ALMA opens another window to the universe in the 500 GHz frequency band. Astronomers successfully synthesized the distribution of atomic carbon around a planetary nebula NGC 6302 in test observations with the ALMA Band 8 receiver, developed by the National Astronomical Observatory of Japan (NAOJ). This is the first 500 GHz band astronomical image captured by a radio interferometer with unprecedentedly high resolution.

Figure 1
Planetary Nebula NGC 6302. The right image is the composite of ALMA Band 8 (yellow) and the Hubble Space Telescope (gray). Upper left image is the whole view of NGC 6302 taken by the Hubble Space Telescope. Lower left panel shows the line profile of atomic carbon.
Credit: ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope

NGC 6302 is a planetary nebula, which is in the final stage of the life of a star with a mass several times that of the Sun. Visible light image shows a bipolar shape of gas ejected from the dying star. ALMA with the Band 8 receivers targeted at the center of the nebula and revealed that the distribution of carbon atom is concentrated in a small part, which is similar to a dust and gas disk around the central star that has been found by previous observations with other telescopes. Further observations of carbon atom with better resolution will give us more detailed view of the chemical environment in the nebula.

Figure 2
ALMA Band 8 receiver cartridge
Credit: NAOJ

So far, observations in the 500 GHz band, including emission line from cosmic carbon atom, have been made with single dish radio telescopes. The typical spatial resolution of those observations is 15 arcseconds or larger (1 arcsecond corresponds to 1/3600 of 1 degree), however, ALMA achieved a high resolution of 3.5 arcseconds in this test observations. By installing the receiver into all the ALMA antennas, the resolution becomes even better by 400 times. Astronomers around the world have high expectations for observations with Band 8.

Yutaro Sekimoto, an associate professor at NAOJ and the leader of the Band 8 receiver development team at the NAOJ’s advanced Technology Center says “I deeply appreciate long and hard efforts of all staff to realize ALMA observation of carbon atom. I expect further ALMA observations will unveil the evolution process of interstellar matter.”

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