0 Assigned ID: 4653 ----- Attempting Submission 1 (Wed May 24 21:09:48 GMT 2023) ----- 0 ----- Attempting Submission 1 (Thu Aug 31 04:15:13 GMT 2023) ----- ----- Attempting Submission 2 (Wed Oct 11 20:04:59 GMT 2023) ----- The Milky Way high-velocity cloud (HVC) Complex M offers several advantages for investigation of gas physics in the disk-halo interface of the Galactic circumgalactic medium (CGM). First, there are three UV-bright objects that are in the direction of Complex M that are closely spaced in the sky: two stars (HD93521 and BD+38d2182) and an extragalactic AGN (MRK421) that constrain the location of the gas: absorption lines at the velocity of the HVC are not detected in the spectrum of the closest object (HD93521, Gaia distance = 1.2 kpc), but the HVC is detected in absorption toward the more distant star (BD+38d2182, Gaia distance = 3.8 kpc) and the extragalactic sightline. The targets are at high latitudes, so the gas is constrained to be at z-heights > 1.1 kpc. Second, the targets are extremely bright, so they can be observed with the highest-resolution STIS E140H grating with good S/N. Third, the close projected spacing constrains the transverse dimensions of the gas clouds. We propose to use new STIS E140H observations of BD+38d2182 and MRK421, combined with archival HD93521 spectra to study CGM gas physics in this important region. With these data we will: (1) constrain the dimensions and kinematics of the HVC, (2) constrain the line-broadening mechanism, (3) derive the physical conditions in the HVC as well as the lower-velocity IVCs, (4) constrain important gas-physics time scales, (5) study abundance and dust-depletion patterns, and (6) investigate the ionization and origin of the highly-ionized gas including non-equilibrium and interface models. The targets have been safely observed previously with COS or STIS, but not with the E140H mode that we require. These are very bright targets, which enables our use of the E140H grating. However, we have used the STIS exposure-time calculator to check whether the targets exceed the bright-object limits in this STIS mode, and we find that these objects can be safely observed without endangering the instrument. Our goal is to obtain STIS E140H spectra that are as good as those used by Tripp (2022) so that we can carry out a similar analysis, and we want to cover a wavelength range that includes the O I, N I, S II, C II, C II*, C IV, Si II, Si III, Si IV, and Ni II lines at the highest spectral resolution. To do this we will need to be able to detect individual components with equivalent widths as weak as 6 mA . For BD+38 2182, this is straightforward. Using the fluxes recorded in the archival STIS E140M observation of BD+38 2182, we find that a one-orbit observation with the E140H grating tilt at lambda(cen) = 1271 and a one-orbit observation with the grating tilt at lambda(cen) = 1453 A will provide this signal-to-noise per resolution element or better. For MRK421 we are faced with a more expensive program because this target is fainter. Therefore to achieve our goals while using the telescope as efficiently as possible, for MRK421 we will follow the procedure successfully employed by Tripp (2022): we will obtain one STIS E140H spectrum with good S/N that will provide a high-resolution template for the component structure of the low-ionization stages (based on O I, S II, and Si II) and a separate template for the higher ionization stages (based on Si IV). This STIS E140H spectrum will be obtained with the lambda(cen) = 1343 A grating tilt so that all of these species are recorded at the highest spectral resolution. For the MRK421 E140H spectrum, we find that we require an exposure time of 9100 seconds for our weakest line, and we request 4 orbits for this observation including overheads. We will also obtain a STIS E140M observation of MRK421, which will add coverage of N I, Si III, C IV, Fe II, Al II, and several additional lines of Si II, Ni II, and C I. Again based on STIS ETC calculation for the addtional important lines, we request a 2-orbit observation of MRK421 with the E140M grating. To avoid possible problems arising from STIS focus issues (Proffit et al. 2017), we will use the 0.2$'' \times 0.2''$ aperture for both the E140H and the E140M observations. IMPACT OF REDUCED-GYRO OBSERVING: Based on the reports presented to the Space Telescope Users Committee, we expect that reduced-gyro observing would have only very minor impacts on this program. The increased target acquisition times would likely have negligible effect: the targets are very bright and the acq times are already very short, so increase of acquistion times by a ~2 minutes would have a very small impact on the final S/N of the spectra. The observations are: (1) not time-critical, (2) not coordinated with another observatory, and (3) not constrained to require certain orientations. The program does not require any of the special observing modes that would be impacted by reduced-gyro telescope operation. Therefore this study is a robust program for HST in any situation that requires <3 gyros. Principal Investigator Todd Tripp has used the HST spectrographs for >25 years and has led or coauthored >125 refereed papers using ultraviolet spectrographs in space. He has extensive experience with HST spectroscopic data and the science of the ISM, CGM, and IGM ranging from his doctoral work on very high S/N (>100:1) GHRS observations of QSOs, his research as a postdoctoral member of the Space Telescope Imaging Spectrograph Instrument Definition Team, and his roles in the first large QSO absorption-line projects with COS. CoI David Bowen at Princeton has been a pioneer in the study of the circumgalactic media of galaxies using absorption spectroscopy of background QSOs (e.g., Bowen, Blades, & Pettini 1995, ApJ, 448, 634, and many other papers). NMSU CoI Joseph Burchett has led several innovative studies of CGM absorption systems with an emphasis on environmental effects (e.g., Burchett et al. 2016, ApJ, 832, 124; Burchett et al. 2018, MNRAS, 475, 2067), and he adds a unique perspective and personal energy to the team. Finally, Notre Dame CoIs J. Chris Howk and Nicolas Lehner are experts in the study of high-velocity clouds, the physics of the interstellar medium, and using sightline pairs to constrain the sizes and nature of interstellar and circumgalactic clouds. Intergalactic Medium and the Circumgalactic Medium Galaxies 6 false false false false false false false false AVAILABLE STAR B3-B5 V-IV This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 B-V=-0.18, Flambda(1254) = 3.8e-12, Flambda(1403) = 2.0e-12 GALAXY BL LAC This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 B = 13.5, Flambda(1254) = 2.0e-13, Flambda(1549) = 1.3e-13 STIS/FUV-MAMA Spectroscopic No No E140H 1271 STIS/FUV-MAMA Spectroscopic No No E140H 1453 STIS/FUV-MAMA Spectroscopic No No E140H 1343 STIS/FUV-MAMA Spectroscopic No No E140M 1425 1717787283808 /private/var/folders/q9/0jb3sqc10kx2dw3wnl21b_dw000702/T/OPVisit3779727069030803141.xml The scheduling data was generated by CASM 31.1. CASM was run in Phase II mode. 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With a Kurucz model for a B3V star and V = 11.19, the STIS acquisition ETC indicates that the time to saturation is 71 seconds with this filter, so there should be plenty of buffer between the exposure time and the saturation time. 1717787289249 /private/var/folders/q9/0jb3sqc10kx2dw3wnl21b_dw000702/T/OPVisit5673243155906231424.xml The scheduling data was generated by CASM 31.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 17532 :visit-id "02" :proposal-version -1 :trans-version "20240604" :date "07-Jun-2024 15:08:09.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 313504 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17532 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17532 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2659 :al-overhead-at-end 0 :internal-dur-at-end 178 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3039 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17532 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2659 :al-overhead-at-end 0 :internal-dur-at-end 578 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3039 :pcs-gap 0 ) true 2 0 MRK421 is somewhat variable. Used V = 13.3 (historical average) to calculate acquisition exposure time, but we also checked that the brightest magnitude observed (V = 12.87) would not saturate the CCD with this exposure time. 1717787294059 /private/var/folders/q9/0jb3sqc10kx2dw3wnl21b_dw000702/T/OPVisit16992909017573412352.xml The scheduling data was generated by CASM 31.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 17532 :visit-id "03" :proposal-version -1 :trans-version "20240604" :date "07-Jun-2024 15:08:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 313504 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17532 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17532 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2659 :al-overhead-at-end 0 :internal-dur-at-end 178 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3039 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17532 :visit-id "03" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2659 :al-overhead-at-end 0 :internal-dur-at-end 578 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3039 :pcs-gap 0 ) true 2 0 MRK421 is somewhat variable. 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(Tic-Visit :proposal-id 17532 :visit-id "04" :proposal-version -1 :trans-version "20240604" :date "07-Jun-2024 15:08:18.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 383088 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17532 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17532 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2659 :al-overhead-at-end 0 :internal-dur-at-end 178 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3039 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17532 :visit-id "04" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2659 :al-overhead-at-end 0 :internal-dur-at-end 578 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3039 :pcs-gap 0 ) true 2 0 MRK421 is somewhat variable. Used V = 13.3 (historical average) to calculate acquisition exposure time, but we also checked that the brightest magnitude observed (V = 12.87) would not saturate the CCD with this exposure time.