Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 6294 Report Date: 18-Jul-95:21:52 Version: ********** Check-in Date: ********** 1.Proposal Title: DETERMINATION OF THE EXTRAGALACTIC DISTANCE SCALE - N7331 HOPR ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID GALAXIES & CLUSTERS GO 3 Long Term yrs 5397 Sub Category Large Project DISTANCE SCALE ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Dr Jeremy R. Mould CALTECH USA 818-395-4168 ------------------------------------------------------------------------------------ 7. Abstract Many fundamental problems in cosmology and astrophysics remain unsettled because the value of the expansion rate is uncertain to a factor of two. The refurbished HST will provide the opportunity to break this impasse. We propose a program which in combination with other GTO and GO work should lead to a measurement of H_0 to 10 % accuracy. Our main goal is the observation of Cepheids in 21 fields in 19 nearby galaxies, for the purpose of calibrating the best secondary distance indicators, including the infrared Tully-Fisher relation the Planetary Nebula Luminosity Function, the Surface Brightness Fluctuation method, the type Ia supernovae standard candle and the type II supernova Expanding Photosphere Method. Measurement of Cepheids in the Virgo and Fornax clusters will also be attempted. A necessary associated goal of our proposal is strengthening the calibration of the Cepheid PL relation itself, largely via resolved study of star clusters in the LMC and M33. Highlights of the proposal include a review of recent progress towards H_0 (2.2) and a critique and reaffirmation of the distance ladder approach (2.3). A project overview (2.4) and error budget are given (2.7). The details follow in subsequent sections. Now is the time to carry out this fundamental Hubble Space Telescope program. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 161.0 par: 0 10. Num targs pri: 18 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: WF/PC ------------------------------------------------------------------------------------ 12. Special sched req: Time Critical obs. ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 6294 PI: Dr Jeremy R. Mould Proposal Title: DETERMINATION OF THE EXTRAGALACTIC DISTANCE SCALE - N7331 HOPR ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ P.I. Jeremy R. Mould CALTECH USA James E. Gunn PRINCETON UNIVERSITY USA John G. Hoessel WISCONSIN, UNIVERSITY OF USA Robert C. Kennicutt Jr. ARIZONA, UNIVERSITY OF USA Sandra M. Faber CALIFORNIA, UNIVERSITY OF, SANTA USA CRUZ Garth D. Illingworth CALIFORNIA, UNIVERSITY OF, SANTA USA CRUZ Peter B. Stetson DOMINION ASTROPHYSICAL CANADA OBSERVATORY Barry F. Madore CALTECH USA John P. Huchra CFA USA John A. Graham DEPARTMENT OF TERRESTRIAL USA MAGNETISM, CIW Holland C. Ford STSCI USA Wendy L. Freedman MT WILSON & LAS CAMPANAS USA OBSERVATORIES Abhijit Saha STSCI USA Shaun M. Hughes CALTECH USA Robert Hill OBSERVATORIES OF THE CARNEGIE USA INSTITUTION OF WASHINGTON ------------------------------------------------------------------------------------ 3. Description of proposed observations. Target Cycle #U #V #I Hours Source Goal NGC 3031 4 4 2 2 2.0 M81 Complement Cycle 1 NGC 5457 4 2 1 4 4.9 Outer Field Complete Cycle 2/3 NGC 5457 4 2 12 4 10.0 Inner Field Gradient in PL NGC 925 4 2 13 4 13.3 Galaxy Cepheids NGC 3351 4 2 13 4 13.3 Galaxy Cepheids NGC 3621 4 2 13 4 10.0 Galaxy Cepheids NGC 4321 4 2 13 4 13.3 Galaxy Cepheids NGC 7331 4 2 13 4 13.3 Galaxy Cepheids NGC 2090 5 2 13 4 13.3 Galaxy Cepheids NGC 2541 5 2 13 4 13.3 Galaxy Cepheids NGC 3198 5 2 13 4 13.3 Galaxy Cepheids NGC 4414 5 2 13 4 13.3 Galaxy Cepheids NGC 4535 5 2 13 4 13.3 Galaxy Cepheids NGC 4725 5 2 13 4 13.3 Galaxy Cepheids NGC 224 4 0 2 0 0.3 Photometry test NGC 247 4 0 2 0 0.3 Photometry test NGC 598 4 0 2 0 0.3 Photometry test Cycle 4 Primary Hours: Parallel Hours: Exposures: Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. Crowding and confusion ultimately limit the detection and measurement of Cepheids in nearby galaxies. Ground-based telescopes at the best sites have been able to successfully undertake such searches routinely out to distances of 3 -4 Mpc and in exceptional cases a factor of two further. Unfortunately the distribution of galaxies is very non-uniform being locally confined primarily to the Local Group, the M81 Group in the north and the Sculptor Group in the south, with a substantial void just beyond these structures. When additional restrictions concerning luminosity, Hubble type and especially inclination are added in, the sample of galaxies of potential interest to this distance scale project becomes very small. Indeed, all such galaxies (M31, M33, NGC 247, NGC 253, NGC 300, NGC 2403, NGC 3031, and NGC 7930) have been, or are in the final stages of being surveyed for Cepheids by members of our Team using the facilities available to us, including the CFHT, KPNO, CTIO, Palomar and Las Campanas. With factors of 5-10 times increased resolution expected to be available to the refurbished HST (as compared to typical ground- based seeing) the volume of space (and the numbers of target galaxies) accessible for Cepheid searches increases by 2 to 3 orders of magnitude. Given the pressing need to deal with systematics in the zero points of any secondary distance indicators to be used at cosmologically interesting distances it is clear that sample size becomes the crucial factor in reducing the error on the mean. We cannot increase the galaxy sample size from the ground. HST is the only realistic path to follow in this regard. But recent experience with HST by our Team and the SN Type Ia Calibration effort has shown one other powerful advantage of HST: optimal scheduling. Being able to specify the entire sampling strategy in advance of the observing has allowed an extremely efficient use of the telescope. Unlike ground-based efforts that are continuously compromised by weather, day-night cycles, phase of the moon, and instrument conflicts, etc. HST can and has been successfully scheduled in such a way as to maximize the scientific return of each and every phase point with minimal aliasing in the period determinations and with maximally uniform coverage of the light curves when the data are eventually folded. Precise and repeatable re-acquisition of the target fields by HST, has also aided immensely in our ability to efficiently and effectively reduce the data, and quantify the errors. Variable seeing on ground-based data severely compromise all efforts at quality control, ranging from determining true variability, to assessing crowding errors on the photometry. In all, the unique and highly controlled circumstances involved in the HST survey as compared to any comparable ground-based effort gives our Key Project access to a galaxy sample size at least one hundred times larger than that available to ground-based telescopes, and given our adopted search strategy, the telescope is at least an order of magnitude more efficient, when compared to any of the ground-based observing programs ever attempted in the last half of this century. Some of the results of our simulations of crowded field photometry in galaxies at different distances, luminosities, and inclinations are represented below: 10 Mpc distance, M_v = -21, inclination = 60 deg A_v = 0.1, scale length = 4 kpc, bulge r_e = 3.2 kpc, B/D ratio = 0.2, (B--V)_0 = 0.7 Exposure Radius V for 3sigma (secs) (kpc) mu_v Crowding V S/N I S/N 2500 14 24.0 27.7 26.0 13 25.5 7.0 1500 14 11 6.6 3000 14 14 7.5 2500 16 24.5 27.9 26.0 15 25.5 9.0 1500 16 16 8.2 3000 16 16 9.3 For an exposure time given in column (1), at a distance from the nucleus (column 2), column (4) gives the V mag at which resolved stars protrude 3sigma above the crowding noise. If stars brighter than the V mag in column (5) are removed, column (6) gives the S/N of the resulting photometry at that magnitude. Columns (7) and (8) give the same data for I. In M81 we obtained 18 epochs of V observations in Cycles 1 and 2. In IC 4182 Sandage etal obtained 20 epochs of observation. With the higher S/N photometry expected with WFPC2 our simulations of period determination from Cepheid light curves lead us to believe that 12 optimally spaced epochs with a followup epoch a year later will suffice. Page 4 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. Time-critical observations: in a coherent set of observations we must determine accurate periods for Cepheids with a wide range of possible periods. Optimal usage of HST time therefore requires a carefully planned sequence. As an example, let us look at the case of NGC 7331. We propose to begin the sequence on 24 August 1994 +/- 5 with the first V and U exposures, followed with observations spaced at 1.4 +/- 0.2 days, 3.1 +/- 0.2 days (V+I), 5.1 +/- 0.3 days, 7.5 +/- 0.4 days, 10.4 +/- 0.5 days (V+I), 14.0 +/- 0.7 days, 18.3 +/- 0.9 days, 23.8 +/- 1.2 days (V+I), 30.5 +/- 1.5 days, 39.1 +/- 2.0 days, 50.0 +/- 2 days (V+I+U), and finally 365 +/- 5 days. The last observation is to minimize aliasing problems for the longer period Cepheids. Special orientation: because of undersampling, position and orientation must be kept fixed for the maximum number of exposures. The length of the cycle, coupled to the roll constraints, allow only a few days tolerance in the start of a sequence, & once initiated the observing cycle must be completed as specified in the given interval without omission. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. Data rights: Our suite of galaxy observations should be reserved for our exclusive use until one year after the last epoch for any individual galaxy is obtained. It would be counterproductive if partial analysis of light curves were carried out as archival research outside the control of the PI. After this time the data will be available to the community as a database constructed under the aegis of a Key Project. The above request was granted for M81, but we have to apply again to the Director at the end of Cycle 3 in the case of M101. We would like to see data for our new Cycle 4 targets protected for 2 years from the outset. Page 5 ------------------------------------------------------------------------------------ 9. Description of previous HST work. 2227GO The Extragalactic Distance Scale. I. M81 3905GO The Extragalactic Distance Scale. II. M81 & M101 4658GO The Extragalactic Distance Scale. III. M101 2684GO HST Medium Deep Survey (Huchra and Illingworth -- co-Is) 3551GO Ellipticals with Kinematically-distinct nuclei (Illingworth--PI) Faber, Gunn and Hoessel are GTO WF/PC1 Team members. Hoessel and Mould are WFPC2 Team members. Ford is a GTO FOC Team member. No other work on the distance scale is planned by any of these teams. Saha is a co-investigator on 2547GO Calibration of Supernovae of Type I as Standard Candles Progress Report for Cycles 1 through 3 Our main goals for Cycles 1-3 were to learn to find Cepheids & measure their periods and amplitudes from WFPC2 images, and to determine reliable distances to M81 and M101, thus furnishing important calibrators for all four of the secondary distance indicators discussed in 2.7. Two years of GO observations have shown HST to be remarkably well suited to the discovery of Cepheids in nearby galaxies (Freedman etal 1993, Sandage etal 1992). In both M81 (GO 2227) and IC 4182 (GO 2547) an optimized program of observations was carried out on schedule, allowing identification and preliminary period measurements for 37 and 27 Cepheids respectively. These results go a long way towards demonstrating logistical and scientific feasibility of the Key Project. Some of the light curves of our newly discovered Cepheids in M81 are collected in Figure 4. Most of these light curves are unmistakably those of Cepheids. Moreover, almost all of our 37 good candidates (24 in the major axis field and 13 in the V30 field) lie in the instability strip. The PL relation for M81 is shown in Fig. 5 (Freedman etal 1993). We find an absolute distance modulus of 27.74 mag for M81, assuming (m- M)_0 = 18.47 for the LMC. M81 has a well-defined 21 cm velocity width and well- determined disk inclination, making it a prime calibrator for the Tully-Fisher relation. It has a planetary nebula luminosity function measured by Jacoby, Ciardullo, Ford and Booth (1989). It also has a measurement of the surface brightness fluctuations (Tonry 1990). M81 was the host of type II supernova 1993J. In Cycle 2 we also began a program (GO 3905/4658) to find & study Cepheids to V = 26 in M101. We observed the field of Cook etal (1986), which contains the two known (R = 23) Cepheids in M101, V1 and V2. The data obtained so far have been of excellent quality. Cepheids in Nearby Galaxies, Freedman, W. IAU Colloquium 139 Faint Stellar Photometry with HST, Hughes, S., in IAU Colloquium 136, in press, 1992 Stellar Populations in Neighboring Galaxies, Mould, J., in Science with the Hubble Space Telescope, eds. P. Benvenuti & E. Schrier, ESO Conf. and Workshop Proc., p. 339, 1992. The distance of M81 from the Cepheid Period Luminosity Relation, Freedman, W. etal, ApJ, submitted, 1993. The H$_0$ Key Project: Photometry of WFPC2 Images of M81, Hughes, S. etal, B.A.A.S., in press, 1993. HST Observations of Cepheids in M81: Dealing with Extinction Madore, B. etal, B.A.A.S., in press, 1993. HST Observations of Cepheids in M81: Light Curves Graham, J. etal, B.A.A.S., in press, 1993. A Color Magnitude diagram of M81 Turner, A. etal, B.A.A.S., in press, 1993. An HST Determination of the distance to M81 Freedman, W. etal, B.A.A.S., in press, 1993. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Our institutions have provided a number of the computer workstations plus networked computer facilities for reading data supplied by STScI. As regards manpower, of our team of 13 investigators, 8 are being supplied to the project by their institutions free of charge, and 4 are requesting summer salary only. Hughes is half time on WFPC2 work. Three students work on the project: Laura Ferrarese at JHU, Anne Turner at U of A, and Doug Kelson at UCSC. Ground-based support of this project is considerable.The resources of Palomar, Las Campanas, University of California, N.O.A.O, and University of Arizona Observatories are being supplied for this purpose at no charge to the project. ------------------------------------------------------------------------------------ 11. Address Information Page 6 Name: JEREMY R MOULD Category: PI Institution: CALTECH Address: CALTECH 105-24 City: PASADENA State: CA Zip Code: 91125 Country: USA Telephone: 818 395 4168 Telex (or e-mail): 675425 ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 6294 [ 7] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC7331 E,301 RA=22H 37M 1.63S +/- 2", 2000 V=1097 1 SURF(V)=24 DEC=+34D 28' 18" +/- 2" ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 6294 [ 8] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 691 DEFINE # WFPC2 IMAGE WFALL- F555W CR-SPLIT=0.5 1 2800S 10 1 # AT 20-JUN-95 +/- VI7331 FIX CR- 3D TOLERANCE=0.1 POS TARG +10 , +10 CYCLE 4 / 691 - 696 Comments: THIS POSITION PUTS TARGET ON PCS MODE F APEX ORIENT 221D +/- 0D ------------------------------------------------------------------------------------------------------------------------------------ 692 DEFINE # WFPC2 IMAGE WFALL- F814W CR-SPLIT=NO 1 1200S 10 1 # GROUP 691, 692 NO VI7331 FIX GAP SAME POS FOR 692 AS 691 SAME ORIENT FOR 692 AS 691 PCS MODE F ------------------------------------------------------------------------------------------------------------------------------------ 692.1 DEFINE # WFPC2 IMAGE WFALL- F814W CR-SPLIT=NO 1 1600S 10 1 # GROUP 691 - 692.1 VI7331 FIX NO GAP SAME POS FOR 692.1 AS 691 SAME ORIENT FOR 692.1 AS 691 PCS MODE F ------------------------------------------------------------------------------------------------------------------------------------ 694 DEFINE # WFPC2 IMAGE WFALL- F555W CR-SPLIT=0.5 1 2800S 10 1 # AFTER 691 BY 15.4D VI7331 FIX CR- +/- 1.5D TOLERANCE=0.1 SAME POS FOR 694 AS 691 SAME ORIENT FOR 694 AS 691 Comments: SAME GUIDE STARS FOR 694 AS 691 PCS MODE F (RETURNING TO THE SAME POSITION AND SAME ORIENTATION IS CRUCIAL) ------------------------------------------------------------------------------------------------------------------------------------ 694.1 DEFINE # WFPC2 IMAGE WFALL- F555W CR-SPLIT=NO 1 280S 10 1 # GROUP 694 - 694.2 VI7331 FIX NO GAP SAME POS FOR 694.1 AS 691 SAME ORIENT FOR 694.1 AS 691 PCS MODE F ------------------------------------------------------------------------------------------------------------------------------------ 694.2 DEFINE # WFPC2 IMAGE WFALL- F814W CR-SPLIT=NO 1 280S 10 1 # SAME POS FOR 694.2 VI7331 FIX AS 691 SAME ORIENT FOR 694.2 AS 691 PCS MODE F ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 6294 [ 9] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 695 DEFINE # WFPC2 IMAGE WFALL- F555W CR-SPLIT=0.5 1 2800S 10 1 # AFTER 691 BY 34.9D VI7331 FIX CR- +/- 1.5D TOLERANCE=0.1 SAME POS FOR 695 AS 691 SAME ORIENT FOR 695 AS 691 Comments: SAME GUIDE STARS FOR 695 AS 691 PCS MODE F (RETURNING TO THE SAME POSITION AND SAME ORIENTATION IS CRUCIAL) ------------------------------------------------------------------------------------------------------------------------------------ 696 DEFINE # WFPC2 IMAGE WFALL- F555W CR-SPLIT=0.5 1 2800S 10 1 # AFTER 691 BY 60.0D VI7331 FIX CR- +/- 1.5D TOLERANCE=0.1 SAME POS FOR 696 AS 691 SAME ORIENT FOR 696 AS 691 Comments: SAME GUIDE STARS FOR 696 AS 691 PCS MODE F (RETURNING TO THE SAME POSITION AND SAME ORIENTATION IS CRUCIAL) ------------------------------------------------------------------------------------------------------------------------------------ 962 USE NGC7331 1 VI7331 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 6294 [ 10] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=0.5 CR-TOLERANCE=0.1 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 161.00 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES & CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category DISTANCE SCALE ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AT 20-JUN-95 +/- 3D; POS TARG +10 , +10; CYCLE 4 / 691 - 696; PCS MODE F; ORIENT 221D +/- 0D GROUP 691, 692 NO GAP; SAME POS FOR 692 AS 691; SAME ORIENT FOR 692 AS 691; PCS MODE F GROUP 691 - 692.1 NO GAP; SAME POS FOR 692.1 AS 691; SAME ORIENT FOR 692.1 AS 691; AFTER 691 BY 15.4D +/- 1.5D; SAME POS FOR 694 AS 691; SAME ORIENT FOR 694 AS 691; GROUP 694 - 694.2 NO GAP; SAME POS FOR 694.1 AS 691; SAME ORIENT FOR 694.1 AS 691; SAME POS FOR 694.2 AS 691; SAME ORIENT FOR 694.2 AS 691; AFTER 691 BY 34.9D +/- 1.5D; SAME POS FOR 695 AS 691; SAME ORIENT FOR 695 AS 691; AFTER 691 BY 60.0D +/- 1.5D; SAME POS FOR 696 AS 691; SAME ORIENT FOR 696 AS 691; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC7331 ------------------------------------------------------------------------------------------------------------------------------------