9410( 2) - 05/08/03 10:37 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9410 Version: 2 Check-in Date: 08-May-2003 10:36:26 1.Proposal Title: The Galactic Warm Ionized Medium: the First Direct Measures of its Ionization and Abundances ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: J. Christopher Howk The Johns Hopkins University CoI: Dr. Kenneth Sembach Space Telescope Science Institute N CoI: Dr. W. Van Dyke Dixon The Johns Hopkins University N ------------------------------------------------------------------------------------ 5. Abstract The warm ionized medium (WIM) is the dominant gaseous component of the Galactic halo and represents an important sink of the radiative and kinetic energy output of stars and supernovae, though the source of its ionization remains unknown. We will use \stis\ spectroscopy of the post-AGB stars ROB 162 and ZNG 1 in the globular clusters NGC 6397 and Messier 5 to measure directly the abundances and ionization states of several key metals in the Galactic WIM. These sight lines are unique: because the two clusters also contain pulsars with published radio dispersion measurements, these are the only sight lines for which we can derive the column densities of both HI, em and ionH2, as well as the columns of multiple ionization stages of the important metals S, P, and Fe. We will use the proposed \stis\ observations with existing \fuse\ data to derive the total gas-phase abundances of S, P, and Fe for the material along these sight lines with no ionization uncertainties. We will directly measure the ionization fractions of S and P in the WIM. We will also infer the dust content of the WIM. Our study of the ionization state and dust content of the WIM will provide the best yet constraints for models of this gas. Our work will also provide the best constraint for the fundamental ``cosmic'' reference abundance (averaged over these sight lines) of the undepleted elements S and P. ------------------------------------------------------------------------------------ 9410( 2) - 05/08/03 10:37 - [ 2] Observations Description ------------------------ Hot PAGB stars are among the best probes for studying the Galactic halo; they typically have continua that rival the best QSOs and AGNs in their simplicity while being significantly brighter in the FUV than even the brightest QSO in the sky. Our observations of interstellar absorption along the two lines of sight will use the E140M echelle grating with the 0arcs2*0arcs2 aperture to cover the wavelength region ~1120-1710 Angstrom\ at ~7 km s^-1 resolution. This wavelength region includes transitions from the ions \HI, ionS2, ionS3, ionFe2, ionP2, and ionC2^*, among others. Most important among these is ionS2, since it is not observable in the FUSE bandpass. The ionH1 21-cm emission line data from the Leiden/Dwingeloo Survey of Hartmann & Burton (1998) shows the sight line towards ZNG 1 contains a narrow \HI component. We predict the ionS2 absorption towards ZNG 1 may require a moderate saturation correction for this component (<0.15 dex), although the total integrated data should require a correction of <~ 0.05 dex at the E140M resolution. We have three transitions (at 1250, 1253, and 1259 Angstrom) upon which to base such a saturation correction if necessary. Thus the ~6 km s^-1 resolution of the E140M should be sufficient for our purposes. For ionFe2 and ionP2 we have several transitions over a wide range of f Lambda values with which to derive the column densities (e.g., ionFe2 Lambda 1133, 1143, 1145, and 1608; ionP2 Lambda 1152, 1301, 1532). We believe saturation will not be a problem for these species. No \HI\ data is available for ROB 162. Table 1 lists the effective temperatures of the two stars as well as the flux of each at 1200 Angstrom. We propose to observe each star for five orbits. Given the acquisition and MAMA overheads and the visibilities for each object, we estimate total exposure times with the E140M grating of ~14 ksec and ~13 ksec for ROB 162 and ZNG 1, respectively. Using the on- line exposure time calculator and the fluxes given in Table 1 (derived from IUE and FOS observations), we estimate the observations should yield S/N>~35 near the ionS2 transitions (1250 Angstrom). Such high signal-to-noise is necessary to insure that we are truly able to derive accurate ionS2 columns. We note that ZNG 1 is an unusual PAGB star; it is the only globular cluster PAGB star to show evidence for a hot, line-driven wind similar to those seen in Population I OB stars. Our proposed observations will allow us to study this wind further. Both objects have been observed with \fuse\ over the wavelength region 905 -- 1187 Angstrom. This bandpass contains transitions of ionFe3, ionS3, ionP3, ionN2^*, ionN2^**, and ionC3. The FUSE data will compliment the proposed high-quality STIS measurements of ionFe2, ionS2, and ionP2. The STIS observations are crucial for measuring the column density of ionS2 and \HI\ along these sightlines. We will also make use of data from the WHAM HAlpha survey (Reynolds et al. 1998) where appropriate. These data may make possible studies of the ionization state of the gas as a function of velocity. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments 9410( 2) - 05/08/03 10:37 - [ 3] ------------------- ------------------------------------------------------------------------------------ 9410( 2) - 05/08/03 10:37 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M5-ZNG1 STAR, POST-AGB STAR RA=15H 18M 34.10S +/- 0.01S, J2000 V = 14.2+/-0.2 DEC=02D 4' 59.43" +/- 0.04", B-V = -0.2+/-0.2 PLATE-ID=0175 F(1200)=6+/-0.5e-13 E(B-V) = 0.03+/-0.01 Coordinate Source: HST_IMAGE Comments: Coordinates from WFPC2/PC observations including F225W/F336W/F555W data. Equivalent to those used for previous GHRS observations of this target by Heber (PID#5865). 2 NGC6397- STAR, POST-AGB STAR RA=17H 40M 38.35S +/- 0.02S, J2000 V = 13.2+/-0.2 ROB162 DEC=-53D 38' 31.6" +/- 0.3", F(1200)=8+/-0.5e-13 PLATE-ID=0688 E(B-V) = 0.18+/-0.05 Coordinate Source: GUIDE_STAR_CATALOG Comments: Coordinates same as those used previously by Napiwotzki (PID#6456). 9410( 2) - 05/08/03 10:37 - [ 5] 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 NGC6397-ROB STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2 S 162 CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC6397-ROB STIS/F ACCUM 0.2X0.2 E140M 1425 1 2640 S 162 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 21 NGC6397-ROB STIS/F ACCUM 0.2X0.2 E140M 1425 1 3100 S 162 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 22 NGC6397-ROB STIS/F ACCUM 0.2X0.2 E140M 1425 1 3100 S 162 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9410( 2) - 05/08/03 10:37 - [ 6] 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 NGC6397-ROB STIS/C ACQ F28X50L MIRROR 1 2 S 162 CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC6397-ROB STIS/F ACCUM 0.2X0.2 E140M 1425 1 2640 S 162 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 21 NGC6397-ROB STIS/F ACCUM 0.2X0.2 E140M 1425 1 3100 S 162 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9410( 2) - 05/08/03 10:37 - [ 7] Visit: 03 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: O II filter required for acquisition in order to enhance contrast of target O star over nearby G star. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 M5-ZNG1 STIS/C ACQ F28X50O MIRROR 1 90 S CD II ------------------------------------------------------------------------------------------------------------------------------------ 20 M5-ZNG1 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2050 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 21 M5-ZNG1 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2900 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 22 M5-ZNG1 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2900 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9410( 2) - 05/08/03 10:37 - [ 8] Visit: 04 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: O II filter used for acquisition in order to enhance contrast of target O star over nearby G star. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 M5-ZNG1 STIS/C ACQ F28X50O MIRROR 1 90 S CD II ------------------------------------------------------------------------------------------------------------------------------------ 20 M5-ZNG1 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2050 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 21 M5-ZNG1 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2900 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9410( 2) - 05/08/03 10:37 - [ 9] Summary Form for Proposal 9410 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 0.2X0.2 F28X50OII ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6397-ROB162 M5-ZNG1 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------