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2006AJ....131.2934R - Astron. J., 131, 2934-2948 (2006/June-0)

Chandra X-ray observations of young clusters. III. NGC 2264 and the Orion flanking fields.


Abstract (from CDS):

Chandra observations of solar-like pre-main-sequence (PMS) stars in the Orion flanking fields (FFs; age ∼1 Myr) and NGC 2264 (∼3 Myr) are compared with the results of the Chandra Orion Ultradeep Project survey of similar objects in the Orion Nebula cluster (ONC; ∼0.5 Myr). The correlations between logLXand mass found for PMS stars on convective tracks in these clusters are consistent with the relationships found for the ONC, indicating little change in the median values of either logLXor logLX/Lbol during the first ∼3-5 Myr of evolution down convective tracks. The fraction of stars with extreme values of LX, more than 10 times higher than the average for a given Lbol, or with logLX/Lbolgreater than the canonical saturation value of -2.9, is, however, larger by a factor of 2 in the younger ONC when compared with the Orion FFs and NGC 2264. PMS stars in NGC 2264 on radiative tracks have LX/Lbolvalues that are systematically lower by a factor of ∼10 than those found for stars of similar mass on convective tracks. The dramatic decrease in flux from convective to radiative phases of PMS evolution is likely related to major structural changes that influence the efficiency of magnetic field generation and thus the level of magnetic activity. As in the ONC, we find that stars with measured periods have, on average, higher X-ray luminosities. However, there is a wide range in LXand LX/Lbolfor both periodic and nonperiodic stars of similar mass. Among stars with measured periods, the level of X-ray emission does not correlate with the rotation rate. For this data set, we find no statistically significant correlation between X-ray flux and (1) the presence or absence of circumstellar accretion disks or (2) disk accretion rates as assessed from ultraviolet excesses.

Abstract Copyright:

Journal keyword(s): open clusters and associations: individual (NGC 2264) - Galaxy: Open Clusters and Associations: Individual: Name: Orion - X-Rays: Stars

Simbad objects: 11

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