Astrophys. J., 834, 176-176 (2017/January-2)
Chromospheric and coronal activity in the 500 Myr old open cluster M37: evidence for coronal stripping?
NUNEZ A., AGUEROS M.A., COVEY K.R. and LOPEZ-MORALES M.
Abstract (from CDS):
We present the results of a spectroscopic survey to characterize chromospheric activity, as measured by Hαemission, in low-mass members of the 500 Myr old open cluster M37. Combining our new measurements of Hαluminosities (LHα) with previously cataloged stellar properties, we identify saturated and unsaturated regimes in the dependence of the LHα-to-bolometric luminosity ratio, LHα/Lbol, on the Rossby number Ro. All rotators with Ro smaller than 0.03 ± 0.01 converge to an activity level of LHα/Lbol=(1.27±0.02)×10–4. This saturation threshold (Ro,sat=0.03±0.01) is statistically smaller than that found in most studies of the rotation-activity relation. In the unsaturated regime, slower rotators have lower levels of chromospheric activity, with LHα/Lbol(Ro) following a power-law of index β=-0.51±0.02, slightly shallower than that found for a combined ≃650 Myr old sample of Hyades and Praesepe stars. By comparing this unsaturated behavior to that previously found for coronal activity in M37 (as measured via the X-ray luminosity, LX), we confirm that chromospheric activity decays at a much slower rate than coronal activity with increasing Ro. While a comparison of LHα and LX for M37 members with measurements of both reveals a nearly 1:1 relation, removing the mass-dependencies by comparing instead LHα/Lbol and LX/Lbol does not provide clear evidence for such a relation. Finally, we find that Ro,sat is smaller for our chromospheric than for our coronal indicator of activity (Ro,sat=0.03±0.01 versus 0.09 ± 0.01). We interpret this as possible evidence for coronal stripping.
© 2017. The American Astronomical Society. All rights reserved.
open clusters and associations: individual: M37 - stars: activity - stars: chromospheres - stars: low-mass - stars: low-mass
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