Recurring millimeter flares as evidence for star-star magnetic reconnection events in the DQ Tauri PMS binary system

Abstract

Observations of the T Tauri spectroscopic binary DQ Tau in April 2008 captured an unusual flare at 3 mm, which peaked at an observed maximum flux of ∼0.5 Jy (about 27 times the quiescent value). Here we present follow-up millimeter observations that demonstrate a periodicity to the phenomenon. While monitoring 3 new periastron encounters, we have detected flares within 17.5 h (or 4.6%) of the orbital phase of the first reported flare and constrained the main emitting region to a stellar height of 3.7-6.8 R . The recorded activity is consistent with the proposed picture for synchrotron emission initiated by a magnetic reconnection event when the two stellar magnetospheres of the highly eccentric (e = 0.556) binary are believed to collide near periastron as the stars approach a minimum separation of 8 R (∼13 R ). The similar light curve decay profiles allow us to estimate an average flare duration of 30 h. Assuming one millimeter flare per orbit, DQ Tau could spend approximately 8% of its 15.8-day orbital period in an elevated flux state. These findings continue to serve as a small caution for millimeter flux points in spectral energy distributions that could contain unrecognized flare contributions. Our analysis of the millimeter emission provides an upper limit of 5% on the linear polarization. We discuss the extent to which a severely entangled magnetic field structure and Faraday rotation effects are likely to reduce the observed polarization fraction. We also predict that, for the current picture, the stellar magnetospheres must be misaligned at a significant angle or, alternatively, that the topologies of the outer magnetospheres are poorly described by a well-ordered dipole inside a radius of 7 R . Finally, to investigate whether reorganization of the magnetic field during the interaction affects mass accretion, we also present simultaneous optical (VRI) monitoring of the binary, as an established tracer of accretion activity in this system. We find that an accretion event can occur coincident in both time and duration with the synchrotron fallout of a magnetic reconnection event. While the pulsed accretion mechanism has been attributed previously to the dynamical motions of the stars alone, the similarities between the millimeter and optical light curves evoke the possibility of a causal or co-dependent relationship between the magnetospheric and dynamical processes.

Hunting for millimeter flares from magnetic reconnection in pre-main sequence spectroscopic binaries

“…In this half of the sample, the binary components are suspected to undergo a change in their large-scale magnetospheric topology as the binary separation distance varies greatly and rapidly near periastron. This group is most likely to experience a merging of the two magnetospheres near closest approach with a subsequent detachment at larger separations -much like the current picture for DQ Tau (Salter et al 2010). Although we note that none of the targets quite approach the exceptional combination of large eccentricity and close approach as DQ Tau (with its e = 0.556 and d min = 13 R ).…”

“…In the case of the WTTS binary system V773 Tau A, two separate coronal structures extending to ≥15 R each are necessary to bridge the interbinary gap (Massi et al 2008). Toward DQ Tau the derived loop lengths from both X-ray and millimeter analyses are 5 R in height Salter et al 2010). If the giant X-ray flare statistics correctly predict a common oncea-week occurrence with consistently large loop lengths, then more interbinary collisions might be expected in a number of close-separation binaries, in addition to any single-star events that may occur.…”

“…Powerful, transient millimeter flares attributed to synchrotron continua have now been reported toward two embedded protostars in the Corona Australis cloud (Choi et al 2009), one protostar in the Orion BN/KL star-forming region (Forbrich et al 2008), the embedded YSO GMR-A in Orion (Bower et al 2003;Furuya et al 2003), the classical T Tauri star (CTTS) DQ Tau in Taurus (Salter et al 2008(Salter et al , 2010, and the weak-line T Tauri star (WTTS) V773 Tau A, also in Taurus (Massi et al 2002(Massi et al , 2006(Massi et al , 2008.…”

“…Since in both the DQ Tau and UZ Tau E cases, optical brightenings are common near periastron due to periodic accretion events (Jensen et al 2007), and because the optical light curve of DQ Tau was found to mirror its millimeter flare activity in both time and duration (Salter et al 2010), we complemented our millimeter data with simultaneous optical monitoring of our targets.…”

Analysis of combined radial velocities and activity of BD+20 1790: evidence supporting the existence of a planetary companion

“…It is well established that binary stars are more active than the same spectral type and age single active stars (Glebocki et al 1986;Ayres & Linsky 1980). Extensive literature has shown significant chromospheric and coronal activity (Siarkowski et al 1996;Ferreira 1998), and spectacular flare activity, in some cases occurring even in the inter-binary space and during periastron (Graffagnino et al 1995;Massi et al 2002Massi et al , 2008Salter et al 2010). Rotationally modulated flares have been found to occur in A66, page 10 of 16 several binary systems (García-Álvarez et al 2003;Doyle et al 1990).…”