From dtupper@hq.nasa.gov Sun Dec 19 14:56:49 1999 Date: Mon, 04 Oct 1999 11:34:31 -0400 From: Craig Tupper To: oss-research@lists.hq.nasa.gov Subject: WIRE science Greetings, research community, Below is a message from Dr. Philippe Crane, WIRE Program Scientist. Please note that any responses should go to him, not to me, the humble list manager. Thanks! --------------------- Dear Colleagues: As many of you are aware, the WIRE satellite, whose primary scientific mission has not succeeded, has nevertheless been used to perform time resolved stellar photometry and, in particular, stellar seismology using the 5 cm star-tracker telescope and its associated CCD camera. The WIRE star-tracker presents a unique opportunity to the astronomy community to utilize the CCD camera from a stabilized platform in space. At present, there are no plans to continue WIRE astronomical observations past the beginning of the next calendar year. However, if there is sufficient interest in the community to make use of the WIRE satellite star-tracker for continued astronomical observations, NASA Headquarters is prepared to provide an opportunity through the ADP program. Please read the attached short description of the capabilities of the WIRE star-tracker. Most importantly, if you think that you would be interested in observations with this instrument, please send me a brief note before the end of October indicating what you have in mind. Not only does this letter not commit NASA to implement an observing program with WIRE, nor would your note commit you to participate in such a program. Sincerely yours, Philippe Crane WIRE Program Scientist NASA Headquarters, Code SR 300 E St. S.W. Washington, D.C. 20546 Tel: 202/358 0377 Fax: 202/358 3097 Email: pcrane@hq.nasa.gov WIRE Star Camera Technical Information The WIRE star camera is a Ball Aerospace and Technologies Corporation model CT-601. It consists of a 52 mm aperture feeding light to a 5122 SiTe CCD. The field of view is 8 x 8 degrees, with a pixel size of 1 arc minute. The gain is approximately 15 electrons/ADU, and the bandpass (which is unfiltered) is roughly V+R. Data is digitized using a 16-bit ADC. The limiting magnitude of the star camera is approximately 6, and pointing is severely degraded beyond this limit. The star camera can be operated in one of two modes. First, single-target mode, where an 8 x 8 pixel box is returned to the ground surrounding a single target. In single-target mode, the observing cadence is 10 Hz. This mode is essentially absolute photometry, and as such is dependent on the pointing characteristics of the satellite (since the CCD FOV is asymmetrically vignetted) and the drift characteristics of the star camera itself. When observing bright stars (m < 2), we have observed little drift: the rms pointing precision of WIRE typically is better than one arc second. Non-Poisson noise in the data appears to be primarily due to thermal drifts in the detector, which for brighter targets (2nd magnitude) contributes a signal less than the Poisson noise. Temperature information is available from a thermistor mounted on the rear of the CCD assembly, should observers wish to attempt correcting for thermal drifts. The second operating mode is multi-target, where up to five targets can be observed simultaneously, though the observing cadence drops to 1 Hz. In this mode, an 8 x 8 pixel box around each star is returned, and relatively crude ensemble photometry can be performed. For observations of a mv = 0 solar-like star, we obtain an integrated count rate of approximately 1.2 x 10**6 electrons/sec. The PSF of the instrument is such that essentially all of the stellar flux is contained in the central 4 pixels of the 64-pixel box, and an annulus around the outer portion of the box can be used for background subtraction. For such a star, the rms noise from all sources in the extracted aperture photometry is approximately 1.3 - 1.5 millimagnitudes. ------------------- To subscribe, unsubscribe, or change your address for this list please follow the directions at: http://spacescience.nasa.gov/announce/listserv.htm#research