6526( 5) - 12/02/96 16:09 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6526 Version: 5 Check-in Date: 02-Dec-1996 16:06:17 1.Proposal Title: Distance, Proper Motion and Colors of the Vela Pulsar. ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Patrizia Caraveo Istituto di Fisica Cosmica del CNR CoI: Giovanni F. Bignami Istituto di Fisica Cosmica del CNR N CoI: Roberto P. Mignani Istituto di Fisica Cosmica del CNR N CoI: Lawrence Taff Dept. of Physics and Astronomy,JHU N ------------------------------------------------------------------------------------ 6. Abstract PSR0833-45 is, with the Crab pulsar and PSR0540-69, one of the few Isolated Neutron Stars (INSs) associated with a SNR. Moreover, these are, so far, the only INSs known to pulsate in the optical domain. Although the optical counterpart of the Vela Pulsar has been identified since 1977, nothing is known about its UV emission beyond a limited, ground based point in the U band. Blueward of it, the FOC could easily measure, for the first time, the presumably non-thermal radiation of the pulsar. On the other hand, recent results in X and Gamma-ray domains have challenged the commonly accepted value of 500 pc for the source distance, suggesting the need for a significant downward revision. The distance to the Vela Pulsar is a quite important piece of information, since this object is used as a calibrator for SNRs. Thus, it seems worthwhile to address this point with a set of three high accuracy WFPC2 observations aimed at measuring (or set limit on) the parallactic displacem. ent of the Vela Pulsar optical cou nterpart. At 250 pc, for instance, Vela should show a parallactic displacement of 0.004", equivalent to 0.09 PC pixels, a value which, according to our experience, is certainly within the instrument capabality. These high accuracy observations would also yield a precise measure of the pulsar's proper motion. This is yet another open point in the complex Vela Pulsar phenomenology, since, although proper motion is certainly present, existing radio and optical observations yield conflicting results. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to do very accurate positioning of the PSR0833-45 optical counterpart exploiting the sharp angular resolution of the PC (0."0455/pixel) to perform relative astrometry. Since the source V and B mags are similar, about 23.7, we propose to use the PC associated with the "V filter" F555W. Using the WFPC2 exposure simulator available in STEIS, we estimate that a PC exposure of 2000 sec would be sufficient to detect the target with a high S/N. This one-orbit observation should be repeated three times (two visit in cycle 6 and one in cycle 7), scheduled six months apart when the parallactic displacement is expected to be maximum i.e. at days 7 and 191. Attached to one of these visits, we plan to get deep FOC exposures of the source using two near UV filters. The FOC should be used in the nominal "f/151" mode. According to FOCSIM, an exposure time of about 4500 sec in the F275W and F195W filters is required to detect the target with a high S/N. Thus, 4 orbits will be needed for the FOC pointings. Real Time Justification ----------------------- The three PC observations should be scheduled at the time of the maximum parallactic displacement around days 7 and 191 of each calendar year. At those times the total parallactic displacment is a maximum, reaching 92\\% of the theoretically largest values. The time constraint associated with these dates is +/- 1 week but as the maximum displacement only slowly falls off from the extreme values, +/- 3 weeks is possible too. Hence, this restriction is not very tight one. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6526( 5) - 12/02/96 16:09 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 01 STAR-0835- STAR,NEUTRON STAR RA=8H 35M 20.67S +/- 0.019S, J2000 V = 23.6 4510 DEC=-45D 10' 35.75" +/- 0.29" B-V = 0.2 6526( 5) - 12/02/96 16:09 - [ 2] Visit: 01 Visit Requirements: PCS MODE F BETWEEN 30-JUN-97 AND 30-JUL-97 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 STAR-0835-4 WFPC2 IMAGE PC1-FIX F555W 5407 CR-SPLIT=DEF,CR-TOLERANCE=0.2 1 2600 S 510 ------------------------------------------------------------------------------------------------------------------------------------ 6526( 5) - 12/02/96 16:09 - [ 3] Visit: 02 Visit Requirements: PCS MODE F BETWEEN 1-JAN-98 AND 30-JAN-98 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 STAR-0835-4 WFPC2 IMAGE PC1-FIX F555W 5407 CR-SPLIT=DEF,CR-TOLERANCE=0.2 1 2600 S 510 ------------------------------------------------------------------------------------------------------------------------------------ 6526( 5) - 12/02/96 16:09 - [ 4] Summary Form for Proposal 6526 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=DEF CR-TOLERANCE=0.2 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE F BETWEEN 30-JUN-97 AND 30-JUL-97 PCS MODE F BETWEEN 1-JAN-98 AND 30-JAN-98 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W ------------------------------------------------------------------------------------------------------------------------------------ Target Names STAR-0835-4510 ------------------------------------------------------------------------------------------------------------------------------------