Computer Science
Scientific paper
Jul 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008hst..prop11660b&link_type=abstract
HST Proposal ID #11660. Cycle 17
Computer Science
Scientific paper
In recent years we have successfully harnessed the high resolution of STIS in the optical to reveal asymmetries in Doppler shifts transverse to the flow direction in 8 T Tauri jets {Bacciotti ea 2002; Woitas ea 2005; Coffey ea 2004; 2007}. We interpret the findings, just 100 AU above the disk, as signatures of jet rotation. The significance of these results is considerable. They form the only existing observational indications supporting the theory that jets extract angular momentum from star-disk systems. Furthermore, they hold the potential to discriminate between the main model contenders: X-wind and Disk-wind {Ferreira ea 2006}. Although our results are encouraging, it is evident that we are only marginally resolving the effects of rotation because of the limiting resolution {spatially and spectrally} of STIS in the optical. Therefore, in Cycle 12 we proposed to extend this study into the near-ultraviolet {NUV}, giving double the spatial and spectral resolution {proposal ID 9807}. Unfortunately, only 3 targets in our survey were observed before the failure of STIS {Coffey ea 2007}. Nevertheless, the results were very exciting. Agreement was found between the optical and NUV results in terms of the magnitude and sense of the Doppler shift gradient across the jet. Furthermore, the NUV lines indicated that the observed high velocity gas was launched from about 0.2-0.5 AU, compared to the lower velocity gas traced in optical lines which originates from as far as 2 AU. This puts a strong contraint on MHD launch models, and indeed holds the potential to differentiate between them. Given that the strength of a rotation argument lies in the survey nature of the findings, we need to resume this program in order to see if the same rotation signatures are commonly seen in the NUV, as they are in the optical. Furthermore, the higher spatial and spectral resolution of STIS in the NUV will allow us to more accurately quantify the variation in toroidal velocity as a function of distance from the jet axis. This study will provide an invaluable statistical argument to support the fact that we are indeed observing jet rotation. Such a conclusion is critical to providing observational backing to the widely accepted but untested theory of magnetocentrifugal ejection.;
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