! Proposal 6434, submission 2 ! PI: A. J. S. Hamilton ! Received Tue Jun 18 21:38:09 EDT 1996 ! From: ajsh@casa.Colorado.EDU ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6434,v 4.1 1996/06/27 18:38:45 pepsa Exp $ ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6434,v 4.1 1996/06/27 18:38:45 pepsa Exp $ ! ! Refer to the HST Phase II Proposal Instructions to fill this out ! ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Sleiman ! Phone: 410-338-4753 , E-mail: sleiman@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Name of Phase I Proposal: archive-0116.hamilton.prop ! Date generated: Fri Dec 22 18:10:47 EST 1995 ! Proposal_Information ! Section 4 Title: UV Imaging of S Andromedae (SN 1885) in M31 Proposal_Category: GO Scientific_Category: INTERSTELLAR MEDIUM Cycle: 6 Investigators PI_name: A. J. S. Hamilton PI_Institution: JILA CoI_Name: Robert A. Fesen CoI_Institution: Dartmouth College Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) We propose WFPC2 UV imaging of the remnant of S Andromedae, the 1885 supernova which exploded in the bulge of M31. Optical HST images obtained by us early in Cycle 5 show the remnant as a 0''.6 diameter (= +/- 9,000 : km : s^-1) absorption spot silhouetted against the bulge of M31. Unexpectedly, the absorption appears to be mainly caused by Ca II LambdaLambda3934,3968 (H & K) and not by Fe I 3860 as earlier suspected. We propose WFPC2 F255W imaging to detect the expected 0.5--1 Msun \ of iron ejecta in the remnant through background light absorption by the Fe II resonance line complexes at 2350 and 2600 Angstrom. A detection in the UV would: (1) confirm the presence of iron in this suspected, albeit peculiar, Type Ia supernova, (2) determine the Fe II expansion velocity, and (3) provide valuable information on the mass of Fe II in this 110 year old remnant. Questions ! Free format text (please update) Observing_Description: We will image S And using the F255W 2597 +/- 197 Angstrom \ filter on WFC The WFC is preferable to FOC here because of its lower effective detector background for this extended (0''.6 diameter) faint source. The surface brightness of the center of M31 at 2600 Angstrom \ observed through the 154 : arcsec^2 aperture of IUE is 6.76 * 10^-15 : erg : s^-1 \: cm^-2 : ang^-1 (Burstein et al. 1988, ApJ, 328, 440; cf. Bertola et al. 1995, ApJ, 438, 680). We estimate that the surface brightness at the position of S And is about half this value, and we adopt 3 * 10^-15 : erg \: s^-1 : cm^-2 : ang^-1 per 154 : arcsec^2. This translates into a surface brightness per \ln Lambda of wavelength interval at S And's position of 6.6 * 10^-3 \: phot : s^-1 : cm^-2 : arcsec^ -2. Dark counts and readout noise are significant for this observation. Sky brightness is negligible (about 0.01 of the signal). To reduce the dark counts, we especially request the WF2 chip, which has the lowest dark count rate (WFPC2 Handbook, Figure 4.5; the WF2 has the highest readout noise, Table 4.3, but its lower dark count still gives it the edge). To reduce the contribution of readout noise, we propose (a) to use WFPC2 in AREA mode, (WFPC2 Handbook, Section 2.8) where counts are read out with 2 * 2 on-chip binning, and (b) to take the longest possible exposures, using a full orbit for each single exposure. At declination 41^degrees, orbital visibility is 54 minutes (Phase II Proposal Instructions Table 2). Subtracting 15 minutes of overhead time (WFPC2 Handbook, Section 2.7) leaves an exposure time of 39 minutes, which quantizes to 2300 seconds (WFPC2 Handbook, Table 2.3). We request that exposures not be split into shorter units, in spite of the increased risk of cosmic ray hits. In subsequent orbits, with 8 minutes of overhead time, the exposure time is 46 minutes, which quantizes to 2700 seconds. Below we will calculate numbers for a 2500 second exposure. In a 2500 sec exposure, cosmic rays will affect approximately 4.6 percent of pixels (WFPC2 Handbook, Section 4.2.9). At 1.8 events per second, there is a 19 percent probability of the `center' of a cosmic ray event hitting somewhere inside the 0''.6 diameter spot of S And during a 2500 second exposure. Thus cosmic rays pose a significant but not insurmountable problem. To allow adequate removal of cosmic rays, we request 3 separate exposures. To convert the above surface brightness to counts through the F255W filter, we multiply by the dimensionless efficiency \int Q T d Lambda / Lambda = 0.00078 (WFPC2 handbook Table 6.2), by the HST primary area 45238.9 : cm^2, by the binned pixel area 0''.2 * 0''.2, and by the exposure time 2500 sec. This gives 23 counts of signal per 2 * 2 binned pixel. The dark count rate with the WF2 chip is 0.0025 : cts : s^-1 : pix^-1 (WFPC2 handbook Table 4.2) which yields 25 counts per 2 * 2 binned pixel in a 2500 sec exposure. Thus the dark count rate is comparable to the signal. The noise per 2 * 2 binned pixel in each exposure comes from the signal, the dark count, and the readout noise of 5.51 electrons for the WF2 chip (again, the sky count is negligible). The noise is then ( 23 + 25 + 5.51^2 )^1/2 = 8.9 counts. The resulting S/N ratio is therefore 23/8.9 = 2.6 in each 2 * 2 binned pixel. At 0''.6 diameter, S And is extended over approximately 7 of the 2 * 2 binned pixels. Thus the overall S/N for the region of S And is 7^1/2 times the S/N for each binned pixel, yielding a S/N ratio of 6.9 from each 2500 second exposure. To remove cosmic ray hits, we request three exposures, each exposure taking one orbit. To improve flat-fielding (correction for dark counts), we request that the exposures be dithered by 10 pixels (1'') in each of the x and y directions between each exposure. Real_Time_Justification: The special requests made in the previous section are: begindescription em (1) use of the low dark count WF2 chip; em (2) 2 * 2 pixel on-chip binning; em (3) exposures should fill out a full orbit, and not be split for cosmic ray removal. enddescription Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: S-AND Alternate_Names: NGC224-SN1885,M31-BULGE Description: EXT-MEDIUM,SNR Position: ! Most common specification format is ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 RA = 0H 42M 43.04S +/- 0.01S, DEC = +41D 16' 4.49" +/- 0.1" Equinox: J2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: ! Include at least V and B-V SURF(V) = 16.60 +/- 0.1 SURF(B) = 17.63 +/- 0.1 SURF-CONT(2600) = 2.0 +/- 0.6 E-17 Comments: !Solar_System_Targets ! Section 5.2 ! Target_Number: ! Target_Name: ! Description: ! Level_1: ! Satellite of Sun ! Level_2: ! Satellite of Level_1 ! Level_3: ! Satellite of Level_2 ! Ephem_Uncert: ! Needed for REQ EPHEM CORR sp req ! Acq_Uncert: ! Needed for SAVE and USE OFFSET sp reqs ! Window: ! Flux: ! Include at least V and B-V ! Comments: ! ! !Generic_Targets ! Section 5.3 ! Target_Number: ! Target_Name: ! Description: ! Criteria: ! Flux: ! Comments: ! ! !Scan_Data ! Appendix B ! Scan_Number: ! FGS_Scan: ! Cont_or_Dwell: ! Dwell_Points: ! Dwell_Secs: ! Scan_Width: ! Scan_Length: ! Sides_Angle: ! Number_Lines: ! Scan_Rate: ! First_Line_PA: ! Scan_Frame: ! Length_Offset: ! Width_Offset: ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number: 1 Visit_Requirements: ! Section 7.1 ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling ! PCS MODE [Fine | Gyro] ! GUIDing TOLerance ! DROP TO GYRO IF NECESSARY [NO REACQuisition] ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! SCHEDulability ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN