Vanderbilt Scientists Draw Rare Star System Using Over A Century Of Astronomical Observations | Vanderbilt News

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Vanderbilt astronomers have painted their best picture to date of a variable RV Tauri – a rare type of stellar binary, in which two stars orbit in a disk of dust. To sketch out its characteristics, scientists extracted a 130-year-old dataset that covers the widest range of light ever collected for any of these systems, from radio waves to x-rays.

Laura Vega

“There are only about 300 RV Tauri variables known in the Milky Way galaxy,” said Laura Vega, former graduate student of Fisk-Vanderbilt Master-to-Ph.D. Bridge program and postdoctoral fellow of the Heising-Simons Foundation in a Release. “We focused our study on the second brightest system, called U Monocerotis, which is now the first of these systems from which x-rays have been detected.”

Led by Vega, the article describing the results has been published online in The astrophysical journal March 12.

U Mon is located in the constellation Monoceros, about 3,600 light years from Earth. Its two stars rotate every six and a half years or so.

Keivan Stassun (Vanderbilt University / Susan Urmy)

This evolved system has many features and behaviors in common with the newly formed binaries, said co-author Keivan Stassun, Stevenson Professor of Physics and Astronomy and Doctoral Advisor to Vega. Both types of binaries are embedded in gas and dust disks, and in both cases the disks can warp or clump. In young binaries, these distortions could signal the beginnings of the formation of planets.

“We still have questions about a feature of U Mon’s disk that may be answered by future radio observations,” Stassun said. “It is fascinating to see how closely these two stages of binary life are mirrored.”

The main star, an aged yellow supergiant, is about twice the mass of the Sun, but has grown to 100 times the size of the Sun. Scientists know less about the companion star, but they believe it is of similar mass and much younger than the main star.

The cold disc around the two stars is made up of gas and dust ejected by the primary star during its evolution. Using radio observations from the Sub-millimeter network in Maunakea, Hawaii, the Vega team estimated the disk surrounding the binary to be 51 billion kilometers in diameter.

The components of U Mon at scale. Image from NASA’s Goddard Space Flight Center / Chris Smith (USRA / GESTAR)

As part of their dance, the companion star is believed to channel gas from the primary star into its own disk, which heats up accordingly and generates x-rays. This could explain the x-rays detected in 2016 by the European Space Agencyof XMM-Newton satellite.

“XMM observations make U Mon the first RV Tauri variable detected in x-rays,” Kim Weaver, US project scientist and astrophysicist Kim Weaver at NASA Goddard Space Flight Center in Greenbelt, Maryland. “It’s exciting to see multi-wavelength measurements based on the ground and in space coming together to give us new insights into a system that has been studied for a long time.

The oldest available measurement of the system, collected on December 25, 1888, came from the archives of the American Association of Variable Star Observers, the international network of amateur and professional astronomers. The AAVSO has provided additional historical measurements ranging from the mid-1940s to the present day.

The researchers also used archived images cataloged by the Digital Access to a Heavenly Century at Harvard, a program at Harvard College Observatory dedicated to the digitization of astronomical images from photographic glass plates made by ground-based telescopes between the 1880s and the 1990s.

Vega completed his analysis of the U Mon system as Harriett G., a program funded by the NASA’s Office of STEM Engagementof Research and University Education Project for Minorities.

“Laura used this historical data set to detect a feature that would otherwise only appear once in an astronomer’s career,” said co-author Rodolfo Montez Jr., astrophysicist at the Astrophysics Center | Harvard and Smithsonian. “It’s a testament to how our knowledge of the universe is built over time.”



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