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Session 40 - The Environment of Stars: From Protostars to the Main Sequence.
Display session, Tuesday, June 11
We report the results of spectroscopic and photometric monitoring of the classical T Tauri star (CTTS) DQ Tau. Radial-velocity variations show DQ Tau to be a double-lined spectroscopic binary, one of only three spectroscopic binaries known amongst CTTSs (see also abstract on UZ Tau E by Mathieu et al.). We have determined an orbit solution for DQ Tau characterized by a large eccentricity (e = 0.58) and an orbital period of 15.8 days. The mass ratio is indistinguishable from unity.
During our photometric monitoring of this system over three observing seasons, we observed recurring flare-like brightening events (\sim0.5 mag in V). A Scargle periodogram analysis of these brightenings reveals a highly significant period that is, remarkably, identical to the binary orbital period. These brightening events are phased at or near periastron. Furthermore, as the system brightens, it becomes bluer (\DeltaV-I \approx -0.2 mag). We find this periodic photometric signature throughout our data, spanning \sim5000 days.
We find continuum veiling at low levels throughout the orbit. There is a suggestion in our data that enhanced continuum veiling accompanies the photometric brightening. The emission lines also sometimes brighten near periastron. In one case, the CaII IR triplet shows spectacular brightening and blue-shifted emission just after periastron.
DQ Tau's large infrared excess (K-N = 4.2 mag), IRAS fluxes, and millimeter-wave emission attest to the presence of a massive circumbinary disk. Thus, one possible interpretation for the photometric brightening and veiling is periodic accretion events fueled by the circumbinary disk. Recent theory suggests that accretion streams may occur in such highly eccentric systems. Alternatively, the flaring may be due to interacting magnetospheres; at periastron the stars are only a few stellar radii apart. In any case, our data strongly imply that the activity is directly connected to the orbital kinematics of the system.
Program listing for Tuesday