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We report the detection during the Chandra Orion Ultradeep Project(COUP) of two soft, constant, and faint X-ray sources associated with the Herbig-Haro object HH 210. HH 210is located at the tip of the NNE finger of the emission line system bursting out of the BN-KL complex, northwest of the Trapezium cluster in the OMC-1 molecular cloud. Using a recent Hαimage obtained with the ACSimager on board HST, and taking into account the known proper motions of HH 210emission knots, we show that the position of the brightest X-ray source, COUP 703, coincides with the emission knot 154-040a of HH 210, which is the emission knot of HH 210having the highest tangential velocity (425 km s-1). The second X-ray source, COUP 704, is located on the complicated emission tail of HH 210close to an emission line filament and has no obvious optical/infrared counterpart. Spectral fitting indicates for both sources a plasma temperature of ~0.8 MK and absorption-corrected X-ray luminosities of about 1030erg s-1(0.5–2.0 keV). These X-ray sources are well explained by a model invoking a fast-moving, radiative bow shock in a neutral medium with a density of ~12 000 cm-3. The X-ray detection of COUP 704therefore reveals, in the complicated HH 210region, an energetic shock not yet identified at other wavelengths.

Context.The soft X-ray emission from high density plasma observed in several CTTS is usually associated with the accretion process. However, it is still unclear whether this high density “cool” plasma is heated in the accretion shock, or if it is coronal plasma fed or modified by the accretion process.Aims.We conducted a coordinated quasi-simultaneous optical and X-ray observing campaign of the CTTS V2129 Oph. In this paper, we analyze Chandra grating spectrometer data and attempt to correlate the observed X-ray emitting plasma components with the characteristics of the accretion process and the stellar magnetic field constrained by simultaneous optical observations.Methods.We analyze a 200 ks Chandra/HETGS observation, subdivided into two 100 ks segments, of the CTTS V2129 Oph. For the two observing segments corresponding to two different phases within one stellar rotation, we measure the density of the cool plasma component and the emission measure distribution.Results.The X-ray emitting plasma covers a wide range of temperatures: from 2 up to 34 MK. The cool plasma component of V2129 Oph(T≈ 3−4 MK) varies between the two segments of the Chandra observation: during the first observing segment high density plasma (\hbox{$\log N_{\rm e} = 12.1^{+0.6}_{-1.1}$}) with high EMat ~3−4 MK is present, whereas, during the second segment, this plasma component has lower EMand lower density (log Ne< 11.5), although the statistical significance of these differences is marginal. Hotter plasma components, T≥ 10 MK, vary on short timescales (~10 ks), which are typical of coronal plasma. A clear flare, detected during the first segment, might be located in a large coronal loop (half length >3 R⋆). Conclusions.Our observation provides additional confirmation that the dense cool plasma at a few MK in CTTS is material heated in the accretion shock. The variability of this cool plasma component on V2129 Ophmay be explained in terms of X-rays emitted in the accretion shock and seen with different viewing angles at the two rotational phases probed by our observation. In particular, during the first time interval a direct view of the shock region is possible, while, during the second, the accretion funnel itself intersects the line of sight to the shock region, preventing us from observing the accretion-driven X-rays.

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 $R_\star$. 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 $R_\star$(~13 $R_\odot$). 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 $R_\star$. 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.