Accretion and Extinction Variations in the Low-mass Pre-main-sequence Binary System WX Cha

Light curves of young star systems show photometric variability due to different kinematic and physical processes. One of the main contributors to the photometric variability is the changing mass accretion rate, which regulates the interplay between the forming young star and the protoplanetary disk. We collected high-resolution spectroscopy in eight different epochs, as well as ground-based and space-borne multiepoch optical and infrared photometry of WX Cha, an MO binary system, with an almost edge-on disk (i = 87 degrees) in the Chamaeleon I star-forming region. Spectroscopic observations cover 72 days, the ground-based optical monitoring covers 42 days while space-borne TESS photometry extends for 56 days. The multiwavelength light curves exhibit quasi-periodic variability of 0.35-0.53 mag in the near-infrared, and of 1.3 mag in the g band. We studied the variability of selected emission lines that trace the accretion, computed the accretion luminosity and the mass accretion rate using empirical relations, and obtained values between L-acc similar to 1.6 L-circle dot - 3.2 L-circle dot and (M) over dot(acc) similar to 3.31 x 10(-7) M-circle dot yr(-1) - 7.76 x 10(-7) M-circle dot yr(-1). Our results show that WX Cha is accreting at a rate larger than what is typical for T Tauri stars in the same star-forming region with the same stellar parameters. We theorize that this is due to the higher disk mass of WX Cha than what is usual for stars with similar stellar mass and to the binary nature of the system. Daily changes in the accretion luminosity and in the extinction can explain the photometric variability.

Automated summary

Light curves of young star systems show photometric variability mainly due to changing mass accretion rate. In this study, we conducted optical and infrared photometry measurements of the MO binary system WX Cha, which has an almost edge-on disk. We calculated the accretion luminosity and mass accretion rate and found that WX Cha has a higher accretion rate compared to T Tauri stars in the same star-forming region. We propose that this is due to the higher disk mass and the binary nature of the system. Daily changes in the accretion luminosity and extinction can explain the observed photometric variability.