J/A+A/618/A113ivo://CDS.VizieR/J/A+A/618/A113doi:10.26093/cds/vizier.36180113CDSBagnulo S.Landstree J.D.2018-11-05T10:52:51Z2018-10-23T08:44:44ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frwhite-dwarf-starsspectroscopyOur knowledge of the magnetism in white dwarfs is based on an observational dataset that is biased in favour of stars with very strong magnetic fields. Most of the field measurements available in the literature have a relatively low sensitivity, while current instruments allow us to detect magnetic fields of white dwarfs with sub-kG precision. With the aim of obtaining a more complete view of the incidence of magnetic fields in degenerate stars, we have started a long-term campaign of high-precision spectropolarimetric observations of white dwarfs. Here we report the results obtained so far with the low-resolution FORS2 instrument of the ESO VLT and the medium-resolution ISIS instrument of the WHT. We have considered a sample of 48 stars, of which five are known magnetic or suspected magnetic stars, and obtained new longitudinal magnetic field measurements with a mean uncertainty of about 0.6kG. Overall, in the course of our survey (the results of which have been partially published in papers devoted to individual stars) we have discovered one new weak-field magnetic white dwarf, confirmed the magnetic nature of another, found that a suspected magnetic star is not magnetic, and suggested two new candidate magnetic white dwarfs. Even combined with data previously obtained in the literature, our sample is not sufficient yet to reach any final conclusions about the actual incidence of very weak magnetic fields in white dwarfs, but we have set the basis to achieve a homogeneous survey of an unbiased sample of white dwarfs. As a by-product, our survey has also enabled us to carry out a detailed characterisation of the ISIS and the FORS2 instruments for the detection of extremely weak magnetic fields in white dwarfs, and in particular to relate the signal-to-noise ratio to measurement uncertainty for white dwarfs of different spectral types. This study will help the optimisation of future observations.2018A&A...618A.113Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/618/A113CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/583/A115 : FORS1 catalogue of stellar magnetic fields (Bagnulo+, 2015)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/618/A113https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/618/A113http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/618/A113https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/618/A113https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/618/A113http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/618/A113GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/618/A113/mwds (Table with star names, information about spectra, and link to 109 ASCII tables)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/618/A113/mwds?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/618/A113/mwds?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/618/A113/mwds?GETtext/xml+votable180.050000true0.544685-43.16538720.0055555555555555566/743 1890 2536 3345 4067 5827 6705 8361 9336 10173 10999 11642 11984 12738 13013 13295 14391 14667 15391 15462 16158 16344 17625 18139 19970 20404 22709 23789 24204 24795 25792 26678 26916 27078 28559 29182 29855 30754 31290 31735 32436 32847 33015 35490 35573 40944 42700 45110 46841 48724 48728https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/618/A113?format=asciidefaultJ/A+A/618/A113/mwdsTable with star names, information about spectra, and link to 109 ASCII tablesSettingGrims or gratinginstr.setupcharNameName of the starmeta.id;meta.maincharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintONameAlternative name of the starmeta.idcharObsObservation datestime.epoch;obsnullableTexpTotal exposure timestime.duration;obs.exposureintInstInstrument and telescopeinstrcharSlitSlit widtharcsecspect.line.widthfloatspShow the spectrummeta.ref.urlcharFileNameFilename of the ASCII table with spectra in subdirectory spmeta.id;meta.tablecharSimbadSimbad column added by the CDSmeta.ref.urlchar_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.main