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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
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) 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).

File Summary:

       FileName      Lrecl  Records   Explanations

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)


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

   Bytes Format Units   Label     Explanations

   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


Byte-by-byte Description of file: table1.dat

   Bytes Format Units     Label   Explanations

   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)

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)
     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
      b = Reiners & Basri, 2009A&A...496..787R
      c = Mohanty & Basri, 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).
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). 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). 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.


Byte-by-byte Description of file: tables.dat

   Bytes Format Units   Label     Explanations

   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)

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 )


Acknowledgements:
    Julien Morin, jmorin(at)cp.dias.ie
(End)                                        Patricia Vannier [CDS]  05-Jun-2010