Measuring starspots on magnetically active stars with the VLTI

Wittkowski, M.; Schöller, M.; Hubrig, S.; Posselt, Bettina; Lühe, O. von der

doi:10.1002/1521-3994(200208)323:3/4<241::aid-asna241>3.0.co;2-d

Cited by 12 publications

(7 citation statements)

References 27 publications

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“…A list of resolvable giants with predicted surface activity was given in Wittkowski et al (2002). Early images reconstructed with bispectrum speckle interferometry were obtained for VY CMa by Wittkowski et al (1998) and, e.g.…”

Section: Direct Spot Detectionsmentioning

confidence: 99%

Starspots

Strassmeier

2009

Astron Astrophys Rev

444

378

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Starspots are created by local magnetic fields on the surfaces of stars, just as sunspots. Their fields are strong enough to suppress the overturning convective motion and thus block or redirect the flow of energy from the stellar interior outwards to the surface and consequently appear as locally cool and therefore dark regions against an otherwise bright photosphere (Biermann in Astronomische Nachrichten 264: 361, 1938; Z Astrophysik 25:135, 1948). As such, starspots are observable tracers of the yet unknown internal dynamo activity and allow a glimpse into the complex internal stellar magnetic field structure. Starspots also enable the precise measurement of stellar rotation which is among the key ingredients for the expected internal magnetic topology. But whether starspots are just blown-up sunspot analogs, we do not know yet. This article is an attempt to review our current knowledge of starspots. A comparison of a white-light image of the Sun (G2V, 5 Gyr) with a Doppler image of a young solar-like star (EK Draconis; G1.5V, age 100 Myr, rotation 10 × Ω Sun ) and with a mean-field dynamo simulation suggests that starspots can be of significantly different appearance and cannot be explained with a scaling of the solar model, even for a star of same mass and effective temperature. Starspots, their surface location and migration pattern, and their link with the stellar dynamo and its internal energy transport, may have far reaching impact also for our understanding of low-mass stellar evolution and formation. Emphasis is given in this review to their importance as activity tracers in particular in the light of more and more precise exoplanet detections around solar-like, and therefore likely spotted, host stars.

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Section: Direct Spot Detectionsmentioning

confidence: 99%

Starspots

Strassmeier

2009

Astron Astrophys Rev

444

378

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“…For magnetically active stars such observations can provide orientation of the stellar rotation axis with respect to the line of sight (Lagarde et al, 1995), which is important for interpretation of spectroscopic and photometric observations of spotted stars. Also, differential fringe phases can be used to locate spots on the stellar surface (Wittkowski et al, 2002;Jankov et al, 2003;Rousselet-Perraut et al, 2004), even in such difficult cases as pole-on and equator-on orientations of the star which cannot be resolved by traditional Doppler spectroscopy. In addition, the stellar differential rotation rate and the inclination angle can be disentangled (de Souza et al, 2004).…”

Section: Interferometrymentioning

confidence: 99%

Starspots: A Key to the Stellar Dynamo

Berdyugina

2005

Living Rev. Solar Phys.

577

530

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Magnetic activity similar to that of the Sun is observed on a variety of cool stars with external convection envelopes. Stellar rotation coupled with convective motions generate strong magnetic fields in the stellar interior and produce a multitude of magnetic phenomena including starspots in the photosphere, chromospheric plages, coronal loops, UV, X-ray, and radio emission and flares. Here I review the phenomenon of starspots on different types of cool stars, observational tools and diagnostic techniques for studying starspots as well as starspot properties including their temperatures, areas, magnetic field strengths, lifetimes, active latitudes and longitudes, etc. Evolution of starspots on various time scales allows us to investigate stellar differential rotation, activity cycles, and global magnetic fields. Together these constitute the basis for our understanding of stellar and solar dynamos and provide valuable constraints for theoretical models.

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“…Therefore, for resolving starspots one must use much larger telescopes or optical/near‐infrared interferometry. Wittkowski et al () investigated the possibility of using Very Large Telescope Interferometer (VLTI) for studying starspots. The first attempt using AMBER (Astronomical Multi‐BEam combineR) at VLT was carried out by Korhonen et al ().…”

Section: Imaging Stellar Surfaces With Near‐infrared Interferometrymentioning

confidence: 99%

Surface magnetism of cool stars

et al. 2017

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Magnetic fields are essential ingredients of many physical processes in the interiors and envelopes of cool stars. Yet their direct detection and characterization is notoriously difficult, requiring high-quality observations and advanced analysis techniques. Significant progress has been recently achieved by several types of direct magnetic field studies on the surfaces of cool, active stars. In particular, complementary techniques of field topology mapping with polarization data and total magnetic flux measurements from intensity spectra have been systematically applied to different classes of active stars, leading to interesting and occasionally controversial results. In this paper, we summarize the current status of direct magnetic field studies of cool stars and investigations of surface inhomogeneities caused by the field, based on the material presented at the Cool Stars 19 splinter session.

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Measuring starspots on magnetically active stars with the VLTI

Cited by 12 publications

References 27 publications

Starspots

Starspots

Starspots: A Key to the Stellar Dynamo

Surface magnetism of cool stars

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