member of Cygnus OB2 that is among the brightest members of the association sharing some characteristics with luminous blue variable (LBV) candidates, located at a projected distance of 5 pc from another LBV candidate. A new O5If member of Cygnus OB9 is found, as well as several other O stars and B supergiants. On the other hand, while no obvious clustering is found around the apparently isolated O stars, the fields around two of them seem to contain objects with strong ultraviolet excesses, which perhaps indicates that they are accreting, although their nature and possible relationship to the O stars in the field are unclear. Conclusions. Star formation in Cygnus has been taking place in a sustained manner for well over 10 Myr, with a large-scale trend of proceeding from lower to higher Galactic longitudes. Star formation inside Cygnus OB2 follows this trend, with indications of intense star formation activity having started in the southern (lower galactic latitude) part of the association about 10 Myr ago and probably continuing at present in the north.

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“…Core accretion models of massive stars on the contrary allow rather isolated O-stars to form (Krumholz et al 2009). Isolated O-type stars that are still in their formation region are surrounded by residual gas that can be seen through Hα observations (Lamb et al 2010;Selier et al 2011) and some of them are found in sparse clusters with less than ten lower-mass companions (Lamb et al 2010). Monte Carlo simulations by Lamb et al (2010) indicate that the existence of such sparse clusters is more in favour of the core accretion models and suggest that "clusters are built stochastically by randomly sampling stars from a universal initial mass function (IMF)".…”

Section: The Surroundings Of Hd 93521mentioning

confidence: 99%

The nature of the high Galactic latitude O-star HD 93521: new results from X-ray and optical spectroscopy

Rauw¹,

Morel²,

Palate³

2012

A&A

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Context. Owing to its unusual location and its isolation, the nature of the high Galactic latitude O9.5 Vp object HD 93521 is still uncertain. Aims. We have collected X-ray and optical observations to characterize the star and its surroundings. Methods. X-ray images and spectra are analysed to search for traces of a recent star formation event around HD 93521 and to search for the signature of a possible compact companion. Optical echelle spectra are analysed with plane-parallel model atmosphere codes, assuming either a spherical star or a gravity darkened rotationally flattened star, to infer the effective temperature and surface gravity, and to derive the He, C, N and O abundances of HD 93521.Results. The X-ray images reveal no traces of a population of young low-mass stars coeval with HD 93521. The X-ray spectrum of HD 93521 is consistent with a normal late O-type star although with subsolar metallicity. No trace of a compact companion is found in the X-ray data. In the optical spectrum, He and N are found to be overabundant, in line with the effect of rotational mixing in this very fast rotator, whilst C and O are subsolar. A critical comparison with the properties of subdwarf OB stars, indicates that, despite some apparent similarities, HD 93521 does not belong to this category. Conclusions. Despite some ambiguities on the runaway status of the star, the most likely explanation is that HD 93521 is a Population I massive O-type star that was ejected from the Galactic plane either through dynamical interactions or a result of a supernova event in a binary system.

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An interesting candidate for isolated massive-star formation in the Small Magellanic Cloud

Cited by 21 publications

References 84 publications

STELLAR CLUSTERINGS AROUND “ISOLATED” MASSIVE YSOs IN THE LMC

STELLAR CLUSTERINGS AROUND “ISOLATED” MASSIVE YSOs IN THE LMC

New members of the massive stellar population in Cygnus

The nature of the high Galactic latitude O-star HD 93521: new results from X-ray and optical spectroscopy

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