Now showing 1 - 10 of 17
  • Publication
    A combined MUSE/X-Shooter study of the TH28 jet
    (Società Astronomica Italiana, 2017-06-09) ; ; ; ;
    Here we present the first results from a MUSE/X-Shooter study of the jet from the classical T Tauri star TH 28. The combination of MUSE and X-Shooter enables us to take advantage of both spectro-imaging and broadband spectroscopy to comprehensively investigate the TH 28 jet. We present a MUSE spectro-image and PV plot of the Hα emission line and use flux ratios from the X-Shooter spectrum to estimate the mass accretion rate at log(Ṁacc) = -9.4. Future work will focus on diagnostic analyses on both sets of data, including estimating the mass outflow rate (Ṁout) and the extinction of the jet.
      154
  • Publication
    Hydrogen permitted lines in the first near-ir spectra of th 28 microjet: Accretion or ejection tracers?
    We report the first near-infrared detection of the bipolar microjet from T Tauri star ThA 15-28 (hereafter Th 28). Spectra were obtained with Very Large Telescope (VLT)/ISAAC for the slit both perpendicular and parallel to the flow to examine jet kinematics and gas physics within the first arcsecond from the star. The jet was successfully detected in bothmolecular and atomic lines. The H2 component was found to be entirely blueshifted around the base of the bipolar jet. It shows that only the blue lobe is emitting in H2 while light is scattered in the direction of the red lobe, highlighting an asymmetric extinction and/or excitation between the two lobes. Consistent with this view, the red lobe is brighter in all atomic lines. Interestingly, the jet was detected not only in [Fe ii], but also in Brγ and Paβ lines. Though considered tracers mainly of accretion, we find that these high excitation hydrogen permitted lines trace the jet as far as 150 AU from the star. This is confirmed in a number of ways: the presence of the [Fe ii] 2.13μm line which is of similarly high excitation; Hi velocities which match the jet [Fe ii] velocities in both the blue and red lobe; and high electron density close to the source of >6 × 104 cm-3 derived from the [Fe ii] 1.64, 1.60μm ratio. These near-infrared data complement Hubble Space Telescope Imaging Spectrograph (HST/STIS) optical and near-ultraviolet data for the same target which were used in a jet rotation study, although no rotation signature could be identified here due to insufficient angular resolution. The unpublished HST/STIS Hα emission is included here alongside the other Hi lines. Identifying Brγ and Paβ as tracers of ejection is significant because of the importance of finding strong near-infrared probes close to the star, where forbidden lines are quenched, which will help understand accretion ejection when observed with high spatial resolution instruments such as VLTI/AMBER. © 2010. The American Astronomical Society. All rights reserved.
      313Scopus© Citations 10
  • Publication
    Unveiling the Role of Jets in Star Formation
    We describe the role of HST in providing the first and long-awaited observational backing for the role of bipolar jets in the star formation process.
      250
  • Publication
    Jet rotation: Launching region, angular momentum balance and magnetic properties in the bipolar outflow from RW Aur
    Using STIS on board the HST we have obtained a spectroscopic map of the bipolar jet from RW Aur with the slit parallel to the jet axis and moved across the jet in steps of 0″.07. After applying a velocity correction due to uneven slit illumination we find signatures of rotation within the first 300 AU of the jet (1″.5 at the distance of RW Aur). Both lobes rotate in the same direction (i.e. with different helicities), with toroidal velocities in the range 5-30 km s-1 at 20 and 30 AU from the symmetry axis in the blueshifted and redshifted lobes, respectively. The sense of rotation is anti-clockwise looking from the tip of the blue lobe (PA 130° north to east) down to the star. Rotation is more evident in the [OI] and [NII] lines and at the largest sampled distance from the axis. These results are consistent with other STIS observations carried out with the slit perpendicular to the jet axis, and with theoretical simulations. Using current magneto-hydrodynamic models for the launch of the jets, we find that the mass ejected in the observed part of the outflow is accelerated from a region in the disk within about 0.5 AU from the star for the blue lobe, and within 1.6 AU from the star for the red lobe. Using also previous results we estimate upper and lower limits for the angular momentum transport rate of the jet. We find that this can be a large fraction (two thirds or more) of the estimated rate transported through the relevant portion of the disk. The magnetic lever arm (defined as the ratio r A/r0 between the Alfvèn and footpoint radii) is in the range 3.5-4.6 (with an accuracy of 20-25%), or, alternatively, the ejection index ξ = d ln(Ṁacc)/dr is in the range 0.025-0.046 (with similar uncertainties). The derived values are in the range predicted by the models, but they also suggest that some heating must be provided at the base of the flow. Finally, using the general disk wind theory we derive the ratio Bφ/Bp of the toroidal and poloidal components of the magnetic field at the observed location (i.e. about 80-100 AU above the disk). We find this quantity to be 3.8 ± 1.1 at 30 AU from the axis in the red lobe and -8.9 ± 2.7 at 20 AU from the axis in the blue lobe (assuming cylindrical coordinates centred on the star and with positive z along the blue lobe). The toroidal component appears to be dominant, which would be consistent with magnetic collimation of the jet. The field appears to be more tightly wrapped on the blue side. © ESO 2005.
      260Scopus© Citations 86
  • Publication
    Jet rotation investigated in the near-ultraviolet with the Hubble Space Telescope imaging spectrograph
    We present results of the second phase of our near-ultraviolet investigation into protostellar jet rotation using the Hubble Space Telescope Imaging Spectrograph. We obtain long-slit spectra at the base of five T Tauri jets to determine if there is a difference in radial velocity between the jet borders which may be interpreted as a rotation signature. These observations are extremely challenging and push the limits of current instrumentation, but have the potential to provide long-awaited observational support for the magnetocentrifugal mechanism of jet launching in which jets remove angular momentum from protostellar systems. We successfully detect all five jet targets (from RW Aur, HN Tau, DP Tau, and CW Tau) in several near-ultraviolet emission lines, including the strong Mg II doublet. However, only RW Aur's bipolar jet presents a sufficiently high signal-to-noise ratio to allow for analysis. The approaching jet lobe shows a difference of 10kms-1 in a direction which agrees with the disk rotation sense, but is opposite to previously published optical measurements for the receding jet. The near-ultraviolet difference is not found six months later, nor is it found in the fainter receding jet. Overall, in the case of RW Aur, differences are not consistent with a simple jet rotation interpretation. Indeed, given the renowned complexity and variability of this system, it now seems likely that any rotation signature is confused by other influences, with the inevitable conclusion that RW Aur is not suited to a jet rotation study. © 2012. The American Astronomical Society. All rights reserved.
      258Scopus© Citations 28
  • Publication
    ALMA Polarimetric Studies of Rotating Jet/Disk Systems
    We have recently obtained polarimetric data at mm wavelengths with ALMA for the young systems DG Tau and CW Tau, for which the rotation properties of jet and disk have been investigated in previous high angular resolution studies. The motivation was to test the models of magneto-centrifugal launch of jets via the determination of the magnetic configuration at the disk surface. The analysis of these data, however, reveals that self-scattering of dust thermal radiation dominates the polarization pattern. It is shown that even if no information on the magnetic field can be derived in this case, the polarization data are a powerful tool for the diagnostics of the properties and the evolution of dust in protoplanetary disks.
      311
  • Publication
    Organic molecules in the protoplanetary disk of DG Tauri revealed by ALMA
    Context. Planets form in protoplanetary disks and inherit their chemical compositions. Aims. It is thus crucial to map the distribution and investigate the formation of simple organics, such as formaldehyde and methanol, in protoplanetary disks. Methods. We analyze ALMA observations of the nearby disk-jet system around the T Tauri star DG Tau in the o-H2CO 31, 2-21, 1 and CH3OH 3-2, 2-4-1, 4 E, 50, 5-40, 4 A transitions at an unprecedented resolution of $ ∼0.15 $, i.e., ∼18 au at a distance of 121 pc. Results. The H2CO emission originates from a rotating ring extending from ∼40 au with a peak at ∼62 au, i.e., at the edge of the 1.3 mm dust continuum. CH3OH emission is not detected down to an rms of 3 mJy beam-1 in the 0.162 km s-1 channel. Assuming an ortho-to-para ratio of 1.8-2.8 the ring-and disk-height-averaged H2CO column density is ∼0.3-4 × 1014 cm-2, while that of CH3OH is < 0.04-0.7 × 1014 cm-2. In the inner 40 au no o-H2CO emission is detected with an upper limit on its beam-averaged column density of ∼0.5-6 × 1013 cm-2. Conclusions. The H2CO ring in the disk of DG Tau is located beyond the CO iceline (RCO ∼ 30 au). This suggests that the H2CO abundance is enhanced in the outer disk due to formation on grain surfaces by the hydrogenation of CO ice. The emission peak at the edge of the mm dust continuum may be due to enhanced desorption of H2CO in the gas phase caused by increased UV penetration and/or temperature inversion. The CH3OH/H2CO abundance ratio is < 1, in agreement with disk chemistry models. The inner edge of the H2CO ring coincides with the radius where the polarization of the dust continuum changes orientation, hinting at a tight link between the H2CO chemistry and the dust properties in the outer disk and at the possible presence of substructures in the dust distribution.
      330Scopus© Citations 30
  • Publication
    The near-UV: The true window on jet rotation
    (Società Astronomica Italiana, 2017-01-01) ; ; ;
    High resolution observations of jet rotation in newly forming stars have the potential to support theories of magneto-centrifugal jet launching. We report a detection of a radial velocity difference across the blue-shifted jet from RY Tau, the direction of which matches the CO disk rotation sense. Now, in 3 of 3 cases, the sense of the near-UV jet gradient matches the disk rotation sense, implying that we are indeed observing jet rotation. It seems the jet core, probed at near-UV wavelengths, is protected by the outer jet layers from kinematic contaminations, and thus represents the only true window on jet rotation.
      190
  • Publication
    The accretion/ejection paradigm of low mass stars tested with HST
    In the last few years new investigation techniques have allowed us to study in depth the spectacular phenomenon of protostellar jets, and to test the validity of the proposed models for their acceleration. In this contribution we review the current knowledge on the subject, with a special emphasis on the recent achievements obtained thanks to observations at high angular resolution, like those performed at subarcsecond scales with the Hubble Space Telescope. These results have made us able to define more clearly the morphology, kinematics, excitation of the flows on small scales, and, in turn, to derive stringent constraints for the physical processes at work. The novel information acquired puts us in a very good position to plan theoretical and observational studies aimed at understanding if similar accretion/ejection processes are also at work during the formation of Brown Dwarfs. If scaled-down versions of Herbig-Haro jets are found associated to these objects, then it would mean that the wellknown formation scenario of solar–mass stars is truly universal.
      89
  • Publication
    Further indications of jet rotation in new ultraviolet and optical Hubble Space Telescope STIS spectra
    We present survey results that suggest rotation signatures at the base of T Tauri jets. Observations were conducted with the Hubble Space Telescope Imaging Spectrograph at optical and near-ultraviolet (NUV) wavelengths. Results are presented for the approaching jet from DG Tau, CW Tau, HH 30, and the bipolar jet from TH 28. Systematic asymmetries in Doppler shift were detected across the jet, within 100 AU from the star. At optical wavelengths, radial velocity differences were typically (10-25) ± 5 km s-1, while differences in the NUV range were consistently lower, at typically 10 ± 5 km s-1. Results are interpreted as possible rotation signatures. Importantly, there is agreement between the optical and NUV results for DG Tau. Under the assumption of steady magnetocentrifugal acceleration, the survey results lead to estimates for the distance of the jet footpoint from the star, and give values consistent with earlier studies. In the case of DG Tau, for example, we see that the higher velocity component appears to be launched from a distance of 0.2-0.5 AU from the star along the disk plane, while the lower velocity component appears to trace a wider part of the jet launched from as far as 1.9 AU. The results for the other targets are similar. Therefore, if indeed the detected Doppler gradients trace rotation within the jet, then under the assumption of steady MHD ejection, the derived footpoint radii support the existence of magnetized disk winds. However, since we do not resolved the innermost layers of the flow, we cannot exclude the possibility that there also exists an X-wind or stellar wind component. © 2007, The American Astronomical Society, All rights reserved.
      276Scopus© Citations 108