! Proposal 6821, submission 3 ! PI: Adrienne Cool ! Received Sat Apr 5 20:52:40 EST 1997 ! From: cool@stars.sfsu.edu ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6821,v 5.1 1997/04/18 16:55:36 pepsa Exp $ ! Proposal_Information Title: Optical Counterparts for Low-Luminosity X -ray Sources in Globular Clusters Proposal_Category: GO Scientific_Category: BINARIES AND STAR FORMATION Cycle: 6 Investigators PI_name: Adrienne Cool PI_Institution: San Francisco State University CoI_Name: Paul Hertz CoI_Institution: Naval Research Laboratory Contact: CoI_Name: Charles Bailyn CoI_Institution: Yale University Contact: CoI_Name: Jonathan Grindlay CoI_Institution: Harvard University Contact: CoI_Name: Paul Callanan CoI_Institution: Center for Astrophysics Contact: CoI_Name: Haldan Cohn CoI_Institution: Indiana University Contact: CoI_Name: Phyllis Lugger CoI_Institution: Indiana University Contact: Abstract: This project uses narrow band H-alpha imaging with the WFPC2 to search for optical counterparts for low-luminosity X-ray sources in the globular cluster Omega Cen. Remarkably little is known about this class of cluster X-ray sources, yet it apparently constitutes the largest known population of compact binary stars in globulars. Optical identifications are the critical first step in learning more about these systems. H-alpha imaging has a proven track record in identifying promising counterparts for low-luminosity X-ray sources in two globular clusters, NGC 6397 and NGC 6752. Optical identifications of the X-ray sources in Omega Cen will increase our database of compact, interacting binaries in clusters, allowing us to address fundamental questions about the formation of binaries and their role in cluster dynamical evolution. Questions Observing_Description: The program consists of images in the R (F675W), H-alpha (F656N), and U (F336W) filters of the core of the globular cluster Omega Cen. The goal is to identify optical counterparts for faint X-ray sources which are expected to be unusually bright in H-alpha vs. R and/or U vs. R. In each orbit we will take two long H-alpha exposures, together with a small number of shorter R, U, and/or H-alpha exposures. All images must be taken at the identical orientation. Several different orientations will allow the error circles of all three sources to be encompassed. However, the allowable orientations are not all contiguous. Since RPS2 allows for only one range of continguous orientations to be specified, and since different target coordinates would be required for each orientation, we have picked the orientation that provides for the maximum contiguous range of possible angles. We have done this in order to minimize the complexity of our Phase II plan. However, if it necessary or advantageous for the scheduling of this program, additional orientations and their corresponding target coordinates can be provided by the PI. For the range of orientations we have specified (67.5D to 82D), one of the three X-ray sources will be placed in the PC1 chip, and the other two in the WF2 and WF4 chips, respectively. In order to achieve a maximum range of orientations, and still encompass the error circles for the three sources, it is necessary to place the source that will fall in PC1 not at the center of the chip, but in one corner. In the system of (x,y) coordinates for the PC1 chip shown in Fig. 9-1 (p.9-14) of the Phase II Proposal Instructions, the required corner is 10 arcsec from the top (outer) edge and 12 arcsec from the left edge (side adjacent to WF2). In order to place the target at this position, we use the PC1-FIX designation, which corresponds to pixel position (420,424), and specify POS TARG -7.5, +7.5. This should cause the target of WFPC2 to shift to the left by 7.5 arcsec and upward by 7.5 arcsec, placing it in the desired corner of the PC1. The individual exposures are as follows. In F656N, a total of 10 exposures with durations of 700-1100s (or longer if visibility times permit) will be obtained, two at each of five positions. In F675W, we will also obtain 2 exposures at four of the five dither position, each of duration 100s. Two exposures at each position will allow for cosmic ray removal. The use of five different target positions will remove ambiguities associated with CCD defects (e.g. hot pixels). We adopt a non-integral offset between four of the five positions ("dithering") in order to effectively enhance the spatial resolution. We designate these four positions using identical target coordinates but different POS TARG values, shifting by 0.25 arcsec between consecutive dither positions. Many stars will be saturated in the 10 "long" F656N exposures. To correct for saturation, we will take, at two of the dither positions, one medium-length (160 sec) and one short exposure (20 sec). Saturation will also be a serious problem in F675W, thus the longest exposures we use are 100s. A total of 8 100s exposures will be obtained for a total exposure time of 800s. When stacked, the F675W images will contain a more than a factor of 4 more counts than the F656N stacked images for typical stars. The strategy adopted with the F336W filter is slightly different, in order to save time. Two "long" exposures (>=260s) will be taken, and offset from each other by an integral number of pixels (in orbit 3). The integral pixels shift will enable both cosmic rays and chip defects to be identified. One short exposure (26s) will suffice to correct for saturation in the 260s exposures. Real Time_Justification: None. Calibration_Justification: Additional_Comments: The orientation contraint we have specified for this program limits the possible dates it can be scheduled to about 32 days during two periods in May-July of 1996, or to a similar number of days in 1997. These dates represent the longest contiguous periods in which the spacecraft orientation will allow the scientific aims of the project to be fully achieved. We respectfully request that the program be scheduled during the period of May-July 1996 if at all possible. The specific dates that are feasible in 1996 are May 8-13 and June 18 through July 15. Fixed_Targets Target_Number: 1 Target_Name: NGC5139 Alternate_Names: OMEGA-CEN Description: STELLAR CLUSTER, GLOBULAR CLUSTER Position: RA=13H 26M 53.52S +/- 0.01S,DEC=-47D 29' 01.40" +/- 0.10", PLATE-ID=ZZZR Equinox: J2000 RV_or_Z: V = +232 RA_PM: Dec_PM: Epoch: Annual_Parallax: Flux: SURF(V) = 16.8 V = 11 B-V = 0.8 V-R = 0.5 U-B = 0.2 E(B-V) = 0.15 Comments: All images will contain many thousands of stars, the brightest of which will have V magnitudes of 11 to 12. Visits Visit_Number: 01 Visit_Requirements: ORIENT 67.5D TO 82D On_Hold_Comments: Visit_Comments: All exposures in this visit must be done at the identical orientation. Images taken in the same filters are best done as close in time to one-another as possible. Exposure_Number: 101 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: POS TARG -7.5000, +7.5000 MIN DUR 100S MAX DUR 100S Exposure_Number: 102 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: POS TARG -7.5000, +7.5000 MIN DUR 100S MAX DUR 100S Exposure_Number: 103 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F656N Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 20S Special_Requirements: POS TARG -7.5000, +7.5000 MIN DUR 20S MAX DUR 20S Exposure_Number: 104 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F656N Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 160S Special_Requirements: POS TARG -7.5000, +7.5000 MIN DUR 160S MAX DUR 160S Exposure_Number: 105 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F656N Wavelength: Optional_Parameters: CR-SPLIT=0.5, CR-TOLERANCE=0.15 Number_of_Iterations: 1 Time_Per_Exposure: 1800S Special_Requirements: POS TARG -7.5000, +7.5000 MIN DUR 1700S Exposure_Number: 201 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: POS TARG -7.2500, +7.5000 MIN DUR 100S MAX DUR 100S Exposure_Number: 202 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1S Special_Requirements: POS TARG -7.2500, +7.5000 MIN DUR 1S MAX DUR 1S Exposure_Number: 203 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 10S Special_Requirements: POS TARG -7.2500, +7.5000 MIN DUR 10S MAX DUR 10S Exposure_Number: 204 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: POS TARG -7.2500, +7.5000 MIN DUR 100S MAX DUR 100S Exposure_Number: 205 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F656N Wavelength: Optional_Parameters: CR-SPLIT=0.5, CR-TOLERANCE=0.15 Number_of_Iterations: 1 Time_Per_Exposure: 2200S Special_Requirements: POS TARG -7.2500, +7.5000 MIN DUR 2100S Exposure_Number: 301 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F336W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 260S Special_Requirements: POS TARG -7.2500, +7.5000 MIN DUR 260S MAX DUR 260S Exposure_Number: 302 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F336W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 26S Special_Requirements: POS TARG -7.2500, +7.5000 MIN DUR 26S MAX DUR 26S Exposure_Number: 303 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F336W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 260S Special_Requirements: POS TARG -7.7500, +7.0000 MIN DUR 260S MAX DUR 260S Exposure_Number: 304 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F656N Wavelength: Optional_Parameters: CR-SPLIT=0.5, CR-TOLERANCE=0.15 Number_of_Iterations: 1 Time_Per_Exposure: 1600S Special_Requirements: POS TARG -7.7500, +7.0000 MIN DUR 1500S Exposure_Number: 401 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: POS TARG -7.5000, +7.2500 MIN DUR 100S MAX DUR 100S Exposure_Number: 402 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: POS TARG -7.5000, +7.2500 MIN DUR 100S MAX DUR 100S Exposure_Number: 403 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F656N Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 20S Special_Requirements: POS TARG -7.5000, +7.2500 MIN DUR 20S MAX DUR 20S Exposure_Number: 404 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F656N Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 160S Special_Requirements: POS TARG -7.5000, +7.2500 MIN DUR 160S MAX DUR 160S Exposure_Number: 405 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F656N Wavelength: Optional_Parameters: CR-SPLIT=0.5, CR-TOLERANCE=0.15 Number_of_Iterations: 1 Time_Per_Exposure: 2000S Special_Requirements: POS TARG -7.5000, +7.2500 Exposure_Number: 501 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: POS TARG -7.2500, +7.2500 MIN DUR 100S MAX DUR 100S Exposure_Number: 502 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1S Special_Requirements: POS TARG -7.2500, +7.2500 MIN DUR 1S MAX DUR 1S Exposure_Number: 503 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 10S Special_Requirements: POS TARG -7.2500, +7.2500 MIN DUR 10S MAX DUR 10S Exposure_Number: 504 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F675W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 100S Special_Requirements: POS TARG -7.2500, +7.2500 MIN DUR 100S MAX DUR 100S Exposure_Number: 505 Target_Name: NGC5139 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F656N Wavelength: Optional_Parameters: CR-SPLIT=0.5, CR-TOLERANCE=0.15 Number_of_Iterations: 1 Time_Per_Exposure: 2200S Special_Requirements: POS TARG -7.2500, +7.2500 MIN DUR 2100S Data_Distribution Medium: 8MM Blocking_Factor: 10 Ship_To: Department of Physics and Astronomy San Francisco State University San Francisco, CA 94132 Ship_Via: UPS Recipient_Email: !num_orbits: 5