GG Tauri: the fifth element Di Folco, E.; Dutrey, A.; Le Bouquin, J.-B. ...
Astronomy and astrophysics (Berlin),
05/2014, Volume:
565
Journal Article
Peer reviewed
Open access
We aim at unveiling the observational imprint of physical mechanisms that govern planetary formation in young, multiple systems. In particular, we investigate the impact of tidal truncation on the ...inner circumstellar disks. We observed the emblematic system GG Tau at high-angular resolution: a hierarchical quadruple system composed of low-mass T Tauri binary stars surrounded by a well studied, massive circumbinary disk in Keplerian rotation. We used the near-IR 4-telescope combiner PIONIER on the VLTI and sparse-aperture-masking techniques on VLT/NaCo to probe this proto-planetary system at sub-au scales. We report the discovery of a significant closure-phase signal in H and Ks bands that can be reproduced with an additional low-mass companion orbiting GG Tau Ab, at a (projected) separation ρ = 31.7 ± 0.2 mas (4.4 au) and PA = 219.6 ± 0.3°. This finding offers a simple explanation for several key questions in this system, including the missing-stellar-mass problem and the asymmetry of continuum emission from the inner dust disks observed at millimeter wavelengths. Composed of now five co-eval stars with 0.02 ≤ M⋆ ≤ 0.7 M⊙, the quintuple system GG Tau has become an ideal test case to constrain stellar evolution models at young ages (few 106 yr).
We present a new millimeter survey of 23 pre-main-sequence stars in the Taurus-Auriga star-forming region. The main goal of the project was to identify circumstellar disks around stars of late ...spectral types (M * lsim 0.7 M sun). We used the IRAM Plateau de Bure Interferometer to obtain observations at 1.3 mm, 2.7 mm, and the CO J = 1-0 and J = 2-1 lines. We detected eight sources in continuum emission, with new detections of CIDA-1 and CIDA-8 at 1.3 mm. Overall, we find that circumstellar disks around stars with spectral types later than M2 tend to have smaller millimeter continuum fluxes than those around earlier type stars. We also present four detections of disks in their CO line emission (LkHα 358, GO Tau, Haro 6-13, IRAS 04385+2550). By mapping the rotation of the resolved CO emission from the circumstellar disks, we obtain estimates of the dynamical mass of the central stars.
Extreme outbursts in young stars may be a common stage of pre-main-sequence stellar evolution. These outbursts, caused by enhanced accretion and accompanied by increased luminosity, can also strongly ...impact the evolution of the circumstellar environment. We present Atacama Large Millimeter Array (ALMA) and Very Large Array observations of EX Lupi, a prototypical outburst system, at 100, 45, and 15 GHz. We use these data, along with archival ALMA 232 GHz data, to fit radiative transfer models to EX Lupi's circumstellar disk in its quiescent state following the extreme outburst in 2008. The best-fit models show a compact disk with a characteristic dust radius of 45 au and a total mass of 0.01 M . Our modeling suggests grain growth to sizes of at least 3 mm in the disk, possibly spurred by the recent outburst, and an ice line that has migrated inward to 0.2-0.3 au post-outburst. At 15 GHz, we detected significant emission over the expected thermal disk emission which we attribute primarily to stellar (gyro)synchrotron and free-free disk emission. Altogether, these results highlight what may be a common impact of outbursts on the circumstellar dust.
Context.HH 30 is a well-known Pre-Main-Sequence star in Taurus. HST observations have revealed a flared, edge-on disk driving a highly-collimated optical jet, making this object a case study for the ...disk-jet-outflow paradigm. Aims.We searched for a molecular outflow, and attempted to better constrain the star and disk parameters. Methods.We obtained high angular resolution ($\sin 1''$) observations of the dust continuum at 2.7 and 1.3 mm, and of the $\rm ^{12}CO~J=2{-}1$, $\rm ^{13}CO~J=2{-}1$ and $J=1{-}0$, $\rm C^{18}O~J=1{-}0$ emissions around HH 30. A standard disk model is used to fit the $\rm ^{13}CO$ $J=2{-}1$ uv-plane visibilities and derive the disk properties, and the stellar mass. An ad hoc outflow model is used to reproduce the main properties of the $\rm ^{12}CO~J=2{-}1$ emission. Results.The rotation vector of the disk points toward the North-Eastern jet. The disk rotation is Keplerian: using a distance of 140 pc, we deduce a mass of 0.45 Msun for the central star. The disk outer radius is 420 AU. A highly asymmetric outflow originates from the inner parts of the disk. Only its North-Eastern lobe was detected: it presents to first order a conical morphology with a $30\degr$ half opening angle and a constant (12 km s-1) radial velocity field. Outflow rotation was searched for but not found. The upper limit of the outflow rotation velocity is 1 km s-1 at 200 AU of the jet axis. Conclusions.HH 30 is a low mass TTauri of spectral type around M1 and age 1 to 4 Myr, surrounded by a medium size Keplerian disk, of mass around 4 $\times$ 10-3 Msun. It beautifully illustrates the jet-disk-outflow interaction, being so far the only star to display a jet and outflow connected to a well defined Keplerian disk, but reveals a surprisingly asymmetric (one-sided) outflow despite a relatively symmetric jet. Furthermore, these observations do not enable to assign the origin of the molecular outflow to entrainment by the optical jet or to a disk wind. In the latter hypothesis, the lack of rotation would imply an origin in the inner 15 AU of the disk.
Context. Because of new telescopes that will dramatically improve our knowledge of the interstellar medium, chemical models will have to be used to simulate the chemistry of many regions with diverse ...properties. To make these models more robust, it is important to understand their sensitivity to a variety of parameters. Aims. In this article, we report a study of the sensitivity of a chemical model of a cold dense core, with homogeneous and time-independent physical conditions, to variations in the following parameters: initial chemical inventory, gas temperature and density, cosmic-ray ionization rate, chemical reaction rate coefficients, and elemental abundances. Methods. We used a Monte Carlo method to randomly vary individual parameters and groups of parameters within realistic ranges. From the results of the parameter variations, we can quantify the sensitivity of the model to each parameter as a function of time. Our results can be used in principle with observations to constrain some parameters for different cold clouds. We also attempted to use the Monte Carlo approach with all parameters varied collectively. Results. Within the parameter ranges studied, the most critical parameters turn out to be the reaction rate coefficients at times up to 4 × 105 yr and elemental abundances at later times. At typical times of best agreement with observation, models are sensitive to both of these parameters. The models are less sensitive to other parameters such as the gas density and temperature. Conclusions. The improvement of models will require that the uncertainties in rate coefficients of important reactions be reduced. As the chemistry becomes better understood and more robust, it should be possible to use model sensitivities concerning other parameters, such as the elemental abundances and the cosmic ray ionization rate, to yield detailed information on cloud properties and history. Nevertheless, at the current stage, we cannot determine the best values of all the parameters simultaneously based on purely observational constraints.
We study the content in S-bearing molecules of protoplanetary disks around low-mass stars. We used the new IRAM 30-m receiver EMIR to perform simultaneous observations of the $1_{10}-1_{01}$ line of ...H$_2$S at 168.8 GHz and $2_{23}-1_{12}$ line of SO at 99.3 GHz. We compared the observational results with predictions coming from the astrochemical code NAUTILUS, which has been adapted to protoplanetary disks. The data were analyzed together with existing CS J=3-2 observations. We fail to detect the SO and H$_2$S lines, although CS is detected in LkCa15, DM\,Tau, and GO\,Tau but not in MWC\,480. However, our new upper limits are significantly better than previous ones and allow us to put some interesting constraints on the sulfur chemistry. Our best modeling of disks is obtained for a C/O ratio of 1.2, starting from initial cloud conditions of H density of $2\times 10^5$ cm$^{-3}$ and age of $10^6$ yr. The results agree with the CS data and are compatible with the SO upper limits, but fail to reproduce the H$_2$S upper limits. The predicted H$_2$S column densities are too high by at least one order of magnitude. H$_2$S may remain locked onto grain surfaces and react with other species, thereby preventing the desorption of H$_2$S.
Context.The jet-disk connection is an important part of the star formation process. HH 30 is a rare and beautiful example of a system exhibiting a flared edge-on disk, an optical jet and a CO ...molecular outflow. A recent analysis of the jet wiggling has revealed that the central star is in reality a binary object. Therefore, the dust and gas disk observed around HH 30 is circumbinary. Aims.In this paper, we attempt to better constrain the system (disk + stars) properties, as well as the system age. Methods.We obtained very high angular resolution ($\sim 0.4''$) observations in continuum at 1.3 mm with the IRAM interferometer. A standard disk model is used to fit the continuum and line data in the Fourier-plane and derive the disk properties. Results.We find that the disk of HH 30 is truncated at an inner radius 37 ± 4 AU. The simplest explanation is tidal truncation in a binary system. This confirms the binarity of the HH 30 system, which consists of two stars on a low eccentricity, 15 AU semi-major axis orbit. The jet wiggling is due to orbital motion. The mass ratio is poorly constrained. The system age may be less than 2 Myr. The disk is optically thin at 1.3 mm and the dust opacity index, $\beta \approx 0.4$, indicates the presence of cm size grains. Conclusions.These observations confirm that HH 30, often presented as an archetypal example of the jet-disk paradigm, is a binary star, with one of the components at the origin of the optical jet. This suggests that many other objects similar to HH 30 may be unknown binary or multiple systems. These new data confirm that high angular resolution observations at millimeter wavelengths are powerful tools to unveil the inner dust disk properties. In this domain, ALMA will likely change our observational vision of these objects.
Context. The gas and dust dissipation processes of proto-planetary disks are hardly known. Transition disks between Class II (proto-planetary disks) and Class III (debris disks) remain difficult to ...detect. Aims. We investigate the carbon chemistry of the peculiar CQ Tau gas disk. It is likely to be a transition disk because it exhibits weak CO emission with a relatively strong millimeter continuum, indicating that the disk may currently be dissipating its gas content. Methods. We used APEX to observe the two C i transitions 3P1 $\rightarrow$ 3P0 at 492 GHz and 3P2 $\rightarrow$ 3P1 at 809 GHz in the disk orbiting CQ Tau. We compare the observations to several chemical model predictions. We focus our study on the influence of the stellar UV radiation shape and gas-to-dust ratio. Results. We did not detect the C i lines. However, our upper limits are deep enough to exclude high-C i models. The only available models compatible with our limits imply very low gas-to-dust ratios, of the order of only a few. Conclusions. These observations strengthen the hypothesis that CQ Tau is likely to be a transition disk and suggest that gas disappears before dust.
We present high spatial resolution maps, obtained with the Plateau de Bure Interferometer, of the blue lobe of the L1157 outflow. We observed four lines at 3 mm, namely CH3OH (2K–1K), HC3N (11–10), ...HCN (1–0) and OCS (7–6). Moreover, the bright B1 clump has also been observed at better spatial resolution in CS (2–1), CH3OH (21–11)A− and 34SO (32–21). These high spatial resolution observations show a very rich structure in all the tracers, revealing a clumpy structure of the gas superimposed to an extended emission. In fact, the three clumps detected by previous IRAM 30‐m single‐dish observations have been resolved into several subclumps and new clumps have been detected in the outflow. The clumps are associated with the two cavities created by two shock episodes driven by the precessing jet. In particular, the clumps nearest the protostar are located at the wall of the younger cavity with a clear arch shape form while the farthest clumps have slightly different observational characteristics indicating that they are associated with the older shock episode. The emission of the observed species peaks in different part of the lobe: the eastern clumps are brighter in HC3N (11–10), HCN (1–0) and CS (2–1) while the western clumps are brighter in CH3OH (2K–1K), OCS (7–6) and 34SO (32–21). This peak displacement in the line emission suggests a variation of the physical conditions and/or the chemical composition along the lobe of the outflow at small scale, likely related to the shock activity and the precession of the outflow. In particular, we observe the decoupling of the silicon monoxide and methanol emission, common shock tracers, in the B1 clump located at the apex of the bow shock produced by the second shock episode.
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