Learning about stellar dynamos from long-term photometry of starspots

Hall, D. S.

doi:10.1007/3-540-53955-7_156

Cited by 42 publications

(13 citation statements)

References 23 publications

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“…Given the differential rotation law we derive, these periods suggest that spots preferentially cluster at low to intermediate latitudes (15-40 • ) on V2247 Oph; this is at least qualitatively compatible with the fact that no high-contrast polar spot is present at the surface. This is the first time that differential rotation is detected on a cTTS; the recent claim (Herbst et al 2006) that the high-mass cTTS HBC 338 (spectral type G9) is differentially rotating (given the observed variations of the pho-tometric period) needs confirmation, cTTSs with massive accretion discs being prone to photometric perturbations (including sudden changes of the light-curve period) likely caused by accretion (e.g., Simon et al 1990;Donati et al 2008b) rather than resulting from differential rotation.…”

Section: Summary and Discussionmentioning

confidence: 73%

“…From photometric modulation presumably caused by the presence of cool surface spots going in and out of view of Earth-based observers, V2247 Oph is reported to be rotating with a period of about 3.5 d (Bouvier & Bertout 1989;Schevchenko & Herbst 1998). Long term photometric monitoring moreover reveals that this period is significantly changing with time (from about 3.4 to 3.6 d, Grankin et al 2008); it suggests that V2247 Oph (as many other cool active stars, e.g., Hall 1991) is experiencing photospheric shearing due to latitudinal differential rotation, which generates different modulation periods for spots located at different latitudes.…”

Section: V2247 Oph = Sr 1= Rox 21 = Hbc 263mentioning

confidence: 98%

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Complex magnetic topology and strong differential rotation on the low-mass T Tauri star V2247 Oph

Donati

Skelly

Bouvier

et al. 2010

Monthly Notices of the Royal Astronomical Society

101

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From observations collected with the ESPaDOnS spectropolarimeter at the Canada–France–Hawaii Telescope, we report the detection of Zeeman signatures on the low‐mass classical T Tauri star (cTTS) V2247 Oph. Profile distortions and circular polarization signatures detected in photospheric lines can be interpreted as caused by cool spots and magnetic regions at the surface of the star. The large‐scale field is of moderate strength and highly complex; moreover, both the spot distribution and the magnetic field show significant variability on a time‐scale of only 1 week, as a likely result of strong differential rotation. Both properties make V2247 Oph very different from the (more massive) prototypical cTTS BP Tau; we speculate that this difference reflects the lower mass of V2247 Oph. During our observations, V2247 Oph was in a low‐accretion state, with emission lines showing only weak levels of circular polarization; we nevertheless find that excess emission apparently concentrates in a mid‐latitude region of a strong radial field, suggesting that it is the footpoint of an accretion funnel. The weaker and more complex field that we report on V2247 Oph may share similarities with those of very‐low‐mass late‐M dwarfs and potentially explain why low‐mass cTTSs rotate on average faster than intermediate‐mass ones. These surprising results need confirmation from new independent data sets on V2247 Oph and other similar low‐mass cTTSs.

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Section: Summary and Discussionmentioning

confidence: 73%

Section: V2247 Oph = Sr 1= Rox 21 = Hbc 263mentioning

confidence: 98%

Complex magnetic topology and strong differential rotation on the low-mass T Tauri star V2247 Oph

Donati

Skelly

Bouvier

et al. 2010

Monthly Notices of the Royal Astronomical Society

101

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“…As described in Sect. 4.1, many of the most significant results on long-term stellar activity have emerged from the decades-long Mount Wilson Observatory (MWO) Calcium (Ca) H+K Project (Wilson 1978;Noyes et al 1984a;Baliunas et al 1985;Hall 1991;Soon et al 1993;Baliunas et al 1995;Hempelmann et al 1995;Pizzolato et al 2003;Wright et al 2004;Böhm-Vitense 2007;Mamajek and Hillenbrand 2008;Wright et al 2011;García et al 2014;Oláh et al 2016). As noted earlier, emission in these lines is a proxy for the non-thermal heating of the chromosphere, and so long-term variation of the Ca H+K index is related to variability in the stellar magnetic fields (see review in Hall 2008).…”

Section: Main Sequence Solar-like Starsmentioning

confidence: 97%

Magnetism, dynamo action and the solar-stellar connection

Brun

Browning

2017

Living Rev Sol Phys

238

182

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The Sun and other stars are magnetic: magnetism pervades their interiors and affects their evolution in a variety of ways. In the Sun, both the fields themselves and their influence on other phenomena can be uncovered in exquisite detail, but these observations sample only a moment in a single star's life. By turning to observations of other stars, and to theory and simulation, we may infer other aspects of the magnetism-e.g., its dependence on stellar age, mass, or rotation rate-that would be invisible from close study of the Sun alone. Here, we review observations and theory of magnetism in the Sun and other stars, with a partial focus on the "Solar-stellar connection": i.e., ways in which studies of other stars have influenced our understanding of the Sun and vice versa. We briefly review techniques by which magnetic fields can be measured (or their presence otherwise inferred) in stars, and then highlight some key observational findings uncovered by such measurements, focusing (in many cases) on those that offer particularly direct constraints on theories of how the fields are built and maintained. We turn then to a discussion of how the fields arise in different objects: first, we summarize some essential elements of convection and dynamo theory, including a very brief discussion of mean-field theory and related concepts. Next we turn to simulations of convection and magnetism in stellar interiors, highlighting both some peculiarities of field generation in different types of stars and some unifying physical processes that likely influence dynamo action in general. We conclude with a brief

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“…Long term photometric monitoring of starspot modulation in magnetically-active binary stars by Hall (1991) and Henry et al (1995) (H95) has revealed secular changes in rotation period which are strongly indicative of rotational shearing. As a stellar activity cycle progresses, starspots should emerge at different latitudes.…”

Section: Introductionmentioning

confidence: 99%

The dependence of differential rotation on temperature and rotation

Barnes

Cameron

Donati

et al. 2005

Monthly Notices of the Royal Astronomical Society: Letters

272

352

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The definitive version is available at www.blackwell-synergy.com '. Copyright Blackwell PublishingWe use Doppler imaging techniques to determine the dependence of starspot rotation rates on latitude in an homogeneous sample of young, rapidly-rotating solar analogues. A solar-like differential rotation law is used, where the rotation depends on sin2(??), where ?? is the stellar latitude. By including this term in the image reconstruction process, using starspots as tracers, we are able to determine the magnitude of the shear over more than one rotation cycle. We also consider results from matched filter starspot tracking techniques, where individual starspot rotation rates are determined. In additionwe have re-analysed published results and present a new measurement for the K3 dwarf, Speedy Mic. A total of 10 stars of spectral type G2 - M2 are considered. We find a trend towards decreasing surface differential rotation with decreasing effective temperature. The implied approach to solid body rotation with increasing relative convection zone depth implies that the dynamo mechanism operating in low-mass stars may be substantially different from that in the Sun

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Learning about stellar dynamos from long-term photometry of starspots

Cited by 42 publications

References 23 publications

Complex magnetic topology and strong differential rotation on the low-mass T Tauri star V2247 Oph

Complex magnetic topology and strong differential rotation on the low-mass T Tauri star V2247 Oph

Magnetism, dynamo action and the solar-stellar connection

The dependence of differential rotation on temperature and rotation

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