9150( 3) - 04/12/01 10:17 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9150 Version: 3 Check-in Date: 12-Apr-2001 10:17:04 1.Proposal Title: Understanding the Warm Ionized Medium of the Galactic Halo ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: J. Howk The Johns Hopkins University CoI: Dr. Kenneth Sembach The Johns Hopkins University N ------------------------------------------------------------------------------------ 5. Abstract We propose to obtain STIS observations of the post-AGB star von Zeipel 1128 (l = 42.5; b=+78.7; z=9.5 kpc) in the globular cluster M 3, which will be used to study the warm ionized medium (WIM) of the Galactic halo. The proposed observations, together with FUSE data, will cover key diagnostics of the warm ionized medium, namely S III, Al III, and Fe III. We will use the proposed observations to study the interactions and energy exchange between the WIM, the warm neutral medium, and the hot ionized medium along this sightline. We will do this by determining the relative dust content of the warm ionized and neutral media, by producing a census of and determining the relative ionization states of each phase along the sightline, and by investigating the relative kinematics of each of the three phases. The observations will provide the highest quality dataset yet available for studying the global connections between the warm ionized, hot ionized, and warm neutral phases of the Galactic halo. They will be a critical link between the extensive database of emission line observations of the WIM and absorption line studies of the other phases of the ISM. A by- product of this work will be a set of high-quality gas- phase abundances for the integrated Galactic halo; the relative abundances (e.g., Zn/Cr, Zn/Fe) for this sightline will be important for comparison with the high- redshift damped Lyman- Alpha absorbers. ------------------------------------------------------------------------------------ 9150( 3) - 04/12/01 10:17 - [ 2] Observations Description ------------------------ Our observations of the interstellar absorption lines along the vZ1128 sightline will use the E140M (Lambda_0 = 1425 Angstrom) and E230M(Lambda_0 = 1978 Angstrom) echelle gratings with the 0.2x0.06 aperture. We will cover the wavelength region 1120-1710 Angstrom at ~7 kms resolution, and the region 1574- 2382 Angstrom at ~10 kms resolution. The wavelength region covered by the E140M observations contain the ions SII, SIII, FeII, AlII, PII, PIII, SiII, SiIII, SiIV, NI, NV, C IV, CII, MgII, GeII, and NiII. The wavelength range covered by the E230M observations will contain SiII, ZnII, Al III, and FeII lines. The most important of these for studying the WIM are the Al III lines at 1854.7 and 1862.8 Angstrom. We expect a 3-sigma detection limit of ~6 mAngstrom, which will be sufficient to detect the above species given the HI column density of log N(HI) = 20.06 (Danly et al. 1992). Species such as MgII and SiII will be useful for connecting the properties of the WNM along this sightline with other observations of material in the low-halo of the Milky Way (see Savage & Sembach 1996). This project cannot be accomplished with FUSE data alone. Connecting the WIM absorption to the lower- and higher-ionization material requires a more extensive range of ions than can be covered by FUSE. Among the high- and low- ionization species provided by STIS, SII, NV, SiIV, and CIV are the most important. Furthermore, the E230M observations covering Al III are extremely important for reducing any systematic effects in determining the dust content of the medium. Of particular importance for our investigation are the lines of adjacent ionization states, such as SII and S III. In a few cases, notably SII, the observed lines could potentially be slightly saturated. However, for almost all of the species of interest, we will cover a range of line strengths, allowing us to use curve-of-growth techniques to estimate saturation corrections. We are proposing to observe vZ 1128 for a total of 5 orbits with each setup (requiring a total of 2 visits). With a visibility of 52 minutes for our target, this program will provide a signal-to-noise ratio of >~25 per resolution element at the wavelengths of C IV and Al III. This signal-to-noise level is needed to provide a sufficiently high-quality detection of the Al III lines (see, e.g., the Al III spectra shown for Mu Col and Rho Leo in Howk & Savage 1999) and for detailed line-shape analyses. The works of Savage et al. (1994) and Sembach & Savage (1994) are examples of line-profile analyses of various types for the sightlines to the stars HD 167756 and HD 116582, respectively, with signal-to-noise ratios similar to that proposed here. Such analyses with the higher-resolution STIS data (compared with FUSE resolution) will allow us to investigate the kinematic correspondence between the various phases of the ISM. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9150( 3) - 04/12/01 10:17 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 VZ1128 STAR, POST-AGB STAR, RA=13H 42M 16.75S +/- 0.02S, J2000 V = -145 F(1250)=3.5+/-0.3e-13 ISM, ABSORPTION LINE DEC=28D 26' 1.1" +/- 0.2", PLATE F(1850)=1.5+/-0.2e-13 SYSTEM - GALACTIC -ID=009L V = 15.03+/-0.10 Coordinate Source: GUIDE_STAR_CATALOG 9150( 3) - 04/12/01 10:17 - [ 4] Visit: 01 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 VZ1128 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 VZ1128 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 5 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 30 VZ1128 STIS/N ACCUM 0.2X0.0 E230M 1978 1 1930 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 40 VZ1128 STIS/N ACCUM 0.2X0.0 E230M 1978 6 1400 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 50 VZ1128 STIS/N ACCUM 0.2X0.0 E230M 2707 2 1400 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9150( 3) - 04/12/01 10:17 - [ 5] Visit: 02 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 VZ1128 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 VZ1128 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 5 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 30 VZ1128 STIS/F ACCUM 0.2X0.0 E140M 1425 1 1960 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 40 VZ1128 STIS/F ACCUM 0.2X0.0 E140M 1425 8 1400 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9150( 3) - 04/12/01 10:17 - [ 6] Summary Form for Proposal 9150 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 0.2X0.06 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E230M E140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names VZ1128 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1978 2707 1425 ------------------------------------------------------------------------------------------------------------------------------------