8567( 2) - 02/07/00 12:39 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8567 Version: 2 Check-in Date: 07-Feb-2000 12:39:19 1.Proposal Title: Confirming the parallax of the neutron star RX J185635-3754 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Frederick Walter State University of New York at Stony Brook CoI: Prof. James Lattimer State University of New York N CoI: Dr. Maddapa Prakash State University of New York N ------------------------------------------------------------------------------------ 5. Abstract Cycle 6 and 7 observations of the isolated neutron star RX J185635-3754 have revealed a motion of 0.8 arcsec in 2.5 years. This is a combination of the annual parallax and the proper motion. A third observation, planned for this fall, will formally yield sufficient information to solve for the parallax and proper motion independently. This first ever measurement of the distance of an isolated neutron star has important ramifications for astrophysics and for nuclear physics. The magnitude of the expected parallactic shift is less than one PC pixel, and must be measured against a far larger shift due to the proper motion. While this parallactic shift is in principle measurable for distance up to about 100 pc, these real data are subject to subtle instrumental effects which may skew the results. Given the scientific importance of obtaining an accurate distance, we request a fourth epoch observation to confirm the parallax. ------------------------------------------------------------------------------------ 8567( 2) - 02/07/00 12:39 - [ 2] Observations Description ------------------------ The observation will result in a single image using F606W. It will be taken during a single visit, between 24 March and 15 April when the parallactic shift is greatest. The observations will be dithered. In 3 orbits (about 7200 seconds) we will detect about 560 counts above background, for a 9-10 Sigma detection (based on the results of program 7408). The target will be near the center of the PC camera. We will use the same pointing coordinates as for the previous images, so as to minimize the effect of geometrical distortions of the PC camera and optics. We will use the F606W filter. By using the same filter for all observations, systematic effors are minimized. Also, observations in this filter provide a high quality detection while maximizing the number of background stars for the astrometric calibration. Real Time Justification ----------------------- The target must be observed when the parallactic shift is greatest, or within 2 weeks of March 31 or October 3. As we have two observations in October, the observation should occur near the 30 March opportunity. No real-time contacts are planned. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8567( 2) - 02/07/00 12:39 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 RXJ185635- STAR, Neutron Star RA=18H 56M 35.35S +/- 0.12S, J2000 V = 25.8+/-0.3 3754 DEC=-37D 54' 32.0" +/- 1.5" B-V = -0.3+/-0.1 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1994 0.0 0.0 0.0 8567( 2) - 02/07/00 12:39 - [ 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 NO ------------------------------------------------------------------------------------------------------------------------------------ 8567( 2) - 02/07/00 12:39 - [ 5] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 24-Mar-2001 AND 15-Apr-2001 On Hold Comments: Additional Comments: Maximum parallactic shift on 7 April Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 RXJ185635-3 WFPC2 IMAGE PC1 F606W CR-SPLIT=NO 1 1100 S PATTERN 1 10-11 754 ------------------------------------------------------------------------------------------------------------------------------------ 11 RXJ185635-3 WFPC2 IMAGE PC1 F606W CR-SPLIT=DEF 1 2600 S 754 ------------------------------------------------------------------------------------------------------------------------------------ 8567( 2) - 02/07/00 12:39 - [ 6] Summary Form for Proposal 8567 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO CR-SPLIT=DEF ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 24-Mar-2001 AND 15-Apr-2001 PATTERN 1 10-11 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names RXJ185635-3754 ------------------------------------------------------------------------------------------------------------------------------------