Removed C IV flux in target description, because it is not important for this proposal.840866514Assigned ID: 271
----- Attempting Submission 1 (Thu Apr 10 21:56:22 GMT 2014) -----
HST Phase I Proposal 271 (dg.apt) successfully submitted.
----- Attempting Submission 2 (Fri Apr 11 00:07:24 GMT 2014) -----
HST Phase I Proposal 271 (dg.apt) successfully submitted.
----- Attempting Submission 3 (Fri Apr 11 18:46:49 GMT 2014) -----
HST Phase I Proposal 271 (dg.apt) successfully submitted.
----- Attempting Submission 4 (Fri Apr 11 22:27:38 GMT 2014) -----Initial phase II submission.-77312989----- Attempting Submission 1 (Tue Jul 22 15:47:47 GMT 2014) -----The nature of stationary components in jets from young stellar objectsThere is increasing evidence that jets are essential for the star formation process. Our understanding of the jet launching process is, however, still fragmentary. In particular, new observations revealed (a) that jets from young stellar sources possess hot, stationary components close to the driving source that contrast the well-known moving parts of the jets further out and (b) possible evidence for plasma acceleration within a few 10 AU from the source.
We propose to follow-up these new results by providing the required diagnostics to uncover the controversial origin of the stationary component and to constrain the location where the outflowing plasma is accelerated. Specifically, we propose to observe the classical T Tauri star DG Tau with STIS and the slit oriented along the jet axis to measure the plasma density of the warm (1e4 K) and hot (1e5 K) parts of the jet to distinguish between proposed models for the stationary component, as well as to follow the plasma traveling through the jet collimation region to test current jet launching models.The goal of the proposed observations is to spatially resolve the intermediate (T = 10e5 K) and
low temperature (T = 10e4 K) material within DG Tau's jet as well as to provide a large set of
diagnostic lines for a detailed study of the plasma properties within the innermost jet region.
We propose to use STIS with the slit oriented along the jet axis. Specifically, we propose a
hybrid approach using a combination of the low and medium resolution STIS gratings, which
requires only four HST orbits to provide velocity resolution as well as wavelength coverage.
In particular, we dedicate one orbit each for the strongest lines tracing the 10e4 and 10e5 K
plasma, respectively. Another two orbits provide the large wavelength coverage required for
the proposed studies.
One orbit is dedicated to provide velocity resolved data for the traditional jet tracers of
the 10e4 K plasma using the G750M grating ([O i] 6363 A, [N ii] 6548 A and the [S ii] doublet
around 6720 A). These data will be used to compare the velocity of the 10e4 with the 10e5 K
plasma and to follow the knot evolution by comparison with existing HST data. We know from
archival STIS G750M data that a single orbit is sufficient to resolve [O i] 6363 A close to the star
against the bright stellar background and that other diagnostic lines like [N ii] 6548 A can also
be resolved against the nearby bright Halpha line with sufficient S/N > 10.
One orbit using the G430M will provide velocity resolution for the strongest line tracing
the 10e5 K plasma ([O iii] 5007 A). For the estimate of the required exposure time, we again
relied on archival HST data (a short 180 s G430L exposure) and estimate a representitive
flux of 10e14 erg/s/cm2 (this value is about half the total flux given in Schneider et al.
2013, because the emission is spatially distributed). However, the dominant noise source is
the subtraction of the stellar continuum. Using the STIS ETC, we estimate from the archival
data a continuum rate of 2.4 counts/pixel/s at the peak of the stellar continuum and < 1
counts/pix/s 0. 1 away from the stellar position so that we achieve S/N > 9 farther than
0. 1 arcsec from DG Tau and a single orbit will be sufficient for our science goals.
Lastly, two orbits using the L-mode gratings are required to reach sufficient S/N in lower
luminosity diagnostic lines. The exposure time for the G430L (one orbit) is driven by the
[Ne iii] 3968 line seen in the short (180 s) G430L exposure at low S/N of about 3. Thus,
one orbit providing 2800 s on target time will allow us to measure the line with S/N of 11.
The exposure time for the G750L grating (one orbit) is more difficult to estimate, because
no HST data of the [Fe ii] lines exist and we extrapolate from the Fe lines and [O i] 6300 A
measured by Hartigan et al. (2004) for HN Tau. The [O i] flux is larger in DG Tau (about
about a factor of seven). On the other hand, the continuum emission is also stronger by a
factor of about 3 so that we expect to detect the lines with similar or better S/N as Hartigan
et al. using a single orbit of integration time which was sufficient to derive the density with
0.15 dex accuracy close to the source.
The position angle of the jet (PA=226 degree) is known from previous observations (HST and
ground based AO). A tolerance of +-1 deg in position angle is acceptable for this jet. We will
use the same successful acquisition strategy as in previous programs (e.g. Prop-ID 12199).
In summary, we request a single visit consisting of four orbits (each providing 50 min
visibility time when using increased scheduling flexibility).RESOLVED STAR FORMATION12falsefalse0.00.0falsefalsefalseSUPPORTEDSTART TAURI STARThe coordinates are from 2MASS and corrected for proper-motion as measured by Zacharias et al. (2003) for 2015. The proper-motion is small with
2.9 and -18.2 mas/yr for RA and Dec, respectively. Therefore, we do not enter proper-motion values into the form, but rather use a value appropriate for the approx. observing time.
From previous observations, we know that these coordinates almost perfectly center the star in the ACQ aperture.J2000J2000STIS/CCDSpectroscopicNoNoG750M6581STIS/CCDSpectroscopicNoNoG430M4961STIS/CCDSpectroscopicNoNoG430L4300STIS/CCDSpectroscopicNoNoG750L7751POS-TARGDITHER0.5078This pattern is applied to all observations to mitigate the effects of hot pixels. The source is placed at three different positions along the
slit with offsets of 0.5 arcsec each (or more precisely 10 pixel each).LINEfalsefalse390.0STIS-ALONG-SLIT1falsePOS-TARGDITHER0.35546Seven pixel steps. Provides approximately the same offset as the three point dither.LINEfalsefalse490.0STIS-ALONG-SLIT2falseThe scheduling data was generated by CASM 22.2.CASM was run in Phase II mode.All observations within one visit to provide near-simultaneous coverage of all diagnostics.(Tic-Visit
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