The Factory and the Beehive. V. Chromospheric and Coronal Activity and Its Dependence on Rotation in Praesepe and the Hyades

Abstract Low-mass (≲1.2 M ⊙ ) main-sequence stars lose angular momentum over time, leading to a decrease in their magnetic activity. The details of this rotation–activity relation remain poorly understood, however. Using observations of members of the ≈700 Myr old Praesepe and Hyades open clusters,...

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Published in:	The Astrophysical journal Vol. 962; no. 1; pp. 12 - 34
Main Authors:	Núñez, Alejandro, Agüeros, Marcel A., Curtis, Jason L., Covey, Kevin R., Douglas, Stephanie T., Chu, Sabine R., DeLaurentiis, Stanislav, Wang, Minzhi (Luna), Drake, Jeremy J.
Format:	Journal Article
Language:	English
Published:	Philadelphia The American Astronomical Society 01-02-2024 IOP Publishing
Subjects:	Angular momentum Chromosphere Corona Coronal activity H alpha line Late-type stars Main sequence stars Open clusters Open star clusters Power law Rotation Stars Stellar atmospheres Stellar chromospheres Stellar coronae Stellar evolution Supersaturation Tracers
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Summary:	Abstract Low-mass (≲1.2 M ⊙ ) main-sequence stars lose angular momentum over time, leading to a decrease in their magnetic activity. The details of this rotation–activity relation remain poorly understood, however. Using observations of members of the ≈700 Myr old Praesepe and Hyades open clusters, we aim to characterize the rotation–activity relation for different tracers of activity at this age. To complement published data, we obtained new optical spectra for 250 Praesepe stars, new X-ray detections for 10, and new rotation periods for 28. These numbers for Hyads are 131, 23, and 137, respectively. The latter increases the number of Hyads with periods by 50%. We used these data to measure the fractional H α and X-ray luminosities, L H α / L bol and L X / L bol , and to calculate Rossby numbers R o . We found that at ≈700 Myr almost all M dwarfs exhibit H α emission, with binaries having the same overall color–H α equivalent width distribution as single stars. In the R o – L H α / L bol plane, unsaturated single stars follow a power law with index β = −5.9 ± 0.8 for R o > 0.3. In the R o – L X / L bol plane, we see evidence for supersaturation for single stars with R o ≲ 0.01, following a power law with index β sup = 0.5 − 0.1 + 0.2 , supporting the hypothesis that the coronae of these stars are being centrifugally stripped. We found that the critical R o value at which activity saturates is smaller for L X / L bol than for L H α / L bol . Finally, we observed an almost 1:1 relation between L H α / L bol and L X / L bol , suggesting that both the corona and the chromosphere experience similar magnetic heating.
Bibliography:	AAS48595 Stars and Stellar Physics
ISSN:	0004-637X 1538-4357
DOI:	10.3847/1538-4357/ad117e