We propose using STIS to spectrally image the radial profile of resonantly scattered Lyman-alpha from the protoplanetary disk of TW Hya. Recent HST results have demonstrated that strong Lyman-alpha emission dominates the FUV radiation field of TW Hya. This has significant consequences for the chemical equilibrium of key species such as water within the planet-forming zone. Exploratory radiative transfer modeling predicts that the dominant Lyman-alpha component should resonantly scatter from the atomic layers of such disks at levels easily detectable with STIS. Using careful PSF subtraction, S/N ratios greater than 5 should be obtainable between 6-25AU from the central star. A detection of extended, resonantly scattered Lyman-alpha will reveal new information about the disk properties that cannot be obtained directly from other methods of observation. This includes constraining the morphology of the upper layers of the gas disk and possibly revealing the existence of a puffed-up inner disk. We will also be able to place limits on the Lyman-alpha flux driving chemistry in the disk interior.

We require high SNR, spatially resolved spectra of the Ly-alphga emission in the vicinity of the star TW Hya. To extract the Ly-alpha excess above the stellar PSF we use PSF subtraction by obtaining the instrument PSF from a WD. The basic observations employ long slit spectroscopy using STIS FUV-MAMA, the 52x0.2" slit, and the G140M grating which will select the Ly-alpha spectrum (that must be subsequently separated from the continuum emission in the case of TW Hya). This requires an identical sequence of exposures for TW Hya and the WD. Long slit observation will be made at offset -0.4,-0.2,0,0.2,0.4" relative to each star. This is achieved by defining a single perpendicular-to-slit pattern. In general the exposures are limited by available orbits, although the SNR will be enhanced by integrating over wavelength space. Regardless, the Ly-alpha line of TW Hya is sufficiently broad (~400km/s) to be resolved by the G140M grating. The most important exposure is the 0 offset, which has the longest exposure times. The other offsets are provided to reveal (albeit crudely) any 2D asymmetries in TW Hya's emission. The Peak-up exposure for TW Hya employs the G430L and may provide usual scientific information regarding the accretion rate. None. None. STAR FORMATION 12 false 0.0 0.0 false false false false false false SUPPORTED STAR CIRCUMSTELLAR MATTER EXTRA-SOLAR PLANETARY SYSTEM PROTOPLANETARY DISK T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. Proper motions and fluxes from Simbad entry. Proper motion RA has been transformed from arsec/yr to sec/yr B=11.8 CD34D7151 J2000 11 01 51.9063 -34 42 17.02 J2000 STAR DA This object was generated by the targetselector and retrieved from the SIMBAD database. Coordinates were updated to more accurate and recent (2006-2007 epoch observations) J2000/ICRS coordinates to meet STIS accuracy requirements. Coordinates and proper motions taken from Landolt 2007 AJ. Proper motion RA has been converted from arcsec/yr to sec/yr. Chosen for its proximity to Target 1 (TW Hya). This object is used primarily to obtain the instrument PSF. GSC-07724-01874 J2000 10 58 20.4000 -38 44 51.00 J2000 STIS/CCD Imaging No No F28X50OII STIS/FUV-MAMA Spectroscopic No No G140M 1222 STIS/CCD Imaging No No F28X50OII STIS/FUV-MAMA Spectroscopic No No G140M 1222 POS-TARG DITHER DITHER 0.2 STIS-ALONG-SLIT false true 5 0.0 POS-TARG STIS-PERP-TO-SLIT 90.0 1 false The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. TW Hya visit. Acquisition followed by Peak-up followed by series of five offset science exposures from -0.4 to +0.4" 1259995354000 288.0 (Tic-Visit :proposal-id 11607 :visit-id "01" :proposal-version -1 :trans-version "20080515" :date "02-Jul-2008 19:43:06.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 401136 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11607 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11607 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2950 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11607 :visit-id "01" :orbit-number 2 :pcs-time 195 :si-vis-utilization 3088 :al-overhead-at-end 125 :internal-dur-at-end 134 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11607 :visit-id "01" :orbit-number 3 :pcs-time 195 :si-vis-utilization 3088 :al-overhead-at-end 125 :internal-dur-at-end 396 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) false 3 0 ACQ ETC used to calculate ACQ exposure time. Trebled time required for SNR=40, as recommended. STIS Spectroscopic ETC used. Exposure time treble that required for SNR=40. The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. Visit WD 1056-384. Same sequence of exposures as visit 1, although the acquisition filters/gratings differ. This visit uses a special requirement on the orientation. 1260070206000 288.0 (Tic-Visit :proposal-id 11607 :visit-id "02" :proposal-version -1 :trans-version "20080624" :date "09-Jul-2008 13:31:28.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 400624 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11607 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11607 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2976 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3310 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11607 :visit-id "02" :orbit-number 2 :pcs-time 195 :si-vis-utilization 3115 :al-overhead-at-end 125 :internal-dur-at-end 134 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3310 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11607 :visit-id "02" :orbit-number 3 :pcs-time 195 :si-vis-utilization 3114 :al-overhead-at-end 125 :internal-dur-at-end 396 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3310 :pcs-gap 0 ) false 3 0 Exposure time calculated using ACQ ETC. ACQ PEAK ETC used. Exposure time (for SNR=40) multiplied by five.