5955( 0) - 07/18/95 18:51 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5955 Version: ********** Check-in Date: ********** 1.Proposal Title: Direct Measurement of Galaxy Distances ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Galaxies & Clusters GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: William Sparks Space Telescope Science Institute CoI: Nino Panagia Space Telescope Science Institute N CoI: Ferdinando Macchetto Space Telescope Science Institute N CoI: David Branch University of Oklahoma N CoI: Schuyler Van Dyk University of California, Berkeley N CoI: Martha Hazen Harvard College Observatory N ------------------------------------------------------------------------------------ 6. Abstract We propose to use a powerful new geometrical method for the determination of galaxy distances, based on imaging polarization of supernova light echoes. The proposal has two parts: (1) to seek new candidates for polarization observation and (2) to execute imaging polarization observations for the best candidates. The proposed method requires no secondary distance indicators, may work to distances well in excess of the distance of the Virgo cluster, and may be tied to traditional methods through galaxies hosting `standard candle' supernovae and galaxies with Cepheid distances. The measurements should enable an unambiguous resolution of the current bi-modal determination of H_0. ------------------------------------------------------------------------------------ 5955( 0) - 07/18/95 18:51 - [ 2] Observations Description ------------------------ sectionSearching for light echoes We propose to seek candidate echoes using a simple but powerful technique: namely to obtain B and V direct images using the Planetary Camera relay of WFPC-2. The defining characteristics of light echoes are (\romannumeral1) they will be very blue, B- V<0.0, and (\romannumeral2) they will be extended 0.1 < Phi_0 < 0.6 arcsec. The total luminosity of an echo is the luminosity of the original supernova times the fraction of light intercepted and scattered by a dusty medium, which is the optical depth through the flash (of order a light-month in spatial thickness) times the albedo (~ 0.6), Sparks (1994). For reasonable parameters, e.g. n_e ~ 30 cm^-3, say, the optical depth for a Type Ia is 1.3* 10^-3, resulting in an echo 7.8 mag fainter than the original supernova, and brighter than the realistic limit of around B~ 22---23 for polarization observations, see Sparks (1994). The small angular size of the echoes precludes measurement of any extension from ground based observations, and requires the use of HST. The best possible resolution is also required in order to distinguish the echo from the complex of surrounding stars typically present (recall the Early Release Observations of M100, for example). Since supernovae are very blue, Type Ia B-V ~ 0.0 at peak, Vaughan et al. (1994), and since the scattering process causes a further `bluening' of the light like 1/Lambda, the double coincidence of a very blue and slightly resolved patch of light will be an extremely strong echo candidate. Young composite stellar populations at their very bluest seldom reach B-V = -0.2, and so anything as blue or bluer than this is unlikely to be a region of star formation, Leitherer &\ Heckman (1995), ApJSupp in press. We calculate that for a V exposure of 400s and a B exposure of 1600s, both CR- SPLIT, we will obtain a S/N ~ 8 per PC pixel for an echo of total magnitude 22 (B- V=0), and diameter 0.2 arcsec. This represents typical echo parameters for feasibility for follow-on polarization observations and requires exactly one orbit per target to execute. In addition we have a ground-based program to search for light echoes, one observing run awarded. We will be using a similar color discriminant, but of course will lack the resolution of HST to assess target extent, and HST's ability to explore fainter, more distant candidates and candidates in crowded regions. The ground based program does have the advantage that a larger number of targets may be searched albeit with a lower detection threshold. The imaging polarization observations, below, can ONLY be made with HST. sectionImaging Polarization Observations We identified above the three best candidates for making HST imaging polarization observations immediately, in Cycle 5. If the search strategy for new echoes reveals promising candidates we would clearly wish to follow with imaging polarization. Therefore, we request time for additional observations of up to three more new candidates. The choice of these three new targets must await the result of the search for new candidates, and of course is conditional upon success in locating such, therefore we request that this time be awarded for Cycle 6. Note that the deadline for new Cycle 6 proposals will be too soon to defer application until then (i.e. the Cycle 5 results will not yet be available), and so given a good expectation of success (reasonable physical requirements for the production of an echo; sensible choice of targets to search) we request the Cycle 6 time in this proposal. Table 1 presents the optical continuum fluxes from the three best candidate echoes, the predicted angular sizes of the polarization ring given the assumed distance tabulated, H_0 = 50 km.s$^-1.Mpc^- 1. Calculations indicate that the level of polarization for 90^degrees scattering will be in the range 40\ nature of the scattering particles, Sparks (1994). Measurement of such levels is straightforward even for relatively faint targets. Astrometry is not a problem for these objects since all have good radio positions. The very blue nature of the echoes, combined with the need for extremely high spatial resolution and robust imaging polarization capability leads to a natural choice of the FOC/COSTAR for these observations. The observations will be exposures with the three polarizing Rochon prisms at position angles oriented 60^degrees from one another, each exposure one orbit in duration. The S/N will then be quite adequate to determine the location of polarization maximum for a source of magnitude V ~ 22 extended over a few tenths arcsec, see last column Table 1. This corresponds to of order a few counts per pixel for the larger echoes, and of order a few tens for the smallest. The higher surface brightness of the smaller echo, and therefore higher S/N compensates for its smaller size. For the larger echoes, these count rates are acceptable since both spatial binning and azimuthal averaging are used as a matter of course in polarization analyses. The FWHM of the FOC/COSTAR PSF at 3400Angstrom\ is ~ 0.04 arcsec, with a pixel size 0.014 arcsec. begintabularlccccc multicolumn6cTable 1: Historical Supernova Optical Counterpart Properties, Galaxy& SN & Assumed distance & F_Lambda & Diameter & Counts per orbit, & & (Mpc) & (erg.s^-1.cm^-2.A^-1) & (arcsec) & (FOC/COSTAR) , M83 & SN1957D & 7 & 30* 10^-18 & 0.69 & 8400 , M100 & SN1979C & 20 & 5* 10^-18 & 0.10 & 1400 , NGC6946 & SN1980K & 7 & 5* 10^-18 & 0.27 & 1400, endtabular begintabularllcl multicolumn4cTable 2: Galaxies Hosting Historical Supernovae to be Imaged, Galaxy& SN & velocity & Comments, & & (km.s^-1) & , NGC2276 & SN1962Q, SN1968V, SN1968W & 2369& , NGC2535 & SN1901A & 4135 & , NGC2608 & SN1920A & 2119 & , NGC3913 & SN1963J, SN1979B & 855 & Two reddened Type Ia, NGC4273 & SN1936A & 2378 & , M100 & SN1901B, SN1914A & 1568 & Virgo, Cepheid program, older SNe, NGC4545 & SN1940D & 2721 & , NGC4753 & SN1965I, SN1983G & 1255 & Virgo, SNe Type Ia, one reddened , IC4182 & SN1937C & 225 & Cepheid program, bright Ia , M83 & SN1983N, SN1945B & 506 & Circumstellar interaction, NGC5253 & SN1895B, SN1972E & 403 & Cepheid program, bright Ia, NGC6181 & SN1926B, SN1951I & 2158 & , endtabular Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 5955( 0) - 07/18/95 18:51 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5955( 0) - 07/18/95 18:51 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SN1957D EXT-STAR, SUPERNOVA RA=13H 34M 14.3S +/- 0.1S, DEC=- 1950.0 F(5500)=3E-17 29D 34' 24.0" +/- 1.0", PLATE- B-V=0.0 ID=02EF 2 SN1980K EXT-STAR, SUPERNOVA RA=20H 34M 26.68S +/- 0.01S, 1950.0 F(5500)=5E-18 DEC=+59D 55' 56.5" +/- 0.2", B-V=0.0 PLATE-ID=02RK 5955( 0) - 07/18/95 18:51 - [ 5] Visit: 01 Visit Requirements: 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 SN1957D FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 994S EXPAND; MAX DUR 120% 4 0 ------------------------------------------------------------------------------------------------------------------------------------ 2 SN1957D FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 994S EXPAND; MAX DUR 120% 4 60 ------------------------------------------------------------------------------------------------------------------------------------ 3 SN1957D FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 994S EXPAND; MAX DUR 105% 4 120 ------------------------------------------------------------------------------------------------------------------------------------ 4 SN1957D FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 1229S EXPAND; MAX DUR 120% 4 0 ------------------------------------------------------------------------------------------------------------------------------------ 5 SN1957D FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 1229S EXPAND; MAX DUR 120% 4 60 ------------------------------------------------------------------------------------------------------------------------------------ 6 SN1957D FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 1229S EXPAND; MAX DUR 120% 4 120 ------------------------------------------------------------------------------------------------------------------------------------ 5955( 0) - 07/18/95 18:51 - [ 6] Visit: 02 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 7 SN1980K FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 1085S 4 0 ------------------------------------------------------------------------------------------------------------------------------------ 8 SN1980K FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 1085S 4 60 ------------------------------------------------------------------------------------------------------------------------------------ 9 SN1980K FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 1085S EXPAND; MAX DUR 101% 4 120 ------------------------------------------------------------------------------------------------------------------------------------ 10 SN1980K FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 1320S EXPAND; MAX DUR 120% 4 0 ------------------------------------------------------------------------------------------------------------------------------------ 11 SN1980K FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 1320S 4 60 ------------------------------------------------------------------------------------------------------------------------------------ 12 SN1980K FOC/96 IMAGE 512x102 F342W,POL PIXEL=50x25 1 1320S 4 120 ------------------------------------------------------------------------------------------------------------------------------------ 5955( 0) - 07/18/95 18:51 - [ 7] Summary Form for Proposal 5955 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOC/96 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters PIXEL=50x25 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Galaxies & Clusters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements EXPAND; MAX DUR 120% EXPAND; MAX DUR 120% EXPAND; MAX DUR 105% EXPAND; MAX DUR 101% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F342W,POL0 F342W,POL60 F342W,POL120 ------------------------------------------------------------------------------------------------------------------------------------ Target Names SN1957D SN1980K ------------------------------------------------------------------------------------------------------------------------------------