J/ApJ/935/L12 Magnetic field measurements of young white dwarfs (Bagnulo+, 2022)
Multiple Channels for the Onset of Magnetism in Isolated White Dwarfs.
Bagnulo S., Landstreet J.D.
<Astrophys. J., 935, L12 (2022)>
=2022ApJ...935L..12B 2022ApJ...935L..12B
ADC_Keywords: Stars, white dwarf; Magnetic fields; Stars, ages
Keywords: Magnetic stars ; White dwarf stars ; Spectropolarimetry
Abstract:
The presence of a strong magnetic field is a feature common to a
significant fraction of degenerate stars, yet little is understood
about the field's origin and evolution. New observational constraints
from volume-limited surveys point to a more complex situation than a
single mechanism valid for all stars. We show that in high-mass white
dwarfs, which are probably the results of mergers, magnetic fields are
extremely common and very strong and appear immediately in the cooling
phase. These fields may have been generated by a dynamo active during
the merging. Lower-mass white dwarfs, which are often the product of
single-star evolution, are rarely detectably magnetic at birth, but
fields appear very slowly, and very weakly, in about a quarter of
them. What we may see is an internal field produced in an earlier
evolutionary stage that gradually relaxes to the surface from the
interior. The frequency and strength of magnetic fields continue to
increase to eventually rival those of highly massive stars,
particularly after the stars cool past the start of core
crystallization, an effect that could be responsible for a dynamo
mechanism similar to the one that is active in Earth's interior.
Description:
For our observations, we have used the FOcal Reducer and low
dispersion Spectrograph (FORS2) instrument of the ESO Very Large
Telescope, the Echelle SpectroPolarimetric Device for the Observation
of Stars (ESPaDOnS) instrument of the Canada-France-Hawaii telescope,
and the Intermediate-dispersion Spectrograph and Imaging System (ISIS)
on the William Herschel Telescope.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 82 124 New magnetic field measurements of young WDs
between 20 and 40pc
table2.dat 111 264 Physical parameters of the WDs checked for magnetic
field in the context of a volume-limited survey
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See also:
III/210 : Spectroscopically Identified White Dwarfs (McCook+, 1999)
III/235 : Spectroscopically Identified White Dwarfs (McCook+, 2008)
J/MNRAS/390/545 : Magnetic field & velocity of early M dwarfs (Donati+, 2008)
J/MNRAS/425/1394 : High proper-motion white dwarfs (Kawka+, 2012)
J/MNRAS/429/2934 : SDSS magnetic white dwarf stars (Kepler+, 2013)
J/MNRAS/467/4970 : Cool DZ white dwarfs. I. (Hollands+, 2017)
J/A+A/618/A113 : Spectropolarimetric survey of white dwarfs (Bagnulo+, 2018)
J/MNRAS/499/1890 : Gaia white dwarfs within 40pc. II. (McCleery+, 2020)
J/A+A/638/A131 : Radial velocities of 643 DA white dwarfs (Napiwotzki+, 2020)
J/MNRAS/508/3877 : Catalogue of white dwarfs in Gaia EDR3 (Gentile+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Name WD name (1)
15- 22 A8 --- Instr Instrument
24- 29 A6 --- Grism Grism or Grating
31- 34 I4 yr Obs.Y [2015/2022] Observation date, year
36- 37 I2 "month" Obs.M Observation date, month
39- 40 I2 d Obs.D Observation date, day in month
42- 43 I2 h Obs.h Observation date, hour
45- 46 I2 min Obs.m Observation date, minute
48- 51 I4 s ExpTime [1368/7060] Exposure time
53- 55 I3 --- SN [34/720] Signal-noise, Angstrom-1
57- 61 F5.2 kG Bz [-6.39/10.0]? Mean Longitudinal Magnetic Field
63- 67 F5.2 kG e_Bz [0.31/12.0]? Uncertainty in Bz
71- 82 A12 --- Notes Notes on source (2)
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Note (1): The naming system based on 1950 coordinates created at the
Villanova University, which was originally introduced by McCook &
Sion, 1977csiw.book.....M 1977csiw.book.....M, and defined in more detail by McCook &
Sion, 1999, III/210 as "WD" followed by the first four digits of the
right ascension, the sign of the declination, the first two digits of
the declination, and a third digit in which minutes of declination are
expressed as the truncated fraction of degree. The WD names of some
stars were assigned in previous literature in a way which was not
consistent with these definitions; these names have been kept
unchanged to minimise confusions. For all entries, alternative names
(used as main identifier in the Simbad database) can be found in Table
2.
Note (2): If the spectrum is featureless, an upper limit of the
fraction of circular polarisation in the continuum is provided.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 1 A1 --- f_Name [b] b=Magnetic WD flag
3- 15 A13 --- Name WD Name (1)
17- 45 A29 --- SName Simbad main identifier(s)
47- 55 A9 --- SpT WD Spectral class (2)
57- 60 F4.1 mag Gmag [8.5/17.2] G magnitude (3)
62- 63 A2 --- ATM Chemical composition of atmosphere (4)
65- 69 I5 K Teff [3821/39304] Effective temperature
71- 74 F4.2 Msun WDM [0.39/1.28] WD Mass, solar units (5)
76- 79 F4.2 Gyr Age [0.02/9.62] Age, Gyr (6)
81- 84 F4.1 pc Dist [2.7/39.7] Distance, parsecs (7)
86- 91 F6.2 MG B [0.0/670.0] Mean magnetic field modulus, MG (8)
93-111 A19 --- Ref References (9)
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Note (1): The naming system based on 1950 coordinates created at the
Villanova University, which was originally introduced by McCook &
Sion, 1977csiw.book.....M 1977csiw.book.....M, and defined in more detail by McCook &
Sion, 1999, III/210 as "WD" followed by the first four digits of the
right ascension, the sign of the declination, the first two digits of
the declination, and a third digit in which minutes of declination are
expressed as the truncated fraction of degree. The WD names of some
stars were assigned in previous literature in a way which was not
consistent with these definitions; these names have been kept
unchanged to minimise confusions. For all entries, alternative names
(used as main identifier in the Simbad database) can be found in Table
2.
Note (2): Magnetic white dwarfs are identified with the symbol "H" in their
spectral classification. Suspected magnetic white dwarfs are identified
with "H?".
Note (3): Gaia G magnitude as reported by Gentile Fusillo+, 2021,
J/MNRAS/508/3877
Note (4): The chemical composition of the atmosphere was obtained from the
literature or from visual inspection of our spectra --
H = thick H-layer models for H-rich atmospheres;
He = thin H-layer models for He-rich atmospheres.
Note (5): Mass deduced from Gaia photometry by Gentile Fusillo+, 2021,
J/MNRAS/508/3877.
Note (6): Ages were estimated using the online cooling tables of the
Montreal group, Bedard+, 2020, J/ApJ/901/93, and a two-dimensional
logarithmic interpolation on the Teff and WDM.
Note (7): Distance from the Gaia parallax as reported by Gentile Fusillo+, 2021,
J/MNRAS/508/3877
Note (8): Mean field modulus |B| obtained as explained by
Bagnulo & Landstreet, 2021MNRAS.507.5902B 2021MNRAS.507.5902B.
Note (9): References to the measurements of magnetic field as follows:
B+L21 = original references are given in Table 1 of
Bagnulo & Landstreet, 2021MNRAS.507.5902B 2021MNRAS.507.5902B
Etw = this work, using the ESPaDOnS instrument;
Itw = this work, using the ISIS instrument;
Ftw = this work, using the FORS instrument;
Azn+04 = Aznar Cuadrado+, 2004A&A...423.1081A 2004A&A...423.1081A
B+L18 = Bagnulo & Landstreet, 2018A&A...618A.113B 2018A&A...618A.113B
Baretal95 = Barstow+, 1995, J/MNRAS/277/971
Jor+07 = Jordan+, 2007A&A...462.1097J 2007A&A...462.1097J
Kaw+07 = Kawka+, 2007ApJ...654..499K 2007ApJ...654..499K
Koe+98 = Koester+, 1998A&A...338..612K 1998A&A...338..612K
Lan+12 = Landstreet+,2012A&A...545A..30L 2012A&A...545A..30L
L+B19 = Landstreet & Bagnulo, 2019A&A...628A...1L 2019A&A...628A...1L
L+B20 = Landstreet & Bagnulo, 2020A&A...634L..10L 2020A&A...634L..10L
Lie+77 = Liebert+, 1977ApJ...214..457L 1977ApJ...214..457L
Lie+93 = Liebert+, 1993ApJ...418..426L 1993ApJ...418..426L
S+S95 = Schmidt & Smith, 1995ApJ...448..305S 1995ApJ...448..305S
Sch+92 = Schmidt+, 1992AJ....104.1563S 1992AJ....104.1563S
Swe+94 = Swedlund+, 1974ApJ...187L.121S 1974ApJ...187L.121S
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 10-Jun-2024