Infrared Telescopes

1. Infrared Telescopes

2. The Electromagnetic Spectrum

3. see different phenomena at different wavelengths

4. 1800: Discovery of IR Light Herschel used a prism to separate sunlight into colors. He used a thermometer to determine the temperature in each color. Two were placed off to the side as controls. The highest temperature was found beyond red light where no light was seen.

5. Optical IR penetrates dust more easily than optical Infrared

6. Optical Dust glows at the longest IR (and radio) wavelengths Near-Infrared Far-infrared

10. Because the most distant galaxies are highly redshifted, IR telescopes are needed to detect them

11. The atmosphere produces many absorption lines at IR wavelengths (called telluric absorption); some wavelength ranges are totally opaque Challenges for IR telescopes

12. Challenges for IR telescopes The telescope and atmosphere glow brightly at IR wavelengths, which hampers detection of faint IR photons from space. It’s like trying to observe stars at optical wavelengths during the day! on the ground in space

13. Designing an Infrared Telescope The same basic design and materials are used for collecting both optical and IR light. As a result, telescopes often can observe in both wavelength regimes. However, telescopes are usually optimized for specific wavelengths through the details of their design (mirror coatings, camera detectors, etc.).

14. Designing an Infrared Telescope To reduce the absorption of starlight by the atmosphere (mostly water vapor) and thermal emission from the atmosphere, place a telescope on a high mountain, on an airplane, or in space.

15. Designing an Infrared Telescope To reduce the thermal emission by the telescope and instrument, make them as cold as possible. For shorter IR wavelengths, it is sufficient to cool the instrument with liquid nitrogen (77 K); the telescope can be at room temperature. But for longer IR wavelengths, both the telescope and instrument need to be close to absolute zero, so they are placed in space.

16. Mauna Kea IR telescopes became possible in the 1960's with the advances in IR detectors. At an elevation of 13,796 ft., the summit of Mauna Kea on the island of Hawaii is above much of the absorbing water vapor in the atmosphere. It was one of the first sites for IR telescopes.

17. IRAS In 1983, the Infrared Astronomical Satellite (IRAS) scanned most of the sky at far-IR wavelengths. IRAS doubled the number of cataloged astronomical sources by detecting about 500,000 IR sources. IRAS discoveries included a disk of dust grains around the star Vega, six new comets, and ultra-luminous IR galaxies, as well as wisps of warm dust called IR cirrus.

18. 2MASS Between 1997 and 2001, the Two Micron All-Sky Survey (2MASS) imaged the entire sky at near-IR wavelengths using two telescopes in Arizona and Chile. 2MASS has been valuable for many topics in astronomy, including the structure of the Milky Way and the discovery of brown dwarfs.

19. 2MASS movie of Milky Way

20. Hubble Space Telescope Although it focuses primarily on optical wavelengths, Hubble does operate at near-IR wavelengths as well. As in the optical, Hubble provides very sharp images at IR wavelengths because it is above the atmosphere. 2MASS Hubble

21. Spitzer Space Telescope The Spitzer Space Telescope was full operational from 2003-2009, and continues to function in a more limited capacity. It operates from near- to far-IR wavelengths and is the last of NASA's "great observatories”. Like Hubble, Spitzer observes specific targets rather than the entire sky. Spitzer

23. Finding brown dwarfs companions with Spitzer optical

24. Finding brown dwarfs companions with Spitzer infrared with Spitzer

25. Finding brown dwarfs companions with Spitzer optical

26. Finding brown dwarfs companions with Spitzer infrared with Spitzer

30. Herschel Space Observatory Herschel was launched in 2009 by the European Space Agency for a 3 year mission. It operates at far-IR wavelengths. Because it has a larger mirror than Spitzer (3.5 m vs. 0.85 m), it produces sharper images.

32. Herschel’s Orbit

33. Wide-field Infrared Survey Explorer (WISE) WISE was launched by NASA in late 2009 and completed a mid-IR imaging survey of the entire sky in July 2010. The survey is a new version of IRAS with much sharper and more sensitive images. WISE will be used to search for objects that are cold, dusty, or highly redshifted. IRAS WISE (predicted)

34. Orbit of Wise

35. As Earth orbits the Sun, WISE’s orbit also rotates to maintain the spacecraft’s orientation to Earth and Sun. Orbit of Wise

36. Each orbit, a circular strip of the sky is imaged. As the orbit itself rotates, a slightly different strip is imaged. Orbit of Wise

37. Which of these 3 space telescopes would be best for detecting light from a brown dwarf? (Brown dwarfs are very cold objects, sort of like planets free-floating in space.) Compton C) Spitzer A) Chandra B) Hubble

38. Which of these 3 space telescopes would be best for detecting light from very hot gas spiraling into a black hole? Compton C) Spitzer A) Chandra B) Hubble

39. Which of these 3 space telescopes would be best for obtaining a sharp image of Mars to study its surface features? Compton C) Spitzer A) Chandra B) Hubble