On the Problem of the Mechanism of the Origin of Stars in Stellar Associations

Ambartsumian, V. A.

doi:10.1103/revmodphys.30.944

Cited by 27 publications

(12 citation statements)

References 4 publications

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“…This follows from the work of Vázquez‐Semadeni, Passot & Pouquet (1995) who showed that transient (unbound) GMC‐sized objects can be formed from flows in the interstellar medium (ISM). We also find that unbound GMCs may provide a natural mechanism for the creation of OB associations, a notion first suggested by Ambartsumian (1958).…”

Section: Introductionsupporting

confidence: 71%

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Star formation in unbound giant molecular clouds: the origin of OB associations?

Clark

Bonnell

Zinnecker

et al. 2005

Monthly Notices of the Royal Astronomical Society

113

109

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We investigate the formation of star clusters in an unbound giant molecular cloud, where the supporting kinetic energy is twice as large as the cloud's self‐gravity. This cloud manages to form a series of star clusters and disperse, all within roughly two crossing times (10 Myr), supporting recent claims that star formation is a rapid process. Simple assumptions about the nature of the star formation occurring in the clusters allows us to place an estimate for the star formation efficiency at about 5–10 per cent, consistent with observations. We also propose that unbound clouds can act as a mechanism for forming OB associations. The clusters that form in the cloud behave as OB subgroups. These clusters are naturally expanding from one another due to the unbound nature of the flows that create them. The properties of the cloud we present here are consistent with those of classic OB associations.

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Section: Introductionsupporting

confidence: 71%

“…We argue that unbound GMCs may provide a simple mechanism for forming OB associations, a concept that was touched upon by Ambartsumian (1955, 1958). OB stars form at the centre of a population of SFCs.…”

Section: Discussionmentioning

confidence: 91%

Star formation in unbound giant molecular clouds: the origin of OB associations?

Clark

Bonnell

Zinnecker

et al. 2005

Monthly Notices of the Royal Astronomical Society

113

109

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“…According to the often-cited work of Lada & Lada (2003), most or all stars are formed in bound clusters but as they evolve, the vast majority of them become unbound as the total kinetic energy of the stars does not change very much while their potential energy becomes less negative (closer to zero) when the associated molecular gas is dispersed. In the view of Lada & Lada (2003), most clusters evolve into low-density OB associations (Ambartsumian 1958) with sizes of tens of parsecs that eventually dissolve into the Galactic disc. In an alternative view to the "most stars form in clusters" scenario, star formation is a hierarchical process that can take place in both bound and unbound clouds with a wide range of scales (Elmegreen 2010;Ward et al 2020).…”

Section: Introductionmentioning

confidence: 99%

The Villafranca catalog of Galactic OB groups

Apellániz

Bellido

Barbá

et al. 2020

A&A

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Context. The spectral classifications of the Galactic O-Star Spectroscopic Survey (GOSSS) and the astrometric and photometric data from Gaia have significantly improved our ability to measure distances and determine memberships of stellar groups (clusters, associations, or parts thereof) with OB stars. In the near future, the situation will be further improved thanks to subsequent Gaia data releases and new photometric and spectroscopic surveys. Aims. We initiated a program to identify and determine the membership of Galactic stellar groups with OB stars and measure distances to them. Given the data currently available, we started with the identification and distance determinations of groups with O stars. In this paper, we concentrate on groups that contain stars with the earliest spectral subtypes. Methods. We used GOSSS to select Galactic stellar groups with O2–O3.5 stars and the method described in paper 0 of this series, which combines Gaia DR2 G + GBP + GRP photometry, positions, proper motions, and parallaxes to assign robust memberships and measure distances. We also included Collinder 419 and NGC 2264, the clusters cited in that paper, to generate our first list of 16 O-type Galactic stellar groups. Results. We derived distances, determined the membership, and analyzed the structure of sixteen Galactic stellar groups with O stars, Villafranca O-001 to Villafranca O-016, including the fourteen groups with the earliest-O-type optically accessible stars known in the Milky Way. We compared our distance with previous results from the literature and establish that the best consistency is with (the small number of) VLBI parallaxes and the worst is with kinematic distances. Our results indicate that very massive stars can form in relatively low-mass clusters or even in near-isolation, as is the case for the Bajamar star in the North America nebula. This lends support to the hierarchical scenario of star formation, where some stars are born in well-defined bound clusters but others are born in associations that are unbound from the beginning: groups of newborn stars come in many shapes and sizes. We propose that HD 64 568 and HD 64 315 AB could have been ejected simultaneously from Haffner 18 (Villafranca O-012 S). Our results are consistent with a difference of ≈20 μas in the Gaia DR2 parallax zero point between bright and faint stars.

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“…The presence of large gaseous nebulae which form part of O-associations, close stellar groups and systems of the Trapezium type, in an association and, especially, in the central regions, was shown [8] to be inconsistent with the idea that stellar associations are formed from diffuse nebulae. The presence of large gaseous nebulae which form part of O-associations, close stellar groups and systems of the Trapezium type, in an association and, especially, in the central regions, was shown [8] to be inconsistent with the idea that stellar associations are formed from diffuse nebulae.…”

Section: Introductionmentioning

confidence: 97%

Rotating superdense configurations: pulsars and their astrophysical manifestations

Sedrakian¹,

Чубарян²

2009

Astrophysics

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This paper is a discussion of some results from papers by followers of V. A. Ambartsumyan, whose fundamental articles serve as the beginning of research on superdense stars: white dwarfs and neutron stars. Solutions of the Einstein equations are given for the case of axial symmetry and are used to determine the integral parameters of rotating neutron stars and white dwarfs. A theory of magnetic field generation in neutron stars has been developed and is consistent with the existence of high, nonuniform magnetic fields on the order of 10 14 G in pulsars. A theory has been proposed for the dynamics of neutron vortices and used to explain the observed relaxation of the angular velocity of pulsars following glitches.

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On the Problem of the Mechanism of the Origin of Stars in Stellar Associations

Cited by 27 publications

References 4 publications

Star formation in unbound giant molecular clouds: the origin of OB associations?

Star formation in unbound giant molecular clouds: the origin of OB associations?

The Villafranca catalog of Galactic OB groups

Rotating superdense configurations: pulsars and their astrophysical manifestations

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