Doyle, Lauren, Bagnulo, Stefano, Ramsay, Gavin, Doyle, J. Gerry and Hakala, Pasi (2022) The puzzling story of flare inactive ultra fast rotating M dwarfs. I. Exploring their magnetic fields. Monthly Notices of the Royal Astronomical Society, 512 (1). pp. 979-988. doi:10.1093/mnras/stac464 ISSN 1745-3933.

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Abstract

Stars which are rapidly rotating are expected to show high levels of activity according to the activity-rotation relation. However, previous TESS studies have found Ultra Fast Rotating (UFR) M dwarfs with periods less than one day displaying low levels of flaring activity. As a result, in this study, we utilize VLT/FORS2 spectropolarimetric data of ten M dwarf UFR stars between spectral types ∼M2 - M6 all with Prot < 1, to detect the presence of a magnetic field. We divide our sample into rotation period bins of equal size, with one star having many more flares in the TESS lightcurve than the other. We also provide an analysis of the long-term variability within our sample usingTESS lightcurves taken during Cycles 1 and 3 (up to three years apart). We identify 605 flares from our sample which have energies between 2.0× 1031 and 5.4× 1034 erg. Although we find no significance difference in the flare rate between the Cycles, two of our targets display changes in their lightcurve morphology, potentially caused by a difference in the spot distribution. Overall, we find five stars (50 per cent) in our sample have a detectable magnetic field with strengths ∼1–2 kG. Of these five, four were the more flare active stars within the period bins with one being the less flare active star. It would appear the magnetic field strength may not be the answer to the lack of flaring activity and supersaturation or magnetic field configuration may play a role. However, it is clear the relationship between rotation and activity is more complex than a steady decrease over time.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
SWORD Depositor:	Library Publications Router
Library of Congress Subject Headings (LCSH):	Dwarf stars , Dwarf stars -- Magnetic properties, Low mass stars -- Magnetic properties, Flare stars
Journal or Publication Title:	Monthly Notices of the Royal Astronomical Society
Publisher:	Oxford University Press
ISSN:	1745-3933
Official Date:	May 2022
Dates:	Date Event May 2022 Published 21 February 2022 Available 10 February 2022 Accepted
Volume:	512
Number:	1
Page Range:	pp. 979-988
DOI:	10.1093/mnras/stac464
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Open Access (Creative Commons)
Date of first compliant deposit:	22 March 2022
Date of first compliant Open Access:	23 March 2022
RIOXX Funder/Project Grant:	Project/Grant ID RIOXX Funder Name Funder ID UNSPECIFIED Northern Ireland Executive https://www.northernireland.gov.uk/ MR/S035214/1 UK Research and Innovation http://dx.doi.org/10.13039/100014013 Emeritus Fellowship Leverhulme Trust http://dx.doi.org/10.13039/501100000275

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