0Assigned ID: 205
----- Attempting Submission 1 (Thu Apr 10 16:17:46 GMT 2014) ------Original Phase II .apt was given pre-submittal review by Miranda Link.
- This resubmittal on 6 Sep. 2014 is in response to email from P. Sonnentrucker
on 4 Sept. noting that Visit 01 G140M central wavelengths were different for
the 5 V01 orbits. All G140M exposures have now been set to central 1550 Ang.8956498----- Attempting Submission 1 (Thu Jul 17 16:24:08 GMT 2014) -----
----- Attempting Submission 2 (Sat Sep 06 20:05:53 GMT 2014) -----Tracing Hot Plasma in the RY Tau JetThe accreting T Tauri star RY Tau drives a spectacular bipolar jet
whose blueshifted component is traced optically at separations of
1.3" - 30" from the star. Optical studies probe cool jet plasma
(T ~ 1e4 K) but evidence for much hotter plasma (T ~ 1e5 - 1e6 K)
is seen in UV spectral lines and Chandra X-ray images. We propose
to obtain STIS UV spectra of RY Tau with the slit aligned along
the jet. HST's high spatial resolution and UV spectral line
diagnostics will determine the spatial extent and properties of
the hot plasma in the inner jet and will test jet-heating models.
Only HST provides the capabilities needed to study conditions in the
hot dense plasma in the physically important inner jet where launching
and collimation occur.Observations: We will obtain 1st-order STIS/MAMA UV grating spectra of the RY Tau
jet with the 52" x 0.2" slit, which is well-matched to the jet dimensions. The brightest
knots lie within 15" of the star (Fig. 1) and the jet width is FWHM = 0.2" - 0.3" (AA09).
We request G140L (2 orbits), G140M (5 orbits), and G230L (1 orbit) gratings. G140L
and G230L will provide complete spectral coverage of the FUV and NUV including several
important emission lines as specified below. The higher spectral resolution of G140M (1523
- 1577 Ang. ) will fully resolve the C IV doublet at 1548.2/1550.7 Ang . G140M will provide
accurate measurements of jet velocity (resolution delta_V = 25 km s^-1) and will allow any weak
contribution from fluorescent H2 lines to be discerned (Fig. 6). STIS is clearly preferred
over COS since STIS provides spatially-resolved spectra along the jet.
Stellar Parameters: RY Tau is a F8-G1 TTS with Teff =5945 K (C04) and variable
V = 10.3 +- 0.9 mag. The most recent AAVSO photometry in April 2014 give a range V = 10.5 - 11.
Target MAMA brightness limits are not exceeded. The extinction
toward the disked star is AV = 2.2 +- 0.2 mag (C04) but may well be lower toward the jet
offset from the star. No companion has yet been found (e.g. Leinert et al. 1993; Pott et
al. 2010). Observed (absorbed) UV continuum flux densities are
Fcont(1760 Ang.) = 1.9e-15 and Fcont(1958 Ang.) = 2.07e-15 ergs cm^-2 s^-1 Ang.^-1
(Valenti et al. 2000 [V00]; C04).
Previous STIS G140L/230L observations with the slit nearly perpendicular to the jet (Fig.
5; C04) give observed (absorbed) line fluxes in units of 10^-14 ergs cm^-2 s^-1: C IV = 5.93;
Si III] = 7.70; C III] = 5.37. ETC predicts S/N = 35 - 50 for G140L/230L in these lines.
Sensitivity: Allowing for overheads (Sec. 6.4 of the Primer), we estimate usable exposures
of 13080 s (G140M), 4800 s (G140L), and 2040 s (G230L). Our requested exposures (orbits)
are driven by the need to obtain adequate sensitivity and SNR in faint emission lines for flux
measurement and line analysis. As a benchmark, we use the C IV flux detected in the DG
Tau jet during a 14 ksec STIS G140M slit observation (S13). The observed (absorbed) jet
flux is F1548+1551 = 2.0 e-14 erg cm^=2 s^-1 at offsets of 0.15" - 0.3" from the star, of which
2/3 comes from the 1548 Ang. line (Fig. 6-left). Continuum emission in the jet is expected to
be very low (Fig. 6-left). Assuming a similar C IV flux for RY Tau's jet, the ETC predicts
SNR = 10 in C IV for G140M (Fig. 6-right) and SNR = 30 for G140L. G140L will reach a
line detection threshold (SNR = 10) at C IV for absorbed line fluxes 10 times lower than
that measured for DG Tau's jet. For G230L, ETC predicts an absorbed line flux detection
threshold of Fline (3.0-3.6) e-15 erg cm^-2 s^-1 for Si III] (1892Ang. ) and C III] (1909 Ang. ),
more than an order of magnitude fainter than the stellar line fluxes.
UV Line Diagnostics: The most important spectral lines for diagnosing physical conditions
in the jet will be the C IV doublet at 1548/1551 (G140L, G140M) and the optically thin Si
III] 1892 and C III] 1909 lines (G230L). The C IV line traces hotter plasma. The flux ratio
of the Si III] and C III] lines provides density information and can diagnose higher densities
(n_e = 10^10 cm^-3) that are present in shock regions near the star (Lamzin 2000b; GV07).
Other useful G140L lines are: Si IV 1394/1403, He II 1640 (tracers of intermediate-T
plasma), C III 1176 and Si III 1206 (densities; C04).
Special Requirements
Since our primary goal is to study emission from the jet, we require that the 52" x 0.2" slit
be oriented along the jet axis, so PA APER = 114 deg. or PA APER = 294 deg. is requested. These
values correspond to ORIENT = 159.35 deg. and ORIENT = 339.35 deg.. The Visit Planner shows
that the observations are schedulable in Cycle 22 at ORIENT = 159.35 deg. The first available
window occurs from 28 Nov. - 6 Dec. 2014 and a second window on similar dates in 2015.RESOLVED STAR FORMATIONDefaultfalsetruefalsefalsefalseSUPPORTEDSTARF3-F9G III-IJETT TAURI STARVariable star. AAVSO gives V magnitudes in range V = 9.6 - 11.2 from
April 2013 - April 2014. During the same period, B ranged from B = 10.75 - 12.1.
Most recent AAVSO values in April 2014 are V = 10.8 +- 0.2 and B = 11.8 +- 0.2.
During the period 1983 - 2004 the range was V = 9.3 - 11.6 (Ref. Ismailov & Adygezalzade 2012).
Colors are: U-B = +0.48, B-V = +1.03 (Herbig and Bell catalog).
U-B = +0.49, B-V = +1.11 (Schegerer et al. 2008).
Field star search: A search of GSCv2.3.2 with the HEASARC Browse utility using a circular search region of
radius 30 arcsecs centered on RY Tau returns only one object: RY Tau. A search of the USNO B1 catalog using
the same search region returns 7 objects of which RY Tau is the brightest (B1 = 11.34) and the second
brightest is USNO 1184-0061103 (B1 = 16.69, offset 16.6 arcsec from RY Tau).J2000J2000STIS/FUV-MAMASpectroscopicNoNoG140L1425STIS/NUV-MAMASpectroscopicNoNoG230L2376STIS/FUV-MAMASpectroscopicNoNoG140M1550POS-TARGDITHER0.2750.275 arcsec spacing is approximaely 11 native pixelsLINEfalsefalse390.0STIS-ALONG-SLIT1false/Users/skinners/OP-cache/fix5rytau_2v_phase2_dither_rev2-v01.xmlTiming link suitability includes constraints ([Group (01 02) Within 30.0 days])The scheduling data was generated by CASM 22.2.CASM was run in Phase II mode.Visit schedulability is very sensitive to science target exposure times.
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Ref. Email discussion between S. Skinner and Miranda Link on 7-14-2014.(Tic-Visit
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)true30ETC simulation uses archived STIS G140L spectrum as input spectrum (dataset O5EX01020).ETC simulation uses archived STIS G140L spectrum as input spectrum (dataset O5EX01020).ETC simulation uses archived STIS G230L spectrum as input spectrum (dataset O5EX01010).