X-ray Properties of Pre-Main-Sequence Stars in the Orion Nebula Cluster with Known Rotation PeriodsReportar como inadecuado



 X-ray Properties of Pre-Main-Sequence Stars in the Orion Nebula Cluster with Known Rotation Periods


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We re-analyze all archival Chandra-ACIS observations of the Orion Nebula Cluster ONC to study the X-ray properties of a large sample of pre-main-sequence PMS stars with optically determined rotation periods. Our goal is to elucidate the origins of X-rays in PMS stars by seeking out connections between the X-rays and the mechanisms most likely driving their production-rotation and accretion. In our sample X-ray luminosity is significantly correlated with stellar rotation, in the sense of decreasing Lx-Lbol with more rapid rotation, suggesting that these stars are in the -super-saturated- regime of the rotation-activity relationship. However, we also find that stars with optical rotation periods are significantly biased to high Lx. This is not the result of magnitude bias in the optical rotation-period sample but rather to the diminishingly small amplitude of optical variations in stars with low Lx. Evidently, there exists in the ONC a population of stars whose rotation periods are unknown and that possess lower average X-ray luminosities than those of stars with known rotation periods. These stars may sample the linear regime of the rotation-activity relationship. Accretion also manifests itself in X-rays, though in a somewhat counterintuitive fashion: While stars with spectroscopic signatures of accretion show harder X-ray spectra than non-accretors, they show lower X-ray luminosities and no enhancement of X-ray variability. We interpret these findings in terms of a common origin for the X-ray emission observed from both accreting and non-accreting stars, with the X-rays from accreting stars simply being attenuated by magnetospheric accretion columns. This suggests that X-rays from PMS stars have their origins primarily in chromospheres, not accretion.



Autor: Keivan G. Stassun; David R. Ardila; Mary Barsony; Gibor Basri; Robert D. Mathieu

Fuente: https://archive.org/







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