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First Light of Mosfire Celebrated

WAIMEA, Hawaii, April 12, 2012 — The Mosfire instrument observed the universe with its near-infrared sensing eyes for the first time on April 4, capturing images of a pair of interacting galaxies known as The Antennae. The new device will enable astronomers to study space phenomena more clearly than ever before.

“This is a near-infrared multi-object spectrograph, similar to our popular LRIS and DEIMOS instruments, only at longer wavelengths,” said Bob Goodrich, Keck Observatory’s observing support manager.

An unprocessed image from the Mosfire instrument made on the “first light” night of April 4, 2012. The powerful Keck I telescope and sensitive new instrument gathered this infrared image of two interacting galaxies called The Antennae, despite fast-moving high clouds over Mauna Kea that night. (Images: W.M. Keck Observatory)

Installed on the Keck I telescope at W.M. Keck Observatory, the Mosfire (Multi-Object Spectrometer for Infrared Exploration) gathers spectra, which at infrared wavelengths contain chemical signatures in the light of everything from stars to galaxies. The instrument was developed by engineers and astronomers at Keck Observatory, Caltech, and at the University of California, Los Angeles, and Santa Cruz. 

The first images were taken despite thick cirrus clouds over Mauna Kea. Additional images and spectra were gathered April 5 as part of the continuing commissioning of the instrument.

The Mosfire commissioning team celebrates first light in the Keck I remote operations room at Keck Observatory headquarters. First row from left: Chuck Steidel, co-principal investigator (CIT); Gwen Rudie, graduate student (CIT); Sean Adkins, instrument program manager (WMKO); Ian McLean, co-principal investigator (UCLA); Kristen Kulas, graduate student (UCLA); and Greg Mace, graduate student (UCLA). Second row from left: Nick Konidaris, Mosfire postdoc (CIT); Ryan Trainor, graduate student (CIT); Jason Weiss, software engineer (UCLA); Keith Matthews, instrument scientist (CIT); Marc Kassis, Mosfire support astronomer (WMKO); Allen Honey, software engineer (WMKO); and Shui Kwok, software engineer (WMKO).

Observing in the infrared enables researchers to penetrate cosmic dust clouds and to peer at objects otherwise invisible, like the stars circling the supermassive black hole at the center of the Milky Way.

Mosfire can also image the most distant objects, the light of which has been stretched beyond the red end of the spectrum by the expansion of the universe. This will allow astronomers to study the time when most galaxies formed as well as the period of re-ionization, when the universe was just 500 million to 1 billion years old. Other targets will be nearby stars, young stars and brown dwarfs, which are stars not quite massive enough for normal nuclear fusion to ignite their cores.

Unprocessed April 5, 2012, infrared image of M82, an exotic galaxy in Ursa Major.

The device’s light-sensitive camera and its ability to survey up to 46 objects at a time, then switch targets in only a few minutes, sets it apart from other infrared instruments, which would take days to change targets. It scans the sky with a 6.1-arcmin field of view, which is about 20 percent of a full moon and almost 100 times more sky than the Keck’s current near-infrared camera.

The spectrometer consists of 46 pairs of sliding bars, aligned in rows, that open and close like curtains to image multiple objects in the universe. Each pair of bars blocks the sky, leaving only small slits between them that allow slivers of light from multiple stars or galaxies to be recorded. Light from each slit then enters the spectrometer, which breaks down the objects’ light into their spectrum of wavelengths.

The instrument must be kept at -153 °C to prevent heat from contaminating the infrared signals from space.

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