Chromospheric and Coronal Activity in the 500 Myr old Open Cluster M37: Evidence for Coronal Stripping?
Abstract
We present the results of a spectroscopic survey to characterize chromospheric activity, as measured by {{H}}α emission, in low-mass members of the 500 Myr old open cluster M37. Combining our new measurements of {{H}}α luminosities ({L}{{H}α }) with previously cataloged stellar properties, we identify saturated and unsaturated regimes in the dependence of the {L}{{H}α }-to-bolometric luminosity ratio, {L}{{H}α }/{L}{bol}, on the Rossby number Ro. All rotators with Ro smaller than 0.03 ± 0.01 converge to an activity level of {L}{{H}α }/{L}{bol}=(1.27+/- 0.02)× {10}-4. This saturation threshold ({R}o,{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 {L}{{H}α }/{L}{bol}(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, {L}{{X}}), we confirm that chromospheric activity decays at a much slower rate than coronal activity with increasing Ro. While a comparison of {L}{{H}α } and {L}{{X}} for M37 members with measurements of both reveals a nearly 1:1 relation, removing the mass-dependencies by comparing instead {L}{{H}α }/{L}{bol} and {L}{{X}}/{L}{bol} does not provide clear evidence for such a relation. Finally, we find that {R}o,{sat} is smaller for our chromospheric than for our coronal indicator of activity ({R}o,{sat}=0.03+/- 0.01 versus 0.09 ± 0.01). We interpret this as possible evidence for coronal stripping.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2017
- DOI:
- 10.3847/1538-4357/834/2/176
- arXiv:
- arXiv:1611.09313
- Bibcode:
- 2017ApJ...834..176N
- Keywords:
-
- open clusters and associations: individual: M37;
- stars: activity;
- stars: chromospheres;
- stars: low-mass;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Accepted for publication on the Astrophysical Journal