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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
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:
FileName Lrecl Records Explanations
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
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
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 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)
Note (2): b = Proper motion from Vrba et al. (2004AJ....127.2948V). Note (3): Reference for parallax is only listed if the distance given is a parallax measurement.
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)
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.
Byte-by-byte Description of file: refs.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Ref Reference number 4- 22 A19 --- BibCode BibCode 24- 49 A26 --- Aut Author's name 51- 79 A29 --- Com Comments
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, Cat. J/AJ/123/2806 Reid et al., Paper II 2002AJ....123.2822R, Cat. J/AJ/123/2822 Cruz et al., Paper III 2002AJ....123.2828C, Cat. J/AJ/123/2828 Reid et al., Paper IV 2003AJ....125..354R Cruz et al., Paper V 2003AJ....126.2421C, Cat. J/AJ/126/2421 Reid Paper VI 2003AJ....126.2449R, Cat. J/AJ/126/2449 Reid et al., Paper VII 2003AJ....126.3007R, Cat. J/AJ/126/3007 Reid et al., Paper VIII 2004AJ....128..463R, Cat. J/AJ/128/463 Cruz et al., Paper IX 2007AJ....133..439C, Cat. J/AJ/133/439
(End) Patricia Vannier [CDS] 17-Aug-2007
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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