J/MNRAS/489/5669 MiMeS Magnetic properties of O-type stars (Petit+, 2019)
The MiMeS survey of magnetism in massive stars:
magnetic properties of the O-type star population.
Petit V., Wade G.A., Schneider F.R.N., Fossati L., Kamp K., Neiner C.,
David-Uraz A., Alecian E., (the MiMeS Collaboration)
<Mon. Not. R. Astron. Soc., 489, 5669-5687 (2019)>
=2019MNRAS.489.5669P 2019MNRAS.489.5669P (SIMBAD/NED BibCode)
ADC_Keywords: Stars, early-type ; Stars, O ; Magnetic fields ; Stars, ages ;
Spectral types ; Optical
Keywords: stars: early-type - stars: magnetic field - stars: massive
Abstract:
In this paper, we describe an analysis of the MiMeS (Magnetism in
Massive Stars) survey of O-type stars to explore the range of dipolar
field strengths permitted by the polarization spectra that do not
yield a magnetic detection. We directly model the Stokes V profiles
with a dipolar topology model using Bayesian inference. The noise
statistics of the Stokes V profiles are in excellent agreement with
those of the null profiles. Using a Monte Carlo approach, we conclude
that a model in which all the stars in our sample were to host 100G,
dipolar magnetic field can be ruled out by the MiMeS data.
Furthermore, if all the stars with no detection were to host a
magnetic field just below their detection limit, the inferred
distribution in strength of these undetected fields would be distinct
from the known distribution in strength of the known magnetic O-type
stars. This indicates that the 'initial magnetic field function' (IBF)
is likely bimodal - young O-type stars are expected to have either
weak/absent magnetic fields or strong magnetic fields. We also find
that better upper limits, by at least a factor of 10, would have been
necessary to rule out a detection bias as an explanation for the
apparent lack of evolved main-sequence magnetic O-type stars reported
in the literature, and we conclude that the MiMeS survey cannot
confirm or refute a magnetic flux decay in O-type stars.
Description:
The spectropolarimetric observations used here and in Paper I (Grunhut
et al. 2017MNRAS.465.2432G 2017MNRAS.465.2432G, Cat. J/MNRAS/465/2432) were obtained in
the larger context of the MiMeS survey, described by Wade et al.
(2016MNRAS.456....2W 2016MNRAS.456....2W, Cat. J/MNRAS/456/2). To summarize,
high-resolution echelle spectropolarimetric observations enable the
measurement of the change in polarization across spectral lines
induced by the Zeeman effect.
The sample of Paper I consists of 432 nightly averaged Stokes V
observations of 97 O-type stars obtained with the Echelle
SpectroPolarimetric Device for the Observations of Stars (ESPaDOnS),
Narval, and HARPSpol echelle spectropolarimeters. Our sample here
consists of stars without definite magnetic detection, reducing it to
the 91 stars listed in Table 2 (which additionally contains the 11
O-type secondary stars in the SB2/SB3 system discussed in Section 3.1).
We use the Bayesian code BONNSAI (Schneider et al.
2014A&A...570A..66S 2014A&A...570A..66S, 2017A&A...598A..60S 2017A&A...598A..60S)
(http://www.astro.uni-bonn.de/stars/bonnsai) to infer the fractional
main-sequence ages and other stellar parameters of our sample.
Table 3 contains the BONNSAI analysis results.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 83 102 Results from our Bayesian analysis
table3.dat 58 102 Results from the BONNSAI analysis
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See also:
J/MNRAS/456/2 : MiMeS survey of magnetism in massive stars (Wade+, 2016)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/102] Internal object identifier
5- 7 A3 --- f_ID Flag on ID (G1)
9- 21 A13 --- Name Star name
23- 37 A15 --- SpType Spectral type reproduced from
Grunhut et al. (2017MNRAS.465.2432G 2017MNRAS.465.2432G,
Cat. J/MNRAS/465/2432) (Paper I)
39- 40 I2 --- Nobs Number of nightly averaged observations
42- 44 I3 km/s vsini Rotational broadening adopted in our models
46- 50 F5.2 --- OddsV Odds ratio obtained from the Stokes V
profile (1)
52- 57 F6.2 --- OddsN Odds ratio obtained from the null profile (1)
59- 61 I3 10-4T 68V Upper limit to the 68.3 per cent credible
region obtained from Stokes V
63- 66 I4 10-4T 95V Upper limit to the 95.4 per cent credible
region obtained from Stokes V
68- 70 I3 10-4T 68N Upper limit to the 68.3 per cent credible
region obtained from the null profile
72- 75 I4 10-4T 95N Upper limit to the 95.4 per cent credible
region obtained from the null profile
77- 79 I3 10-4T ModeV Mode of the probability density function
marginalized for Bpole obtained from
Stokes V
81- 83 I3 10-4T ModeN Mode of the probability density function
marginalized for Bpole obtained from the
null profile
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Note (1): To assess the presence of a dipole-like signal in our observations,
we compute the odds ratio of the null model (MBpole=0; no magnetic
field implying Stokes V=0) with the dipole model (MBpole).
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/102] Internal object identifier
5- 7 A3 --- f_ID Flag on ID (G1)
9- 21 A13 --- Name Star name
23- 37 A15 --- SpType Spectral type reproduced from
Grunhut et al. (2017MNRAS.465.2432G 2017MNRAS.465.2432G,
Cat. J/MNRAS/465/2432) (Paper I)
39- 42 F4.2 Myr Age ? Star age
44- 47 F4.1 Msun M* ? Star mass
49- 53 F5.2 Rsun R* ? Star radius
55- 58 F4.2 --- fracAge ? Fractional main-sequence age
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Global Notes:
Note (G1): Flag as follows:
a = Star identified as binary in Grunhut et al. (2017MNRAS.465.2432G 2017MNRAS.465.2432G,
Cat. J/MNRAS/465/2432) (Paper I), but for which an SB2 treatment was
unnecessary (SB1, large luminosity ratio, etc.) or unfeasible
SB2 = Double-lined spectroscopic binary
SB3 = Triple-lined spectroscopic binary
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History:
From electronic version of the journal
References:
Grunhut et al., Paper I 2017MNRAS.465.2432G 2017MNRAS.465.2432G, Cat. J/MNRAS/465/2432
(End) Ana Fiallos [CDS] 19-Jan-2023