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J/ApJ/834/176    Spectroscopic survey of M37 candidate members    (Nunez+, 2017)

Chromospheric and coronal activity in the 500 Myr old open cluster M37: evidence for coronal stripping? Nunez A., Agueros M.A., Covey K.R., Lopez-Morales M. <Astrophys. J., 834, 176-176 (2017)> =2017ApJ...834..176N (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Photometry, ugriz ; Equivalent widths ; Stars, masses ; Spectroscopy Keywords: open clusters and associations: individual: M37; stars: activity; stars: chromospheres; stars: low-mass Abstract: We present the results of a spectroscopic survey to characterize chromospheric activity, as measured by Hα emission, in low-mass members of the 500Myr old open cluster M37. Combining our new measurements of Hα luminosities (L) with previously cataloged stellar properties, we identify saturated and unsaturated regimes in the dependence of the L-to-bolometric luminosity ratio, L/Lbol, on the Rossby number Ro. All rotators with Ro smaller than 0.03±0.01 converge to an activity level of L/Lbol=(1.27±0.02)x10-4. 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 L/Lbol(Ro) following a power-law of index β=-0.51±0.02, slightly shallower than that found for a combined ∼650Myr 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 L and LX for M37 members with measurements of both reveals a nearly 1:1 relation, removing the mass-dependencies by comparing instead L/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. Description: In Paper I (Nunez+ 2015, J/ApJ/809/161) we used the gri photometry (Sloan system) from Hartman+, J/ApJ/675/1233 and the distance from the cluster core to identify cluster members. We obtained spectra of M37 stars with Hectospec on the MMT 6.5m telescope in 2015 Feb 18,19,20, 2015 Apr 18, 2015 Sep 20 and 2015 Nov 21, 22. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 144 294 M37 members
See also: VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006) J/AJ/130/873 : Properties of BQS objects in the SDSS DR3 area (Jester+, 2005) J/AJ/134/2340 : Praesepe & Coma Berenices clusters' membership (Kraus+, 2007) J/ApJ/675/1233 : gri photometry in M37 (NGC 2099) (Hartman+, 2008) J/ApJ/675/1254 : M37 variable stars (Hartman+, 2008) J/A+A/483/253 : BV photometry of NGC 2099 variables (Messina+, 2008) J/ApJS/181/444 : X-emitting stars identified from RASS/SDSS (Agueros+, 2009) J/ApJ/691/342 : griBVI photometry in M37 (Hartman+, 2009) J/MNRAS/407/465 : Fast-rotating M dwarfs in NGC2516 (Jackson+, 2010) J/ApJ/743/48 : Stellar rotation periods & X-ray luminosities (Wright+, 2011) J/MNRAS/431/2063 : UV/X-ray activity of M dwarfs within 10pc (Stelzer+, 2013) J/ApJ/809/161 : X-ray obs. and membership probabilities of M37 (Nunez+, 2015) J/A+A/589/A113 : PMS stars in h Per (Argiroffi+, 2016) J/ApJ/829/23 : Stellar flares from Q0-Q17 Kepler LCs (Davenport, 2016) J/ApJ/822/47 : K2 rotation periods for 65 Hyades members (Douglas+, 2016) J/ApJ/830/44 : M37 low-mass stars X-ray luminosity functions (Nunez+, 2016) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 6 I6 --- OID [2321/360125] Optical ID as in Paper I (Nunez+, 2015, J/ApJ/809/161) 8- 16 F9.6 deg RAdeg Right ascension of object (J2000) 18- 26 F9.6 deg DEdeg Declination of object (J2000) 28- 33 F6.2 --- PMm [0.2/0.95]?=999 Probability that object is cluster member 35 I1 --- Bin Binarity flag (0=likely a single member; 1=likely a binary member) 37- 41 F5.2 mag gmag [15.8/24.4] Megacam/MMT g magnitude (1) 43- 47 F5.2 mag imag [15/20.9] Megacam/MMT i magnitude (1) 49- 53 F5.2 mag Jmag [13.8/17.2]? 2MASS J magnitude 55- 58 F4.2 Msun Mass [0.2/1.3] Stellar mass (2) 60- 65 F6.4 --- Ro [0.005/1]? Rossby number Ro (3) 67- 71 F5.2 0.1nm EWHa [-7.6/2.8]? Hα line equivalent width 73- 76 F4.2 0.1nm e_EWHa [0/1]? Standard deviation of Hα line equivalent width 78- 83 F6.2 0.1nm EWNII6584 [-20.8/-0.06]? [NII]6584-Angstrom line equivalent width 85- 88 F4.2 0.1nm e_EWNII6584 [0.02/3]? Standard deviation of EWNII6584 90- 94 F5.2 0.1nm EWNII6548 [-7/0.3]? [NII]6548-Angstrom line equivalent width 96- 99 F4.2 0.1nm e_EWNII6548 [0/3]? Standard deviation of EWNII6548 101-108 E8.2 --- chi ? chi value (χ=f0/fbol) (4) 110-117 E8.2 --- LHa/Lbol [/0.0003]? Hα to bolometric luminosity ratio 119-126 E8.2 --- e_LHa/Lbol ? Standard deviation of LHa/Lbol 128-135 E8.2 --- LX/Lbol [/0.004]? X-ray to bolometric luminosity ratio 137-144 E8.2 --- e_LX/Lbol ? Standard deviation of LX/Lbol
Note (1): gi photometry from Hartman et al. (2008, J/ApJ/675/1233) Note (2): Stellar mass derived from g photometry using the mass-absolute magnitude relation of Kraus & Hillenbrand (2007, J/AJ/134/2340) Note (3): Ro=Prot/τ where τ is the convective turnover time. See section 3.4. Note (4): where f0 is the continuum flux near the Hα line, and fbol is the apparent bolometric flux. See section 3.2.
History: From electronic version of the journal References: Nunez et al. Paper I 2015ApJ...809..161N Cat. J/ApJ/809/161
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 10-Jul-2017
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