HST/STIS observations of the RW Aurigae bipolar jet: mapping the physical parameters close to the source

Abstract

Context. We present the results of new spectral diagnostic investigations applied to high-resolution long-slit spectra obtained with the Hubble Space Telescope Imaging Spectrograph (HST/STIS) of the jet from the T Tauri star RW Aur. Aims. Our primary goal is to determine basic physical parameters (electron density n e and electron temperature T e , hydrogen ionisation fraction x e , total hydrogen density n H , radial velocity v r and the mass outflow rateṀ j ) along both the red-and blueshifted lobes of the RW Aur jet. Methods. The input dataset consists of seven long-slit spectra, of 0. 1 spatial resolution, taken with the STIS slit parallel to the jet, and stepped across it. We use the Bacciotti & Eislöffel (1999, A&A, 342, 717) Results. We were able to extract the parameters as far as 3. 9 in the red-and 2. 1 in the blueshifted beam. The electron density at the base of both lobes is close to the critical density for [S II] emission but then it decreases gradually with distance from the source. The range of electron temperatures derived for this jet (T e = 10 4 −2 × 10 4 K) is similar to those generally found in other outflows from young stars. The ionisation fraction x e varies between 0.04 and 0.4, increasing within the first few arcseconds and then decreasing in both lobes. The total hydrogen density, derived as n H = n e /x e , is on average 3.2 × 10 4 cm −3 and shows a gradual decrease along the beam. Variations of the above quantities along the jet lobes appear to be correlated with the position of knots. Combining the derived parameters with v r measured from the HST spectra and other characteristics available for this jet, we estimateṀ j following two different procedures. The mass-outflow rateṀ j is moderate and similar in the two lobes, despite the fact that the well-known asymmetry in the radial velocity persists close to the source. Using the results of the BE diagnostics we find averages along the first 2. 1 of both flows (a region presumably not yet affected by interaction with the jet environment) of 2.6 × 10 −9 M yr −1 for the red lobe and 2.0 × 10 −9 M yr −1 for the blueshifted flow, with an uncertainty of ±log M = 1.6. Conclusions. The fact that the derived mass outflow rate is similar in the two lobes appears to indicate that the central engine is constrained on the two sides of the system and that the observed asymmetries are due to environmental conditions. Possible suggestions for the origin of the differences are discussed. The RW Aur jet appears to be the second densest outflow from a T Tauri star studied so far, but its other properties are quite similar to those found in other jets from young stars, suggesting that a common acceleration mechanism operates in these sources.

POISSON project

“…Hirth et al 1997;Melnikov et al 2009), so that where [O i] is detected at the 10 −15 erg s −1 cm −2 level we expect [S ii] fluxes of order 10 −16 erg s −1 cm −2 , which are again too low for the sensitivity of our survey. In agreement with this picture, we remark that The molecular transitions of H 2 (in particular the 2.12 μm line), which is another typical tracer of shocks from protostellar jets, are detected at a significant level only in four sources.…”

Relating jet structure to photometric variability: the Herbig Ae star HD 163296

“…However, the uncertainties in these earlier measurements are quite large because of the low S/N of the spectra used. The absolute value ofṀ jet is up to two orders of magnitude lower than A87, page 12 of 20 sources with similar masses and accretion rates (Melnikov et al 2008(Melnikov et al , 2009Agra-Amboage et al 2009. In these studies, the mass flux is obtained within a few arcseconds from the source.…”

LBT/LUCIFER near-infrared spectroscopy of PV Cephei

“…HV and LV extinction values are identical (within the error bar) in each lobe, thus we derive a weighted mean for the extinction of the red-shifted lobe (A V (red) = 10.1 ± 0.7 mag), and the blue-shifted lobe (A V (blue) = 6.5 ± 0.4 mag). The difference in the extinction between the red-and blue-shifted lobes is due to the circumstellar matter (mostly caused by the disc in PV Cep), and it is usually observed in protostellar jets close to the source (see e.g., Garcia Lopez et al 2008;Melnikov et al 2009). Finally, we note that the A V towards PV Cep varies with time, due to circumstellar extinction variability, related to dust condensation in the inner disc region after the outburst and/or to the large amount of dust lifted by the jet from the disc during and after the outbursts (Kun et al 2011).…”