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Register a new userThe Inner Disk and Accretion Flow of the Close Binary DQ Tau
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We present multi-epoch optical and near-infrared (NIR) photometry and spectroscopy of the spectroscopic binary T Tauri star DQ Tau. The photometric monitoring, obtained using SMARTS ANDICAM, recovers the previously-seen correlation between optical flux and the 15.8-day binary orbital period, with blue flux peaks occurring close to most observed periastron passages. For the first time, we find an even more consistent correlation between orbital period and NIR brightness and color. The onset of pulse events in the NIR on average precedes those in the optical by a few days, with the rise usually starting near apastron orbital phase. We further obtained five epochs of spectroscopy using IRTF SpeX, with a wavelength range of 0.8 to 5 microns, and derived spectra of the infrared excess emission. The shape and strength of the excess varies with time, with cooler and weaker characteristic dust emission (T ~ 1100-1300 K) over most of the binary orbit, and stronger/warmer dust emission (T ~ 1600 K, indicative of dust sublimation) just before periastron passage. We suggest our results are broadly consistent with predictions of simulations of disk structure and accretion flows around close binaries, with the varying dust emission possibly tracing the evolution of accretion streams falling inwards through a circumbinary disk cavity and feeding the accretion pulses traced by the optical photometry and NIR emission lines. However, our results also show more complicated behavior that is not fully explained by this simple picture, and will require further observations and modeling to fully interpret.
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We present new ALMA observations of CO $J$=2$-$1 line emission from the DQ Tau circumbinary disk. These data are used to tomographically reconstruct the Keplerian disk velocity field in a forward-modeling inference framework, and thereby provide a dynamical constraint on the mass of the DQ Tau binary of $M_ast = 1.27_{-0.27}^{+0.46} ,M_odot$. Those results are compared with an updated and improved orbital solution for this double-lined system based on long-term monitoring of its stellar radial velocities. Both of these independent dynamical constraints on the binary mass are in excellent agreement: taken together, they demonstrate that the DQ Tau system mass is $1.21pm0.26,M_odot$ and that the disk and binary orbital planes are aligned within $3^circ$ (at 3$sigma$ confidence). The predictions of various theoretical models for pre-main sequence stellar evolution are also consistent with these masses, although more detailed comparisons are difficult due to lingering uncertainties in the photospheric properties of the individual components. DQ Tau is the third nearly equal-mass double-lined spectroscopic binary with a circumbinary disk that has been dynamically weighed with these two independent techniques: all show consistent results, validating the overall accuracy of the disk-based approach and demonstrating that it can be robustly applied to large samples of young, single stars as ALMA ramps up to operations at full capacity.
We present a photometric and spectroscopic study of HD 50526, an ellipsoidal binary member of the group Double Periodic Variable stars. Performing data-mining in photometric surveys and conducting new spectroscopic observations with several spectrographs during 2008 to 2015, we obtained orbital and stellar parameters of the system. The radial velocities were analyzed with the genetic PIKAIA algorithm, whereas Doppler tomography maps for the H$alpha$ and H$beta$ lines were constructed with the Total Variation Minimization code. An optimized simplex-algorithm was used to solve the inverse-problem adjusting the light curve with the best stellar parameters for the system. We find an orbital period of $6.701 pm 0.001 ~mathrm{d}$ and a long photometric cycle of $191 pm 2 ~mathrm{d}$. We detected the spectral features of the coldest star, and modeled it with a $log{g} = 2.79 pm 0.02 ~mathrm{dex}$ giant of mass $1.13 pm 0.02 ~mathrm{M_{odot}}$ and effective temperature $10500 pm 125 ~mathrm{K}$. In addition, we determine a mass ratio $q= 0.206 pm 0.033$ and that the hot star is a B-type dwarf of mass $5.48 pm 0.02 ~mathrm{M_{odot}}$. The $V$-band orbital light curve can be modeled including the presence of an accretion disk around the hotter star. This fills the Roche lobe of the hotter star, and has a radius $14.74 pm 0.02 ~mathrm{R_{odot}}$ and temperature at the outer edge $9400 ~mathrm{K}$. Two bright spots located in the disk account for the global morphology of the light curve. The Doppler tomography maps of H$alpha$ and H$beta$, reveal complex structures of mass fluxes in the system.
The young high-eccentricity binary DQ Tau exhibits powerful recurring millimeter-band (mm) flaring attributed to collisions between the two stellar magnetospheres near periastron, when the stars are separated by only ~8Rstar. These magnetospheric interactions are expected to have scales and magnetic field strengths comparable to those of large X-ray flares from single pre-main-sequence (PMS) stars observed in the Chandra Orion Ultradeep Project (COUP). To search for X-rays arising from processes associated with colliding magnetospheres, we performed simultaneous X-ray and mm observations of DQ Tau near periastron phase. We report here several results. 1) As anticipated, DQ Tau was caught in a flare state in both mm and X-rays. A single long X-ray flare spanned the entire 16.5 hour Chandra exposure. 2) The inferred morphology, duration, and plasma temperature of the X-ray flare are typical of those of large flares from COUP stars. 3) However, our study provides three lines of evidence that this X-ray flare likely arises from colliding magnetospheres: the chance of capturing a large COUP-like flare within the span of our observation is small; the relative timing of the X-ray and mm flares indicates the Neupert effect and is consistent with a common coronal structure; the size of the emitting coronal structure (4-5Rstar) inferred from our analysis (which is admittedly model-dependent and should be considered with caution) is comparable to half the binary separation. 4) The peak flare X-ray luminosity is in agreement with an estimate of the power dissipated by magnetic reconnection within the framework of a simple model of interacting magnetospheres.
We analyze the CoRoT and V-passband ground-based light curves of the interacting close binary AU Mon, assuming that there is a geometrically and optically thick accretion disk around the hotter and more massive star, as inferred from photometric and spectroscopic characteristics of the binary. Our model fits the observations very well and provides estimates for the orbital elements and physical parameters of the components and of the accretion disk.
We present a spectroscopic and photometric study of the Double Period Variable HD170582. Based on the study of the ASAS V-band light curve we determine an improved orbital period of 16.87177 $pm$ 0.02084 days and a long period of 587 days. We disentangled the light curve into an orbital part, determining ephemerides and revealing orbital ellipsoidal variability with unequal maxima, and a long cycle, showing quasi-sinusoidal changes with amplitude $Delta V$= 0.1 mag. Assuming synchronous rotation for the cool stellar component and semi-detached configuration we find a cool evolved star of $M_{2}$ = 1.9 $pm$ 0.1 $M_{odot}$, $T_{2}$ = 8000 $pm$ 100 $K$ and $R_{2}$ = 15.6 $pm$ 0.2 $R_{odot}$, and an early B-type dwarf of $M_{1}$ = 9.0 $pm$ 0.2 $M_{odot}$. The B-type star is surrounded by a geometrically and optically thick accretion disc of radial extension 20.8 $pm$ 0.3 $R_{odot}$ contributing about 35% to the system luminosity at the $V$ band. Two extended regions located at opposite sides of the disc rim, and hotter than the disc by 67% and 46%, fit the light curve asymmetries. The system is seen under inclination 67.4 $pm$ 0.4 degree and it is found at a distance of 238 $pm$ 10 pc. Specially interesting is the double line nature of HeI 5875; two absorption components move in anti-phase during the orbital cycle; they can be associated with the shock regions revealed by the photometry. The radial velocity of one of the HeI 5875 components closely follows the donor radial velocity, suggesting that the line is formed in a wind emerging near the stream-disc interacting region.
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