! Proposal 5929, submission 1 ! PI: Ivan R. King ! Received Tue Mar 14 19:32:34 EST 1995 ! From: csosin@physics.Berkeley.EDU ! Hubble Space Telescope Cycle 5 (1995) Phase II Proposal Template ! $Id: 5929,v 3.1 1996/01/07 05:18:48 pepsa Exp $ ! ! 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: Ray Lucas ! Phone: 410 338-4716 , E-mail: lucas@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Name of Phase I Proposal: king-735.prop ! Date generated: Sat Dec 17 10:45:02 EST 1994 ! Proposal_Information Title: White Dwarfs and their Binary Progeny in the Core-Collapsed Globular Cluster NGC 6397 Proposal_Category: GO Scientific_Category: Stellar Populations Cycle: 5 Investigators PI_name: Ivan R. King PI_Institution: University of California CoI_Name: Adrienne M. Cool CoI_Institution: University of California, Berkeley Contact: Y CoI_Name: Craig Sosin CoI_Institution: University of California, Berkeley Contact: CoI_Name: Haldan N. Cohn CoI_Institution: Indiana University Contact: CoI_Name: Phyllis M. Lugger CoI_Institution: Indiana University Contact: CoI_Name: J. E. Grindlay CoI_Institution: Harvard University Contact: CoI_Name: Paul J. Callanan CoI_Institution: Harvard University Contact: CoI_Name: Charles D. Bailyn CoI_Institution: Yale University Contact: Abstract: ! Free format text 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. Questions Observing_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. Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: NGC6397 Alternate_Names: Description: STELLAR CLUSTER Position: RA=17H 40M 42.17S +/- 0.5", DEC=-53D 40' 23.7" +/- 0.5" Equinox: 2000 RV_or_Z: RA_PM: Dec_PM: Epoch: 2000.0 Annual_Parallax: 0 Flux: V=5.25, B-V=0.73, E(B-V)=0.18, SURF(V)=13.45 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: ! Section 7.1 ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling ! PCS MODE [Fine | Gyro] ! GUIDing TOLerance ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN