The interesting events marking the end of accretion and the dispersal of gas in circumstellar disks are not well understood. This is due, in part, to the difficulty of detecting very low accretion rates, as accretion indicators become masked by stellar emission. At the same time, observing gas in the inner disk is difficult. The majority of the mass is in H2, which has no strong transitions in the optical and infrared. However, strong FUV H2 lines, excited by the high energy fields of young stars, are conspicuous in accreting stars and can be used as a probe of low accretion, detecting accretion rates four orders of magnitude lower than traditional accretion indicators. We propose to obtain FUV spectra of 13 Weak-line T Tauri stars with the ACS PR130L prism. Our previous work has shown that the presence of H2 is linked to accretion onto the star, so our observations will test if these supposedly non-accreting stars are still accreting at previously undetectable rates. Our results will have significant impact on the understanding of the end of the accretion phase.

We follow an observing strategy which was successful in previous ACS/SBC observations of T Tauri stars. For each object, we will obtain an FUV spectrum and a brief FUV image for wavelength calibration. Each target will require one orbit of observations in which we will spend approximately 200s (exposure times vary between sources and are slightly longer for dimmer or more extincted sources) using the F165LP filter and the remaining time, around 2,000 to 2,400 seconds, with the PR130L prism. In the BOT checker, several objects were flagged as Unknown or Health/Safety objects in the GSC II catalog and these have been manually checked. All objects in visits 8-13 were safe according to the GALEX BOT tool. No information was available for GALEX objects in visits 1-7. Actual spectral types and spectral type references are provided where necessary. Visit 1: Unknown source is the target source LkCa 3, which is an M1 (KH95). Using the ACS ETC, and a PR130L spectrum of a K7 WTTS, we expect <0.14 cts/s in the F165LP filter and <0.10 cts/s using the PR130L grating. Visit 2: Health/Safety source is mis-identified as an O5, and is actually a K7 pre-main sequence object (Hartmann et al. 1991). Visit 3: Unknown source is the target V1075 Tau, which is a K7 (KH95) and does not exceed the brightness limits determined using the exposure time calculator. Visit 4: Health/Safety source is the target V827 Tau, is mis-identified as an O5, and is actually a K7 (KH95). Visit 5: Health/Safety source is the target V826 Tau, is mis-identified as an O5, and is actually a K7 (KH95). Visit 6: Health/Safety source is the target V830 Tau, is mis-identified as an O5, and is actually a K7 (KH95). Visit 7: Health/Safety source is the target LkCa 14, is mis-identified as an O5, and is actually a M0 (KH95). Visit 8: Health/Safety source is the target FN Tau, is mis-identified as an O5, and is actually a M5 (KH95). Visit 9: Health/Safety source at 11 04 51.0498, -76 25 24.27 is the target CHXR-14N, is mis-identified as an O5, and is a K8 (L07). Health/Safety source at 11 04 52.8625, -76 25 51.76 is mis-identified as an O5 and is actually a pre-main sequence object (CHXR-14S), a M2 (L07). Visit 10: Health/Safety source is the target UV Cha, is mis-identified as an O5, and is actually a M2 (L07). Unknown Source cannot be identified; however, FUV images obtained by GALEX show no strong FUV emission from this source, ~0.05 cts/s/ACS pix are expected, 400x less than local screening limit for a variable source. Visit 11: Unknown Source at 11 12 45.0732, -76 37 11.63 cannot be identified; however, FUV images obtained by GALEX show no strong FUV emission from this source, ~0.01 cts/s/ACS pix are expected, 2000x less than local screening limit for a variable source. Unknown Source at 11 12 43.0518, -76 37 5.03 is the target source CHXR 55, a K4 (L07) and does not exceed the brightness limits determined using the exposure time calculator. Visit 12: Unknown source at 11 18 20.2808, -76 21 57.81 is the target source CHXR 68A, a K8 (L07) and does not exceed the brightness limits determined using the exposure time calculator. Unknown source at 11 18 19.7791, -76 22 0.56 is a weak T Tauri star, CHXR 68B, a M2 (L07) and does not exceed the brightness limits determined using the exposure time calculator. Visit 13: Unknown source at 11 08 15.1355, -77 33 53.21 is the target source T33A a G9 (L07) and does not exceed the brightness limits determined using the exposure time calculator. Visit 12: CHXR 68A and CHXR 68B is a triple system. A and B components are separated by 4.4''. CHXR 68A is itself a binary with a separation of 0.1'' and a period of 60 years. With a mass ratio of 0.84, the objects are likely similar. Visit 13: T33A is a binary (companion T33B) with a 2.4'' separation. The target source, T33A, has a bolometric luminosity 3.5x stronger than the companion. (Lafreniere et al. 2008) References Hartmann, L, et al. 1991, AJ, 101, 1050 Kenyon, S. J, & Hartmann, L. 1995, ApJS, 101, 117 (KH95) Lafreniere, D, et al. 2008, ApJ, 683, 844 Luhman, K. 2007, ApJS, 173, 104 (L07 STAR FORMATION 12 false 0.0 0.0 false false false false SUPPORTED STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR T TAURI STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L ACS/SBC Imaging No No F165LP ACS/SBC Spectroscopic No No PR130L The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1316707750000 257.0787904004486 (Tic-Visit :proposal-id 12211 :visit-id "01" :proposal-version -1 :trans-version "20100505" :date "06-Jul-2010 17:05:50.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2924 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1316702038000 247.67122527964239 (Tic-Visit :proposal-id 12211 :visit-id "02" :proposal-version -1 :trans-version "20100505" :date "06-Jul-2010 17:06:27.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2924 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1315775953000 262.06939939262634 (Tic-Visit :proposal-id 12211 :visit-id "03" :proposal-version -1 :trans-version "20100505" :date "06-Jul-2010 17:06:43.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2916 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1316601121000 275.4615439103409 (Tic-Visit :proposal-id 12211 :visit-id "04" :proposal-version -1 :trans-version "20100505" :date "06-Jul-2010 17:06:57.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2916 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1316109596000 262.3245087069023 (Tic-Visit :proposal-id 12211 :visit-id "05" :proposal-version -1 :trans-version "20100505" :date "06-Jul-2010 17:07:11.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2916 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12211 :visit-id "06" :proposal-version -1 :trans-version "20100505" :date "06-Jul-2010 17:07:25.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2916 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1316788339000 239.52066076800747 (Tic-Visit :proposal-id 12211 :visit-id "07" :proposal-version -1 :trans-version "20100505" :date "06-Jul-2010 17:07:37.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "07" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2924 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1311371406000 268.40290138652847 (Tic-Visit :proposal-id 12211 :visit-id "08" :proposal-version -1 :trans-version "20100505" :date "06-Jul-2010 17:08:03.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "08" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2924 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1316264471000 188.56809343025662 (Tic-Visit :proposal-id 12211 :visit-id "09" :proposal-version -1 :trans-version "20100505" :date "06-Jul-2010 17:08:41.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "09" :obset-id "09" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "09" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3300 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3633 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1316350704000 189.23500933324573 (Tic-Visit :proposal-id 12211 :visit-id "10" :proposal-version -1 :trans-version "20100505" :date "09-Jul-2010 10:30:29.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "10" :obset-id "10" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "10" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3300 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3633 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1321771121000 252.05642034947658 (Tic-Visit :proposal-id 12211 :visit-id "11" :proposal-version -1 :trans-version "20100505" :date "09-Jul-2010 10:30:30.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "11" :obset-id "11" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "11" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3300 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3633 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1316356347000 186.11831755863352 (Tic-Visit :proposal-id 12211 :visit-id "12" :proposal-version -1 :trans-version "20100505" :date "09-Jul-2010 10:29:46.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "12" :obset-id "12" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "12" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3300 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3633 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1318153412000 208.51884811571506 (Tic-Visit :proposal-id 12211 :visit-id "13" :proposal-version -1 :trans-version "20100505" :date "09-Jul-2010 10:33:45.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "13" :obset-id "13" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "13" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3300 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3633 :pcs-gap 0 ) false 1 0 This is a copy of visit 05 which failed due to a guide star problem. (Tic-Visit :proposal-id 12211 :visit-id "05" :proposal-version -1 :trans-version "20100505" :date "06-Jul-2010 17:07:11.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12211 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12211 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2916 :al-overhead-at-end 0 :internal-dur-at-end 119 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) false 1 0