Justification may be needed for use of certain lifetime positions with G160M. See "Errors and Warnings" for more details. Justification may be needed for use of certain lifetime positions with G160M. See "Errors and Warnings" for more details. Justification may be needed for use of certain lifetime positions with G160M. See "Errors and Warnings" for more details. 0 Assigned ID: 3755 ----- Attempting Submission 1 (Fri Mar 25 23:54:44 GMT 2022) ----- Routine warnings about new G160M LP For the best data quality, it is generally required to use all four FP-POS positions when observing at a given COS cenwave. See the COS Instrument Handbook for exceptions that may apply to observations with G130M/1291 or G160M. Adding repeat of failed orbit of Visit 2 as new Visit 52, per HOPR 92557 739714792 ----- Attempting Submission 1 (Thu Jul 14 21:26:36 GMT 2022) ----- ----- Attempting Submission 2 (Mon Oct 17 06:48:25 GMT 2022) ----- ----- Attempting Submission 3 (Thu Jun 22 22:44:40 GMT 2023) ----- Visit 52 is a repeat of half of visit 2; data has already been taken at the other 2 FP-POS settings and will be used in combination. Despite a substantial investment of HST orbits over the last five years, the intense nebular CIV detected at z>6 remains mysteriously without precedent among star-forming galaxies in the local Universe. The persistent difficulty in interpreting this emission with the launch of JWST looming foreshadows potentially significant challenges in the coming years. Uncertain photoionization models suggest that extraordinarily metal-poor massive stellar populations at <5% solar are likely to be the most efficient engines for this high-ionization emission. However, UV and most optical observations have so far been restricted to relatively bright and unfortunately low specific star-formation rate regions at these lowest metallicities. The relatively recent unveiling of a significant population of extremely metal-deficient galaxies dominated by young stars below the detection limits of previous surveys promises to at last open a window onto the highly uncertain ionzing spectrum of massive stellar populations below 5% solar. Here we propose G160M observations to constrain CIV and HeII at gas-phase oxygen abundances below 5% and effective ages <~5 Myr for the first time, targeting the only three systems known in this regime which are sufficiently bright and low-redshift to be amenable to relatively inexpensive UV spectroscopic follow-up. These data will provide unique insight onto the high-energy radiation fields powered by very low-metallicity massive stars, immediately either resolving or significantly heightening the tension between local galaxy populations and the first systems targeted with rest-UV spectroscopy in the reionization era. This program will acquire FUV spectroscopy designed to constrain high-ionization nebular emission in C IV and He II for three extremely metal-deficient nearby dwarf galaxies dominated by very young stellar populations. The targets are each covered by SDSS and GALEX imaging which we leverage in planning their observation. Coordinates and acquisiton: Each target is a compact source unresolved in ground-based imaging. The target coordinates are determined from the SDSS photometric outputs and confirmed to agree precisely with the peak of u-band emission for each target in the ICRS-aligned SDSS imaging. Each target is thus acquired with a standard ACQ/IMAGE exposure, with exposure time chosen to deliver S/N=50 for a point source with an NUV AB magnitude equal to the faintest of the u-band fiber and cModel magnitudes (assuming a flat continuum in F_nu, appropriate for such sources). We confirm that all three have GALEX/NUV magnitudes in-excess of this conservative estimate; and to ensure detector safely, we likewise confirm that no warnings are raised for a Mirror A+PSA observation of a point source with the brightest GALEX/NUV magnitude among the three. Based upon previous observations of similar sources (and exisiting HST optical imagery for J210455), we expect these targets to be more extended than a point source, but with FWHM at NUV wavelengths significantly smaller than 0.6''; given this, the large requested S/N provides an appropriate buffer to ensure accurate acquisition of such targets. Observing plan: Our primary objective is nebular line measurement; our observations are thus in the low-S/N regime (<5 /resel in the continuum). To maximize the exposure time on-source, we thus devote each orbit to a single spectroscopic exposure, which enables us to relegate most of the buffer dump and expensive SPLIT wavecal overheads to occultation. Thus, 2-3 FP-POS positions are observed for each object (always including FP-POS=1 and 4), as allowed under the updated Cycle 30 requirements. A full buffer dump is requested for each exposure given the uncertain FUV countrates and the unimportant impact on overheads. A warning is generated and acknowledged for the full-orbit spectroscopic exposures which exceed 2400s; the potentially reduced wavelength calibration accuracy is unlikely to impact our primary science, and the follow-up wavecal will allow us to correct for some drift in the mechanism settings. For the 3-orbit Visit 1, we choose to observe FP-POS=3 for the short orbit 1 integration and the primary FP-POS=1+4 in the subsequent orbits; the resulting warning about inefficient FP-POS ordering is ignored as the grating shifts occur during occultation. Safety: The only health and safety warning presented is associated with J210455, which has a bright (V~16 according to the BOT) neighbor star. This exposures presents a potential danger only under the incorrect default assumption that it has an O5 spectrum. The SDSS imaging confirms that this star is located 3.77'' to the W of the target, and GAIA position and PM measurements indicate that it is moving further away to the SW; thus we are confident that it will be outside the PSA extent given typical pointing uncertainties. In addition, the SDSS photometry for this source (u,g,r,i,z = 20.49, 18.03, 17.01, 16.66, 16.47) is consistent with a ~4500K K-type star, which places the expected AB NUV magnitude negligbly faint (>26). GALEX NUV and FUV imaging, while low-resolution, confirms that there is no excess detected UV flux consistent with the position of this nearby star. Existing WFC3/F336W imaging for this source further confirms that the target star-forming region is well-isolated from both this star (located at a similar distance to that measured from SDSS) and from the remaining extent of the galaxy, and is compact relative to the PSA at blue wavelengths as expected. Thus, we proceed with a standard target acquisition for this source. The assembled team has extensive experience using HST/COS to study nearby dwarf galaxies with medium-resolution FUV+NUV spectroscopy. Over the past five cycles, members of our team have successfully led many proposals targeting similar samples of star-forming dwarfs with COS spectroscopy and published the results expediently (GO:14168, 14679, 15646, 15881, 16677 PI: Stark; GO: 13312, 14628, 15422, 15465, PI: Berg; and the CLASSY Treasury Program GO: 15840, PI: Berg, Co-PI Stark). Results from these programs have been published in Senchyna et al. 2017, 2019, 2021, 2022; Berg et al. 2016, 2019a,b, 2021, 2022; Chevallard+2018; and several in-preparation manuscripts. The proposed COS G160M observations are very similar in nature to the G160M data collected in these previous programs, and will be reduced and analyzed using the techniques we have developed and tested already. PI Senchyna and Co-I Stark are experienced with planning and analyzing HST/COS FUV spectroscopy of nearby dwarf galaxies, and will be responsible for data reduction and analysis. This will involve designing target acquisition and observing strategy, optimally combining exposures, and cleaning spectra of MW absorption lines. PI Senchyna and Co-Is Stark, Berg, Chisholm, and Chen are experts in the measurement and interpretation of high-ionization nebular emission lines, and will drive the measurement and interpretation of the CIV and He II targeted in the context of high-redshift and local galaxies as well as nebular gas and chemical evolution models. Co-Is Chevallard, Charlot, and Plat have developed a full suite of both population synthesis + nebular photoionzation models and a robust model comparison framework, and will lead comparison of the nebular line strengths measured in our data to state-of-the-art population synthesis models using BEAGLE (Chevallard & Charlot 2016). This will involve both full-spectrum and isolated model comparison experiments, and will require an awareness of model limitations and HST/COS data subtleties that our group has developed. Galaxies 6 false false true false false false false false SUPPORTED GALAXY DWARF COMPACT EMISSION LINE NEBULA STAR FORMING REGION NO J2000 J2000 GALAXY DWARF COMPACT EMISSION LINE NEBULA STAR FORMING REGION NO J2000 J2000 GALAXY DWARF COMPACT EMISSION LINE NEBULA STAR FORMING REGION NO J2000 J2000 COS/FUV Spectroscopic No No G160M 1589 COS/FUV Spectroscopic No No G160M 1623 COS/FUV Spectroscopic No No G160M 1533 1664910788699 The scheduling data was generated by CASM 31.0. CASM was run in Phase II mode. 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