9331( 3) - 02/13/02 17:36 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9331 Version: 3 Check-in Date: 13-Feb-2002 17:35:43 1.Proposal Title: Variable Interstellar Absorption toward HD 219188 --- Probing the Structure of an Interstellar Cloud ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Daniel Welty University of Chicago ------------------------------------------------------------------------------------ 5. Abstract Within the last 10 years, strong, narrow Na I absorption has appeared at v_SUN ~ -38 km s^-1 toward the halo star HD 219188; that absorption has continued to strengthen, by a factor 2--3, over the past three years. The line of sight appears to be moving into/through a relatively cold, quiescent intermediate velocity (IV) cloud, due to the 13 mas/year proper motion of HD 219188. We propose to monitor the continuing changes in the IV absorption toward HD 219188 over the next three years with STIS echelle spectra --- making use of the rich diagnostics provided by the UV lines of various neutral and singly ionized species to determine abundances/depletions and physical conditions (temperature, density, ionization) as functions of depth within the cloud. In addition to providing a unique view of the detailed structure of an interstellar cloud, these data will yield constraints on grain scattering parameters (from the variation of ionization with depth) and on any dependence of depletion on local density. ------------------------------------------------------------------------------------ 9331( 3) - 02/13/02 17:36 - [ 2] Observations Description ------------------------ In order to monitor changes in the strength of the intermediate velocity cloud toward HD 219188, we will observe the star once a year over the next three years, at intervals of at least 9--12 months. (Noticeable changes have been seen in the optical lines over such intervals.) Wavelength settings: We will observe HD 219188 with STIS using the E230H/NUV MAMA (two settings) and the E140H/FUV MAMA (one setting), with the 0.1X0.03 aperture. HD 219188 is (slightly) too bright for the standard 0.2X0.09 aperture, and high spectral resolution and a clean line spread function are very desirable, to measure accurate line widths and velocities. The narrowest STIS slit yields a good match to the resolution achieved in the optical spectra. The chosen wavelength settings include both strong and weak lines of multiple ionization stages of (roughly) a dozen elements (both depleted and undepleted). At the desired S/N ratio, simultaneous fits to the profiles of lines of different strength (of the same or similarly distributed species) yield well-defined, consistent component structures and accurate abundances for a range in component N(H) (e.g., Fitzpatrick & Spitzer 1997; Welty et al. 1997, 1999b). The lines of C I are particularly important for deriving cloud pressures; lines from several trace and dominant species, and from several depleted and undepleted elements, will be valuable for comparing the depth (and density) dependence of those species. Only STIS can cover these crucial UV lines at the required high spectral resolution. Grat Set Range Species E140H 1271 1170-1372 CI (many), CII, CII*, NI (3), NV (2), OI (2), MgII (2 weak), SiII (4), SiII*, SiIII, PII, SII (3), SIII, MnII (3 weak), NiII (2) E230H 2363 2224-2501 FeII (5), FeI E230H 2812 2673-2950 MgII (2), MgI Exposure times: Exposure times of about 20 min and 7.5- 9 min will yield S/N of about 31--86 for the E140H spectrum and 51--60 for the E230H spectra, respectively. With the standard overheads for acquisition and instrument setup and readout, the 3 exposures should fit in two orbits. We have used the on-line (web-based) exposure calculator for these estimates. The fluxes are from low- dispersion IUE spectra; the values are consistent as well with fluxes from archival GHRS echelle spectra. Grat Set Range Res S/N Target Flux Exp (kms) (min) E140H 1271 1170-1372 1.5 31--86 HD219188 1.4e-10 20.0 E230H 2363 2224-2501 1.5 52--60 3.5e-11 7.5 E230H 2812 2673-2950 1.5 51--59 2.8e-11 9.0 Acquisition: From inspection of the guide star catalogue and the digitized sky survey plates, HD 219188 is the brightest source within 5 arcsec of the nominal position. (And we have successfully observed it from the ground.) A standard CCD point source acquisition should be sufficient, with the time dominated by overhead. Since we are using the 0.1x0.03 slit, a two-stage acq/peakup is needed --- first using the 0.2x0.09 slit and G430M, then using the 0.1x0.03 slit and G430M. The peakup will be repeated at the start of the second orbit, prior to switching to the NUV-MAMA. This procedure was successful for the cycle 10 observations. Real Time Justification ----------------------- In order to monitor changes in the strength of the intermediate velocity cloud toward HD 219188, we will observe the star once a year over the next three years, at intervals of at least 9--12 months. (Noticeable changes have been seen in the optical lines over such intervals.) The visit-level constraint (AFTER 30-JUN-2002) assures that the cycle 11 data will be obtained at least 9 months after the cycle 10 data. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9331( 3) - 02/13/02 17:36 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD219188 STAR, B0-B2 III-I, ISM, RA=23H 14M 0.53S +/- 0.05S, J2000 V = 6.93 Intermediate Velocity DEC=+04D 59' 49.6" +/- 0.1" B-V = -0.18 Cloud E(B-V) = 0.06 F(1271)=1.4+/-0.1e-10 F(2363)=3.5+/-0.2e-11 F(2812)=2.8+/-0.2e-11 Coordinate Source: HIPPARCOS_INPUT_CATALOGUE Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.0 0.0 0.0 9331( 3) - 02/13/02 17:36 - [ 4] Visit: 01 Visit Priority: Visit Requirements: AFTER 30-JUN-2002 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 HD219188 STIS/C ACQ F25ND3 MIRROR ACQTYPE=POINT 1 1 S CD ------------------------------------------------------------------------------------------------------------------------------------ 2 HD219188 STIS/C ACQ/PEA 0.2X0.0 G430M 4194 1 3 S CD K 9 ------------------------------------------------------------------------------------------------------------------------------------ 3 HD219188 STIS/C ACQ/PEA 0.1X0.0 G430M 4194 1 5 S CD K 3 ------------------------------------------------------------------------------------------------------------------------------------ 10 HD219188 STIS/F ACCUM 0.1X0.0 E140H 1271 1 20 M UV-MAM 3 A ------------------------------------------------------------------------------------------------------------------------------------ 12 HD219188 STIS/C ACQ/PEA 0.2X0.0 G430M 4194 1 3 S CD K 9 ------------------------------------------------------------------------------------------------------------------------------------ 13 HD219188 STIS/C ACQ/PEA 0.1X0.0 G430M 4194 1 5 S CD K 3 ------------------------------------------------------------------------------------------------------------------------------------ 40 HD219188 STIS/N ACCUM 0.1X0.0 E230H 2363 1 7.5 M UV-MAM 3 A ------------------------------------------------------------------------------------------------------------------------------------ 50 HD219188 STIS/N ACCUM 0.1X0.0 E230H 2812 1 9 M UV-MAM 3 A ------------------------------------------------------------------------------------------------------------------------------------ 9331( 3) - 02/13/02 17:36 - [ 5] Summary Form for Proposal 9331 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F25ND3 0.2X0.09 0.1X0.03 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 30-JUN-2002 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G430M E140H E230H ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD219188 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4194 1271 2363 2812 ------------------------------------------------------------------------------------------------------------------------------------