! Proposal 5887, submission 1 ! PI: Katherine Roth ! Received Wed Mar 8 03:01:38 EST 1995 ! From: kroth@stsci.edu ! Hubble Space Telescope Cycle 5 (1995) Phase II Proposal Template ! $Id: 5887,v 7.1 1995/05/10 18:25:36 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: Alice Berman ! Phone: 410 338-4462 , E-mail: aberman@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Proposal_Information ! Section 4 Title: The Depletion Behavior of Chromium Relative to Zinc in the Magellanic Clouds Proposal_Category: GO Scientific_Category: Interstellar Medium Cycle: 5 Investigators PI_name: Katherine Roth PI_Institution: Space Telescope Science Institute CoI_Name: J. Chris Blades CoI_Institution: Space Telescope Science Institute Contact: ! Y or N (designate at most one contact) CoI_Name: Claus Leitherer CoI_Institution: Space Telescope Science Institute Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) Observations of singly ionized zinc and chromium in the ISM primarily trace the depletion characteristics of metals in H I gas. Zn II does not deplete onto dust grains, and can provide an accurate metallicity measure. Conversely, Cr II is readily removed from the gas phase, and the Cr/Zn column density ratio provides a sensitive measure of dust destruction and contributing physical conditions within the absorbing material. In this proposal we are seeking time to use the GHRS ECH-B to measure the Cr/Zn ratio in Magellanic Cloud gas using four background sources. We will use these measurements to help interpret values obtained in high redshift (0.6 <= z <= 3) damped Lyman-Alpha systems which to date have only been compared to published Galactic values toward two stars, namely Zeta Ophiuchi and Chi Persei. From an archive study of 10 Galactic stars we have just finished, we have discovered that these 2 stars are not typical: rather, there is a much larger spread in the Cr/Zn ratio than previously thought, thus complicating but not invalidating comparison with high- redshift systems. Our proposed determination of Cr/Zn in two external galaxies known to have different extinction curves than the Milky Way will be used to construct a valid extragalactic baseline against which the Galactic and QSO observations can be compared. Questions ! Free format text (please update) Observing_Description: We are proposing ECH-B observations through the small science aperture of Zn II Lambda 2026 and Mg I Lambda 2026 in order 28 and of Cr II LambdaLambda 2056,2062 and Zn II Lambda 2063 in order 27. We have calculated exposure times based on the values found in the GHRS Instrument Handbook 5.0 (Figures 8-4 and 8-6, Table 8-4), and Figure 5 of GHRS Instrument Science Report \#62. For ECH-B-28, we use a sensitivity S_lambda=3.04*10^11, mLambda=56750 for a blaze function sensitivity of 0.76, and a post-costar SSA/LSA transmission factor of 0.575 to derive an effective sensitivity of S_lambda^ eff=1.328times10^11 counts s^-1 diode^-1 (erg s^-1 cm^-2 AA^-1)^-1. For ECH-B-27 these values are 4.29times10^11, 55680, 0.74, and 0.575 for an S_lambda^ eff=1.825times10^11. In all calculations we have assumed an average D2 dark count rate of 0.011 counts diode^-1 s^-1. vspace*0.1in For our LMC targets, one of us (CL) has measured accurate fluxes at Lambda 2050 based on low-resolution FOS spectra of 7times10^-13 and 2.3times10^-13 erg s^-1 cm^-2 AA^ -1 for Sk -69 175 and Sk -68 33, respectively. These spectra indicate no problems due to narrow stellar line contamination, and also reveal interstellar Zn II and Cr II absorption is present. Images obtained of these fields verify that these are single stars, and we expect no difficulty with the standard 11+8 minute SSA target acquisition. Our SMC stars were selected for similar reasons, and we have estimated the flux at Lambda 2050 based on the spectral types (Garmany et al.\ 1987, AJ, 93, 1070) to be 4times10^-13 erg s^-1 cm^-2 AA^-1. We have calculated exposure times and orbits based on the requirement that we achieve a S/N ratio diode^-1 of 15. At a resolution of R=80,000 (Delta v=3.75 km s^-1 diode^-1, DeltaLambda=0.026 Angstrom\ diode^- 1), this would allow for a 2Sigma detection limit of 3.5 mAngstrom in one diode. For comparison, the S/N per diode in Figure 2 ranges from ~ 20 to >= 100. All orbits assumed a target visibility of 59 minutes (96 minutes target visibility in the CVZ), a 12 minute guide star acquisition and 6 minute reacquisition (no reacquisition in our CVZ observation) an 11+8 minute SSA target acquisition and peakup, a 3 minute SPYBAL per grating setting (2 per object), and 20-24 minute FPSPLITs with a 4 minute overhead. In the table below we summarize the resulting observation parameters. vspace*0.2in begincenter begintabularlccccccc multicolumn8cObservations Summary, ,-0.1in underlineStar & multicolumn3c *0.3inECH-B-28 *0.3in& multicolumn3c *0.3inECH-B-27 *0.3in& underlineOrbits, & Counts^ a & Delta t^ b & S/N & Counts^ a & Delta t^ b & S/N &, ,-0.1in Sk - 69 175 & 0.093 & 60 & 17 & 0.128 & 40 & 17 & 3, Sk -68 73 & 0.031 & 160 & 15 & 0.042 & 120 & 15 & hspace*0.065in4^ c, Sk 157 & 0.053 & 88 & 15 & 0.073 & 64 & 16 & 4, Sk 94 & 0.053 & 88 & 15 & 0.073 & 64 & 16 & 4, multicolumn8l a: counts diode^-1 s^-1, multicolumn8l b: exposure time (minutes), multicolumn8l c: CVZ orbits, endtabular endcenter Real_Time_Justification: We have flagged the LMC star Sk -68 73 for continuous viewing zone observations. The LMC and SMC provide only limited CVZ opportunities; for example, there were only 3 CVZ opportunities at this position last year for a total of 69 hours. For this reason we are not requesting CVZ status for all our targets. However, the measured FOS flux at 2050 Angstrom\ for this object (2.3times10^-13) is sufficiently faint that we feel the extra efficiency afforded by the CVZ is necessary in this case. We have 4 nights observing time with the CTIO 4-m echelle spectrograph in November of this year with which we will obtain high signal-to-noise spectra of Ti II and Ca II of several stars in both the Large and Small Magellanic Clouds at comparable resolution to the proposed HST GHRS observations. Ti II and Ca II are both also heavily depleted onto dust grains in H I regions, although Ca II is additionally complicated by recombination of Ca III in hotter material (T >= 10,000 K). By comparing the relative depletions of these ions to Zn II and Cr II we can better understand the physical processes and dust destruction mechanisms within the intervening gas. Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: Sk-68D73 Alternate_Names: HDE269445 Description: EXT-MEDIUM, HI Cloud, High Velocity Cloud, Halo, IGM; EXT-STAR, Wolf Rayet Position: RA = 05H 22M 59.87S +/- 0.1S, DEC = -68D 01' 46.7" +/- 0.1", PLATE-ID=05ZW ! Most common specification format is ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: 2000 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: V = 11.46 B-V = +0.27 ! Include at least V and B-V F(2050) = 2.3 E-13 E(B-V) = 0.23 F(5160) = 5.4 E-12 Comments: spectral type Ofpe/WN9 Target_Number: 2 Target_Name: Sk-69D175 Alternate_Names: HDE269687 Description: EXT-MEDIUM, HI Cloud, High Velocity Cloud, Halo, IGM; EXT-STAR, Wolf Rayet Position: RA = 05H 31M 25.66S +/- 0.1S, DEC = -69D 05' 38.6" +/- 0.1", PLATE-ID=05ZW ! Most common specification format is ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: 2000 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: V = 11.90 B-V = -0.07 ! Include at least V and B-V F(2050) = 7.0 E-13 Comments: spectral type Ofpe/WN9 Target_Number: 3 Target_Name: Sk157 Alternate_Names: AV486 Description: EXT-MEDIUM, HI Cloud, High Velocity Cloud, Halo, IGM; EXT-STAR, Wolf Rayet Position: RA = 01H 15M 51.91S +/- 0.1S, DEC = -73D 20' 48.7" +/- 0.1",PLATE-ID=06B1 ! Most common specification format is ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: 2000 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: V = 12.12 B-V = -0.16 ! Include at least V and B-V F(2050) = 4 E-13 Comments: spectral type O9.5III Target_Number: 4 Target_Name: Sk94 Alternate_Names: AV264 Description: EXT-MEDIUM, HI Cloud, High Velocity Cloud, Halo, IGM; EXT-STAR, Wolf Rayet Position: RA = 01H 01M 07.72S +/- 0.1S, DEC = -71D 59' 58.6" +/- 0.1",PLATE-ID=06B1 ! Most common specification format is ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: 2000 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: V = 12.36 B-V = -0.15 ! Include at least V and B-V F(2050) = 4 E-13 Comments: spectral type B2Iab ! 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: CVZ ! 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 ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN