5929( 3) - 01/07/96 00:28 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5929 Version: 3 Check-in Date: 07-Jan-1996 00:18:51 1.Proposal Title: White Dwarfs and their Binary Progeny in the Core-Collapsed Globular Cluster NGC 6397 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Stellar Populations GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Ivan R. King University of California CoI: Phyllis M. Lugger Indiana University N CoI: J. E. Grindlay Harvard University N CoI: Paul J. Callanan Harvard University N CoI: Charles D. Bailyn Yale University N CoI: Adrienne M. Cool University of California, Berkeley Y CoI: Craig Sosin University of California, Berkeley N CoI: Haldan N. Cohn Indiana University N ------------------------------------------------------------------------------------ 6. Abstract We propose to image the central region of the dynamically evolved globular cluster NGC 6397 with the WFPC2 through the F336W and F439W filters in order to measure and characterize the populations of white dwarfs (WDs) and cataclysmic variables (CVs) it contains. This study will provide new constraints on models of stellar evolution, on dynamical models of globular clusters, and on the consequences of stellar interactions in globular cluster cores. The principal objectives are: (1) to measure the luminosity function, colors, and spatial distribution of an estimated 100 to 200 WDs in the central 5 sq arcmin of the cluster, thereby measuring the WD cooling curve with unprecedented statistical accuracy, and providing a constraint on the WD masses; (2) to measure the quiescent-state variability characteristics of 10 candidate CVs that lie within 10" of the cluster center, which will provide a strong test of their CV nature and an opportunity to identify periodic variations in their light curves; (3) to measure the U - B and B - V colors of the CV candidates, which will provide independent constraints on the orbital periods and CV classes of these objects; (4) to identify additional CV candidates and other possible short- period variable stars in the large field of view of the WFPC2. HST's high spatial resolution is essential for this investigation, as neither WDs nor quiescent CVs can be observed in the central regions of globular clusters from ground-based observatories, owing to extreme crowding conditions. ------------------------------------------------------------------------------------ 5929( 3) - 01/07/96 00:28 - [ 2] Observations Description ------------------------ The monitoring portion of the program will be carried out with a series of five F336W exposures per orbit for 7 orbits, and five F439W exposures per orbit for 4 orbits, for a total of 35 exposures in F336W and 20 exposures in F439W. With the RPS2-estimated visibility time of 57 minutes, each of these monitoring exposures will be 400 seconds long; however, the visibility of NGC 6397 is occasionally much longer, which would allow these monitoring exposures to be expanded to up to 700 seconds. It would thus be quite advantageous if this program could be scheduled during a period of long visibility (see the Visit_Comments below). We are using the POS TARG command on about half of the orbits, so that no object of interest will fall on an unusable part of the chip for the entire program, and are obtaining short and medium-duration F336W and F439W exposures in each position, in order to correct for saturated pixels. In 3-pixel-radius apertures (28 pixel area AND 80% encircled energy) we will get S/N = 50 or better on all the CV candidates, which will therefore be adequate to perform relative photometry at the ~2% level. We are also obtaining F555W and F814W images (requiring much less exposure time), as well as even shorter F555W and F814W images to correct for saturation in these filters. Our total of 4 minutes of exposure time in each of these filters will suffice to obtain S/N in excess of 50 on all the CV candidates. All of the short exposures will fit into the first few minutes of our orbits, before the five monitoring exposures. NOTE: F814W replaced the original F675W we had planned since we determined that it would be better scientifically. The objective of measuring the WD sequence in NGC 6397 will be carried out by combining the 35 F336W exposures into a single deep U image, and the 20 F439W exposures into a single deep B image. The relative total exposure time of these two deep images was chosen so that they go equally deep along the faint WD sequence. We choose the standard U and B WFPC2 filters in order to facilitate calibration and comparisons to other studies of globular cluster CMDs, and to WD models in particular. We have also constructed a simulated combined U exposure of NGC 6397 based on a detailed Fokker-Planck model including neutron stars, white dwarfs, and a full color- magnitude array. The underlying cluster structure is a deeply collapsed core, with r_c << 1". A DAOPHOT analysis of the simulated image indicates that stars can be detected with a typical accuracy of <0.2 mag at U >= 24.5, in reasonable agreement with our calculated S/N values. Star count profiles calculated from this photometry are able to detect the central cusp in the cluster structure down to a radius of 0.5". Thus the deep, combined U image that will be generated in this program will be extremely useful for constraining the core radius of NGC 6397. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- Please see the Visit Comments below. ------------------------------------------------------------------------------------ 5929( 3) - 01/07/96 00:28 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5929( 3) - 01/07/96 00:28 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6397 STELLAR CLUSTER RA=17H 40M 42.17S +/- 0.5", DEC= 2000 V = 5.25 -53D 40' 23.7" +/- 0.5" B-V = 0.73 E(B-V) = 0.18 SURF(V) = 13.45 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000.0 0.0 0.0 0 5929( 3) - 01/07/96 00:28 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: (1) Each orbit contains five long "monitoring" exposures, of at least 400 sec. This exposure time was chosen to fill the RPS2 visibility period. If a longer visibility time is available when the visit is scheduled, we would like the five long exposures per orbit to be expanded to fill all of the available time, while keeping them as close to equal duration as possible (i.e., expand all five approximately equally, rather than giving all available time to the last exposure). (2) This visit consists of 11 consecutive orbits. According to our Program Coordinator, Ray Lucas, it should be possible to schedule the entire visit in one block of time, without intersecting the SAA; we are therefore ignoring the RPS2 warning message. If this scheduling is impossible, we would prefer to split the visit between orbits 7 and 8, i.e., at the transition between monitoring in U and monitoring in B. (3) We do not wish to impose any additional constraint on the date on which this visit could be scheduled. However, it would be highly advantageous if it were scheduled between 14-Sep-1995 and 18 -Sep-1995; if this were the case observing efficiency would be increased by 75%. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 4 400S EXPAND MIN DUR 400S MAX DUR 700S -GAIN=7 Comments: U monitoring 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 1 400S EXPAND MIN DUR 400S MAX DUR 700S END ORBIT -GAIN=7 Comments: U monitoring 1, end of orbit ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6397 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO,ATD 1 1S -GAIN=7 Comments: short I ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6397 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO,ATD 1 40S -GAIN=7 Comments: I 1 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 4 400S EXPAND MIN DUR 400S MAX DUR 700S -GAIN=7 Comments: U monitoring 2 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 1 400S EXPAND MIN DUR 400S MAX DUR 700S END ORBIT -GAIN=7 Comments: U monitoring 2, end of orbit ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 1 10S -GAIN=7 Comments: short U, position 1 ------------------------------------------------------------------------------------------------------------------------------------ 5929( 3) - 01/07/96 00:28 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 1 90S -GAIN=7 Comments: medium U, position 1 ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 4 400S EXPAND MIN DUR 400S MAX DUR 700S -GAIN=7 Comments: U monitoring 3 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 1 400S EXPAND MIN DUR 400S MAX DUR 700S END ORBIT -GAIN=7 Comments: U monitoring 3, end of orbit ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC6397 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO,ATD 2 40S POS TARG 0.501, 0.501 -GAIN=7 Comments: V, 1 and 2 ------------------------------------------------------------------------------------------------------------------------------------ 12 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 4 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S Comments: U monitoring 4 ------------------------------------------------------------------------------------------------------------------------------------ 13 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 1 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S END ORBIT Comments: U monitoring 4, end of orbit ------------------------------------------------------------------------------------------------------------------------------------ 14 NGC6397 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO,ATD 1 1S POS TARG 0.501, 0.501 -GAIN=7 Comments: short V ------------------------------------------------------------------------------------------------------------------------------------ 15 NGC6397 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO,ATD 1 8S POS TARG 0.501, 0.501 -GAIN=7 Comments: medium V ------------------------------------------------------------------------------------------------------------------------------------ 16 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 4 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S Comments: U monitoring 5 ------------------------------------------------------------------------------------------------------------------------------------ 17 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 1 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S END ORBIT Comments: U monitoring 5, end of orbit ------------------------------------------------------------------------------------------------------------------------------------ 18 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 1 10S POS TARG 0.501, 0.501 -GAIN=7 Comments: short U, position 2 ------------------------------------------------------------------------------------------------------------------------------------ 19 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 1 90S POS TARG 0.501, 0.501 -GAIN=7 Comments: medium U, position 2 ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 4 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S Comments: U monitoring 6 ------------------------------------------------------------------------------------------------------------------------------------ 5929( 3) - 01/07/96 00:28 - [ 7] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 21 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 1 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S END ORBIT Comments: U monitoring 6, end of orbit ------------------------------------------------------------------------------------------------------------------------------------ 22 NGC6397 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO,ATD 2 40S POS TARG 0.501, 0.501 -GAIN=7 Comments: V, 3 and 4 ------------------------------------------------------------------------------------------------------------------------------------ 23 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 4 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S Comments: U monitoring 7 ------------------------------------------------------------------------------------------------------------------------------------ 24 NGC6397 WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=NO,ATD 1 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S END ORBIT Comments: U monitoring 7, end of orbit ------------------------------------------------------------------------------------------------------------------------------------ 25 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 1 10S POS TARG 0.501, 0.501 -GAIN=7 Comments: short B, position 2 ------------------------------------------------------------------------------------------------------------------------------------ 26 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 1 90S POS TARG 0.501, 0.501 -GAIN=7 Comments: medium B, position 2 ------------------------------------------------------------------------------------------------------------------------------------ 27 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 4 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S Comments: B monitoring 1 ------------------------------------------------------------------------------------------------------------------------------------ 28 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 1 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S END ORBIT Comments: B monitoring 1, end of orbit ------------------------------------------------------------------------------------------------------------------------------------ 29 NGC6397 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO,ATD 2 40S POS TARG 0.501, 0.501 -GAIN=7 Comments: V, 5 and 6 ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 4 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S Comments: B monitoring 2 ------------------------------------------------------------------------------------------------------------------------------------ 31 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 1 400S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S -GAIN=7 MAX DUR 700S END ORBIT Comments: B monitoring 2, end of orbit ------------------------------------------------------------------------------------------------------------------------------------ 32 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 1 10S -GAIN=7 Comments: short B, position 1 ------------------------------------------------------------------------------------------------------------------------------------ 33 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 1 90S -GAIN=7 Comments: medium B, position 1 ------------------------------------------------------------------------------------------------------------------------------------ 5929( 3) - 01/07/96 00:28 - [ 8] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 34 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 4 400S EXPAND MIN DUR 400S MAX DUR 700S -GAIN=7 Comments: B monitoring 3 ------------------------------------------------------------------------------------------------------------------------------------ 35 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 1 400S EXPAND MIN DUR 400S MAX DUR 700S END ORBIT -GAIN=7 Comments: B monitoring 3, end of orbit ------------------------------------------------------------------------------------------------------------------------------------ 36 NGC6397 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO,ATD 1 8S -GAIN=7 Comments: medium I ------------------------------------------------------------------------------------------------------------------------------------ 37 NGC6397 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO,ATD 1 40S -GAIN=7 Comments: I 2 ------------------------------------------------------------------------------------------------------------------------------------ 38 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 4 400S EXPAND MIN DUR 400S MAX DUR 700S -GAIN=7 Comments: B monitoring 4 ------------------------------------------------------------------------------------------------------------------------------------ 39 NGC6397 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO,ATD 1 400S EXPAND MIN DUR 400S MAX DUR 700S END ORBIT -GAIN=7 Comments: B monitoring 4, end of orbit ------------------------------------------------------------------------------------------------------------------------------------ 5929( 3) - 01/07/96 00:28 - [ 9] Summary Form for Proposal 5929 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ATD-GAIN=7 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Stellar Populations ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements EXPAND MIN DUR 400S MAX DUR 700S EXPAND MIN DUR 400S MAX DUR 700S END ORBIT POS TARG 0.501, 0.501 POS TARG 0.501, 0.501 EXPAND MIN DUR 400S MAX DUR 700S POS TARG 0.501, 0.501 EXPAND MIN DUR 400S MAX DUR 700S END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F336W F814W F555W F439W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6397 ------------------------------------------------------------------------------------------------------------------------------------