A1 Refereed original research article in a scientific journal
No Sun-like dynamo on the active star zeta Andromedae from starspot asymmetry
Authors: Roettenbacher RM, Monnier JD, Korhonen H, Aarnio AN, Baron F, Che X, Harmon RO, Kovari Z, Kraus S, Schaefer GH, Torres G, Zhao M, ten Brummelaar TA, Sturmann J, Sturmann L
Publisher: NATURE PUBLISHING GROUP
Publication year: 2016
Journal: Nature
Journal name in source: NATURE
Journal acronym: NATURE
Volume: 533
Issue: 7602
First page : 217
Last page: +
Number of pages: 16
ISSN: 0028-0836
DOI: https://doi.org/10.1038/nature17444(external)
Abstract
Sunspots are cool areas caused by strong surface magnetic fields that inhibit convection(1,2). Moreover, strong magnetic fields can alter the average atmospheric structure(3), 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(4). 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(5). 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(6). Here we report imaging of the old, magnetically active star zeta 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(7) is absent on zeta And, which hosts global spot patterns that cannot be produced by solar-type dynamos(8).
Sunspots are cool areas caused by strong surface magnetic fields that inhibit convection(1,2). Moreover, strong magnetic fields can alter the average atmospheric structure(3), 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(4). 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(5). 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(6). Here we report imaging of the old, magnetically active star zeta 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(7) is absent on zeta And, which hosts global spot patterns that cannot be produced by solar-type dynamos(8).
UTU Research Portal