! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6686,v 6.1 1996/08/01 20:10:29 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: Karla Peterson ! Phone: 410-338-4774 , E-mail: peterson@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. Proposal_Information ! Section 4 Title: On the Nature of Dust Mineralogy Proposal_Category: GO Scientific_Category: INTERSTELLAR MEDIUM Cycle: 6 Investigators PI_name: Ulysses J. Sofia PI_Institution: Villanova University CoI_Name: Jason A. Cardelli CoI_Institution: Villanova University Contact: N ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) The Lambda1240 Angstrom transitions of Mg ii have been, and remain, the primary absorption lines used for determining the abundance of interstellar Mg, an element which represents an important constituent of interstellar dust. However, there are strong indications that the f-values (oscillator strengths) commonly used to derive column densities from these lines are too small by nearly a factor of 5. This has very important implications for dust mineralogy since Mg is one of the more abundant elements in interstellar dust grains. We propose to empirically derive the Mg ii Lambda1240 Angstrom f-values through an analysis of high signal-to-noise observations of these lines in comparison with those of the strong transition doublet near Lambda2800 Angstrom for which accurate f-values are available. Since the f-values for the Lambda1240 Angstrom doublet likely cannot be measured in the laboratory and theoretical determinations are extremely complex and unreliable, empirical analysis via Cycle 6 GHRS observations offer the last opportunity in the forseeable future to determine reliable oscillator strengths for these critical transitions. The results of this project will greatly benefit the analysis and understanding of previously acquired data from Copernicus, IUE, and the GHRS as well as future data obtained with STIS. Questions ! Free format text (please update) Observing_Description: We propose to obtain Ech-A and Ech-B data in the LSA (4 samples/diode) on the Mg ii doublet at Lambda1240 Angstrom and Lambda2800 Angstrom toward gamma Ara. We use the LSA to maximize the throughput (the 20\% reduction in resolution over the SSA will have no impact on the science goals). Since our goal is to produce accurate empirical f- values for the Lambda1240 Angstrom doublet, we require very high S/N values at each diode substep for both observations. Accounting for guide star acquistion, target ACQ, and exposure overhead times, the observations require two orbits. The necessity for two orbits results from the fact that we using both side 1 and side 2 (the overhead required to side switch means that both observations cannot be obtained in a single orbit). However, to maximize the efficiency, we shall specify the observation sequence such that the side switch can be done during the unusable portion of the first orbit (the occultation). The required S/N values will be achieved through analysis of multiple grating position subexposures, each obtained with the FP-SPLIT command. We are well versed in both the development and use of the techniques for obtaining high S/N GHRS data -- Cardelli & Ebbets 1994, ``Attaining High Signal-to-Noise Data with the Goddard High Resolution Spectrograph", in Calibrating the Hubble Space Telescope, (STScI: Baltimore) and Cardelli 1995, ``High S/N Spectroscopy with the GHRS: Methods and Applications", in Calibrating HST in the Post- Costar Era (STScI: Baltimore), in press. Given that STIS will be unable to obtain such precise measures, this represents the only foreseeable opportunity to do this project. Real_Time_Justification: NONE NONE Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number:1 Target_Name:HD157246 Alternate_Names:GSC8736-03875, GAMMA-ARA, CPD-56D8225 Description:STAR,B0-B2 III-I Position:RA=17H 25M 23.63S +/-0.02S, ! Most common specification format is DEC=-56D 22' 39.5" +/-0.2", ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox:J2000 RV_or_Z: RA_PM:0.0002 ! Units are seconds of time per year Dec_PM:-0.012 ! Units are seconds of arc per year Epoch:2000.000 Annual_Parallax: Flux:V=3.4 +/- 0.10, B-V=-0.14, E(B-V)=0.06, TYPE=B1Ib ! Include at least V and B-V Comments: Coordinates are from Hipparcos INCA. This value is from the final version of the Hipparcos catalog and disagrees slightly in RA and Dec with the preliminary Hipparchos value listed in the HST Guide Star Catalog. ! 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