X-ray emission from the young brown dwarfs of the Taurus Molecular Cloud
Abstract
We surveyed with 15 XMM-Newton pointings, supplemented with one archival Chandra observation, 17 young brown dwarfs (BDs) with late M spectral types in the Taurus Molecular Cloud. Half of this sample (9 out of 17 BDs) is detected; 7 BDs are detected here for the first time in X-rays. We confirm several previous findings on BD X-ray activity: a log-log relation between X-ray and bolometric luminosity for stars and BDs detected in X-rays; a shallow log-log relation between X-ray fractional luminosity and mass; a log-log relation between X-ray fractional luminosity and effective temperature; a log-log relation between X-ray surface flux and effective temperature. We find no significant log-log correlation between the X-ray fractional luminosity and EW(Halpha ). Accreting and nonaccreting BDs have a similar X-ray fractional luminosity. The X-ray fractional luminosity declines from low-mass stars to M-type BDs and, as a sample, the BDs are less efficient X-ray emitters than low-mass stars. We thus conclude that while the BD atmospheres observed here are mostly warm enough to sustain coronal activity, a trend is seen that may indicate its gradual decline due to the drop in photospheric ionization degree.
- Publication:
-
Memorie della Societa Astronomica Italiana
- Pub Date:
- 2007
- Bibcode:
- 2007MmSAI..78..368G
- Keywords:
-
- Stars: low-mass;
- brown dwarfs;
- X-rays: stars;
- ISM: individual objects: the Taurus Molecular Cloud