DQ Tau Research Articles

INTERFEROMETRIC EVIDENCE FOR RESOLVED WARM DUST IN THE DQ TAU SYSTEM

We report on near-infrared (IR) interferometric observations of the double-lined pre-main sequence binary system DQ Tau. We model these data with a visual orbit for DQ Tau supported by the spectroscopic orbit and analysis of Mathieu et al. Further, DQ Tau exhibits significant near-IR excess; modeling our data requires inclusion of near-IR light from an source. Remarkably, the excess source is resolved in our data, similar in scale to the binary itself (~0.2 AU at apastron), rather than the larger circumbinary disk (~0.4 AU radius). Our observations support the Mathieu et al. and Carr et al. inference of significant warm material near the DQ Tau binary.

Captured at millimeter wavelengths: a flare from the classical T Tauri star DQ Tauri

For several hours on 2008 April 19, the T Tauri spectroscopic binary DQ Tau was observed to brighten, reaching a maximum detected flux of 468 mJy and likely making it (briefly) the brightest object at 3mm in the Taurus star-forming region. We present the light curve of a rarely before observed millimeter flare originating in the region around a pre-main-sequence star, and the first from a classical T Tauri star. We discuss the properties and nature of the flaring behavior in the context of pulsed accretion flows (the current picture based largely on studies of this object's optically variable spectrum), as well as magnetospheric re-connection models (a separate theory that predicts millimeter flares for close binaries of high orbital eccentricity). We believe that the flare mechanism is linked to the binary orbit, and therefore periodic. DQ Tau makes a strong case for multi-wavelength follow-up studies, performed in parallel, of future flares to help determine whether magnetospheric and dynamical interactions in a proto-binary system are independent.

Forbidden Line Emission in the Eccentric Spectroscopic Binaries DQ Tauri and UZ Tauri E Monitored over an Orbital Period

We present echelle spectroscopy of the close pre-main-sequence binary star systems DQ Tau and UZ Tau-E. Over a 16 day time interval we acquired 14 nights of spectra for DQ Tau and 12 nights of spectra for UZ Tau-E. This represents the entire phase of DQ Tau, and 63 percent of the phase of UZ Tau-E. As expected, photospheric lines such as Li I 6707 clearly split into two components as the primary and secondary orbit one another, as did the permitted line He I 5876. Unlike the photospheric features, the forbidden lines of [O I] 6300 and [O I] 5577, retain the same shape throughout the orbit. Therefore these lines must originate outside of the immediate vicinity of the two stars and any circumstellar disks that participate in the orbital motion of the stars.

The pre-main sequence spectroscopic binary UZ Tau East: Improved orbital parameters and accretion phase dependence

We present radial-velocity measurements obtained using high- and intermediate-resolution spectroscopic observations of the classical T Tauri star UZ Tau East from 1994 to 1996. We also provide measurements of H α equivalent widths and optical veiling. Combining our radial-velocity data with those recently reported by Prato et al. (2002), we improve the orbital elements for this spectroscopic binary. The orbital period is $18.979\pm0.007$ days and the eccentricity is $e=0.14$. We find variability in the H α emission and veiling, signposts of accretion, but at periastron passage the accretion is not as clearly enhanced as in the case of the binary DQ Tau. The difference in the behaviour of these two binaries is consistent with the hydrodynamical models of accretion from circumbinary disks because UZ Tau East has lower eccentricity than DQ Tau. It seems that enhanced periastron accretion may occur only in systems with very high eccentricity ($e>0.5$).

Evolution of irradiated circumbinary disks

We study the evolution and emission of circumbinary disks around close classical T Tauri binary systems. High resolution numerical hydrodynamical simulations are employed to model a system consisting of a central eccentric binary star within an irradiated accretion disk. A detailed energy balance including viscous heating, radiative cooling and irradiation from the central star is applied to calculate accurately the emitted spectral energy distribution. Numerical simulations using two different methods, the previously developed Dual-Grid technique with a finite difference discretization, and the Smoothed Particle Hydrodynamics method are employed to compare the hydrodynamical features and strengthen our conclusions. Physical parameters of the setup are chosen to model the close systems of DQ Tau and AK Sco. Using the self-consistent models, we are able to fit the observed spectral energy distributions by constraining parameters such as disk mass, density profile and radial extension for those systems. We find that the incorporation of irradiation effects is necessary to obtain correct disk temperatures.

The pre-main sequence spectroscopic binary AK Scorpii revisited

We present an analysis of 32 high-resolution echelle spectra of the pre-main sequence spectroscopic binary AK Sco obtained during 1998 and 2000, as well as a total of 72 photoelectric radial-velocity observations from the period 1986-1994. These data allow considerable improvement of the period and other orbital parameters of AK Sco. Our analysis also includes eight series of photometric observations in the uvby and Geneva seven-color systems from 1987, 1989, 1990, 1992, 1994 and 1997. No eclipses or other periodic variations are seen in the photometry, but the well-determined HIPPARCOS parallax allows us to constrain the orbital inclination of the system to the range 65 < i< 70, leading to the following physical parameters for the two near-identical stars: M= 1:35 0:07 M, R= 1:59 0:35 R ,a ndv sin i= 18:5 1: 0k m s 1 . Disk models have been fit to the spectral energy distribution of AK Sco from 350 nm to 1100 m. The above stellar parameters permit a consistent solution with an inner rim temperature of 1250 K, instead of the usual 1500 K corresponding to the dust evaporation temperature. Dynamical eects due to tidal interaction of the binary system are supposed to be responsible for pushing the inner disk radius outwards. Combining simultaneous photometric and spectroscopic data sets allows us to compute the dust obscuration in front of each star at several points over the orbit. The results demonstrate the existence of substructure at scales of just a single stellar diameter, and also that one side of the orbit is more heavily obscured than the other. The spectrum of AK Sco exhibits emission and absorption lines that show substantial variety and variability in shape. The accretion-related lines may show both outflow and infall signatures. The system displays variations at the binary orbital period in both the photospheric and accretion-related line intensities and equivalent widths, although with appreciable scatter. The periodic variations in the blue and red wing of H are almost 180 out of phase. We find no evidence of enhanced accretion near the periastron passage in AK Sco as expected theoretically and observed previously in DQ Tau, a similarly young binary system with a mass ratio near unity and an eccentric orbit. The H equivalent width displays rather smooth variations at the stellar period, peaking around phases 0.6-0.7, far away from periastron where theory expects the maximum accretion rate to occur.

Circumbinary disk evolution

We study the evolution of circumbinary disks surrounding classical T Tau stars. High resolution numerical simulations are employed to model a system consisting of a central eccentric binary star within an accretion disk. The disk is assumed to be infinitesimally thin, however a detailed energy balance including viscous heating and radiative cooling is applied. A novel numerical approach using a parallelized Dual-Grid technique on two different coordinate systems has been implemented. Physical parameters of the setup are chosen to model the close system of DQ Tau and AK Sco, as well as the wider systems of GG Tau and UY Aur. Our main findings are for the tight binaries a substantial flow of material through the disk gap which is accreted onto the central stars in a phase dependent process. We are able to constrain the parameters of the systems by matching both accretion rates and derived spectral energy distributions to observational data where available.

Evidence for Residual Material in Accretion Disk Gaps: CO Fundamental Emission from the T Tauri Spectroscopic Binary DQ Tauri

Abstract : We present the discovery of CO fundamental rovibrational emission from the classical T Tauri spectroscopic binary DQ Tau. The high-resolution infrared echelle spectra reveal emission lines from both the gamma = 1 and gamma = 2 vibrational levels with line widths of roughly 70 km s(exp -1). The average CO excitation temperature is approximately 1200 K. We model the spectra as arising from gas in Keplerian rotation about the center of mass of the binary. The disk model requires gas with an average surface density of 5x10(exp -4) g sq cm that extends outward to 0.5 plus or minus 0.1 AU and inward to at least 0.1 AU from the center of mass. The radial extent for the emitting gas is close to the predicted size of the gap in the DQ Tau accretion disk that is expected to be dynamically cleared by the binary. We interpret these results, and previous modeling of DQ TauSs spectral energy distribution, as evidence for a small amount (~10(exp 10) M circle dot solar of diffuse material residing within the optically thin disk gap. Thus, dynamical clearing has not been completely efficient in the DQ Tau binary. We suggest that the material is associated with a flow from the circumbinary disk which feeds the ongoing accretion at the stellar surfaces.

A Brief Introduction to DQ Tau

We review the salient observational properties of DQ Tau, with an emphasis on the photometric and spectroscopic time-variability of the system. We summarize the evidence for this variability being linked to the orbital dynamics of the underlying close, eccentric, binary.

Lunar Occultations of Young Stars in Southern Taurus

We have obtained lunar occultation observations of NTT 042916+1751, V826 Tau, L1551-55, HN Tau, DQ Tau, and DR Tau by high-speed single-channel photometry in the IR K band. We detect no companions in the angular separation range 0020–10'' to a magnitude limit typically 2 mag fainter than the target. Additional occultation observations of GG Tau and HL Tau using IR cameras at K reveal no new stars in the GG Tau A binary within ~2 mag of the primary in the range ~008–10'' and no companion of HL Tau within 1.5 mag and ~009–10''. The binary fraction of the 56 systems in the Taurus star formation region that have been surveyed by lunar occultation and imaging is 61%. Of the 56 systems, 53 have been surveyed for companions in the angular separation range 0020–10''. Their binary frequency is at least 1.4 ± 0.3 times that measured by Duquennoy & Mayor for the nearby F and G stars. These values for the binary frequency are lower bounds because they contain no corrections for incompleteness.

The Classical T Tauri Spectroscopic Binary DQ Tau. II. Emission Line Variations with Orbital Phase.

view Abstract Citations (78) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Classical T Tauri Spectroscopic Binary DQ Tau. II. Emission Line Variations with Orbital Phase. Basri, Gibor ; Johns-Krull, Christopher M. ; Mathieu, Robert D. Abstract We report on echelle observations of a variety of line profiles taken throughout the orbit of the close, eccentric binary T Tauri system DQ Tau. The stars themselves exhibit puzzling inconsistencies in the spectral types inferred from atomic vs. molecular lines. The system shows clear evidence of an extensive circumbinary disk. The binary is expected to clear a central hole in the disk, however the line profiles are similar to those from single classical T Tauri stars. This indicates that similar infall and outflow activities are taking place. The implication is that material is flowing through the supposed gap in the disk. It also means that these ``classical'' profiles do not require a stable circumstellar disk for their formation, since the stellar separation at periastron is too small to allow such disks. We present evidence that accretion increases (sometimes dramatically) as the stars approach each other. Both continuum veiling and emission line intensities can increase. In one outburst the \caII IR lines brighten by a factor of 5. We discuss the line profiles during such outbursts in some detail. Along with increased accretion, the lines sometimes also imply high velocity outflows. Given the fact that outbursts can occur as much as 0.15 in phase away from closest approach, we favor accretion over direct magnetospheric interactions as the power source of the outbursts. Away from each other, the stars resemble moderate- to low-activity classical T Tauri stars. There is evidence that some material is stored near the stars and ingested throughout the orbit. These observations are generally consistent with a model for disks in binary systems proposed by \cite{al96}. The importance of this system is that it provides empirical support for continuing accretion through dynamical tidal gaps in disks. It demonstrates that very close binaries can be classical T Tauri systems. Publication: The Astronomical Journal Pub Date: August 1997 DOI: 10.1086/118510 Bibcode: 1997AJ....114..781B Keywords: STARS: PRE-MAIN SEQUENCE; BINARIES: SPECTROSCOPIC; CIRCUMSTELLAR MATTER full text sources ADS | data products SIMBAD (6) Related Materials (1) Part 1: 1997AJ....113.1841M

The Classical T Tauri Spectroscopic Binary DQ Tau.I.Orbital Elements and Light Curves

view Abstract Citations (157) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Classical T Tauri Spectroscopic Binary DQ Tau.I.Orbital Elements and Light Curves Mathieu, Robert D. ; Stassun, Keivan ; Basri, Gibor ; Jensen, Eric L. N. ; Johns-Krull, Christopher M. ; Valenti, J. A. ; Hartmann, L. W. Abstract We report the discovery that the classical T Tauri star DQ Tan is a double-lined spectroscopic binary. The orbital period is 15.804 days, with a large orbital eccentricity e=0.556. The mass ratio is 0.97±0.15. We have monitored DQ Tau photometrically over two observing seasons and observed recurring episodes during which the stars get brighter (≍0.5 mag in V) and bluer (≍-0.2 mag in V-I). When combined with photometry in the literature (time span ≍5000 days), a Scargle periodogram analysis reveals a highly significant periodicity of 15.80 days, essentially identical to the binary orbital period. These brightening events occur shortly before or at periastron passage. They occur during at least 65% of periastron passages, but not during all periastron passages. DQ Tau is surrounded by a circumbinary disk with mass of 0.002-0.02 Msun. The infrared spectral energy distribution resembles a power law from 1 to 60 μm. Remarkably, there is no paucity of near-infrared emission indicative of the inner disk having been cleared by the binary; there is clearly warm material within the binary orbit. We interpret the brightening events as due to a variable mass accretion rate regulated by the binary orbit. The periodic brightenings, the associated increases in emission line strength and veiling reported in an accompanying paper [Basri et al., submitted (1997)], and the circumstellar material together are consistent with a recent theoretical finding that circumbinary disk material can stream across a binary orbit at certain orbital phases, resulting in a pulsed accretion flow onto the stars [Artymowicz & Lubow, ApJ, 467, L77 (1996)]. The theoretically predicted phase of maximum accretion rate is shortly before periastron, in good agreement with the phasing of the brightenings of DQ Tan. At the same time the periastron separation is smaller than the inferred stellar magnetospheric radii of classical T Tauri stars, so that such magnetospheres would interact at each periastron passage. The magnetic energies are plausibly adequate to power the brightenings. However, the strongly enhanced continuum veiling and long duration of some of the brightenings are not naturally explained in a pure flaring scenario. Nonetheless, magnetospheres likely play a role in the detailed accretion flow near the stars. Publication: The Astronomical Journal Pub Date: May 1997 DOI: 10.1086/118395 Bibcode: 1997AJ....113.1841M Keywords: STARS: INDIVIDUAL: DQ TAU; BINARIES: SPECTROSCOPIC full text sources ADS | data products SIMBAD (3) Related Materials (1) Part 2: 1997AJ....114..781B