6742( 7) - 07/15/96 08:51 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6742 Version: 7 Check-in Date: 15-Jul-1996 08:48:42 1.Proposal Title: Spectroscopic Study of Origin and Nature of CVs in Globular Clusters ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle BINARIES AND STAR FOR GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: JONATHAN GRINDLAY HARVARD OBSERVATORY CoI: Paul Callanan Harvard University N CoI: Adrienne Cool University of California, Berkeley N CoI: Charles Bailyn Yale University N CoI: Haldan Cohn Indiana University N CoI: Phyllis Lugger Indiana University N ------------------------------------------------------------------------------------ 6. Abstract In our revised (Phase II submission) program, we propose to determine whether H Alpha emission objects discovered in our H Alpha vs. R imaging studies of the globular cluster NGC 6397 are cataclysmic variables (CVs) and possibly magnetic CVs as suggested by our recent FOS discovery of 3 probable DQ Her systems in NGC 6397. If the two additional (fainter) H Alpha candidates in NGC 6397 are as similar as the first three, which are nearly identical, it will provide strong evidence that CVs in globulars are not only formed by capture or exchanges (as expected), but that moderately massive cluster white dwarfs (WDs) may be preferentially magnetic (totally unexpected). This would have fundamental implications for stellar and dynamical evolution on globulars. By obtaining spectra of all candidates in the visible range (c. 4500 - 6700 Angstrom), probable magnetic systems can be identified by their usually significant He II emission. By obtaining a separate uv (1300 - 2200 Angstrom) spectrum on the brightest of the original 3 CV candidates in NGC 6397, as well as a prism observation (1600 - 4800 Angstrom), we shall both obtain the complete spectrum of a cluster CV as well as measure uv line ratios (e.g. HeII(1640)/CIV(1550)) that are sensitive to whether it is a magnetic CV. The uv spectrum and complete energy distribution will also allow future comparisons with quiescent LMXB spectra, which we shall propose to obtain in future HST cycles. ------------------------------------------------------------------------------------ 6742( 7) - 07/15/96 08:51 - [ 2] Observations Description ------------------------ The goal is to obtain spectra of three faint stars in the crowded field of a globular cluster core. All are stars that were detected in a WFPC1 imaging study with the Planetary Camera. The science targets are too faint relative to nearby bright neighbors to permit peak-ups to be performed on them directly. We are therefore using blind offsets from a nearby bright star to reach the science targets. The target acquisition begins with an ACQ/BINARY on the RED side on a bright, isolated star (Target 1). This star is about 30" from the science targets, and does not appear on the PC image on which the science targets appear and from which their coordinates were measured (see note about coordinate system below). It was chosen as the nearest available star that is sufficiently isolated for the use of an ACQ/BINARY. Following the ACQ/BIN, we offset to Target 2, which is also a bright star. This star is closer to the science targets, and is on the same PC image as the science targets. We perform a series of two 3x3 ACQ/PEAK observations on the RED side on this target to refine our coordinate system, the first with 0.29" steps and the 0.5" aperture, and the second with 0.11" steps and the 0.3" aperture. Following the two peak- ups, the pointing should be accurate to 0.08" or better. We then perform a series of blind offsets to each of the three science targets, in turn. No peak- ups are planned between the three blind offsets. As we are using the 0.43" aperture on all the science targets, it is critical that the total uncertainty in the pointing be no worse than about 0.15" after the third blind offset, which will occur 4 orbits after the peak-up was done. The following estimates suggest that this should be possible. If for any reason this accuracy is not possible, we can modify our program to include peak-ups between science targets. Blind offsets are said to be accurate to 0.08" for a 1 arcmin offset, and proportional to the offset angle. Each of our blind offsets will be no more than 16", and the maximum distance from the offset star (Target 2) is no more than 16". We thus expect that the cumulative pointing error due to the blind offset will be no more than 0.02"-0.03". Combining this in quadrature with the 0.08" accuracy following the second peak-up on Target 2, the overall pointing should be no worse than 0.09". This accuracy is sufficient to insure that the science targets will fall well inside the 0.43" aperture that we are using. These peak-ups, blind offsets, and observations of the three science targets will occupy 5 of the program's 7 orbits. Spectra of the first two science targets (Targets 4 and 5) will be taken with the G570H grating on the RED side. For the third science target (Target 3), we will obtain a spectrum with the PRISM on the RED side. The last 2 orbits will be devoted to taking a UV spectrum of Target 3 on the BLUE side with the G160L grating. We will switch to the BLUE side during occultation after the 5th orbit, and begin the 6th orbit with a peak-up on on Target 2. This peak-up will insure a pointing accuracy of 0.08" following the switch to the BLUE side. We then perform a blind offset to Target 3, less than 2" away, and again use the 0.43" aperture for the observation. Please note that in our Fixed_Targets list, we have specified the coordinates of all the Targets relative to Target 1, for convenience. Target 1 was successfully acquired in our Cycle 4 FOS observation of this cluster, and we are using the identical RA and DEC for this star that we used in that program. However, the coordinates of the science targets (Targets 3, 4, and 5) are best determined relative to Target 2, which is the offset star that appears on the Planetary Camera image on which the science targets also appear. The coordinates are significantly less certain relative to Target 1, and are insufficiently accurate relative to that star for the purposes of this program. Thus our final peak-ups are always done on Target 2. Our understanding is that the final peak-up on Target 2 will determine the coordinate system, and that, in effect, all the offsets will be done relative to the final peak-up position on that star. Exposure times were computed based on data supplied in the FOS Handbook and/or by scaling from our Cycle 4 FOS observations of other faint stars in this cluster. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6742( 7) - 07/15/96 08:51 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6742( 7) - 07/15/96 08:51 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6397- STAR RA = 17H 40M 40.570S +/- 0.020S, J2000 V = 14 174041- DEC = -53D 40' 01.10" +/- 0.20", B-V = 0.85 534001- PLATE-ID=0688 E(B-V) = 0.2 OFFSET 2 NGC6397- STAR RA-OFF = 0.910S +/- 0.010S, DEC- J2000 V = 14 174041- OFF = -20.00" +/- 0.10", FROM 1, B-V = 0.85 534021- PLATE-ID=0688 E(B-V) = 0.2 OFFSET 3 NGC6397- STAR, DC RA-OFF = 0.932S +/- 0.005S, DEC- J2000 V = 18 174042- OFF = -18.71" +/- 0.05", FROM 1, B-V = 0.5 534020 PLATE-ID=0688 E(B-V) = 0.2 4 NGC6397- STAR RA-OFF = 0.416S +/- 0.005S, DEC- J2000 V = 20 174041- OFF = -26.46" +/- 0.05", FROM 1, B-V = 0.5 534028 PLATE-ID=0688 E(B-V) = 0.2 5 NGC6397- STAR, DC RA-OFF = 1.164S +/- 0.005S, DEC- J2000 V = 20 174042- OFF = -20.77" +/- 0.05", FROM 1, B-V = 0.5 534022 PLATE-ID=0688 E(B-V) = 0.2 6742( 7) - 07/15/96 08:51 - [ 5] Visit: 01 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 ------------------------------------------------------------------------------------------------------------------------------------ 101 NGC6397-174 FOS/RD ACQ/BIN 4.3 MIRROR 1 2.1 S ONBOARD ACQ FOR 102 041-534001- ARY OFFSET ------------------------------------------------------------------------------------------------------------------------------------ 102 NGC6397-174 FOS/RD ACQ/PEA 0.5 MIRROR SCAN-STEP-X=0.29,SCAN-STEP-Y=0.29 1 2.1 S ONBOARD ACQ FOR 103 041-534021- K ,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 OFFSET ------------------------------------------------------------------------------------------------------------------------------------ 103 NGC6397-174 FOS/RD ACQ/PEA 0.3 MIRROR SCAN-STEP-X=0.11,SCAN-STEP-Y=0.11 1 2.1 S ONBOARD ACQ FOR 201-501 041-534021- K ,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 OFFSET Comments: This peak-up acquisition is followed by three consecutive pointing offsets of up to 9" to science targets. These targets must be acquired in a 0.43" aperture. An accuracy of 0.1" per offset is required. ------------------------------------------------------------------------------------------------------------------------------------ 201 NGC6397-174 FOS/RD ACCUM 0.5 G570H 1 70 M 041-534028 ------------------------------------------------------------------------------------------------------------------------------------ 301 NGC6397-174 FOS/RD ACCUM 0.5 G570H 1 90 M 042-534022 ------------------------------------------------------------------------------------------------------------------------------------ 401 NGC6397-174 FOS/RD ACCUM 0.5 PRISM 1 15 M 042-534020 ------------------------------------------------------------------------------------------------------------------------------------ 501 NGC6397-174 FOS/BL ACQ/PEA 0.25-PA MIRROR SCAN-STEP-X=0.11,SCAN-STEP-Y=0.11 1 12.0 S ONBOARD ACQ FOR 601 041-534021- K IR-A ,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 OFFSET ------------------------------------------------------------------------------------------------------------------------------------ 601 NGC6397-174 FOS/BL ACCUM 0.5-PAI G160L STEP-PATT=SINGLE 1 65 M 042-534020 R-A ------------------------------------------------------------------------------------------------------------------------------------ 6742( 7) - 07/15/96 08:51 - [ 6] Summary Form for Proposal 6742 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCAN-STEP-X=0.29 SCAN-STEP-Y=0.29 SEARCH-SIZE-X=3 SEARCH-SIZE-Y=3 SCAN-STEP-Y=0.11 SCAN-STEP-X=0.11 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category BINARIES AND STAR FORMATION ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 102 ONBOARD ACQ FOR 103 ONBOARD ACQ FOR 201-501 ONBOARD ACQ FOR 601 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G570H PRISM G160L ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6397-174041-534001-OFFSET NGC6397-174041-534021-OFFSET NGC6397-174041-534028 NGC6397-174042-534022 NGC6397-174042-534020 ------------------------------------------------------------------------------------------------------------------------------------