Astrophys. J., 691, 1128-1144 (2009/February-1)
Multiwavelength signatures of magnetic activity from young stellar objects in the LkHα 101 cluster.
OSTEN R.A. and WOLK S.J.
Abstract (from CDS):
We describe the results of our multiwavelength observing campaign on the young stellar objects in the LkHα 101 cluster. Our simultaneous X-ray and multifrequency radio observations are unique in providing simultaneous constraints on short-timescale variability at both wavelengths as well as constraints on the thermal or nonthermal nature of radio emission from young stars. Focussing on radio-emitting objects and the multiwavelength data obtained for them, we find that multifrequency radio data indicate nonthermal emission even in objects with infrared evidence for disks. We find radio variability on timescales of decades, days, and hours. About half of the objects with X-ray and radio detections were variable at X-ray wavelengths, despite lacking large-scale flares or large variations. Variability appears to be a bigger factor affecting radio emission than X-ray emission. A star with infrared evidence for a disk, [BW88] 3, was observed in the decay phase of radio flare. In this object and another ([BW88] 1), we find an inverse correlation between radio flux and spectral index, which contrasts with behavior seen in the Sun and active stars. We interpret this behavior as the repopulation of the hardest energy electrons due to particle acceleration. A radio and X-ray source lacking an infrared counterpart, [BW88] 1, may be near the substellar limit; its radio properties are similar to other cluster members, but its much higher radio to X-ray luminosity ratio is reminiscent of behavior in nearby very low-mass stars/brown dwarfs. We find no correspondence between signatures of particle acceleration and those of plasma heating, both time-averaged and time-variable. The lack of correlated temporal variability in multiwavelength behavior, the breakdown of multiwavelength correlations of time-averaged luminosities, and the optical thickness of X-ray emitting material at radio wavelengths support the idea that radio and X-ray emission on young stars are physically and/or energetically distinct.
radio continuum: stars - stars: activity - stars: coronae - stars: pre-main sequence - X-rays: stars
Table 1: LkHa101VLA JHHMMSS.ss+DDMMSS.s N=23. Table 2, col(3): LkHa101CXO JHHMMSS.s+DDMMSS N=8. Table 2, col(4): LkHa101SST JHHMMSS.ss+DDMMSS.s N=7.
Calibrator 0414+343 is not identified.
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