Spots, flares, accretion, and obscuration in the pre-main sequence binary DQ Tau

TL;DR

This study analyzes multi-wavelength light curves of the young binary DQ Tau, revealing stellar spots, flares, accretion bursts, and obscuration events, providing insights into the complex variability and disk interactions in pre-main sequence binaries.

Contribution

It presents a comprehensive analysis of DQ Tau's variability, including the first detailed modeling of stellar spots, accretion behavior, and disk structure in this binary system.

Findings

Detected 40 stellar flares with energies up to 1.2×10^{35} erg.

Observed increased accretion rates around periastron.

Inner disk radius measured at 0.13 au, in corotation with the binary orbit.

Abstract

DQ Tau is a young low-mass spectroscopic binary, consisting of two almost equal-mass stars on a 15.8 d period surrounded by a circumbinary disk. Here, we analyze DQ Tau's light curves obtained by Kepler K2, the Spitzer Space Telescope, and ground-based facilities. We observed variability phenomena, including rotational modulation by stellar spots, brief brightening events due to stellar flares, long brightening events around periastron due to increased accretion, and short dips due to brief circumstellar obscuration. The rotational modulation appears as sinusoidal variation with a period of 3.017 d. In our model this is caused by extended stellar spots 400 K colder than the stellar effective temperature. During our 80-day-long monitoring we detected 40 stellar flares with energies up to 1.2$\times$10$^{35}$ erg and duration of a few hours. The flare profiles closely resemble those in older late-type stars, and their occurrence does not correlate with either the rotational or the orbital period. We observe elevated accretion rate up to 5$\times$10$^{-8} M_{\odot}$ yr$^{-1}$ around each periastron. Our Spitzer data suggests that the increased accretion luminosity heats up the inner part of the circumbinary disk temporarily by about 100 K. We found an inner disk radius of 0.13 au, significantly smaller than expected from dynamical modeling of circumbinary disks. Interestingly, the inner edge of the disk is in corotation with the binary's orbit. DQ Tau also shows short dips of < 0.1 mag in its light curve, reminiscent of the well-known "dipper phenomenon" observed in many low-mass young stars.