8149( 9) - 09/07/00 13:03 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8149 Version: 9 Check-in Date: 07-Sep-2000 13:02:32 1.Proposal Title: The Spectral Energy Distribution of a Neutron Star Photosphere ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Frederick Walter State University of New York at Stony Brook CoI: Prof. James M. Lattimer State University of New York at Stony N Brook CoI: Dr. Madappa Prakash State University of New York at Stony N Brook CoI: Mr. Penghui An State University of New York at Stony N Brook CoI: Dr. Ralph Neuhaeuser Max-Planck-Institut fuer Extraterrestriche N Physik ------------------------------------------------------------------------------------ 5. Abstract There exists not a single direct measurement of the radius or mass of any neutron star outside a binary system. As part of our study of the photospheres of neutron stars, we seek to obtain the spectral energy distribution of the isolated neutron star, RX J185635-3754. The spectrum is very nearly thermal from 10 A through 6000 A. A STIS/MAMA FUV spectrum will sample the brightest observable part of the continuum longward of the peak emissivity, and will include the wavelength of the gravitationally-redshifted Lyman Alpha line. Other data in hand include an EUVE spectrum, a second ROSAT observation revealing a possible proper motion, and ground- based images with detections at B and V. Second epoch HST images to measure proper motion and parallax are planned for cycle 7. We are developing model atmospheres for neutron stars, with an aim to using the observed spectral energy distribution to determine the radius and surface composition of this neutron star. We will use the measurements of radius, surface gravity, and gravitational redshift to constrain the interior equation of state. ------------------------------------------------------------------------------------ 8149( 9) - 09/07/00 13:03 - [ 2] Observations Description ------------------------ We request a single G140L exposure without any constraints. We estimated the required exposure time by running the STIS Exposure Time Calculator. We modelled the input spectrum as a 660, 000K black body with V=25.7, E(B-V)=0.02 and average background and Earthshine levels. We will use the 52X0.5 slit in order to obtain absolute photometry. Any spectral features from the neutron star should be broad, so high spectral resolution is not important. We request TIMETAG mode. Although there is no evidence that the target is variable, if a period is eventually found, we will want to be able to undertake phase-resolved spectroscopy. Rotational modulation could indicate temperature variations over the surface, or a small non-thermal component. The minimum useful exposure time is 4 orbits (10 ksec). This would yield a spectrum with S/N~5 per 1.2A bin near 1300A in the continuum. After binning over 6 A the S/N per bin ranges from about 11 near 1300 A to 2 at 1600 A. This is sufficient to determine the spectral energy distribution, and to measure deviations from a black body, or our atmosphere models. In a 10 orbit exposure (~27 ksec), we have a good chance of detecting a weak Lyman Alpha absorption line from the surface of the neutron star. For reasonable values of M and R, the gravitationally redshifted line should be found at about 1530 A. In the 10 orbit integration, we obtain S/N~5 at 1530 A in a 6 A bin. This allows detection of an ~50 Angstrom-wide Lyman Alpha absorption line with 10 Angstrom equivalent width. The sensitivity to the absorption, of course, decreases as the line width increases, but we can compensate by using larger bins. In addition to Lyman Alpha, there are 2 other interesting spectral features of hydrogen in the FUV. The redshifted Lyman break falls shortward of the HST cutoff at 1150 A for z<1.3, and the 1405 Angstrom Lyman Alpha satellite line, the strongest feature in our H model, is detectable only for z<1.17 (our current best fit H model atmosphere has z=1.13). NUV observations with G230L are not feasible; exposure times are about ten times longer than for G140L to reach comparable S/N. There are no UV-bright objects within 30 arcsec of the target on the F300W image, so instrument safety is not an issue. According to the STIS ETC, target acquisition will require a 10 minute integration with the CCD/clear to attain S/N=20. *********** Section added May 1999 We have measured the motion of the target over the 2.5 years between the U3IM0103T (October 1996) and U51G01 (March 1999) obervations. This motion is 0.34 arcsec/year at position angle 100 degrees, and includes the proper motion and a small (still unmeasured) parallactic shift. Because the target is very faint, we will acquire a brighter star (target 2; star I) with V approx. 19, and then do a blind offset to the target. The offset position was measured on PC image U51G01... and is current as of 3/30/99. If this target remains in the current long term plan windows (4/14-5/11/2000), then the offset will need to be updated by 1.1 times the annual proper motion. The measured position for the target on 3/30/99 is RA= 18 56 35.4628, DEC=-37 54 36.463 (J2000) on the reference frame supplied with the U51G01 images. The offset given for target 1 is this position minus the position of target 2. We expect to obtain a third observation in October 1999 (unless the servicing mission precludes this). If the parallax is significant, we will provide an improved offset and proper motion at that time. However, by using the 52X0.5 slit, there is essentially no chance that the target will not end up in the slit. ****** REVISION June 2000 The coordinate of the offset star has been remeasured on the most recent images (U51G02*). The proper motion and parallax are both incorporated in the offset. In the FIXED_TARGET list, I give the expected offsets for 8/17/00. I specify the visits occur between 7/28/00 and 9/7/00. Within this window, the offset is good to within +/- 0.02 arcsec. ****** REVISION September 2000 I give the expected offsets for 10/15/00. I specify the visits occur between 9/21/00 and 11/3/00. Within this window, the offset is good to within +/- 0.02 arcsec. Real Time Justification ----------------------- We have no special requirements We need not coordinate with any other observations. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8149( 9) - 09/07/00 13:03 - [ 3] Data Distribution Paper Products: YES Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8149( 9) - 09/07/00 13:03 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 RXJ185635- STAR, NEUTRON STAR RA-OFF=0.776S+/- 0.004S, DEC- J2000 V = 25.8+/-0.3 3754 OFF=-11.16"+/- 0.05", FROM 2 B-V = -0.3+/-0.1 Coordinate Source: Comments: The offset position is epoch 1999.25 (3/30/99) Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1999.25 0.028 -0.056 0.0 2 STAR-I- STAR RA=18H 56M 35.003S +/- 0.002S, J2000 V = 18.9+/-0.3 OFFSET DEC=-37D 54' 25.25" +/- 0.05" B-V = 0.7+/-0.1 Coordinate Source: Comments: Positions from WFPC2 image U51G01, Proper Motions from images U51G01 and U3IM0103T 3 RXJ185635- STAR, NEUTRON STAR RA-OFF=0.8173S+/- 0.0010S, DEC- J2000 V = 25.8+/-0.3 3754-Y OFF=-11.289999999999999"+/- B-V = -0.3+/-0.1 0.01", FROM 52 Coordinate Source: Comments: The offset position is effective 10/15/00 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1999.75 0.0 0.0 0.0 51 RXJ185635- STAR, NEUTRON STAR RA-OFF=0.8128S+/- 0.0010S, DEC- J2000 V = 25.8+/-0.3 3754-X OFF=-11.289999999999999"+/- B-V = -0.3+/-0.1 0.01", FROM 2 Coordinate Source: Comments: The offset position is effective 8/17/00 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1999.75 0.0 0.0 0.0 52 STAR-J- STAR RA=18H 56M 34.8470S +/- 0.0011S, J2000 V = 18.9+/-0.3 OFFSET-X DEC=-37D 54' 25.589" +/- 0.008" B-V = 0.7+/-0.1 Coordinate Source: Comments: Position from WFPC2 image U51G0203R 8149( 9) - 09/07/00 13:03 - [ 5] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 STAR-I-OFFS STIS/C ACQ 50CCD MIRROR 1 6 S ET CD ------------------------------------------------------------------------------------------------------------------------------------ 11 STAR-I-OFFS STIS/C ACQ/PEA 52X0.1 MIRROR 1 20 S ET CD K ------------------------------------------------------------------------------------------------------------------------------------ 21 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 1780 S 754 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 22 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2950 S 754 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 23 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2720 S 754 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 24 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2720 S 754 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 25 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2420 S 754 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8149( 9) - 09/07/00 13:03 - [ 6] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 30 STAR-I-OFFS STIS/C ACQ 50CCD MIRROR 1 6 S ET CD ------------------------------------------------------------------------------------------------------------------------------------ 31 STAR-I-OFFS STIS/C ACQ/PEA 52X0.1 MIRROR 1 20 S ET CD K ------------------------------------------------------------------------------------------------------------------------------------ 41 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 1800 S 754 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 42 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2950 S 754 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 43 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2720 S 754 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 44 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2720 S 754 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 45 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2420 S 754 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8149( 9) - 09/07/00 13:03 - [ 7] Visit: 03 Visit Priority: Visit Requirements: BETWEEN 21-Sep-2000 AND 03-Nov-2000 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 80 STAR-J-OFFS STIS/C ACQ 50CCD MIRROR 1 6 S ET-X CD ------------------------------------------------------------------------------------------------------------------------------------ 81 STAR-J-OFFS STIS/C ACQ/PEA 52X0.1 MIRROR 1 20 S ET-X CD K ------------------------------------------------------------------------------------------------------------------------------------ 82 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 1780 S 754-Y UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 83 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2970 S 754-Y UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 84 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-Y UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 85 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-Y UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 86 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-Y UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8149( 9) - 09/07/00 13:03 - [ 8] Visit: 04 Visit Priority: Visit Requirements: BETWEEN 21-Sep-2000 AND 03-Nov-2000 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 90 STAR-J-OFFS STIS/C ACQ 50CCD MIRROR 1 6 S ET-X CD ------------------------------------------------------------------------------------------------------------------------------------ 91 STAR-J-OFFS STIS/C ACQ/PEA 52X0.1 MIRROR 1 20 S ET-X CD K ------------------------------------------------------------------------------------------------------------------------------------ 92 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 1780 S 754-Y UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 93 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2970 S 754-Y UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 94 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-Y UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 95 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-Y UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 96 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-Y UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8149( 9) - 09/07/00 13:03 - [ 9] Visit: 51 Visit Priority: Visit Requirements: BETWEEN 28-Jul-2000 AND 07-Sep-2000 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 STAR-J-OFFS STIS/C ACQ 50CCD MIRROR 1 6 S ET-X CD ------------------------------------------------------------------------------------------------------------------------------------ 11 STAR-J-OFFS STIS/C ACQ/PEA 52X0.1 MIRROR 1 20 S ET-X CD K ------------------------------------------------------------------------------------------------------------------------------------ 21 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 1780 S 754-X UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 22 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2970 S 754-X UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 23 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-X UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 24 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-X UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 25 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-X UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8149( 9) - 09/07/00 13:03 - [ 10] Visit: 52 Visit Priority: Visit Requirements: BETWEEN 28-Jul-2000 AND 07-Sep-2000 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 30 STAR-J-OFFS STIS/C ACQ 50CCD MIRROR 1 6 S ET-X CD ------------------------------------------------------------------------------------------------------------------------------------ 31 STAR-J-OFFS STIS/C ACQ/PEA 52X0.1 MIRROR 1 20 S ET-X CD K ------------------------------------------------------------------------------------------------------------------------------------ 41 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 1800 S 754-X UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 42 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2970 S 754-X UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 43 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-X UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 44 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-X UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 45 RXJ185635-3 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=3000.0 1 2900 S 754-X UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8149( 9) - 09/07/00 13:03 - [ 11] Summary Form for Proposal 8149 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD 52X0.1 52X0.5 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=3000.0 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 21-Sep-2000 AND 03-Nov-2000 BETWEEN 28-Jul-2000 AND 07-Sep-2000 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names STAR-I-OFFSET RXJ185635-3754 STAR-J-OFFSET-X RXJ185635-3754-Y RXJ185635-3754-X ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------