15903( 3) - 09-Sep-2019 20:27:43 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15903 Version: 3 Check-in Time: 09-Sep-2019 20:27:43 STScI Edit Number: 0 Title Imaging a Nearby Red Giant Astrosphere ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Brian Erland Wood Naval Research Laboratory Y CoI: Dr. Hans-Reinhard Mueller Dartmouth College N CoI: Dr. Graham M. Harper University of Colorado at Boulder N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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 15903( 3) - 09-Sep-2019 20:27:43 - [ 2] 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. ------------------------------------------------------------------------------------ 15903( 3) - 09-Sep-2019 20:27:43 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD25025 STAR, M III-I, SHOCK RA=03H58M1.7664S +/- 0.1", J2000 V = V = 2.94 +/- 0.01 TYPE=M1III FRONT, WIND DEC=-13D30'30.66" +/- 0.1" 60.81 Reference Frame: ICRS Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000.0 0.004221452259312732 -0.11311 0.01604 ------------------------------------------------------------------------------------------------------------------------------------ 15903( 3) - 09-Sep-2019 20:27:43 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-MOS-DITH-LINE WFC3-UVIS-MOS-DITH-LINE Pattern_Purpose MOSAIC DITHER Number_Of_Points 3 2 Point_Spacing 2.4 0.119 Line_Spacing Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 85.754 33.606 Angle_Between_Sides Center_Pattern YES NO ------------------------------------------------------------------------------------------------------------------------------------ 15903( 3) - 09-Sep-2019 20:27:43 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HD25025 WFC3/UVI ACCUM UVIS F275W FLASH=10 1 450 S PATTERN 1 1-2 S see below (3638 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 HD25025 WFC3/UVI ACCUM UVIS F275W FLASH=10 1 450 S S see below (3638 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ HD25025 1 WFC3/UVI ACCUM UVIS F275W 1 1 none none 1 601.0 S S HD25025 1 WFC3/UVI ACCUM UVIS F275W 1 2 none none 1 601.0 S S HD25025 1 WFC3/UVI ACCUM UVIS F275W 2 1 none none 2 609.0 S S HD25025 1 WFC3/UVI ACCUM UVIS F275W 2 2 none none 2 609.0 S S HD25025 1 WFC3/UVI ACCUM UVIS F275W 3 1 none none 3 609.0 S S HD25025 1 WFC3/UVI ACCUM UVIS F275W 3 2 none none 3 609.0 S S HD25025 2 WFC3/UVI ACCUM UVIS F275W 1 1 none none 1 601.0 S S HD25025 2 WFC3/UVI ACCUM UVIS F275W 1 2 none none 1 601.0 S S HD25025 2 WFC3/UVI ACCUM UVIS F275W 2 1 none none 2 609.0 S S HD25025 2 WFC3/UVI ACCUM UVIS F275W 2 2 none none 2 609.0 S S HD25025 2 WFC3/UVI ACCUM UVIS F275W 3 1 none none 3 609.0 S S HD25025 2 WFC3/UVI ACCUM UVIS F275W 3 2 none none 3 609.0 S S 15903( 3) - 09-Sep-2019 20:27:43 - [ 6] Summary Form for Proposal 15903 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=10 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1-2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F275W ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD25025 ------------------------------------------------------------------------------------------------------------------------------------