Images of the UY Aur system courtesy of NAOJ showing the approaching and receding jets.

The majority of stars form together in clusters or with companions known as binaries. Understanding these stellar systems is integral to understanding how stars and even planets form. Jets (narrow streams of gas) and outflows (flows of gas) from single infant stars are quite common, but only a handful of jets or outflows have been observed from multiple low-mass young stars. Astronomers chose to study the outflow structure of UY Aur (Aurigae), a binary star system separated by a distance of less than one arcsecond.

A team of astronomers led by Dr. Tae-Soo Pyo (Subaru Telescope, NAOJ) discovered the complex outflow structure in the binary pair. Using Gemini North’s Near-Infrared Integral Field Spectrometer (NIFS) with the Altair adaptive optics system, the team observed UY Aur and found the primary star has a wide open outflow, while the secondary star has a well-defined jet.

UY Aur A is the more massive and brighter primary star in the stellar duo, while its companion, UY Aur B is fainter and cooler. Both stars have small disks of gas and dust orbiting them as well as a disk that orbits the pair. Receding or “redshifted” jets as well as approaching or “blueshifted” jets have been discovered in this system. The sources behind these jets are still unknown as higher resolution images of the system are needed.

In order to get a better grasp of the system’s complexity, the team tried to identify the source of the receding jets. By using ionized iron gas [FeII], the team was able to study the emission gas distribution and determine that [FeII] is associated with both stars in the system. They were also able to determine the shape of the gas distribution and discovered it originates from the close vicinity of the stars and did not come from the disk of gas surrounding the two stars.

Further study revealed that the gas distribution was different for each star. The approaching gas was spread out in a wide outflow from the primary star with only slight connections to the secondary star, while the receding gas was spread toward the secondary star and beyond.

What makes this possible? Each member of this stellar duo has a disk and both approaching and receding outflows. The primary star produces wide, open bipolar outflows and its receding outflow approaches the secondary star. On the other hand, the approaching gas from the secondary is in a well-defined collimate bipolar jet, with its receding jet aimed at the wide outflow of the primary star. Infrared observations confirm the secondary star’s circumstellar disk is not lined up with the pair’s circumbinary disk; a trait that is indicative of a jet in line with the primary star’s wide outflow.

In a binary system, two jets can be possible if they originate from each of the star’s disks; however, some binaries only show one jet. A more massive sample of [FeII] gas distribution in binary and multiple infant star systems can help shed light on how common the outflow structure of the UY Aur system really is.


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