Hubble Status Report - February 2006
In October 2005 an electronic anomaly was discovered in the WF4 CCD of the Wide-Field and Planetary Camera 2 (WFPC2), where the bias level occasionally becomes unstable causing corrupted photometry or blank images. Early indications of the problem occurred in 2002, and serious impacts began in 2004 with a small fraction of images having significantly degraded photometry. By late 2005 the anomaly grew more severe. Special calibrations of the anomalous WF4 photometry were performed on-orbit, and scripts to correct science images were created and tested. The root cause may be an anomalous hyper-sensitivity to temperature swings in the camera head amplifier, perhaps due to radiation damage. A mitigation strategy was created where the electronic bay temperatures are lowered and stabilized; plans are underway to test this in January 2006.
The 2005 HST Calibration Workshop was held at Space Telescope Science Institute in October 2005. Charge transfer inefficiency, time-dependent sensitivity, fringing effects, point-spread functions, line-spread functions, scattered light, echelle blaze function shifts, charge trapping, hot pixels, cosmic ray persistence... the correctness of interpretation of data from the Hubble Space Telescope hinges on understanding these complex effects and calibrating them out. Other topics covered included the calibration status of COS and WFC3; cross-calibration efforts between HST, Spitzer, and JWST instruments; analysis of dithered undersampled data; HST archive enhancements; and specific software packages. Proceedings of the meeting are planned to be published in early 2006.
In a November 2005 press release an image of star cluster NGC 346 and its surrounding star-formation region was presented using the Advanced Camera for Surveys. Located 210 000 light-years away in the Small Magellanic Cloud (SMC), the cluster is one of the most dynamic and intricately detailed star-forming regions in space. A dramatic structure of arched, ragged filaments with a distinct ridge encircles the cluster.
It has always been a source of frustration that the nearest white-dwarf star is buried in the glow of the bright star Sirius. An international team of astronomers has used the Hubble Space Telescope to isolate the light from the white dwarf and the new results allow them to measure precisely its mass based on how its intense gravitational field alters the wavelengths of light emitted by the star. The team found that Sirius B has a mass that is 98 percent that of the sun.
Even though the Voyager 2 spacecraft paid a close-up visit to Uranus in 1986, the distant planet continues revealing surprises to the eye of NASA's Hubble Space Telescope. Hubble's high sensitivity and sharp view has uncovered a pair of giant rings girdling the planet. The largest is twice the diameter of the planet's previously known ring system, first discovered in the late 1970s. Hubble also spied two small satellites, named Mab and Cupid. One of the satellites shares an orbit with the outermost of the new rings. The satellite is probably the source of fresh dust that keeps replenishing the ring with new material knocked off the satellite from meteoroid impacts. Without such replenishment, the dust in the ring would slowly spiral in toward Uranus.