This special call in Cycle 16 is a unique opportunity to measure fine-scale proper motions with the same WFPC2 camera after more than a decade has elapsed, and is the last time such an opportunity is likely to be available. We aim to apply this powerful tool to the ring nebulae around two hot supergiants: the set of ionized double-rings around the massive eclipsing binary RY Scuti, and the equatorial ring and bipolar lobes around Sher 25. These are the only two Galactic analogs of SN1987A for which this proper motion measurement is possible (others lack a first-epoch image with HST, and SN1987A is too distant). In the case of RY Scuti, the expected motions are small because the compact ring nebula is only 1-arcsec in diameter. For Sher 25 the expected motions are small because the object is thought to be at d=6 kpc. The 10-12 years that have elapsed since earlier imaging epochs for these sources make it possible to accurately measure their expected sub-pixel proper motion, and hence, their ages and distances. We can discriminate between specific proposed models for the formation of these ring nebulae by measuring the relative ages of these ionized equatorial rings compared to outer structures: the bipolar lobes in the case of Sher 25, and an outer dust shell in the case of RY Scuti. These will provide the first quantitative tests of binary merger vs. rapidly rotating single star models for the shaping of SN1987A and related ring nebulae around massive stars, which until now have relied upon qualitative comparisons to structues seen in single-epoch images. The expected expansion is less than 0.1 arcsec, so there is no hope of making either measurement from the ground, and increased systematic errors associated with switching to new instruments (with different pixel scales and distortion corrections) will make this measurement more difficult even for HST after SM4.

The purpose of these observations is to obtain H-alpha F656N and [N II] F658N images of two targets, RY Scuti and Sher 25. These images will duplicate previous observations made about 10 years ago in order to measure proper motion expansion of the circumstellar nebular rings around these stars. Both targets are centered on the PC chip. ISM AND CIRCUMSTELLAR MATTER 12 false 0.0 0.0 false false false false false SUPPORTED STAR CIRCUMSTELLAR MATTER EMISSION LINE NEBULA INTERACTING BINARY SUPERGIANT O WOLF RAYET This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 18 25 31.4785 -12 41 24.19 J2000 STAR B0-B2 III-I CIRCUMSTELLAR MATTER EMISSION LINE NEBULA RING J2000 11 15 7.8000 -61 15 17.00 J2000 WFPC2 Imaging No F656N WFPC2 Imaging No F658N WFPC2 Imaging No F656N WFPC2 Imaging No F658N The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 11977 :visit-id "01" :proposal-version -1 :trans-version "20080624" :date "26-Jan-2009 15:02:41.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 358528 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11977 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11977 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2700 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 11977 :visit-id "02" :proposal-version -1 :trans-version "20080624" :date "26-Jan-2009 16:27:40.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 358528 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11977 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11977 :visit-id "02" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2840 :al-overhead-at-end 160 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3243 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11977 :visit-id "02" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2820 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3243 :pcs-gap 0 ) false 2 0