T. P. Ray

The spatial distribution of star formation in the solar neighbourhood: do all stars form in dense clusters?

We present a global study of low mass, young stellar object (YSO) surface densities (�) in nearby (< 500 pc) star forming regions based on a comprehensive collection of Spitzer Space Telescope surveys. We show that the distribution of YSO surface densities in the solar neighbourhood is a smooth distribution, being adequately described by a lognormal function from a few to 10 3 YSOs per pc 2 , with a peak at � 22 stars pc

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.

Observations of Shocked H2 and Entrained CO in Outflows from Luminous Young Stars

Narrowband, H2 (1–0) S(1) images of six luminous outflow regions are presented and discussed. In five of these regions, W75 N, S140 N, NGC 7538, AFGL 5180, and AFGL 490, H2 shock features associated with molecular (CO) outflows are observed. We have discovered faint, though extensive, bow shocks in the W75 N outflow that indicate a total flow length of at least 3 pc. The Herbig-Haro knots that make up the HH 251–254 outflow in S140 N are also observed in H2; in addition, knots in the counterflow are discovered. Copious H2 emission is also observed throughout the NGC 7538 region; filamentary structures to the northeast of the central cluster (IRS 1) are probably photodissociation fronts, although a jetlike structure is observed associated with the IRS 9 CO outflow. In AFGL 5180, a new, collimated H2 jet is discovered to the east of the central cluster, and numerous knots and filaments are observed around the cluster itself that could be associated with the known CO outflow there. Last, H2 line emission is observed southwest of AFGL 490; in particular, a bright peak is found associated with a warm molecular clump in the CO outflow. To complement these data, wide-field CO J = 2–1 maps have also been obtained toward three regions, W75 N, S140 N, and NGC 7538. When compared with the H2 images, these provide new insight into each outflow region. Indeed, analysis of these data suggests that although these flows are more massive and more energetic than their low-mass counterparts, they are nevertheless well collimated, bipolar, and possibly jet-driven. Molecular bow shocks, driven by an underlying, possibly variable stellar jet, may play a major role in this entrainment process.

The JWST MIRI instrument concept

The MIRI is the mid-IR instrument for JWST and provides imaging, coronography and low and medium resolution spectroscopy over the 5-28μm band. In this paper we provide an overview of the key driving requirements and design status.

Paschen beta emission as a tracer of outflow activity from T-Tauri stars, as compared to optical forbidden emission

The Paschen beta (1.2822 μ m) emission line found in the near-infrared spectra of T-Tauri stars (TTSs) is believed to trace the accretion of material onto the central star. We present spectroscopic data which suggests that this may not always be the case. The technique of spectro-astrometry is used by us to measure positional displacements in the Pa β emission from four T-Tauri stars, namely DG Tau, V536 Aql, LkH α 321 and RW Aur. We also observed the optical forbidden emission from these sources, for example the [SII]

LAMP: the long-term accretion monitoring programme of T Tauri stars in Chamaeleon I

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Near-IR echelle spectroscopy of Class I protostars: Mapping Forbidden Emission-Line (FEL) regions in [FeII]

6716, 6731, [OI]

POISSON project - I. Emission lines as accretion tracers in young stellar objects: results from observations of Chamaeleon I and II sources

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The Spitzer Survey of Interstellar Clouds in the Gould Belt. II. The Cepheus Flare Observed with IRAC and MIPS

6300, 6363 and [NII]

Temperaments of young stars: rapid mass accretion rate changes in T Tauri and Herbig Ae stars

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