T. P. Ray

Dublin Institute for Advanced Studies, Dublin, Leinster, Ireland

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Publications (112)248.44 Total impact

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    ABSTRACT: As the number of observed brown dwarf outflows is growing it is important to investigate how these outflows compare to the well studied jets from young stellar objects. A key point of comparison is the relationship between outflow and accretion activity and in particular the ratio between the mass outflow and accretion rates ($\dot{M}_{out}$/$\dot{M}_{acc}$). The brown dwarf candidate ISO-ChaI 217 was discovered by our group, as part of a spectro-astrometric study of brown dwarfs, to be driving an asymmetric outflow with the blue-shifted lobe having a position angle of $\sim$ 20$^{\circ}$. The aim here is to further investigate the properties of ISO-ChaI 217, the morphology and kinematics of its outflow, and to better constrain ($\dot{M}_{out}$/$\dot{M}_{acc}$). The outflow is spatially resolved in the $[SII]\lambda \lambda 6716,6731$ lines and is detected out to $\sim$ 1\farcs6 in the blue-shifted lobe and ~ 1" in the red-shifted lobe. The asymmetry between the two lobes is confirmed although the velocity asymmetry is less pronounced with respect to our previous study. Using thirteen different accretion tracers we measure log($\dot{M}_{acc}$) [M$_{sun}$/yr]= -10.6 $\pm$ 0.4. As it was not possible to measure the effect of extinction on the ISO-ChaI 217 outflow $\dot{M}_{out}$ was derived for a range of values of A$_{v}$, up to a value of A$_{v}$ = 2.5 mag estimated for the source extinction. The logarithm of the mass outflow ($\dot{M}_{out}$) was estimated in the range -11.7 to -11.1 for both jets combined. Thus $\dot{M}_{out}$/$\dot{M}_{acc}$ [\Msun/yr] lies below the maximum value predicted by magneto-centrifugal jet launching models. Finally, both model fitting of the Balmer decrements and spectro-astrometric analysis of the H$\alpha$ line show that the bulk of the H I emission comes from the accretion flow.
    08/2014;
  • The Astrophysical Journal 06/2014; 788(2):194. · 6.73 Impact Factor
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    ABSTRACT: Spectroscopic follow-up is a pre-requisite for studies of the formation and early evolution of brown dwarfs. Here we present IRTF/SpeX near-infrared spectroscopy of 30 candidate members of the young Upper Scorpius association, selected from our previous survey work. All 24 high confidence members are confirmed as young very low mass objects with spectral types from M5 to L1, 15-20 of them are likely brown dwarfs. This high yield confirms that brown dwarfs in Upper Scorpius can be identified from photometry and proper motions alone, with negligible contamination from field objects (<4%). Out of the 6 candidates with lower confidence, 5 might still be young very low mass members of Upper Scorpius, according to our spectroscopy. We demonstrate that some very low mass class II objects exhibit radically different near infrared (0.6 - 2.5micron) spectra from class III objects, with strong excess emission increasing towards longer wavelengths and partially filled in features at wavelengths shorter than 1.25micron. These characteristics can obscure the contribution of the photosphere within such spectra. Therefore, we caution that near infrared derived spectral types for objects with discs may be unreliable. Furthermore, we show that the same characteristics can be seen to some extent in all class II and even a significant fraction of class III objects (~40%), indicating that some of them are still surrounded by traces of dust and gas. Based on our spectra, we select a sample of objects with spectral types of M5 to L1, whose near-infrared emission represents the photosphere only. We recommend the use of these objects as spectroscopic templates for young brown dwarfs in the future.
    05/2014;
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    ABSTRACT: We present the results of a multi-wavelength study of circumstellar discs around 44 young stellar objects in the 3 Myr old nearby Chamaeleon I star-forming region. In particular, we explore the far-infrared/submm regime using Herschel fluxes. We show that Herschel fluxes at 160-500$\,\mu$m can be used to derive robust estimates of the disc mass. The median disc mass is 0.005$M_{\odot}$ for a sample of 28 Class IIs and 0.006$M_{\odot}$ for 6 transition disks (TDs). The fraction of objects in Chamaeleon-I with at least the `minimum mass solar nebula' is 2-7%. This is consistent with previously published results for Taurus, IC348, $\rho$ Oph. Diagrams of spectral slopes show the effect of specific evolutionary processes in circumstellar discs. Class II objects show a wide scatter that can be explained by dust settling. We identify a continuous trend from Class II to TDs. Including Herschel fluxes in this type of analysis highlights the diversity of TDs. We find that TDs are not significantly different to Class II discs in terms of far-infrared luminosity, disc mass or degree of dust settling. This indicates that inner dust clearing occurs independently from other evolutionary processes in the discs.
    05/2014;
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    ABSTRACT: In this review we focus on the role jets and outflows play in the star and planet formation process. Our essential question can be posed as follows: are jets/outflows merely an epiphenomenon associated with star formation or do they play an important role in mediating the physics of assembling stars both individually and globally? We address this question by reviewing the current state of observations and their key points of contact with theory. Our review of jet/outflow phenomena is organized into three length-scale domains: Source and Disk Scales ($0.1-10^2$ au) where the connection with protostellar and disk evolution theories is paramount; Envelope Scales ($10^2-10^5$ au) where the chemistry and propagation shed further light on the jet launching process, its variability and its impact on the infalling envelope; Parent Cloud Scales ($10^5-10^6$ au) where global momentum injection into cluster/cloud environments become relevant. Issues of feedback are of particular importance on the smallest scales where planet formation regions in a disk may be impacted by the presence of disk winds, irradiation by jet shocks or shielding by the winds. Feedback on envelope scales may determine the final stellar mass (core-to-star efficiency) and envelope dissipation. Feedback also plays an important role on the larger scales with outflows contributing to turbulent support within clusters including alteration of cluster star formation efficiencies (feedback on larger scales currently appears unlikely). A particularly novel dimension of our review is that we consider results on jet dynamics from the emerging field of High Energy Density Laboratory Astrophysics (HEDLA). HEDLA is now providing direct insights into the 3-D dynamics of fully magnetized, hypersonic, radiative outflows.
    02/2014;
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    ABSTRACT: We derive the physical properties at the base of the jet from DG Tau both along and across the flow and as a function of velocity. We analysed seven optical spectra of the DG Tau jet, taken with the Hubble Space Telescope Imaging Spectrograph. The spectra were obtained by placing a long-slit parallel to the jet axis and stepping it across the jet width. The resulting position-velocity diagrams in optical forbidden emission lines allowed access to plasma conditions via calculation of emission line ratios. We find at the base of the jet high electron density, $n_e \sim $ 10$^5$, and very low ionisation, $x_e \sim 0.02-0.05$, which combine to give a total density up to $n_H \sim $ 3 10$^6$. This analysis confirms previous reports of variations in plasma parameters along the jet, (i.e. decrease in density by several orders of magnitude, increase of $x_e$ from 0.05 to a plateau at 0.7 downstream at 2$''$ from the star). Furthermore, a spatial coincidence is revealed between sharp gradients in the total density and supersonic velocity jumps. This strongly suggests that the emission is caused by shock excitation. The position-velocity diagrams indicate the presence of both fast accelerating gas and slower, less collimated material. We derive the mass outflow rate, $\dot{M}_j$, in the blue-shifted lobe in different velocity channels, that contribute to a total of $\dot{M}_j \sim$ 8 $\pm$ 4 10$^{-9}$ M$_\odot$ yr$^{-1}$. We estimate that a symmetric bipolar jet would transport at the low and intermediate velocities probed by rotation measurements, an angular momentum flux of $\dot{L}_j \sim$ 2.9 $\pm$ 1.5 10$^{-6}$ M$_\odot$ yr$^{-1}$ AU km s$^{-1}$. The derived properties of the DG Tau jet are demonstrated to be consistent with magneto-centrifugal theory. However, non-stationary modelling is required in order to explain all of the features revealed at high resolution.
    01/2014;
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    ABSTRACT: The POISSON project (Protostellar Optical-Infrared Spectral Survey On NTT) has collected low resolution spectra (0.6-2.5 um) of about 150 Spitzer-selected Class I/II Young Stellar Objects located in five different star-forming regions (ChaI-II, L1641, Ser, Lup, CrA). The main goal of the project is to study the accretion properties of the sources in relationship with their stellar parameters and circumstellar environment, and to investigate how these differ in the various parental clouds. The accretion luminosity (Lacc) and mass accretion rate (Macc) of the sources were derived from different optical/NIR emission lines commonly employed as tracers (namely [OI], Halpha, CaII, PaBeta, BrGamma) making use of the relevant empirical relationships present in the literature, which connect the line luminosity to Lacc. The accretion properties thus derived were then put in correlation with other source parameters, such as the stellar luminosity, mass, IR excess, and age. The results of this analysis will be presented and discussed, focusing in particular on the following aspects: i) the reliability and limitations of the different accretion tracers relationships; ii) the time evolution of the mass accretion rate and the Macc dependence on source mass.
    Protostars and Planets VI, Heidelberg; 07/2013
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    ABSTRACT: The 24 Jupiter Mass brown dwarf (BD), 2MASSJ12073347-3932540 (2M1207A), was first discovered to be driving an outflow through the spectro-astrometric analysis of its [OI]6300 emission region (Whelan et al. 2007). It is now known to drive a bipolar outflow with a position angle (PA) of 65 degrees. [SII] narrowband images obtained by us revealed a series of knots along the PA of the outflow (Whelan et al. 2012). The furthest knot from the BD was bow-shock shaped and these results confirmed for the first time that BD outflows could be well collimated i.e. are jets, and episodic. In order to conduct a proper motion study of the knots we obtained follow-up images in [SII] and Hα using FORS-2 / VLT, in Feb / Jan 2013. The proper motion of the source is an important consideration as it is approximately along the same direction as the jet and likely has a similar magnitude. While no significant proper motion is detected in the [SII] knots there are morphological changes. It is possible that the velocity of the knots has slowed significantly with distance. From the comparison of the [SII] and Halpha images, Halpha seems to trace the shock fronts whereas [SII] the cooling zone behind the shock front. Future work includes simulations the jet to try to understand how the proper motion of source effects the morphology of the jet and the analysis of spectra of the knots. Spectra will facilitate the measurement of the knot velocities
    07/2013;
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    ABSTRACT: SONYC, short for "Substellar Objects in Nearby Young Clusters", is a survey program to provide a census of the substellar population in nearby star forming regions. We have conducted deep optical and near-infrared photometry in five young regions (NGC1333, rho Ophiuchi, Chamaeleon-I, Upper Sco, and Lupus-3), combined with proper motions, and followed by extensive spectroscopic campaigns with Subaru and VLT, in which we have obtained more than 700 spectra of candidate low-mass objects. We have identified and characterized more than 60 new substellar objects, among them a handful of objects with masses close to, or below the Deuterium burning limit. Through SONYC and surveys by other groups, the substellar IMF is now well characterized down to ~ 5 - 10 MJup, and we find that the ratio of the number of stars with respect to brown dwarfs lies between 2 and 6. A comprehensive survey of NGC 1333 reveals that, down to ~5MJup, free-floating objects with planetary masses are 20-50 times less numerous than stars, i.e. their total contribution to the mass budget of the clusters can be neglected.
    06/2013;
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    ABSTRACT: Studies of brown dwarf (BD) outflows provide information pertinent to questions on BD formation, as well as allowing outflow mechanisms to be investigated at the lowest masses. Here new observations of the bipolar outflow from the 24 M JUP BD 2MASS J12073347−3932540 are presented. The outflow was originally identified through the spectro-astrometric analysis of the [O i]λ6300 emission line. Follow-up observations consisting of spectra and [S ii], R-band and I-band images were obtained. The new spectra confirm the original results and are used to constrain the outflow position angle (P.A.) at ∼65 • . The [O i]λ6300 emission line region is spatially resolved and the outflow is detected in the [S ii] images. The detection is firstly in the form of an elongation of the point-spread function (PSF) along the direction of the outflow P.A. Four faint knot-like features (labeled A–D) are also observed to the southwest of 2MASS J12073347−3932540 along the same P.A. suggested by the spectra and the elongation in the PSF. Interestingly, D, the feature furthest from the source, is bow shaped with the apex pointing away from 2MASS J12073347−3932540. A color–color analysis allows us to conclude that at least feature D is part of the outflow under investigation while A is likely a star or galaxy. Follow-up observations are needed to confirm the origin of B and C. This is a first for a BD, as BD optical outflows have to date only been detected using spectro-astrometry. This result also demonstrates for the first time that BD outflows can be collimated and episodic.
    The Astrophysical Journal 12/2012; · 6.73 Impact Factor
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    ABSTRACT: We present a census of the disk population for UKIDSS selected brown dwarfs in the 5-10 Myr old Upper Scorpius OB association. For 116 objects originally identified in UKIDSS, the majority of them not studied in previous publications, we obtain photometry from the WISE database. The resulting colour-magnitude and colour-colour plots clearly show two separate populations of objects, interpreted as brown dwarfs with disks (class II) and without disks (class III). We identify 27 class II brown dwarfs, 14 of them not previously known. This disk fraction (27 out of 116 or 23%) among brown dwarfs was found to be similar to results for K/M stars in Upper Scorpius, suggesting that the lifetimes of disks are independent of the mass of the central object for low-mass stars and brown dwarfs. 5 out of 27 disks (19%) lack excess at 3.4 and 4.6 microns and are potential transition disks (i.e. are in transition from class II to class III). The transition disk fraction is comparable to low-mass stars. We estimate that the timescale for a typical transition from class II to class III is less than 0.4 Myr for brown dwarfs. These results suggest that the evolution of brown dwarf disks mirrors the behaviour of disks around low-mass stars, with disk lifetimes on the order of 5-10 Myr and a disk clearing timescale significantly shorter than 1 Myr.
    Monthly Notices of the Royal Astronomical Society 11/2012; · 5.52 Impact Factor
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    ABSTRACT: We present the results of a variability study of accreting young stellar objects in the Chameleon I star-forming region which is based on ~300 high resolution optical spectra from the multi-object fibre spectrograph FLAMES/GIRAFFE at the ESO/VLT. Twenty five objects with spectral types from G2-M5.75 were observed 12 times over the course of 15 months. Using the emission lines Ha (6562.81 A) and Ca II (8662.1 A) as accretion indicators we found 10 accreting and 15 non-accreting objects. We derived accretion rates for all accretors in the sample using the Ha equivalent width, Ha 10% width and the CaII equivalent width. The mean amplitude of variations in derived accretion rate from Ha equivalent width was ~ 0.37 dex, from Ca II equivalent width ~0.83 dex and from Ha 10% width ~1.11 dex. Based on the large amplitude of variations in accretion rates derived from the Ha 10% width with respect to the other diagnostics, we do not consider it to be a reliable accretion rate estimator. Taking the variations in Ha equivalent width and CaII equivalent width accretion rates to be closer to the true value, they suggest that the spread which has been found around the accretion rate to stellar mass relation is not due to the variability of individual objects on time-scales of weeks to ~1 year. From these variations we can also infer that the accretion rates are stable within < 0.37 dex over time-scales of less than 15 months. A major portion of the accretion variability was found to occur on less than the shortest time-scales in our observations, 8-25 days, which is comparable with the rotation periods of these young stellar objects. This could be an indication that what we are probing is spatial structure in the accretion flows, and also suggests that observations on time-scales of ~a couple of weeks are sufficient to limit the total extent of accretion rate variations in typical young stars.
    Monthly Notices of the Royal Astronomical Society 09/2012; 427(2). · 5.52 Impact Factor
  • P. Dawson, A. Scholz, T. P. Ray
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    ABSTRACT: The United Kingdom Infra-Red Telescope (UKIRT) is currently conducting the United Kingdom UKIDSS - the results of which are being made available in a series of releases. This work used the 8th Data Release (DR8Plus). (2 data files).
    VizieR Online Data Catalog. 06/2012;
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    ABSTRACT: Characterising stellar and circumstellar properties of embedded young stellar objects (YSOs) is mandatory for understanding the early stages of the stellar evolution. This task requires the combination of both spectroscopy and photometry, covering the widest possible wavelength range, to disentangle the various protostellar components and activities. As part of the POISSON project, we present a multi-wavelength spectroscopic and photometric investigation of embedded YSOs in L1641, aimed to derive the stellar parameters and evolutionary stages and to infer their accretion properties. Our database includes low-resolution optical-IR spectra from the NTT and Spitzer (0.6-40 um) and photometric data covering a spectral range from 0.4 to 1100 um, which allow us to construct the YSOs spectral energy distributions (SEDs) and to infer the main stellar parameters. The SED analysis allows us to group our 27 YSOs into nine Class I, eleven Flat, and seven Class II objects. However, on the basis of the derived stellar properties, only six Class I YSOs have an age of ~10^5 yr, while the others are older 5x10^5-10^6 yr), and, among the Flat sources, three out of eleven are more evolved objects (5x10^6-10^7 yr), indicating that geometrical effects can significantly modify the SED shapes. Inferred mass accretion rates (Macc) show a wide range of values (3.6x10^-9 to 1.2x10^-5 M_sun yr^-1), which reflects the age spread observed in our sample. Average values of mass accretion rates, extinction, and spectral indices decrease with the YSO class. The youngest YSOs have the highest Macc, whereas the oldest YSOs do not show any detectable jet activity in either images and spectra. We also observe a clear correlation among the YSO Macc, M*, and age, consistent with mass accretion evolution in viscous disc models.
    Astronomy and Astrophysics 11/2011; · 5.08 Impact Factor
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    ABSTRACT: Most of our knowledge about star formation is based on studies of low-mass stars, whereas very little is known about the properties of the circumstellar material around young and embedded intermidiate-mass T Tauri stars (IMTTSs). We present an analysis of the excitation and accretion properties of the young IMTTS DK Cha. The nearly face-on configuration of this source allows us to have direct access to the star-disk system through the excavated envelope and outflow cavity. Based on LR optical and IR spectroscopy obtained with SofI/EFOSC2 on the NTT we derive the spectrum of DK Cha from ~0.6 to 2.5 \mu m. From the detected lines we probe the conditions of the gas that emits the HI IR emission lines. In addition, we derive the mass accretion rate (Macc) from the relationships that connect the luminosity of the Br\gamma\ and Pa\beta\ lines with the accretion luminosity (Lacc). The observed optical/IR spectrum is extremely rich in forbidden and permitted atomic and molecular emission lines, which makes this source similar to very active low-mass T Tauri stars. Some of the permitted emission lines are identified as being excited by fluorescence. We derive Brackett decrements and compare them with different excitation mechanisms. The Pa\beta/Br\gamma\ ratio is consistent with optically thick emission in LTE at a temperature of ~3500 K, originated from a compact region of ~5 Rsun in size: but the line opacity decreases in the Br lines for high quantum numbers n_{up}. A good fit to the data is obtained assuming an expanding gas in LTE, with an electron density at the wind base of ~10^13 cm-3. In addition, we find that the observed Brackett ratios are very similar to those reported in previous studies of low-mass CTTSs and Class I sources, indicating that these ratios are not dependent on masses and ages. Finally, Lacc~9 Lsun and Macc~3x10-7 Msun/yr values were found.
    Astronomy and Astrophysics 09/2011; · 5.08 Impact Factor
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    P. Dawson, A. Scholz, T. P. Ray
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    ABSTRACT: This paper presents the results of a search for brown dwarfs in the Upper Scorpius Association using data from the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Cluster Survey. Candidate young brown dwarfs were first chosen by their position in colour magnitude diagrams with further selection based on proper motions to ensure Upper Scorpius membership. Proper motions were derived by comparing UKIDSS and 2MASS data. Using that method we identify 19 new brown dwarfs in the southern part of the association. In addition there are up to 8 likely members with slightly higher dispersion velocity. The ratio of brown dwarfs to stars was found to be consistent with other areas in Upper Scorpius. It was also found to be similar to other results from young clusters with OB associations, and lower than those without, suggesting the brown dwarf formation rate may be a function of environment.
    Monthly Notices of the Royal Astronomical Society 08/2011; 418. · 5.52 Impact Factor
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    ABSTRACT: We present results from a survey program to investigate the population of brown dwarfs in a number of star-forming regions. In the framework of the SONYC project (Substellar Objects in Nearby Young Clusters) we have surveyed three regions (NGC 1333, Rho-Ophiuchus, Chamaeleon-I) and identified ˜ 30 new young VLM objects. In addition, we found 19 new high-confidence members of the Upper Scorpius region, most of them likely to be substellar. Among the new brown dwarfs are a few planetary-mass objects, including one with spectral type ˜ L3, which puts its mass at ˜ 6 MJup - one of the lowest mass free-floating objects identified thus far. In NGC 1333 we present a census of 51 VLM members by combining our work with literature studies. The spatial distribution of these objects is indistinguishable from the total population of Class I/II objects in this cluster. In comparison with other nearby star-forming regions, NGC 1333 harbours an unusually large number of substellar objects (relative to the number of low-mass stars). If confirmed, this is a sign of environmental differences in the formation of brown dwarfs.
    01/2011;
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    ABSTRACT: Aims: We present near-infrared spectroscopy of the forbidden emission line (FEL) and molecular hydrogen emission line (MHEL) regions at the bases of Herbig-Haro (HH) jets from seven embedded protostars: SVS 13 (the HH 7-11 progenitor), HH 26-IRS, HH 34-IRS, HH 72-IRS, HH 83-IRS, HH 300-IRS (IRAS 04239+2436) and HH 999-IRS (IRAS 06047-1117) Methods: The integral field spectrograph, SINFONI, on the European Southern Observatory's Very Large Telescope (VLT) was used to characterise jet parameters in these formative regions, where the jets are collimated and accelerated. Results: We find considerable differences in the spectra of HH 83-IRS when compared to the other six sources; CO bandhead and atomic permitted lines from Ca i, Na i, Mg i and Al i are observed in emission in all but HH 83-IRS, where they are detected in absorption. It is likely that this source is more evolved than the others (or at the very least considerably less active). Strong CO bandhead emission is also detected in emission in the other six sources, while extended H2 ro-vibrational and [Fe ii] forbidden emission lines trace the outflows (only the HH jet from HH 83-IRS is undetected). CO bandhead and Brgamma emission peaks are in most cases coincident with the jet source continuum position, consistent with excitation in an accretion disk or accretion flow. However, in the closest source, HH 300-IRS, we do find evidence for excitation in the outflow: here the emission peak is offset by 3.6(±0.7) AU along the flow axis. We also note a correlation between CO and Mg i, Na i and Ca i intensities, which supports the idea that these atomic permitted lines are associated with accretion disks. From H2 and [Fe ii] images we measure jet widths and derive upper limits to flow component opening angles. Although we do not find that the ionised [Fe ii] component is consistently narrower than the H2 flow component, we do find that narrower H2 and/or [Fe ii] flow components are associated with higher radial velocities (as reported in the literature). Flow opening angles, over the first few hundred AU in each source, are measured to be in the range 21°-42° in both H2 and [Fe ii]. Finally, from our 3-D data we are also able to map the extinction and electron density at the base of the outflows from some of our targets: within a few hundred AU, both decrease sharply with distance from the source. Conclusions: It seems clear that collimated atomic and molecular jets, which may initially exhibit a wide opening angle, are a feature of outflows from Class I protostars, Class II T Tauri stars, and possibly even Class 0 sources, and that these jets can be traced to within a few hundred AU of the driving source. A common jet collimation and acceleration mechanism seems inescapable for all stages of low mass star formation. Data obtained at the VLT under project 078.C-0390(B)Appendices are only available in electronic form at http://www.aanda.org
    Astronomy and Astrophysics 01/2011; 528. · 5.08 Impact Factor
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    ABSTRACT: Strong outbursts in very young and embedded protostars are rare and not yet fully understood. They are believed to originate from an increase of the mass accretion rate onto the source. We report the discovery of a strong outburst in a low-mass embedded young stellar object (YSO), namely 2MASS-J05424848-0816347 or [CTF93]216-2, as well as its photometric and spectroscopic follow-up. Using near- to mid-IR photometry and NIR low-resolution spectroscopy, we monitor the outburst, deriving its magnitude, duration, as well as the enhanced accretion luminosity and mass accretion rate. [CTF93]216-2 increased in brightness by ~4.6, 4.0, 3.8, and 1.9 mag in the J, H, Ks bands and at 24 um, respectively, corresponding to an L_bol increase of ~20 L_sun. Its early spectrum, probably taken soon after the outburst, displays a steep almost featureless continuum, with strong CO band heads and H_2O broad-band absorption features, and Br gamma line in emission. A later spectrum reveals more absorption features, allowing us to estimate T_eff~3200 K, M~0.25 M_sun, and mass accretion rate~1.2x10^{-6} M_sun yr^{-1}. This makes it one of the lowest mass YSOs with a strong outburst so far discovered. Comment: To be published in A&A letter; 5 pages, 4 figures
    Astronomy and Astrophysics 12/2010; · 5.08 Impact Factor
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    ABSTRACT: Recently it has become apparent that proto-stellar-like outflow activity extends to the brown dwarf (BD) mass regime. While the presence of accretion appears to be the common ingredient in all objects known to drive jets fundamental questions remain unanswered. The more prominent being the exact mechanism by which jets are launched, and whether this mechanism remains universal among such a diversity of sources and scales. To address these questions we have been investigating outflow activity in a sample of protostellar objects that differ considerably in mass and mass accretion rate. Central to this is our study of brown dwarf jets. To date Classical T Tauri stars (CTTS) have offered us the best touchstone for decoding the launching mechanism. Here we shall summarise what is understood so far of BD jets and the important constraints observations can place on models. We will focus on the comparison between jets driven by objects with central mass < 0.1M \odot and those driven by CTTSs. In particular we wish to understand how the the ratio of the mass outflow to accretion rate compares to what has been measured for CTTSs. Comment: Proceedings of IAU meeting 275, "Jets at All Scales"
    Proceedings of the International Astronomical Union 10/2010;

Publication Stats

1k Citations
248.44 Total Impact Points

Institutions

  • 1997–2014
    • Dublin Institute for Advanced Studies
      Dublin, Leinster, Ireland
  • 2005
    • University of Hertfordshire
      • Centre for Astrophysics Research (CAR)
      Hatfield, England, United Kingdom
  • 1992–2002
    • Joint Astronomy Centre
      Hilo, Hawaii, United States
  • 1988–1998
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 1991
    • Cornell University
      Ithaca, New York, United States