SCYON Abstract

Received on December 18 2007

X-ray properties of protostars in the Orion Nebula

AuthorsL. Prisinzano (1), G. Micela (1), E. Flaccomio (1), J.R. Stauffer (2), T. Megeath (3), L. Rebull (2), M. Robberto (4), K. Smith (4), E.D. Feigelson (5), N. Grosso (6), and S. Wolk (7)
Affiliation(1) INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1,I-90134 Palermo, Italy
(2) Spitzer Science Center, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125
(3) Department of Physics, University of Toledo, 2801 W. Bancroft Ave, Toledo OH 43606
(4) Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218
(5) Department of Astronomy and Astrophysics, Penn State University, 525 Davey Lab, University Park, PA 16802, USA
(6) Observatoire astronomique de Strasbourg, Universit\'e Louis-Pasteur, CNRS, INSU, 11 rue de l'Université, 67000 Strasbourg, France
(7) Harvard Smithsonian Center for Astrophysics, MS 65, 60 Garden Street, Cambridge, MA 02138
Accepted byAstrophysical Journal
Contactloredana@astropa.inaf.it
URLhttp://www.astropa.unipa.it/Library/preprint.html
Links Orion Nebula Cluster

Abstract

The origin and evolution of the X-ray emission in very young stellar objects (YSOs) are not yet well understood because it is very hard to observe YSOs in the protostellar phase. We study the X-ray properties of Class 0-I objects in the Orion Nebula Cluster (ONC) and compare them with those of the more evolved Class II and III members. Using Chandra Orion Ultradeep Project (COUP) data, we study the X-ray properties of stars in different evolutionary classes: luminosities, hydrogen column densities NH, average plasma temperatures and time variability are compared in order to understand if the interaction between the circumstellar material and the central object can influence the X-ray emission. We have assembled the deepest and most complete photometric catalog of objects in the ONC region from the UV to 8 μm using data from the HST Treasury Program, deep and almost simultaneous UBVI and JHK images taken, respectively, with WFI@2.2m ESO and ISPI@4m CTIO telescopes, and Spitzer IRAC imaging. We select high probability candidate Class 0-I protostars, distinguishing between those having a spectral energy distribution which rises from K up to 8 μm (Class 0-Ia) from those where the SED rises from K up to 4.5 μm and decreasing afterwards (Class 0-Ib). In addition, we select a sample of "bona fide" Class II stars and a set of Class III stars with IR emission consistent with normal photospheres. Our principal result is that Class 0-Ia objects are significantly less luminous in X-rays, both in the total and hard bands, than the more evolved Class II stars with mass larger than 0.5 M(sun); these latter show X-ray luminosities similar to those of Class 0-Ib stars. This result supports the hypothesis that the onset of X-ray emission occurs at a very early stage of star formation and is in agreement with the result found in Giardino et al. (2007). Spectral properties of Class 0-I stars are similar to those of the more evolved Class II and III objects, except for a larger absorption likely due to gas in the envelope or disk of the protostellar objects. Our data suggest that the three different classes have similar X-ray temporal variability.