THE PANCHROMATIC HUBBLE ANDROMEDA TREASURY

摘要: The Panchromatic Hubble Andromeda Treasury is an ongoing Space Telescope Multi-Cycle program to image ~1/3 of M31's star-forming disk in six filters, spanning from the ultraviolet (UV) near-infrared (NIR). We use Wide Field Camera 3 (WFC3) and Advanced for Surveys (ACS) resolve galaxy into millions individual stars with projected radii 0 20 kpc. full survey will cover a contiguous 0.5 deg^(2)area 828 orbits. Imaging being obtained F275W F336W filters on WFC3/UVIS camera, F475W F814W ACS/WFC, F110W F160W WFC3/IR. resulting wavelength coverage gives excellent constraints stellar temperature, bolometric luminosity, extinction most spectral types. data produce photometry signal-to-noise ratio 4 at m F_(275W) = 25.1, m_(F336W) 24.9, m_(F475W) 27.9, m_(F814W) 27.1, m_(F110W) 25.5, m_(F160W) 24.6 single pointings uncrowded outer disk; inner disk, however, optical NIR are crowding limited, deepest reliable magnitudes up 5 mag brighter. Observations carried out two orbits per pointing, split between WFC3/IR cameras primary mode, ACS/WFC run parallel. All dithered Nyquist-sampled images F475W, F814W, F160W. describe observing strategy, photometry, astrometry, products available survey, along extensive testing photometric stability, errors, spatially dependent biases, telescope pointing control. also report initial fits structure derived density red giant branch stars, way that independent assumed mass-to-light ratios robust variations dust extinction. These show 10 kpc ring not just region enhanced recent star formation, but instead dynamical containing significant overdensity ages >1 Gyr.