8250( 4) - 05/05/00 15:09 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8250 Version: 4 Check-in Date: 12-Apr-1999 11:54:12 1.Proposal Title: Proper motions of bulge stars ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Konrad Kuijken Kapteyn Astronomical Institute CoI: Dr. R. Michael Rich University of California at Los Angeles N ------------------------------------------------------------------------------------ 5. Abstract We request second-epoch observations of two fields in the galactic bulge for proper motion measurements, using WFPC2. These observations will allow velocities to be measured with an accuracy of 70km/s, sufficient to study the rotation properties of the bulge and disk in these fields, the vertical kinematics as a function of stellar type, and the presence of kinematic substructure such as might be caused by accretion of small satellites or dissolution of globular clusters. Further, a proper motion selected color-magnitude diagram will yield the best possible depiction of the Galactic bulge turnoff point. The first epoch observations were two-band, single - dither exposures. For the second epoch we will only use one band, but use two half -pixel dithered positions to improve the position accuracy. ------------------------------------------------------------------------------------ 8250( 4) - 05/05/00 15:09 - [ 2] Observations Description ------------------------ The quality of the repeat observations should be at least equal to that of the first epoch data, so that the errors in the proper motions not be dominated by the newer observations. We therefore propose to follow the same observing strategy as the first-epoch teams: a combination of short- and longer exposures with which brighter and fainter stars can be centroided without running into saturation problems. Each of the two fields thus requires two orbits integration. Spacecraft orientation should be the same for the second epoch observations as they were for the first epoch. The first epoch data were taken through several filters. We will only repeat the deepest data here, which use the F814W filter. Unlike the first-epoch data, we propose to dither the exposures to better sample the WFPC PSF, so that the position accuracy of the stars may be increased. This will ensure that the error budget in the proper motions is dominated by the pre-existing data. The WF CCD pixels do not s ample the PSF well, so centroiding stars accurately is a delicate task. King et al (1998) show that a careful analysis of dithered exposures of a globular cluster can lead to centroid shifts measured to an accuracy of better than 5mas down to I=23. To evaluate the positional accuracy that can be achieved in the first- epoch, undithered data, we have carried out simulations with Tiny Tim model PSF's, calculated to high resolution and then binned onto 0.1arcsec pixels. Centroids are then determined by least-squares fitting of star images to the grid of binned PSFs. Simulations with Tiny Tim models show that a centroiding accuracy for point sources of \ sigma_x=6.5 rms noise per pixel/ hboxdetected photons from star \ \ hbox0.1 arcsec pixels \ can be achieved this way (depending somewhat on where the star falls with respect to the pixel grid: the number above is for a worst- case scenario in which the star sits in the center of a pixel). Similarly, the photometric accuracy res ul ting from PSF fitting is \ sigma_ Flux=5.5\ hbox(rms noise per p ixel) \ Thus, dividing these two equations, the accuracy in the centroiding is \ sigma_x=1.2/ S/N of star detection \ \ hbox0.1 arcsec pixels. \ Our science goal is to centroid stars to an accuracy of 5milli-arcsec (mas), or 0.05 pixels. This means that the difference in position between the two epochs can be determined to an accuracy of 7mas, for a proper motion accuracy over a four-year baseline of 1.8mas/yr (70km/s/8kpc). The calculation above shows that this can be done for stars with photometry S/N of 25 or better. In the work of Holtzman et al. (1998) this S/N is achieved for stars above I_814W~eq 22.5. At the distance of 8kpc of the bulge (distance modulus 14.5) this corresponds to M_I~eq8. Brighter than this limiting magnitude, Holtzman et al find several thousand stars per square arcmin in their data, corresponding to a total of over 10000 over the observed field. Since the fitting of the PSF is dominated by the few pixels near the peak, crowding is not a significan t problem in the centroiding algorithm--- though iterative subtraction of nearby brighter neighbours may be required for the fainter stars in the image. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8250( 4) - 05/05/00 15:09 - [ 3] Data Distribution Paper Products: NO Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8250( 4) - 05/05/00 15:09 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 FIELD180310- GALAXY, BULGE RA=18H 3M 10S +/- 0.1S, DEC=-29D 2000 V = 27+/-0.5 295143 51' 43" +/- 1" 2 SGR-I GALAXY, BULGE RA=17H 55M 50.0S +/- 0.1S, DEC=- B1950 V = 27+/-0.5 29D 12' 0" +/- 1" 8250( 4) - 05/05/00 15:09 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 84D TO 85D On Hold Comments: Additional Comments: 4-position dither 0.55 arcsec square. At each position a 1000S and a 80S exposure. ORIENT is sci_v3_pos_angle value from 1st epoch data +/- 180D Note: RPS2 turns exposures 30, 50, 70 into 800S. This is fine, but generates warnings. If I manually specify these exposure times, then they get scheduled over 3 orbits. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 FIELD180310 WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 700 S POS TARG 12, 12 EXPAND -295143 ------------------------------------------------------------------------------------------------------------------------------------ 20 FIELD180310 WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 80 S POS TARG 12, 12 -295143 ------------------------------------------------------------------------------------------------------------------------------------ 30 FIELD180310 WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 700 S POS TARG 12.55, 12 EXPAND -295143 ------------------------------------------------------------------------------------------------------------------------------------ 40 FIELD180310 WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 80 S POS TARG 12.55, 12 -295143 ------------------------------------------------------------------------------------------------------------------------------------ 50 FIELD180310 WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 700 S POS TARG 12.55, 12.55 -295143 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 60 FIELD180310 WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 80 S POS TARG 12.55, 12.55 -295143 ------------------------------------------------------------------------------------------------------------------------------------ 70 FIELD180310 WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 700 S POS TARG 12, 12.55 EXPAND -295143 ------------------------------------------------------------------------------------------------------------------------------------ 80 FIELD180310 WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 80 S POS TARG 12, 12.55 -295143 ------------------------------------------------------------------------------------------------------------------------------------ 8250( 4) - 05/05/00 15:09 - [ 6] Visit: 02 Visit Priority: Visit Requirements: ORIENT 86D TO 87D On Hold Comments: Additional Comments: 4-position dither 0.55 arcsec square. At each position a 1000S and a 80S exposure. ORIENT is sci_v3_pos_angle value from 1st epoch data +/- 180D Note: RPS2 turns exposures 30, 50, 70 into 800S. This is fine, but generates warnings. If I manually specify these exposure times, then they get scheduled over 3 orbits. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 SGR-I WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 700 S POS TARG 12, 12 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 20 SGR-I WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 80 S POS TARG 12, 12 ------------------------------------------------------------------------------------------------------------------------------------ 30 SGR-I WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 700 S POS TARG 12.55, 12 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 40 SGR-I WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 80 S POS TARG 12.55, 12 ------------------------------------------------------------------------------------------------------------------------------------ 50 SGR-I WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 700 S POS TARG 12.55, 12.55 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 60 SGR-I WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 80 S POS TARG 12.55, 12.55 ------------------------------------------------------------------------------------------------------------------------------------ 70 SGR-I WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 700 S POS TARG 12, 12.55 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 80 SGR-I WFPC2 IMAGE WFALL F814W CR-SPLIT=0.5,CR-TOLERANCE=0.15 1 80 S POS TARG 12, 12.55 ------------------------------------------------------------------------------------------------------------------------------------ 8250( 4) - 05/05/00 15:09 - [ 7] Summary Form for Proposal 8250 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFALL ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=0.5 CR-TOLERANCE=0.15 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 84D TO 85D POS TARG 12, 12 EXPAND POS TARG 12, 12 POS TARG 12.55, 12 EXPAND POS TARG 12.55, 12 POS TARG 12.55, 12.55 EXPAND POS TARG 12.55, 12.55 POS TARG 12, 12.55 EXPAND POS TARG 12, 12.55 ORIENT 86D TO 87D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names FIELD180310-295143 SGR-I ------------------------------------------------------------------------------------------------------------------------------------