Abstract is limited to 1700 characters (about 20 lines). Science Keywords: Select from 2 to 5 items. Science Keywords is a required field. 0 Assigned ID: 1233 ----- Attempting Submission 1 (Wed Sep 07 14:08:52 GMT 2016) ----- Joint Spitzer/Hst Spitzer & HST observations need to be occur within a few weeks of each other. The Spitzer cycle is 2 years long, but the observations should be scheduled Spring 2017 and I've constrained the HST observations to reflect that. However, there's a chance Spitzer won't schedule until Spring 2018 - I'm not sure how best to handle that. 1745022633 ----- Attempting Submission 1 (Mon Sep 26 20:40:02 GMT 2016) ----- The origin of dust in the early Universe is a matter of debate. One of the main potential dust contributors are Asymptotic Giant Branch (AGB) stars, and several studies have been devoted to investigating whether and how AGB dust production changes in metal-poor environments. Of particular interest are the most massive AGB stars (8-10 Msun), which can in principle enter the dust-producing phase <50 Myr after they form. However, these stars cannot produce their own condensable material (unlike carbon AGB stars), so the efficiency of dust production decreases with metallicity. Evidence for dust production in massive AGB stars more metal-poor than the Magellanic Clouds is scarce due both to the rarity of chemically-unevolved, star-forming systems reachable in the infrared and to the short lifetimes of these stars. The recently discovered galaxy Leo P provides an irresistible opportunity to search for these massive AGB stars: Leo P is a gas-rich, star-forming galaxy, it is nearby enough for resolved star photometry with Spitzer, and its interstellar medium is 0.4 dex more metal-poor than any other accessible star-forming galaxy. Models predict ~3 massive AGB stars may be present in Leo P, and optical HST observations reveal 7 candidates. We propose to use Spitzer to determine whether these stars are dusty, providing valuable constraints to the dust contribution from AGB stars up to at least redshift 3.2, or 11.7 Gyr ago, when massive spheroidals and Galactic globular clusters were still forming. This is a gain of 2.8 Gyr compared to other accessible galaxies. We also request 1 orbit of joint HST time to confirm whether the AGB candidates in Leo P are indeed massive AGB stars belonging to the galaxy. These observations will provide information crucial for potential JWST followup spectroscopy. Targets: We will target 1 field in Leo P that overlaps with Spitzer cycle-13 coverage and existing HST optical coverage. Filters: To take full advantage of the CN+C2 and water features near 1.4 microns, we require observations with F127M, F139M, and F153M. All three filters are necessary, since combinations with the broad-band optical, near-IR, and IR filters do not successfully isolate the carbon stars. Required exposure times and photometric depth: In order to detect all AGB stars, we must achieve full photometric completeness at the tip of the red giant branch (TRGB). The orbit time for our target is 54 min, so we can achieve the necessary photometric depth within a single orbit (as demonstrated by Boyer et al. 2013). This allows for total exposure times of 800-850s in each filter, resulting in S/N > 7 in F139M for mF160W = 23 mag, using a Bruzual template for an M6III star. The S/N is even better in the F127M and F153M filters, owing to a higher throughput. For reference, the TRGB in the F160W filter corresponds to mF160W ~19 mag at the distance of Leo P. Dithering Strategy: Dithering diminishes errors associated with where a source is placed on a pixel, undersampling of the WFC3/IR channel, and image artifacts such as cosmic rays. We choose a 4-point dithering strategy to acheive Nyquist sampling of the PSF & to simultaneously allow us to fit the three selected filters into a single orbit. We have entered the dither offsets manually into the target offset entries following the WFC3 handbook WFC3-IR-DITHER-BOX-MIN values from table C.3 Avoiding Saturation: The brightest AGB stars in our sample may reach m_F160W ~ 16.5 mag (or M_F160W = -8 mag). Stars brighter than m_F160W ~ 16.7 mag are in danger of saturating in 460 s exposures in the medium-band filters. Our longest exposures are only 300s, so saturation of our targets will not be an issue. Other bright stars in the field will be recovered by the WFC3/IR MULTIACCUM sampling. Parallels: There are no parallel observations for this program. Scheduling Constraints: We require observations to be concurrent with Spitzer cycle 13 observations (PI Boyer, GO-13009) to avoid uncertainties that arise in non-contemporaneous observations of large-amplitude variable stars. Spitzer observations are not yet scheduled, but we do know that they will occur in specific known windows. We've designed constraints here to ensure that HST observations will occur within 20 days of Spitzer (we'd prefer <15 days). However, the timing constraints entered here are flexible depending on exactly when the Spitzer observations are finally scheduled. The Spitzer window is entered under "Comments" in the Visit. Stellar Physics 12 false false false false false false SUPPORTED GALAXY STAR FORMING REGION UNDESIGNATED NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F139M WFC3/IR Imaging No No F153M 1474058684501 /Users/mboyer/Proposals/HST2016/LeoP/OP-cache/LeoP_phase2_v1-v01.xml The scheduling data was generated by CASM 24.2. CASM was run in Phase II mode. Timing constraints on this visit ensure the data are obtained within a few weeks of joint Spitzer observations to minimize variability affects (periods > 200 days). The Spitzer observing window is Feb 25, 2017 to Apr 04, 2017. The Spitzer cycle is 2 years long, so its possible the target won't be observed until similar windows in 2018. (Tic-Visit :proposal-id 14845 :visit-id "01" :proposal-version -1 :trans-version "20160601" :date "16-Sep-2016 16:44:44.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1915040 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14845 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14845 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2882 :al-overhead-at-end 0 :internal-dur-at-end 633 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3221 :pcs-gap 0 ) true 1 0