11685( 2) - 24-Jun-2008 14:22:14 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11685 Version: 2 Check-in Time: 24-Jun-2008 14:22:14 STScI Edit Number: 0 Title Supermassive Neutron Stars or Odd binaries: Searching for Companions to Pulsars NGC 6440B and Terzan 5J ------------------------------------------------------------------------------------ Type Cycle GO 17 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Marten H. van Kerkwijk University of Toronto CoI: Dr. Cees G. Bassa Space Research Organization Netherlands N ------------------------------------------------------------------------------------ Abstract Recent sensitive pulsar searches of globular clusters uncovered four pulsars with very high inferred masses, between 1.7 and 2.7 solar masses. These strongly constrain the behaviour of matter in the ultra-dense interiors of neutron stars, since for most models such massive neutron stars could not exist. All four masses are inferred from the measured advance of periastron with time, under the assumption that it is due to General Relativity only. Here, we propose to test whether part of the observed periastron advance could be induced by the quadrupole moment of a suitably large, rotationally distorted companion. We infer the radii such companions need to have and show that they would be relatively bright, easily detectable with HST. For one pulsar, M 5B, we find a plausible candidate counterpart in archival data. We propose to use 2 orbits with WFC3 to search for suitably large counterparts to two of the other systems, including the one with the highest inferred mass. ------------------------------------------------------------------------------------ Observations Description ------------------------ Our goal is to detect possible companions to the pulsars NGC 6440B and Terzan 5J, at brightnesses appropriate for the case that the companions are sufficiently big to cause significant classical periastron advance. For Terzan 5J, we infer a companion similar to a 0.4 Msun main-sequence star, with predicted magnitudes of V=31.5, I=26.8, J=23.5, and H=22.3. In the optical, the magnitudes cannot be reached in a single orbit, but in the infrared this is easy with WFC3/IR. We plan two dither boxes, of 4x350 s in F125W and 4x300 s in F160W. These times are sufficiently long to allow buffer dumps during the exposures. We fill the small amount of unused visibility with a partly exectuted RAPID sequence in F160W (where stars are predicted to be brightest, due to the large extinction). With this, we should detect the source at the above magnitudes at between 15 and 20 sigma in F125W and F160W (better including PSF fitting); these should thus be good detections even including the effects of crowding. We will point slightly towards the core of Terzan 5, in order to try to detect other pulsar companions. Nominally, we should be able to detect Terzan 5I, for which a massive neutron star has been inferred as well, but crowding may prevent it. For NGC 6440B, for a radius of 1.1 Rsun and the lowest possible temperature, of 3200K (where the star is at the Hayashi limit), we predict V~27.4, I~22.3, and H~19.5. Obviously, the temperature can be higher, and indeed there is a 11685( 2) - 24-Jun-2008 14:22:14 - [ 2] possible counterpart in archival WFPC2 data at V~21.8. We aim to detect any possible counterpart in I and H at high significance, and somewhat hotter ones in V. This is possible in 1 orbit. Specifically, we plan to take dithered exposures of 300 and 350s in WFC3/IR F160W, 15, 348, and 394s in WFC3/UVIS F606W, and 10, 261, and 348s in WFC3/UVIS F814W, which completely fills the visibility without losing time to buffer dumps. This gives excellent detections for all possibilities. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 11685( 2) - 24-Jun-2008 14:22:14 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PSR-TERZAN5J STAR, BINARY PULSAR RA=17H48M4.4107S +/- 0.1", J2000 Predicted J=23.5, H=22.3 -OFFSET DEC=-24D47'10.05" +/- 0.1" Reference Frame: ICRS Comments: This position is offset by exactly +0.4s and +30" from that of PSR Terzan 5J to ensure that the center of Terzan 5, and all the pulsars in it, will be observed together with primary target Terzan 5J. To determine the offset, I used that the cluster center is +0.86s and +52" away from Terzan 5J, but that Ter 5J should be at least 20" away from the detector edge, or at most 40" away from the detector centre. To be save, I used an offset of just over 30" total. ------------------------------------------------------------------------------------------------------------------------------------ 2 PSR-NGC6440B STAR, BINARY PULSAR RA=17H48M52.9529S +/- 0.1", J2000 V = 21.8 Possible counterpart has DEC=-20D21'38.86" +/- 0.1" V=21.8. Predictions V<27.4, I<23.3, H<19.5 Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 11685( 2) - 24-Jun-2008 14:22:14 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO Pattern_Comments: Default dithers: 0, 0; 1.5, 4; 4, 4; 4, 1.5 ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.145 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO Pattern_Comments: Default dithers: 0, 0 and 2.5, 2.5 ------------------------------------------------------------------------------------------------------------------------------------ 11685( 2) - 24-Jun-2008 14:22:14 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: - FOV including PSR TERZAN 5J as well as the cluster core, by pointing at an intermediate position - Two dither boxes, one each for F125W (4xSTEP50/12=4x349s) and F160W (4xSTEP50/10=4x249s). - Less time for F160W given huge reddening. In left-over time, include a RAPID/10=29s for F160W to get the bright stars (even) better. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PSR-TERZAN5 WFC3/IR MULTIAC IR-FIX F160W NSAMP=10, SAMP-SEQ=RAPID 1 DEF J-OFFSET CUM Comments: - Without this exposure, there was some unused visibility. It also serves to measure the brighter stars better in the band they likely are brightest. - Use IR-FIX since the position is offset from the target and the core of Terzan 5. ------------------------------------------------------------------------------------------------------------------------------------ 2 PSR-TERZAN5 WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=STEP50, NSAMP=10 1 DEF PATTERN 1 2 J-OFFSET CUM Comments: - NSAMP set to minimum required to be able to dump data during integration. - Use IR-FIX since the position is offset from the target and the core of Terzan 5. ------------------------------------------------------------------------------------------------------------------------------------ 3 PSR-TERZAN5 WFC3/IR MULTIAC IR-FIX F125W SAMP-SEQ=STEP50, NSAMP=12 1 DEF PATTERN 1 3 J-OFFSET CUM Comments: - Using F125W which is closer to J rather than wider F110W, since reddening makes latter only marginally more efficient. - Use IR-FIX since the position is offset from the target and the core of Terzan 5. ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ PSR-TERZAN5J-OFFSET 1 WFC3/IR MULTIAC IR-FIX F160W none none none none 1 N/A CUM PSR-TERZAN5J-OFFSET 2 WFC3/IR MULTIAC IR-FIX F160W 1 none none none 1 N/A CUM PSR-TERZAN5J-OFFSET 2 WFC3/IR MULTIAC IR-FIX F160W 2 none none none 1 N/A CUM PSR-TERZAN5J-OFFSET 2 WFC3/IR MULTIAC IR-FIX F160W 3 none none none 1 N/A CUM 11685( 2) - 24-Jun-2008 14:22:14 - [ 6] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ PSR-TERZAN5J-OFFSET 2 WFC3/IR MULTIAC IR-FIX F160W 4 none none none 1 N/A CUM PSR-TERZAN5J-OFFSET 3 WFC3/IR MULTIAC IR-FIX F125W 1 none none none 1 N/A CUM PSR-TERZAN5J-OFFSET 3 WFC3/IR MULTIAC IR-FIX F125W 2 none none none 1 N/A CUM PSR-TERZAN5J-OFFSET 3 WFC3/IR MULTIAC IR-FIX F125W 3 none none none 1 N/A CUM PSR-TERZAN5J-OFFSET 3 WFC3/IR MULTIAC IR-FIX F125W 4 none none none 1 N/A CUM 11685( 2) - 24-Jun-2008 14:22:14 - [ 7] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: - FOV automatically includes cluster core. - One short and two long for each of UVIS/F606W and UVIS/F814W, and two intermediate-length sets of STEP50 for IR/F160W. - Put WFC3/IR in between the WFC3/UVIS exposures since it allows one to dump a preceding UVIS image, and leave a relatively small image in the buffer, so that the next UVIS image can be shorter. (With IR in front, two IR dithers becomes impossible; with it at the end, cannot have a second short UVIS exposure.) Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PSR-NGC6440 WFC3/UVI ACCUM UVIS F606W CR-SPLIT=NO 1 15 S B S ------------------------------------------------------------------------------------------------------------------------------------ 2 PSR-NGC6440 WFC3/UVI ACCUM UVIS F606W CR-SPLIT=NO 1 348 S PATTERN 2 2 B S Comments: Second exposure made slightly longer than minimal required for buffer dump to use up visibility. ------------------------------------------------------------------------------------------------------------------------------------ 3 PSR-NGC6440 WFC3/IR MULTIAC IR F160W SAMP-SEQ=STEP50, NSAMP=12 1 DEF B CUM Comments: Exposure time chosen to just allow buffer dump from previous WFC3/UVIS exposure. ------------------------------------------------------------------------------------------------------------------------------------ 4 PSR-NGC6440 WFC3/IR MULTIAC IR F160W SAMP-SEQ=STEP50, NSAMP=11 1 DEF POS TARG 0.424, 0.474 B CUM Comments: - POS-TARG offset by 3.5, 3.5 pixels --as for WFC3-IR-DITHER-LINE-- to allow pixel phase sampling. - Exposure time just long enough to dump buffer from previous exposure. ------------------------------------------------------------------------------------------------------------------------------------ 5 PSR-NGC6440 WFC3/UVI ACCUM UVIS F814W CR-SPLIT=NO 1 348 S PATTERN 2 5 B S see below Comments: Exposure times chosen to allow buffer dumps, from previous WFC3/IR exposure, and first UVIS one. Buffer dumps from second and short following exposures to happen after occultation. ------------------------------------------------------------------------------------------------------------------------------------ 6 PSR-NGC6440 WFC3/UVI ACCUM UVIS F814W CR-SPLIT=NO 1 10 S POS TARG 0.1058, 0.0992 B S Comments: Use POSTARG of 2.5, 2.5 pixels to keep same position as last integration. ------------------------------------------------------------------------------------------------------------------------------------ 11685( 2) - 24-Jun-2008 14:22:14 - [ 8] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ PSR-NGC6440B 1 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S PSR-NGC6440B 2 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 N/A S PSR-NGC6440B 2 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 394.0 S S PSR-NGC6440B 3 WFC3/IR MULTIAC IR F160W none none none none 1 N/A CUM PSR-NGC6440B 4 WFC3/IR MULTIAC IR F160W none none none none 1 N/A CUM PSR-NGC6440B 5 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 261.0 S S PSR-NGC6440B 5 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 N/A S PSR-NGC6440B 6 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S 11685( 2) - 24-Jun-2008 14:22:14 - [ 9] Summary Form for Proposal 11685 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR, IR-FIX, UVIS ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO, NSAMP=10, NSAMP=11, NSAMP=12, SAMP-SEQ=RAPID, SAMP-SEQ=STEP50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 2, PATTERN 1 3, PATTERN 2 2, PATTERN 2 5, POS TARG 0.1058, 0.0992, POS TARG 0.424, 0.474 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F125W, F160W, F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names PSR-NGC6440B, PSR-TERZAN5J-OFFSET ------------------------------------------------------------------------------------------------------------------------------------