! Proposal 6729, submission 1 ! PI: Peter Edmonds ! Received Tue Feb 6 16:04:23 EST 1996 ! From: pedmonds@stsci.edu ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! Refer to the HST Phase II Proposal Instructions to fill this out ! ! 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: Alice Berman ! Phone: 410-338-4462 , E-mail: aberman@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. Proposal_Information ! Section 4 Title: Spectra of Faint Variables in 47 Tuc: CVs or LMXBs? Proposal_Category: GO Scientific_Category: BINARIES AND STAR FORMATION Cycle: 6 Investigators PI_name: Peter Edmonds PI_Institution: Space Telescope Science Institute CoI_Name: Ron Gilliland CoI_Institution: Space Telescope Science Institute Contact: N ! Y or N (designate at most one contact) CoI_Name: Mario Livio CoI_Institution: Space Telescope Science Institute Contact: N ! Y or N (designate at most one contact) CoI_Name: Larry Petro CoI_Institution: Space Telescope Science Institute Contact: N ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) 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. Questions ! Free format text (please update) Observing_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: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: NGC104-OFFSET1 Description: STAR, K V-IV Position: RA = 0H 24M 1.024S +/- 0.2S, DEC = -72D 5' 7.831" +/- 1.0", PLATE-ID = 06B1 Equinox: 2000.0 Epoch: 1985.963 Flux: V = 12.6 +/- 0.2 B-V = 1.23 +/- 0.2 TYPE= KV Comments: Red giant star used for initial acquisition Target_Number: 2 Target_Name: NGC104-E8 Description: STAR, ALGOL SYSTEM Position: RA-OFF = 2.241S +/- 0.01S, DEC-OFF = 2.977" +/- 0.05", FROM 1, PLATE-ID = 06B1 Equinox: 2000.0 Epoch: 1985.963 Flux: U = 19.1 +/- 0.3 Comments: Probable X-ray source Target_Number: 3 Target_Name: NGC104-OFFSET2 Description: STAR, K V-IV Position: RA-OFF = 5.006S +/- 0.01S, DEC-OFF = 19.373" +/- 0.05", FROM 1, PLATE-ID=06B1 Equinox: 2000.0 Epoch: 1985.963 Flux: V = 13.73 +/- 0.2 B-V = 1.04 +/- 0.2 TYPE = KIII Comments: Red giant star used for improving positional accuracy Target_Number: 4 Target_Name: NGC104-E7 Description: STAR, ALGOL SYSTEM Position: RA-OFF = 3.997S +/- 0.01S, DEC-OFF = 16.879" +/- 0.05", FROM 1, PLATE-ID = 06B1 Equinox: 2000.0 Epoch: 1985.963 Flux: U = 19.9 +/- 0.5 Comments: Probable X-ray source Target_Number: 5 Target_Name: NGC104-E11 Description: STAR, ALGOL SYSTEM Position: RA-OFF = 3.695S +/- 0.01S, DEC-OFF = 12.751" +/- 0.05", FROM 1, PLATE-ID = 06B1 Equinox: 2000.0 Epoch: 1985.963 Flux: U = 18.9 +/- 0.3 Comments: Target_Number: 6 Target_Name: NGC104-PV2 Description: STAR, DWARF NOVA Position: RA-OFF = 4.768S +/- 0.01S, DEC-OFF = 12.023" +/- 0.05", FROM 1, PLATE-ID = 06B1 Equinox: 2000.0 Epoch: 1985.963 Flux: U = 20.1 +/- 0.5 Comments: Target_Number: 7 Target_Name: NGC104-SV3 Description: STAR, INTERMEDIATE POLAR Position: RA-OFF = 5.142S +/- 0.01S, DEC-OFF = 25.184" +/- 0.05", FROM 1, PLATE-ID = 06B1 Equinox: 2000.0 Epoch: 1985.963 Flux: U = 20.4 +/- 0.2 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: CVZ Visit_Comments: All targets fall within 40" so the same guide stars can be used. Exposure_Number: 1 Target_Name: NGC104-OFFSET1 Config: FOS/RD Opmode: ACQ/PEAK Aperture: 4.3 Sp_Element: G570H Wavelength: Optional_Parameters: SCAN-STEP-Y=1.23, SEARCH-SIZE-X=1, SEARCH-SIZE-Y=3 Number_of_Iterations: 1.0 Time_Per_Exposure: 0.13S Special_Requirements: ONBOARD ACQ FOR 2 Comments: STAGE 1 OF 4-STAGE PEAKUP FOR 0.04 ARCSEC POINTING ACCURACY Exposure_Number: 2 Target_Name: NGC104-OFFSET1 Config: FOS/RD Opmode: ACQ/PEAK Aperture: 1.0 Sp_Element: G570H Wavelength: Optional_Parameters: SCAN-STEP-X=0.61, SCAN-STEP-Y=0.61, SEARCH-SIZE-X=6, SEARCH-SIZE-Y=2 Number_of_Iterations: 1.0 Time_Per_Exposure: 0.14S Special_Requirements: ONBOARD ACQ FOR 3 Comments: STAGE 2 OF 4-STAGE PEAKUP Exposure_Number: 3 Target_Name: NGC104-OFFSET1 Config: FOS/RD Opmode: ACQ/PEAK Aperture: 0.3 Sp_Element: G570H Wavelength: Optional_Parameters: SCAN-STEP-X=0.17, SCAN-STEP-Y=0.17, SEARCH-SIZE-X=5, SEARCH-SIZE-Y=5 Number_of_Iterations: 1.0 Time_Per_Exposure: 1.0S Special_Requirements: ONBOARD ACQ FOR 4 Comments: STAGE 3 OF 4-STAGE PEAKUP Exposure_Number: 4 Target_Name: NGC104-OFFSET1 Config: FOS/RD Opmode: ACQ/PEAK Aperture: 0.3 Sp_Element: G570H Wavelength: Optional_Parameters: SCAN-STEP-X=0.052, SCAN-STEP-Y=0.052, SEARCH-SIZE-X=5, SEARCH-SIZE-Y=5 Number_of_Iterations: 1.0 Time_Per_Exposure: 1.0S Special_Requirements: ONBOARD ACQ FOR 5-7 Comments: STAGE 4 OF 4-STAGE PEAKUP Exposure_Number: 5 Target_Name: NGC104-E8 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: G570H Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 1571S Special_Requirements: Exposure_Number: 6 Target_Name: NGC104-E8 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: PRISM Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 924S Special_Requirements: Exposure_Number: 7 Target_Name: NGC104-OFFSET2 Config: FOS/RD Opmode: ACQ/PEAK Aperture: 0.3 Sp_Element: G570H Wavelength: Optional_Parameters: SCAN-STEP-X=0.052, SCAN-STEP-Y=0.052, SEARCH-SIZE-X=5, SEARCH-SIZE-Y=5 Number_of_Iterations: 1.0 Time_Per_Exposure: 2.33S Special_Requirements: ONBOARD ACQ FOR 8-17 Exposure_Number: 8 Target_Name: NGC104-E7 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: G570H Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 3326S Special_Requirements: Exposure_Number: 9 Target_Name: NGC104-E7 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: PRISM Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 1940S Special_Requirements: Exposure_Number: 10 Target_Name: NGC104-E11 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: G570H Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 1800S Special_Requirements: Exposure_Number: 11 Target_Name: NGC104-E11 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: PRISM Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 1100S Special_Requirements: Exposure_Number: 12 Target_Name: NGC104-PV2 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: G570H Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 2125S Special_Requirements: Exposure_Number: 13 Target_Name: NGC104-PV2 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: PRISM Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 1201S Special_Requirements: Exposure_Number: 14 Target_Name: NGC104-SV3 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: G570H Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 2772S Special_Requirements: Exposure_Number: 15 Target_Name: NGC104-SV3 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: PRISM Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 1571S Special_Requirements: Exposure_Number: 16 Target_Name: NGC104-E7 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: G570H Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 3326S Special_Requirements: Exposure_Number: 17 Target_Name: NGC104-E7 Config: FOS/RD Opmode: ACCUM Aperture: 0.3 Sp_Element: PRISM Wavelength: Optional_Parameters: Number_of_Iterations: 1.0 Time_Per_Exposure: 1940S Special_Requirements: ! Uncomment or copy exposure level special requirements needed ! INTeractive ACQuisition FOR ! ONBOARD ACQuisition FOR ! SAVE OFFSET ! USE OFFSET ! POSition TARGet , ! SAME POSition AS ! DO FOR TARGets ! FGS only ! PARallel WITH ! GROUP-FGS WITHIN