0 Assigned ID: 760 ----- Attempting Submission 1 (Fri Apr 10 20:14:46 GMT 2015) ----- Please check the proper motion as well as the units since the entered value exceeds the fastest object in Luyten's Half-Second Catalogue. 0 ----- Attempting Submission 1 (Fri Jul 17 17:27:41 GMT 2015) ----- The proper motion of this object is correct (and very large). Taming the Tepid Three With atmospheric conditions similar to those of the Solar System giant planets, cold (Teff<700 K) brown dwarfs are excellent proxies with which to test the ultracool model atmospheres that are critical to our understanding of gas giant exoplanets. A complete census of these objects is also essential for measuring the low-mass stellar mass function and the low-mass limit of star formation. The three coldest known brown dwarfs (WISE 1828+2650, WD 0806-661B, and WISE 0855-0714) all have effective temperature estimates of less than approximately 300 K. Previous HST and Spitzer observations of WISE 1828+2650 and WD 0806-661B provide near complete coverage of the 1 to 5 micron wavelength range. Unfortunately, the coldest of the three, WISE 0855-0714, has yet to be securely detected at near-infrared wavelengths which limits our ability to precisely measure many of its basic properties. We therefore propose to obtain near-infrared photometry of WISE 0855-0714 with WFC3 with the F105W, F125W, and F160W filters. These observations will complete HST's reconnaissance of the tepid three and, when combined with published Spitzer photometry, will allow us to compute a more precise estimate of its effective temperature and search for the presence of water clouds in its atmosphere. We propose to observe W0855 with WFC3 in the F105W, F125W, and F160W filters. Estimating the required exposure time in each of these bands is not straightforward, primarily because WISE 0855 currently remains undetected at F105W and F160W and only marginally detected at J. In addition, this is currently a unique object so it is difficult to bootstrap from similar objects. We therefore use a combination of the low signal-to-noise ratio Faherty et al. detection at J and model spectrum from Morley et al. (2014). By comparing the F125W and J-band magnitudes for the sample of Y dwarfs from Schneider et al. 2015, we find the average F125W-J mag difference to be ~0.7 mag. If we apply this to the 2.6 sigma J-band detection of W0855 from Faherty et al. 2014, we find an approximate F125W mag for W0855 of 25.5. We then scale the 250 K, log g = 4.0 model from Figure 2 to this magnitude and use the WFC3 Exposure Time Calculator to estimate exposure times to achieve a signal-to-noise ratio of 10 in each of the bands. We choose to implement dither sequences in which each individual frame is no longer than 1000 seconds. The number of orbits required is determined by dividing the estimated exposure time by 3600 s (the time available for 1 orbit). The expected magnitude from the model, exposure time estimates, and requested number of orbits for each filter is provided below. We therefore request a total of thirteen orbits for this program. We note that the F160W observations make up just over 75% of the requested number of orbits, but this band (when combined with either F125W or Spitzer [4.5]) has the largest sensitivity to the presence or absence water clouds (Morley et al. 2014) and therefore is critical to our science goals. F105W: Expected Magnitude = 26.0 Exposure Time = 4,011 s Orbits Required = 2 F125W: Expected Magnitude = 25.5 Exposure Time = 3155 s Orbits Required = 1 F160W: Expected Magnitude = 26.5 Exposure Time = 34,605 s Orbits Required = 10 COOL STARS 12 false false false false SUPPORTED STAR BROWN DWARF NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 J=24.8 WFC3/IR Imaging No No F105W WFC3/IR Imaging No No F125W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1 false /Users/aschneid10/Desktop/Observations/HST/Cycle_23/OP-cache/cycle23-14233-v01.xml The scheduling data was generated by CASM 23.2. CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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