Classical T Tauri-like Outflow Activity in the Brown Dwarf Mass Regime

Over the last number of years spectroscopic studies have strongly supported the assertion that protostellar accretion and outflow activity persists to the lowest masses. In this paper we present the results of our latest investigation of brown dwarf (BD) outflow activity and report on the discovery of two new outflows. Here ISO-Oph 32 is shown to drive a blue-shifted outflow with a radial velocity of 10-20 km/s and spectro-astrometric analysis constrains the position angle of this outflow to 240 +/- 7 degrees. The BD candidate ISO-Cha1 217 is found to have a bipolar outflow bright in several key forbidden lines (radial velocity = -20 km/s, +40 km/s) and with a PA of 190-210 degrees. A striking feature of the ISO-Cha1 217 outflow is the strong asymmetry between the red and blue-shifted lobes. This asymmetry is revealed in the relative brightness of the two lobes (red-shifted lobe is brighter), the factor of two difference in radial velocity (the red-shifted lobe is faster) and the difference in the electron density (again higher in the red lobe). Such asymmetries are common in jets from low mass protostars and the observation of a marked asymmetry at such a low mass supports the idea that BD outflow activity is scaled down from low mass protostellar activity. In addition to presenting these new results, a comprehensive comparison is made between BD outflow activity and jets launched by CTTSs. In particular, the application of current methods for investigating the excitation conditions and mass loss rates in CTT jets to BD spectra is explored.Comment: Accepted by Astrophysical Journa

Periodic Variation of Stress in Sputter Deposited Si/WSi2 Multilayers

A tension increment after sputter deposition of 1 nm of WSi2 onto sputtered Si was observed at low Ar gas pressures. Wafer curvature data on multilayers were found to have a periodic variation corresponding to the multilayer period, and this permitted statistical analyses to improve the sensitivity to small stresses. The observation of tension instead of compression in the initial stage of growth is new and a model invoking surface rearrangement is invoked. The data also bear on an unusual surface smoothing phenomena for sputtered Si surfaces caused by the sputter deposition of WSi2 . We furthermore report that for low Ar pressures the Si layers are the predominant source of built-up stress

Accretional heating of the satellites of Saturn and Uranus

Voyager images of the satellites of Saturn and Uranus have shown that these bodies are characterized by remarkable diversity and surprisingly complex geologic histories. Despite their small sizes, a number of the satellites show unambiguous evidence for resurfacing. The goal was to develop a detailed model for heating of these small satellites, and then to explore the consequences of variations in the free parameters in the model. Specifically an attempt was made to determine for what range of conditions melting will occur in these satellites. Along with varying a number of model parameters, the important effects of inclusion of small amounts of ammonia and methane in the system were considered

Physical properties of the jet from DG Tauri on sub-arcsecond scales with HST/STIS

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.Comment: 16 pages, 18 figure

Spatial and Temporal Patterns in Arctic Fox Diets at a Large Goose Colony

We studied diets of arctic foxes (Alopex lagopus) associated with a large nesting colony of lesser snow and Ross's geese in the central Canadian Arctic. From 15 May to 5 August 1994 and from 18 May to 7 August 1995, we examined arctic fox diets using frequency of occurrence of prey remains in faeces. Most scats (n=791 of 817, or 97%) were collected from den sites. Scats from foxes with dens inside the goose colony contained eggs more frequently than those of foxes that depended more on small mammals outside the colony. Foxes were opportunistic in their feeding habits, as prey use was linked to the nesting cycle of geese, coinciding to periods of egg, goose, and gosling abundance. However, diets in spring, i.e., before geese arrive, reflected the importance to arctic foxes of caching geese and eggs from the previous summer at Karrak Lake. We suggest that large increases in nesting populations of lesser snow and Ross's geese may have beneficial implications for arctic fox populations over a large area.On a étudié le régime alimentaire du renard arctique (Alopex lagopus) associé à une vaste colonie nicheuse de petites oies blanches et d'oies de Ross dans le centre de l'Arctique canadien. Du 15 mai au 5 août 1994, et du 18 mai au 7 août 1995, on a examiné le régime alimentaire du renard arctique en utilisant la fréquence de l'occurrence de restes de proies dans les crottes. La plupart (n = 792 sur 817, ou 97 p. cent) ont été recueillies sur les sites des terriers. Les crottes des renards dont le terrier se trouvait à l'intérieur de la colonie d'oies contenaient plus souvent des oeufs que celles des renards dont le terrier était situé en dehors de la colonie et qui dépendaient plus des petits mammifères. Les renards se montraient opportunistes dans leurs habitudes alimentaires, l'utilisation des proies étant liée au cycle nicheur des oies et coïncidant avec des périodes d'abondance d'oeufs, d'oies et d'oisons. Toutefois, les régimes alimentaires au printemps, c'est-à-dire avant l'arrivée des oies, reflétaient l'importance pour les renards de Karrak Lake des réserves d'oies et d'oeufs de l'été précédent. On suggère que de fortes augmentations dans les populations nicheuses de la petite oie blanche et de l'oie de Ross pourraient avoir des retombées bénéfiques à grande échelle sur les populations de renards arctiques