A1 Vertaisarvioitu alkuperäisartikkeli tieteellisessä lehdessä
The puzzling story of flare inactive ultra-fast-rotating M dwarfs - III. Investigating X-ray activity; 
Tekijät: Doyle, Lauren; King, George W.; Ramsay, Gavin; Corrales, Lía R.; Bagnulo, Stefano; Doyle, J. Gerry; Hakala, Pasi
Kustantaja: Oxford University Press
Julkaisuvuosi: 2026
Lehti: Monthly Notices of the Royal Astronomical Society
Artikkelin numero: stag681
Vuosikerta: 548
Numero: 3
ISSN: 0035-8711
eISSN: 1365-2966
DOI: https://doi.org/10.1093/mnras/stag681
Julkaisun avoimuus kirjaamishetkellä: Avoimesti saatavilla
Julkaisukanavan avoimuus : Kokonaan avoin julkaisukanava
Verkko-osoite: https://academic.oup.com/mnras/article/548/3/stag681/8651297
Rinnakkaistallenteen osoite: https://research.utu.fi/converis/portal/detail/Publication/526493316
Rinnakkaistallenteen lisenssi: CC BY
Rinnakkaistallennetun julkaisun versio: Kustantajan versio
According to activity-rotation relations, rapid rotators are expected to show high levels of magnetic activity. However, recent studies with TESS have found ultra-fast-rotating (UFR) M dwarfs with periods d displaying low levels of flaring activity. There have been efforts to explore their magnetic field strengths through spectropolarimetric measurements and to assess the potential for binarity. However, neither could fully explain the lack of observed flaring activity despite their rapid rotation. Another avenue for investigation is to measure their coronal emission for signs of supersaturation: an underluminosity in X-rays observed for some rapidly rotating FGK stars. Therefore, in this study, we utilize X-ray observations from Swift and XMM–Newton of 10 M dwarf ultra-fast rotators with P < 1 d to determine their X-ray luminosities. Overall, we do not find evidence for supersaturation amongst our UFR M dwarf stars, instead determining them to be at the saturated level, or perhaps even enhanced. Therefore, supersaturation seems not to be the main driver behind the reduced level of flaring activity observed in these stars, and the mystery behind the magnetic activity of UFR low-mass stars remains. Additionally, we provide an updated analysis on the long-term variability within our sample using TESS light curves taken during Cycles 5 and 7. We identify 352 optical flares from our sample with energies between 1.2 × 1031 and 8.7 × 1034 erg. We determine flare rates for each TESS cycle, compare them, identifying variations across a 7-yr timespan and attribute this to potential activity cycles.
Avainsanat:
stars: activity, stars: flare, stars: low-mass, stars: rotation, X-rays: stars
Ladattava julkaisu This is an electronic reprint of the original article. |  |
Julkaisussa olevat rahoitustiedot:
LD would like to acknowledge funding from the UK Space Agency. We include data in this paper collected by the TESS mission, where funding for the TESS mission is provided by the NASA Explorer Program. This work presented results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC was provided by national institutions, in particular, the institutions participating in the Gaia MultiLateral Agreement (MLA). The Gaia mission website is https://www.cosmos.esa.int/gaia. The Gaia archive website is https://archives.esac.esa.int/gaia. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. We also used observations obtained with XMM–Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.
