7507( 4) - 05/22/97 18:59 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7507 Version: 4 Check-in Date: 22-May-1997 18:58:49 1.Proposal Title: Determining Peculiar Motions by Observing Cepheids at 3,000 km/s ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle COSMOLOGY GO 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: STEPHEN ZEPF University of California, Berkeley CoI: Nancy Silbermann JPL/IPAC N CoI: Marc Davis University of California N CoI: Wendy Freedman Carnegie Institution of Washington N CoI: Barry Madore NASA/IPAC Extragalactic Database N CoI: Peter B. Stetson DAO N ------------------------------------------------------------------------------------ 6. Abstract We have used WFPC2 V-band observations to successfully detect Cepheids in the galaxy NGC 4603, which is believed to be in the Cen30 cluster at a redshift of 3,000 kms . These are the most distant Cepheids known. We propose to follow up this result in two ways. First, I-band observations of our field in NGC 4603 are required in order to determine the reddening and true distance modulus, All of our orbits in the previous cycle were dedicated to V-band observations in order to maximize the discovery of Cepheids and demonstrate the feasibility of the project. Second, we propose to observe a second galaxy in the Cen30 cluster to confirm our distance for this cluster derived from these observations. The Cen30 cluster is of particular interest because secondary distance indicators suggest it has a large peculiar velocity, but no mass distribution is found in IRAS or optical galaxy maps which can produce the inferred motion. Therefore, either there are mass distributions not traced by galaxies, or there are systematic problems with secondary distance indicators. Our preliminary result (awaiting further scheduled epochs and the I-band data proposed here) for NGC 4603 favors the hypothesis that the secondary indicators are correct. However, any single galaxy might be in the foreground of the cluster, so we propose to observe a second Cen30 spiral, NGC 4575. ------------------------------------------------------------------------------------ 7507( 4) - 05/22/97 18:59 - [ 2] Observations Description ------------------------ We propose to obtain WFPC2 F814W images of the spiral galaxy NGC 4603 in order to determine its true distance modulus and the reddening to the Cepheids we have detected in this galaxy with our Cycle 6 F555W imaging. We also propose to obtain both F555W and F814W images of NGC 4575, a spiral galaxy also believed to be in the Cen30 cluster in order to determine its distance, and confirm the high peculiar velocity which our initial observations appear to suggest for the Cen30 cluster. For NGC 4603, we have already detected Cepheids in the first seven epochs of our Cycle 6 program of V-band imaging. We have two more epochs coming up in the summer of 1997, one a result of our own planning to avoid aliasing, and another the result of a 1996 visit lost due to a safing event. Our goal for the proposed observations of NGC 4603 is to obtain mean I magnitudes for the Cepheids. These will allow us to account for reddening in our determination of the true distance modulus. In order to obtain good magnitudes for Cepheids at these distances, three orbits are required, and in order to derive a mean I magnitude, two epochs are required to account for uncertainties in the phases, and therefore the mean magnitude. We note that it should be possible to schedule these two I-band visit simultaneously with the two V-band epochs we have remaining from our Cycle 6 program. This scheduling both increases observational efficiency and reduces the uncertainties in the phases of the I-band data. For NGC 4575, we propose to detect Cepheids through a series of V-band observations, and to use corresponding I-band imaging to account for reddening, in order to derive the distance to the galaxy and the Cen30 cluster. We will adopt the search methodology used successfully in many HST Cepheid programs by the Key Project team and others (Madore & Freedman 1995). As in our study of NGC 4603, we will tailor the observing sequence and numbers of epochs to the target galaxy and its expected sample of long-period Cepheids. We are requesting 8 epochs of V data distributed within a single window of approximately 60-days duration (chosen to preserve the spacecraft roll angle) We will use an optimally scheduled pattern of observations within that window so as to maximize the uniformity of phase coverage for all Cepheids with periods in the expected range of 40-60 days regardless of their individual periods and particular phasing. We will also schedule a ninth epoch a year later to further guard against aliasing effects. I-band observations are requested to be scheduled contiguously at two of the V- band epochs to allow for a determination of a reddening correction for the Cepheid moduli. Six of the V-band epochs will be executed as three-orbit observations, and three as two-orbit observations. Combined with two I-band epochs of three orbits each, the total time requested is 30 orbits. Our experience with NGC 4603 indicates that these exposure times are sufficient to determine the periods and luminosities of Cepheids. Discovery of the variables, determination of periods, phases and total light curves will be made in the V band; colors will be derived from the I-band data giving reddening corrections to the apparent Cepheid moduli. Because of the significantly lower amplitudes in the near infrared as compared to the visual, many fewer I-band observations are needed for mean I magnitude determinations, once the V-band light curves are defined (e.g., Freedman 1988, Ap.J., 326, 691). Real Time Justification ----------------------- The observations are not time-critical. However, once they have begun, we request that our program scheduled according to the optimal sampling strategy described in the previous section. Such a sampling strategy is critical for obtaining the most uniform phase coverage for the target Cepheids. None. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7507( 4) - 05/22/97 18:59 - [ 3] Data Distribution Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7507( 4) - 05/22/97 18:59 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4603-POS1 galaxy,spiral RA=12H 40M 58.77S +/- 5",DEC=- 2000 V= 2562 SURF(V) = 24 40D 58' 2.5" +/- 5",PLATE- ID=00ZD Comments: Use absolutely same position as program 6439. This should not be difficult, since the observations should be scheduled concurrently with the remaining two visits in program 6439 7507( 4) - 05/22/97 18:59 - [ 5] Visit: 01 Visit Requirements: BETWEEN 16-JUN-97 AND 19-JUN-97 ORIENT 98.5D TO 99.5D SCHED 50% On Hold Comments: Additional Comments: This visit should occur right after or right before the 8th visit of program 6439. The orientation should be identical to that of program 6439 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4603-POS WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=0.5,CR-TOLERANCE=0.1 1 2300 S 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4603-POS WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=0.5,CR-TOLERANCE=0.1 1 2600 S POS TARG 0.25,0.25 1 Comments: Dithering pattern equal to an offset of 2.5, 2.5 WF pixels is put in by hand. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4603-POS WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=0.5,CR-TOLERANCE=0.1 1 2600 S POS TARG 0.50,0.50 1 Comments: Dithering pattern equal to an offset of 5.0, 5.0 WF pixels is put in by hand. ------------------------------------------------------------------------------------------------------------------------------------ 7507( 4) - 05/22/97 18:59 - [ 6] Visit: 02 Visit Requirements: SAME ORIENT AS 01 SCHED 50% AFTER 01 BY 29.7D TO 31.7D On Hold Comments: Additional Comments: This visit should occur right after or right before the 9th (last visit) of program 6439. The orientation should be identical to that of visit 1 AND program 6439. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4603-POS WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=0.5,CR-TOLERANCE=0.1 1 2300 S 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4603-POS WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=0.5,CR-TOLERANCE=0.1 1 2600 S POS TARG 0.25,0.25 1 Comments: Dithering pattern equal to an offset of 2.5, 2.5 WF pixels is put in by hand. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4603-POS WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=0.5,CR-TOLERANCE=0.1 1 2600 S POS TARG 0.50,0.50 1 Comments: Dithering pattern equal to an offset of 5.0, 5.0 WF pixels is put in by hand ------------------------------------------------------------------------------------------------------------------------------------ 7507( 4) - 05/22/97 18:59 - [ 7] Summary Form for Proposal 7507 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=0.5 CR-TOLERANCE=0.1 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COSMOLOGY ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 16-JUN-97 AND 19-JUN-97 ORIENT 98.5D TO 99.5D SCHED 50% POS TARG 0.25,0.25 POS TARG 0.50,0.50 SAME ORIENT AS 01 SCHED 50% AFTER 01 BY 29.7D TO 31.7D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4603-POS1 ------------------------------------------------------------------------------------------------------------------------------------