Intermediate-mass Stars Become Magnetic White Dwarfs

Caiazzo, Ilaria; Richer, Harvey B.; Cummings, Jeffrey D.; Fleury, Leesa; Hegarty, James; Kalirai, Jason; Kerr, Ronan; Thiele, Sarah; Tremblay, Pier-Emmanuel; Villanueva, Michael R.

doi:10.3847/2041-8213/abb5f7

Cited by 18 publications

(17 citation statements)

References 48 publications

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“…Additionally, a fossil field would have to survive the turbulence associated with the RGB and AGB phases of stellar evolution, although field lines may be trapped and retained in non-convective core regions. Despite these inconsistencies, a recent study found three magnetic white dwarfs identified as members of open clusters, and firmly linked to single, intermediate-mass star evolution (Caiazzo et al 2020). This result supports the idea of fossil field origin in at least some cases.…”

Section: Introductionmentioning

confidence: 67%

A test of the planet–star unipolar inductor for magnetic white dwarfs

Walters

Farihi

Marsh

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Despite thousands of spectroscopic detections, only four isolated white dwarfs exhibit Balmer emission lines. The temperature inversion mechanism is a puzzle over 30 years old that has defied conventional explanations. One hypothesis is a unipolar inductor that achieves surface heating via ohmic dissipation of a current loop between a conducting planet and a magnetic white dwarf. To investigate this model, new time-resolved spectroscopy, spectropolarimetry, and photometry of the prototype GD 356 are studied. The emission features vary in strength on the rotational period, but in anti-phase with the light curve, consistent with a cool surface spot beneath an optically thin chromosphere. Possible changes in the line profiles are observed at the same photometric phase, potentially suggesting modest evolution of the emission region, while the magnetic field varies by 10 per cent over a full rotation. These comprehensive data reveal neither changes to the photometric period, nor additional signals such as might be expected from an orbiting body. A closer examination of the unipolar inductor model finds points of potential failure: the observed rapid stellar rotation will inhibit current carriers due to the centrifugal force, there may be no supply of magnetospheric ions, and no anti-phase flux changes are expected from ohmic surface heating. Together with the highly similar properties of the four cool, emission-line white dwarfs, these facts indicate that the chromospheric emission is intrinsic. A tantalizing possibility is that intrinsic chromospheres may manifest in (magnetic) white dwarfs, and in distinct parts of the HR diagram based on structure and composition.

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Section: Introductionmentioning

confidence: 67%

A test of the planet–star unipolar inductor for magnetic white dwarfs

Walters

Farihi

Marsh

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…The astrometric data provide the strongest case for membership of any WD found in our survey with all properties lying within about 1σ of the mean cluster values. The cluster age from the CMD is 90 ± 20 Myr (Caiazzo et al 2020), and the photometry suggests a WD that is extremely hot and luminous. As we showed in Caiazzo et al, the WD is a hot magnetic DA, in fact the hottest and youngest WD known in any open star cluster.…”

Section: Ascc 47mentioning

confidence: 94%

“…The CMD of this cluster, Figure 15, suggests an age near 280 ± 20 Myr and yields a photometric mass for its WD near 0.9 M e . The spectrum of the WD was discussed in detail in Caiazzo et al (2020) and yielded =  g log 8.87 0.07 and a temperature of 18,400 ± 300 K. This apparently high gravity is partially due to the presence of a magnetic field, which has the effect of broadening the spectral lines, hence mimicking a higher-mass WD. The photometric g log , which we use in this case as it is largely unaffected by the presence of the magnetic field, suggested a value of 8.54 ± 0.04 for g log and together with the temperature yielded a mass of 0.95 ± 0.02 M e .…”

Section: Messier 39 (Ngc 7092)mentioning

confidence: 99%

Massive White Dwarfs in Young Star Clusters

Richer

Caiazzo²,

Du³

et al. 2021

ApJ

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We have carried out a search for massive white dwarfs (WDs) in the direction of young open star clusters using the Gaia DR2 database. The aim of this survey was (1) to provide robust data for new and previously known high-mass WDs regarding cluster membership, (2) to highlight WDs previously included in the initial final mass relation (IFMR) that are unlikely members of their respective clusters according to Gaia astrometry, and (3) to select an unequivocal WD sample that could then be compared with the host clusters' turnoff masses. All promising WD candidates in each cluster color-magnitude diagram were followed up with spectroscopy from Gemini in order to determine whether they were indeed WDs and derive their masses, temperatures, and ages. In order to be considered cluster members, white dwarfs were required to (1) have proper motions and parallaxes within 2σ, 3σ, or 4σ of those of their potential parent cluster based on how contaminated the field was in their region of the sky, (2) have a cooling age that was less than the cluster age, and (3) have a mass that was broadly consistent with the IFMR. A number of WDs included in current versions of the IFMR turned out to be nonmembers, and a number of apparent members, based on Gaia's astrometric data alone, were rejected, as their mass and/or cooling times were incompatible with cluster membership. In this way, we developed a highly selected IFMR sample for high-mass WDs that, surprisingly, contained no precursor masses significantly in excess of ∼ 6 M e .

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“…It is worth noting the recent detection claimed by Caiazzo et al (2020) of magnetic fields in three young WDs that are members of open clusters, in which the mass and age of the progenitor of each can be determined fairly accurately. All three WDs have quite high masses (around 1 𝑀 ) and progenitor masses of around 5 or 6 𝑀 .…”

Section: Origin Of the Fields As A Results Of Deep-seated Convective ...mentioning

confidence: 95%

“…All three WDs have quite high masses (around 1 𝑀 ) and progenitor masses of around 5 or 6 𝑀 . Caiazzo et al (2020) argue that these new MWDs are so young that it is very unlikely that they formed from binary merger processes discussed in Sect. 7.2.3 below; instead they are almost certainly descended from single upper main sequence stars.…”

Section: Origin Of the Fields As A Results Of Deep-seated Convective ...mentioning

confidence: 98%

New insight into the magnetism of degenerate stars from the analysis of a volume limited sample of white dwarfs

Bagnulo,

Landstreet

2021

Preprint

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Many stars evolve into magnetic white dwarfs, and observations may help to understand when the magnetic field appears at the stellar surface, if and how it evolves during the cooling phase, and, above all, what are the mechanisms that generate it. After obtaining new spectropolarimetric observations and combining them with previous literature data, we have checked almost the entire population of about 152 white dwarfs within 20 pc from the Sun for the presence of magnetic fields, with a sensitivity that ranges from better than 1 kG for most of the stars of spectral class DA, to 1 MG for some of the featureless white dwarfs. We find that 33 white dwarfs of the local 20 pc volume are magnetic. Statistically, the data are consistent with the possibility that the frequency of the magnetic field occurrence is similar in stars of all spectral classes, except that in the local 20 pc volume, either DQ stars are more frequently magnetic, or host much stronger fields than average. The distribution of the observed field strength ranges from 40 kG to 300 MG and is uniform per decade, in striking contrast to the field frequency distribution resulting from spectroscopic surveys. Remarkably, no fields weaker than 40 kG are found. We confirm that magnetic fields are more frequent in white dwarfs with higher than average mass, especially in younger stars. We find a marked deficiency of magnetic white dwarfs younger than 0.5 Gyr, and we find that the frequency of the occurrence of the magnetic field is significantly higher in white dwarfs that have undergone the process of core crystallisation than in white dwarfs with fully liquid core. There is no obvious evidence of field strength decay with time. We discuss the implications of our findings in relation to some of the proposals that have been put forward to explain the origin and evolution of magnetic fields in degenerate stars, in particular those that predict the presence of a dynamo acting during the crystallisation phase.

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Intermediate-mass Stars Become Magnetic White Dwarfs

Cited by 18 publications

References 48 publications

A test of the planet–star unipolar inductor for magnetic white dwarfs

A test of the planet–star unipolar inductor for magnetic white dwarfs

Massive White Dwarfs in Young Star Clusters

New insight into the magnetism of degenerate stars from the analysis of a volume limited sample of white dwarfs

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