J/MNRAS/407/2269 Polarisation of a sample of late M dwarfs (Morin+, 2010)
Large-scale magnetic topologies of late M dwarfs.
Morin J., Donati J.-F., Petit P., Delfosse X., Forveille T., Jardine M.M.
<Mon. Not. R. Astron. Soc. 407, 2269 (2010)>
=2010MNRAS.407.2269M 2010MNRAS.407.2269M
ADC_Keywords: Stars, M-type ; Stars, dwarfs ; Magnetic fields
Keywords: techniques: polarimetric - stars: low-mass - stars: magnetic field -
stars: rotation
Abstract:
We present here the final results of the first spectropolarimetric
survey of a small sample of active M dwarfs, aimed at providing
observational constraints on dynamo action on both sides of the
full-convection threshold (spectral type M4). Our two previous studies
(Donati et al. 2008. Cat. J/MNRAS/390/545; Morin et al., 2008, Cat.
J/MNRAS/384/77) were focused on early and mid M dwarfs. The present
paper examines 11 fully convective late M dwarfs (spectral types
M5-M8). Tomographic imaging techniques were applied to time-series of
circularly polarised profiles of 6 stars, in order to infer their
large-scale magnetic topologies. For 3 other stars we could not
produce such magnetic maps, because of low variability of the Stokes V
signatures, but were able to derive some properties of the magnetic
fields. We find 2 distinct categories of magnetic topologies: on the
one hand strong axisymmetric dipolar fields (similar to mid M dwarfs),
and on the other hand weak fields generally featuring a significant
non-axisymmetric component, and sometimes a significant toroidal one.
Comparison with unsigned magnetic fluxes demonstrates that the second
category of magnetic fields shows less organization (less energy in
the large scales), similarly to partly convective early M dwarfs.
Stars in both categories have similar stellar parameters, our data do
not evidence a separation between these 2 categories in the
mass-rotation plane. We also report marginal detection of a
large-scale magnetic field on the M8 star VB 10 featuring a
significant toroidal axisymmetric component, whereas no field is
detectable on VB 8 (M7).
Description:
We have collected 174 pairs of Stokes I (unpolarised) and V
(circularly polarised) spectra with ESPaDOnS at CFHT
(2003ASPC..307...41D 2003ASPC..307...41D) between June 2006 and July 2009. 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 (Donati et al., 1997MNRAS.291..658D 1997MNRAS.291..658D).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 51 11 Stars positions
table1.dat 82 11 Stars fundamental parameters
tables.dat 78 174 Dates, magnetic field and radial velocity
(tables A1-A11 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/MNRAS/390/545 : Magnetic topologies of early M dwarfs (Donati+, 2008)
J/MNRAS/390/567 : Magnetic topologies of mid M dwarfs (Morin+, 2008)
Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Designation of the star
10- 11 I2 h RAh Simbad Hour of Right Ascension (J2000.0)
13- 14 I2 min RAm Simbad Minute of Right Ascension (J2000.0)
16- 20 F5.2 s RAs Simbad Second of Right Ascension (J2000.0)
22 A1 --- DE- Simbad Sign of the Declination (J2000.0)
23- 24 I2 deg DEd Simbad Degree of Declination (J2000.0)
26- 27 I2 arcmin DEm Simbad Arcminute of Declination (J2000.0)
29- 33 F5.2 arcsec DEs Simbad Arcsecond of Declination (J2000.0)
34- 42 A9 --- GJ Gliese-Jahreiss designations
44- 46 A3 --- File Number of the corresponding table in the paper
49- 51 A3 --- ZDI [yes no] Zeeman Doppler Imaging was conducted
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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- 13 A4 --- SpT MK spectral type (1)
15- 18 F4.2 solMass Mass Mass of the star (2)
20 A1 --- leMass Limit flag on e_Mass (2)
21- 24 F4.2 solMass e_Mass Formal 1-sigma error bar on Mass (2)
26 A1 --- l_vsini Limit flag on vsini (3)
27- 28 I2 km/s vsini Equatorial rotational velocity along line of
sight (3)
29 A1 --- r_vsini ? Reference for vsini (3)
31 A1 --- l_Bf Limit flag on Bf (4)
32- 34 F3.1 0.1T Bf ? Magnetic flux (4)
35 A1 --- r_Bf [a-c] Reference for Bf (5)
37 A1 --- l_Prot Limit flag for Prot (6)
38- 42 F5.3 d Prot Rotation period (6)
44- 48 F5.3 d e_Prot ? 3-sigma error bar on Prot (6)
50- 52 I3 d tauc Empirical convective turnover time (7)
54 A1 --- l_Ro Limit flag on empirical Rossby number (7)
55- 57 F3.1 10-2 Ro Empirical Rossby number (7)
59- 62 F4.2 solRad Rsini ? Stellar radius times sini (8)
64 A1 --- leRsini Limit flag on error on Rsini (8)
65- 68 F4.2 solRad e_Rsini ? Formal 1-sigma error bar on Rsini (8)
70- 73 F4.2 solRad Rad Theoretical stellar radius (9)
75 A1 --- leRad Limit flag on error on Rad (9)
76- 79 F4.2 solRad e_Rad Formal 1-sigma error bar on Rad (9)
81- 82 I2 deg incl ? Inclination of the stellar rotation axis (10)
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Note (1): SpType is from III/198 (Hawley+ 1997)
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 0.01 solMass lower limit).
Note (3): Most vsini values are taken from studies of FeH molecular bands
(see r_Bf). For GJ 51 we derive vsini from our spectra. Typical
uncertainty is of the order of 1km/s.
Note (4): Unsigned magnetic fluxes are taken from studies of FeH molecular
bands whenever available. Typical uncertainties are in the 0.05-0.1T
range (i.e. 0.5-1kG in CGS units).
Note (5): References as follows:
a = Reiners & Basri, 2007ApJ...656.1121R 2007ApJ...656.1121R
b = Reiners & Basri, 2009A&A...496..787R 2009A&A...496..787R
c = Mohanty & Basri, 2003ApJ...583..451M 2003ApJ...583..451M
Note (6): Rotation periods are derived from Zeeman-Doppler Imaging analysis
(ZDI) of time-series of Least-Squares Deconvolution (LSD) circularly
polarised spectra. Prot and e_Prot are derived by fitting a paraboloid
to the χ2 surface as in Petit et al. (2002MNRAS.334..374P 2002MNRAS.334..374P).
Note (7): 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/τc.
Note (8): Rsini[solRad]=Prot[d]*vsini[km/s]/50.6145. Error bars are
propagated and mentioned in e_Rsini (with a 0.01solRad lower limit).
Note (9): 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
0.01solRad lower limit).
Note (10): Rough estimate of the inclination used for Zeeman-Doppler
Imaging (ZDI), 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 "DD/MM/YYYY" Date UT date
21- 33 F13.5 d HJD UT heliocentric Julian date
35- 37 I3 --- S/N Signal to noise ratio
39- 42 F4.1 10-4 rms rms noise of circular polarisation in units of
10-4Ic (Ic=unpolarised continuum) (4)
44- 48 I5 10-4T Bl Longitudinal magnetic field (Gauss) (1)
50- 52 I3 10-4T e_Bl rms uncertainty on Bl (1)
54- 59 F6.2 km/s RV Radial velocity (2)
61- 68 F8.3 --- E ? Rotation cycle (3)
70- 78 F9.1 --- HJD0 ? Reference HJD for E (3)
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Note (1): Bl is measured from the Least-Squares Deconvolution (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): rms noise level in the circular polarisation profile produced by
Least-Squares Deconvolution (LSD), and expressed in units of 10-4Ic,
where Ic is the unpolarised continuum level )
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Acknowledgements:
Julien Morin, jmorin(at)cp.dias.ie
(End) Patricia Vannier [CDS] 05-Jun-2010