Abstract
Pre-main-sequence (PMS) stars of mass ≳0.35 M☉ transition from hosting fully convective interiors to configurations with a radiative core and outer convective envelope during their gravitational contraction. This stellar structure change influences the external magnetic field topology and, as we demonstrate herein, affects the coronal X-ray emission as a stellar analogue of the solar tachocline develops. We have combined archival X-ray, spectroscopic, and photometric data for ̃1000 PMS stars from five of the best studied star-forming regions: the Orion Nebula Cluster, NGC 2264, IC 348, NGC 2362, and NGC 6530. Using a modern, PMS calibrated, spectral type-to-effective temperature and intrinsic colour scale, we de-redden the photometry using colours appropriate for each spectral type, and determine the stellar mass, age, and internal structure consistently for the entire sample. We find that PMS stars on Henyey tracks have, on average, lower fractional X-ray luminosities (LX/L*) than those on Hayashi tracks, where this effect is driven by changes in LX. X-ray emission decays faster with age for higher mass PMS stars. There is a strong correlation between L* and LX for Hayashi track stars but no correlation for Henyey track stars. There is no correlation between LX and radiative core mass or radius. However, the longer stars have spent with radiative cores, the less X-ray luminous they become. The decay of coronal X-ray emission from young early K to late G-type PMS stars, the progenitors of main-sequence A-type stars, is consistent with the dearth of X-ray detections of the latter.
Original language | English |
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Pages (from-to) | 3836-3858 |
Number of pages | 23 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 457 |
Issue number | 4 |
Early online date | 2 Feb 2016 |
DOIs | |
Publication status | Published - Apr 2016 |
Keywords
- stars: coronae
- stars: evolution
- stars: interiors
- stars: magnetic field
- stars: pre-main-sequence
- X-rays: stars
ASJC Scopus subject areas
- Astronomy and Astrophysics