Near-Infrared Variability of Classical T Tauri Stars as the Result of Changes in Their Mass Accretion Rates

Fernández, M.
Protostars and Planets V, Proceedings of the Conference held October 24-28, 2005, in Hilton Waikoloa Village, Hawai'i. LPI Contribution No. 1286., p.8089


The broad-band near-infrared (JHK) variability of classical T Tauri stars seems to show the same irregular pattern than the variability that has often been observed at visible wavelengths. The same, however, cannot be said about the behaviour of the amplitude versus wavelength: in the visible range the amplitude decreases towards longer wavelengths, as expected from the stellar spots that dominate the variability, while near-infrared observations sometimes show the opposite
A quantitative analysis of 35 stars, whose near-infrared amplitudes increase towards longer wavelengths, has been carried out. All the data have been taken from the literature. From the comparison with the catalog of accretion disk models of D’Alessio et al. (2005), we can conclude that this type of near-infrared variability can be explained as due to changes of the mass accretion rates of the stars.
We also show that stars can change from this type of variability to variability due to stellar spots or inhomogeneous obscurations with time scales of days, or even longer. In the two best examples of such a change, the variability related to the mass accretion rate takes place at high brightness levels of the K band of the stars.
From the comparison with the above mentioned theoretical models we can also conclude that different amplitudes are expected for inclination angles of the disks of 30 and 60 degrees, and that the maximum amplitude of the variability will be observed between 4.5 and 8 m, depending on the disk and stellar parameters. The new mid-infrared utilities will allow to confirm this prediction.