0 Assigned ID: 2989 ----- Attempting Submission 1 (Thu Mar 24 15:03:59 GMT 2022) ----- FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser There is currently a FLASH warning for orbit 1, but as described in Observing Description, we believe it is a good idea to add some FLASH due to CTE degradation. 740505316 ----- Attempting Submission 1 (Tue Jul 12 08:24:26 GMT 2022) ----- The warning is related to FLASH. We added some FLASH to all filters to minimize CTE effects. We propose UV and optical UVIS/WFC3 photometry of M51, a face-on Milky Way-like galaxy at d = 8.5 Mpc, in which individual luminous stars can be spatially resolved. Previous HST programs obtained 70 epochs of photometry in the red optical F606W and F814 filters, producing high-precision light curves of the 20,000 most luminous stars in the galaxy. Among these are hundreds of massive eclipsing binaries (EBs) and luminous blue variables (LBVs). These light curves are a treasure trove for studies of massive star evolution and population demographics, enabling a homogenous census of luminous star variability that would be impossible in the Milky Way. However, the existing photometry is in the Rayleigh-Jeans tail for hot stars and thus cannot constrain their temperatures and luminosities reliably. We propose 1 epoch in each of the F275W, F336W, F475W, F606W, and F814W filters (5 orbits total), enabling measurement of temperatures, radii, and luminosities for all hot stars, and masses for EBs. This program will significantly increase the utility of the existing 70 epochs of photometry, enabling a wealth of science related to massive star evolution and binary population modeling. We adopt the well-tested strategy of observing in the UV-optical filters F275W, F336W, F475W, F606W, and F814W. Several authors have demonstrated that this combination of filters enables strong separation of temperature and dust effects, and a similar strategy was adopted by the Multi-Cycle Treasury program PHAT. We request one orbit depth in each of the F275W, F336W, F475W, F606W, and F814 filters. We will split each orbit into 4 sub-exposures using a standard dither pattern. The UVIS ETC predicts SNR=20 at F275W=23.0, F336W=24.0, F475W=25.0, F606W=24.5, F814=24.0. These depths are necessary to: a) measure photometry at the few percent level; b) derive stellar parameters at the 10% level, and (c) enable longer-baseline analysis of optical CMD variability, when combined with archival data. Given that the sources of greatest interest will be time-variable, it is essential that the five filters be observed in consecutive orbits so that reliable stellar parameters can be derived. They are thus grouped into a single visit. The proposed field overlaps with existing WFPC2 data from 1995, existing ACS data from 2005, and the high cadence observations from the Cycle 24 ACS program ID 14704. The orientation constaints are chosen to maximize overlap with the archival data. We add a small amount of FLASH to all filters. This may slightly reduce SNR (and it produces a warning in F606W), but experience suggests that it will make the data more generally usable due to CTE degradation. Kareem El-Badry (PI) is an expert on binary stars and stellar evolution. He has worked extensively on population modeling of binaries in the Milky Way using a combination of photometric and spectroscopic surveys and binary evolution models. Charlie Conroy is an expert on stellar populations, galaxy formation, and HST photometry. He lead a previous HST program that obtained 68 epochs of red optical photometry of M51; this is the dataset from which the variable stars we wish to target were selected. Daniel Weisz is an expert in modeling HST photometry, particularly with a focus on constraining star formation histories from resolved color-magnitude diagrams. Stellar Physics and Stellar Types Galaxies 6 false false false false false false false SUPPORTED GALAXY DISK INTERACTING GALAXY SPIRAL This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F275W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false /Users/kareem/Downloads/OP-cache/APT_m51-v01.xml 1657569532015 The scheduling data was generated by CASM 30.3. CASM was run in Phase II mode. 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