J/A+A/598/A62ivo://CDS.VizieR/J/A+A/598/A62doi:10.26093/cds/vizier.35980062CDSMosser B.Belkacem K.Pincon C.Takata M.Vrard M.Barban C.,Goupil M.-J.Kallinger T.Samadi R.2017-07-17T11:35:27Z2017-06-12T08:04:21ZCDS support team

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

cds-question@unistra.frgiant-starsspectroscopymagnetic-fieldsSeismic observations with the space-borne Kepler mission have shown that a number of evolved stars exhibit low-amplitude dipole modes, which is referred to as depressed modes. Recently, these low amplitudes have been attributed to the presence of a strong magnetic field in the stellar core of those stars. Subsequently, and based on this scenario, the prevalence of high magnetic fields in evolved stars has been inferred. It should be noted, however, that this conclusion remains indirect. We intend to study the properties of mode depression in evolved stars, which is a necessary condition before reaching conclusions about the physical nature of the mechanism responsible for the reduction of the dipole mode amplitudes. We perform a thorough characterization of the global seismic parameters of depressed dipole modes and show that these modes have a mixed character. The observation of stars showing dipole mixed modes that are depressed is especially useful for deriving model-independent conclusions on the dipole mode damping. We use a simple model to explain how mode visibilities are connected to the extra damping seen in depressed modes. Results. Observations prove that depressed dipole modes in red giants are not pure pressure modes but mixed modes. This result, observed in more than 90% of the bright stars (m_V_<=11), invalidates the hypothesis that depressed dipole modes result from the suppression of the oscillation in the radiative core of the stars. Observations also show that, except for visibility, seismic properties of the stars with depressed modes are equivalent to those of normal stars. The measurement of the extra damping that is responsible for the reduction of mode amplitudes, without any prior on its physical nature, potentially provides an efficient tool for elucidating the mechanism responsible for the mode depression. The mixed nature of the depressed modes in red giants and their unperturbed global seismic parameters carry strong constraints on the physical mechanism responsible for the damping of the oscillation in the core. This mechanism is able to damp the oscillation in the core but cannot fully suppress it. Moreover, it cannot modify the radiative cavity probed by the gravity component of the mixed modes. The recent mechanism involving high magnetic fields proposed for explaining depressed modes is not compliant with the observations and cannot be used to infer the strength and prevalence of high magnetic fields in red giants.2017A&A...598A..62Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/598/A62CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toV/133 : Kepler Input Catalog (Kepler Mission Team, 2009)J/A+A/525/A131 : Solar-like oscillations in Kepler red giants (Hekker+, 2011)J/A+A/540/A143 : Oscillations of red giants observed by Kepler (Mosser+, 2012)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/598/A62https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/598/A62http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/598/A62https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/598/A62https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/598/A62http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/598/A62GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/598/A62/tablea1 (Seismic properties of 71 stars showing depressed mixed modes)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/598/A62/tablea1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/598/A62/tablea1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/598/A62/tablea1?GETtext/xml+votable180.050000true290.8571537.875991940.0055555555555555566/14579 14581 14584-14585 14591 14731-14734 14746 14751-14752 14760 14762 14765 14768 14773-14774 14777-14778 14782 14792 14816 14818 14824 14827 14830 14918 14929 14931 14934 14936 14939 14941 14946 14957 14959 14961 14968 15106-15110 15115-15116 15119 15122 15129 15135 15139 15141 15150 15156 15158 15168 15172 15200https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/598/A62?format=asciiOpticaldefaultJ/A+A/598/A62/tablea1Seismic properties of 71 stars showing depressed mixed modesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintKICKIC identification numbermeta.id;meta.mainintEvolEvolutionary stage (1)src.classcharnumaxMaximum frequencyuHzem.freqfloatDnuFrequency separationuHzem.freq;src.varfloatDPI1Period spacing ({DELTA}{PI}_1_)stime.periodfloatqCoupling factor (2)meta.codefloatMassMasssolMassphys.massfloatGamma0Radial mode width (defined as full width as half maximum) (3)uHzspect.line.widthfloatdnurotRotational splitting (4)nHzem.freq;src.varintV1Total dipole visibilityobs.paramfloatVlowLow visibilityobs.paramfloatVstrongStrong visibilityobs.paramfloatSimbadSimbad column added by the CDSmeta.ref.urlchar_RAPositions from KIC catalog (right ascension part)degpos.eq.ra;meta.main_DEPositions from KIC catalog (declination part)degpos.eq.dec;meta.main