8154( 3) - 11/09/99 17:01 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8154 Version: 3 Check-in Date: 01-Feb-1999 10:31:32 1.Proposal Title: The Massive Binary Pulsar 2303+46: An unexpected companion ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Marten van kerkwijk Astronomical Institute Utrecht CoI: Prof. Shri Kulkarni California Institute of Technology N CoI: Prof. Sterl Phinney California Institute of Technology N ------------------------------------------------------------------------------------ 5. Abstract Double neutron star systems are objects of fundamental interest to physics (tests of GR) and astronomy (sources of gravitational wave radiation, possible progenitors of GRBs). The nature of their companion, specifically the size, is clearly of importance for these issues and has historically motivated deep optical observations. To our surprise and delight, we have found a faint blue optical object within 0.25 arcsec of the location of one such presumed double neutron star system, PSR B2303+46. From pulsar timing we know securely that the companion is more massive than 1.2 M_\odot. We suggest that the companion is a massive hot white dwarf formed before the pulsar; such an unorthodox solution is possible by adding a twist to the usual evolutionary scenario. Here, we propose UV imaging with STIS to confirm that the object is stellar, to confirm its energy distribution is thermal, and to get a rough constraint on its temperature. Confirmation is not only important for the reasons discussed above, but also for our ideas about the evolution of these systems, and of considerable interest for verifying white-dwarf cooling models. If confirmed, the companion is the only white dwarf securely known to be so massive, and one of only a few for which two independent age estimates are available. ------------------------------------------------------------------------------------ 8154( 3) - 11/09/99 17:01 - [ 2] Observations Description ------------------------ We require 10-Sigma detections with the NUV and FUV MAMAs. Less would mean our science is compromised, while there is not much point to better measurements given the uncertainties in the optical flux and the reddening. For our estimates, we assume a black-body emitter with T_rmeff=50000 K, E_B-V=0.24, with its flux normalized such that B=26.52. For the calculation of the number of orbits, we followed the instructions in the call for proposals. At Delta=+46^degrees, the orbital visibility is 55 minutes. In a first orbit, 6 minutes are required for guide-star acquisition, and 5 minutes for starting MAMA imaging, leaving 44 minutes for integration on target. In any subsequent orbit, 5 minutes are required for guide-star re-acquisition, and 1 minute for restarting the MAMA if no change is made. For observations requiring being in the Earth's shadow, 25 minutes of integration time is available per orbit Using the STIS imaging exposure time calculator, we find that for the FUV 10-Sigma detections are reached in about 50 minutes with the SrF2 filter, if one observes while in the Earth's shadow. We therefore require two orbits. We verified that one cannot improve the signal-to-noise ratio with another choice of filter. With no filter, the background is much higher. With the QTZ filter, observing in the shadow is not required, and in two orbits one thus has 93 minutes available. Even so, however, the signal-to-noise ratio reached is only 8. For the NUV MAMA, the clear option again suffers from high background, while the QTZ and SrF2 filters give approximately the same signal-to-noise ratios. In order to have as little overlap as possible between the NUV and FUV band passes, we prefer the QTZ filter. For 93 minutes of integration on source, the expected signal-to-noise ratio is 11. We propose to do all observations in TIMETAG mode. This will allow us to test for periodicity at the pulsar period (as noted above, we believe it highly unlikely the pulsar is responsible for the optical emission, but it does not hurt to check); to observe even outside of shadow time in the FUV (useful if the source is hotter than expected; if not, we simply select only the shadow time interval in the analysis); and to look for possible other variability, in our source (if hot, so that we get enough photons), and in other stars in the field. We verified carefully whether any stars in the field would violate the MAMA bright-star limits. The only object within 15 arcsec visible on the digitized sky survey -- and hence of possible worry -- is the star to the NE of our candidate (see Fig. reffig:psrb2303keck). The object to the WSW is a galaxy. From our images, we measure B=19.8, R=19.0. From Table 14.44 in the STIS manual, we infer that this object poses no risk. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- Shadow time is required for the FUV-MAMA imaging to obtain the best signal-to- noise ratio in the minimum number of orbits. The BETWEEN limits for the one visit below are to ensure shadow time during the FUV-MAMA TIME-TAG integrations. Selection for shadow time will be done off-line. In this way, the non-shadow time can still be used (which may be useful if the source is towards the bright end of our estimated range). ------------------------------------------------------------------------------------ 8154( 3) - 11/09/99 17:01 - [ 3] Data Distribution Paper Products: YES Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8154( 3) - 11/09/99 17:01 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 STAR- STAR, Binary Pulsar, DA RA=23H 05M 55.842S +/- 0.017S, J2000 V = 26.6+/-0.2 230556+47074 DEC=47D 07' 45.32" +/- 0.17" B-V = 0.0+/-0.2 5 E(B-V) = 0.22+/-0.03 Comments: Spectrum likely that of a hot white dwarf with Teff~50000 K 8154( 3) - 11/09/99 17:01 - [ 5] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 3-AUG-1999:12 AND 14-AUG-1999:12 BETWEEN 19-SEP-1999:12 AND 09-OCT- 1999:12 BETWEEN 27-NOV-1999:12 AND 11-DEC-1999:12 BETWEEN 22-JAN-2000:12 AND 27-JAN-2000:12 BETWEEN 06-JUL-2000:12 AND 11-JUL-2000:12 BETWEEN 26-AUG -2000:12 AND 13-SEP-2000:12 BETWEEN 30-OCT-2000:12 AND 16-NOV-2000:12 On Hold Comments: Additional Comments: Ensured Shadow time falls within orbital visibility using the BETWEEN statements. Thus, shadow time can be selected off-line, and the full time can be used if the source is bright enough. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 STAR-230556 STIS/F TIME-TA F25SRF2 MIRROR BUFFER-TIME=356 1 2852.0 +470745 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 2 STAR-230556 STIS/F TIME-TA F25SRF2 MIRROR BUFFER-TIME=356 1 3055.0 POS TARG 0.12, 0.12 +470745 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 3 STAR-230556 STIS/N TIME-TA F25QTZ MIRROR BUFFER-TIME=725 1 2906.0 +470745 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 4 STAR-230556 STIS/N TIME-TA F25QTZ MIRROR BUFFER-TIME=725 1 3055.0 POS TARG 0.12, 0.12 +470745 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8154( 3) - 11/09/99 17:01 - [ 6] Summary Form for Proposal 8154 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F25SRF2 F25QTZ ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=356 BUFFER-TIME=725 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 3-AUG-1999 12 AND 14-AUG-1999 12 BETWEEN 19-SEP-1999 12 AND 09-OCT-1999 12 BETWEEN 27-NOV-1999 12 AND 11-DEC-1999 12 BETWEEN 22-JAN-2000 12 AND 27-JAN-2000 12 BETWEEN 06-JUL-2000 12 AND 11-JUL-2000 12 BETWEEN 26-AUG-2000 12 AND 13-SEP-2000 12 BETWEEN 30-OCT-2000 12 AND 16-NOV-2000 12 POS TARG 0.12, 0.12 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names STAR-230556+470745 ------------------------------------------------------------------------------------------------------------------------------------