Deirdre Coffey

Rotation of jets from young stars: New clues from the Hubble space telescope imaging spectrograph

We report findings from the first set of data in a current survey to establish conclusively whether jets from young stars rotate. We observed the bipolar jets from the T Tauri stars TH 28 and RW Aur and the blueshifted jet from T Tauri star LkHα 321, using the Hubble Space Telescope Imaging Spectrograph. Forbidden emission lines show distinct and systematic velocity asymmetries of 10-25 (±5) km s-1 at a distance of 03 from the source, representing a (projected) distance of ≈40 AU along the jet in the case of RW Aur, ≈50 AU for TH 28, and 165 AU in the case of LkHα 321. These velocity asymmetries are interpreted as rotation in the initial portion of the jet where it is accelerated and collimated. For the bipolar jets, both lobes appear to rotate in the same direction. Values obtained were in agreement with the predictions of MHD disk-wind models. Finally, we determine, from derived toroidal and poloidal velocities, values for the distance from the central axis of the footpoint for the jets low-velocity component of ≈0.5-2 AU, consistent with the models of magnetocentrifugal launching.

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 (1.5at 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 /r 0 between the Alfven and footpoint radii) is in the range 3.5-4.6 (with an accuracy of 20-25%), or, alternatively, the ejection index ξ = d In(M acc )/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 B Φ /B p 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 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.

JET ROTATION INVESTIGATED IN THE NEAR-ULTRAVIOLET WITH THE HUBBLE SPACE TELESCOPE IMAGING SPECTROGRAPH

We present results of the second phase of our near-ultraviol et investigation into protostellar jet rotation using HST/STIS. We obtain long-slit spectra at the base of five T Tauri je ts to determine if there is a di fference in radial velocity between the jet borders which may be interpr ted as a rotation signature. These observations are extremely challenging and push the limits of current ins trumentation, but have the potential to provide long-awaited observational support for the magneto-centr ifugal mechanism of jet launching in which jets remove angular momentum from protostellar systems. We succ e sfully detect all five jet targets (from RW Aur, HN Tau, DP Tau and CW Tau) in several near-ultraviolet emissi on lines, including the strong Mg II doublet. However, only RW Aur’s bipolar jet presents su fficient signal-to-noise for analysis. The approaching jet lo be shows a di fference of 10 km s −1 in a direction which agrees with the disk rotation sense, but is opposite to previously published optical measurements for the recedin g jet. The near-ultraviolet di fference is not found six months later, nor is it found in the fainter receding jet. Overall, in the case of RW Aur, di fferences are not consistent with a simple jet rotation interpretation. Inde e , 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.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 Aurs bipolar jet presents a sufficiently high signal-to-noise ratio to allow for analysis. The approaching jet lobe shows a difference of 10 km s–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.

The Evolution and Simulation of the Outburst from XZ Tauri - A Possible EXor?

Received date ;accepted date Abstract. We report on multi-epoch HST/WFPC2 images of the XZ Tauri binary, and its outflow, covering the period from 1995 to 2001. Data from 1995 to 1998 have already been published in the literature. Additional images, from 1999, 2000 and 2001 are presented here. These reveal not only further dynamical and morphological evolution of the XZ Tauri outflow but also that the suspected outflow source, XZ Tauri North has flar ed in EXor-type fashion. In particular our proper motion studies suggests that the recently discovered bubble-like shock, driven by the the XZ Tauri outflow, is slowing down (its tangent ial velocity decreasing from 146 km s 1 to 117 km s 1 ). We also present simulations of the outflow itself, with pla usible ambient and outflow parameters, that appear to reproduce not only the dynamical evolution of the flow, but also its shape and emissi on line luminosity.

Searching for jet rotation in Class 0/I sources observed with GEMINI/GNIRS.

Context. In recent years, there has been a number of detections of gradients in the radial velocity profile across jets from young stars. The significance of these results is considerable. They may be interpreted as a signature of jet rotation about its symmetry axis, thereby representing the only existing observational indications supporting the theory that jets extract angular momentum from stardisk systems. However, the possibility that we are indeed observing jet rotation in pre-main sequence systems is undergoing active debate. Aims. To test the validity of a rotation argument, we must extend the survey to a larger sample, including younger sources. Methods. We present the latest results of a radial velocity analysis on jets from Class 0 and I sources, using high resolution data from the infrared spectrograph GNIRS on GEMINI South. We obtained infrared spectra of protostellar jets HH 34, HH 111-H, HH 212 NK1 and SK1. Results. The [Fe II] emission was unresolved in all cases and so Doppler shifts across the jet width could not be accessed. The H2 emission was resolved in all cases except HH 34. Doppler profiles across the molecular emission were obtained, and gradients in radial velocity of typically 3 km s −1 identified. Conclusions. Agreement with previous studies implies they may be interpreted as jet rotation, leading to toroidal velocity and angular )

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 both molecular 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] 2.13 μm line which is of similarly high excitation; H I 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, 1.60 μm 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 H I 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.

Rotation of Jets From T-Tauri Stars: New Clues From HST/STIS Observations

Whether jets from newly forming stars rotate is a fundamental question in star formation research. Theoretical models propose jet rotation as a means of removing angular momentum from the young star and disk system, thus allowing accretion. While widely accepted, this idea has not yet been tested observationally due to the high resolution requirement of examining jets close to their launching point. Previous findings from the Hubble Space Telescope Imaging Spectrograph (HST/STIS) and Owens Valley Radio Observatory (OVRO) give indications of same rotation of the jet and disk respectively, of T Tauri star DG Tau. We report preliminary findings from STIS data for 3 of 8 sources in a current survey to establish conclusively whether protostellar jets rotate. The results were positive, yielding evidence of radial velocity differences about the axis at the base of all three jets of 10–25 km s−1.

Searching for Jet Rotation Signatures in Class 0 and I Jets

In recent years, there has been a number of detections of asymmetries in the radial velocity profile across jets from young stars. The significance of these results is considerable. They may be interpreted as a signature of jet rotation about its symmetry axis, thereby representing the only existing observational indications supporting the theory that jets extract angular momentum from star-disk systems. However, the possibility that we are indeed observing jet rotation in pre-main sequence systems is undergoing active debate. To test the validity of a rotation argument, we must extend the survey to a larger sample, including younger sources. We present the latest results of a radial velocity analysis on jets from Class 0 and I sources, using high resolution data from the infrared spectrograph GNIRS on GEMINI South. These observations demonstrate the difficulty of conducting this study from the ground, and highlight the necessity for high angular resolution via adaptive optics or space-based facilities.

X-RED: a satellite mission concept to detect early universe gamma ray bursts

Gamma ray bursts (GRBs) are the most energetic eruptions known in the Universe. Instruments such as Compton-GRO/BATSE and the GRB monitor on BeppoSAX have detected more than 2700 GRBs and, although observational confirmation is still required, it is now generally accepted that many of these bursts are associated with the collapse of rapidly spinning massive stars to form black holes. Consequently, since first generation stars are expected to be very massive, GRBs are likely to have occurred in significant numbers at early epochs. X-red is a space mission concept designed to detect these extremely high redshifted GRBs, in order to probe the nature of the first generation of stars and hence the time of reionisation of the early Universe. We demonstrate that the gamma and x-ray luminosities of typical GRBs render them detectable up to extremely high redshifts (z ~ 10to30), but that current missions such as HETES and SWIFT operate outside the observational range for detection of high redshift GRB afterglows. Therefore, to redress this, we present a complete mission design from teh science case to the mission architecture and payload, the latter comprising three instruments, namely wide field x-ray cameras to detect high redshift gamma-rays, an x-ray focussing telescope to determine accurate coordinates and extract spectra, and an infrared spectrograph to observe the high redshift optical afterglow. The mission is expected to detect and identify for the first time GRBs with z > 10, thereby providing constraints on properties of the first generation of stars and the history of the early Universe.