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The NASA Infrared Telescope Facility (NASA IRTF) is a 3-meter (9.8 ft) telescope optimized for use in infrared astronomy and located at the Mauna Kea Observatory in Hawaii. It was first built to support the Voyager missions and is now the US national facility for infrared astronomy, providing continued support to planetary, solar neighborhood, and deep space applications. The IRTF is operated by the University of Hawaii under a cooperative agreement with NASA. According to the IRTF's time allocation rules, at least 50% of the observing time is devoted to planetary science.[1]
Location(s) | Hawaii County, Hawaii |
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Coordinates | 19°49′35″N 155°28′23″W / 19.8263°N 155.473°W |
Observatory code | T13 |
Telescope style | astronomical observatory Cassegrain reflector infrared telescope |
Diameter | 126 in (3.2 m) |
Website | irtfweb |
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Telescope
editThe IRTF is a 3.0 m (118" effective aperture) classical Cassegrain telescope. The Cassegrain focus f/ratio is f/38 and the primary mirror f/ratio is 2.5. Several aspects of the design of IRTF are optimized for IR observations. The secondary mirror is undersized to prevent the instrument from seeing the thermal emission from the telescope structure around the primary mirror. The primary mirror itself is 126" in diameter, but only the center 118" is used. A small mirror in the center of the secondary mirror prevents the instrument from seeing its own thermal emission. The f/ratio is long to have a small secondary mirror, again to minimize the telescope's thermal emission. The mirror coatings are chosen to have minimal thermal emission. The emissivity of the telescope is usually below 4%. The secondary mirror is mounted on a chopping mechanism to rapidly switch the pointing of the telescope from target to sky at up to 4 Hz.
The IRTF is mounted on a large English yoke equatorial mount. The mount is very stiff, reducing flexure and allowing for accurate pointing of the telescope. Since the telescope is on an equatorial mount, the telescope can observe targets through the zenith without concern for field rotation. The yoke mount prevents the telescope from pointing north of +69 degrees declination. Since the telescope was primarily intended for planetary science, this restriction was considered to be acceptable. Since the telescope is on a heavy mounting, it is relatively immune from vibration or wind shake.
Instrumentation
editThe IRTF hosts four facility instruments: SpeX, NSFCam2, iSHELL, and MIRSI. IRTF also hosts a number of visiting instruments.
SpeX
editSpeX is a medium-resolution 0.8-5.4
iSHELL
editiSHELL is a 1 - 5.3
MIRSI
editMIRSI is a 2.2 to 25
MORIS
editMORIS (MIT Optical Rapid Imaging System) s a high-speed, visible-wavelength camera for use on IRTF using an electron multiplying CCD. MORIS is mounted on the side window of SpeX, and is fed by the internal cold dichroic in SpeX. The design is based on POETS (Portable Occultation, Eclipse, and Transit Systems), which were developed by a collaboration between MIT and Williams College. MORIS is available for open use on IRTF and its user interface has been converted to the IRTF standard interface. In addition to visible light photometry, MORIS is also used as a visible light guider for SpeX, allowing guiding on targets as faint as V=20. The guiding software includes atmospheric dispersion correction to move the visible light guide box to keep the IR image on the SpeX slit.
Visiting instruments
editIRTF also hosts a number of visitor instruments, usually thermal infrared spectrographs. These have recently included TEXES, EXES, BASS, and HIPWAC. And others.
Future instruments
editThe IRTF staff are currently developing SPECTRE, an optical-to-infrared seeing-limited integral field unit.
Past instruments
editCSHELL was retired when iSHELL began operations at IRTF. CSHELL was a 1 - 5.5
NSFCAM2 was a 1-5
Remote observing
editThe majority of IRTF users prefer to use IRTF remotely. Observers can use IRTF from any location with a high speed internet connection, such as their office or home, anywhere around the world. The observer controls the instrument via a VNC session, just as they would at the summit, and communicates with the telescope operator via phone, Polycom, or Skype. The observer calls in and logs in for their time allocation. Remote observing has several advantages. Remote observing spares the observer the time and cost of traveling from their home institution to Hawaii. In the past, when observers traveled to the telescope, the telescope was scheduled in full nights. With remote observing, observers only need to submit a request for the amount of time they need, when they need it, instead of asking for whole nights. Since the observers do not travel to Hawaii, they can also request to use the telescope more frequently. This has enabled the IRTF to support many programs where frequent observations of targets are necessary, such as weekly monitoring of solar system objects. Remote observing has also allowed the IRTF to support target-of-opportunity (ToO) programs. These are programs of high scientific merit where the timing of the observation cannot be predicted at the time that telescope is scheduled. Examples include supernovae, which explode unexpectedly, or near-earth asteroids that may be discovered shortly before their closest approach to the Earth. Although the observers are usually remote, the telescope operator is at the summit to ensure the safety of the facility, assist the observer, and troubleshoot problems that may arise during the night.
Observations
editNASA's Infrared Telescope Facility (IRTF) also made observations of P/2016 BA14, which is a comet that came within about 9 lunar distances of Earth in 2016.[2]
Comparison to contemporaries
editNASA IRTF was built at the same time as the United Kingdom Infrared Telescope; John Jefferies of the Institute for Astronomy, which built the first telescope in the area, said "it has been sometimes a source of embarrassment ... that there are two of them at the same place at the same time. The natural question is asked, Why two? Why don't you build one and share it?".[3]
Dedicated infrared telescopes require a high and dry location, special instrumentation, and similar high-quality mirrors and optics as for visible wavelength observations. Other large optical infrared and near-infrared telescopes circa 1980:
# | Name(s) / Observatory |
Image | Aperture | Spectrum | Altitude | First Light |
---|---|---|---|---|---|---|
1 | United Kingdom Infrared Telescope Joint Astronomy Centre |
380 cm (150 in) | Infrared | 4,205 m (13,796 ft) | 1979 | |
2 | ESO 3.6 m Telescope ESO La Silla Obs. |
357 cm (141 in) | Visible Infrared |
2,400 m (7,874 ft) | 1977 | |
3 | NASA Infrared Telescope Facility Mauna Kea Observatory |
300 cm (118 in) | Infrared | 4,205 m (13,796 ft) | 1979 |
There have been two other smaller near-infrared telescopes: the 150 cm (59 in) Gornergrat Infrared Telescope in the Swiss Alps, and the 160 cm (63 in) telescope at the Mont Mégantic Observatory in Canada.
Location
editSee also
editReferences
edit- ^ IRTF homepage
- ^ "Comet Scanned by NASA Radar". www.jpl.nasa.gov. Retrieved 2018-11-10.
- ^ Jefferies, John (1977-07-29). "John Jefferies" (Oral history). Interviewed by Spencer Weart. American Institute of Physics. Retrieved 2023-01-26.