Physics
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21442202d&link_type=abstract
American Astronomical Society, AAS Meeting #214, #422.02; Bulletin of the American Astronomical Society, Vol. 41, p.691
Physics
Scientific paper
We have developed and successfully tested a new self-consistent method to reliably identify pre-main sequence (PMS) objects actively undergoing mass accretion in a resolved stellar population, regardless of their age. The method does not require spectroscopy and combines broad-band V and I photometry with narrow-band Hα imaging to: (1) identify all stars with excess Hα emission; (2) convert the excess Hα magnitude into Hα luminosity L(Hα) (3) estimate the Hα emission equivalent width; (4) derive the accretion luminosity Lacc and finally (5) obtain the mass accretion rate Macc from Lacc and the appropriate stellar mass and radius. By selecting stars with an accuracy of 15% or better in the Hα photometry, the statistical uncertainty on the derived Macc is typically <17% and is dictated by the precision of the Hα photometry. Systematic uncertainties, of up to a factor of 3 on the value of Macc, are caused by our incomplete understanding of the physics of the accretion process and as such affect all determinations of the mass accretion rate, including those based on a spectroscopic Hα line analysis.
As an application of our method, we study the accretion process in a
field of 9.2 arcmin2 around SN 1987A, using existing HST photometry. We identify as bona-fide PMS stars a total of 133 objects with a Hα excess above the 4σ level and a median age of 14.5 Myr. Their median mass accretion rate of 2.9x10-8 Msolar/yr is in excellent agreement with the value measured for G-type PMS stars of comparable mass and age in the Milky Way. The accretion luminosity of these PMS objects shows a strong dependence on their distance from a group of hot massive stars in the field and suggests that the ultraviolet radiation of the latter is rapidly eroding the circumstellar discs around PMS stars.
de Marchi Guido
Panagia Nino
Romaniello Martino
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