6729( 4) - 06/20/96 11:01 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6729 Version: 4 Check-in Date: 20-Jun-1996 10:57:13 1.Proposal Title: Spectra of Faint Variables in 47 Tuc: CVs or LMXBs? ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle BINARIES AND STAR FOR GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: PETER EDMONDS SPACE TELESCOPE SCIENCE INSTITUTE CoI: Ron Gilliland Space Telescope Science Institute N CoI: Mario Livio Space Telescope Science Institute N CoI: Larry Petro Space Telescope Science Institute N ------------------------------------------------------------------------------------ 6. Abstract We propose to obtain Faint Object Spectrograph (FOS) spectra of four CV/LMXB candidates discovered in the core of 47 Tuc. All of these stars are faint and variable, three of them lie near X-ray sources, and two of them are blue (where colors are available). We will use the spectra to determine whether these stars contain accretion disks, and to help distinguish between dwarf novae, magnetic CVs and neutron star systems. These observations are important for testing a new hypothesis that magnetic CVs may be overabundant in globular clusters. Only one confirmed dwarf nova has been detected in 47 Tuc, although some theoretical estimates using tidal capture theory have predicted that dozens should be found. The recent detection by us of 9 eclipsing binaries in the core of 47 Tuc using HST shows that binaries can form (or primordial binaries survive) in the core of this dense cluster. These results may further exacerbate the problem of the dearth of CVs in 47 Tuc. The confirmation that some of the dim X-ray sources in globular clusters are binaries containing neutron stars would be important for the formation of millisecond pulsars and for the dynamics of dense clusters. Further study of the unusually rich and variable population of X-ray sources in 47 Tuc may also give us a new class of X-ray binaries. ------------------------------------------------------------------------------------ 6729( 4) - 06/20/96 11:01 - [ 2] Observations Description ------------------------ Spectra of IPs, quiescent SXTs, and quiescent DN differ in continuum shape, absorption line strength, Balmer emission, and HeII Lambda4686 emission. Specifically the spectrum of intermediate polars contains strong and comparable HBeta and HeII Lambda4686 emission and a blue continuum extending into the ultraviolet. The spectrum of quiescent SXTs contains strong HBeta emission, no HeII Lambda4686 emission, absorption lines of a late-type star, and no blue UV continuum. The spectrum of quiescent DN contains strong HBeta emission, weak HeII Lambda4686 emission, and a blue continuum. Therefore, UV and HBeta/Lambda4686 spectra of the four candidate CV/LMXB systems in 47 Tuc will allow us to distinguish between these possible kinds of degenerate star binary systems in our study of their nature. To this end, we propose to obtain spectra with the FOS of four candidate CV/LMXB systems. The spectrum of each system in the range containing the CIII - N III LambdaLambda 4640 - 50, HeII Lambda4686, HBeta, and HAlpha lines will be obtained with the FOS/RD G570H configuration, and the UV and visual continuum will be measured with the FOS/RD PRISM configuration. The G570H configuration provides the necessary spectral resolution (4.5 Angstrom, 300 km s^-1) and sensitivity to detect the above- mentioned diagnostic emission lines, and the PRISM observations will allow detection of an accretion disk of characteristic temperature as low as 10,000 K. Use of the FOS prism, rather than a grating, will reduce possible contamination of the UV spectrum by grating scatter of the red spectrum of a non-degenerate companion star. The exposures will be obtained with the 0.26'' FOS aperture, in order that the flux of nearby stars is excluded and the sky background is minimized. To provide greater observing efficiency, we propose these observations be obtained during a Continuous Viewing Zone (CVZ) passage of 47 Tuc. The average sky background (Zodiacal Light and OTA-scattered earthshine) during the CVZ passage will be less than 24^th mag in the 0.3- aperture, and therefore negligible compared to the stellar flux of these 21^st mag targets. To estimate the required exposure times we have used our PC1 F336W flux measurements of V7, V8 and PV1 and the FOC F220W measurement of Shara et al. (1995) of SV3. To extrapolate the flux from those measurement passbands to our G570H and PRISM passbands and to calculate the instrumental responses we have used the SYNPHOT throughput calculator. Since these systems may comprise a non-degenerate, nuclear-powered star and an accretion disk or column we considered a broad range of spectral types (G2 - M0) and characteristic accretion flow temperatures (10,000 K - 100,000 K). We find that PRISM exposures times of 1,000 - 2,100 sec (depending on the star considered) will provide SNR >= 10 per diode at 2500 Angstrom if the previously measured flux is due to a hot accretion disk, and SNR >= 10 will be achieved at 3000 Angstrom if that flux is from a worst-case, late-type star (G5). This will be sufficient to place useful limits on a possible accretion disk in these systems. We further find that G570H exposure times of 1,700 - 3,600 sec will provide SNR >= 20 per diode at Lambda4686 if the previously measured flux is from a late-type star, or SNR >= 10 will be obtained if that flux is from a hot accretion disk. The stellar signal exceeds the FOS dark current at all wavelengths considered. The necessary exposure times to achieve these SNR are as follows: vspace2mm begintabularlll Star & PRISM & G570H, V7 & 2100s & 3600s , V8 & 1000s & 1700s , PV1 & 1300s & 2300s , SV3 & 1700s & 3000s endtabular vspace2mm The exposures of V7 will be repeated since it is a large amplitude, ~10 hr variable. Including overheads, these ten exposures will require 433 minutes. Target acquisition (TA) is obviously crucial for these crowded-field observations, and the FOS group lead at STScI has been consulted to ensure a robust strategy is used. The general strategy is to acquire a bright offset star outside the crowded core, and then to perform a blind slew to each program star. A 4-stage ACQ/PEAK (A, B1, D1, D3) on the offset star will provide 0.04'' positioning and require 61 min of spacecraft time. This TA will position the targets in the 0.26'' aperture with sufficient accuracy (0.04'') to assure negligible loss of stellar flux at the aperture. A 15'' slew to a program star will result in an additional, negligible 0.02'' uncertainty. The blind slews between program stars will be computed from our 1993 PC1 images of the core and archival FOC F220W images. The total spacecraft time required for TA and exposures is 507 min, which will require 5.3 CVZ orbits. Real Time Justification ----------------------- The calculation of the number of orbits assumes CVZ observations. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6729( 4) - 06/20/96 11:01 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6729( 4) - 06/20/96 11:01 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC104- STAR, K V-IV RA = 0H 24M 1.024S +/- 0.2S, DEC 2000.0 V = 12.6+/-0.2 OFFSET1 = -72D 5' 7.831" +/- 1.0", PLATE B-V = 1.23+/-0.2 -ID = 06B1 TYPE=KV Comments: Red giant star used for initial acquisition Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1985.963 0.0 0.0 0.0 2 NGC104-E8 STAR, ALGOL SYSTEM RA-OFF = 2.241S +/- 0.01S, DEC- 2000.0 U = 19.1+/-0.3 OFF = 2.977" +/- 0.05", FROM 1, PLATE-ID = 06B1 Comments: Probable X-ray source Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1985.963 0.0 0.0 0.0 3 NGC104- STAR, K V-IV RA-OFF = 5.006S +/- 0.01S, DEC- 2000.0 V = 13.73+/-0.2 OFFSET2 OFF = 19.373" +/- 0.05", FROM 1, B-V = 1.04+/-0.2 PLATE-ID=06B1 TYPE=KIII Comments: Red giant star used for improving positional accuracy Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1985.963 0.0 0.0 0.0 4 NGC104-E7 STAR, ALGOL SYSTEM RA-OFF = 3.997S +/- 0.01S, DEC- 2000.0 U = 19.9+/-0.5 OFF = 16.879" +/- 0.05", FROM 1, PLATE-ID = 06B1 Comments: Probable X-ray source Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1985.963 0.0 0.0 0.0 5 NGC104-E11 STAR, ALGOL SYSTEM RA-OFF = 3.695S +/- 0.01S, DEC- 2000.0 U = 18.9+/-0.3 OFF = 12.751" +/- 0.05", FROM 1, PLATE-ID = 06B1 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1985.963 0.0 0.0 0.0 6 NGC104-PV2 STAR, DWARF NOVA RA-OFF = 4.768S +/- 0.01S, DEC- 2000.0 U = 20.1+/-0.5 OFF = 12.023" +/- 0.05", FROM 1, PLATE-ID = 06B1 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1985.963 0.0 0.0 0.0 7 NGC104-SV3 STAR, INTERMEDIATE RA-OFF = 5.142S +/- 0.01S, DEC- 2000.0 U = 20.4+/-0.2 POLAR OFF = 25.184" +/- 0.05", FROM 1, PLATE-ID = 06B1 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1985.963 0.0 0.0 0.0 6729( 4) - 06/20/96 11:01 - [ 5] Visit: 01 Visit Requirements: CVZ On Hold Comments: Additional Comments: All targets fall within 40" so the same guide stars can be used. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC104-OFFS FOS/RD ACQ/PEA 4.3 G570H SCAN-STEP-Y=1.23,SEARCH-SIZE-X=1, 1 0.13 S ONBOARD ACQ FOR 2 ET1 K SEARCH-SIZE-Y=3 Comments: STAGE 1 OF 4-STAGE PEAKUP FOR 0.04 ARCSEC POINTING ACCURACY ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC104-OFFS FOS/RD ACQ/PEA 1.0 G570H SCAN-STEP-X=0.61,SCAN-STEP-Y=0.61 1 0.14 S ONBOARD ACQ FOR 3 ET1 K ,SEARCH-SIZE-X=6,SEARCH-SIZE-Y=2 Comments: STAGE 2 OF 4-STAGE PEAKUP ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC104-OFFS FOS/RD ACQ/PEA 0.3 G570H SCAN-STEP-X=0.17,SCAN-STEP-Y=0.17 1 1.0 S ONBOARD ACQ FOR 4 ET1 K ,SEARCH-SIZE-X=5,SEARCH-SIZE-Y=5 Comments: STAGE 3 OF 4-STAGE PEAKUP ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC104-OFFS FOS/RD ACQ/PEA 0.3 G570H SCAN-STEP-X=0.052, 1 1.0 S ONBOARD ACQ FOR 5-7 ET1 K SCAN-STEP-Y=0.052,SEARCH-SIZE-X=5 ,SEARCH-SIZE-Y=5 Comments: STAGE 4 OF 4-STAGE PEAKUP ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC104-E8 FOS/RD ACCUM 0.3 G570H 1 1571 S ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC104-E8 FOS/RD ACCUM 0.3 PRISM 1 924 S ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC104-OFFS FOS/RD ACQ/PEA 0.3 G570H SCAN-STEP-X=0.052, 1 2.33 S ONBOARD ACQ FOR 8-17 ET2 K SCAN-STEP-Y=0.052,SEARCH-SIZE-X=5 ,SEARCH-SIZE-Y=5 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC104-E7 FOS/RD ACCUM 0.3 G570H 1 3326 S ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC104-E7 FOS/RD ACCUM 0.3 PRISM 1 1940 S ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC104-E11 FOS/RD ACCUM 0.3 G570H 1 1800 S ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC104-E11 FOS/RD ACCUM 0.3 PRISM 1 1100 S ------------------------------------------------------------------------------------------------------------------------------------ 12 NGC104-PV2 FOS/RD ACCUM 0.3 G570H 1 2125 S ------------------------------------------------------------------------------------------------------------------------------------ 13 NGC104-PV2 FOS/RD ACCUM 0.3 PRISM 1 1201 S ------------------------------------------------------------------------------------------------------------------------------------ 14 NGC104-SV3 FOS/RD ACCUM 0.3 G570H 1 2772 S ------------------------------------------------------------------------------------------------------------------------------------ 15 NGC104-SV3 FOS/RD ACCUM 0.3 PRISM 1 1571 S ------------------------------------------------------------------------------------------------------------------------------------ 16 NGC104-E7 FOS/RD ACCUM 0.3 G570H 1 3326 S ------------------------------------------------------------------------------------------------------------------------------------ 17 NGC104-E7 FOS/RD ACCUM 0.3 PRISM 1 1940 S ------------------------------------------------------------------------------------------------------------------------------------ 6729( 4) - 06/20/96 11:01 - [ 6] Summary Form for Proposal 6729 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCAN-STEP-Y=1.23 SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SEARCH-SIZE-Y=2 SEARCH-SIZE-Y=5 SEARCH-SIZE-X=5 SCAN-STEP-Y=0.052 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category BINARIES AND STAR FORMATION ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 3 ONBOARD ACQ FOR 4 ONBOARD ACQ FOR 5-7 ONBOARD ACQ FOR 8-17 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G570H PRISM ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC104-OFFSET1 NGC104-E8 NGC104-OFFSET2 NGC104-E7 NGC104-E11 NGC104-PV2 NGC104-SV3 ------------------------------------------------------------------------------------------------------------------------------------