We recently found a new sample of edge-on debris disks using the Spitzer Space Telescope. These disks are particularly valuable because they have observable circumstellar gas as well as dust. They double the small number of debris disks that can be used to study gas-dust interactions in optically-thin disks, as well as the evolution of circumstellar gas during the terrestrial planet-forming phase. We propose HST-STIS coronagraphic imaging of the two closest disks from our sample, in order to image light scattered from the dust disks in a broad optical bandpass. These observations will provide a wealth of information about the disks, including their sizes, radial surface brightness profiles, and basic morphologies (ring-like or smooth disk). They may also reveal dust structures (e.g. clumps) that are often seen in optical images of debris disks and may be generated by the influence of unseen planets. This proposed program is a crucial step towards full characterization of the circumstellar material in two important debris disks.

General Strategy: STIS coronagraphic imaging of two known debris disks, HD158352 and HD118232. Each target will be observed at two different telescope roll angles, to allow more accurate removal of scattered and diffracted starlight. A point-spread function (PSF) reference star will also be coronagraphically imaged along with each target star. The sequence of observations for each target is as follows: disk at one arbitrary telescope orientation (1 orbit), disk at telescope orientation roughly 30 degrees from the first (1 orbit), then PSF star (1 orbit). These observations are done in three sequential orbits to minimize telescope thermal changes. [2009-07-20] We originally planned to use the ACS coronagraph for these observations. Since it is not available, the program was switched to the STIS coronagraph (see our Program Change Request for details). In sum, we found that the STIS observations are feasible without requesting any additional observing time. Our original allocation of 6 orbits will be sufficient to fully achieve our science goals. The PSF stars (HD159170 for HD158352 and HD119024 for HD118232) are bright, non-variable, single stars. Their B-V colors and spectral types are close to those of the target stars. The PSF stars are near the target stars on the sky and have no other stars within 30 arcsec. The stellar data appear below. In Phase I, we had suggested different PSFs; subsequent investigation revealed other stars that are better suited. HD158352: A8V, B = 5.697, V = 5.442, B-V = 0.255 HD159170: A5V, B = 5.836, V = 5.631, B-V = 0.205, dist. from HD158352 = 6.2 deg HD118232: A5V, B = 4.840, V = 4.685, B-V = 0.155 HD119024: A3V, B = 5.602, V = 5.472, B-V = 0.130, dist. from HD118232 = 4.0 deg [2009-07-20] The STIS 50CCD band is broader than the F606W band we planned for the ACS orbits. Therefore, it is even more important to have a close color match between the target and PSF stars. In both cases, the difference in B-V color between the target and PSF star is less than the maximum recommended value of 0.08. Observation Details: We will take our science observations with the 50CORON clear aperture, using the WEDGEA1.0 position (r = 0.5 arcsecs). The coronagraphic images will be done in two exposures: 1) a short exposure to image bright regions near the wedge without saturating and 2) a long exposure to sensitively image the faint outer regions of the disks. All ACQ images will be taken with the F28X50OII filter. We have used the STIS ETC to verify that none of the stars saturate with this filter and that we achieve S/N > 200 for every target in the requested ACQ exposure times. The ETC ACQ calculations were done with GAIN=4 and CR-SPLIT=1; the results appear below. S/N in ACQ image Exp. time HD158352 252 0.2 sec HD159170 232 0.2 sec HD118232 255 0.1 sec HD119024 251 0.2 sec [2010-01-14] The coronagraphic exposures of HD118232 and its PSF reference star executed in Dec. 2009 were badly saturated. Therefore, we have adjusted the planned observations of HD158352 in the following fashion. 1) All coronagraphic observations were set to GAIN=4. 2) For all coronagraphic observations, the CR-SPLIT number was increased. For the short (100 sec) coronaghraphic exposure, we set CR-SPLIT=8, giving 12.5 sec sub-exposures. None of the pixels in these sub-exposure should saturate; we estimate that the pixels at the edge of the wedge will have around 80,000 electrons. This short exposure allows a long exposure of 1568 sec to fit within the same orbit. With CR-SPLIT=8, the sub-exposures will have a duration of 196 sec. We have verified that the expected saturated region of the long sub-exposures is well-detected in the short exposure. Even with the reduced total time for the long exposure, we should detect the disk out to a large distance from the star (S/N > 3 out to 7 arcsec in one roll, S/N > 3 out to 7.6 arcsec combing both rolls). STAR FORMATION 12 false 0.0 0.0 false false false false false false SUPPORTED STAR A4-A9 V-IV DISK GSC00401-02211 HIP85537 J2000 17 28 49.6549 +00 19 50.25 J2000 CALIBRATION POINT SPREAD FUNCTION PSF reference star for HD158352 GSC05092-00788 HIP85922 J2000 15 28 38.2371 +01 50 31.49 J2000 STAR A4-A9 V-IV DISK GSC03466-01270 24-CVN J2000 13 34 27.2593 +49 00 57.50 J2000 CALIBRATION POINT SPREAD FUNCTION PSF reference star for HD118232 GSC03851-00126 82-UMA J2000 19 29 42.3591 +51 43 47.20 J2000 ACS/HRC Imaging No No F606W ACS/HRC Imaging Yes No F606W ACS/HRC Imaging Yes No F606W ACS/HRC Imaging No No F606W ACS/HRC Imaging Yes No F606W ACS/HRC Imaging No No F606W ACS/HRC Imaging Yes No F606W ACS/HRC Imaging Yes No F606W ACS/HRC Imaging No No F606W ACS/HRC Imaging Yes No F606W Timing link suitability includes constraints ([02 After 01 by at most 0.1 days]) The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. HD158352 roll 1 (Tic-Visit :proposal-id 11596 :visit-id "01" :proposal-version -1 :trans-version "20091209" :date "14-Jan-2010 17:13:18.0" :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 294880 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11596 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11596 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2896 :al-overhead-at-end 0 :internal-dur-at-end 362 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) false 1 0 Timing link suitability includes constraints ([02 After 01 by at most 0.1 days] [03 After 02 by at most 0.1 days]) The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. HD158352 roll 2 (Tic-Visit :proposal-id 11596 :visit-id "02" :proposal-version -1 :trans-version "20091209" :date "14-Jan-2010 17:13:24.0" :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 294880 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11596 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11596 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2896 :al-overhead-at-end 0 :internal-dur-at-end 362 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) true 1 0 Timing link suitability includes constraints ([03 After 02 by at most 0.1 days]) The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. PSF for HD158352 (Tic-Visit :proposal-id 11596 :visit-id "03" :proposal-version -1 :trans-version "20091209" :date "14-Jan-2010 17:13:29.0" :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 294880 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11596 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11596 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2904 :al-overhead-at-end 0 :internal-dur-at-end 362 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) true 1 0 Timing link suitability includes constraints ([05 After 04 by at most 0.1 days]) The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. HD118232 roll 1 1261151113000 290.0 (Tic-Visit :proposal-id 11596 :visit-id "04" :proposal-version -1 :trans-version "20100218" :date "08-Mar-2010 14:56:02.0" :trans-errors '(:WARNINGS 1 :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 11596 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11596 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3065 :al-overhead-at-end 0 :internal-dur-at-end 421 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) true 1 1 Timing link suitability includes constraints ([05 After 04 by at most 0.1 days] [06 After 05 by at most 0.1 days]) The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. HD118232 roll 2 1261156860000 315.0 (Tic-Visit :proposal-id 11596 :visit-id "05" :proposal-version -1 :trans-version "20100218" :date "08-Mar-2010 14:56:03.0" :trans-errors '(:WARNINGS 1 :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 11596 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11596 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3065 :al-overhead-at-end 0 :internal-dur-at-end 421 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) true 1 1 Timing link suitability includes constraints ([06 After 05 by at most 0.1 days]) The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. PSF for HD118232 1261162417000 305.9843567048032 (Tic-Visit :proposal-id 11596 :visit-id "06" :proposal-version -1 :trans-version "20100218" :date "08-Mar-2010 14:56:04.0" :trans-errors '(:WARNINGS 1 :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 11596 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11596 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3117 :al-overhead-at-end 0 :internal-dur-at-end 421 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3445 :pcs-gap 0 ) true 1 1