Prof Patrick Roche

Abstract:

By the end of 2001, the two Gemini telescopes will be in full operation, with the UK community having access to about 70 nights per year on each. With the WHT, UKIRT and the AAT, the community has access to over 600 nights per year of 4 m time. It is clear that most programmes will continue to he conducted on our existing telescopes, with Gemini being used only where the programmes cannot be completed on the 4 m instruments. Gemini has the advantages of large collecting area and active optics to ensure that observations are site-limited. However it also has a restricted field of view (<10 arcmin) and, initially will have a restricted instrument suite. The excellent sites and ability to apply aluminium or silver coatings to the telescope mirrors will ensure high throughput. Gemini is well-suited for deep observation over small fields. with the best results obtained over fields where tip-tilt or higher degrees of correction are effective (3 arcmin). The largest gains arise where the full gain of the increased area is realised, in near-diffraction-limited observations, e.g at thermal infrared wavelengths and with adaptive correction in the near-infrared, and in photon-starved applications such as high spectral resolution, faint object spectroscopy. Many programmes carried out with Gemini will rely on supporting observations from 4 m telescopes for target selection and complementary observations such as sample completion, simultaneous measurements in different wavebands etc. In the next decade, the UK will have access of right to almost one half of an 8 m telescope in a world where about a dozen 8-10 m class telescopes will be in operation. We enjoy a much greater fraction of the total 4 m telescopes and it will be imperative that they are used effectively with Gemini in order to ensure that our highest priority scientific programmes are completed efficiently. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract:

We report the results of a survey of low mass Class I protostars in the cm continuum. In the initial survey, seven sources in the Taurus star formation were observed with the VLA at 0``.25 resolution. All seven sources drive CO outflows and display Herbig-Haro flows in the optical or near infrared wavebands. 4/7 sources were detected, two of which are new discoveries in systems of very low luminosity, one being the lowest luminosity system detected to date in the cm continuum. Notably, three sources were not detected to a 3-sigma limit of 0.10 mJy/beam, which indicates that significant cm continuum emission is not a universal feature of Class I systems with outflow activity. Subsequent observations of HH30, a more evolved Class II system, found no emission to a 3-sigma limit of 0.03 mJy/beam. After comparison with near infrared data, we suggest that the discriminating feature of the detected systems is a relatively high ionisation fraction in the stellar wind. Temporal variability of the outflow may also play a role. The one relatively bright source, IRAS 04016+2610 (L1489 IRS), is clearly resolved on a 0``.4 scale at 2 cm and 3.5 cm. Follow-up imaging with MERLIN did not detect this source with a 0``.04 beam, indicating that the radio emission is generated in a region with a radius of about 25 au, which is broadly similar to the radius of the bipolar cavities inferred from models of near infrared data. Interpretation of this system is complicated by the existence of a quadrupolar outflow, which we originally detected through polarimetric imaging. We present a near infrared H2 image in which a bow shock in the secondary outflow is clearly seen. This complicated structure may have been caused by a gravitational interaction between two protostars.

Abstract:

We describe the results of a very deep imaging survey of the Trapezium cluster in the IJH bands, using the UKIRT high-resolution camera UFTI. Approximately 32 per cent of the 515 point sources detected are brown dwarf candidates, including several free-floating objects with masses below the deuterium-burning (planetary) threshold at 0.013 M⊙, which are detectable because of their extreme youth. We have confidence that almost all the sources detected are cluster members, since foreground contamination is minimal in the 33-arcmin² area surveyed, and the dense backdrop of OMC-1 obscures all background stars at these wavelengths. Extinction is calculated from the (J - H) colours, permitting accurate luminosity estimates, and temperatures are derived from the dereddened (I - J) colours. There is some evidence for a cut-off in the luminosity function below the level corresponding to several Jupiter masses, which may represent the bottom end of the initial mass function. Since star formation is complete in the Trapezium, this limit could have wide significance, if confirmed. However, it could well be an effect of the dispersal of the molecular cloud by the central O-type stars, a process for which the time-scale will vary between star formation regions.

Abstract:

We report on advances in the study of the cores of NGC 6302 and 6537 using infrared grating and echelle spectroscopy. In NGC 6302, emission lines from species spanning a large range of ionization potential, and in particular [Si IX] 3.934 μm, are interpreted using photoionization models (including CLOUDY), which allow us to re-estimate the temperature of the central star to be about 250 000 K. All of the detected lines are consistent with this value, except for [Al V] and [Al VI]. Aluminium is found to be depleted to one hundredth of the solar abundance, which provides further evidence for some dust being mixed with the highly ionized gas (with photons harder than 154 eV). A similar depletion pattern is observed in NGC 6537. Echelle spectroscopy of IR coronal ions in NGC 6302 reveals a stratified structure in ionization potential, which confirms photoionization to be the dominant ionization mechanism. The lines are narrow (<22km s-1 FWHM), with no evidence of the broad wings found in optical lines from species with similar ionization potentials, such as [Ne V] 3426 Å. We note the absence of a hot bubble, or a wind-blown bipolar cavity filled with a hot plasma, at least on 1 arcsec and 10 km s-1 scales. The systemic heliocentric velocities for NGC 6302 and 6537, measured from the echelle spectra of IR recombination lines, are found to be -34.8±1 km s-1 and -17.8±3 km s-1. We also provide accurate new wavelengths for several of the infrared coronal lines observed with the echelle.