Red supergiants and the past of Cygnus OB2

Comerón, F.; Djupvik, A. A.; Schneider, N.; Pasquali, A.

doi:10.1051/0004-6361/201527517

Cited by 19 publications

(28 citation statements)

References 44 publications

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“…The association, which formed massive stars over an extended period lasting from ∼ 30 Myr to ∼ 10 Myr ago, may have hosted several tens of O stars and the precursors of around one hundred supernovae up to the present time. Such an extended period of star formation may not be an anomalous feature of large, rich OB associations, based on similar recent findings on the younger, more nearby Cygnus OB2 association (Hanson 2003;Comerón & Pasquali 2012;Comerón et al 2016;Berlanas et al 2018).…”

Section: Discussionsupporting

confidence: 73%

The possible common origin of M 16 and M 17

Comerón

Torra

2018

A&A

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Context. It has been suggested that the well-studied giant HII regions M16 and M17 may have had a common origin, being an example of large-scale triggered star formation. While some features of the distribution of the interstellar medium in the region support this interpretation, no definitive detection of an earlier population of massive stars responsible for the triggering has been made thus far. Aims. We have carried out observations looking for red supergiants in the area covered by a giant shell seen in HI and CO centered on galactic coordinates l ∼ 14 • 5, b ∼ +1 • that peaks near the same radial velocity as the bulk of the emission from both giant HII regions, which are located along the shell. Red supergiants have ages in the range expected for the parent association whose most massive members could have triggered the formation of the shell and of the giant HII regions along its rim. Methods. We have obtained spectroscopy in the visible of a sample of red stars selected on the basis of their infrared colors, whose magnitudes are consistent with them being red supergiants if they are located at the distance of M16 and M17. Spectroscopy is needed to distinguish red supergiants from AGB stars and RGB stars, which are expected to be abundant along the line of sight.Results. Out of a sample of 37 bright red stars, we identify four red supergiants that confirm the existence of massive stars in the age range between ∼ 10 and ∼ 30 Myr in the area. At least three of them have Gaia DR2 parallaxes consistent with them being at the same distance as M16 and M17. Conclusions. The evidence of past massive star formation within the area of the gaseous shell lends support to the idea that it was formed by the combined action of stellar winds and ionizing radiation of the precursors of the current red supergiants. These could be the remnants of a richer population, whose most massive members have exploded already as core-collapse supernovae. The expansion of the shell against the surrounding medium, perhaps combined with the overrun of preexisting clouds, is thus a plausible trigger of the formation of a second generation of stars currently responsible for the ionization of M16 and M17.F. Comerón and J. Torra: On the possible common origin of M16 and M17 selection criteria and our findings, through which we produce a crude estimate of the overall massive star content of the association and the mechanical energy deposited in the bubble, which suggest that the scenario of triggered formation of M16 and M17 is indeed plausible.

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Section: Discussionsupporting

confidence: 73%

The possible common origin of M 16 and M 17

Comerón

Torra

2018

A&A

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“…They found no signs of dynamical evolution of Cyg OB2 which is inconsistent with the idea that all stars form in dense, compact clusters. On the other hand, Comerón et al (2016) investigated the past star formation history of Cygnus OB2 using the red supergiants detectable in the near infrared as a probe to trace massive stars with initial masses between 7 and 40 M ⊙ . They concluded that Cygnus OB2 has a history of star formation extending into the past for at least 20 Myr.…”

Section: Cosmic Rays In Superbubblesmentioning

confidence: 99%

Cosmic Ray Production in Supernovae

et al. 2018

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We give a brief review of the origin and acceleration of cosmic rays (CRs), emphasizing the production of CRs at different stages of supernova evolution by the first-order Fermi shock acceleration mechanism. We suggest that supernovae with trans-relativistic outflows, despite being rather rare, may accelerate CRs to energies above 10 18 eV over the first year of their evolution. Supernovae in young compact clusters of massive stars, and interaction powered superluminous supernovae, may accelerate CRs well above the PeV regime. We discuss the acceleration of the bulk of the galactic CRs in isolated supernova remnants and re-acceleration of escaped CRs by the multiple shocks present in superbubbles produced by associations of OB stars. The effects of magnetic field amplification by CR driven instabilities, as well as superdiffusive CR transport, are discussed for nonthermal radiation produced by nonlinear shocks of all speeds including trans-relativistic ones.

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“…But only a fraction <1/3 of the SN II come from the prominent O-stars all of which explode by the first ~13 Myr of an OB association's life, leaving all of the remaining SN II progenitors uncounted in the surveys of OB associations which are based only on the O-star counts. Recently, however, (Comeron et al 2016) has successfully surveyed the early B-star Red supergiants in the Cygnus OB2 association significantly increasing the potential CCSN count in that association and since these are roughly half of the cosmic ray sources more such surveys need to be made.…”

Section: Summary and Further Workmentioning

confidence: 99%