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Object Name
   NGC 1333 IRAS 4A
Position: RA, Dec (J2000)
   03:29:10.4 31:13:33
   1000 light year (320 pc)
   Very Large Array (VLA)
   23.7 GHz / 1.26 cm [NH3 (2, 2)]
   23.9 GHz / 1.26 cm [NH3 (3, 3)]
   22.2 GHz / 1.35 cm (H2O 616-523)
   22.5 GHz / 1.33 cm (continuum)


    Minho Choi, KASI

Twin Protostellar Disks with Vastly Dissimilar Characters

Astronomers in Korea and Japan observed both gaseous and solid material in a pair of protostellar disks and found that the twin disks have very different properties. There are two protostars, NGC 1333 IRAS 4A1/2, at the center of the new radio images. Among them, A1 is brighter in the radio emission from interstellar dust while A2 is brighter in the emission from molecular gas. A1 and A2 are located in a single molecular cloud. That is, they are twin baby stars being made in a single mother body.
    By comparing the strength of radio waves from A1 and A2, it was found that the rotating disk around the protostar A2 is relatively rich in gaseous material while the A1 disk is relatively dusty. Their gas-to-dust ratios are different by a factor or about 7 even though they belong to a single molecular cloud. A possible explanation for this difference may be that the star formation of A2 is unusually active and that its accretion disk may contain a large amount of warm gas heated by shock waves. A2 may be growing faster than A1.
    It is very rare to detect all the members of a protobinary system in images of both gas and dust, and such observations make it possible to compare two protostars in the same environment. In addition, because accretion disks will become planetary systems, these two stars will later have planetary systems with chemical compositions very different from each other.
    Protostars are young stellar objects in a stage of rapid growth. They are found in interstellar molecular clouds and grow by accumulating material from the parental cloud. The material pulled in by gravity does not directly fall to the protostar but make a rotating disk around the star, and we can observe the radio emission from the disk. The NGC 1333 IRAS 4A1/2 protostars are expected to become Sun-like stars in about a million years. They are located in a dark cloud in the constellation of Perseus.

Choi, M., Tatematsu, K., Park, G., & Kang, M.
    Astrophysical Journal, 667, L183 (2007 Oct. 1)
    Ammonia Imaging of the Disks in the NGC 1333 IRAS 4A Protobinary System

Park, G., & Choi, M.
    Astrophysical Journal, 664, L99 (2007 Aug. 1)
    Observations of Water Masers in the NGC 1333 IRAS 4 Region

In this image, color represents the kind of material emitting radio wave. Ammonia gas is in blue, and interstellar dust in red. Yellow spots represent maser (laser in radio wavelength) emission from water vapor. Green shows the silicon monoxide gas outflowing from the protostar.
    To study the IRAS 4A1/2 protobinary, the research team observed the ammonia gas, water vapor, and interstellar solid dust in the accretion disks using the Very Large Array radio telescope in the USA.
    NGC 1333 IRAS 4A is at a distance of about 1000 light year. The separation between A1 and A2 is about 1.8 arcseconds or 580 AU. The angular resolution of the image is about 1.0 arcsecond.

Minho Choi (KASI)
Ken'ichi Tatematsu (NAOJ)
Geumsook Park (KASI, CNU)
Miju Kang (KASI, CNU)

External Links
Very Large Array (VLA)