27 research outputs found

    Probing the accretion-ejection connection with VLTI/AMBER: High spectral resolution observations of the Herbig Ae star HD163296

    Full text link
    Accretion and ejection are tightly connected and represent the fundamental mechanisms regulating star formation. However, the exact physical processes involved are not yet fully understood. We present high angular and spectral resolution observations of the Br Gamma emitting region in the Herbig Ae star HD163296 (MWC275) in order to probe the origin of this line and constrain the physical processes taking place at sub-AU scales in the circumstellar region. By means of VLTI-AMBER observations at high spectral resolution (R~12000), we studied interferometric visibilities, wavelength-differential phases, and closure phases across the Br Gamma line of HD163296. To constrain the physical origin of the Br Gamma line in Herbig Ae stars, all the interferometric observables were compared with the predictions of a line radiative transfer disc wind model. The measured visibilities clearly increase within the Br Gamma line, indicating that the Br Gamma emitting region is more compact than the continuum. By fitting a geometric Gaussian model to the continuum-corrected Br Gamma visibilities, we derived a compact radius of the Br Gamma emitting region of ~0.07+/-0.02AU (Gaussian half width at half maximum; or a ring-fit radius of ~0.08+/-0.02AU). To interpret the observations, we developed a magneto-centrifugally driven disc wind model. Our best disc wind model is able to reproduce, within the errors, all the interferometric observables and it predicts a launching region with an outer radius of ~0.04AU. However, the intensity distribution of the entire disc wind emitting region extends up to ~0.16AU. Our observations, along with a detailed modelling of the Br Gamma emitting region, suggest that most of the Br Gamma emission in HD163296 originates from a disc wind with a launching region that is over five times more compact than previous estimates of the continuum dust rim radius.Comment: Accepted for publication in A&

    Accretion bursts in high-mass protostars: a new testbed for models of episodic accretion

    Full text link
    It is well known that low mass young stellar objects (LMYSOs) gain a significant portion of their final mass through episodes of very rapid accretion, with mass accretion rates up to M˙104M\dot M_* \sim 10^{-4} M_{\odot}~yr1^{-1}. Recent observations of high mass young stellar objects (HMYSO) with masses M10MM_* \gtrsim 10 M_{\odot} uncovered outbursts with accretion rates exceeding M˙103M\dot M_*\sim 10^{-3}M_{\odot}~yr1^{-1}. Here we examine which scenarios proposed in the literature so far to explain accretion bursts of LMYSOs can apply to the episodic accretion in HMYSOs. We utilise a 1D time dependent models of protoplanetary discs around HMYSOs to study burst properties. We find that discs around HMYSOs are much hotter than those around their low mass cousins. As a result, much more extended regions of the disc are prone to the thermal hydrogen ionisation and MRI activation instabilities. The former in particular is found to be ubiquitous in a very wide range of accretion rates and disc viscosity parameters. The outbursts triggered by these instabilities, however, always have too low M˙\dot M_*, and are one to several orders of magnitude too long compared to those observed from HMYSOs so far. On the other hand, bursts generated by tidal disruptions of gaseous giant planets formed by the gravitational instability of the protoplanetary discs yield properties commensurate with observations, provided that the clumps are in the post-collapse configuration with planet radius Rp10R_{\rm p} \gtrsim 10 Jupiter radii. Furthermore, if observed bursts are caused by disc ionisation instabilities then they should be periodic phenomena with the duration of the quiescent phase comparable to that of the bursts. This may yield potentially observable burst periodicity signatures in the jets, the outer disc, or the surrounding diffuse material of massive HMYSOs. (abridged)Comment: 8 pages, 6 figures, Accepted to A&A Letter

    Investigating episodic accretion in a very low-mass young stellar object

    Get PDF
    Very low-mass Class I protostars have been investigated very little thus far. Variability of these young stellar objects (YSOs) and whether or not they are capable of strong episodic accretion is also left relatively unstudied. We investigate accretion variability in IRS54, a Class I very low-mass protostar with a mass of M_{\star} ~ 0.1 - 0.2 M_{\odot}. We obtained spectroscopic and photometric data with VLT/ISAAC and VLT/SINFONI in the near-infrared (JJ, HH, and KK bands) across four epochs (2005, 2010, 2013, and 2014). We used accretion-tracing lines (Paβ\beta and Brγ\gamma) and outflow-tracing lines (H2_2 and [FeII] to examine physical properties and kinematics of the object. A large increase in luminosity was found between the 2005 and 2013 epochs of more than 1 magnitude in the KK band, followed in 2014 by a steep decrease. Consistently, the mass accretion rate (M˙acc\dot{M}_{acc}) rose by an order of magnitude from ~ 108^{-8} M_{\odot} yr1^{-1} to ~ 10710^{-7} M_{\odot} yr1^{-1} between the two early epochs. The visual extinction (AVA_V) has also increased from ~ 15 mag in 2005 to ~ 24 mag in 2013. This rise in AVA_V in tandem with the increase in M˙acc\dot{M}_{acc} is explained by the lifting up of a large amount of dust from the disc of IRS54, following the augmented accretion and ejection activity in the YSO, which intersects our line of sight due to the almost edge-on geometry of the disc. Because of the strength and timescales involved in this dramatic increase, this event is believed to have been an accretion burst possibly similar to bursts of EXor-type objects. IRS54 is the lowest mass Class I source observed to have an accretion burst of this type, and therefore potentially one of the lowest mass EXor-type objects known so far

    An SMA and HERSCHEL view of the HMSFR G23.01-0.41

    Get PDF
    We present here the results of our recent SMA observations at 1.3 mm toward the high-mass star-forming region (HMSFR) G23.01-0.41, with both the most extended and compact array configurations, providing sub-arcsecond and high sensitivity maps for different molecular lines (e.g., 12CO and isotopomers, SiO, CH3CN, and CH3OH). We also complement this dataset with the spectral energy distribution (SED) between 3.4 μm and 1.1 mm and the continuum images from the Hi-GAL/Herschel survey. The aim of these observations is twofold: 1) to image at high angular and spectral resolution the flattened, hot molecular core (HMC) detected toward G23.01-0.41, which contains strong masers and a radio continuum source; 2) to compare the spatial distribution and velocity field of the gas close to the central YSO with those of the associated molecular outflow. The dust and molecular line emission trace a flattened structure inside a radius of 8000 AU from the center of radio continuum and maser line emission in the region. The equatorial plane of this HMC is strictly perpendicular to the main elongation of the outflow emission onto the plane of the sky, which extends over a ten times larger region (~0.5 pc). The inner velocity field mapped with the CH3CN (12K-11K) lines outlines that molecular gas rotates about the outflow axis and is simultaneously dragged along the outflow direction indicating Hubble-law expansion. The IR SED from the HMC suggests the presence of a single O9.5 ZAMS star with a mass ~19 M⊙, consistent with the mass required for centrifugal equilibrium

    GIARPS/GRAVITY Survey: Broad-Band 0.44-2.4 Micron High-Resolution Spectra of T-Tauri and Herbig AeBe Stars - Combining High Spatial and High Spectral Resolution Data to Unveil the Inner Disc Physics

    Get PDF
    The GIARPS/GRAVITY survey aims to obtain a set of high spatial and spectral resolution data for a sample of T-Tauri and Herbig AeBe stars (∼100 objects) selected from the VLTI/GRAVITY GTO sample of Young Stellar Objects (YSOs). GIARPS is a broad-band spectrometer combining HARPS-N and GIANO which allows high-resolution spectra from 0.44 μm (R ∼ 115, 000) to 2.44 μm (R ∼ 50, 000) in one observation. By combining this high spectral resolution with the high spatial resolution (∼1 mas) of GRAVITY, a view of unprecedented detail can be obtained of the innermost regions of circumstellar discs in YSOs spanning a wide range of masses (0.1–5 M⊙) and ages (105–107 yr). The ultimate goal is to model the accretion and ejection mechanisms, and study how they evolve as a function of YSO mass and age, using the spatially and spectrally resolved atomic and molecular lines from the inner gaseous regions

    The Spitzer Survey of Interstellar Clouds in the Gould Belt. III. A Multi-Wavelength View of Corona Australis

    Full text link
    We present Spitzer Space Telescope IRAC and MIPS observations of a 0.85 deg^2 field including the Corona Australis (CrA) star-forming region. At a distance of 130 pc, CrA is one of the closest regions known to be actively forming stars, particularly within its embedded association, the Coronet. Using the Spitzer data, we identify 51 young stellar objects (YSOs) in CrA which include sources in the well-studied Coronet cluster as well as distributed throughout the molecular cloud. Twelve of the YSOs discussed are new candidates, one of which is located in the Coronet. Known YSOs retrieved from the literature are also added to the list, and a total of 116 candidate YSOs in CrA are compiled. Based on these YSO candidates, the star formation rate is computed to be 12 M_o Myr^-1, similar to that of the Lupus clouds. A clustering analysis was also performed, finding that the main cluster core, consisting of 68 members, is elongated (having an aspect ratio of 2.36), with a circular radius of 0.59 pc and mean surface density of 150 pc^-2. In addition, we analyze outflows and jets in CrA by means of new CO and H_2 data. We present 1.3 mm interferometric continuum observations made with the Submillimeter Array (SMA) covering R CrA, IRS 5, IRS 7, and IRAS 18595-3712 (IRAS 32). We also present multi-epoch H_2 maps and detect jets and outflows, study their proper motions, and identify exciting sources. The Spitzer and ISAAC/VLT observations of IRAS 32 show a bipolar precessing jet, which drives a CO (2-1) outflow detected in the SMA observations. There is also clear evidence for a parsec-scale precessing outflow, E-W oriented, and originating in the SMA 2 region, likely driven by SMA 2 or IRS 7A.Comment: Accepted for publication in ApJS. 112 pages, 42 figures (quality reduced), 13 tables. Full resolution version can be found at http://www.cfa.harvard.edu/~dpeterson/CrA/CrA_highres.pd

    Investigating Protostellar Accretion-Driven Outflows Across the Mass Spectrum: JWST NIRSpec IFU 3-5~μ\mum Spectral Mapping of Five Young Protostars

    Full text link
    Investigating Protostellar Accretion (IPA) is a Cycle 1 JWST program using the NIRSpec+MIRI IFUs to obtain 2.9--28 μ\mum spectral cubes of five young protostars with luminosities of 0.2 to 10,000 L_{\odot} in their primary accretion phase. This paper introduces the NIRSpec 2.9--5.3 μ\mum data of the inner 840-9000 au with spatial resolutions from 28-300 au. The spectra show rising continuum emission, deep ice absorption, emission from H2_{2}, H~I, and [Fe~II], and the CO fundamental series in emission and absorption. Maps of the continuum emission show scattered light cavities for all five protostars. In the cavities, collimated jets are detected in [Fe~II] for the four <320< 320~L_{\odot} protostars, two of which are additionally traced in Br-α\alpha. Knots of [Fe~II] emission are detected toward the most luminous protostar, and knots of [FeII] emission with dynamical times of <30< 30~yrs are found in the jets of the others. While only one jet is traced in H2_2, knots of H2_2 and CO are detected in the jets of four protostars. H2_2 is seen extending through the cavities showing they are filled by warm molecular gas. Bright H2_2 emission is seen along the walls of a single cavity, while in three cavities, narrow shells of H2_2 emission are found, one of which has an [Fe~II] knot at its apex. These data show cavities containing collimated jets traced in atomic/ionic gas surrounded by warm molecular gas in a wide-angle wind and/or gas accelerated by bow shocks in the jets.Comment: 30 pages, 11 figure
    corecore