9129( 4) - 09/18/01 15:26 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9129 Version: 4 Check-in Date: 18-Sep-2001 15:26:19 1.Proposal Title: Evolution of the Bow Shock in the Guitar Nebula ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: James Cordes Cornell University CoI: Mr. Shami Chatterjee Cornell University Y ------------------------------------------------------------------------------------ 5. Abstract We propose WFPC2 observations of the Guitar Nebula, a bow shock produced by the high -velocity (V>1000 kms) pulsar B2224+65. By comparison with a previous observation in 1994, a new narrow-band H-alpha image will allow exploitation of the change in pulsar location (~1"), in order to: (a) quantify ambient interstellar density variations on scales <=10^-3 pc that perturb the shape of the bowshock near the contact discontinuity (size ~0.2"); and (b) better model the bowshock to determine the orientation of the pulsar velocity vector. The results will be combined with a prior ROSAT image and a deep X-ray exposure (Chandra, October 2000) and ground based images from Palomar Observatory that constrain the shock heating and large scale structure of the nebula. PSR B2224+65 has the highest estimated space velocity of any pulsar: these results will also improve the pulsar distance and velocity estimates, which are important inputs for the study of pulsar kicks and supernovae asymmetry. ------------------------------------------------------------------------------------ 9129( 4) - 09/18/01 15:26 - [ 2] Observations Description ------------------------ We will obtain high-resolution images of the head of the bow shock using the PC1 CCD of the WFPC2. We estimate that the H-alpha emission from the limb- brightened nebula has a flux ~2*10^-15 erg cm^-2 s^-1 arcsec^-2. Our previous HST observation has a S/N ratio of about 4, which is in good agreement with the predicted S/N for a two hour exposure. While this S/N is sufficient for a detection, it does not provide enough flux for a robust model-fitting procedure: here, we propose to detect the evolution of the nebula and obtain enough photons for model-fitting with higher confidence. For this, we desire a S/N ratio ~7, which requires ~20 ksec (5.6 hour) integration time with a narrow -band filter (F656N). Additionally, we require the higher spatial resolution provided by image dithering: we shall use a standard 2-point dither with a 5.5 pixel shift on the PC (0.25"). In order to subtract the background, we also require an R band image (filter F675W) with a higher S/N ratio than the line image. Given the 48 * higher (integrated) QT of the wide-band filter, we need only a 1500 second integration to achieve sufficient S/N for background subtraction. Placing the head of the bow shock in PC1 requires that the spacecraft be positioned so that the U3 axis is oriented at sky position angle +45 degrees (i.e. toward the north east) in order that the dimmer portions of the nebula (the Guitar `body') fall on CCDs WF2, WF3, and WF4. It is mandatory that the narrow and R-band images be obtained with the same camera orientation on the sky. Our observing plan includes guide star acquisiton, 3 CR-split exposures at each of two dither positions using F656N, a CR-split exposure using F675W, WFPC2 readout and overhead time, and time for the SAM required for dithering. This can be distributed over 4 CVZ orbits with minimal dead time (~40 seconds). Real Time Justification ----------------------- The Guitar Nebula is at a sky position with 6 predicted CVZ opportunities during Cycle 10, with a maximum of 41 orbits at one such opportunity (a total of 144 CVZ orbits). We request CVZ observations in order to eliminate reacquisition of guide stars at the beginning of each orbit, and allow continuous exposures on the target. This improves the efficiency of our observations by 75% and enables us to achieve our requested S/N ratio in 4 CVZ orbits rather than 7 regular ones. Calibration Justification ------------------------- Our last exposure uses the `R' filter (F675W) to obtain a continuum image that may be subtracted from the narrow H-alpha images, in order to remove the two stars that appear in or adjacent to the brighter portion of the bow-shock nebula. Additional Comments ------------------- ------------------------------------------------------------------------------------ 9129( 4) - 09/18/01 15:26 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NEB- STAR, EMISSION LINE RA=22H 25M 52.6052S +/- 0.2", J2000 F-LINE(6563)=2e-15 222552+65353 NEBULA, NEUTRON STAR DEC=65D 35' 34.963" +/- 0.3" 1 Coordinate Source: OTHER_SOURCE 9129( 4) - 09/18/01 15:26 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFPC2-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.3535 Coordinate_Frame POS-TARG Pattern_Orient 45 Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ 9129( 4) - 09/18/01 15:26 - [ 5] Visit: 01 Visit Priority: Visit Requirements: CVZ ORIENT 10D TO 80D On Hold Comments: Additional Comments: Guitar Nebula position angle is roughly 45D. We require the head of the bow -shock in PC1, with the rest of the body distributed over WF1--4. Thus, the nominal orientation is 45D (axis PA) + (-45D) (PA to X axis on WFPC) + 45D (WFPC to U3) = 45D. We can accept a large range about this nominal angle (45D+/-35D), but all exposures should use the same orientation. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NEB-222552+ WFPC2 IMAGE PC1 F656N 6563 CR-SPLIT=DEF 1 3000 S PATTERN 1 10-30 653531 ------------------------------------------------------------------------------------------------------------------------------------ 20 NEB-222552+ WFPC2 IMAGE PC1 F656N 6563 CR-SPLIT=DEF 1 3000 S 653531 ------------------------------------------------------------------------------------------------------------------------------------ 30 NEB-222552+ WFPC2 IMAGE PC1 F656N 6563 CR-SPLIT=DEF 1 2900 S 653531 ------------------------------------------------------------------------------------------------------------------------------------ 40 NEB-222552+ WFPC2 IMAGE PC1 F675W 6563 CR-SPLIT=DEF 1 1500 S 653531 ------------------------------------------------------------------------------------------------------------------------------------ 9129( 4) - 09/18/01 15:26 - [ 6] Summary Form for Proposal 9129 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=DEF ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ORIENT 10D TO 80D PATTERN 1 10-30 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F656N F675W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NEB-222552+653531 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 6563 ------------------------------------------------------------------------------------------------------------------------------------