0 Assigned ID: 258 ----- Attempting Submission 1 (Thu Apr 04 20:13:00 GMT 2019) ----- HST Phase I Proposal 258 (gameri.apt) successfully submitted. Receipt: # 258-1 changed the dither pattern to WFC3-UVIS-MOS-DITH-LINE to fill in chip gaps. -1291576414 ----- Attempting Submission 1 (Fri Jul 19 18:25:42 GMT 2019) ----- HST Phase II Proposal 15903 (gameri_phase2_v1.apt) successfully submitted. Receipt: # 15903-1 ----- Attempting Submission 2 (Mon Sep 09 17:38:46 GMT 2019) ----- Imaging a Nearby Red Giant Astrosphere We propose to use WFC3/UVIS to make the first image of the astrosphere around a normal, non-pulsating red giant, specifically Gamma Eri (M1 III). This will allow a direct measurement of the wind's termination shock distance from the star, an excellent measure of the ISM pressure at the star, which is within the Local Bubble at a distance of d=62.3 pc. This would be the closest astrosphere to Earth ever imaged. The data will be used to test hydrodynamic models of the stellar-wind/ISM interaction, and we will look for signs of asymmetry in the astrosphere that could be indicative of asymmetries in the stellar wind outflow or effects of the ISM magnetic field. The only method for studying red giant astrospheres in the past has been spectroscopically, in absorption, and our chosen target is one of only three red giants with detected Mg II 2800 astrospheric absorption. Our proposed observation complements this previous HST/STIS observation nicely, as the UVIS/F275W exposure will be attempting to image the astrosphere in scattered Mg II emission. We will observe the astrosphere of Gamma Eri for 3 orbits with the F275W filter of WFC3/UVIS. Estimating exposure times requires first estimating Mg II surface brightness. To do this, we first measure the Mg II flux absorbed by the astrosphere in the previous HST/STIS spectrum shown in Figure 2: f=6.4e-14 ergs/cm2/s in the k line, f=3.2e-14 ergs/cm2/s in the h line. We then divide this by the size of the astrosphere on the sky, which based on Figure 4 we estimate to be about 400 arcsec^2. The wavelength integrated average Mg II surface brightness is therefore sigma=2.4e-16 ergs/cm2/s/arcsec^2 for both lines combined. Taking into account overhead and our expected target visibility per orbit, we expect roughly 46 minutes per orbit to be available for target exposure time. Using the online WFC3 ETC, we find that in a 3 orbit observation (138 min), we can achieve an average signal-to-noise within a 25x25 pixel box (1" x 1") of S/N=5.0, which should be good enough for our purposes. We don't need particularly high spatial resolution, so even coarser binning could be used if necessary. The chosen F275W filter is the one that yields the best S/N, superior to the narrow F280N filter, for example. We will use the WFC3-UVIS-MOS-DITH-LINE dither pattern, a pattern involving 6 positions that allows a final combined image that will fill in chip gaps, and we will do two separate exposures for each position. The combination will enable the removal of hot pixels, cosmic rays, and other artifacts. The aforementioned WFC3 ETC calculation includes a modest 10 e post-flash background enhancement to ensure acceptable charge transfer efficiency. Dr. Brian Wood has extensive experience in the analysis of UV observations from HST. Dr. Graham Harper is an expert on observational and theoretical studies of red giants and supergiants, particularly their winds. Dr. Hans Mueller has a long history of studying solar/stellar winds and their interactions with the ISM. Stellar Physics 6 false false true false false false false SUPPORTED STAR M III-I SHOCK FRONT WIND GAMMA-ERI J2000 J2000 TYPE=M1III WFC3/UVIS Imaging No No F275W POS-TARG MOSAIC DITHER 2 2.4 WFC3-UVIS-MOS-DITH-LINE false true 0.119 3 85.754 POS-TARG WFC3-UVIS-MOS-DITH-LINE 33.606 1 true /home/wood/marmoset/props/hst19/OP-cache/gameri_phase2_v2-v01.xml The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. 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