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 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 (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)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 LHα/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 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.
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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 144 294 M37 members
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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
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Bytes Format Units Label Explanations
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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- 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
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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.
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History:
From electronic version of the journal
References:
Nunez et al. Paper I 2015ApJ...809..161N 2015ApJ...809..161N Cat. J/ApJ/809/161
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 10-Jul-2017