A search for magnetic fields in cool sdB stars

Mathys, G.; Hubrig, S.; Mason, E.; Michaud, G.; Schöller, M.; Wesemaël, F.

doi:10.1002/asna.201111618

Cited by 20 publications

(19 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Extensive searches for magnetic fields in central stars of planetary nebulae and in hot subdwarfs have until now yielded negative results (Asensio Leone et al 2014;Mathys et al 2012;Savanov et al 2013). Should this finding be verified by further spectropolarimetric observations, it would again be consistent with the view that the origin of fields in MWDs is intimately related to their binary nature.…”

Section: Origin Of Magnetic Fields In White Dwarfs and Magnetic Catacsupporting

confidence: 53%

“…Therefore, the magnetic field distribution of WDs could be bimodal exhibiting a high field (1-1000 MG) population and a low field (< 0.1 MG) one. Intensive searches for magnetic fields in the direct progenitors of MWDs have so far drawn a blank, both among planetary nebulae (Asensio Leone et al 2014), and hot subdwarfs (Mathys et al 2012;Savanov et al 2013).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Magnetic White Dwarfs

2015

View full text Add to dashboard Cite

In this paper we review the current status of research on the observational and theoretical characteristics of isolated and binary magnetic white dwarfs (MWDs). Magnetic fields of isolated MWDs are observed to lie in the range 10^3-10^9G. While the upper limit cutoff appears to be real, the lower limit is more difficult to investigate. The incidence of magnetism below a few 10^3G still needs to be established by sensitive spectropolarimetric surveys conducted on 8m class telescopes. Highly magnetic WDs tend to exhibit a complex and non-dipolar field structure with some objects showing the presence of higher order multipoles. There is no evidence that fields of highly magnetic WDs decay over time, which is consistent with the estimated Ohmic decay times scales of ~10^11 yrs. MWDs, as a class, also appear to be more massive than their weakly or non-magnetic counterparts. MWDs are also found in binary systems where they accrete matter from a low-mass donor star. These binaries, called magnetic Cataclysmic Variables (MCVs) and comprise about 20-25\% of all known CVs. Zeeman and cyclotron spectroscopy of MCVs have revealed the presence of fields in the range $\sim 7-230$\,MG. Complex field geometries have been inferred in the high field MCVs (the polars) whilst magnetic field strength and structure in the lower field group (intermediate polars, IPs) are much harder to establish. The origin of fields in MWDs is still being debated. While the fossil field hypothesis remains an attractive possibility, field generation within the common envelope of a binary system has been gaining momentum, since it would explain the absence of MWDs paired with non-degenerate companions and also the lack of relatively wide pre-MCVs.Comment: 73 pages, 22 figures, 2 large tables. Invited review chapter on Magnetic White Dwarfs to appear in Space Science Reviews, Springe

show abstract

Section: Origin Of Magnetic Fields In White Dwarfs and Magnetic Catacsupporting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

Magnetic White Dwarfs

2015

View full text Add to dashboard Cite

show abstract

“…2. We believe that it is quite important to carry out substantial further surveys for hot subdwarf fields, similar to the ones carried out by O'Toole et al (2005) and Mathys et al (2012), and particularly to re-observe hot subdwarfs for which field detections have been reported and not later shown to be spurious.…”

Section: Discussionmentioning

confidence: 83%

The magnetic fields of hot subdwarf stars

Landstreet

Bagnulo

Fossati

et al. 2012

A&A

View full text Add to dashboard Cite

Context. Detection of magnetic fields has been reported in several sdO and sdB stars. Recent literature has cast doubts on the reliability of most of these detections. The situation concerning the occurrence and frequency of magnetic fields in hot subdwarfs is at best confused. Aims. We revisit data previously published in the literature, and we present new observations to clarify the question of how common magnetic fields are in subdwarf stars. Methods. We consider a sample of about 40 hot subdwarf stars. About 30 of them have been observed with the FORS1 and FORS2 instruments of the ESO VLT. Results have been published for only about half of the hot subdwarfs observed with FORS. Here we present new FORS1 field measurements for 17 stars, 14 of which have never been observed for magnetic fields before. We also critically review the measurements already published in the literature, and in particular we try to explain why previous papers based on the same FORS1 data have reported contradictory results. Results. All new and re-reduced measurements obtained with FORS1 are shown to be consistent with non-detection of magnetic fields. We explain previous spurious field detections from data obtained with FORS1 as due to a non-optimal method of wavelength calibration. Field detections in other surveys are found to be uncertain or doubtful, and certainly in need of confirmation. Conclusions. There is presently no strong evidence for the occurrence of a magnetic field in any sdB or sdO star, with typical longitudinal field uncertainties of the order of 2-400 G. It appears that globally simple fields of more than about 1 or 2 kG in strength occur in at most a few percent of hot subdwarfs. Further high-precision surveys, both with high-resolution spectropolarimeters and with instruments similar to FORS1 on large telescopes, would be very valuable.

show abstract

“…High magnetic fields that may cause a Zeeman-splitting of the lines as observed in magnetic white dwarfs can be excluded. Most recently, Mathys et al (2012) have measured the magnetic field of SB 290 using the FORS2 instrument at ESO-VLT in spectropolarimetric mode. Although they report a marginal detection of a few hundred kG, this field strength is much too small to cause the observed line broadening.…”

Section: Possible Line Broadening Mechanismsmentioning

confidence: 99%

The subdwarf B star SB 290 – A fast rotator on the extreme horizontal branch

Geier

Heber

Heuser

et al. 2013

A&A

View full text Add to dashboard Cite

Hot subdwarf B stars (sdBs) are evolved core helium-burning stars with very thin hydrogen envelopes. To form an sdB, the progenitor has to lose almost all of its hydrogen envelope right at the tip of the red giant branch. In close binary systems, mass transfer to the companion provides the extraordinary mass loss required for their formation. However, apparently single sdBs exist as well, and their formation has been unclear for decades. The merger of helium white dwarfs leading to an ignition of core helium-burning or the merger of a helium core and a low-mass star during the common envelope phase have been proposed. Here we report the discovery of SB 290 as the first apparently single, fast-rotating sdB star located on the extreme horizontal branch, indicating that those stars may form from mergers.

show abstract

A search for magnetic fields in cool sdB stars

Cited by 20 publications

References 21 publications

Magnetic White Dwarfs

Magnetic White Dwarfs

The magnetic fields of hot subdwarf stars

The subdwarf B star SB 290 – A fast rotator on the extreme horizontal branch

Contact Info

Product

Resources

About