J/MNRAS/390/567 Magnetic field and velocity of mid M dwarfs (Morin+, 2008)
Large-scale magnetic topologies of mid M dwarfs.
Morin J., Donati J.-F., Petit P., Delfosse X., Forveille T., Albert L.,
Auriere M., Cabanac R., Dintrans B., Fares R., Gastine T., Jardine M.M.,
Lignieres F., Paletou F., Ramirez Velez J.C., Theado S.
<Mon. Not. R. Astron. Soc., 390, 567-581 (2008)>
=2008MNRAS.390..567M 2008MNRAS.390..567M
ADC_Keywords: Stars, M-type ; Magnetic fields
Keywords: stars: magnetic field - stars: low-mass, brown dwarfs -
stars: rotation - techniques: spectroscopy - techniques: polarimetry
Abstract:
We present in this paper, the first results of a spectropolarimetric
analysis of a small sample (∼20) of active stars ranging from spectral
type M0 to M8, which are either fully convective or possess a very
small radiative core. This study aims at providing new constraints on
dynamo processes in fully convective stars. This paper focuses on ve
stars of spectral type ∼M4, i.e. with masses close to the full
convection threshold (0.35M☉), and with short rotational periods.
Tomographic imaging techniques allow us to reconstruct the surface
magnetic topologies from the rotationally modulated time-series of
circularly polarized profiles. We find that all stars host mainly
axisymmetric large-scale poloidal fields. Three stars were observed at
two different epochs separated by 1yr; we find the magnetic topologies
to be globally stable on this time-scale. We also provide an accurate
estimation of the rotational period of all stars, thus allowing us to
start studying how rotation impacts the large-scale magnetic field.
Description:
We have collected 107 pairs of Stokes I (unpolarised) and V
(circularly polarised) spectra with the twin instruments ESPaDOnS at
CFHT (2003ASPC..307...41D 2003ASPC..307...41D) and NARVAL at TBL between January 2006 and
February 2008. All spectra were reduced using the Libre-Esprit
pipeline, and the mean I and V line profiles were extracted using the
Least-Squares Deconvolution (LSD) technique (1997MNRAS.291..658D 1997MNRAS.291..658D). The
star V374 Peg (2008MNRAS.384...77M 2008MNRAS.384...77M) is also included in the discussion
and in table1.dat.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 132 6 Fundamental parameters
tables.dat 90 105 Dates, magnetic field and radial velocity
(tables 2-6 of the paper)
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See also:
B/cfht : Log of CFHT Exposures (CADC, 1979-)
I/239 : The Hipparcos and Tycho Catalogues (ESA 1997)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
III/198 : Palomar/MSU nearby star spectroscopic survey (Hawley+ 1997)
J/A+A/331/581 : Rotation and activity in field M dwarfs (Delfosse+ 1998)
J/A+A/417/651 : NEXXUS ROSAT survey of coronal X-ray (Schmitt+ 2004)
J/MNRAS/390/545 : Magnetic topologies of early M dwarfs (Donati+ 2008)
J/MNRAS/407/2269 : Magnetic topologies of late M dwarfs (Morin+, 2010)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Designations of the star
10- 16 A7 --- SName GJ name
18- 19 I2 h RAh Simbad Hour of Right Ascension (J2000.0)
21- 22 I2 min RAm Simbad Minute of Right Ascension (J2000.0)
24- 28 F5.2 s RAs Simbad Second of Right Ascension (J2000.0)
30 A1 --- DE- Simbad Sign of the Declination (J2000.0)
31- 32 I2 deg DEd Simbad Degree of Declination (J2000.0)
34- 35 I2 arcmin DEm Simbad Arcminute of Declination (J2000.0)
37- 40 F4.1 arcsec DEs Simbad Arcsecond of Declination (J2000.0)
42 I1 --- Tab ? Number of the corresponding table with
observations in the paper
44- 47 A4 --- SpT MK spectral type (1)
49- 52 F4.2 solMass Mass Mass of the star (2)
54 A1 --- l_Mass Limit flag on e_Mass (2)
55- 58 F4.2 solMass e_Mass Formal 1-σ error bar on Mass (2)
60- 64 F5.2 [10-7W] Lbol Logarithmic bolometric luminosity (3)
66- 70 F5.2 [---] LX/Lbol Ratio of X-ray to bolometric luminosity (4)
72- 75 F4.1 km/s vsini Equatorial rotational velocity along line of
sight (5)
76 A1 --- r_vsini [a] a: vsini from Reiners & Basri,
2007ApJ...656.1121R 2007ApJ...656.1121R
78 A1 --- l_Bf Limit flag on Bf (6)
79- 81 F3.1 0.1T Bf ? Magnetic flux (6)
82 A1 --- r_Bf [a] a: Bf from Reiners & Basri,
2007ApJ...656.1121R 2007ApJ...656.1121R
84- 91 F8.6 d Prot Rotation period (7)
93-100 F8.6 d e_Prot 3-σ error bar on Prot (7)
102-103 I2 d tauc Empirical convective turnover time (8)
105-107 F3.1 --- Ro Empirical Rossby number (8)
109-112 F4.2 solRad Rsini ?Stellar radius times sini (9)
114 A1 --- l_Rsini Limit flag on error on Rsini (9)
115-118 F4.2 solRad e_Rsini Formal 1-σ error bar on Rsini (9)
120-123 F4.2 solRad Rad Theoretical stellar radius (10)
125 A1 --- l_Rad Limit flag on error on Rad (10)
126-129 F4.2 solRad e_Rad Formal 1-σ error bar on Rad (10)
131-132 I2 deg i Inclination of the stellar rotation axis (11)
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Note (1): SpType is from Reid et al., (1995, Cat. III/198).
Note (2): Absolute J-Band magnitudes are computed from Hipparcos parallaxes
(I/239) and 2MASS (II/246) apparent magnitudes. Stellar masses are
then derived using the Delfosse et al. (2000A&A...364..217D 2000A&A...364..217D)
mass-luminosity relation. Uncertainties on parallax and mass are
propagated and mentioned in e_Mass (with a 0.01M_☉ lower limit).
Note (3): Bolometric luminosities suited to Mass are computed from NextGen
models by Baraffe et al. 1998 (1998A&A...337..403B 1998A&A...337..403B).
Note (4): X-ray luminosities LX are taken from Schmitt et al.(2004, Cat.
J/A+A/417/651) and averaged, excluding outliers supposedly due to flares.
Note (5): Most vsini values are taken from studies of FeH molecular bands
(see refs.dat). For GJ 51 we derive vsini from our spectra. Typical
uncertainty is of the order of 1km/s, see references.
Note (6): Unsigned magnetic fluxes are taken from studies of FeH molecular
bands (see refs.dat) whenever available. Typical uncertainties are in
the 0.05-0.1T range (i.e. 0.5-1kG in CGS units), see references.
Note (7): Rotation periods are derived from Zeeman-Doppler Imaging analysis
of time-series of LSD circularly polarised spectra. Prot and e_Prot
are derived by fitting a paraboloid to the chi2 surface as in Petit
et al. (2002MNRAS.334..374P 2002MNRAS.334..374P).
Note (8): Empirical convective turnover times suited to the stellar mass
are derived using the rotation-X-ray luminosity relation from Kiraga &
Stepien (2007AcA....57..149K 2007AcA....57..149K). The Rossby number is then Ro=Prot/tauc.
Note (9): Rsini[solRad]=Prot[d]*vsini[km/s]/50.6145. Error bars are
propagated and mentioned in e_Rsini (with a 0.01R☉ lower limit).
Note (10): Radii suited to Mass are computed from NextGen models by Baraffe
et al. (1998A&A...337..403B 1998A&A...337..403B). Error bar on Mass is propagated (with a
0.01R☉ lower limit).
Note (11): Rough estimate of the inclination used for Zeeman-Doppler
imaging, derived by comparing Rad and Rsini.
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Byte-by-byte Description of file: tables.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Designation of the star
10- 19 A10 "YYYY/DD/MM" Obs.date UT date of observation
21- 28 A8 "h:m:s" Obs.time Time of observation (hh:mm:ss)
30- 42 F13.5 d HJD UT heliocentric Julian date of observation
44- 47 A4 --- Site Observation site (CFHT or TBL = Telescope
Bernard Lyot)
49- 56 A8 s Texp Exposure time (NxNNNN.N in s)
58- 60 I3 --- S/N Signal to noise ratio
62- 64 F3.1 10-4 sigma rms noise level in polarisation profile (4)
66- 71 F6.1 10-4T Bl Longitudinal magnetic field (Gauss) (1)
73- 76 F4.1 10-4T e_Bl rms uncertainty on Bl (1)
78- 84 F7.3 --- E Rotation cycle (3)
86- 90 F5.2 km/s RV Radial velocity (2)
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Note (1): Bl is measured from the LSD Stokes I and V line profiles.
Note (2): The absolute RV accuracy of ESPaDOnS data calibrated with the
Libre-Esprit pipeline is estimated to be of the order of 100m/s. The
internal accuracy within a time-series is estimated to be of the order
of 30m/s.
Note (3): E is computed with the ephemeris: HJD=HJD0+Prot*E. Prot is
taken from table1 except for VB 10, in this case Prot=0.69d.
Note (4): noise level in the circular polarisation profile produced by
the Least-Square Deconvolution (LSD) algorithm. It is expressed in
10-4Ic units, if Ic is the unpolarised continuum level
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Acknowledgements:
Julien Morin, jmorin(at)cp.dias.ie
References:
Donati et al., Paper I 2008MNRAS.390..545D 2008MNRAS.390..545D, J/MNRAS/390/545
(End) Patricia Vannier [CDS] 24-Jun-2010