title: No Sun-like dynamo on the active star ζ Andromedae from starspot asymmetry.
abstract: Sunspots are cool areas caused by strong surface magnetic fields that inhibit convection. Moreover, strong magnetic fields can alter the average atmospheric structure, degrading our ability to measure stellar masses and ages. Stars that are more active than the Sun have more and stronger dark spots than does the Sun, including on the rotational pole. Doppler imaging, which has so far produced the most detailed images of surface structures on other stars, cannot always distinguish the hemisphere in which the starspots are located, especially in the equatorial region and if the data quality is not optimal. This leads to problems in investigating the north-south distribution of starspot active latitudes (those latitudes with more starspot activity); this distribution is a crucial constraint of dynamo theory. Polar spots, whose existence is inferred from Doppler tomography, could plausibly be observational artefacts. Here we report imaging of the old, magnetically active star ζ Andromedae using long-baseline infrared interferometry. In our data, a dark polar spot is seen in each of two observation epochs, whereas lower-latitude spot structures in both hemispheres do not persist between observations, revealing global starspot asymmetries. The north-south symmetry of active latitudes observed on the Sun is absent on ζ And, which hosts global spot patterns that cannot be produced by solar-type dynamos.
authors.affiliation: Department of Astronomy, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Roettenbacher
authors.affiliation: Department of Astronomy, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Monnier
authors.affiliation: Finnish Centre for Astronomy with ESO (FINCA), University of Turku, FI-21500 Piikkiö, Finland.|Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø, Denmark.
authors.forename: H
authors.initials: H
authors.lastname: Korhonen
authors.affiliation: Department of Astronomy, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: A N
authors.initials: AN
authors.lastname: Aarnio
authors.affiliation: Department of Astronomy, University of Michigan, Ann Arbor, Michigan 48109, USA.|Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, USA.
authors.forename: F
authors.initials: F
authors.lastname: Baron
authors.affiliation: Department of Astronomy, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: X
authors.initials: X
authors.lastname: Che
authors.affiliation: Department of Physics and Astronomy, Ohio Wesleyan University, Delaware, Ohio 48103, USA.
authors.forename: R O
authors.initials: RO
authors.lastname: Harmon
authors.affiliation: Konkoly Observatory, Research Center for Astronomy and Earth Sciences, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary.
authors.forename: Zs
authors.initials: Z
authors.lastname: Kővári
authors.affiliation: Department of Astronomy, University of Michigan, Ann Arbor, Michigan 48109, USA.|School of Physics, University of Exeter, Exeter, EX4 4QL, UK.
authors.forename: S
authors.initials: S
authors.lastname: Kraus
authors.affiliation: Center for High Angular Resolution Astronomy, Georgia State University, Mount Wilson, California 91023, USA.
authors.forename: G H
authors.initials: GH
authors.lastname: Schaefer
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA.
authors.forename: G
authors.initials: G
authors.lastname: Torres
authors.affiliation: Department of Astronomy, University of Michigan, Ann Arbor, Michigan 48109, USA.|Department of Astronomy and Astrophysics, Pennsylvania State University, State College, Pennsylvania 16802, USA.
authors.forename: M
authors.initials: M
authors.lastname: Zhao
authors.affiliation: Center for High Angular Resolution Astronomy, Georgia State University, Mount Wilson, California 91023, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: ten Brummelaar
authors.affiliation: Center for High Angular Resolution Astronomy, Georgia State University, Mount Wilson, California 91023, USA.
authors.forename: J
authors.initials: J
authors.lastname: Sturmann
authors.affiliation: Center for High Angular Resolution Astronomy, Georgia State University, Mount Wilson, California 91023, USA.
authors.forename: L
authors.initials: L
authors.lastname: Sturmann