A revisit to the enigmatic variable star 21 Comae
| Autor: | Gerald Handler, Stefan Wallner, Anna Gütl-Wallner, Martin Vaňko, Ewa Niemczura, Theodor Pribulla, Klaus Bernhard, Tomasz Różański, Ernst Paunzen, Werner W. Weiss, Jaymie M. Matthews, Przemysław Walczak, Miroslav Fedurco, Stefan Hümmerich, Thomas Kallinger |
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| Rok vydání: | 2019 |
| Předmět: |
Physics
010308 nuclear & particles physics FOS: Physical sciences Astronomy and Astrophysics Radius Astrophysics Star (graph theory) 01 natural sciences Photometry (optics) Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science 0103 physical sciences Variable star Spectroscopy 010303 astronomy & astrophysics Solar and Stellar Astrophysics (astro-ph.SR) |
| Zdroj: | Monthly Notices of the Royal Astronomical Society. 485:4247-4259 |
| ISSN: | 1365-2966 0035-8711 |
| DOI: | 10.1093/mnras/stz413 |
| Popis: | The magnetic chemically peculiar (Ap/CP2) star 21 Com has been extensively studied in the past, albeit with widely differing and sometimes contradictory results, in particular concerning the occurrence of short term variability between about 5 to 90 minutes. We have performed a new investigation of 21 Com using MOST satellite and high-cadence ground-based photometry, time series spectroscopy, and evolutionary and pulsational modeling. Our analysis confirms that 21 Com is a classical CP2 star showing increased abundances of, in particular, Cr and Sr. From spectroscopic analysis, we have derived Teff = 8900(200) K, log g = 3.9(2), and vsini = 63(2) km/s. Our modeling efforts suggest that 21 Com is a main sequence (MS) star seen equator-on with a mass of 2.29(10) M(Sun) and a radius of R = 2.6(2) R(Sun). Our extensive photometric data confirm the existence of rotational light variability with a period of 2.05219(2) d. However, no significant frequencies with a semi-amplitude exceeding 0.2 mmag were found in the frequency range from 5 to 399 c/d. Our RV data also do not indicate short-term variability. We calculated pulsational models assuming different metallicities and ages, which do not predict the occurrence of unstable modes. The star 18 Com, often employed as comparison star for 21 Com in the past, has been identified as a periodic variable (P = 1.41645 d). While it is impossible to assess whether 21 Com has exhibited short-term variability in the past, the new observational data and several issues/inconsistencies identified in previous studies strongly suggest that 21 Com is neither a delta Scuti nor a roAp pulsator but a "well-behaved" CP2 star exhibiting its trademark rotational variability. 14 pages, 14 figures |
| Databáze: | OpenAIRE |
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