! File: 2370C.PROP ! Database: PEPDB ! Date: 17-FEB-1994:05:37:02 coverpage: title_1: GLOBULAR CLUSTER SYSTEMS IN THE COMA SUPERGIANT ELLIPTICALS sci_cat: GALAXIES & CLUSTERS sci_subcat: DISTANCE SCALE proposal_for: GO pi_title: DR. pi_fname: WILLIAM pi_mi: E. pi_lname: HARRIS pi_inst: MCMASTER UNIVERSITY pi_country: CANADA pi_phone: 416-525-9140 keywords_1: GLOBULAR CLUSTERS, ELLIPTICAL GALAXIES, HALO, DISTANCE keywords_2: SCALE hours_pri: 11.60 num_pri: 2 wf_pc: X pi_position: PROFESSOR off_fname: P. off_mi: G. off_lname: SUTHERLAND off_title: CHAIRMAN off_inst: DEPARTMENT OF PHYSICS off_addr_1: MCMASTER UNIVERSITY off_city: HAMILTON off_state: ON off_zip: L8S4M1 off_country: CANADA ! end of coverpage abstract: line_1: We propose to use the Wide Field Camera in the V and I bands for imaging of line_2: the globular cluster systems around NGC 4874 and NGC 4889, the two central line_3: supergiant ellipticals in the Coma Cluster.Photometry of the globular clusters line_4: around these galaxies will accomplish three principal scientific goals: 1) We line_5: will obtain the globular cluster luminosity function (number of clusters per line_6: unit magnitude) to approximately Mv~-6.6, fully one magnitude fainter than LF line_7: peak frequency or "turnover." Fitting the LFs directly to those from the Local line_8: Group galaxies and the giant Virgo ellipticals in a single step will then yield line_9: a pure Population II distance calibration for Coma with an internal uncertainty line_10: of + 1-0.2 mag and a clean determination of HO, completely independent of the line_11: entire chain of Population I standard candles.2)We will obtain the total line_12: cluster populations (specific frequencies) in each galaxy, thus sampling the line_13: formation efficiency of globular clusters in a much richer and denser galaxy line_14: environment than any accessible from ground-based imaging.3) We will obtain the line_15: radial distribution and color (metallicity) gradient within each cluster line_16: system. By comparing these with the same quantities for the underlying halo line_17: light of the galaxies, we will determine how distinct these two components of line_18: the halo are in their structure and chemical enrichment history. ! ! end of abstract general_form_proposers: lname: HARRIS fname: WILLIAM title: P.I. mi: E. inst: MCMASTER UNIVERSITY country: CANADA ! lname: HANES fname: DAVID mi: A. inst: QUEEN'S UNIVERSITY country: CANADA ! lname: HESSER fname: JAMES mi: E. inst: DOMINION ASTROPHYSICAL OBSERVATORY country: CANADA ! lname: PRITCHET fname: CHRISTOPHER mi: J. inst: VICTORIA, UNIVERSITY OF country: CANADA ! lname: HARRIS fname: HUGH mi: C. inst: US NAVAL OBSERVATORY country: USA ! ! end of general_form_proposers block general_form_text: question: 3 section: 1 line_1: For each of the primary targets NGC 4874 and 4889, line_2: we have identified one WFC field which places the line_3: galaxy center toward one edge of the frame and avoids any line_4: bright stars that would saturate in 2500 sec. line_5: Our primary filter for the deep GCLF study and line_6: the radial distribution will be 555W = V, line_7: which gives the best compromise for photometric S/N, line_8: reproducibility of a standard magnitude system, line_9: and contrast between the globular clusters and the line_10: underlying (redder) galaxy light. line_11: Our second filter for color index measurement is line_12: 791W = I to maximize the sensitivity to GC line_13: metallicity variations at a given S/N, and will line_14: allow strict comparability with GTO observations line_15: of other globular cluster systems. line_16: We choose the WFC for the following reasons: line_17: (i) A 2.6-arcmin field is large enough that the outer line_18: parts of it will provide its own background, thus line_19: allowing the radial structure and composition line_20: gradients in the GCSs to be studied on a single frame. line_21: For each of the two fields (NGC 4874 line_22: and 4889), the galaxy center will be line_23: positioned such that the farthest corners of ! question: 3 section: 2 line_1: the field will be 2.4 arcmin from galaxy center, or line_3: 70 kpc in linear scale. At this distance, the line_4: projected number density of globular clusters is line_5: 30 times lower than in the central regions, so that line_6: the radial distribution of the GCS can be derived line_7: for the most important (r < 30 kpc) region. line_8: (ii) Even with the WFC, image crowding will not be line_9: important for either galaxy even in the inner regions. line_10: Since Coma is 5.6 times more distant than Virgo, line_11: the projected number density of globular clusters around the line_12: Coma galaxies will be 30 times higher line_13: for the same limiting absolute magnitude. line_14: Scaling from the GCSs around the Virgo giants line_15: M87 and M49, we find that the maximum surface density line_16: of images around NGC 4874 will be sigma(r) line_17: = 1.5--2.0 images/arcsec**2 brighter than V=29 line_18: for r < 7" from galaxy center (in these giant ellipticals, line_19: sigma(r) does not increase all the line_20: way in to the center but rather is line_21: observed to level off inwards of r=3 kpc. line_22: These estimates apply if NGC 4874 has an line_23: anomalously populous GCS like M87; if the system is ! question: 3 section: 3 line_1: more normal, then the density will be 2--3 times lower. line_2: Even the extreme upper limit corresponds to 50 pixels/image, line_3: and since the FWHM for starlike images is 1 pixel, line_4: the frames will be relatively 'uncrowded' even line_5: fairly close to galaxy center. ! question: 4 section: 1 line_1: (No relevant Phase II information in this item) ! question: 5 section: 1 line_1: The V data will be primarily for the deep GCLF and the line_2: radial distribution, while the I band will be used line_3: to obtain color indices (hence metallicities) line_4: for the brighter clusters. line_5: Our exposure times in V and I are calculated line_6: on the basis of the following: line_7: Given (S/N) = (r t) / [(r t) + n(eff) (s t + R**2)]**0.5 line_8: where r = count rate from star image (e-/sec) line_9: and s = count rate from background (e-/sec/pixel) line_10: and t = integration time (sec), R = read noise line_11: and n(eff) = no. of pixels per image (3.2 in V, 5.0 in I). line_12: Our goal is S/N of about 10 in V at the turnover level line_13: of the GCLF, which is expected to be at V=27.7 line_14: and (V-I) =1.0. The parameters listed above then line_15: yield S/N = 5.0 (V) in 2500sec, 3 (I) in 2400 sec line_16: for globular cluster images just at the turnover, line_17: or S/N = 11 (V) in 5 x 2500 sec and S/N = 4.3 (I) line_18: in 3 x 2400 sec. The I-band data will effectively reach line_19: about one magnitude shallower than V, line_20: but our intention is to use them primarily for line_21: the color-distribution program and therefore they need not line_22: be ultra-deep. For clusters brighter than V=27 line_23: (I=26, or <1 mag above the turnover), the ! question: 5 section: 2 line_1: measured V-I indices will have internal uncertainties of at line_3: most 0.10 mag, which is sufficient to trace out the line_4: intrinsic color distribution and metallicity line_5: gradient within the cluster system (the line_6: range between the metal-poorest and metal-richest line_7: globular clusters is delta(V-I)=0.5 mag). line_8: The effective useful limit of the photometry line_9: will be V=29, more than one magnitude past the turnover. line_10: Note that in practice, the actual S/N will vary slightly line_11: across the frame, since the background changes continuously line_12: with radius from the galaxy center and its line_13: contribution dominates over the readnoise in line_14: most of the field. The numbers here assume an line_15: `average' radial location s(V)=22 mag/arcsec**2, line_16: which corresponds to 3-4 times dark sky. line_17: For NGC 4874 we request exposure sequences of line_18: (6 x 2500) sec (V) and (3 x 2400) sec (I). line_19: For NGC 4889 we request exposure sequences of line_20: (5 x 2500) sec (V) and (3 x 2400) sec (I), for a line_21: grand total of 11.6 hours of exposure, plus line_22: overhead spacecraft time (quite small in this case). line_23: Our maximum TAC-assigned spacecraft time is 13.3 hours. ! question: 6 section: 1 line_1: No special requirements for scheduling or calibration ! question: 7 section: 1 line_1: Final absolute calibration of the pseudo-V,I data line_2: will be carried out by ground-based CCD imaging line_3: of the program fields, through copies line_4: of the HST broadband filters that we will have line_5: made for the purpose. The sequence of line_6: deep V exposures will allow us to filter out cosmic-ray line_7: events and to correctly identify all true starlike line_8: images on the frames (the catalog of images line_9: detected on the V frames can also be applied line_10: to the pair of I frames as a crosscheck). line_11: The subsequent photometry (including line_12: sample incompleteness and background noise line_13: as a function of location on line_14: the frame; characterizing stellar and nonstellar images) line_15: will require only the application of the codes line_16: that we already have in place and line_17: their modifications to apply specifically to the WFC CCDs. ! question: 8 section: 1 line_1: No additional requests ! question: 9 section: 1 line_1: No previous HST time ! question: 10 section: 1 line_1: Our home institutions will supply all necessary line_2: computing facilities and reduction software line_3: (IRAF, DAOPHOT and their updates, on Sun and VAX line_4: machines). ! !end of general form text general_form_address: lname: HARRIS fname: WILLIAM mi: E. title: DR. category: PI addr_1: PHYSICS DEPARTMENT addr_2: MCMASTER UNIVERSITY city: HAMILTON L8S 4M1 state: ON country: CANADA ! ! end of general_form_address records fixed_targets: targnum: 1 name_1: NGC4874-NORTH descr_1: GALAXY; ELLIPTICAL GALAXY pos_1: RA = 12H 59M 36.4S +/- 2.0", pos_2: DEC = +27D 58' 20" +/- 2.0" equinox: J2000 rv_or_z: V=+7184 comment_1: V,I PHOTOMETRY OF GLOBULAR CLUSTERS comment_2: IN HALO OF E GALAXY fluxnum_1: 1 fluxval_1: V = 27.7 +/- 0.1 fluxnum_2: 2 fluxval_2: SURF-BKG(V)=22.0 +/- 2.0 ! targnum: 2 name_1: NGC4889-WEST descr_1: GALAXY; ELLIPTICAL GALAXY pos_1: RA = 13H 00M 4.1S +/- 2.0", pos_2: DEC = +27D 58' 20" +/- 2.0" equinox: J2000 rv_or_z: V=+6512 comment_1: V,I PHOTOMETRY OF GLOBULAR CLUSTERS comment_2: IN HALO OF E GALAXY fluxnum_1: 1 fluxval_1: V = 27.7 +/- 0.1 fluxnum_2: 2 fluxval_2: SURF-BKG(V)=22.0 +/- 2.0 ! ! end of fixed targets ! No solar system records found ! No generic target records found exposure_logsheet: linenum: 1.000 targname: NGC4874-NORTH config: WFC opmode: IMAGE aperture: ALL sp_element: F555W num_exp: 6 time_per_exp: 2500S s_to_n: 5 fluxnum_1: 1 fluxnum_2: 2 priority: 1 param_1: CLOCKS=YES req_1: DARK TIME; req_2: GUIDE TOL 0.020"; req_3: POS TARG 0.0, 0.0 ! linenum: 2.000 targname: ^ config: ^ opmode: ^ aperture: ^ sp_element: F791W num_exp: 3 time_per_exp: 2400S s_to_n: 3 fluxnum_1: 1 fluxnum_2: 2 priority: 3 param_1: CLOCKS=YES req_1: DARK TIME; req_2: GUIDE TOL 0.020"; req_3: SAME POS FOR 2 AS 1 ! linenum: 3.000 targname: NGC4889-WEST config: ^ opmode: ^ aperture: ^ sp_element: F555W num_exp: 5 time_per_exp: 2500S s_to_n: 5 fluxnum_1: 1 fluxnum_2: 2 priority: 2 param_1: CLOCKS=YES req_1: DARK TIME; req_2: GUIDE TOL 0.020"; req_3: POS TARG 0.0, 0.0; req_4: ORIENT 45D +/- 20D; req_5: SEQ 3-4 NO GAP comment_1: X-AXIS OFFSET OF 45D ASSUMED comment_2: ANY ORIENTATION +/- 90D OR +/- 180D comment_3: FROM SPECIFIED VALUE IS ACCEPTABLE ! linenum: 4.000 targname: ^ config: ^ opmode: ^ aperture: ^ sp_element: F791W num_exp: 3 time_per_exp: 2400S s_to_n: 3 fluxnum_1: 1 fluxnum_2: 2 priority: 3 param_1: PURGE=YES, param_2: CLOCKS=YES req_1: DARK TIME; req_2: GUIDE TOL 0.020"; req_3: SAME POS FOR 4 AS 3; req_4: SAME ORIENT FOR 4 AS 3 ! ! end of exposure logsheet ! No scan data records found