Spitzer

The SPITZER space mission is an infrared telescope launched on 25 August 2003 by NASA, which is comparable in size to its European predecessor ISO. SPITZER consists of an 85-cm diameter, f/12 telescope, cooled both passively (its orbit maintaining it behind the Earth) and actively (3601 of liquid helium are carried on board to cool the instrument and the focal plane to about 5K) (Fig. 8.19).

Fig. 8.19 Artist's impression of the SPITZER observatory (image credit: courtesy NASA, JPL Caltech)

Fig. 8.19 Artist's impression of the SPITZER observatory (image credit: courtesy NASA, JPL Caltech)

The telescope is fitted with three instruments:

• The IRAC camera (InfraRed Array Camera) with a detector matrix of 256 x 256 pixels, capable of recording the image of a field of 5.12 x 5.12 arcminutes in four spectral bands simultaneously: at 3.6, 4.5, 5.8, and 8 |m

• the IRS spectrograph (InfraRed Spectrograph) consisting of four modules, two giving low-resolution spectra (over the ranges 5.3-14 |m and 14-40 |m) and two giving high-resolution spectra (over the ranges 10-19.9 |m and 19-37 |m)

• the imaging spectrophotometer MIPS (Multiband Imaging Photometer for Spitzer) providing imagery at 24, 70, and 160 |m, as well as spectrometry over a range of 50-100 | m.

Initially, the lifetime of the mission was to be at least 2.5 years, with operation nominally expected to last 5 years.

Because of its size and limited angular resolution (about 5 as at 10 |m), SPITZER was not designed to image exo-systems. It may, however, be used to study the environment of certain stars and detect the presence of discs of dust from the excess infrared radiation.

SPITZER has also been used to study planetary systems that transit (HD 209458b and TrES-1 are examples). Observation of the star before and during a secondary transit (the planet passing behind the star) has enabled us, by photometric comparison, to determine the flux from the planet in a few spectral regions (Charbonneau et al., 2005).

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