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Register a new userAperture Synthesis Imaging of the Circumstellar Dust Disk Around DO Tauri
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We have detected the T~Tauri star, DO Tauri, in a 0.6$$-resolution VLA map of 43.3 GHz ($lambda$ = 7 mm) continuum emission. The 43 GHz flux density lies on the same power-law slope defined by 89 to 232 GHz measurements, F$_ u$ $propto u^{alpha}$ with index $alpha$ = 2.39$pm$0.23, confirming that the 43.3 GHz emission is thermal radiation from circumstellar dust. Upper limits to the flux densities at 8.4 and 22.5 GHz constrain the contribution of free-free emission from a compact ionized wind to less than 49%. The dust emissivity index, $beta$, is $0.39pm$0.23, if the emission is optically thin. Fitting a model of a thin circumstellar disk to the observed spectral energy distribution gives $beta = 0.6pm0.3$, consistent with the power-law derivation. Both values are substantially lower than is generally accepted for the interstellar medium, suggesting grain growth. Given the youth of DO Tau and the early evolutionary state of its circumstellar disk, this result implies that mm-size grains have already formed by the early T-Tauri phase.
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We have detected circumstellar molecular gas around a small sample of T Tauri stars through aperture synthesis imaging of CO(2-1) emission at ~2-3 resolution. RY Tauri, DL Tauri, DO Tauri, and AS 209 show resolved and elongated gaseous emission. For RY Tau, the deconvolved, half-maximum radius along the direction of elongation, PA~48deg, is 110 AU. Corresponding radii and orientations for the other sources are: DL Tau -- 250 AU at PA~84deg; DO Tau -- 350 AU at PA~160deg; AS 209 -- 290 AU at PA~138deg. RY Tau, DL Tau, and AS 209 show velocity gradients parallel to the elongation, suggesting that the circumstellar material is rotating. RY Tau and AS 209 also exhibit double-peaked spectra characteristic of a rotating disk. Line emission from DO Tau is dominated by high-velocity blue-shifted gas which complicates the interpretation. Nevertheless, there is in each case sufficient evidence to speculate that the circumstellar emission may arise from a protoplanetary disk similar to that from which our solar system formed.
We present the first detection and mapping of the HD 32297 debris disk at 1.3 mm with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). With a sub-arcsecond beam, this detection represents the highest angular resolution (sub)mm debris disk observation made to date. Our model fits to the spectral energy distribution from the CARMA flux and new Spitzer MIPS photometry support the earlier suggestion that at least two, possibly three, distinct grain populations are traced by the current data. The observed millimeter map shows an asymmetry between the northeast and southwest disk lobes, suggesting large grains may be trapped in resonance with an unseen exoplanet. Alternatively, the observed morphology could result from the recent breakup of a massive planetesimal. A similar-scale asymmetry is also observed in scattered light but not in the mid-infrared. This contrast between asymmetry at short and long wavelengths and symmetry at intermediate wavelengths is in qualitative agreement with predictions of resonant debris disk models. With resolved observations in several bands spanning over three decades in wavelength, HD 32297 provides a unique testbed for theories of grain and planetary dynamics, and could potentially provide strong multi-wavelength evidence for an exoplanetary system.
We present high-resolution imaging of the young binary T Tauri in 3 mm continuum emission. Compact dust emission with integrated flux density 50 +/- 6 mJy is resolved in an aperture synthesis map at 0.5 resolution and is centered at the position of the optically visible component, T Tau N. No emission above a 3 sigma level of 9 mJy is detected 0.7 south of T Tau N at the position of the infrared companion, T Tau S. We interpret the continuum detection as arising from a circumstellar disk around T Tau N and estimate its properties by fitting a flat-disk model to visibilities at wavelengths of 1 and 3 mm and to the flux density at 7 mm. Given the data, probability distributions are calculated for values of the free parameters, including the temperature, density, dust opacity, and the disk outer radius. The radial variation in temperature and density is not narrowly constrained by the data. The most likely value of the frequency dependence of the dust opacity, beta = 0.53^{+0.27}_{-0.17}, is consistent with that of disks around other T Tauri stars in which grain growth is believed to have taken place. The outer radius, R = 41^{+26}_{-14} AU, is smaller than the projected binary separation, and may indicate truncation of the disk. The total mass estimated for the disk, log(M/M_sun) = {-2.4}^{+0.7}_{-0.6}, is similar to masses observed around many young single sources and to the minimum nebular mass required to form a planetary system like our own. This observation strongly suggests that the presence of a binary companion does not rule out the formation of a sizeable planetary system.
We present results of high-resolution imaging toward HL Tau by the Combined Array for Research in Millimeter-wave Astronomy (CARMA). We have obtained 1.3 and 2.7 mm dust continua with an angular resolution down to 0.13 arc second. Through model fitting to the two wavelength data simultaneously in Bayesian inference using a flared viscous accretion disk model, we estimate the physical properties of HL Tau, such as density distribution, dust opacity spectral index, disk mass, disk size, inclination angle, position angle, and disk thickness. HL Tau has a circumstellar disk mass of 0.13 solar mass, a characteristic radius of 79 AU, an inclination of 40 degree, and a position angle of 136 degree. Although a thin disk model is preferred by our two wavelength data, a thick disk model is needed to explain the high mid- and far-infrared emission of the HL Tau spectral energy distribution. This could imply large dust grains settled down on the mid plane with fine dust grains mixed with gas. The HL Tau disk is likely gravitationally unstable and can be fragmented between 50 and 100 AU of radius. However, we did not detect dust thermal continuum supporting the protoplanet candidate claimed by a previous study using observations of the Very Large Array at 1.3 cm.
The circumstellar environments of classical T Tauri stars are challenging to directly image because of their high star-to-disk contrast ratio. One method to overcome this is by using imaging polarimetry where scattered and consequently polarised starlight from the stars circumstellar disk can be separated from the unpolarised light of the central star. We present images of the circumstellar environment of SU Aur, a classical T Tauri star at the transition of T Tauri to Herbig stars. The images directly show that the disk extends out to ~500 au with an inclination angle of $sim$ 50$^circ$. Using interpretive models, we derived very small grains in the surface layers of its disk, with a very steep size- and surface-density distribution. Additionally, we resolved a large and extended nebulosity in our images that is most likely a remnant of the prenatal molecular cloud. The position angle of the disk, determined directly from our images, rules out a polar outflow or jet as the cause of this large-scale nebulosity.
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