Subject: WIRE science

From: Craig Tupper <[email-masked]>
Date: Mon, 04 Oct 1999 11:34:31 -0400

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: [email-masked]

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.

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