9899( 5) - 05/19/03 09:51 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9899 Version: 5 Check-in Date: 19-May-2003 09:50:25 1.Proposal Title: Geometrical Distance of NGC 2808 and NGC 6752 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 12 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Prof. Giampaolo Piotto Universita di Padova CoI: Dr. Ivan R. King University of Washington N CoI: Dr. Jay Anderson Rice University N CoI: Dr. Luigi Bedin Universita di Padova N CoI: Dr. Alvio Renzini European Southern Observatory - Germany N CoI: Dr. Manuela Zoccali Universita di Padova N CoI: Dr. Yazan Momany Universita di Padova N CoI: Dr. Alejandra Recio-Blanco Universita di Padova N CoI: Dr. Francesca De Angeli Universita di Padova N ------------------------------------------------------------------------------------ 5. Abstract This is a proposal to estabilsh a globular cluster distance scale of unprecedented accuracy and reliability, with far-reaching impact on the distance scales of cosmology. Our methd is to compare iternal dipersion proper motions with ground- based determination of the dispersion of the radial velocities (with time already allocated at VLT). The prospect is a geometrically based distance with an accuracy of better than 2%. Results already in hand for M4 and 47 Tuc, estabilish our ability to make such measurements of proper motions. Our projects has two parts: (1) use archival observation for both epochs when available, (2) The present proposal cover an external field of NGC 2808 and give a second epoch for the cluster NGC6752. Thanks to the ACS features, we will be able to extend the sample in just 2-4 orbits. ------------------------------------------------------------------------------------ 9899( 5) - 05/19/03 09:51 - [ 2] Observations Description ------------------------ This is an astrometric project aimed at measuring the proper motion internal dispersion in the outer fields of two globular clusters: NGC2808 and NGC 6752. The current ACS/WFC observations are designed to obtain the highest overlap with archive WFC2 observations of the two clusters. To maximize the overlap between the WFC2 and ACS observations, we are obliged to choose particular orientation angles and target positions, as specified in this Phase II. In particular, for NGC2808 we want to maximaze the overlap with the external field taken in 1998 (GO-6804), and for NGC6752 the field mapped in 1995 (G0-5439). Where possible, we have also tried to overlap other fields taken in different epochs, close to the first priority epochs. In the case of NGC6752, the orientation and position has was been choosen in order to superpose the WFC/ACS gap with the unusable regions (because of the gap, the geometric distorsion, and the vignetting) of the first epoch WFPC2 images. The region close to the WFPC2 gap, in fact, is affected by the residual distortions introduced by the prism pyramid, which make it unsuitable for high precision astrometry. In the case of NGC2808 the superposition of the gaps of the two cameras is less convenient in terms of area usable for proper motion determination. To get good astrometry we need to finely sample the PSF. In order to do this we need the highest number of images, with an appropriate dither pattern. For the dither patterns we followed the recipe given by Anderson and King (2000 PASP, 112, 1360, 2003 PASP, 115, 113). The images have different offsets corresponding to different pixel phases, and are large enough to allow the identification of bad pixels. The exposure times represent the best compromise to reach the needed limiting magnitude, maintaining a large enough number of images to allow accurate proper motion accuracy. The adopted exposure times are long enough to measure proper motions of more than 1600 stars in NGC 2808 and 3000 stars in NGC 6752. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9899( 5) - 05/19/03 09:51 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2808Y98B STELLAR CLUSTER, RA=09H11M37.9S +/- 0.1", DEC=- J2000 V = 6.20 GLOBULAR CLUSTER 64D54'8.8" +/- 0.1", PLATE- ID=06PQ Coordinate Source: GUIDE_STAR_CATALOG Comments: integrated v magnitude given 2 NGC6752Y95 STELLAR CLUSTER, RA=19H11M2.8S +/- 0.1", DEC=- J2000 V = 5.40 GLOBULAR CLUSTER 60D00'51.7" +/- 0.1", PLATE- ID=03D3 Coordinate Source: GSC_SURVEY_PLATE Comments: integrated v magnitude given 9899( 5) - 05/19/03 09:51 - [ 4] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE ORIENT 85.0D TO 95.0 D ORIENT 265.0D TO 275.0 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2808Y98B ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG 0,-7 SEQ 1-6 C R COMPRESSION=NONE NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC2808Y98B ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG 0.117,-6.892 C R COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC2808Y98B ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG 0.233,-6.783 C R COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC2808Y98B ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG 0.108,-6.975 C R COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC2808Y98B ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG 0.225,-6.867 C R COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC2808Y98B ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG 0.342,-6.758 C R COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 9899( 5) - 05/19/03 09:51 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT 29.0D TO 37.0 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6752Y95 ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG -28, 9 SEQ 1-6 C R COMPRESSION=NONE NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6752Y95 ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG -27.883, 9.108 C R COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6752Y95 ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG -27.767, 9.217 C R COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6752Y95 ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG -27.892, 9.025 C R COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6752Y95 ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG -27.775, 9.133 C R COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6752Y95 ACS/WF ACCUM WFCENTE F475W CR-SPLIT=NO,GAIN=2, 1 340 S POS TARG -27.658, 9.242 C R COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 9899( 5) - 05/19/03 09:51 - [ 6] Summary Form for Proposal 9899 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFCENTER ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO GAIN=2 COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE ORIENT 85.0D TO 95.0 D ORIENT 265.0D TO 275.0 D POS TARG 0,-7 SEQ 1-6 NON-INT POS TARG 0.117,-6.892 POS TARG 0.233,-6.783 POS TARG 0.108,-6.975 POS TARG 0.225,-6.867 POS TARG 0.342,-6.758 ORIENT 29.0D TO 37.0 D POS TARG -28, 9 SEQ 1-6 NON-INT POS TARG -27.883, 9.108 POS TARG -27.767, 9.217 POS TARG -27.892, 9.025 POS TARG -27.775, 9.133 POS TARG -27.658, 9.242 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F475W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC2808Y98B NGC6752Y95 ------------------------------------------------------------------------------------------------------------------------------------