Chromospheric and coronal activity in the 500 MYR old open cluster M37: evidence for coronal stripping?

Journal Article · Tue Jan 10 04:00:00 EST 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/834/2/176· OSTI ID:22869531

Núñez, Alejandro; Agüeros, Marcel A. ^[1]; Covey, Kevin R. ^[2]; López-Morales, Mercedes ^[3]

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1. Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)
2. Department of Physics and Astronomy, Western Washington University, Bellingham WA 98225 (United States)
3. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02183 (United States)

We present the results of a spectroscopic survey to characterize chromospheric activity, as measured by Hα emission, in low-mass members of the 500 Myr old open cluster M37. Combining our new measurements of Hα luminosities (L{sub Hα}) with previously cataloged stellar properties, we identify saturated and unsaturated regimes in the dependence of the L{sub Hα}-to-bolometric luminosity ratio, L{sub Hα}/L{sub bol}, on the Rossby number R{sub o}. All rotators with R{sub o} smaller than 0.03 ± 0.01 converge to an activity level of L{sub Hα}/L{sub bol}=(1.27±0.02)×10{sup −4}. This saturation threshold (R{sub 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{sub Hα}/L{sub bol}(R{sub o}) 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{sub X}), we confirm that chromospheric activity decays at a much slower rate than coronal activity with increasing R{sub o}. While a comparison of L{sub Hα} and L{sub X} for M37 members with measurements of both reveals a nearly 1:1 relation, removing the mass-dependencies by comparing instead L{sub Hα}/L{sub bol} and L{sub X}/L{sub bol} does not provide clear evidence for such a relation. Finally, we find that R{sub o,sat} is smaller for our chromospheric than for our coronal indicator of activity (R{sub o,sat}=0.03±0.01 versus 0.09 ± 0.01). We interpret this as possible evidence for coronal stripping.

• OSTI ID: 22869531
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 834; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACTIVITY LEVELS
BOLOMETERS
CATALOGS
CHROMOSPHERE
COMPARATIVE EVALUATIONS
EMISSION
LUMINOSITY
MASS
ROTATION
SATURATION
STARS
STELLAR CORONAE
STRIPPING
X RADIATION