Beta Ceti is a slowly rotating (v sin i = 3.5 kms−1) single giant. In our previous study (Tsvetkova et al. (2013)) we showed that it is in the core He-burning phase and we reconstructed two Zeeman Doppler imaging (ZDI) maps (using data from 2010 and 2011) revealing a simple large-scale magnetic field structure. We concluded that the magnetic field of beta Ceti could have a fossil field origin. In addition, the study of Aurière et al. (2015) about the properties and origin of the magnetism of late-type giants, where beta Ceti was a member of that sample, revealed that this star did not follow the general trends for dynamo-generated magnetic fields. Now, we present a new ZDI map of beta Ceti and compare the new results with our previous study. This monitoring for several years of the magnetic field topology and line activity indicators variability supports our previous conclusion about the fossil field origin of the magnetic field of beta Ceti

Aurière, Michel

Bogdanovski, Rumen

Borisova, Ana

Charbonnel, Corinne

Konstantinova-Antova, Renada

Petit, Pascal

Tsvetkova, Svetla

Wade, Gregg A.

English

<p>Beta Ceti is a slowly rotating (v sin i = 3.5 kms−1) single giant. In our previous study (Tsvetkova et al. (2013)) we showed that it is in the core He-burning phase and we reconstructed two Zeeman Doppler imaging (ZDI) maps (using data from 2010 and 2011) revealing a simple large-scale magnetic field structure. We concluded that the magnetic field of beta Ceti could have a fossil field origin. In addition, the study of Aurière et al. (2015) about the properties and origin of the magnetism of late-type giants, where beta Ceti was a member of that sample, revealed that this star did not follow the general trends for dynamo-generated magnetic fields. Now, we present a new ZDI map of beta Ceti and compare the new results with our previous study. This monitoring for several years of the magnetic field topology and line activity indicators variability supports our previous conclusion about the fossil field origin of the magnetic field of beta Ceti.</p

Tsvetkova, Svetla (5300401)

Petit, Pascal (5283913)

Konstantinova-Antova, Renada (5300398)

Aurière, Michel (5300389)

Wade, Gregg A. (5300383)

Charbonnel, Corinne (5300392)

Bogdanovski, Rumen (5300386)

Borisova, Ana (5300395)

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Monitoring of the magnetic field topology and activity of the core helium-burning giant beta Ceti in the period 2010-2013

Beta Ceti is a slowly rotating (v sin i = 3.5 kms−1) single giant. In our previous study (Tsvetkova et al. (2013)) we showed that it is in the core He-burning phase and we reconstructed two Zeeman Doppler imaging (ZDI) maps (using data from 2010 and 2011) revealing a simple large-scale magnetic field structure. We concluded that the magnetic field of beta Ceti could have a fossil field origin. In addition, the study of Aurière et al. (2015) about the properties and origin of the magnetism of late-type giants, where beta Ceti was a member of that sample, revealed that this star did not follow the general trends for dynamo-generated magnetic fields. Now, we present a new ZDI map of beta Ceti and compare the new results with our previous study. This monitoring for several years of the magnetic field topology and line activity indicators variability supports our previous conclusion about the fossil field origin of the magnetic field of beta Ceti.Poster #212

ZENODO

The 19th Cambridge Workshop on Cool Stars, Stellar Systems, and the SunEdited by G. A. FeidenMonitoring of the magnetic field topology and activity of the corehelium-burning giant β Ceti in the period 2010-2013Svetla Tsvetkova1, Pascal Petit2,3, Renada Konstantinova-Antova1,3, Michel Aurière2,3, Gregg A.Wade4, Corinne Charbonnel5, Rumen Bogdanovski1, Ana Borisova11 Institute of Astronomy and NAO, Bulgarian Academy of Sciences, 72 Tsarigradsko shose, 1784 Sofia, Bulgariastsvetkova@astro.bas.bg2 CNRS, Institut de Recherche en Astrophysique et Planétologie, IRAP, 14 Avenue Edouard Belin, 31400 Toulouse, France3 Université de Toulouse, UPS-OMP, IRAP, Toulouse, France4 Department of Physics, Royal Military College of Canada, PO Box 17000, Station ‘Forces’, Kingston, Ontario, Canada K7K4B45 Geneva Observatory, University of Geneva, 51, Chemin des Maillettes, 1290 Versoix, SwitzerlandAbstractβ Ceti is a slowly rotating (v sin i = 3.5 kms−1) single giant. In our previous study (Tsvetkova et al. (2013)) weshowed that it is in the core He-burning phase and we reconstructed two Zeeman Doppler imaging (ZDI) maps(using data from 2010 and 2011) revealing a simple large-scale magnetic field structure. We concluded that themagnetic field of β Ceti could have a fossil field origin. In addition, the study of Aurière et al. (2015) about theproperties and origin of the magnetism of late-type giants, where β Ceti was a member of that sample, revealed thatthis star did not follow the general trends for dynamo-generated magnetic fields. Now, we present a new ZDI mapof β Ceti and compare the new results with our previous study. This monitoring for several years of the magneticfield topology and line activity indicators variability supports our previous conclusion about the fossil field originof the magnetic field of β Ceti.1 Introductionβ Ceti (HD 4128) is a star of spectral class K0 withV = 2.04 mag and B−V = 1.02 mag. It is a single giantwith the highest X-ray luminosity log Lx = 30.2 erg s−1(Maggio et al. (1998); Hünsch et al. (1996)) in the nearsolar neighborhood (d ≤ 30 pc). Magnetic events such ascoronal loops (Eriksson et al. (1983)) and flares (Ayreset al. (2001)) have been detected. It is a slowly rotatinggiant with v sin i = 3.5 km s−1.In the previous study of Tsvetkova et al. (2013), weshowed that β Ceti is a 3.5 M giant in the core helium-burning phase with a radius of 18 R. The main se-quence progenitor of β Ceti was a late B-type star. Wewere able to reconstruct two magnetic maps of the sur-face magnetic field topology of the star employing theZDI technique. Both maps showed that the large-scalemagnetic field of β Ceti was dominated by the poloidalcomponent. The behavior of the line activity indicatorsHα, CaII K, CaII IR (854.2 nm), and the radial veloc-ity correlated rather well with the longitudinal magneticfield Bl. Our main conclusion was that the magnetismof β Ceti might be (at least partly) of fossil origin andinherited from a main sequence Ap/Bp star.Here, we present a new dataset of β Ceti. We are ableto reconstruct one more ZDI map and to compare thenew results with the previous study.2 Observations and data reduction 1Observational data were obtained with two twinfiber-fed echelle spectropolarimeters – Narval (Aurière(2003)), which operates at the 2-m Bernard Lyot Téle-scope (TBL) at Pic du Midi Observatory, France, andESPaDOnS (Donati et al. (2006a)), which operates atthe 3.6-m Canada-France-Hawaii Telescope (CFHT) ofMauna Kea Observatory, Hawaii. In polarimetric mode,both have a spectral resolution of about 65 000 anda nearly continuous spectrum coverage from the near-ultraviolet (at about 370 nm) to the near-infrared domain(at 1050 nm) in a single exposure, with 40 orders alignedon the CCD frame by two cross-disperser prisms. StokesI (unpolarized light) and Stokes V (circular polarization)parameters are simultaneously obtained by four subex-posures between which the retarders – Fresnel rhombs– are rotated in order to exchange the beams in the in-strument and to reduce spurious polarization signatures(Semel et al. (1993)).Seven spectra have been collected for β Ceti in theperiod June – November 2013. Reduced spectra were1Based on observations obtained at the Bernard Lyot Télescope(TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory,which is operated by the Institut National des Sciences de l’Universof the Centre National de la Recherche Scientifique of France andUniversité de Toulouse, and at the Canada-France-Hawaii Tele-scope (CFHT), which is operated by the National Research Coun-cil of Canada, the Institut National des Sciences de l’Univers ofthe Centre National de la Recherche Scientifique of France, andthe University of Hawaii.1Tsvetkova et al.extracted using the automatic reduction software Li-breEsprit, developed for Narval and ESPaDOnS (Donatiet al. (1997)). The least squares deconvolution (LSD)multiline technique (Donati et al. (1997)) was applied toall observations. This cross-correlation technique enablesaveraging of about 12 700 absorption atomic lines in thecase of β Ceti taken from one spectrum, which increasesthe signal-to-noise ratio (S/N) to the point where weakpolarized Zeeman signatures can be detected. Mean pho-tospheric Stokes I and V profiles were computed for eachspectrum. Then, the surface-averaged longitudinal mag-netic field Bl was computed using the first-order mo-ment method (Donati et al. (1997); Rees & Semel (1979);Wade et al. (2000)).For mapping the magnetic fields at the stellar sur-face from sets of rotationally modulated circularly po-larised profiles we used the Zeeman Doppler Imaging to-mographic method (ZDI; Semel (1989); Donati & Brown(1997); Donati et al. (2006b)). The surface vectorialmagnetic field is modeled using a spherical harmonic ex-pansion, in order to distinguish between the poloidal andtoroidal components of the surface magnetic geometry(Donati et al. (2006b)). This method performs iterativefitting of the observed time series of LSD polarized pro-files by a simulated set of Stokes V profiles computed foran identical sequence of rotational phases. The syntheticStokes profiles are calculated from an artificial star whosesurface is divided into a grid of 2 000 rectangular pixelsof roughly similar area. Each surface pixel is associatedwith a local Stokes I and V profile. The local syntheticStokes I line profile is assumed to possess a Gaussianshape, with a depth and width adjusted to achieve thebest fit between synthetic and observed line profiles. Lo-cal Stokes V profiles are calculated under the weak-fieldassumption (Morin et al. (2008); Petit et al. (2010)). Thelinear limb darkening coefficient is set to 0.75, in agree-ment with Claret & Bloemen (2011). We limited thespherical harmonics expansion to l ≤ 10, since no im-provement was found for the fits between modeled andobserved LSD profiles for higher values of l.3 ResultsWe present a new dataset for the giant β Ceti for theperiod June – November 2013. The data from 2010to 2012 have already been published (Tsvetkova et al.(2013)) and are also shown in Figs. 1 and 2. The newZDI map and the fit of the corresponding Stokes V pro-files are presented in Fig. 3. The input parameters forthe ZDI model are the same as we used for the previousdatasets – v sin i = 3.5 km s−1, inclination angle i = 60◦,rotational period P = 215 days. All the three datasetswere phased according to the following ephemeris:HJD = 2454101.5+ 215φ (1)where HJD is the heliocentric Julian date of the obser-vations and φ is the rotational cycle.We also measured the classical line activity indicatorsHα, CaII K, CaII IR (854.2 nm), and the radial veloc-ity from the spectra. Their variability with time com-pared to the longitudinal magnetic field Bl for the threedatasets is shown in Fig. 4.The percentage of the magnetic energy stored in dif-ferent components is shown in Table 1 for the threedatasets.4 ConclusionsWe present a new dataset of spectropolarimetric ob-servations for the giant β Ceti, which was obtained dur-ing the period June – November 2013. We comparethese results with previous results already published byTsvetkova et al. (2013). Our conclusions are:• the large-scale magnetic topology of β Ceti doesnot change significantly for the three epochs, be-ing dominated by the poloidal component (about97%) and showing a mainly dipolar configuration.• Bl remains of positive polarity for the whole period.It shows sinusoidal variations with time, which isconsistent with a global dipole field configuration(Landstreet & Mathys (2000)).• the new dataset confirms our previous conclusion ofTsvetkova et al. (2013) about the fossil field origin ofthe magnetic field of β Ceti. Even more, the studyof Aurière et al. (2015) about the properties andorigin of the magnetism of late-type giants, whereβ Ceti was a member of that sample, revealed thatthis star did not follow the general trends for a dy-namo generated magnetic fields.• According to our new results, there might be someevidence for a long-term variability of the magneticfeatures, but more observations are needed to con-firm that conclusion.AcknowledgmentsWe thank the TBL and CFHT teams for providingservice observing with Narval and ESPaDOnS. The ob-servations in 2010 with Narval were funded under Bul-garian NSF grant DSAB 02/3/2010. The observationsin 2013 with Narval were funded under the contractBG051PO001-3.3.06-0047. S.Ts. acknowledges the fi-nancial support from the contract DFNP-104 A-1 to at-tend the 19th Workshop on Cool Stars, Stellar Systems,and the Sun (CS19). G.A.W. acknowledges support fromthe Natural Sciences and Engineering Research Councilof Canada (NSERC).ReferencesAurière, M. 2003, In EAS Publications Series, edited byJ. Arnaud & N. Meunier, EAS Publications Series,vol. 9, p. 105.Aurière, M., Konstantinova-Antova, R., Charbonnel, C.,Wade, G. A., Tsvetkova, S., et al. 2015, A&A, 574,A90.Ayres, T. R., Osten, R. A., & Brown, A. 2001, ApJL,562, L83.Claret, A. & Bloemen, S. 2011, A&A, 529, A75.Donati, J.-F. & Brown, S. F. 1997, A&A, 326, 1135.2 Zenodo, 2016The 19th Cambridge Workshop on Cool Stars, Stellar Systems, and the SunFigure 1: β Ceti in the period June 2010 – December 2010 (Tsvetkova et al. (2013)). Left panel: Normalized Stokes Vprofiles - observed profiles (black lines); synthetic profiles (red lines); zero level (dashed lines). All profiles are shiftedvertically for display purposes. The rotational phases of observations are indicated in the right part of the plot andthe error bars are on the left of each profile. Right panel: Magnetic map of β Ceti. The three panels illustrate thefield components in spherical coordinates (from top to bottom – radial, azimuthal, meridional). The magnetic fieldstrength is expressed in gauss. The vertical ticks on top of the radial map show the phases of observations.Figure 2: Same as Fig. 1, for the period June 2011 – January 2012 (Tsvetkova et al. (2013)).Figure 3: Same as Fig. 1, but for the new dataset of β Ceti, containing the period June – November 2013.Zenodo, 2016 3Tsvetkova et al.Table 1: Magnetic characteristics inferred from the three datesets of β Ceti. The first to the last columns list thefraction of the large-scale magnetic energy reconstructed in the poloidal field component, the fraction of the poloidalmagnetic energy stored in the dipolar (l = 1), quadrupolar (l = 2) and octopolar (l = 3) components, and the fractionof the energy stored in the axisymmetric component (m = 0).pol. dipole quad. oct. axi.Epoch comp. comp. comp. comp. comp.(% tot) (% pol) (% pol) (% pol) (% tot)2010 96.7 83.2 20.8 6.2 77.12011/2012 96.5 85.4 11.3 4.0 74.42013 97.5 89.1 17.8 10.3 69.45250 5500 5750 6000 6250 6500 675013,213,313,413,50,200,210,220,230,240,140,160,160,200,240485250 5500 5750 6000 6250 6500 6750RVHJD ( 2 450 000 + )2010 2011-2012 2013HalphaCaII IRTCaII K Bl, [G]Figure 4: From top to bottom are presented the varia-tions of Bl and the activity indicators CaII K, CaII IR,Hα, and the radial velocity for all the three datasets.Donati, J.-F., Catala, C., Landstreet, J. D., & Petit, P.2006a, In Astronomical Society of the Pacific Confer-ence Series, edited by R. Casini & B. W. Lites, Astro-nomical Society of the Pacific Conference Series, vol.358, p. 362.Donati, J.-F., Howarth, I. D., Jardine, M. M., Petit, P.,Catala, C., et al. 2006b, MNRAS, 370, 629.Donati, J.-F., Semel, M., Carter, B. D., Rees, D. E., &Collier Cameron, A. 1997, MNRAS, 291, 658.Eriksson, K., Linsky, J. L., & Simon, T. 1983, ApJ, 272,665.Hünsch, M., Schmitt, J. H. M. M., Schröder, K.-P., &Reimers, D. 1996, A&A, 310, 801.Landstreet, J. D. & Mathys, G. 2000, A&A, 359, 213.Maggio, A., Favata, F., Peres, G., & Sciortino, S. 1998,A&A, 330, 139.Morin, J., Donati, J.-F., Petit, P., Delfosse, X., Forveille,T., et al. 2008, MNRAS, 390, 567.Petit, P., Lignières, F., Wade, G. A., Aurière, M., Böhm,T., et al. 2010, A&A, 523, A41.Rees, D. E. & Semel, M. D. 1979, A&A, 74, 1.Semel, M. 1989, A&A, 225, 456.Semel, M., Donati, J.-F., & Rees, D. E. 1993, A&A, 278,231.Tsvetkova, S., Petit, P., Aurière, M., Konstantinova-Antova, R., Wade, G. A., et al. 2013, A&A, 556, A43.Wade, G. A., Donati, J.-F., Landstreet, J. D., & Shorlin,S. L. S. 2000, MNRAS, 313, 851.4 Zenodo, 2016

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Monitoring of the magnetic field topology and activity of the core helium-burning giant beta Ceti in the period 2010-2013

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