8656( 9) - 10/06/00 15:20 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8656 Version: 9 Check-in Date: 06-Oct-2000 15:19:15 1.Proposal Title: The Hydrogen-Burning Limit in the Globular Cluster NGC 6397 (GO part) ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Ivan King University of California - Berkeley CoI: Dr. Jay Anderson University of California, Berkeley N CoI: Prof. Adrienne Cool San Francisco State University N CoI: Dr. Gordon Drukier Tel Aviv University N ------------------------------------------------------------------------------------ 5. Abstract We propose a major enhancement of an earlier study of the bottom of the main sequence of NGC 6397, the globular cluster with the smallest distance modulus. In earlier work the lowest part of the MS had been lost among the numerically dominant field stars; but accurate astrometry, over a baseline of a few years, now allows an excellent proper-motion separation of faint cluster stars from the field. The purified CMD follows the main sequence to its ``end" (i.e., the terminal plunge of the LF). Just as the MS CMD gives a mass--radius relation, we show in a new way how this LF can give a mass--luminosity relation; both of these offer unique checks on theory. Our single WFPC2 field, however, had only a small number of stars in this range, too few to set firm restraints on the theories. We propose now to increase the number of such stars by a large factor by (1) getting 2nd-epoch images for three more fields in the cluster and (2), in an accompanying AR proposal, remeasuring our previous images, and others that exist, to the deeper limit that we know can be attained. The number and the magnitudes of these faintest stars will greatly strengthen the constraints that we place on structure and atmosphere theories of lower-main-sequence stars. In each field we will also measure the anisotropy of internal stellar motions, which is predicted to be large in a collapsed-core cluster such as this one. ------------------------------------------------------------------------------------ 8656( 9) - 10/06/00 15:20 - [ 2] Observations Description ------------------------ In each case the exposures need to be made at about the same time of year as the 1st epoch, so as to match the orientation. We have examined the 1st-epoch images and therefore know exactly how much saturation, crowding, and background to expect; thus we know that this project is feasible. The only unknowns are how much each star has moved. For these follow-up observations, we expect typical field stars to have random motions of about 1 WF pixel, which is easily measured for any star irrespective of faintness. Internally, cluster stars should have individual relative displacements of ~0.06 pixel in the PC and ~0.03 pixel in the WF. We can now easily measure this for all but the very faintest WF stars. Field B: Since the 1st-epoch exposures (5 images totaling 4600s in F606W and 5 in F814 totaling 5500s, in March 1994) are well balanced between the two colors, for lower-MS stars, we will match them in the 2nd epoch, with 2 orbits in each filter. Each orbit will be divided into 4 images, dithered, with no CR-splits. (We have much experience with such images, and CR removal poses no problem.) Field C: The 1st epoch (Oct.\ 1996) has 4 F300W images, total 5500s, 3 F606W, 3000s, and 4 F814W, 6900s. There are also 2 more F300W images, 4500s total, with a substantial overlap. This would need an Oct.\ 2000 repeat: 4 orbits in F606W and 3 in F814W, to balance the total better in these V and I filters. Each orbit will be divided into 4 images, dithered, with no CR-splits. Field D (GO): The Apr. 1995 1st epoch has 3 long F814 exposures, totaling 4200s. Our repeat, after 6 years, will have 3 orbits with F606W and 1 orbit with F814W. The increased total exposure will yield a CMD about as faint as in the other fields and, of course, field/cluster separation. (Note:\ We would very much like to have these exposures, but if this proposal has to be cut, this is the place, because of the large ratio of new material to archival.) We note that the MLR extension and the anisotropy study could be performed with follow-up F814W images alone. However, without similarly deep exposures in F606W, we would not be able to push the MS ridge-line (hence the mass--radius relation) to fainter magnitudes. Both the M--L and the M--R relations will be invaluable to theorists. Our early measurements of NGC 6397 (Cool et al.\ 1995) were among the most accurate photometric projects ever carried out with HST. We expect comparable accuracy here. As for astrometry, our sub-milli-arcsec accuracy, with the time baselines available here, will allow us easily to measure internal velocity dispersions in the radial and tangential directions. Because of the unique importance of the lowest part of the MS, we have said nothing here about white dwarfs; but it goes without saying that we will increase the number of them, and for the first time derive information on their kinematics. Real Time Justification ----------------------- Orientations and approximate dates will be requested, to match 2nd-epoch to existing 1st-epoch observations. Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ 8656( 9) - 10/06/00 15:20 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6397-B STELLAR CLUSTER, RA=17H 40M 25.70S +/- 0.01S, J2000 SURF(V) = 22.0+/-0.5 GLOBULAR CLUSTER DEC=-53D 36' 38.55" +/- 0.01" Coordinate Source: OTHER_SOURCE Comments: Since globular clusters usually turn out to be burned out and useless on Sky Survey images, we have adopted the following procedure. For the image of which this is intended to be a repeat, we go to the proposal that created that image, and repeat here the exact RA, DEC, and aperture that were used there. We check the header of the first-epoch image to verify that the RA and DEC given there (corrected by POS TARGs if applicable) are very close to what we are using here. If that check succeeds, we are confident that we have the right position. For ORIENT we of course go 180D from the P.A. of V3 in the 1st epoch. 2 NGC6397-C STELLAR CLUSTER, RA=17H 39M 59.99S +/- 0.01S, J2000 SURF(V) = 23.0+/-0.5 GLOBULAR CLUSTER DEC=-53D 45' 50.11" +/- 0.01" Coordinate Source: OTHER_SOURCE 3 NGC6397-D STELLAR CLUSTER, RA=17H 41M 14.16S +/- 0.01S, J2000 SURF(V) = 23.0+/-0.5 GLOBULAR CLUSTER DEC=-53D 33' 45.67" +/- 0.01" Coordinate Source: OTHER_SOURCE 8656( 9) - 10/06/00 15:20 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 265.5D TO 266.5D On Hold Comments: Additional Comments: Orientation must match that of first-epoch exposures. The dither pattern samples every eighth of a pixel in both x and y, both for the WF and for the PC. 4 orbits, 2 long exp in each; Equal amounts of F606W & F814W. 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-B WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1200 S Comments: First orbit. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6397-B WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.250, 0.000 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6397-B WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.000, 0.250 Comments: 2nd orbit. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6397-B WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.250, 0.250 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6397-B WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.125, 0.125 Comments: 3rd orbit. ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6397-B WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.375, 0.125 ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6397-B WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.125, 0.375 Comments: 4th orbit. ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6397-B WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.375, 0.375 ------------------------------------------------------------------------------------------------------------------------------------ 8656( 9) - 10/06/00 15:20 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT 98.9D TO 99.1D On Hold Comments: Additional Comments: Orientation must match that of first-epoch exposures. 3 orbits in F814W; 2 long exp in each. 6-way dither pattern. 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-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1200 S Comments: First orbit. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6397-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.200, 0.033 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6397-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.400, 0.066 Comments: 2nd orbit. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6397-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.050, 0.200 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6397-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.250, 0.233 Comments: 3rd orbit. ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6397-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.450, 0.267 ------------------------------------------------------------------------------------------------------------------------------------ 8656( 9) - 10/06/00 15:20 - [ 6] Visit: 03 Visit Priority: Visit Requirements: ORIENT 98.9D TO 99.1D On Hold Comments: Additional Comments: Orientation must match that of first-epoch exposures. 2 orbits in F606W; 2 long exp in each. 4-way dither pattern. NOTE: It is desirable, but not absolutely essential, that Visits 3 and 4 be close in time. 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-C WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1200 S Comments: 1st orbit. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6397-C WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.250, 0.000 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6397-C WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.000, 0.250 Comments: 2nd orbit. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6397-C WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.250, 0.250 ------------------------------------------------------------------------------------------------------------------------------------ 8656( 9) - 10/06/00 15:20 - [ 7] Visit: 04 Visit Priority: Visit Requirements: ORIENT 98.9D TO 99.1D On Hold Comments: Additional Comments: Orientation must match that of first-epoch exposures. 2 orbits in F606W; 2 long exp in each. 4-way dither pattern. NOTE: It is desirable, but not absolutely essential, that Visits 3 and 4 be close in time. 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-C WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1200 S POS TARG 0.125, 0.125 Comments: 1st orbit. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6397-C WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.375, 0.125 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6397-C WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.125, 0.375 Comments: 2nd orbit. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6397-C WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.375, 0.375 ------------------------------------------------------------------------------------------------------------------------------------ 8656( 9) - 10/06/00 15:20 - [ 8] Visit: 05 Visit Priority: Visit Requirements: ORIENT 265.5D TO 266.5D On Hold Comments: Additional Comments: Orientation must match that of first-epoch exposures. 3 orbits in F606W, 1 in F814W; 2 long exp in each. 8-way dither pattern. 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-D WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1200 S Comments: First orbit. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6397-D WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.250, 0.000 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6397-D WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.000, 0.250 Comments: 2nd orbit. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6397-D WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.250, 0.250 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6397-D WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.125, 0.125 Comments: 3rd orbit. ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6397-D WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 1300 S POS TARG 0.375, 0.125 ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6397-D WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.125, 0.375 Comments: 4th orbit. ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6397-D WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.375, 0.375 ------------------------------------------------------------------------------------------------------------------------------------ 8656( 9) - 10/06/00 15:20 - [ 9] Visit: 12 Visit Priority: Visit Requirements: ORIENT 98.9D TO 99.1D On Hold Comments: Additional Comments: Orientation must match that of first-epoch exposures. 3 orbits in F814W; 2 long exp in each. 6-way dither pattern. 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-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1200 S Comments: First orbit. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6397-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.200, 0.033 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6397-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.400, 0.066 Comments: 2nd orbit. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6397-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.050, 0.200 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6397-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.250, 0.233 Comments: 3rd orbit. ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6397-C WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 1300 S POS TARG 0.450, 0.267 ------------------------------------------------------------------------------------------------------------------------------------ 8656( 9) - 10/06/00 15:20 - [ 10] Summary Form for Proposal 8656 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFALL ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 265.5D TO 266.5D POS TARG 0.250, 0.000 POS TARG 0.000, 0.250 POS TARG 0.250, 0.250 POS TARG 0.125, 0.125 POS TARG 0.375, 0.125 POS TARG 0.125, 0.375 POS TARG 0.375, 0.375 ORIENT 98.9D TO 99.1D POS TARG 0.200, 0.033 POS TARG 0.400, 0.066 POS TARG 0.050, 0.200 POS TARG 0.250, 0.233 POS TARG 0.450, 0.267 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6397-B NGC6397-C NGC6397-D ------------------------------------------------------------------------------------------------------------------------------------