Enabling New Science with WFC3

Jason Kalirai, jkalirai@stsci.edu, John MacKenty, mackenty@stsci.edu, and the WFC3 Team

The new Wide Field Camera 3 (WFC3) on Hubble is in full scientific operation! Still in its first year, the instrument is quickly emerging as one of astronomy’s most important tools, and is likely to answer a wide range of scientific questions about the cosmos. In the first weeks of science operations, WFC3 captured images of an impact on Jupiter and detected the highest redshift galaxies ever observed. Over the coming year, about half of all Hubble observations will use the new instrument. In our local cosmic neighborhood, WFC3 will perform a wide variety of studies, including characterization of planets, brown dwarfs, and hydrogen-burning stars. Beyond, it will improve our understanding the formation of stars and galaxies, map cosmological relationships, and perhaps reveal the fate of the universe.

WFC3 in Orbit: First Performance Results

The cameras on Hubble have profoundly influenced the course of modern astrophysics. Until now, the Wide Field Planetary Camera 2 (WFPC2), the Near Infra-Red Camera and Multi-Object Spectrometer (NICMOS), and the Advanced Camera for Surveys (ACS) provided the deepest and most sensitive images ever of stellar populations in the universe. Observing programs like the deep imaging surveys of star clusters and the Hubble Deep Fields have clarified the basic processes that operate in the formation and evolution of stars and galaxies. WFC3 is the next leap forward. Its ultraviolet-visible (UVIS) and the infrared (IR) cameras both offer fields several arcmin wide. Both have ultra-sensitive detectors: CCD in UVIS and mercury-cadmium-telluride in IR. Both deliver high resolution, with spatial scales of 0.04 arcsec in UVIS and 0.13 arcsec in IR. Together, the two cameras contain 77 narrow-, medium-, and wide-band filters—and 3 grisms. WFC3’s combined capabilities allow panchromatic imaging and spectroscopy over a 0.2–1.7 micron wavelength range. It offers substantially higher imaging sensitivity and resolution than previous instruments in the UV and IR.

Following its installation in Hubble in May 2009 by the crew of STS-125, the WFC3 team conducted a comprehensive checkout and calibration program to measure the on-orbit response of the instrument and characterize its performance. Calibration data from the first 10–12 weeks of operation have been fully analyzed and reported in a series of 30 instrument science reports (ISRs, available here). These calibrations used standard stars and star fields, as well as internal lamps. This effort established the optical alignment, pointing corrections, geometric distortion, point-spread function (PSF), and photometric sensitivity and stability. For the most part, these measurements confirmed our ground-based understanding of the detectors. However, as a pleasant surprise, on-orbit observations of photometric standard stars indicate that the instrument is 10–20% more sensitive than expected—across the entire UV–VIS–IR wavelength range.