12978( 2) - 06-Jul-2012 14:29:35 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12978 Version: 2 Check-in Time: 06-Jul-2012 14:29:35 STScI Edit Number: 0 Title Properties of Diffuse Molecular Gas in the Magellanic Clouds ------------------------------------------------------------------------------------ Type Cycle GO 20 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Daniel E. Welty University of Chicago Y CoI: Dr. James T. Lauroesch University of Louisville Research N Foundation, Inc. CoI: Dr. Tony Wong University of Illinois at Urbana - N Champaign ------------------------------------------------------------------------------------ Abstract Studies of the interstellar medium in the lower-metallicity Magellanic Clouds explore somewhat different environmental conditions from those typically probed in our own Galactic ISM. Recent studies based on optical/UV spectra of SMC and LMC targets, for example, have revealed unexpected differences in gas-phase abundance patterns (for various atomic and molecular species) and have begun to explore the effects of differences in metallicity on the atomic-to-molecular transition and resulting molecular fraction f(H_2) -- a key aspect in the formation of molecular clouds. We propose a more detailed study of the abundances, depletions, and local physical conditions characterizing diffuse molecular material in the Magellanic Clouds, using STIS E140H and E230M spectra of two sight lines with N(H_2) > 10^20 cm^-2 (both probing the outskirts of molecular clouds seen in CO emission). The two STIS settings will include lines from various neutral and ionized species (with a range in depletion behavior), several C I multiplets, and several bands of CO and C_2. By probing and characterizing the atomic-to-molecular transition in the Magellanic Clouds, we will address key issues regarding the effects of differences in metallicity on the relationship between the atomic and molecular gas in galaxies; on cloud structure, physical conditions, and diffuse cloud chemistry; and on the composition and properties of interstellar dust. The results of this project should thus aid in the interpretation of observations of atomic and molecular material in more distant low-metallicity systems. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to obtain high-to-moderate resolution (~2.7-10 km/s), moderate-to-high S/N (~25-70) STIS spectra of interstellar absorption lines from a variety of atomic and molecular species toward 2 moderately reddened LMC and SMC stars with appreciable N(H_2). Targets: The targets are the UV-brightest stars with measured N(H_2) > 10^{20} cm^{-2} in 12978( 2) - 06-Jul-2012 14:29:35 - [ 2] each of the SMC and LMC; both lie near molecular material seen in CO emission. Sk18 lies near the prominent molecular and star-forming regions (strong radiation field?) in the SW part of the main SMC bar. Sk-68d73 lies within the edge of a CO complex, north of the center of the LMC, and shows CO absorption in FUSE spectra. Both have been observed with VLT/UVES (4.5-5.0 km/s; very high S/N) and FUSE; both have high resolution (1.2-2.0 km/s) Na~I spectra. Star & Flux & MC & MC & Location & Other Data & (1500/2050) &E(B-V)& N(H2)& & Sk18 & 6.0e-13/5.0e-13 & 0.14 & 20.6 & SMC - SW bar & FUSE, opt Sk-68d73& 4.0e-13/3.0e-13 & 0.34 & 20.1 & LMC - central & FUSE, HST, opt Wavelength settings: We will observe both stars with STIS using the E140H/1307 and E230M/1978 settings, which include numerous lines from both neutral and singly ionized species of both depleted and undepleted elements, as well as several bands of CO and C_2. Several C I multiplets (important for estimating local thermal pressures and densities) will be included. The high resolution of the E140H spectra is needed to discern the complex component structure known from the existing optical spectra and to resolve the CO rotational structure (though the optical data for CH suggest that only a single component for CO will be detectable in each sight line). While higher resolution would be desirable as well for the near-UV spectra, the NUV-MAMA dark current makes observations with E230H difficult for these faint targets. We have elected to use STIS/E230M instead of COS, to enable somewhat higher resolution and broad wavelength coverage in a single setting. Many of the lines will be detectable, but not saturated -- so that reliable column densities can be derived via simultaneous, multi-component fits to the line profiles. We will use the profiles in the higher resolution E140H spectra -- together with higher-resolution, higher-S/N optical spectra -- to define the component structures for the lines in the lower resolution (but higher S/N) E230M spectra. While the Si II 1808 line may be strong, use of component information from weaker lines (e.g., Mg II 1240) should still enable us to discern deviations from Galactic depletion patterns. Only HST can cover these UV lines. 12978( 2) - 06-Jul-2012 14:29:35 - [ 3] Grating & Setting & Range & Species E140H & 1307 & 1206-1408 & CO, C_2, C~I, C~II, O~I, Mg~II, S~II, P~II, & & & Cl~I, S~I, Cu~II, Ni~II, Si~II, Ge~II E230M & 1978 & 1574-2382 & C~I, C_2, Mg~I, Si~I, S~I, Zn~II, Al~II, Al~III, & & & Si~II, Ti~II, Cr~II, Fe~II, Ni~II Exposure times: For both stars, we aim to achieve a S/N of 25-30 per resolution element in the extracted E140H spectra near 1300\AA\ (comparable to the values obtained for our previous STIS echelle spectra of MC stars), and S/N of 60-70 for the E230M spectra near 2000 A. These S/N should enable detections (or interesting limits) for several of the stronger CO A-X bands, as well as adequate definition of the line profiles for the simultaneous fits. We will use the 0.2x0.2 arcsec slit for all exposures, in order to maximize S/N. We will take advantage of the one CVZ opportunity for Sk$-$68~73 to minimize the total orbits needed. We have used the on-line STIS exposure calculator, with IUE low-dispersion spectra, for these estimates; none of the targets violates any STIS count rate limits. Each visit (<=5 orbits) will have the following overheads: 6 min for initial guide star acquisition (4 min for re-acquisition in subsequent non-CVZ orbits); 6 min for target acquisition (no peakup, with the 0.2x0.2 slit); 8 min for each new MAMA spectroscopic exposure (1 min for subsequent identical exposures). For Sk18, each orbit will have about 51 min visibility (reduced for scheduling flexibility); for Sk-68d73 the CVZ orbits will have 96 min visibility, and the regular orbits will have 60 min visibility. The following table gives the plan for the 4 visits (19 orbits): Star &Grating &Setting & Range&Resolution& Flux &Orbits &Exposure&S/N & & & & (\kms) & & & (min) Sk18 &E140H & 1307 & 1206-1408 & 2.7 & 6.0e-13 & 5 & 226 & 30 &E230M & 1978 & 1574-2382 & 10.0 & 5.0e-13 & 5 & 226 & 68 Sk-68d73 &E140H & 1307 & 1206-1408 & 2.7 & 4.0e-13 & 4CVZ & 346 & 26 &E230M & 1978 & 1574-2382 & 10.0 & 3.0e-13 & 5 & 269 & 60 Acquisition: The stars have accurate coordinates, and are bright enough and isolated enough that a standard STIS CCD point source acquisition should be sufficient, with the time dominated by overhead. Real Time Justification ----------------------- 12978( 2) - 06-Jul-2012 14:29:35 - [ 4] Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12978( 2) - 06-Jul-2012 14:29:35 - [ 5] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SK18 EXT-STAR, GIANT O RA=00H47M50.0500S +/- 0.1", J2000 V = 12.46 +/- 0.03 F(1500)=6.0e-13 DEC=-73D08'21.10" +/- 0.1" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 2 SK-68D73 EXT-STAR, OF, WOLF RA=05H22M59.8000S +/- 0.1", J2000 V = 11.45 +/- 0.03 F(1500)=4.0e-13 RAYET - WN DEC=-68D01'46.60" +/- 0.1" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 12978( 2) - 06-Jul-2012 14:29:35 - [ 6] Visit: 01 Visit Requirements: SCHED 100% On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SK18 STIS/CCD ACQ F28X50LP MIRROR 1 1.0 S ------------------------------------------------------------------------------------------------------------------------------------ 2 SK18 STIS/FUV ACCUM 0.2X0.2 E140H 1307 1 2263 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 3 SK18 STIS/FUV ACCUM 0.2X0.2 E140H 1307 1 2821 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 4 SK18 STIS/FUV ACCUM 0.2X0.2 E140H 1307 1 2821 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 5 SK18 STIS/FUV ACCUM 0.2X0.2 E140H 1307 1 2821 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 6 SK18 STIS/FUV ACCUM 0.2X0.2 E140H 1307 1 2821 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SK18 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SK18 2 STIS/FUV ACCUM 0.2X0.2 E140H 1307 none none none none 1 N/A -MAMA SK18 3 STIS/FUV ACCUM 0.2X0.2 E140H 1307 none none none none 2 N/A -MAMA SK18 4 STIS/FUV ACCUM 0.2X0.2 E140H 1307 none none none none 3 N/A -MAMA SK18 5 STIS/FUV ACCUM 0.2X0.2 E140H 1307 none none none none 4 N/A -MAMA SK18 6 STIS/FUV ACCUM 0.2X0.2 E140H 1307 none none none none 5 N/A -MAMA 12978( 2) - 06-Jul-2012 14:29:35 - [ 7] Visit: 02 Visit Requirements: SCHED 100% On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SK18 STIS/CCD ACQ F28X50LP MIRROR 1 1.0 S ------------------------------------------------------------------------------------------------------------------------------------ 2 SK18 STIS/NUV ACCUM 0.2X0.2 E230M 1978 1 2283 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 3 SK18 STIS/NUV ACCUM 0.2X0.2 E230M 1978 1 2821 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 4 SK18 STIS/NUV ACCUM 0.2X0.2 E230M 1978 1 2821 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 5 SK18 STIS/NUV ACCUM 0.2X0.2 E230M 1978 1 2821 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 6 SK18 STIS/NUV ACCUM 0.2X0.2 E230M 1978 1 2821 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SK18 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SK18 2 STIS/NUV ACCUM 0.2X0.2 E230M 1978 none none none none 1 N/A -MAMA SK18 3 STIS/NUV ACCUM 0.2X0.2 E230M 1978 none none none none 2 N/A -MAMA SK18 4 STIS/NUV ACCUM 0.2X0.2 E230M 1978 none none none none 3 N/A -MAMA SK18 5 STIS/NUV ACCUM 0.2X0.2 E230M 1978 none none none none 4 N/A -MAMA SK18 6 STIS/NUV ACCUM 0.2X0.2 E230M 1978 none none none none 5 N/A -MAMA 12978( 2) - 06-Jul-2012 14:29:35 - [ 8] Visit: 03 Visit Requirements: CVZ On Hold Comments: Additional Comments: If necessary for scheduling, this 4-orbit CVZ visit could be split into two 2-orbit CVZ visits -- each of which would contain three 3240-sec exposures. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SK-68D73 STIS/CCD ACQ F28X50LP MIRROR 1 0.5 S ------------------------------------------------------------------------------------------------------------------------------------ 2 SK-68D73 STIS/FUV ACCUM 0.2X0.2 E140H 1307 5 4150 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SK-68D73 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SK-68D73 2 STIS/FUV ACCUM 0.2X0.2 E140H 1307 none none 1 none 1 N/A -MAMA SK-68D73 2 STIS/FUV ACCUM 0.2X0.2 E140H 1307 none none 2 none 1 N/A -MAMA SK-68D73 2 STIS/FUV ACCUM 0.2X0.2 E140H 1307 none none 3 none 2 N/A -MAMA SK-68D73 2 STIS/FUV ACCUM 0.2X0.2 E140H 1307 none none 4 none 3 N/A -MAMA SK-68D73 2 STIS/FUV ACCUM 0.2X0.2 E140H 1307 none none 5 none 4 N/A -MAMA 12978( 2) - 06-Jul-2012 14:29:35 - [ 9] Visit: 04 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SK-68D73 STIS/CCD ACQ F28X50LP MIRROR 1 0.5 S ------------------------------------------------------------------------------------------------------------------------------------ 2 SK-68D73 STIS/NUV ACCUM 0.2X0.2 E230M 1978 1 2794 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 3 SK-68D73 STIS/NUV ACCUM 0.2X0.2 E230M 1978 1 3330 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 4 SK-68D73 STIS/NUV ACCUM 0.2X0.2 E230M 1978 1 3330 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 5 SK-68D73 STIS/NUV ACCUM 0.2X0.2 E230M 1978 1 3330 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 6 SK-68D73 STIS/NUV ACCUM 0.2X0.2 E230M 1978 1 3330 S -MAMA ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SK-68D73 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SK-68D73 2 STIS/NUV ACCUM 0.2X0.2 E230M 1978 none none none none 1 N/A -MAMA SK-68D73 3 STIS/NUV ACCUM 0.2X0.2 E230M 1978 none none none none 2 N/A -MAMA SK-68D73 4 STIS/NUV ACCUM 0.2X0.2 E230M 1978 none none none none 3 N/A -MAMA SK-68D73 5 STIS/NUV ACCUM 0.2X0.2 E230M 1978 none none none none 4 N/A -MAMA SK-68D73 6 STIS/NUV ACCUM 0.2X0.2 E230M 1978 none none none none 5 N/A -MAMA 12978( 2) - 06-Jul-2012 14:29:35 - [ 10] Summary Form for Proposal 12978 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.2X0.2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ, SCHED 100% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements E140H, E230M, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names SK-68D73, SK18 ------------------------------------------------------------------------------------------------------------------------------------