Astronomers Center for High Angular Resolution Astronomy (CHARA) Array observed Polaris, the nearest and brightest classical Cepheid star, which is part of a triple star system.
This false-color image of Polaris taken by the CHARA array in April 2021 reveals large bright and dark spots on the star's surface. Image credit: Evans others., doi:10.3847/1538-4357/ad5e7a.
PolarisCepheid variable, also known as Polaris, Polaris, Alpha Ursa Minoris, HR 424 or HD 8890, is a type of star known as Cepheid variables.
Astronomers use these stars as “standard luminaries” because their true brightness is determined by their pulsation period: brighter stars pulsate more slowly than fainter stars.
How bright a star appears in the sky depends on the star's actual brightness and its distance.
Because astronomers know a Cepheid star's true brightness based on its pulsation period, they can use it to measure the star's distance to its host galaxy and infer the universe's expansion rate.
Dr. Nancy Evans of the Harvard-Smithsonian Center for Astrophysics and her colleagues observed Polaris using the six-telescope CHARA Optical Interferometer Array on Mount Wilson in California.
Their goal was to map the orbit of a nearby, faint companion star that orbits the North Star every 30 years.
“Binary systems are extremely difficult to resolve at their closest approach due to the small distance between the two stars and the large difference in brightness,” Dr Evans said.
The researchers were able to track the orbit of Polaris's nearby companion star and measure its change in size as Polaris pulsates.
From its orbital motion, we know that Polaris has five times the mass of the Sun.
Images of Polaris reveal that its diameter is 46 times that of the Sun.
CHARA's observations also revealed for the first time what the surfaces of Cepheid variables look like.
“CHARA images revealed large bright and dark spots on Polaris' surface that change over time,” said Dr. Gail Schaefer, director of the CHARA array.
“The presence of sunspots and the rotation of the star could be related to the 120-day variation in the measured speed.”
“We plan to continue photographing the North Star,” said University of Michigan professor John Monnier.
“We hope to better understand the mechanisms that produce the spots on Polaris' surface.”
Team paper Published in Astrophysical Journal.
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Nancy Remage Evans others2024. Orbit and dynamic mass of Polaris: Observations with the CHARA array. ApJ 971, 190;doi:10.3847/1538-4357/ad5e7a
Source: www.sci.news
