8160( 5) - 10/07/99 14:38 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8160 Version: 5 Check-in Date: 07-Oct-1999 14:37:55 1.Proposal Title: A Proper-Motion Study of Two Fields, in the Globular Cluster 47 Tucanae ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Ivan King University of California - Berkeley CoI: Dr. Jay Anderson University of California N CoI: Prof. William Van Altena Yale University N CoI: Dr. Terrence Girard Yale University N CoI: Dr. Georges Meylan European Southern Observatory N ------------------------------------------------------------------------------------ 5. Abstract We propose, using only 5 orbits of HST time, to carry out high-precision astrometry in two fields in the globular cluster 47 Tucanae in order to (1) measure the relative proper motions in the radial and tangential directions, for many thousands of main-sequence stars and white dwarfs, and determine the anisotropy of stellar motions as a function of stellar mass; (2) strengthen our current determination of the distance of the cluster, which depends on comparing proper motions with radial velocities; (3) extend the luminosity function of the cluster 3--4 magnitudes fainter, reaching well below 0.1\>m_\odot; (4) measure the rotation of the cluster in the plane of the sky; (5) measure the absolute proper motion of the cluster; and (6) possibly measure the proper motion of the Small Magellanic Cloud. ------------------------------------------------------------------------------------ 8160( 5) - 10/07/99 14:38 - [ 2] Observations Description ------------------------ All observations will be made with F814W, since proper-motion measurements do not require two-color observations to be repeated. In previous work we found that 3 orbits (each divided into 3 exposures) gave good enough astrometry to derive accurate proper motions for our faintest stars. (We actually used 6 orbits in GO-6797, but only because two pointings were needed to cover our previous fields.) We will devote 3 orbits to the deeper field, at 6arcm 5; in the 4arcm 6 field we feel that 2 orbits will be adequate. In each field, the 9 (or 6) exposures will be made in different dither positions. We have worked out 9-way and 6-way dither patterns that work simultaneously in the PC and the WF pixels. In order to achieve overlap with the first-epoch observations, we will require that each field be observed at the same orientation that was used in the first epoch. Our measuring methods go as follows. First we measure positions and magnitudes for all stars in each individual image by fitting a PSF obtained from the image itself. We then correct each position for the known distortion correction. Although the latter is not known to the accuracy of our final mean positions (which is better than 0.01 pixel), the nominal distortion correction makes the images geometrically flat enough for our differential- astrometry techniques. These rely on measuring each star with respect to a tight reference net of surrounding stars that are all cluster members. This net allows us to convert the measured positions of the star from each individual image to a common coordinate system. Since our measurements are accurate enough to detect the motion of an individual star relative to the centroid of all the others, for second-epoch positions we iterate all the conversions, correcting each reference star for the internal proper motion we have already measured for it. Measuring at this level of care was sufficient to allow us to separate cluster stars from field stars in GO-6797 (King et al. 1998), but we now attain a considerably higher accuracy, by correcting for the systematic errors that depend on the location of the star's center with respect to a pixel center. These are of complicated origin, but they arise basically from the severe degree of under-sampling, especially in the WF frames, and typically have an amplitude of about 0.05 pixel. We remove these errors almost totally, by (1) careful dithering, (2) examination of the distribution, over all measured stars, of the values of the fractional part of the measured position coordinates, and making corrections to flatten this distribution, and (3) examination of the residuals of individual measures of a star from its mean position, again as a function of pixel fraction, and deriving further corrections from these graphs. In addition to all this, we have worked out a way of using comparison with second-epoch images to compensate for inadequate dithering at the first epoch. Real Time Justification ----------------------- In order to measure the largest number of stars in both epochs, we require the same orientations as the 1994 exposures had. This will restrict the scheduling of each visit to about a 30-day window. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8160( 5) - 10/07/99 14:38 - [ 3] Data Distribution Paper Products: NO Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8160( 5) - 10/07/99 14:38 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-104-E STELLAR CLUSTER, RA=00H 25M 03.96S +/- 0.01S, J2000 SURF(V) = 15.0+/-0.5 Globular Cluster DEC=-72D 03' 31.6" +/- 0.1" 2 NGC-104-F STELLAR CLUSTER, RA= 00H 22M 40.97S +/- 0.01S, J2000 SURF(V) = 15.0+/-0.5 Globular Cluster DEC= -72D 03' 53.7" +/- 0.1" 8160( 5) - 10/07/99 14:38 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 17.5D TO 17.6D On Hold Comments: Additional Comments: Orientation must match that of first-epoch exposures. The dither pattern samples every seventh of a pixel in both x and y, both for the WF and for the PC. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-104-E WFPC2 IMAGE WFALL F814W DITHER-TYPE=LINE,CR-SPLIT=NO , 1 500 S DITHER-LINE-SPACING=0.6643, DITHER-LINE-STEPS=4 Comments: First orbit. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-104-E WFPC2 IMAGE WFALL F814W DITHER-TYPE=LINE,CR-SPLIT=NO , 1 23 S DITHER-LINE-SPACING=0.4697, DITHER-LINE-STEPS=3 Comments: Second orbit. Spacing of 3.333 x sqrt\{2\} pixels gives a good dither pattern for both WF and PC. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC-104-E WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 500 S POS TARG -0.2420, -0.2705 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC-104-E WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 500 S POS TARG -0.2705, +0.4840 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC-104-E WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 500 S POS TARG +0.3843, -0.1423 Comments: End of second orbit. ------------------------------------------------------------------------------------------------------------------------------------ 8160( 5) - 10/07/99 14:38 - [ 6] Visit: 02 Visit Priority: Visit Requirements: ORIENT 23.6D TO 23.7D On Hold Comments: Additional Comments: Orientation must match that of first-epoch exposures. The dither pattern samples every eleventh of a pixel in both x and y, both for the WF and for the PC. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-104-F WFPC2 IMAGE WFALL F814W DITHER-TYPE=LINE,CR-SPLIT=NO , 1 500 S DITHER-LINE-SPACING=0.4612, DITHER-LINE-STEPS=4 Comments: First orbit. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-104-F WFPC2 IMAGE WFALL F814W DITHER-TYPE=LINE,CR-SPLIT=NO , 1 23 S DITHER-LINE-SPACING=0.4697, DITHER-LINE-STEPS=3 Comments: Second orbit. Spacing of 3.333 x sqrt\{2\} pixels gives a good dither pattern for both WF and PC. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC-104-F WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 500 S POS TARG -0.2899, -0.3533 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC-104-F WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 500 S POS TARG +0.4348, -0.1902 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC-104-F WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 500 S POS TARG +0.7609, +0.0725 Comments: End of second orbit. ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC-104-F WFPC2 IMAGE WFALL F814W DITHER-TYPE=LINE,CR-SPLIT=NO , 1 500 S POS TARG -0.0091, +0.3352 DITHER-LINE-SPACING=0.4612, DITHER-LINE-STEPS=4 Comments: Third orbit. ------------------------------------------------------------------------------------------------------------------------------------ 8160( 5) - 10/07/99 14:38 - [ 7] Visit: 51 Visit Priority: Visit Requirements: ORIENT 17.5D TO 17.6D On Hold Comments: Additional Comments: Orientation must match that of first-epoch exposures. The dither pattern samples every seventh of a pixel in both x and y, both for the WF and for the PC. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-104-E WFPC2 IMAGE WFALL F814W DITHER-TYPE=LINE,CR-SPLIT=NO , 1 500 S DITHER-LINE-SPACING=0.6643, DITHER-LINE-STEPS=4 Comments: First orbit. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-104-E WFPC2 IMAGE WFALL F814W DITHER-TYPE=LINE,CR-SPLIT=NO , 1 23 S DITHER-LINE-SPACING=0.4697, DITHER-LINE-STEPS=3 Comments: Second orbit. Spacing of 3.333 x sqrt\{2\} pixels gives a good dither pattern for both WF and PC. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC-104-E WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 500 S POS TARG -0.2420, -0.2705 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC-104-E WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 500 S POS TARG -0.2705, +0.4840 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC-104-E WFPC2 IMAGE WFALL F814W CR-SPLIT=NO 1 500 S POS TARG +0.3843, -0.1423 Comments: End of second orbit. ------------------------------------------------------------------------------------------------------------------------------------ 8160( 5) - 10/07/99 14:38 - [ 8] Summary Form for Proposal 8160 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFALL ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters DITHER-TYPE=LINE CR-SPLIT=NO DITHER-LINE-SPACING=0.6643 DITHER-LINE-STEPS=4 DITHER-LINE-STEPS=3 DITHER-LINE-SPACING=0.4612 DITHER-LINE-SPACING=0.4697 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 17.5D TO 17.6D POS TARG -0.2420, -0.2705 POS TARG -0.2705, +0.4840 POS TARG +0.3843, -0.1423 ORIENT 23.6D TO 23.7D POS TARG -0.2899, -0.3533 POS TARG +0.4348, -0.1902 POS TARG +0.7609, +0.0725 POS TARG -0.0091, +0.3352 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC-104-E NGC-104-F ------------------------------------------------------------------------------------------------------------------------------------