The Michelle Spectrometer - Dissecting a Planetary Nebula
Michelle is the world's most versatile astronomical instrument, sensitive to the thermal infrared wavelengths which are emitted most strongly by bodies at temperatures close to that of our own earth. This versatility is well illustrated by the series of pictures below which show the planetary nebula NGC 6572, the expanding bubble of dust and gas which marks the site where a star blew off most of its atmosphere some 1000 years ago.
Image of NGC6572 taken at a wavelength of 11.6microns.
This image was taken when Michelle was mounted on UKIRT, at a wavelength of 11.6 microns, and shows the shell of dust heated to roughly room temperature by the nebula's very hot central star.
Low resolution spectrum of NGC6572 covering the 8 to 13 micron band with a spatial coverage of 0.75 by 8 arcseconds.
Taken only a few minutes after the first image, in this image the light from a narrow slice running north to south through the centre of the nebula has been dispersed into its component thermal infrared colours using one of Michelle's five diffraction gratings. The faint broad yellow band is then a spectrum which covers the wavelength range from 8 to 13 microns. Its pattern can be used to identify the mineralogy, density and temperature of the warm dust. The three bright, narrow vertical lines show where atoms of argon, sulphur and neon are being ionised by the star's intense ultraviolet light.
Velocity structure in the SIV line. The picture covers some 100km/sec, and uses the same spatial coverage as above
This picture is also a spectrum, but this time measured using another diffraction grating which is capable of dispersing a very narrow spectral band across Michelle's light sensitive detector. The lemon shaped feature shows the same spectral line of ionized sulphur seen above, but now with the wavelength scale expanded by a factor of 100. At this level of detail, broadening of the spectral line is seen which is caused by the gas in the nebula expanding at a velocity of around 15 kilometres per second, half that of our earth around the sun. The north to south skew shows that the gas is not expanding in all directions equally, rather, it has a bipolar structure.
Michelle's unprecedented power for analysing an infrared target in the space of a single night has been increased in efficiency by a factor of over 20 by being moved over to the Gemini telescope.
More information about Michelle on Gemini can be found on the Gemini website.