Hubble Status Report - April 2005
The on-orbit two-gyro mode test using all science instruments was carried out from 20 to 23 February 2005. All indications are that the performance in two-gyro mode is very good. Measurements of the point-spread function (PSF) with the Advanced Camera for Surveys (ACS) show extremely small differences, if any, between two-gyro and three-gyro mode. Measurements taken with a 14th magnitude guide star are essentially the same as those made with a brighter guide star. A first look also shows that the NICMOS coronographic performance is unchanged. The three-day duration of the test has accumulated a good variety of circumstances for slews, Fixed-Head Star Tracker (FHST) acquisitions, guide star acquisitions, etc. The performance of the magnetometer guiding has been excellent. The two-gyro mode requires the on-board software to identify star field found by the Fixed-Head Star Trackers and then evaluate and correct the pointing error.
The results from this test will drive the decision, in late spring, whether to make a proactive switch to two-gyro science mode at the beginning of Cycle 14, rather than incur an interruption of the schedule when two more gyros have failed. An early introduction of the two-gyro science mode is expected to extend the observing lifetime of HST with the current set of gyros by at least 9 months to mid-2008.
The Cycle 14 Phase I proposal deadline occurred on Friday, 21 January 2005. In response to the Call for Proposals, a total of 726 proposals were received. Preliminary statistics indicate requests for about 14 144 orbits. The Time Allocation Committee convened from 14 to 19 March to generate the rank-ordered list of proposals for final approval. Notifications were sent to the proposers during the first week of April, with proposal comments following during the next several weeks. The deadline for the selected proposals to submit their Phase II information is 13 May 2005. Routine Cycle 14 observations are expected to commence in July 2005.
To assess the impact of HST observations on astrophysical research, standard objective measures of productivity and impact are used, in particular, the annual number of published papers based on HST data. The numbers for 2004 became available in February 2005 showing a significant increase and reaching a new record value of 601 published papers. The current total of refereed papers based on Hubble data is over 4700.
Science highlights
Surprisingly complex loops and blobs of cosmic dust lie hidden in the giant elliptical galaxy NGC 1316. A HST image reveals the dust lanes and star clusters. The combination of Hubble's superb spatial resolution and the sensitivity of the Advanced Camera for Surveys (ACS) enabled uniquely accurate measurements of a class of red star clusters in NGC 1316. Astronomers conclude that these clusters constitute clear evidence of the occurrence of a major collision of two spiral galaxies that merged together a few billion years ago to shape NGC 1316 as it appears today.
Viewing Saturn's southern polar region for several days, Hubble snapped a series of photographs of the aurora dancing in the sky. Snapshots show that Saturn's auroras differ in character from day to day, as they do on Earth, moving around on some days and remaining stationary on others. But compared with Earth, where auroral storms develop in about 10 minutes and may last for a few hours, Saturn's auroral displays always appear bright and may last for several days. The observations suggest that Saturn's auroral storms are driven mainly by the pressure of the solar wind rather than by the Sun's magnetic field. Seen from space, an aurora appears as a ring of glowing gases circling a planet's polar region. Auroral displays are initiated when charged particles in space collide with a planet's magnetic field. The charged particles are accelerated to high energies and stream into the upper atmosphere.