SBC resumes science activities (2/20/2007)
ACS Suspends Operations (1/27/2007)
Quick Start Guide to WFPC2 Imaging for ACS Proposers
ACS Backup Programs
New ACS+WFPC2 STAN, 07 February, 2008
Revised SBC Bright Object Magnitude Limits (07 Feb., 2008)
Delivery of a new ACS SBC throughput curve for Synphot (TIR 2008-002)
On November 12th, 2007 a new ACS SBC throughput curve was implemented in CDBS, OPUS and DADS. This new curve is an improved version and accounts for SBC red leak. The red leak portion is based on a spectrum of HD 209458 prepared by Paul Goudfrooij.
Boffi, F.R. 21 Apr 2008 (pdf)
A New Geometric Distortion Solution for the ACS/SBC (ISR 08-02)
We have used ACS/SBC observations of two UV astrometric fields derived from ACS/HRC data to create a new geometric distortion solution for the Solar Blind Channel. The new solution consists of three components: (a) a filter-dependent linear part that takes into account the existence of three epoch ranges in the SBC alignment; (b) the remaining 24 higher-order components of a 4th degree polynomial; and (c) a fine-correction look-up table. Some of the previous solutions introduced possible errors of several pixels when producing mosaics due to an incorrect orientation. That issue has been solved and the accuracy due to the solution itself (excluding rotation) has been improved by an additional factor of 1.5-2.0. As a result, it is now possible to measure positions of medium to high S/N stars with a relative astrometric accuracy of 3-4 mas.
Jesus Maiz Apellaniz 10 Apr 2008 (pdf)
HST Focus Variations with Temperature (ACS ISR 08-03)
One of the main advantages of space observatories is the quality and stability of the point spread function that allows programs not feasible from the ground. However, when pushed to the limits, even the Hubble Space Telescope exhibits variations in the PSF that can be problematic for studies like weak lensing or identification of the host halos of bright quasars at high redshift. These variations are primarily due to small displacements in the focus of the telescope, which to a first approximation can be ascribed to temperature variations. The aim of this report is to characterize the variation of the focus position for HST in terms of the average temperature sensor values of the telescope. We propose a comprehensive temperature-focus model able to predict the position of the focus at the micron level over a dynamic range that extends from sub-orbital variations (< 1 hour) to seasonal and yearly variations. This allows us to predict the focus position significantly more accurately than using interpolation of the monthly direct measurements. Our model is also at least as accurate as the previously proposed breathing model for sub-orbital variations and it is the first one that describes longer term variations, potentially helping the determination of the model point spread function for observations lacking reference point sources.
Daiana Di Nino 08 May 2008 (pdf)
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