15921( 3) - 01-May-2020 13:41:50 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15921 Version: 3 Check-in Time: 01-May-2020 13:41:50 STScI Edit Number: 0 Title Uncovering Extremely Metal-Poor Massive Stars in Leo A ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Peter Senchyna University of Arizona Y CoI: Prof. Daniel P. Stark University of Arizona N CoI: Dr. Daniel R. Weisz University of California - Berkeley N ------------------------------------------------------------------------------------ Abstract Young, extremely metal-poor stellar populations are central to our quest to characterize the faintest star-forming galaxies in the Universe at all redshifts. Ongoing efforts to model the nebular and stellar wind lines in extremely metal-poor (< 10% Zsun) star-forming galaxies have revealed substantial disagreements with current stellar models. A primary source of this tension is a lack of calibration at low-metallicites: no UV spectrum of an individual O star at Z/Zsun < 0.1 has ever been taken. We propose to target the brightest two O stars in the extremely metal-poor (Z/Zsun<0.1) dwarf galaxy Leo A (D~700 kpc) with deep HST/COS FUV spectroscopy. Leo A is the nearest galaxy with a population of massive stars at these metallicities, making these the most efficient observations possible. With these COS observations, we will (i) directly constrain the stellar metallicity (independent of the gas phase) by accessing faint photospheric lines of iron and (ii) for the first time, make a precise measurement of the wind strengths these massive low-metallicity stars drive. Our results have significant implications for massive stellar models in this metallicity regime, and consequently for population synthesis techniques applied to galaxies throughout the universe. This experiment relies entirely on FUV spectra to access crucial massive stellar features inaccessible at other wavelengths, and cannot be conducted in the optical. This will constitute the first observational test of stellar models at the metallicities we expect to encounter regularly in reionization-era galaxies with JWST. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will obtain medium-resolution FUV COS spectroscopy for two O stars in the extremely metal-poor nearby dwarf galaxy Leo A. The G160M/1533 grating setting will be used to simultaneously target a set of both stellar wind (O V, Si IV, C IV, and He II) and photospheric absorption lines which are required to address our science goals of constraining the stellar iron abundance and wind strengths. The target stars were identified in HST imaging, and their ICRS coordinates were determined by centroiding the sources in SDSS u-band imaging. Both targets are relatively bright (F275W~17.7, 18.0), and can be successfully acquired in ACQ/IMAGE mode with Mirror A with 8 second exposures. In order to maximize the scheduling flexibility of our program, we split the 8-orbit integration time for each star into 4 visits of 2 orbits each. We will take spectroscopic exposures in TIME-TAG mode with each orbit devoted to a single FP-POS setting such that buffer readouts and grating shifts occur during target 15921( 3) - 01-May-2020 13:41:50 - [ 2] occultation. Although the estimated BUFFER-TIME required is larger than the exposure times, we set the BUFFER-TIME to the exposure time to ensure the entire buffer is read during occultation. We additionally swap the order of the FP-POS grating changes in subsequent visits to ensure each achieves the same amount of integration time. In 8 orbits per star, ETC estimates indicate that our required S/N of 20 per angstrom will be achieved for both stars, enabling confident measurement of both the stellar wind and photospheric features. ------------------------------------------------------------------------------------ 15921( 3) - 01-May-2020 13:41:50 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 J095927.53+3 EXT-STAR, MAIN SEQUENCE RA=09H59M27.5322S +/- 0.1", J2000 V = 20.1 +/- 0.1 04457.7 O DEC=+30D44'57.78" +/- 0.1" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 2 J095930.22+3 EXT-STAR, MAIN SEQUENCE RA=09H59M30.2299S +/- 0.1", J2000 V = 20.2 +/- 0.1 04437.0 O DEC=+30D44'37.07" +/- 0.1" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 15921( 3) - 01-May-2020 13:41:50 - [ 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 J095927.53+ COS/NUV ACQ/IMA PSA MIRRORA 1 8 S (8 S) 304457.7 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J095927.53+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=1, 1 2400 S 304457.7 G BUFFER-TIME=2400 (2400 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J095927.53+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=2, 1 2800 S 304457.7 G BUFFER-TIME=2814 see below (2814 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J095927.53+304457.7 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J095927.53+304457.7 2 COS/FUV TIME-TA PSA G160M 1533 none none none none 1 N/A G J095927.53+304457.7 3 COS/FUV TIME-TA PSA G160M 1533 none none none none 2 2814.0 S G 15921( 3) - 01-May-2020 13:41:50 - [ 5] Visit: 02 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 J095927.53+ COS/NUV ACQ/IMA PSA MIRRORA 1 8 S (8 S) 304457.7 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J095927.53+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=3, 1 2400 S 304457.7 G BUFFER-TIME=2400 (2400 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J095927.53+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=4, 1 2800 S 304457.7 G BUFFER-TIME=2814 see below (2814 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J095927.53+304457.7 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J095927.53+304457.7 2 COS/FUV TIME-TA PSA G160M 1533 none none none none 1 N/A G J095927.53+304457.7 3 COS/FUV TIME-TA PSA G160M 1533 none none none none 2 2814.0 S G 15921( 3) - 01-May-2020 13:41:50 - [ 6] Visit: 03 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 J095927.53+ COS/NUV ACQ/IMA PSA MIRRORA 1 8 S (8 S) 304457.7 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J095927.53+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=2, 1 2400 S 304457.7 G BUFFER-TIME=2400 (2400 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J095927.53+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=1, 1 2800 S 304457.7 G BUFFER-TIME=2814 see below (2814 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J095927.53+304457.7 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J095927.53+304457.7 2 COS/FUV TIME-TA PSA G160M 1533 none none none none 1 N/A G J095927.53+304457.7 3 COS/FUV TIME-TA PSA G160M 1533 none none none none 2 2814.0 S G 15921( 3) - 01-May-2020 13:41:50 - [ 7] 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 J095927.53+ COS/NUV ACQ/IMA PSA MIRRORA 1 8 S (8 S) 304457.7 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J095927.53+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=4, 1 2400 S 304457.7 G BUFFER-TIME=2400 (2400 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J095927.53+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=3, 1 2800 S 304457.7 G BUFFER-TIME=2814 see below (2814 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J095927.53+304457.7 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J095927.53+304457.7 2 COS/FUV TIME-TA PSA G160M 1533 none none none none 1 N/A G J095927.53+304457.7 3 COS/FUV TIME-TA PSA G160M 1533 none none none none 2 2814.0 S G 15921( 3) - 01-May-2020 13:41:50 - [ 8] Visit: 05 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 J095930.22+ COS/NUV ACQ/IMA PSA MIRRORA 1 8 S (8 S) 304437.0 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J095930.22+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=1, 1 2400 S 304437.0 G BUFFER-TIME=2400 (2400 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J095930.22+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=2, 1 2800 S 304437.0 G BUFFER-TIME=2814 see below (2814 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J095930.22+304437.0 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J095930.22+304437.0 2 COS/FUV TIME-TA PSA G160M 1533 none none none none 1 N/A G J095930.22+304437.0 3 COS/FUV TIME-TA PSA G160M 1533 none none none none 2 2814.0 S G 15921( 3) - 01-May-2020 13:41:50 - [ 9] Visit: 06 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 J095930.22+ COS/NUV ACQ/IMA PSA MIRRORA 1 8 S (8 S) 304437.0 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J095930.22+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=3, 1 2400 S 304437.0 G BUFFER-TIME=2400 (2400 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J095930.22+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=4, 1 2800 S 304437.0 G BUFFER-TIME=2814 see below (2814 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J095930.22+304437.0 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J095930.22+304437.0 2 COS/FUV TIME-TA PSA G160M 1533 none none none none 1 N/A G J095930.22+304437.0 3 COS/FUV TIME-TA PSA G160M 1533 none none none none 2 2814.0 S G 15921( 3) - 01-May-2020 13:41:50 - [ 10] Visit: 07 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 J095930.22+ COS/NUV ACQ/IMA PSA MIRRORA 1 8 S (8 S) 304437.0 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J095930.22+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=2, 1 2400 S 304437.0 G BUFFER-TIME=2400 (2400 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J095930.22+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=1, 1 2800 S 304437.0 G BUFFER-TIME=2814 see below (2814 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J095930.22+304437.0 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J095930.22+304437.0 2 COS/FUV TIME-TA PSA G160M 1533 none none none none 1 N/A G J095930.22+304437.0 3 COS/FUV TIME-TA PSA G160M 1533 none none none none 2 2814.0 S G 15921( 3) - 01-May-2020 13:41:50 - [ 11] Visit: 08 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 J095930.22+ COS/NUV ACQ/IMA PSA MIRRORA 1 8 S (8 S) 304437.0 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J095930.22+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=4, 1 2400 S 304437.0 G BUFFER-TIME=2400 (2400 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J095930.22+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=3, 1 2800 S 304437.0 G BUFFER-TIME=2814 see below (2814 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J095930.22+304437.0 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J095930.22+304437.0 2 COS/FUV TIME-TA PSA G160M 1533 none none none none 1 N/A G J095930.22+304437.0 3 COS/FUV TIME-TA PSA G160M 1533 none none none none 2 2814.0 S G 15921( 3) - 01-May-2020 13:41:50 - [ 12] Visit: 23 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 J095927.53+ COS/NUV ACQ/IMA PSA MIRRORA 1 8 S (8 S) 304457.7 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J095927.53+ COS/FUV TIME-TA PSA G160M 1533 FLASH=YES, FP-POS=2, 1 2400 S 304457.7 G BUFFER-TIME=2400 (2400 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J095927.53+304457.7 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J095927.53+304457.7 2 COS/FUV TIME-TA PSA G160M 1533 none none none none 1 N/A G 15921( 3) - 01-May-2020 13:41:50 - [ 13] Summary Form for Proposal 15921 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=2400, BUFFER-TIME=2814, FLASH=YES, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G160M, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names J095927.53+304457.7, J095930.22+304437.0 ------------------------------------------------------------------------------------------------------------------------------------