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Polish Astronomers Discover NSVS 2983201 is a Contact Binary System


The chart of sky around NSVS 2983201. The chart has 15' by 15' size, and is oriented North-down, East-right. The FOV of the CCD camera was shifted slightly to the East, so that the primary comparison star wouldn't be so close to the edge of the frame. Credit: Dębski et al., 2022.
The chart of sky around NSVS 2983201. The chart has 15' by 15' size, and is oriented North-down, East-right. The FOV of the CCD camera was shifted slightly to the East, so that the primary comparison star wouldn't be so close to the edge of the frame. Credit: Dębski et al., 2022.

Polish astronomers from the Jagiellonian University's Astronomical Observatory in Kraków have confirmed that NSVS 2983201, also known as KR00245, is a contact binary system. The team, led by Bartłomiej Dębski, based their findings on photometric data collected in October 2022 using the Apogee Alta U42 camera on the Astronomical Observatory's Cassegrain telescope. Their study was published on December 28th on the arXiv pre-print repository.


What are Contact Binary Systems?


Contact binary systems are composed of two stars that orbit closely around each other and share a common atmosphere. These systems are thought to be formed through the merger of two stars that were once separate, but came into close proximity and eventually coalesced. Contact binary systems are relatively rare, comprising only about 10% of all binary systems.


Why are Contact Binary Systems Important?


The study of variable stars, of which contact binary systems are a subset, can provide important insights into the structure and evolution of stars. Additionally, understanding the distance scale of the universe is closely tied to the study of variable stars. By calculating the distance to NSVS 2983201, the Polish team was able to determine the absolute magnitude of the system and confirm that it is a contact binary.


Observations of NSVS 2983201

The Polish team collected 190 photometric frames in each filter (B, V, R, and I) using exposure times of 40 seconds, 30 seconds, 20 seconds, and 20 seconds, respectively. The data was calibrated using on-sky Flatframes and Bias- and Darkframes collected on the same day as the observations. The team applied two methods to determine the fundamental parameters of NSVS 2983201, resulting in estimated distances of 4,250 light years and 4,560 light years.


Based on the estimated distance, the team calculated the absolute magnitude of NSVS 2983201 to be 4.71 and 4.56 mag, respectively. Using these results and the system's mass ratio of approximately 0.3585, the team was able to determine the orbital separation and masses of the two stars in the system. Depending on the distance and absolute magnitude, the orbital separation was found to be 2.04 or 2.19 solar radii, confirming NSVS 2983201 as a contact binary.


The team also identified a large circumpolar starspot on the surface of the primary star, which they believe to be of magnetic origin and visible as a subluminous region in the visual wavelengths. The authors of the paper speculate that this spot is the result of the primary star having a thicker convective envelope.


Conclusion


The Polish team's observations of NSVS 2983201 have confirmed that it is a contact binary system, providing valuable insights into the nature of this rare type of binary system. Further study of variable stars like NSVS 2983201 has the potential to deepen our understanding of the structure and evolution of stars and the distance scale of the universe.


Journal Information: B. Debski et al, A study of a contact binary system NSVS 2983201, arXiv (2022). DOI: 10.48550/arxiv.2212.14085
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