Can Very Massive Stars form at the low-metallicity threshold of the nearby Universe?

0 Assigned ID: 212 ----- Attempting Submission 1 (Thu Mar 05 04:17:28 GMT 2020) ----- HST Phase I Proposal 212 successfully submitted. Receipt: # 212-1 ----- Attempting Submission 2 (Fri Mar 06 01:38:21 GMT 2020) ----- HST Phase I Proposal 212 successfully submitted. Receipt: # 212-2 ----- Attempting Submission 3 (Fri Mar 06 21:19:08 GMT 2020) ----- This re-submission is for a repeat observation with STIS G140L due to a failed observation. The repeat includes the TA and dither pattern. -469609057 ----- Attempting Submission 1 (Fri Jun 26 19:51:22 GMT 2020) ----- ----- Attempting Submission 2 (Tue Jun 01 23:26:42 GMT 2021) ----- ----- Attempting Submission 3 (Wed Jun 02 21:01:07 GMT 2021) ----- ----- Attempting Submission 4 (Tue Feb 01 17:09:03 GMT 2022) ----- Can Very Massive Stars form at the low-metallicity threshold of the nearby Universe? Very massive stars (VMS, >100 Msun) dominate the ionization and mechanical feedback in star-forming regions for the first few Myr. Evidence for VMS has been found from UV observations of young (< 3 Myr), massive star clusters (>5x10^4 Msun), in the LMC and two nearby starbursts. Larger samples of these stars are needed in order to determine the upper mass limit of the IMF and complete our understanding of massive star evolution. In addition, since JWST will obtain numerous UV rest-frame spectra of young high redshift galaxies, it is essential that we investigate whether VMS are common in local, low metallicity analogs, while we still have access to the UV domain. SBS 0335-052E is one of the nearest most metal-poor analogs and contains several super star clusters (SSC) of 10^5 M_sun. From ground-based optical spectroscopy, candidate Wolf-Rayet (WR) have been found in cluster 3 of the galaxy (SSC3). Given its young age, large mass, and WR-like signatures, SSC3 could host VMS. We request co-spatial STIS G140L UV + G430L optical 52x0.2 long-slit spectroscopy of SSC3 in SBS 0335-052E. The requested observations will cover the high-ionization UV emission lines of C IV, He II, and O III], and the optical He II 4686 line. Dust attenuation will be obtained from the UV to optical He II ratio. We will use the co-spatial UV + optical data to test if WR stars alone can explain the observed properties of SSC3 or if VMS are necessary. The observations will provide important constraints to state-of-the-art spectral synthesis models of the kind that will be used to interpret rest-frame UV spectra of the most distant galaxies, with future large telescopes. We will use 8 orbits of HST and the STIS 52"x0.2" long slit to observe super star cluster 3 in SBS 0335-052E. Two visits are requried because STIS/MAMA visits must not be more than 5 orbit. Orient. We request the same orient of the slit for visits 1 and 2. Target acquisition. An ACS WFC F435W image was used to locate a GSC2 star to use as offset. The offset to cluster 3 was measured from the offset star coordinates on the HST image. We will acquire the GSC2 star with the CCD F28x50LP configuration in ACQ mode. With an exposure time of 3 s, we can reach a SNR of 100 with the latter configuration. We will then offset from the star to cluster 3. Spectroscopy. We will use gratings G140L and G430L in ACCUM mode. Orbits. The Vega magnitudes of SSC3 in ACS HRC filters F435W and F220W are 20.85 and 18.79 mag, respectively. We use the latter magnitues in order to calculate the exposure times to reach a SNR of 10 in the continuum of 4686*(1+z) and SNR of 5 in the continuum of 1640*(1+z). For the G430L observations, we assume that the target is a point source with a power law index of -2.6 and a normalization in the Vega system of 20.85 mag in filter ACS/WFC1/F435W. For the G140L observations we normalize to 18.79 mag in filter WFC3/UVIS1/F225W. The redshift of SBS 0335-052E is z=0.0135. PI Aida Wofford has expertise in spectroscopic observations and analysis of unresolved massive-star clusters, star-forming galaxies, and starburst galaxies; has led three previous COS observational campaings targeting metal-poor star-forming dwarf galaxies (13788, 15220, 15828), where the last program also included the use of the STIS long-slit; and has led many studies of nearby star-forming regions involving UV and optical imaging and spectroscopy with HST STIS, COS, ACS, and WFC3, including the analysis of COS GTO data from programs 11522 and 12027. Co-I expertise can be separated into the following components of the proposed program: (1) Planning of STIS long-slit observations and data reduction: Linda Smith observed a region of SBS 0335-052E with STIS G140L (15116) (2) Spectroscopic analysis of O stars, Wolf-Rayet stars, Very Massive Stars, and B supergiants: Linda Smith (3) Optical and UV imaging of galaxies with ACS and WFC3: Matthew Hayes (13655,14079,15643) (4) Observations and analysis of optical spectroscopy of SBS 0335-052E with VLT/MUSE: Matthew Hayes Galaxies 6 false false true false false false false SUPPORTED STAR F0-F2 J2000 EXT-CLUSTER KNOT STAR FORMING REGION J2000 STIS/CCD Spectroscopic No No G430L 4300 STIS/FUV-MAMA Spectroscopic No No G140L 1425 POS-TARG DITHER 0.5 LINE false false 2 90.0 STIS-ALONG-SLIT 1

false

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