Charge‐Transfer Efficiency of WFPC2

Abstract

Observations of u Centauri have been used to characterize the charge-transfer efficiency (CTE) of the Wide Field and Planetary Camera 2 (WFPC2) on board the Hubble Space T elescope. A set of formulae has been developed to correct aperture photometry for CTE loss with dependencies on the X-and Y -positions, the background counts, the brightness of the star, and the time of the observation. The observations indicate that for very faint stars on a very faint background, the CTE loss from the top to the bottom of a chip has increased from about 3% shortly after the cooldown of WFPC2 (1994 April 23) to roughly 40% in 1999 February. In general, typical WFPC2 exposures are much longer than these shortcalibration images, resulting in higher background which signiÐcantly reduces the CTE loss and minimizes the CTE problem for most science exposures.

Supernova 1991T and the Value of the Hubble Constant

“…1 As was done in Gibson et al (2000b) and Freedman et al (2001), the Wide Field Planetary Camera 2 (WFPC2) photometric zero-point and charge-transfer corrections adopted are essentially those of Stetson (1998), which are nearly identical to those of Whitmore, Heyer, & Casertano (1999) and Dolphin (2000). The quoted systematic uncertainty in our final result incorporates a component that allows for imprecision in our current understanding of the spatial and temporal variations of the WFPC charge-transfer inefficiency.…”

The star cluster population of M 51

“…A final −0.1 mag correction was applied to all sources to correct for the light missed in the 0.5 aperture. After applying the aperture corrections, the magnitudes where corrected for CTE loss according to the equations of Whitmore et al (1999a).…”

“…Indeed, we expect that the first period of disruption is largely mass independent in order that the mass functions (as interpreted through the luminosity function) of extremely young (<10 Myr) cluster systems such as in the Antennae (Whitmore et al 1999a) is similar to that of intermediate-age populations (300 Myr−3 Gyr) such as in NGC 7252 (Miller et al 1997) and NGC 3610 .…”

“…star clusters in the center of spiral galaxies, Böker et al 2001) or star cluster systems in extreme environments such as galactic mergers (e.g. Miller et al 1997;Whitmore et al 1999a). In order to form a baseline to study the effects of environment on cluster formation, evolution and general cluster properties, one must study the properties of clusters in normal (i.e.…”

Hubble Space TelescopeColor‐Magnitude Data for Globular Clusters. I. Transformations between STIS LP Magnitudes and WFPC2 F606W and F814W Magnitudes

“…However, since geometric distortion mainly affects stars lying near the edges of the WFPC2 chips, while our STIS frames tend to overlie the central part of the respective WF images and cover only about 22% of the field of view of a WF camera, we have ignored this correction. The latest correction algorithms for the CTE effect and the LvS anomaly are described by Whitmore, Heyer, & Casertano (1999) and Casertano & Mutchler (1998), respectively, but each depends on the total counts detected for a star and are thus exposure-time dependent and inapplicable to data made up of a combination of images having different exposure times. For this reason, and because the WFPC2 photometry of M15 was not corrected for these two effects by Piotto et al (1997), we have not corrected the WFPC2 magnitudes of the 47 Tuc stars for either the CTE effect or the LvS anomaly.…”