The lifetime of an isolated protoplanetary disk is thought to be set by the combination of viscous accretion and photoevaporation driven by high-energy photons from the central star. While diagnostics of accretion are numerous and mass accretion rates are routinely measured, diagnostics of centrally driven disk photoevaporation are just emerging. The [OI] 6300 angstrom is expected to trace slow disk winds extending out to 30-40 AU from the central star if driven by stellar Xrays. We propose to use this line diagnostic to measure for the first time the radial extent of the photoevaporative flow and the disk photoevaporation rate. Our targets are two nearby T Tauri disks with dust depleted inner regions, low stellar accretion rates, and ancillary evidence for on-going photoevaporation. Slitless spectroscopy with STIS will enable us to map these flows at a spatial resolution of ~6 AU. From their extension we will determine whether stellar EUV or Xrays drive most of the photoevaporation, provide the first measurements of mass flow rates, and thus constrain expected disk lifetimes.

We will perform slitless spectroscopy of two nearb protoplanetary disks around TW Hya and T Cha using the G750M/6252 setting with STIS. Our goal is to spatially resolve the [OI] 6300AA emission from these disks and thus constrain disk photoevaporation models. The [OI] 6300AA line is the brightest emission line in the 5966–6538AA wavelength range covered by the G750M/6252 setting, followed by the [OI] 6364AA (about a factor of 2 weaker). The two lines will be well separated and kinematically unresolved from both targets, which will make it easier to interpret the emission line images. We do not expect to spatially resolve any other emission line from these two disks. For target acquisition we will use the recommended longpass F28X50LP filter and 1sec exposure. For each target we will have two position angles (as much as possible perpendicular to each other) to accurately remove the stellar spectrum. 1 orbit per target times 2 position angles per target times 2 targets = 4 orbits. We estimated that in 1 orbit (about 40min on-source exposure) we will reach a S/N of over 100 per resolution element. We do not require any special calibration STAR FORMATION 12 false 0.0 0.0 false false false false false false SUPPORTED STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. Coordinates are from Hipparcos J2000 11 01 51.9063 -34 42 17.02 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. Coordinates are from Hipparcos J2000 11 57 13.5305 -79 21 31.54 J2000 STIS/CCD Spectroscopic No No G750M 6252 STIS/CCD Spectroscopic No No G750M 6252 POS-TARG DITHER 0.2789 The point spacing is 5.5pixels*0.0507arcsec. This is chosen to improve the spatial resolution LINE false false 2 90.0 STIS-ALONG-SLIT 1 false Timing link suitability includes constraints ([02 After 01]) The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12221 :visit-id "01" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 13:16:54.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 110832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12221 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12221 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2938 :al-overhead-at-end 123 :internal-dur-at-end 421 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) true 1 0 Timing link suitability includes constraints ([02 After 01]) The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12221 :visit-id "02" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 13:16:56.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 110832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12221 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12221 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2938 :al-overhead-at-end 123 :internal-dur-at-end 421 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) false 1 0 Timing link suitability includes constraints ([04 After 03]) The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12221 :visit-id "03" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 13:16:58.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 110832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12221 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12221 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3294 :al-overhead-at-end 123 :internal-dur-at-end 421 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3633 :pcs-gap 0 ) true 1 0 Note: T Cha is higly variable in V: literature values are from 11.2 to 12.7 in Vmag Timing link suitability includes constraints ([04 After 03]) The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12221 :visit-id "04" :proposal-version -1 :trans-version "20100505" :date "07-Jul-2010 13:16:59.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 110832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12221 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12221 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3294 :al-overhead-at-end 123 :internal-dur-at-end 421 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3633 :pcs-gap 0 ) false 1 0