EDP Sciences
Free Access
Issue
A&A
Volume 503, Number 2, August IV 2009
Page(s) 505 - 509
Section Stellar structure and evolution
DOI https://doi.org/10.1051/0004-6361/200811342
Published online 02 July 2009
A&A 503, 505-509 (2009)
DOI: 10.1051/0004-6361/200811342

Research Note

Hard X-ray flux from low-mass stars in the Cygnus OB2 association

M. Caramazza1, 2, J. J. Drake3, G. Micela2, and E. Flaccomio2

1  Dipartimento di Scienze Fisiche ed Astronomiche, Università di Palermo, via Archirafi 36, 90123 Palermo, Italy
    e-mail: mcarama@astropa.unipa.it
2  INAF Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
    e-mail: [giusi;flaccomio]@astropa.unipa.it
3  Smithsonian Astrophysical Observatory, MS-3, 60 Garden Street, Cambridge, MA 02138, USA
    e-mail: jdrake@cfa.harvard.edu

Received 13 November 2008 / Accepted 29 May 2009

Abstract
Context. The Cygnus OB2 association, the central engine of the Cygnus X star-forming region, is the subject of an extensive INTEGRAL Key Project that will accumulate 6Ms of observations. Analysis of 2Ms of observations by De Becker and co-workers provides the most sensitive limit yet obtained on hard X-ray emission from the cluster.
Aims. We investigate the X-ray emission in the 20–40 keV band expected from the flaring low-mass stellar population in Cygnus OB2. We discuss whether such emission needs to be considered in the interpretation of existing and future X-ray observations of the region, and whether such observations might provide insight into the high-energy processes on low-mass pre-main sequence stars.
Methods. The total hard X-ray flux from low-mass stars is estimated by assuming the observed soft X-ray emission stems from a superposition of flares. We further assume the ratio of hard X-ray to soft X-ray emission is described by a scaling found for solar flares by Isola and co-workers.
Results. We estimate the low-mass stellar hard X-ray flux in the 20–40 keV band to lie in the range ~2$\times$1031-6$\times$1032 erg s-1 and discuss some potential biases that might affect this result.
Conclusions. Hard X-ray emission could lie at a level not much below the current observed flux upper limits for Cygnus OB2. If this emission could be detected, it would provide insight into the hard X-ray production of large flares on pre-main sequence stars. We highlight the penetrating power of hard X-rays from low-mass stellar populations as a possible pointer to our Galaxy's hidden star-forming clusters and super-clusters using more sensitive observations from future missions.


Key words: stars: coronae -- stars: flare -- Galaxy: open clusters and associations: individual: Cygnus OB2



© ESO 2009

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.