6135( 0) - 07/18/95 20:15 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6135 Version: ********** Check-in Date: ********** 1.Proposal Title: Uncovering Misidentifications of Bright Galactic X-ray Binaries ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Bruce Margon University of Washington CoI: Stefanie Wachter University of Washington N CoI: Dr. Scott Anderson University of Washington Y ------------------------------------------------------------------------------------ 6. Abstract We discuss three intense galactic X-ray binary stars with low- mass companions: V1727 Cyg (X2129+470), CAL 87, and NP Ser (GX17+2). All three optical counterparts, despite literally decades of intensive study, exhibit important anomalies, not readily interpreted by conventional models. All three sources also lie in severely crowded fields, and in all cases the anomalies would be resolved if much of the light observed from the ground in fact came from a nearby, thus-far-unresolved superposed (unrelated) companion. Recent work on a fourth famous source, Circinus X- 1, shows that this possibility is far from speculative: 15 years after the ``identification" of that object, the optical image has been resolved into three objects within 1.5'', revealing the true counterpart 1.4'' distant from the canonical identification. We propose here a very simple program of PC imaging to explore this problem. One of the three sources is already known to have at least one polluting companion 0.9'' distant, so precision multicolor magnitudes in that system are guaranteed to be of importance in unraveling ground-based photometry. ------------------------------------------------------------------------------------ 6135( 0) - 07/18/95 20:15 - [ 2] Observations Description ------------------------ The choice of WFPC2 vs. FOC for this program is not trivial, and has been examined carefully. Of course only the FOC fully samples the restored HST PSF, so one might argue that if one is searching for interlopers, it is desirable to push to the minimum achievable separation attainable by the HST optics. However, the superposed interlopers in this problem are more likely to be red than blue, both because there are far more faint (intrinsically) red stars than blue, and also because the reddening is significant in all of these fields. For this reason we choose the PC as a compromise, to yield quite good angular resolution, as well as good response all through the visible and near IR. We propose to use the equivalent of UBVR filters for all objects, so that there is reasonable color information available on each of the interlopers uncovered. There would seem to be only limited value in pushing further into the UV, both because interlopers are more likely red, as above, and also because we are searching for sources that provide significant visible-light contamination, to explain already-observed anomalies. EXPOSURE TIME AND ORBIT ESTIMATES. We want to achieve at least S/N>10 (10\ we do not a priori know the precise colors and magnitudes of the suspected superpositions (finding this out is key to the proposed science), it is unlikely that an object fainter than this (of almost any reasonable color) could provide sufficient contamination to have caused confusion in the ground-based studies. Note that it is only essential that we be able to significantly detect a red superposed object in one of the redder filters and a blue superposed object in one of the bluer filters (this also simplifies exposure time estimates, as the AB_Nu term is then small). In setting exposure times, we have conservatively assumed that we will use an aperture including about ~ 9 PC pixels when performing photometry during data reduction. Using formula 6.1, in conjunction with Tables 5.1, 6.2, and 6.3 in the WFPC2 Instrument Handbook, we expect S/N=10-20 for m=22 in the following total exposure times: F336W--600s, F439W--400s, F555W--140s, and F675W--140s. Of course, we want to divide these total times into two exposures for each filter to allow for cosmic ray removal (e.g., a 0.5 ratio CR-SPLIT is fine). We will probably choose the 14e/DN gain option, to ensure that the brightest target objects (which are variable, but conservatively always V>16.5) do not saturate. A specific example of an exposure time estimate is provided at the end of this section. For V1727 Cyg, the typical HST orbital visibility time is 56 min, for NP Ser, 53 min, and for CAL 87, 59 min. (Note also that CAL 87 visibility should be particularly good as it is sometimes in the continuous viewing zone.) One HST orbit is required for each of the three targets: guide- star acquisition (12 min), F336W with CR -SPLIT (600s total science + 5 min total instrument overhead), F439W (400s total science + 6 min total overhead), F555W (140s total science + 6 min total overhead), and F675W (140s total science + 6 min total overhead), or 56 min in total. This example is ~2 min too long in the case of V1727, but we can merely shorten the integration times by about 10\ substantial loss of S/N. For CAL 87, we would similarly add a small amount of time to each exposure to fill the entire 59 min visibility period. We thus request a total of 3 HST orbits, one for each proposed target. Here we provide a specific example S/N estimate, in this case for F336W; the Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6135( 0) - 07/18/95 20:15 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6135( 0) - 07/18/95 20:15 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V1727-CYG STAR,LMXB, RA=21H 31M 26.42S +/- 0.1S, 2000 V=17.8 DEC=47D 17' 22.9" +/- 1", PLATE- B-V=0.8 ID=003P U-B=0.2 2 CAL-87 STAR,LMXB, RA=05H 46M 45.51S +/- 0.1S, DEC= 2000 V=18.9 -71D 08' 53.6" +/- 1" B-V=0.1 U-B=-0.7 3 NP-SER STAR,LMXB, RA=18H 16M 01.44S +/- 0.1S, DEC= 2000 V=17.5 -14D 02' 12.5" +/- 1", PLATE- B-V=1.3 ID=064B U-B=1.1 6135( 0) - 07/18/95 20:15 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: There are bright stars about 20 arcsec to the NE of the target. For most roll angles, these should not compromise the observations. However, we request that STSCI consult us when scheduling is more certain so that we can verify the bright objects will not fall on the PC FOV, and also bleed toward the target position, at tentatively scheduled roll angle. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 101 V1727-CYG WFPC2 IMAGE PC1 F336W CR-SPLIT=NO,ATD 2 300S - GAIN=15,CLOCKS= YES ------------------------------------------------------------------------------------------------------------------------------------ 102 V1727-CYG WFPC2 IMAGE PC1 F439W CR-SPLIT=NO,ATD 2 200S - GAIN=15,CLOCKS= YES ------------------------------------------------------------------------------------------------------------------------------------ 103 V1727-CYG WFPC2 IMAGE PC1 F555W CR-SPLIT=NO,ATD 3 40S - GAIN=15,CLOCKS= YES Comments: Request instrument scientist verify that CLOCKS=YES is OK for exposure of this short duration. CLOCKS=YES is preferred as bright stars may be in FOV. ------------------------------------------------------------------------------------------------------------------------------------ 104 V1727-CYG WFPC2 IMAGE PC1 F675W CR-SPLIT=NO,ATD 3 50S - GAIN=15,CLOCKS= YES Comments: Request instrument scientist verify that CLOCKS=YES is OK for exposure of this short duration. CLOCKS=YES is preferred as bright stars may be in FOV. ------------------------------------------------------------------------------------------------------------------------------------ 6135( 0) - 07/18/95 20:15 - [ 6] Visit: 02 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 ------------------------------------------------------------------------------------------------------------------------------------ 201 CAL-87 WFPC2 IMAGE PC1 F336W CR-SPLIT=NO,ATD 2 300S - GAIN=15,CLOCKS= YES ------------------------------------------------------------------------------------------------------------------------------------ 202 CAL-87 WFPC2 IMAGE PC1 F439W CR-SPLIT=NO,ATD 2 230S - GAIN=15,CLOCKS= YES ------------------------------------------------------------------------------------------------------------------------------------ 203 CAL-87 WFPC2 IMAGE PC1 F555W CR-SPLIT=NO,ATD 3 40S - GAIN=15,CLOCKS= YES ------------------------------------------------------------------------------------------------------------------------------------ 204 CAL-87 WFPC2 IMAGE PC1 F675W CR-SPLIT=NO,ATD 3 50S - GAIN=15,CLOCKS= YES ------------------------------------------------------------------------------------------------------------------------------------ 6135( 0) - 07/18/95 20:15 - [ 7] Visit: 03 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 ------------------------------------------------------------------------------------------------------------------------------------ 301 NP-SER WFPC2 IMAGE PC1 F336W CR-SPLIT=NO,ATD 2 260S - GAIN=15,CLOCKS= YES ------------------------------------------------------------------------------------------------------------------------------------ 302 NP-SER WFPC2 IMAGE PC1 F439W CR-SPLIT=NO,ATD 2 200S - GAIN=15,CLOCKS= YES ------------------------------------------------------------------------------------------------------------------------------------ 303 NP-SER WFPC2 IMAGE PC1 F555W CR-SPLIT=NO,ATD 3 40S - GAIN=15,CLOCKS= YES ------------------------------------------------------------------------------------------------------------------------------------ 304 NP-SER WFPC2 IMAGE PC1 F675W CR-SPLIT=NO,ATD 3 50S - GAIN=15,CLOCKS= YES ------------------------------------------------------------------------------------------------------------------------------------ 6135( 0) - 07/18/95 20:15 - [ 8] Summary Form for Proposal 6135 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ATD-GAIN=15 CLOCKS=YES ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F336W F439W F555W F675W ------------------------------------------------------------------------------------------------------------------------------------ Target Names V1727-CYG CAL-87 NP-SER ------------------------------------------------------------------------------------------------------------------------------------