We combined observations form the Spitzer and the Kepler space telescopes with measurements from ground-based facilities (CFHT, Konkoly Observatory, Telescopio Carlos Sanchez) to analyze its short-term and long-term photometric and spectroscopic variations. Our study revealed stochastic photometric variability on daily and hourly timescales, with mid-IR observations suggesting an optically thick and invariable inner disk. We also analyzed the high-resolution emission line profiles to disentangle variations in the accretion rate, wind, and turbulence. We found that the significance of the physical mechanisms causing the observed variability changes over time.

ADS link: Zsidi, G; Kóspál, Á; Ábrahám, P. et al (2025)

We analyzed high-resolution spectroscopy in eight different epochs, as well as ground-based and space-borne multiepoch optical and infrared photometry of WX Cha, a binary T Tauri system, with an almost edge-on disk (i = 87°) in the Chamaeleon I star-forming region. 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 speculate 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.

ADS link: Fiorellino, E; Zsidi, G. Kóspál, Á. et al. (2022)

We combined high-resolution spectroscopic monitoring observations with high-cadence and multifilter photometric measurements in order to study the variability of the the T Tauri system CR Cha. These revealed periodic brightness changes due stellar rotation, and also more stochastic accretion-related variations. We were also able to study the accretion process on timescales from hours to a decade by including earlier data from the AAT/UCLES and the HARPS instruments. These show that the accretion variations increase on timescales from hours to days/weeks, after which it saturates, and the overall accretion variability is within the factor of ~3 on timescales of a decade.

ADS link: Zsidi, G; Manara, C. F; Kóspál, Á; et al (2022)

DQ Tau is a young low-mass spectroscopic binary, consisting of two almost equal-mass stars on a 15.8 day period surrounded by a circumbinary disk. The system shows complex photomertic behavior 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 system also shows interesting long periastron brightening events due to increased accretion. This pulsed accretion occurs because the stars gravitationally perturb the inner edge of the circumbinary disk during each apoapsis passage and pull some material from the disk that eventually lands on the binary components

ADS link: Kóspál, Á; Ábrahám, P; Zsidi, G. et al. (2018)