15422( 4) - 20-Apr-2018 17:17:21 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15422 Version: 4 Check-in Time: 20-Apr-2018 17:17:21 STScI Edit Number: 1 Title Anchoring C/O with an Extremely Metal Deficient Galaxy ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Danielle Berg The Ohio State University Y CoI: Prof. Dawn K. Erb University of Wisconsin - Milwaukee N CoI: Prof. Max Pettini University of Cambridge N ------------------------------------------------------------------------------------ Abstract Carbon has no strong collisionally excited emission lines in the optical, so that carbon abundances from HII regions are relatively sparse. However, by observing CIII] 1907, 1909 and OIII] 1661, 1666 in the ultraviolet, we can obtain a very secure measurement of the C/O ratio in HII regions. We have been using HST/COS to measure C/O in HII regions in dwarf galaxies from the SDSS which cover a range of roughly one dex in O/H. However, extremely metal poor galaxies are notoriously rare in the SDSS, and our sample lacks targets below 12 + log(O/H) = 7.25. The recent discovery of the nearby dwarf galaxy, Little Cub, with an oxygen abundance of 12 + log(O/H) = 7.13, hosts a sufficiently high surface brightness HII region to allow a C/O measurement in just a few HST orbits. Adding Little Cub to our sample will allow us to extend the metallicity baseline, explore the potential continuity in C/O versus O/H from dwarf galaxies to DLAs, and constrain rest-frame UV emission-line diagnostics in preparation for JWST. ------------------------------------------------------------------------------------ Observations Description ------------------------ Goal: We will obtain NUV target aquisiton images and FUV COS spectroscopy of the recently discovered, nearby, metal-poor, compact "Little Cub" dwarf galaxy in order to anchor the C/O relationship with O/H at the low-metallicity end. Target: Recently, Hsyu et al. (2017) reported the discovery of the Little Cub, the only extremely metal-poor (12+log(O/H)<7.3) star-forming galaxy suitable for UV emissison-line studies with HST. Little Cub has large optical [OIII] emission line surface brightness, is high ionization, is low metallicity (12+log(O/H) < 7.3), and has a compact morphology which allows maximum flux through the 2.5" COS aperture. We use coordinates centered on the maximum surface brightness from the PanSTARRS1 g-band image, which are in the ICRS reference frame. Target Acquisition: Since Little Cub has PanSTARRS imaging, which has excellent astrometry, we do not do an ACQ/SEARCH routine. Further, the peak surface brightness coordinates from the PanSTARRS imagin are within 0.1" of the SDSS imaging. With such precise input coordinates from the PanSTARRS, we aquire our target using the 15422( 4) - 20-Apr-2018 17:17:21 - [ 2] ACQ/IMAGE mode with the PSA aperture and MirrorA for the COS/NUV configuration. For this acquition, we have determined integration times necessary to reach a S/N = 25, which has been demonstrated as sufficient by the execution of very similar programs (HST-GO14168 by PI: Dan Stark and our previous C/O programs: HST-GO13312 and HST-GO14628). We assume a flat spectral distribution normalized by the GALEX FUV surface brightnesses. Each galaxy is compact in the SDSS imaging with a FWHM PSF diameter of ~2". We then divide the GALEX FUV fluxes by the area of the 2" PSF to determine the FUV surface brightnesses. Science Exposures: We will use COS with the G140L grating with a central wavelength of 1280 angstroms in TIMETAG mode in order to obtain simultaneous measurements of the CIV 1548, 1550, HeII 1640, OIII] 1661, 1666, SiIII] 1883, 1892, and CIII] 1907, 1909 emission lines in Detector segment A. We will observe Little Cub for 3 orbits though the PSA aperture with the COS/FUV configuration. After target acquisition, all remaining time was allocated to science exposures for the first orbit. The resulting total science integration time is sufficient to reach S/N ~ 5 per resolution element in the CIII] 1909 line, which our experience has shown to be the weakest / limiting line due to the rapid fall off in sensitivity at the red end of the G140L grating. This will provide enough signal to measure the equivalent widths of the relevant emission lines. For the FUV G140L configuration, no flats are available and so we use FP-POS=ALL, which takes 4 images offset from one another in the dispersion direction and increases S/N. These 4 positions allow a flat to be created and cosmic rays to be eliminated. ------------------------------------------------------------------------------------ 15422( 4) - 20-Apr-2018 17:17:21 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 J1044+6303 GALAXY, DWARF COMPACT RA=10H44M42.6450S +/- 0.1", J2000 V = 19.87 +/- 0.05 M_B=-11.4, GALEX NUV DEC=+63D06'2.10" +/- 0.1" = 19.60, FUV = 19.66, SDSS g = 19.56 Reference Frame: ICRS Extended: YES Comments: V band magnitude determined from the SDSS conversions of Jester+05 ------------------------------------------------------------------------------------------------------------------------------------ 15422( 4) - 20-Apr-2018 17:17:21 - [ 4] Visit: 01 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 J1044+6303 COS/NUV ACQ/IMA PSA MIRRORA 1 100 S (100 GE S) Comments: The GALEX NUV flux per area was determined by assuming an extended target with an approximately 2.5" diameter and used as an input to the ETC. Our experience has show that similar low-metalliciity dwarf galaxies have more compact UV morphologies. ------------------------------------------------------------------------------------------------------------------------------------ 2 J1044+6303 COS/FUV TIME-TA PSA G140L 1280 FP-POS=ALL, SEGMENT=BOTH, 1 850 S G BUFFER-TIME=19383, FLASH=YES see below (2308 S) Comments: The GALEX NUV flux per area was determined by assuming an extended target with an approximately 2.5" diameter and used as an input to the ETC. Our experience has show that similar low-metalliciity dwarf galaxies have more compact UV morphologies. We then used the estimated O III] 1666 and C III] 1909 line fluxes to predcit a range of S/Ns in the desired emission lines. ------------------------------------------------------------------------------------------------------------------------------------ 3 J1044+6303 COS/FUV TIME-TA PSA G140L 1280 FLASH=YES, FP-POS=ALL, 1 850 S G SEGMENT=BOTH, see below BUFFER-TIME=19383 (2870 S) Comments: The GALEX NUV flux per area was determined by assuming an extended target with an approximately 2.5" diameter and used as an input to the ETC. Our experience has show that similar low-metalliciity dwarf galaxies have more compact UV morphologies. We then used the estimated O III] 1666 and C III] 1909 line fluxes to predcit a range of S/Ns in the desired emission lines. ------------------------------------------------------------------------------------------------------------------------------------ 15422( 4) - 20-Apr-2018 17:17:21 - [ 5] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 4 J1044+6303 COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=19383, FLASH=YES, 1 850 S G FP-POS=ALL, SEGMENT=BOTH see below (2870 S) Comments: The GALEX NUV flux per area was determined by assuming an extended target with an approximately 2.5" diameter and used as an input to the ETC. Our experience has show that similar low-metalliciity dwarf galaxies have more compact UV morphologies. We then used the estimated O III] 1666 and C III] 1909 line fluxes to predcit a range of S/Ns in the desired emission lines. ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J1044+6303 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J1044+6303 2 COS/FUV TIME-TA PSA G140L 1280 none none none 1 1 274.0 S G J1044+6303 2 COS/FUV TIME-TA PSA G140L 1280 none none none 2 1 678.0 S G J1044+6303 2 COS/FUV TIME-TA PSA G140L 1280 none none none 3 1 678.0 S G J1044+6303 2 COS/FUV TIME-TA PSA G140L 1280 none none none 4 1 678.0 S G J1044+6303 3 COS/FUV TIME-TA PSA G140L 1280 none none none 1 2 509.0 S G J1044+6303 3 COS/FUV TIME-TA PSA G140L 1280 none none none 2 2 787.0 S G J1044+6303 3 COS/FUV TIME-TA PSA G140L 1280 none none none 3 2 787.0 S G J1044+6303 3 COS/FUV TIME-TA PSA G140L 1280 none none none 4 2 787.0 S G J1044+6303 4 COS/FUV TIME-TA PSA G140L 1280 none none none 1 3 509.0 S G J1044+6303 4 COS/FUV TIME-TA PSA G140L 1280 none none none 2 3 787.0 S G J1044+6303 4 COS/FUV TIME-TA PSA G140L 1280 none none none 3 3 787.0 S G J1044+6303 4 COS/FUV TIME-TA PSA G140L 1280 none none none 4 3 787.0 S G 15422( 4) - 20-Apr-2018 17:17:21 - [ 6] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: HOPR repeat of visit 1. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 J1044+6303 COS/NUV ACQ/IMA PSA MIRRORA 1 100 S (100 GE S) Comments: The GALEX NUV flux per area was determined by assuming an extended target with an approximately 2.5" diameter and used as an input to the ETC. Our experience has show that similar low-metalliciity dwarf galaxies have more compact UV morphologies. ------------------------------------------------------------------------------------------------------------------------------------ 2 J1044+6303 COS/FUV TIME-TA PSA G140L 1280 FP-POS=ALL, SEGMENT=BOTH, 1 850 S G BUFFER-TIME=19383, FLASH=YES see below (2308 S) Comments: The GALEX NUV flux per area was determined by assuming an extended target with an approximately 2.5" diameter and used as an input to the ETC. Our experience has show that similar low-metalliciity dwarf galaxies have more compact UV morphologies. We then used the estimated O III] 1666 and C III] 1909 line fluxes to predcit a range of S/Ns in the desired emission lines. ------------------------------------------------------------------------------------------------------------------------------------ 3 J1044+6303 COS/FUV TIME-TA PSA G140L 1280 FLASH=YES, FP-POS=ALL, 1 850 S G SEGMENT=BOTH, see below BUFFER-TIME=19383 (2870 S) Comments: The GALEX NUV flux per area was determined by assuming an extended target with an approximately 2.5" diameter and used as an input to the ETC. Our experience has show that similar low-metalliciity dwarf galaxies have more compact UV morphologies. We then used the estimated O III] 1666 and C III] 1909 line fluxes to predcit a range of S/Ns in the desired emission lines. ------------------------------------------------------------------------------------------------------------------------------------ 15422( 4) - 20-Apr-2018 17:17:21 - [ 7] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 4 J1044+6303 COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=19383, FLASH=YES, 1 850 S G FP-POS=ALL, SEGMENT=BOTH see below (2870 S) Comments: The GALEX NUV flux per area was determined by assuming an extended target with an approximately 2.5" diameter and used as an input to the ETC. Our experience has show that similar low-metalliciity dwarf galaxies have more compact UV morphologies. We then used the estimated O III] 1666 and C III] 1909 line fluxes to predcit a range of S/Ns in the desired emission lines. ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J1044+6303 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J1044+6303 2 COS/FUV TIME-TA PSA G140L 1280 none none none 1 1 274.0 S G J1044+6303 2 COS/FUV TIME-TA PSA G140L 1280 none none none 2 1 678.0 S G J1044+6303 2 COS/FUV TIME-TA PSA G140L 1280 none none none 3 1 678.0 S G J1044+6303 2 COS/FUV TIME-TA PSA G140L 1280 none none none 4 1 678.0 S G J1044+6303 3 COS/FUV TIME-TA PSA G140L 1280 none none none 1 2 509.0 S G J1044+6303 3 COS/FUV TIME-TA PSA G140L 1280 none none none 2 2 787.0 S G J1044+6303 3 COS/FUV TIME-TA PSA G140L 1280 none none none 3 2 787.0 S G J1044+6303 3 COS/FUV TIME-TA PSA G140L 1280 none none none 4 2 787.0 S G J1044+6303 4 COS/FUV TIME-TA PSA G140L 1280 none none none 1 3 509.0 S G J1044+6303 4 COS/FUV TIME-TA PSA G140L 1280 none none none 2 3 787.0 S G J1044+6303 4 COS/FUV TIME-TA PSA G140L 1280 none none none 3 3 787.0 S G J1044+6303 4 COS/FUV TIME-TA PSA G140L 1280 none none none 4 3 787.0 S G 15422( 4) - 20-Apr-2018 17:17:21 - [ 8] Summary Form for Proposal 15422 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=19383, FLASH=YES, FP-POS=ALL, SEGMENT=BOTH ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names J1044+6303 ------------------------------------------------------------------------------------------------------------------------------------