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WIRE - the high-precision photometry with the 5.2-cm telescope. In 1994, WIRE (Wide Field Infrared Explorer) was selected as the fifth NASA mission under the Small Explorer (SMEX) program.

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Presentation Transcript
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In 1994, WIRE (Wide Field Infrared Explorer) was selected as the fifth NASA mission under the Small Explorer (SMEX) program.

WIRE was successfully launched into a sun-synchronous low-Earth orbit on 4 March 1999. Equipped with a 12’’ telescope and an infrared camera cooled with hydrogen, it was designed to study faint star burst galaxies.

However, due to incorrectly designed electronics box that prematurely fired explosive devices causing early ejection of the instrument’s telescope cover, the coolant was quickly lost. The main mission failed.

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Derek Buzasi, a research physicist at the Space Sciences Laboratory at the University of California, Berkeley,

proposed to use the satellite star camera to observe pulsations in bright stars.

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A Ball Aerospace CT-601 star tracker

52mm refracting telescope, equipped with 512 x 512 SITe CCD, which can be read out at rates as high as 10 Hz.

The high cadence of observations available with this star camera is made possible by software that locates the 5 brightest stars in the field and reads only an 8x8 pixel box around one selected image. An additional mode of operation, available since November 1999, makes count rate data available on all five stellar images, with a consequent loss of read rate (to 2 Hz for 5 stars).

Field of view – 8.2 x 8.2 degrees,

Pixels – 1.01 arcminute on a side

CCD gain = 15 e- /ADU, RN=30 e-

Camera is unfiltered, but effective response is roughly V+R.

Stellar images defocused to a nominal FWHM of 2 pixels.

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The WIRE satellite is in a Sun-synchronous orbit which, when combined with constraints imposed by the solar panels limits pointing to two strips, each o wide, located perpendicular to the Earth-Sun line.

Due to pointing restrictions two fields were observed during each WIRE orbit – up to 40 minutes per target.

The orbital period has decreased from 96 to 93 minutes in the course of the mission.

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WIRE was used for two epochs with slightly different observing modus.

30 April 1999 – 30 September 2000: around 25 stars were monitored.

Primary targets were kept on the same position within a few hundredths

of a pixel.

But, due to the slow rotation of the satellite, the secondary stars drifted

across the CCD and were not usable for detailed studies.

A break due to funding problems.

December 2003 – 23 October 2006: reprogramming of the satellite

made it possible to keep all five stars fixed on the same position.

This resulted in the light curves for about 200 stars.

In January 2004 the mission operations were moved from Goddard to

Bowie Satellite Operations and Control Center.

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Altair (Alpha Aql) is an A7 IV-V

main sequence star.

While it lies inside the instability strip

it has never been detected to oscillate.