The Evolution of X-Ray Emission in Young Stars

By T. Preibisch, Eric D. Feigelson. 2005

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The evolution of magnetic activity in late-type stars is part of the intertwined rotation-age-activity relation, which provides an empirical foundation to the theory of magnetic dynamos. We study the age-activity relation in the pre-main-sequence (PMS) regime, for the first time using mass-stratified subsamples. The effort is based on the Chandra Orion Ultradeep Project (COUP), which provides very sensitive and homogenous X-ray data on a uniquely large sample of 481 optically well-characterized low-extinction low-mass members of the Orion Nebula Cluster, for which individual stellar masses and ages could be determined. More than 98% of the stars in this sample are detected as X-ray sources. Within the PMS phase for stellar ages in the range ~0.1-10 Myr, we establish a mild decay in activity with stellar age τ roughly as LX ∝ τ-1/3. On longer timescales, when the Orion stars are compared to main-sequence stars, the X-ray luminosity decay law for stars in the 0.5 M☉ < M < 1.2 M☉ mass range is more rapid with LX ∝ τ-0.75 over the wide range of ages 5 yr < log τ < 9.5 yr. When the fractional X-ray luminosity LX/Lbol and the X-ray surface flux are considered as activity indicators, the decay law index is similarly slow for the first 1-100 Myr but accelerates for older stars. The magnetic activity history for M stars with masses 0.1 M☉ < M < 0.4 M☉ is distinctly different. Only a mild decrease in X-ray luminosity, and even a mild increase in LX/Lbol and FX, is seen over the 1-100 Myr range, though the X-ray emission does decay over long timescales on the main sequence. Together with COUP results on the absence of a rotation-activity relation in Orion stars, we find that the activity-age decay is strong across the entire history of solar-type stars but is not attributable to rotational deceleration during the early epochs. A combination of tachocline and distributed convective dynamos may be operative in young solar-type stars. The results for the lowest mass stars are most easily understood by the dominance of convective dynamos during both the PMS and main-sequence phases.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/3c1a09b4a395ba5a512c249b7eac2c14a15def42

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Citations in the corpus

X-ray emission from T Tauri stars and the role of accretion: inferences from the XMM-Newton extended survey of the Taurus molecular cloud (2006, methodology): “Preibisch & Feigelson (2005) reported correlations consistent with ours, applying the EM algorithm to the ONC data.”
TOWARD A UNIFICATION OF STAR FORMATION RATE DETERMINATIONS IN THE MILKY WAY AND OTHER GALAXIES (2011, background): “…exhibit powerful convectively-driven magnetic reconnection flaring activity, hence they are 102–103 times more luminous in X-rays than older Galactic field stars, and their X-ray luminosity LX is broadly correlated with bolometric luminosity and hence stellar mass (Preibisch & Feigelson 2005).”
The coronal X-ray - age relation and its implications for the evaporation of exoplanets (2011, result): “However we note that more recent studies, e.g. Soderblom, Duncan & Johnson (1991), Pace & Pasquini (2004), Preibisch & Feigelson (2005) find faster rates for the rotational frequency evolution, mostly in the ranget−0.65 − t−0.75, which is similar to thet−0.61 relation we find assuming anLX/Lbol ∝…”
A CATALOG OF X-RAY POINT SOURCES FROM TWO MEGASECONDS OF CHANDRA OBSERVATIONS OF THE GALACTIC CENTER (2008, background): “Pre–main-sequence (PMS) stars are X-ray sources because of their enhanced magnetic activity (Preibisch & Feigelson 2005).”
Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics (2008, background): “For a brief discussion regarding converting ROSAT and Chandra fluxes, see Preibisch & Feigelson (2005).”
HAZMAT. I. THE EVOLUTION OF FAR-UV AND NEAR-UV EMISSION FROM EARLY M STARS (2014, background): “This is similar behavior to X-ray data (Preibisch & Feigelson 2005).”
IDENTIFYING THE YOUNG LOW-MASS STARS WITHIN 25 PC. I. SPECTROSCOPIC OBSERVATIONS (2009, methodology): “X-ray emission of M dwarfs declines almost linearly in log– log space from ∼1 Myr to the about 650 Myr, the age of the Hyades, with a more rapid drop off after that (Preibisch & Feigelson 2005).”
Stellar Activity on the Young Suns of Orion: COUP Observations of K5-7 Pre-Main-Sequence Stars (2005, background): “Our slower evolution within the COUP age range was also found in the COUP study of Preibisch & Feigelson (2005).”
The Sun in Time: Activity and Environment (2007, background): “A shallower decay was reported by Preibisch and Feigelson (2005) for the same stellar cluster, with an exponent between −0.2 and −0.5, but when considering normalized LX/Lbol or average surface X-ray flux, then both Feigelson et al.’s and Preibisch & Feigelson’s studies indicate that the LX decay…”
Our astrochemical heritage (2012, background): “Last but not least, the study of other small clouds and young Sun-like stars in our Galaxy gives a wide range of possible outcomes of star and planet formation, and we would like to understand why the Solar System and the Earth chose one of them.”
A Perspective from Extinct Radionuclides on a Young Stellar Object: The Sun and Its Accretion Disk (2011, background): “For pre–main sequence stars in the age range of 0.1–10 Myr and the solar mass range of 0.1 M 2 M , the luminosity decreases slightly with stellar age according to , whereas the decrease is more rapid over longer timescales (Preibisch & Feigelson 2005).”
A Spitzer Space Telescope Study of Disks in the Young σ Orionis Cluster (2007, methodology): “Therefore, X-ray emission can be used as an additional criterion supporting membership in young stellar groups (e.g., Carkner et al. 1998; Preibisch & Feigelson 2005; Franciosini et al. 2006).”