10489( 2) - 05/13/05 06:57 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 10489 Version: 2 Check-in Date: 13-May-2005 10:56:33 1.Proposal Title: Imaging Extended UV H2 Emission Around T Tauri ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle 4. Parallel Pointing Tolerance GO 14 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Alexander Brown University of Colorado at Boulder CoI: Dr. Frederick M. Walter State University of New York at Stony N Brook CoI: Mr. Gregory J. Herczeg University of Colorado at Boulder N CoI: Ms. Joanna M. Brown California Institute of Technology N CoI: Dr. Thomas R. Ayres University of Colorado at Boulder N CoI: Dr. Jack J. Lissauer NASA Ames Research Center N ------------------------------------------------------------------------------------ 6. Abstract The interactions between the circumstellar disk, newly-forming star, and bipolar jet outflows play a central role in the process of star formation. These interactions control how disks evolve and dissipate, and, thereby, control the process of planetary system formation. We shall image the UV molecular hydrogen (H2) emission around the pre-main-sequence binary star T Tauri using the ACS SBC (solar blind channel) MAMA detector, thus determining the spatial properties of the H2 emitting regions, and deriving important detailed observational information on the disk-star- jet interaction on scales of order 5 AU. These images will reveal the degree of collimation and opening angles of the innermost parts of the high velocity jets, the shock structure within the jet outflows, the size and morphology of the circumstellar disks, both in emission and in silhouette, and the conditions inside the polar cavities swept clear by Herbig-Haro flows. Fluorescent H2 emission lines dominate the UV spectrum of T Tau. Long-slit (1-D) STIS UV spectra of T Tau show H2 emission with a complex spatial structure extending many arcseconds from the star and the presence of significant shock structures. The H2 must be warm (approx. 2000 K) for the fluorescence to operate. The molecular emission originates in shocks and, perhaps, also from the surfaces of the inner regions of accretion disks. ------------------------------------------------------------------------------------ 10489( 2) - 05/13/05 06:57 - [ 2] Observations Description ------------------------ We shall obtain ACS-SBC images of the H2 emission within the T Tau system. Based on our previous UV (STIS, GHRS, IUE) spectroscopic observations, we have good estimates of the extent and brightness of the extended H2 emission. The T Tau system will be imaged using the ACS-SBC (Solar Blind Channel) detector and the F140LP and F165LP filters. When the F165LP image is subtracted from the F140LP image, a well-defined, effective passband of 1350 - 1650 A results, and the off-star signal will be dominated by H2 emission. The F165LP image is an important control that will be used to characterize the presence of any reflection nebulosity and other confusing (non-H2) features in the field of view, and mitigate the influence of any filter red leak. The F165LP passband contains only a small (and known) amount of H2 flux but will reveal any broadband dust scattering. The F165LP will provide a check of the ACS UV point spread function at exactly the same detector locations as the primary F140LP images. At the 140 pc distance of T Tau the 0.032 arcsec SBC pixels have a size equivalent to 4.5 AU; thus the ACS-SBC offers the possibility to explore detailed spatial structure very close to a low mass PMS star, that is difficult to observe any other way. Such size scales are well matched to MHD models of CTT star outflows (see e.g. Figs. 6-8 of Matt, Winglee, & Bohm 2003). Use of the F140LP and F165LP filters maximizes the signal-to-noise because the H Ly alpha and O I geocoronal emission is suppressed, while the selected passband contains the strongest H2 lines. T Tau does not violate the ACS MAMA bright limits even for the pixels containing the stellar point source, based on existing UV spectra. There are no other bright UV sources within 30 arcseconds of T Tau; this is primarily because of the dark molecular cloud located just behind T Tau. The requested ACS exposures will fill three HST orbits. Eight 11 minute F140LP exposures can be obtained in two orbits and four 11 minute F165LP images in the third orbit. The on-source image will have maximum count rates of 16 ct/sec/pixel for F140LP and 5 ct/sec/pixel for F165LP, corresponding to nominal signal-to-noise (S/N) of 250 and 130 in each individual exposure, respectively. While the higher count rate is within a factor of 3 of the local bright limit, the UV spectrum of T Tau is well known and stable in the wavelength range of interest. Using the bright H2 knot south of T Tau as a test case, for 11 minute exposures each 2x2 pixel resolution element will have a S/N of 9 for F140LP and 2 for F165LP. Thus the combined exposures should have S/N approaching 25 and 4 per resolution element respectively. Therefore, H2 with a surface flux 15% of the brightest knots should be imaged with a S/N of 4 per resolution element, without any binning of the images. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10489( 2) - 05/13/05 06:57 - [ 3] 10489( 2) - 05/13/05 06:57 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD284419 STAR, K V-IV, T TAURI RA=04H21M59.4345S +/- 0.1", J2000 V = 9.6 STAR, YSO DEC=+19D32'6.43" +/- 0.1" Coordinate Source: HIPPARCOS/TYCHO_CATALOGUE Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. 10489( 2) - 05/13/05 06:57 - [ 5] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HD284419 ACS/SBC ACCUM SBC F165LP 4 670 S ------------------------------------------------------------------------------------------------------------------------------------ 2 HD284419 ACS/SBC ACCUM SBC F140LP 4 675 S ------------------------------------------------------------------------------------------------------------------------------------ 3 HD284419 ACS/SBC ACCUM SBC F140LP 4 670 S see below ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ HD284419 1 ACS/SBC ACCUM SBC F165LP none none 1 none 1 N/A HD284419 1 ACS/SBC ACCUM SBC F165LP none none 2 none 1 N/A HD284419 1 ACS/SBC ACCUM SBC F165LP none none 3 none 1 N/A HD284419 1 ACS/SBC ACCUM SBC F165LP none none 4 none 1 N/A HD284419 2 ACS/SBC ACCUM SBC F140LP none none 1 none 2 N/A HD284419 2 ACS/SBC ACCUM SBC F140LP none none 2 none 2 N/A HD284419 2 ACS/SBC ACCUM SBC F140LP none none 3 none 2 N/A HD284419 2 ACS/SBC ACCUM SBC F140LP none none 4 none 2 N/A HD284419 3 ACS/SBC ACCUM SBC F140LP none none 1 none 3 682.0 S HD284419 3 ACS/SBC ACCUM SBC F140LP none none 2 none 3 682.0 S HD284419 3 ACS/SBC ACCUM SBC F140LP none none 3 none 3 682.0 S HD284419 3 ACS/SBC ACCUM SBC F140LP none none 4 none 3 682.0 S 10489( 2) - 05/13/05 06:57 - [ 6] Summary Form for Proposal 10489 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures SBC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/SBC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F165LP F140LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD284419 ------------------------------------------------------------------------------------------------------------------------------------