7261( 10) - 02/02/98 11:16 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7261 Version: 10 Check-in Date: 02-Feb-1998 11:15:32 1.Proposal Title: The distance to M96 from H-band Cepheid observations ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: NIAL TANVIR NSTITUTE OF ASTRONOMY CoI: Thomas Shanks University of Durham N CoI: Henry Ferguson Space Telescope Science Institute N ------------------------------------------------------------------------------------ 5. Abstract Determination of the Hubble constant is a primary goal of HST. A number of galaxies have already been observed for Cepheids using WFPC2 to obtain V and I-band photometry. Tanvir Etal\ 1995 found the distance to the spiral galaxy M96 (NGC3368) in the Leo-I group, and argued that this galaxy was particularly appropriate for calibrating the many elliptical galaxy secondary distance indicators, since there is good evidence that M96 is close to the central ellipticals in the group. Hence they estimated H_0=69+/-8kmsmpc. Here we are proposing to obtain infrared H-band (F160W) observations of a sample of the Cepheids in M96 and the dwarf galaxy UGC5889 with NICMOS. Infrared observations have a number of crucial advantages for Cepheid distance determination, specifically (a) a much reduced sensitivity to extinction (and variations in dust properties), which also results in a lower sensitivity to calibration uncertainties, (b) reduced sensitivity to metallicity variations and (c) reduced dispersion around the period--luminosity relation. Thus these observations should provide a considerably improved distance to the Leo-I group, and a test of the results already obtained using V and I photometry. Combining the new distances with the recent studies of early-type galaxy secondary indicators in the Leo-I group should give an estimate of H_0 to better than 10\ free of potentially unknown systematics due to dust and metallicity, and independent of the velocity of the group. ------------------------------------------------------------------------------------ 7261( 10) - 02/02/98 11:16 - [ 2] Observations Description ------------------------ Our M96 field was deliberately chosen to be in the outer parts of the galaxy with relatively low crowding. This makes these Cepheids particularly appropriate for infrared follow- up observations since the somewhat poorer resolution in the H -band will be managable. With Cepheids already identified we can optimise the NICMOS observations given their distribution over the WFPC2 field. The upshot is that we can identify two NICMOS/NIC3 pointings, each of which picks up 3 of the brighter Cepheids and a few fainter Cepheids. Once again, the fact that our Cepheids are relatively isolated means that the course sampling of NIC3 is not a serious problem. Both pointings could be oriented to pick up further Cepheids if the current problems of focussing NIC3 simultaneously with NIC1 and 2 can be resolved to restore full parallel functionality. The surface-brightness of the galaxy is low in H in this part of M96, and the normal sky and thermal backgrounds dominate (Leo is of course close to the ecliptic and it would be beneficial to observe under low-sky conditions). We consider it is important to improve the reliability of the NICMOS magnitudes by dithering subexposures. This helps remove cosmic rays and hot pixels, and also reduces some of the uncertainty due to the relatively large inter- and intra-pixel sensitivity variations of these detectors. Given that each dithered sub- exposure is of relatively short duration, read noise becomes a factor and we are therefore requesting the ACCUM readout option, with the standard N_read=10 to reduce read noise. We can express the basic uncertainty in distance determination due to fitting the H-band \\\\PL\\\\ relation as: sqrt\\\\frac<=ft\\\\fracSigma_var^2+Sigma_noise^2n_obs\\\\right+Sigma_ PL^2n_cephs By comparison with Cepheids in the LMC, for which V-H~1.7 for Cepheids of these periods, we find an expected mean H magnitude for the faintest Cepheid in our target sample of H~23.5. This corresponds to a flux of ~ 4times10^-7 Jy which should be detected with a S/N~8 in 1 orbit integration, assuming 4 CR-split dither positions in N_read=10 ACCUM exposures. ie. sigma_noise~0.125 for the worst case. The amplitude variations in H are ~0.3* the amplitude in V, so we expect typically to find ~+/-0.2 mag total variation around the mean mag in H. ie. sigma_var~0.1 From two random phase points (n_obs=2) then, the expected uncertainty due to photometric errors and sampling noise will be only 0.11 mag on the mean magnitude of such a Cepheid. Taking a sample of n_cephs=6 Cepheids, given a dispersion around the H-band \\\\PL\\\\ relation of sigma_PL~0.14 mag, means that we would get a distance estimate to ~+/-0.08 mags, or 4\\\\ In fact, this calculation is rather conservative since (a) we have done the calculation for the faintest of the 6 Cepheids; (b) given our knowledge of the periods we can space the observations in such a way as to reduce sigma_var from the random phase case: simulations indicate a spacing of ~15 days will be optimal; and (c) we have ignored the small reduction in effective spread of the \\\\PL\\\\ relation which occurs after reddening correction due to the presence of an intrinsic colour-magnitude correlation. So an internal error of 3\\\\ is more realistic. This is already an improvement on the equivalent uncertainty for the existing V and I measurements, but an even larger improvement comes with the reddening correction which is far smaller for the H-band (ie. mu_0=Mu_AH-0.22(Mu_AV-Mu_AH) compared to mu_0=Mu_AI- 1.45(Mu_AV -Mu_AI)), and consequently much better determined. Finally, the error budget must include the various other uncertainties connected with the calibration in the LMC (assumed to be +/-0.1 mag), metallicity uncertainties (small at H) and the photometric calibration of the HST passbands, all of which will improve with time. In the case of UGC5889, there is a single bright Cepheid suitable for NICMOS observations. A 1-orbit exposure will, following the above procedure, give a distance with internal uncertainty of about 10\\\\ estimate. Real Time Justification ----------------------- None. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7261( 10) - 02/02/98 11:16 - [ 3] Data Distribution Media: DAT Blocking Factor: 10 Ship To: Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, United Kingdom Ship Via: Email: ------------------------------------------------------------------------------------ 7261( 10) - 02/02/98 11:16 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3368-POS1 GALAXY, SPIRAL RA=10H 46M 46.63S +/- J2000 V=900 V = 25+/-1.0 0.03S,DEC=11D 52' 1.0" +/- 0.5" B-V = 0.9+/-0.4 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1997.5 0 0 0 2 NGC3368-POS2 GALAXY, SPIRAL RA=10H 46M 42.20S +/- J2000 V=900 V = 25+/-1.0 0.03S,DEC=11D 52' 7.0" +/- 0.5" B-V = 0.9+/-0.4 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1997.5 0 0 0 3 NGC3368-PAR1 GALAXY, SPIRAL RA=10H 46M 46.63S +/- J2000 V=900 V = 25+/-1.0 0.03S,DEC=11D 52' 1.0" +/- 0.5" B-V = 0.9+/-0.4 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1997.5 0 0 0 4 NGC3368-PAR2 GALAXY, SPIRAL RA=10H 46M 46.63S +/- J2000 V=900 V = 25+/-1.0 0.03S,DEC=11D 52' 1.0" +/- 0.5" B-V = 0.9+/-0.4 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1997.5 0 0 0 5 NGC3368-PAR3 GALAXY, SPIRAL RA=10H 46M 42.20S +/- J2000 V=900 V = 25+/-1.0 0.03S,DEC=11D 52' 7.0" +/- 0.5" B-V = 0.9+/-0.4 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1997.5 0 0 0 6 NGC3368-PAR4 GALAXY, SPIRAL RA=10H 46M 42.20S +/- J2000 V=900 V = 25+/-1.0 0.03S,DEC=11D 52' 7.0" +/- 0.5" B-V = 0.9+/-0.4 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1997.5 0 0 0 7261( 10) - 02/02/98 11:16 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 223D TO 250D SCHED 90% 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 NGC3368-POS NIC1 MULTIAC NIC1-FI F160W SAMP-SEQ=STEP32,NSAMP=15, 1 DEF PAR 2-3 WITH 1 1 CUM X PATTERN=SPIRAL-DITH,NUM-POS=9, DITH-SIZE=0.3,CAMERA-FOCUS=1-2 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3368-PAR NIC2 MULTIAC NIC2-FI F160W SAMP-SEQ=STEP32,NSAMP=15 1 DEF 1 CUM X ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC3368-PAR NIC3 MULTIAC NIC3-FI F160W SAMP-SEQ=STEP32,NSAMP=15 1 DEF 2 CUM X ------------------------------------------------------------------------------------------------------------------------------------ 7261( 10) - 02/02/98 11:16 - [ 6] Visit: 02 Visit Priority: Visit Requirements: SAME ORIENT AS 01 AFTER 01 BY 11 D TO 17 D SCHED 90% 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 NGC3368-POS NIC1 MULTIAC NIC1-FI F160W SAMP-SEQ=STEP32,NSAMP=15, 1 DEF PAR 2-3 WITH 1 1 CUM X PATTERN=SPIRAL-DITH,NUM-POS=9, DITH-SIZE=0.3,CAMERA-FOCUS=1-2 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3368-PAR NIC2 MULTIAC NIC2-FI F160W SAMP-SEQ=STEP32,NSAMP=15 1 DEF 1 CUM X ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC3368-PAR NIC3 MULTIAC NIC3-FI F160W SAMP-SEQ=STEP32,NSAMP=15 1 DEF 2 CUM X ------------------------------------------------------------------------------------------------------------------------------------ 7261( 10) - 02/02/98 11:16 - [ 7] Visit: 03 Visit Priority: Visit Requirements: ORIENT 138D TO 150D SCHED 50% 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 NGC3368-POS NIC1 MULTIAC NIC1-FI F160W SAMP-SEQ=STEP32,NSAMP=15, 1 DEF PAR 2-3 WITH 1 2 CUM X PATTERN=SPIRAL-DITH,NUM-POS=9, DITH-SIZE=0.3,CAMERA-FOCUS=1-2 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3368-PAR NIC2 MULTIAC NIC2-FI F160W SAMP-SEQ=STEP32,NSAMP=15 1 DEF 3 CUM X ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC3368-PAR NIC3 MULTIAC NIC3-FI F160W SAMP-SEQ=STEP32,NSAMP=15 1 DEF 4 CUM X ------------------------------------------------------------------------------------------------------------------------------------ 7261( 10) - 02/02/98 11:16 - [ 8] Visit: 04 Visit Priority: Visit Requirements: SAME ORIENT AS 03 AFTER 03 BY 11 D TO 15 D SCHED 50% 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 NGC3368-POS NIC1 MULTIAC NIC1-FI F160W SAMP-SEQ=STEP32,NSAMP=15, 1 DEF PAR 2-3 WITH 1 2 CUM X PATTERN=SPIRAL-DITH,NUM-POS=9, DITH-SIZE=0.3,CAMERA-FOCUS=1-2 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3368-PAR NIC2 MULTIAC NIC2-FI F160W SAMP-SEQ=STEP32,NSAMP=15 1 DEF 3 CUM X ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC3368-PAR NIC3 MULTIAC NIC3-FI F160W SAMP-SEQ=STEP32,NSAMP=15 1 DEF 4 CUM X ------------------------------------------------------------------------------------------------------------------------------------ 7261( 10) - 02/02/98 11:16 - [ 9] Visit: 05 Visit Priority: Visit Requirements: SAME ORIENT AS 04 AFTER 04 BY 7 D TO 10 D SCHED 50% 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 NGC3368-POS NIC1 MULTIAC NIC1-FI F160W SAMP-SEQ=STEP32,NSAMP=15, 1 DEF PAR 2-3 WITH 1 2 CUM X PATTERN=SPIRAL-DITH,NUM-POS=9, DITH-SIZE=0.3,CAMERA-FOCUS=1-2 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3368-PAR NIC2 MULTIAC NIC2-FI F160W SAMP-SEQ=STEP32,NSAMP=15 1 DEF 3 CUM X ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC3368-PAR NIC3 MULTIAC NIC3-FI F160W SAMP-SEQ=STEP32,NSAMP=15 1 DEF 4 CUM X ------------------------------------------------------------------------------------------------------------------------------------ 7261( 10) - 02/02/98 11:16 - [ 10] Summary Form for Proposal 7261 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC1 NIC2 NIC3 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SAMP-SEQ=STEP32 NSAMP=15 PATTERN=SPIRAL-DITH NUM-POS=9 DITH-SIZE=0.3 CAMERA-FOCUS=1-2 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 223D TO 250D SCHED 90% PAR 2-3 WITH 1 SAME ORIENT AS 01 AFTER 01 BY 11 D TO 17 D SCHED 90% ORIENT 138D TO 150D SCHED 50% SAME ORIENT AS 03 AFTER 03 BY 11 D TO 15 D SCHED 50% SAME ORIENT AS 04 AFTER 04 BY 7 D TO 10 D SCHED 50% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC3368-POS1 NGC3368-PAR1 NGC3368-PAR2 NGC3368-POS2 NGC3368-PAR3 NGC3368-PAR4 ------------------------------------------------------------------------------------------------------------------------------------