Cannot find file /Users/dokkum/RUNS/Prop/hst_cyc27/df2_uv/prop/vandokkum_uv.pdf 0 Assigned ID: 30 ----- Attempting Submission 1 (Fri Mar 29 02:54:49 GMT 2019) ----- HST Phase I Proposal 30 (df2_uv.apt) successfully submitted. Receipt: # 30-1 ----- Attempting Submission 2 (Fri Mar 29 03:09:31 GMT 2019) ----- This should be pretty straightforward - I used a 10 electrons post flash, and relatively large dithers to move the galaxy over the detector (in 3 independent positions). 1067896138 ----- Attempting Submission 1 (Sun Jul 28 15:55:54 GMT 2019) ----- The galaxy NGC1052-DF2 has been the subject of intense debate in the literature. Not only does it seem to have a very low dark matter content, it also has a peculiar population of very bright globular clusters that make up 3% of the total light. A central question is when the galaxy and its unusual globular clusters were formed. The best constraints have come from optical spectroscopy of the bright globular clusters. The clusters have a metallicity of [Fe/H]=-1.4 and an apparent age of 9 Gyr, consistent with constraints on the metallicity and age of the diffuse light. However, these age measurements are only lower limits, due to the unknown contribution of blue horizontal branch (BHB) stars to the integrated light. If the BHB branch is as strong as in Milky Way globular clusters of the same metallicity, the true age of the globular clusters, and the galaxy, could be 13 Gyr - predating the formation of the massive elliptical galaxy NGC1052. The objective of this proposal is to measure the contribution of hot stars to the integrated light by obtaining F225W UV imaging of NGC1052-DF2 and its globular clusters with UVIS. The F225W-F814W color is sensitive to hot stars and breaks the degeneracy between age and the strength of the BHB. This measurement will pin down the formation epoch of the galaxy, currently only constrained to be at least ~9 Gyr ago; determine whether the globular clusters all have identical UV properties or show variation in their F225W-F814W colors like luminous Milky Way clusters; and test the hypothesis that a significant fraction of the diffuse light comes from disrupted globular clusters. This program aims to obtain 3 orbits of UV F225W imaging of the galaxy NGC1052-DF2 and its globular clusters. The 3 orbits are organized in a single visit. Within each orbit two exposures are obtained, with an exposure time of ~1350 seconds per exposure and a standard chip gap dither between the two exposures. A 10 electron post flash is used to mitigate CTE effects. Large POS_TARGs (of ~25'') are used in between each orbit (so before the first exposure, before the third, and before the fifth) to obtain reliable photometry of the diffuse light. There are no timing or orientation constraints. Pieter van Dokkum wrote the initial papers on this galaxy, on the globular cluster population and the dark matter content. He has extensive experience reducing and analyzing HST data, and was a co-I on the HDUV Legacy program. Shany Danieli has extensive experience with HST data and measured the stellar dynamics of NGC1052-DF2. Roberto Abraham is an expert on galaxies and low surface brightness imaging and identified a possible tidal stream associated with the globular clusters in NGC1052-DF2. Charlie Conroy is an expert on stellar populations, and developed the models that are used in the paper to predict the BHB contribution to the SED. Jean Brodie, Aaron Romanowsky, and Diederik Kruijssen are experts on globular cluster properties and formation scenarios. Dhruba Dutta Chowdhury studied the dynamics of the globular clusters. Galaxies and the IGM Stellar Populations 6 false false true false false false false SUPPORTED GALAXY DWARF SPHEROIDAL J2000 J2000 expected F225W of clusters = 26-26.5 WFC3/UVIS Imaging No No F225W POS-TARG MOSAIC DITHER 4 2.414 WFC3-UVIS-DITHER-BOX false 81.785 false 0.112 0.173 2 85.759 POS-TARG WFC3-UVIS-GAP-LINE 23.884 1 false 1564400399736 /private/var/folders/zc/ljhf1lgn10b1yd9ytmwlp4jr00070l/T/OPVisit2156406296935809125.xml The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. 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