9158( 2) - 02/14/01 11:59 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9158 Version: 2 Check-in Date: 14-Feb-2001 11:59:34 1.Proposal Title: OVI Gas as an Indicator of the Diffuse Web of Baryons ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Eric Miller University of Michigan CoI: Prof. Joel Bregman University of Michigan N ------------------------------------------------------------------------------------ 5. Abstract Most of the baryons in the local universe are expected to be in a hot phase (10^5- 10^7 K), yet direct detection of this material is challenging. The most suitable way of detecting this gas in the UV is through the high-ionization OVI doublet at 1035 Angstrom, which traces collisionally ionized gas at 3x10^5 K. However, OVI can also be produced through photoionization in cooler gas (< 5x10^4 K), which is not part of the web of hot baryons. Tripp & Savage (2000) suggest that they have finally detected the hot baryonic gas in an OVI absorption system without measurable NV, although this combination occurs often in photoionized systems. We propose to resolve this ambiguity by measuring the CIV line, which for the photoionized case occurs at about the same equivalent width as the OVI line. ------------------------------------------------------------------------------------ Observations Description ------------------------ We wish to observe the CIV 1548, 1550 doublet from a z = 0.14232 absorber toward PG0953+415. This doublet will be redshifted to 1770 Angstroms; from published OVI line measurements, we expect the CIV lines to be 50 km/s or 300 Angstroms wide, and we require a 3-sigma equivalent width limit of 45 mAngstroms. These observations use a straightforward setup with the STIS/NUV- MAMA detector, the 52" x 0.5" slit, and the G230M grating centered at 1769 Angstroms. Our target (PG0953+415) appears in the Guide Star Catalog as object GSC2996-00341, therefore the position is well-known in the GSC reference frame. Finally, since we are using a fairly wide slit, no peak-up will be necessary during target acquisition. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9158( 2) - 02/14/01 11:59 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PG0953+415 GALAXY, QSO, QUASAR RA=09H 56M 52.35S +/- .2", J2000 z=0.239 V = 14.5 DEC=41D 15' 22.5" +/- .2", PLATE F(1780)=1.3+/-0.5e-14 -ID=00XW E(B-V) = 0.021 Coordinate Source: GUIDE_STAR_CATALOG 9158( 2) - 02/14/01 11:59 - [ 3] 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 PG0953+415 STIS/C ACQ F28X50L MIRROR 1 1 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 PG0953+415 STIS/N ACCUM 52X0.5 G230M 1769 1 2600 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 30 PG0953+415 STIS/N ACCUM 52X0.5 G230M 1769 3 3000 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9158( 2) - 02/14/01 11:59 - [ 4] Summary Form for Proposal 9158 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.5 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G230M ------------------------------------------------------------------------------------------------------------------------------------ Target Names PG0953+415 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1769 ------------------------------------------------------------------------------------------------------------------------------------