Magnetic Activity–Rotation–Age–Mass Relations in Late-pre-main-sequence Stars

Abstract

We study the four-dimensional relationships between magnetic activity, rotation, mass, and age for solar-type stars in the age range 5–25 Myr. This is the late-pre-main-sequence (l-PMS) evolutionary phase when rapid changes in a star's interior may lead to changes in the magnetic dynamo mechanisms. We carefully derive rotational periods and spot sizes for 471 members of several l-PMS open clusters using photometric light curves from the Zwicky Transient Facility. Magnetic activity was measured in our previous Chandra-based study, and additional rotational data were obtained from other work. Several results emerge. Mass-dependent evolution of rotation through the l-PMS phase agrees with astrophysical models of stellar angular momentum changes, although the data suggest a subpopulation of stars with slower initial rotations than commonly assumed. There is a hint of the onset of unsaturated tachoclinal dependency of X-ray activity on rotation, as reported by Argiroffi et al., but this result is not confidently confirmed. Both X-ray luminosity and starspot area decrease approximately as t −1 for solar-mass stars, suggesting that spot magnetic fields are roughly constant and l-PMS stars follow the universal solar-scaling law between the X-ray luminosity and surface magnetic flux. Assuming convective dynamos are dominant, theoretical magnetic fluxes fail to reveal the universal law for l-PMS stars that enter late Henyey tracks. Altogether we emerge with a few lines of evidence suggesting that the transition from the turbulent to solar-type dynamo occurs at the later stages of l-PMS evolution as stars approach the zero-age main sequence.

X-Ray, Near-ultraviolet, and Optical Flares Produced by Colliding Magnetospheres in the Young High-eccentricity Binary DQ Tau

“…The absence of evidence for long-term variability in the X-ray characteristic emission of the 1-million-year-old DQ Tau aligns with the notion that younger stars possess larger active regions and more extended X-ray coronal structures (Getman et al 2022b;Coffaro et al 2022;Getman et al 2023), which may mitigate the appearance of magnetic dynamo cycling.…”

The Evolution of Stellar X-Ray Activity and Angular Momentum as Seen by eROSITA, TESS, and Gaia

“…Such a surface-area effect could appear as an especially strong correlation with L X if the sample were entirely in the "saturated" regime, with roughly constant L X /L bol . We checked the distribution of L X /L bol for our sample, finding as expected that the stars of a given mass evolve within the age range of our sample (3-500 Myr; see Section 2) from a roughly fully saturated state to a non-fully saturated state (see also, e.g., Getman et al 2023). Therefore, we performed an alternate model fit to Equation (2) with surface area in place of L, finding that the resulting scatter of L X about the model is approximately the same.…”

“…One consequence of these behaviors is that it is possible, in principle, to estimate the ages of stars by measuring the strength of their X-ray emission (e.g., Getman et al 2023) or by measuring their rotation periods (e.g., Barnes 2003), assuming well-calibrated empirical relationships between stellar rotation, X-ray luminosity, and age as functions of basic stellar properties such as mass.…”

Methods for the Detection of Stellar Rotation Periods in Individual TESS Sectors and Results from the Prime Mission

“…It cannot be taken for granted that failure modes address all possible cases of aliasing and incorrect period detection in a LS formulation (e.g., Dawson & Fabrycky 2010). This has recently been noted in the search for spot-induced modulation in ground-based time-series data from the Zwicky Transient Facility (Getman et al 2023), which suggests particular caution using a ground-based data set as our training set. To a large degree, this is avoided in our pipeline by remeasuring groundtruth periods in the O18 data, assuming that the ground truth is a detection of rotation and not an alias.…”