! +====================+ ! | PED OUTPUT PRODUCT | ! +====================+ ! ! /g2/jt/HST/6579.orient/6579.prop ! Generated by PREPROCESSOR, version 6.0e ! Date: Fri Mar 8 16:57:21 EST 1996 Proposal_Information Title: The Cosmic Velocity of the Great Attractor Proposal_Category: GO Scientific_Category: COSMOLOGY Cycle: 6 Investigators PI_Name: John L. Tonry PI_Institution: Massachusetts Institute of Technology CoI_Name: Edward A. Ajhar CoI_Institution: National Optical Astronomy Observatories Contact: CoI_Name: Jon A. Holtzman CoI_Institution: New Mexico State University Contact: CoI_Name: Tod R. Lauer CoI_Institution: National Optical Astronomy Observatories Contact: CoI_Name: Marc Postman CoI_Institution: Space Telescope Science Institute Contact: CoI_Name: Alan Dressler CoI_Institution: Observatories of the Carnegie Institution of Washington Contact: Abstract: We request deep WFPC2 images of five galaxies in clusters near the Centaurus Cluster to determine their distances and peculiar velocities using the Surface Brightness Fluctuation (SBF) method. We expect to determine whether the Centaurus galaxies are falling into the "Great Attractor", and distinguish between the claims that there is convergence of the flow beyond Centaurus (return to CMB rest frame) instead of continued ~600 km/s bulk flow. Confirmation of the latter would indicate that coherent peculiar velocities are generated over an enormous scale. HST is required as the ground-based SBF method becomes impossible beyond 3,000 km/s. The high spatial resolution of HST permits precise measurement of the SBF signal at very large distances, and allows easy recognition of globular clusters and background galaxies in the galaxy images that must be removed prior to SBF detection. The proposing team developed the SBF method, has worked extensively in the field of large scale flows, played major roles in the calibration of WFPC and WFPC2, and are conducting GTO observations which will help validate the zeropoint and application of the SBF method for local galaxies. Questions Observing_Description: We will measure distances to these galaxies by obtaining high signal-to-noise images and observing their surface brightness fluctuations (SBF), the irreduceable mottling of an otherwise smooth galaxy from the finite number of stars. This has been described in detail in Tonry (1991) and Jacoby et al. (1992). The fundamental idea is simply that the finite number of stars in a galaxy gives rise to a measurable bumpiness in its surface brightness, even though individual stars remain completely unresolved. The variance is the product of the galaxy brightness per pixel and what we refer to as the "average luminosity" of the stellar population, the ratio of the second moment of the stellar luminosity function to the first, Lbar. Obviously there are many sources of pixel-to-pixel noise (variance) in an image of a galaxy such as white noise from detector noise and photon statistics, roughness from patchy dust obscuration, spiral arms, and inhomogeneous stellar population, bumpiness from globular clusters (GCs) or background galaxies, and finally the SBF mottling from the Poisson statistics of the finite number of stars in a pixel. Photon shot noise only grows as the square root of time, and the SBF signal becomes detectable when a source of Lbar contributes more than one photon in an image ( i.e., when stellar counting statistics dominate photon counting statistics). We apply the SBF method primarily to E and S0 galaxies, which avoids problems with dust and spiral arms. Unraveling the third source of variance proceeds in two steps. First we identify as many "compact sources" (stars, background galaxies, and primarily GCs) as possible and excise them from the image. Second, we fit a luminosity function to the sources which we found and integrate the extrapolation to fainter magnitudes to determine the residual variance left in the image from the unseen sources. The variance from the SBF of stars in the galaxy is then the difference between that which is measured and the estimate of the residual. The fainter we can identify and remove sources, the smaller the residual correction. In practice, if our compact source completeness dies out two magnitudes brighter than the peak of the GC luminosity function, the resulting SBF measurement is quite uncertain because most of the variance in the picture results from the (uncertain) residual variance. If we can identify sources all the way to the peak of the GC luminosity function, the residual variance is typically only 20% of the net variance and it contributes negligible uncertainty. Removal of compact sources makes it critical that the images be as sharp as possible. Measurement of SBF is accurate and reliable at the distance of Virgo (1300km/s) in 1" seeing, but becomes difficult in 1.5" seeing. At the distance of the Great Attractor environs (three or four times Virgo), even the best seeing from the ground (0.5") becomes inadequate. We believe that our attempts to observe SBF in Centaurus (twice Virgo) from the ground have been successful, but we have reservations about their reliability, since the seeing (0.75") was barely adequate for the distance (2400km/s). However, HST has resolution to spare and we should be able to identify GCs significantly fainter than the peak of the luminosity function. Although the HST PSF is somewhat undersampled even with the PC, we have enough experience with 0.48" pixels in 0.9" seeing at KPNO and CTIO to know that this is not a problem with our power spectrum analysis. One concern might be PSF spatial variability across the CCD fields; however, this is expected to be small within WFPC2, and will be mapped by one of us (Holtzman) as part of WFPC2 calibration. In any case, PSF variability can be included in the SBF analysis and is not a limiting factor. We further note that we will get useful information from both the WF and PC CCDs. Hot pixels had been an initial concern with WFPC2, but they are much less important now that the operating temperature of WFPC has been lowered, and Holtzman has extensive experience with their detection and removal. Further, the observations will be dithered to counter any residual hot pixels or PSF-scale flat-fielding errors (We find the S/N and quality of the WFPC2 F814W flats as produced so far to be more than sufficient for SBF work). A common worry about deriving distances from SBF measurements is the extent to which we can predict the absolute magnitudes Mbar which correspond to the mbar which we measure. We have found empirically that in the I band stellar populations of differing age and metallicity vary predictably with overall color, and this has been confirmed theoretically (Worthey 1993). As a demonstration of this, Figure 2 shows the SBF data we have obtained for the Fornax and Virgo clusters, plotting mbar_I against the (V-I) color of the galaxy. It should be noted that these are all of the galaxies we have observed in these clusters, without regard for E versus S0, presence of dust, specific frequency of GCs (NGC4486, NGC1399, and NGC1316 appear here), etc. The rms scatter about the stellar population line is only 0.16 magnitude. In the case of Fornax we typically have 0.14 mag of observational error (the median seeing was 1.54"), and Virgo has a significant contribution from the depth of the cluster (the core of Virgo has a radius of 0.1 radian across the line of sight which presumably corresponds to a 10% depth as well). These considerations, as well as the repeatability of multiple measurements, suggests that with sufficient resolution we routinely achieve a distance error of 5% per galaxy. A final concern is how well we understand the SBF zero point itself. Ground based application of SBF out to 2,400 km/s has yielded an important determination of H_0 (Tonry 1991), and there are vigorous ongoing efforts to establish this zero point beyond any doubt. For example, at present the SBF zero point is based on Cepheid distances to M31 and M81. However the HST key project and SN1a long term project have produced preliminary Cepheid distances to 6 other galaxies. The difference between SBF and these new Cepheid distances is 0.06 magnitude with a scatter of 0.11 magnitude, indicating that SBF is indeed very accurate. As these Cepheid distances are published our zero point will become firmly tied to the Cepheid distance scale. On the theoretical front, the stellar models and calculations of Worthey (1993) agree well with our empirical calibration of Mbar_I. We know from nearby galaxies in Virgo that the apparent fluctuation magnitude for galaxies of (V-I) = 1.20 is 29.64. Based on estimates of the Coma to Virgo distance ratio (5.6), the distance to Virgo is 1286 km/s, so mbar_I will be 31.48 at 3000km/s. In order to achieve full 5% accuracy, it is essential that the SBF signal significantly exceed the photon/read noise. Since we will have extremely good compact source rejection, experience from ground based observations indicates that we can get by with only 5 photons per mbar_I, but less than this will seriously compromise the accuracy. WFPC2 with the F814W filter detects 1 photon per second from a 23.78 magnitude source, so at a distance D km/s the exposure time required to receive 5 photons per mbar_I is t = 6000 sec (D/3000 km/s)^2 10^[1.6(V-I)-1.20]. The individual exposures will be CR-split. We will request offsets of a few pixels between the exposures to improve flat-fielding and rejection of any residual hot pixels or other CCD defects. Real_Time_Justification: None. We have ground-based V and I images of many of the targets, and we will obtain V and I photometry for the rest at LCO or CTIO. We have extensive (>1500) SBF observations of nearby galaxies which we have used to verify the method and understand systematics. Compared to ground based observations with poor seeing, HST data will be much easier to work with. Calibration_Justification: Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: NGC4767 Alternate_Names: Description: GALAXY,ELLIPTICAL, Position: RA=12H 53M 52.84S +/- 1",DEC=-39D 42' 49.7" +/- 1",PLATE-ID=0162 Equinox: J2000 RV_or_Z: V = 2997 RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: SURF(V) = 21.4+/-0.3 Comments: Target_Number: 2 Target_Name: NGC4709 Alternate_Names: Description: GALAXY,ELLIPTICAL, Position: RA=12H 50M 03.96S +/- 1",DEC=-41D 22' 53.7" +/- 1",PLATE-ID=0162 Equinox: J2000 RV_or_Z: V = 4683 RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: SURF(V) = 21.4+/-0.3 Comments: Target_Number: 3 Target_Name: NGC5516 Alternate_Names: Description: GALAXY,ELLIPTICAL, Position: RA=14H 15M 54.69S +/- 1",DEC=-48D 06' 53.7" +/- 1",PLATE-ID=01F7 Equinox: J2000 RV_or_Z: V = 4460 RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: SURF(V) = 21.4+/-0.3 Comments: Target_Number: 4 Target_Name: ESO507-G045 Alternate_Names: Description: GALAXY,ELLIPTICAL, Position: RA=12H 55M 35.60S +/- 1",DEC=-26D 49' 30.2" +/- 1",PLATE-ID=04LL Equinox: J2000 RV_or_Z: V = 4825 RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: SURF(V) = 21.4+/-0.3 Comments: Target_Number: 5 Target_Name: NGC6876 Alternate_Names: Description: GALAXY,ELLIPTICAL, Position: RA=20H 18M 19.04S +/- 1",DEC=-70D 51' 30.1" +/- 1",PLATE-ID=01CB Equinox: J2000 RV_or_Z: V = 3836 RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: SURF(V) = 21.4+/-0.3 Comments: Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 101 Target_Name: NGC4767 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1100S Special_Requirements: POS TARG 0.00,0.00 Comments: Exposure_Number: 102 Target_Name: NGC4767 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG 0.8969,0.0946 Comments: Exposure_Number: 103 Target_Name: NGC4767 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1100S Special_Requirements: POS TARG 1.0010,0.8908 Comments: Exposure_Number: 104 Target_Name: NGC4767 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 0.1052,0.9954 Comments: Exposure_Number: 105 Target_Name: NGC4767 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1100S Special_Requirements: POS TARG -0.8903,1.1006 Comments: Exposure_Number: 106 Target_Name: NGC4767 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG -0.9965,-0.0940 Comments: Visit_Number: 02 Visit_Requirements: ORIENT 240D TO 40D On_Hold_Comments: Visit_Comments: Exposure_Number: 201 Target_Name: NGC4709 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1100S Special_Requirements: POS TARG 0.00,0.00 Comments: Exposure_Number: 202 Target_Name: NGC4709 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 0.8969,0.0946 Comments: Exposure_Number: 203 Target_Name: NGC4709 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG 1.0010,0.8908 Comments: Exposure_Number: 204 Target_Name: NGC4709 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 0.1052,0.9954 Comments: Exposure_Number: 205 Target_Name: NGC4709 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG -0.8903,1.1006 Comments: Exposure_Number: 206 Target_Name: NGC4709 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG -0.9965,-0.0940 Comments: Visit_Number: 03 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 301 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1100S Special_Requirements: POS TARG 0.00,0.00 Comments: Exposure_Number: 302 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 0.8969,0.0946 Comments: Exposure_Number: 303 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG 1.0010,0.8908 Comments: Exposure_Number: 304 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 0.1052,0.9954 Comments: Exposure_Number: 305 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG -0.8903,1.1006 Comments: Exposure_Number: 306 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG -0.9965,-0.0940 Comments: Exposure_Number: 307 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG -1.1006,-0.8903 Comments: Exposure_Number: 308 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG -0.1052,-0.9954 Comments: Exposure_Number: 309 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG 1.0895,-1.1017 Comments: Exposure_Number: 310 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 1.8857,-1.2058 Comments: Exposure_Number: 311 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG 1.9931,0.1881 Comments: Exposure_Number: 312 Target_Name: NGC5516 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 2.0982,1.1835 Comments: Visit_Number: 04 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 401 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1000S Special_Requirements: POS TARG 0.00,0.00 Comments: Exposure_Number: 402 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 0.8969,0.0946 Comments: Exposure_Number: 403 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1100S Special_Requirements: POS TARG 1.0010,0.8908 Comments: Exposure_Number: 404 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 0.1052,0.9954 Comments: Exposure_Number: 405 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1100S Special_Requirements: POS TARG -0.8903,1.1006 Comments: Exposure_Number: 406 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG -0.9965,-0.0940 Comments: Exposure_Number: 407 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1100S Special_Requirements: POS TARG -1.1006,-0.8903 Comments: Exposure_Number: 408 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG -0.1052,-0.9954 Comments: Exposure_Number: 409 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1100S Special_Requirements: POS TARG 1.0895,-1.1017 Comments: Exposure_Number: 410 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 1.8857,-1.2058 Comments: Exposure_Number: 411 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1100S Special_Requirements: POS TARG 1.9931,0.1881 Comments: Exposure_Number: 412 Target_Name: ESO507-G045 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 2.0982,1.1835 Comments: Visit_Number: 05 Visit_Requirements: CVZ ORIENT 180D TO 335D On_Hold_Comments: Visit_Comments: Exposure_Number: 501 Target_Name: NGC6876 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG 0.00,0.00 Comments: Exposure_Number: 502 Target_Name: NGC6876 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG 0.8969,0.0946 Comments: Exposure_Number: 503 Target_Name: NGC6876 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG 1.0010,0.8908 Comments: Exposure_Number: 504 Target_Name: NGC6876 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG 0.1052,0.9954 Comments: Exposure_Number: 505 Target_Name: NGC6876 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG -0.8903,1.1006 Comments: Exposure_Number: 506 Target_Name: NGC6876 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG -0.9965,-0.0940 Comments: Exposure_Number: 507 Target_Name: NGC6876 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F814W Wavelength: Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: POS TARG -1.1006,-0.8903 Comments: Data_Distribution ! 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