Other
Scientific paper
Feb 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007noao.prop..466p&link_type=abstract
NOAO Proposal ID #2007A-0466
Other
Scientific paper
Outflows from young stars play a major role in star formation, both by removing angular momentum from circumstellar disks (and thus enabling accretion to continue), and by driving turbulence in molecular clouds (and thereby regulating the efficiency of star formation). But the precise physical mechanism powering these jets remains unclear, with the X-wind and disk-wind models offering different theories of magnetocentrifugal jet acceleration. While present observations lack the angular resolution to directly distinguish between the competing theories, high angular resolution observations can nonetheless place indirect constraints on jet models by measuring the physical conditions, mass flux, and collimation of jets. Combined optical/IR spectra offer unprecedented capabilities for sensitively diagnosing the physical conditions in jets. Line ratios of [O I], [S II], [Fe II], [P II] and other species indicate the temperature, density, ionization fraction, and depletion of refractory elements in jets. Measuring these quantities allows calculation of the mass flux, a key measurement for constraining jet models. Both optical and IR spectra together are required for the full suite of diagnostics. We have recently demonstrated the ability to obtain the necessary near-IR observations at very high angular resolution using LGS AO and the new integral field spectrograph OSIRIS at Keck Observatory to observe jets from Herbig Ae stars. It is important to study jets around the massive Herbig Ae stars as well as those around T Tauri stars in order to understand how properties such as mass flux and velocity scale with stellar mass. Our OSIRIS observations of the Herbig Ae Star LkHa 233 show a narrow, tightly collimated, and clumpy jet seen in [Fe II] emission. LkHa 233's jet is very similar in morphology to that of the lower-mass T Tauri star HH 30, but more quantitative comparisons of physical conditions and mass flux are needed. Our OSIRIS near-IR data alone allow only a few of the line ratio diagnostics, but not all; in particular optical spectra are needed to measure the temperature and ionization fraction, both critical quantities for calculating the mass flux. Here we propose to use the GMOS IFU to obtain an optical spectrum of the same jet. Together the GMOS optical and OSIRIS near-IR spectra will enable the most detailed measurements ever of the physical conditions in a Herbig Ae star jet.
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