On the simultaneous optical and near-infrared variability of pre-main sequence stars

Abstract

Abstract. For a complete understanding of the physical processes causing the photometric variability of pre-main sequence systems, simultaneous optical and near-IR observations are required to disentangle the emission from the stars and that from their associated circumstellar disks. Data of this sort are extremely rare and little systematic work has been reported to date. The work presented in this paper is a systematic attempt in this direction. It presents an analysis of the simultaneous optical and near-IR photometric variability of 18 Herbig Ae/Be and T Tauri stars which were observed in October 98 by the EXPORT collaboration. The time difference between the UBVRI and JHK measurements is less than 1 hour in ≈50% of the data and the largest difference is around 2 hours in only ≈10% of the data. Twelve stars appear to show a correlation between the optical and near-IR variability trends, which suggests a common physical origin such as spots and/or variable extinction. The optical and near-IR variability is uncorrelated in the rest of the objects, which suggests it originates in distinctly different regions. In general, the optical variability qualitatively follows the predictions of starspots or variable extinction. As far as the near-IR is concerned, the simultaneity of the observations demonstrates that for most objects the flux is largely produced by their circumstellar disks and, consequently, in many cases the near-IR fluctuations must be attributed to structural variations of such disks producing variations of their thermal emission and/or scattered light. The observed near-IR changes of up to around 1 mag on timescales of 1-2 days provide interesting challenges for understanding the mechanisms generating such remarkable variabilities, an issue insufficiently investigated until now but one which deserves further theoretical and modeling efforts.

Tracing the potential planet-forming regions around seven pre-main-sequence stars

“…A strongly collimated outflow was also found by Kwan & Tademaru (1988). DR Tau is photometrically and spectrally variable on short terms, i.e., in the range of weeks (ΔV = 1.3 mag; Grankin et al 2007;Eiroa et al 2002;Smith et al 1999). This variability is also ascribed to the formation and movement of stellar spots on this star (Ultchin et al 1997).…”

New low-mass members of the Lupus 3 dark cloud: Further indications of pre-main-sequence evolution strongly affected by accretion

“…3.1), are also expected as a consequence of accretion by the formation of hot spots in the surface. The origin of the near-infrared variability of Par-Lup3-4, although probably related also to accretion, may be somewhat different from that at visible wavelengths and related to changes in the inner regions of the accretion disk (Eiroa et al 2002). Nearinfrared monitoring of other star forming regions (Kaas 1999;Carpenter et al 2002) has shown that important variations in the K band, typically around 0.3 mag but reaching up to 1 mag for some sources, is common among young stellar objects, with a trend for larger amplitudes to be associated with stronger near-infrared excesses.…”

Spatially Resolved Spectroscopy of Sub-Au-Sized Regions of T Tauri and Herbig Ae/Be Disks

“…Our present nondetection indicates that the size scale of the K-band emission has varied significantly between 2003 and 2007. The source is also known to be photometrically variable at optical through infrared wavelengths (e.g., Herbst & Shevchenko 1999;Eiroa et al 2002).…”