J/AJ/133/2258 Activity and kinematics of ultracool dwarfs (Schmidt+, 2007)
Activity and kinematics of ultracool dwarfs, including an amazing
flare observation.
Schmidt S.J., Cruz K.L., Bongiorno B.J., Liebert J., Reid I.N.
<Astron. J., 133, 2258-2273 (2007)>
=2007AJ....133.2258S 2007AJ....133.2258S
ADC_Keywords: Stars, dwarfs ; Stars, late-type ; Equivalent widths
Keywords: Galaxy: stellar content - solar neighborhood - stars: activity -
stars: flare - stars: late-type - stars: low-mass, brown dwarfs
Abstract:
We present the activity and kinematics of a representative
volume-limited (20pc) sample of 152 late-M and L dwarfs (M7-L8)
photometrically selected from the Two Micron All Sky Survey (2MASS).
Using new proper-motion measurements and spectrophotometric distance
estimates, we calculate tangential velocities. The sample has a mean
tangential velocity of <Vtan≥31.5km/s, a velocity dispersion of
σtan=20.7km/s, and a maximum tangential velocity of
Vtan=138.8km/s. These kinematic results are in excellent agreement
with previous studies of ultracool dwarfs in the local solar
neighborhood. Hα emission, an indicator of chromospheric
activity, was detected in 63 of 81 late-M dwarfs and in 16 of 69
L dwarfs examined. We find a lack of correlation between activity
strength, measured by log(FHα/Fbol), and Vtan, although
velocity distributions suggest that the active dwarfs in our sample
are slightly younger than the inactive dwarfs. Consistent with
previous studies of activity in ultracool dwarfs, we find that the
fraction of H-emitting objects per spectral type peaks at spectral
type M7 and declines through mid-L dwarfs. Activity strength is
similarly correlated with spectral type for types later than M7.
Eleven dwarfs out of 150 show evidence of variability, ranging from
small fluctuations to large flare events. We estimate a flare cycle of
5% for late-M dwarfs and 2% for L dwarfs. Observations of strong,
variable activity on the L1 dwarf 2MASS J10224821+5825453 and an
amazing flare event on the M7 dwarf 2MASS J1028404-143843 are
discussed.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 114 152 Kinematics of the Two Micron Proper Motion
(2MUPM) sample
table2.dat 113 152 Hα emission data for the 2MUPM sample
refs.dat 79 51 References
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See also:
II/241 : 2MASS Catalog Intermediate Data Release (IPAC/UMass, 2000)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/AJ/123/2806 : Nearby stars in the NLTT catalogue (Reid+, 2002)
J/AJ/123/2822 : Photometry of southern NLTT stars (Reid+, 2002)
J/AJ/123/2828 : Spectroscopy of northern NLTT stars (Cruz+, 2002)
J/AJ/126/2421 : 2MASS-Selected sample of ultracool dwarfs (Cruz+, 2003)
J/AJ/126/2449 : Nearby ultracool dwarfs in galactic plane (Reid+, 2003)
J/AJ/126/3007 : Spectroscopy of faint red NLTT dwarfs (Reid+, 2003)
J/AJ/128/463 : A preliminary 20pc census from the NLTT catalogue (Reid+, 2004)
J/AJ/133/439 : Luminosity function of M7-L8 ultracool dwarfs (Cruz+, 2007)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- 2MASSJ The 2MASS Designation (HHMMSSss+DDMMSSs)
18 A1 --- f_2MASSJ [ac] Flag on binarity (G1)
20- 24 I5 --- UCD ? The Ultra Cool Dwarf number
26- 49 A24 --- OName Other Name
51- 55 A5 --- SpType MK Spectral type
57- 61 F5.2 pc Dist ? Distance
63- 66 F4.2 pc e_Dist ? Uncertainty in Dist
68- 71 F4.2 arcsec/yr mu ? Proper motion
73- 76 F4.2 arcsec/yr e_mu ? Uncertainty in mu
78 A1 --- n_mu [b] Origin of the proper motion (2)
80- 84 F5.1 deg PA ? Position angle
86- 90 F5.1 deg e_PA ? Uncertainty in PA
92- 96 F5.1 km/s Vtan ? Tangential velocity
98-101 F4.1 km/s e_Vtan ? Uncertainty in VTan
103-104 I2 --- r_SpType ? Reference for SpType, in refs.dat file
106-114 A9 --- r_plx Parallax reference, in refs.dat file (3)
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Note (2):
b = Proper motion from Vrba et al. (2004AJ....127.2948V 2004AJ....127.2948V).
Note (3): Reference for parallax is only listed if the distance given is a
parallax measurement.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- 2MASSJ The 2MASS Designation (HHMMSSss+DDMMSSs)
18 A1 --- f_2MASSJ [ac] Flag on binarity (G1)
20- 24 I5 --- UCD ? The Ultra Cool Dwarf number
26- 49 A24 --- OName Other Name
51- 55 A5 --- SpType MK spectral type
57- 61 F5.2 mag Kmag The K band magnitude
63- 67 F5.2 mag mbol The bolometric magnitude
69- 76 E8.3 mW/m2 Fbol The bolometric flux
78 A1 --- l_EW Limit flag on EW
79- 84 F6.2 0.1nm EW ? The Hα equivalent width
86- 93 E8.3 mW/m2 FHa ? The Hα flux
95- 99 F5.2 [---] logFHa/Fbol ? Hα flux to bolometric flux
101-110 A10 "YYYY/DD/MM" Obs.Date UT date of observation
112-113 I2 --- r_Spect ? Spectra reference, in refs.dat (2)
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Note (2): Spectra references are only given when the data used to measure
Hα was not taken as part of the 2MASS sample spectral typing.
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Ref Reference number
4- 22 A19 --- BibCode BibCode
24- 49 A26 --- Aut Author's name
51- 79 A29 --- Com Comments
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Global Notes:
Note (G1): Flags as follows:
a = Binary considered as a single object due to the lack of resolved
spectroscopy.
c = Wide binary.
History:
From electronic version of the journal
References:
Reid et al., Paper I 2002AJ....123.2806R 2002AJ....123.2806R, Cat. J/AJ/123/2806
Reid et al., Paper II 2002AJ....123.2822R 2002AJ....123.2822R, Cat. J/AJ/123/2822
Cruz et al., Paper III 2002AJ....123.2828C 2002AJ....123.2828C, Cat. J/AJ/123/2828
Reid et al., Paper IV 2003AJ....125..354R 2003AJ....125..354R
Cruz et al., Paper V 2003AJ....126.2421C 2003AJ....126.2421C, Cat. J/AJ/126/2421
Reid Paper VI 2003AJ....126.2449R 2003AJ....126.2449R, Cat. J/AJ/126/2449
Reid et al., Paper VII 2003AJ....126.3007R 2003AJ....126.3007R, Cat. J/AJ/126/3007
Reid et al., Paper VIII 2004AJ....128..463R 2004AJ....128..463R, Cat. J/AJ/128/463
Cruz et al., Paper IX 2007AJ....133..439C 2007AJ....133..439C, Cat. J/AJ/133/439
(End) Patricia Vannier [CDS] 17-Aug-2007