! Recieved February 14 !__Proposal-Section__ !6135 ! Hubble Space Telescope Cycle 5 (1995) Phase II Proposal Template ! $Id: 6135,v 8.1 1995/06/09 18:27:47 pepsa Exp $ ! ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Christian Ready ! Phone: 410 338-4546 , E-mail: ready@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Date generated: Mon Dec 19 08:41:46 EST 1994 ! Proposal_Information ! Section 4 Title: Uncovering Misidentifications of Bright Galactic X-ray Binaries Proposal_Category: GO Scientific_Category: Hot Stars Cycle: 5 Investigators PI_name: Dr. Bruce Margon PI_Institution: University of Washington CoI_Name: Stefanie Wachter CoI_Institution: University of Washington Contact: ! Y or N (designate at most one contact) CoI_Name: Dr. Scott Anderson CoI_Institution: University of Washington Contact: Y ! Y or N (designate at most one contact) * Abstract: ! Free format text (please update) 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. Questions Observing_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 ! other filters were handled in analogous fashion. With F336W, ! we expect to detect N_e=(2.5 * 10^11) (300) (0.00425) (0.5) ! 10^-0.4(22)=250 electrons in 300s (one of the two equal CR- ! SPLIT exposures), where 0.00425 is a filter efficiency from ! Table 6.2, and the factor of 0.5 is the expected fraction of ! the total flux in ~ 9 PC pixels, from Table 5.1. The (non- ! source) background noise will be dominated by the read-out ! noise at 7.0 e/pix (for gain of 14e/DN), as the dark-count is ! about 0.016 e/pix/s, and the sky background (from Table 6.1 & ! 6.3) in F336W should be no worse than about 0.0005 e/pix/s. ! Thus in 300s we should achieve a S/N of about 250 / 250 + 9 ! pix * (7.0^2/pix + 5.0/pix)^1/2=9.2. Note, however, that this ! is just one-half of the total integration time with the ! requested CR-SPLIT, so we should achieve S/N=13 in the ! stacked exposure Real_Time_Justification: Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: V1727-CYG Alternate_Names: Description: STAR,LMXB, Position: RA=21H 31M 26.42S +/- 0.1S, ! Most common specification format is * DEC=47D 17' 22.9" +/- 1", PLATE-ID=003P Equinox: 2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: V=17.8, ! Include at least V and B-V B-V=0.8, U-B=0.2 Comments: Target_Number: 2 Target_Name: CAL-87 Alternate_Names: Description: STAR,LMXB, Position: RA=05H 46M 45.51S +/- 0.1S, ! Most common specification format is * DEC=-71D 08' 53.6" +/- 1" !PLATE-ID=06B0 or 014D Equinox: 2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: V=18.9, ! Include at least V and B-V * B-V=0.1, U-B=-0.7 Comments: Target_Number: 3 Target_Name: NP-SER Alternate_Names: Description: STAR,LMXB, Position: RA=18H 16M 01.44S +/- 0.1S, ! Most common specification format is * DEC=-14D 02' 12.5" +/- 1", PLATE-ID=064B Equinox: 2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: V=17.5, ! Include at least V and B-V * B-V=1.3, U-B=1.1 Comments: ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number: 1 Visit_Requirements: ! Section 7.1 ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling ! PCS MODE [Fine | Gyro] ! GUIDing TOLerance ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN