Spot evolution on the red giant star XX Triangulum

Künstler, A.; Carroll, T. A.; Strassmeier, K. G.

doi:10.1051/0004-6361/201525687

Cited by 32 publications

(48 citation statements)

References 85 publications

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“…For red-giant stars, mainly solarlike profiles of differential surface rotation have been detected through Doppler-imaging. For example, Künstler et al (2015) discussed a solar-like latitudinal differential rotation profile at the surface about 10 times weaker than in the Sun. However, in a few cases also the detection of anti-solar differential rotation profiles were reported (Kővári et al 2015).…”

Section: Long Periodic Brightness Variationsmentioning

confidence: 99%

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Beck

Kallinger

Pavlovski

et al. 2018

A&A

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Context. Binaries in double-lined spectroscopic systems (SB2) provide a homogeneous set of stars. Differences of parameters, such as age or initial conditions, which otherwise would have strong impact on the stellar evolution, can be neglected. The observed differences are determined by the difference in stellar mass between the two components. The mass ratio can be determined with much higher accuracy than the actual stellar mass. Aims. In this work, we aim to study the eccentric binary system KIC 9163796, whose two components are very close in mass and both are low-luminosity red-giant stars. Methods. We analyse four years of Kepler space photometry and we obtained high-resolution spectroscopy with the Hermes instrument. The orbital elements and the spectra of both components were determined using spectral disentangling methods. The effective temperatures, and metallicities were extracted from disentangled spectra of the two stars. Mass and radius of the primary were determined through asteroseismology. The surface rotation period of the primary is determined from the Kepler light curve. From representative theoretical models of the star, we derived the internal rotational gradient, while for a grid of models, the measured lithium abundance is compared with theoretical predictions. Results. From seismology the primary of KIC 9163796 is a star of 1.39±0.06 M ⊙ , while the spectroscopic mass ratio between both components can be determined with much higher precision by spectral disentangling to be 1.015±0.005. With such mass and a difference in effective temperature of 600 K from spectroscopy, the secondary and primary are, respectively, in the early and advanced stage of the first dredge-up event on the red-giant branch. The period of the primary's surface rotation resembles the orbital period within 10 days.The radial rotational gradient between the surface and core in KIC 9163796 is found to be 6.9 +2.0 −1.0 . This is a low value but not exceptional if compared to the sample of typical single field stars. The seismic average of the envelope's rotation agrees with the surface rotation rate. The lithium abundance is in agreement with quasi rigidly-rotating models. Conclusions. The agreement between the surface rotation with the seismic result indicates that the full convective envelope is rotating quasi-rigidly. The models of the lithium abundance are compatible with a rigid rotation in the radiative zone during the main sequence. Because of the many constraints offered by oscillating stars in binary systems, such objects are important test beds of stellar evolution.

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Section: Long Periodic Brightness Variationsmentioning

confidence: 99%

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Beck

Kallinger

Pavlovski

et al. 2018

A&A

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“…For the line-profile inversion, we used 40 selected absorption lines simultaneously, which were already listed by Künstler et al (2015) in their Table 2. These lines were chosen from the VALD database on the basis of having a minimum line depth of 0.75 I/I C , being almost blend-free, and having a good continuum definition around them.…”

Section: Data Preparation and Assumptionsmentioning

confidence: 99%

Anti-solar differential rotation on the active sub-giant HU Virginis^,

Harutyunyan

Strassmeier

Künstler

et al. 2016

A&A

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Context. Measuring surface differential rotation (DR) on different types of stars is important when characterizing the underlying stellar dynamo. It has been suggested that anti-solar DR laws can occur when strong meridional flows exist. Aims. We aim to investigate the differential surface rotation on the primary star of the RS CVn binary, HU Vir, by tracking its starspot distribution as a function of time. We also aim to recompute and update the values for several system parameters of the triple system HU Vir (close and wide orbits). Methods. Time-series high-resolution spectroscopy for four continuous months was obtained with the 1.2-m robotic STELLA telescope. Nine consecutive Doppler images were reconstructed from these data, using our line-profile inversion code iMap. An image cross-correlation method was applied to derive the surface differential-rotation law for HU Vir. New orbital elements for the close and the wide orbits were computed using our new STELLA radial velocities (RVs) combined with the RV data available in the literature. Photometric observations were performed with the Amadeus Automatic Photoelectric Telescope (APT), providing contemporaneous Johnson-Cousins V and I data for approximately 20 yrs. This data was used to determine the stellar rotation period and the active longitudes. Results. We confirm anti-solar DR with a surface shear parameter α of −0.029 ± 0.005 and −0.026 ± 0.009, using single-term and double-term differential rotation laws, respectively. These values are in good agreement with previously claimed results. The best fit is achieved assuming a solar-like double-term law with a lap time of ≈400 d. Our orbital solutions result in a period of 10.387678 ± 0.000003 days for the close orbit and 2726 ± 7 d (≈7.5 yr) for the wide orbit. A Lomb-Scarge (L-S) periodogram of the pre-whitened V-band data reveals a strong single peak providing a rotation period of 10.391 ± 0.008 d, well synchronized to the short orbit.

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“…Thus far, this important parameter was obtained only in a few cases using Doppler imaging of stars (i.e., Bradshaw & Hartigan 2014;Künstler et al 2015). In that respect, the vast number of stars observed with the high-precision photometry of the Kepler mission enables the new approach to this task.…”

Section: Diffusive Transport In Stellar Photospheresmentioning

confidence: 99%

Deep Mixing in Stellar Variability: Improved Method, Statistics, and Applications

Arkhypov

Khodachenko

Lämmer

et al. 2016

ApJ

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The preliminary results on deep-mixing manifestations in stellar variability are tested using our improved method and extended data set. We measure the timescales τ m of the stochastic change in the spectral power of rotational harmonics with numbers m 3 in the light curves of 1361 main-sequence stars from the Kepler mission archive. We find that the gradient t t --log log log 2 log 1 2 1has a histogram maximum at −2/3, demonstrating agreement with Kolmogorov's theory of turbulence and therefore confirming the manifestation of deep mixing. The squared amplitudes of the first and second rotational harmonics, corrected for integral photometry distortion, also show a quasi-Kolmogorov character with spectral index ≈−5/3. Moreover, the reduction of τ 1 and τ 2 to the timescales τ lam1 and τ lam2 of laminar convection in the deep stellar layers reveals the proximity of both τ lam1 and τ lam2 to the turnover time τ MLT of standard mixing length theory. Considering this result, we use the obtained stellar variability timescales instead of τ MLT in our analysis of the relation between stellar activity and the Rossby number P/τ MLT . Comparison of our diagrams with previous results and theoretical expectations shows that best-fit correspondence is achieved for τ lam1 , which can therefore be used as an analog of τ MLT . This means that the laminar component (giant cells) of stellar turbulent convection indeed plays an important role in the physics of stars. Additionally, we estimate the diffusivity of magnetic elements in stellar photospheres.

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Spot evolution on the red giant star XX Triangulum

Cited by 32 publications

References 85 publications

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Anti-solar differential rotation on the active sub-giant HU Virginis^,

Deep Mixing in Stellar Variability: Improved Method, Statistics, and Applications

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Spot evolution on the red giant star XX Triangulum

Cited by 32 publications

References 85 publications

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Anti-solar differential rotation on the active sub-giant HU Virginis,

Deep Mixing in Stellar Variability: Improved Method, Statistics, and Applications

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Anti-solar differential rotation on the active sub-giant HU Virginis^,