Astronomical instrumentation

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:

Integral field spectroscopy in the K-band (1.9-2.4um) was performed on four IR-bright star clusters and the two nuclei in NGC 4038/4039 (``The Antennae''). Two of the clusters are located in the overlap region of the two galaxies, and together comprise ~25% of the total 15um and ~10% of the total 4.8 GHz emission from this pair of merging galaxies. The other two clusters, each of them spatially resolved into two components, are located in the northern galaxy, one in the western and one in the eastern loop of blue clusters. Comparing our analysis of Brgamma, CO band-heads, He I (2.058um), Halpha (from archival HST data), and V-K colors with stellar population synthesis models indicates that the clusters are extincted (A_V ~ 0.7 - 4.3 mags) and young, displaying a significant age spread (4-13 Myrs). The starbursts in the nuclei are much older (65 Myrs), with the nucleus of NGC 4038 displaying a region of recent star formation northward of its K-band peak. Using our derived age estimates and assuming the parameters of the IMF (Salpeter slope, upper mass cut-off of 100 M_sun, Miller-Scalo between 1 M_sun and 0.1 M_sun), we find that the clusters have masses between 0.5 and 5 * 10^6M_sun.

Abstract:

We report on the discovery of a double nucleus in M 83, based on measurements of the line of sight velocity distribution of stars observed at near infrared wavelengths with the VLT ISAAC spectrograph. We observe two peaks separated by 2.7" in the velocity dispersion profile of light from late-type stars measured along a slit 0.6" wide, centered on the peak of K band emission and with P.A. 51.7 degrees. The first peak coincides with the peak of the K band light distribution, widely assumed to be the galaxy nucleus. The second peak, of almost equal strength, almost coincides with the center of symmetry of the outer isophotes of the galaxy. The secondary peak location has little K band emission, and appears to be significantly extincted, even at near infrared wavelengths. It also lies along a mid-infrared bar, previously identified by Gallais et al. (1991) and shows strong hydrogen recombination emission at 1.875 microns. If we interpret the observed stellar velocity dispersion as coming from a virialized system, the two nuclei would each contain an enclosed mass of 13.2 x 10^6 M_sun within a radius of 5.4pc. These could either be massive star clusters, or supermassive dark objects.