0 Assigned ID: 219 ----- Attempting Submission 1 (Thu Apr 10 17:52:12 GMT 2014) ----- HST Phase I Proposal 219 (SMC_IMFAPT.apt) successfully submitted. ----- Attempting Submission 2 (Fri Apr 11 22:27:04 GMT 2014) ----- HST Phase I Proposal 219 (SMC_IMFAPT.apt) successfully submitted. ----- Attempting Submission 3 (Fri Apr 11 22:29:20 GMT 2014) ----- HST Phase I Proposal 219 (SMC_IMFAPT.apt) successfully submitted. ----- Attempting Submission 4 (Fri Apr 11 22:35:18 GMT 2014) ----- HST Phase I Proposal 219 (SMC_IMFAPT.apt) successfully submitted. 0 ----- Attempting Submission 1 (Tue Jul 15 14:46:56 GMT 2014) ----- The Metallicity Dependence of the Initial Mass Function We propose to measure the metallicity dependence of the initial mass function (IMF), through a high-precision study of the stellar luminosity function in a remote halo field of the Small Magellanic Cloud (SMC). In a previous HST investigation of an [Fe/H] = -1.1 SMC halo field, we achieved one of the most accurate measurements of the stellar IMF to date. Based on resolved photometry of 10,000 stars, we demonstrated that the IMF over a mass of M = 0.37 to 0.93 Msun is a single power law with slope \alpha = -1.90 (dN/dM = M^\alpha; 3-sigma uncertainty of +0.15, -0.10). Comparing our measurement directly to high-precision local studies of the stellar IMF for stars with the same mass range but [Fe/H] = 0 provides firm new evidence that the IMF is flattening at low metallicities. Using 6 orbits on HST, we propose to now compare our IMF from the Kalirai et al. (2013) study to a new SMC halo field with a very similar set of general properties (e.g., density, star formation history, distance, binary fraction), yet one that is 3 times more metal-poor at [Fe/H] = -1.6. This new field has been carefully chosen from a large ground-based imaging and VLT multiobject spectroscopic survey as the most metal-poor population that is well characterized in the Magellenic Clouds. Using both the ACS and WFC3 instruments simultaneously on HST, we will measure ~3000 stars along the unevolved main-sequence of this population from F606W = 23 - 28.1. Over a mass range of M = 0.40 to 0.90 Msun, these measurements will provide a controlled experiment to determine the power-law slope of the IMF to an accuracy of 0.20, and yield a sensitive characterization of its metallicity dependence. Visits 1 and 2 each target one field in the SMC halo with ACS (primary) and WFC3 (parallel). Each visit has 3 orbits in it, consisting of 6 exposures in F606W and 4 exposures in F814W in both camera. All exposures are dithered. The two fields in each respective visit are offset and placed in locations of the SMC halo that overlap our ground based spectroscopy and avoid obvious bright stars. The same orientation should be used in both visits. RESOLVED STELLAR POPULATIONS Default false false 0.0 0.0 false false false SUPPORTED GALAXY MAGELLANIC IRREGULAR J2000 J2000 GALAXY MAGELLANIC IRREGULAR J2000 J2000 ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W The scheduling data was generated by CASM 22.2. 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