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Pulsational activity changes in the Cepheid Polaris (α UMi) during 2017-2018: a new amplitude decrease
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DOI：10.1093/mnrasl/sly170.png)
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Abstract
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We present an analysis of 67 recent spectra of alpha UMi (Polaris) obtained in 2017 August-2018 May. Frequency analysis reveals an increase in the pulsation period to 3(d).970662 relative to our 2016/17 observations. The radial velocity amplitude was found to be 3.87 km s(-1) in the last half of 2017, but dropped to 2.80 km s(-1) during the first half of 2018. In comparison with 4.16 km s(-1) observed by us in 2015, the observations reveal a new decrease in pulsation amplitude. Such a result is unexpected given that a gradual amplitude growth was evident during the last decade. The average values of T-eff were found to be 6017 K and 6039 K, respectively, but the T-eff amplitude has increased despite the decrease in radial velocity amplitude. Possibly that could be explained by the presence of starspots on the Cepheid's surface.
Keywords:
stars: variables: Cepheids
stars: atmospheres
techniques: radial velocities
stars: individual: alpha UMi
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