9418( 3) - 02/20/03 06:36 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9418 Version: 3 Check-in Date: 20-Feb-2003 06:35:27 1.Proposal Title: The Sight-line toward PHL 1811: A Rare Chance to Probe a Lyman Limit System at Very Low Redshift ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Edward Jenkins Princeton University CoI: Dr. Todd Tripp Princeton University Observatory N CoI: Dr. David Bowen Princeton University Observatory N CoI: Dr. Kenneth Sembach Space Telescope Science Institute N ------------------------------------------------------------------------------------ 5. Abstract The sight-line to an extraordinarily bright quasar, PHL 1811, penetrates four gas systems at z(abs) < z(em) = 0.192. One of them is a Lyman limit system (LLS: N(H I) > 10^17.5 cm^-2) at z(abs) = 0.08088 which is especially well suited for a study of atomic abundances, local density, and ionization state. We propose to obtain a STIS E140M spectrum with moderately good S/N so that we can measure absorption features that will permit the determinations of overall metallicity of the system, its nucleosynthetic ratios Alpha/Fe and Alpha/N, the fractions and kinematics of ionized gas, and the amount of gas-phase element depletions caused by dust. The LLS should be close enough for us to identify an associated galaxy, but to be sure we do not miss one very close to the quasar in projection, we plan to supplement our spectrum with a short- exposure ACS HRC image of the quasar's immediate surroundings. ------------------------------------------------------------------------------------ 9418( 3) - 02/20/03 06:36 - [ 2] Observations Description ------------------------ Table 2: Useful Transitions for the Lyman Limit System at z=0.08088 Species lambda lambda P Comments (lab) (obs) Fe II 1144.94 1237.54 9.59 STIS sens. about 2/3 peak value SiII 1190.42 1286.70 10.09 Possible interference from S III, if the gas is highly ionized in some places Si II 1193.29 1289.80 10.39 N I 1199.55 1296.57 10.34 N I 1200.22 1297.30 10.16 N I 1200.71 1297.82 9.86 SiIII 1206.50 1304.08 10.86 very sens. indicator of H II gas, but might be blocked by Gal. Si II 1304.37 H I 1215.67 1313.99 14.7 Ly-Alpha; visible damping wings would indicate that log N(H I) >= 18.0 Si II 1260.42 1362.37 10.72 O I 1302.17 1407.49 10.75 Si II 1304.27 1409.87 9.61 On top of the quasar's Ly-Alpha emission peak, so increased sens. might compensate for the lower than usual P value C II 1334.53 1442.47 10.79 C II* 1335.71 1443.74 10.79 Useful for indicating the local density of hydrogen and electrons Si IV 1393.76 1484.86 10.41 Good for assessing the ionization by energetic radiation or high temperatures Si IV 1402.71 1516.22 10.11 STIS sens. about 2/3 peak value Si II 1526.71 1650.19 9.85 STIS sens. about 1/4 peak value C IV 1548.20 1673.42 11.03 Supplements Si IV for indicating high ioniz. C IV 1550.77 1676.20 10.73 but STIS sens. only about 1/5 peak value We propose to spend 13 orbits of HST time to obtain a STIS E140M spectrum of PHL 1811. We used the STIS ETC to estimate the target's flux in the relevant wavelength region based on scaling our measured flux at 1180A obtained by FUSE. For a 33, 000 s integration time we should obtain S/N = 10 per resolution element at around 1200A and about 20 or better for 1300A < Lambda < 1550A. With a velocity resolution of 7 km s^-1, we can measure with satisfactory accuracy lines with an equivalent width W_Lambda = 20 mA (and detect somewhat weaker lines). It is important to know which lines in the STIS spectrum should have W_Lambda > 20 mA but are not likely to be strongly saturated (e.g., Tau_0 > 3 for b = 10 km s^-1). From the approximate equivalent widths of O I (two blended lines at Lambda989) and C II Lambda1036 at z = 0.80888 in our FUSE spectrum, we estimate that transitions in the interval 9.8 < P < 10.8 will satisfy these criteria, where P=(A/H)+\log f*Lambda + 12.0 and (A/H) is the solar abundance of the element relative to hydrogen. The lines are listed in Table 2. As the table shows, for the LLS we will be able to obtain useful measurements of 3 N I and 4 (or possibly even 5) Si II lines, all of which have a significant enough spread in strength to permit a determination of a column density, even if the lines are partly saturated. We can use the behavior of these lines to give us guidance on the interpretation of single lines of other species, such as C II, C II* (C II in an excited fine-structure level -- an excellent indicator of local density), O I, and Fe II. We expect the uncertainty in log N(H I) to be about 0.5 dex at worst, since we can measure a lower limit (or actual value) for the Lyman limit opacity (in a high S/N FUSE spectrum) and, in the STIS spectrum, obtain a measurement or upper limit for damping wings which might start to be evident at N(H I) > 10^18 cm^-2 at Ly-Alpha (such wings are not visible at Ly-Beta, but we know that the main absorption profile does not extend beyond about 80 km s^-1 from the line's center). An even more accurate determination of the hydrogen column density might arise if we are able to sense that the highest Lyman series lines in the FUSE spectrum are starting to become unsaturated. For our 1-orbit visit to image the immediate surroundings of PHL 1811 with the ACS HRC in the SDSS r band (F625W), our exposure lasting 2280 seconds should give S/N = 6.0 for a galaxy with a surface brightness as faint as the central part of an LSB galaxy (B=23.2, mag arc-sec^-2) that we identified in another HST observing program as the source of a low-redshift DLA (Bowen, Tripp, & Jenkins 2001) This exposure will be taken in the coronographic mode so that the quasar will not saturate the CCD. Also, we wish to supress the scattered light from PHL1811 so that a faint galaxy can be detected. An orientation that excludes U3 pointing at a position angle = 220 +/- 25 degrees is intended to keep the occulting 9418( 3) - 02/20/03 06:36 - [ 3] finger from blocking a galaxy offset from PHL1811 by about 8 arc sec in a direction PA = 205 degrees. Sources of information about fluxes for the target: UV fluxes from G140L STIS spectrum obtained by HST GO program ID=9181 Visible wavelength information from Leighly, et al (2001: Astron. J., 121, 2889). Magnitudes as published, fluxes as shown in their Fig. 2. except that fluxes "rereddened" by a factor 1.12 and divided by (1+z)^2 Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9418( 3) - 02/20/03 06:36 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PHL1811 GALAXY, QUASAR RA=21H 55M 1.53S +/- 0.3", DEC=- J2000 Z = V = 13.9+/-0.4 09D 22' 24.4" +/- 0.3", PLATE- 0.192 B-V = 0.0+/-0.4 ID=044F E(B-V) = 0.046 F-CONT(1300)=50+/-20e-15 F-LINE(1460)=60+/-25e-15 W-LINE(1460)=90+/-30 F-CONT(6166)=1.9+/-0.8e-15 F-LINE(7821)=13+/-5e-15 W-LINE(7821)=50+/-15 Coordinate Source: GUIDE_STAR_CATALOG Comments: R = 13.9+/-0.4 9418( 3) - 02/20/03 06:36 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.265 Coordinate_Frame POS-TARG Pattern_Orient 20.67 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 9418( 3) - 02/20/03 06:36 - [ 6] 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 PHL1811 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2.0 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 PHL1811 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 4.0 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 30 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 1800 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 40 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 2760 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 50 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 2760 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9418( 3) - 02/20/03 06:36 - [ 7] 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 PHL1811 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2.0 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 PHL1811 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 4.0 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 30 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 1800 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 40 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 2760 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 50 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 2760 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9418( 3) - 02/20/03 06:36 - [ 8] Visit: 03 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 PHL1811 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2.0 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 PHL1811 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 4.0 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 30 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 1800 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 40 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 2760 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 50 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 2760 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9418( 3) - 02/20/03 06:36 - [ 9] Visit: 04 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 PHL1811 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2.0 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 PHL1811 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 4.0 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 30 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 1800 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 40 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 2760 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 50 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 2760 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 60 PHL1811 STIS/F ACCUM 0.2X0.0 E140M 1425 1 2760 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9418( 3) - 02/20/03 06:36 - [ 10] Visit: 05 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 ------------------------------------------------------------------------------------------------------------------------------------ 20 PHL1811 ACS/WF ACCUM WFC F625W GAIN=1,CR-SPLIT=NO 1 520 S PATTERN 1 20 C ------------------------------------------------------------------------------------------------------------------------------------ 9418( 3) - 02/20/03 06:36 - [ 11] Summary Form for Proposal 9418 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 0.2X0.06 WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 20 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E140M F625W ------------------------------------------------------------------------------------------------------------------------------------ Target Names PHL1811 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------