Eclipsing spotted giant star with K2 and historical photometry

K. Oláh, S. Rappaport, T. Borkovits, T. Jacobs, D. Latham, A. Bieryla, I. B. Bíró, J. Bartus, Z. Kővári, K. Vida, A. Vanderburg, D. Lacourse, I. Csányi, G. A. Bakos, W. Bhatti, Z. Csubry, J. Hartman, M. Omohundro

Research output: Contribution to journalArticle

Abstract

Context. Stars can maintain their observable magnetic activity from the pre-main sequence (PMS) to the tip of the red giant branch. However, the number of known active giants is much lower than active stars on the main sequence (MS) since the stars spend only about 10% of their MS lifetime on the giant branch. Due to their rapid evolution it is difficult to estimate the stellar parameters of giant stars. A possibility for obtaining more reliable stellar parameters for an active giant arises when it is a member of an eclipsing binary system. Aims. We have discovered EPIC 211759736, an active spotted giant star in an eclipsing binary system during the Kepler K2 Campaign 5. The eclipsing nature allows us to much better constrain the stellar parameters than in most cases of active giant stars. Methods. We have combined the K2 data with archival HATNet, ASAS, and DASCH photometry, new spectroscopic radial velocity measurements, and a set of follow-up ground-based BVRCIC photometric observations, to find the binary system parameters as well as robust spot models for the giant at two different epochs. Results. We determined the physical parameters of both stellar components and provide a description of the rotational and long-term activity of the primary component. The temperatures and luminosities of both components were examined in the context of the Hertzsprung-Russell diagram. We find that both the primary and the secondary components deviate from the evolutionary tracks corresponding to their masses in the sense that the stars appear in the diagram at lower masses than their true masses. Conclusions. We further evaluate the proposition that traditional methods generally result in higher masses for active giants than what is indicated by stellar evolution tracks in the HR diagram. A possible reason for this discrepancy could be a strong magnetic field, since we see greater differences in more active stars.

Original languageEnglish
Article numberA189
JournalAstronomy and Astrophysics
Volume620
DOIs
Publication statusPublished - Dec 1 2018

Fingerprint

giant stars
photometry
stars
Hertzsprung-Russell diagram
diagram
Advanced Solid-State Array Spectroradiometer
stellar evolution
velocity measurement
radial velocity
diagrams
luminosity
time measurement
parameter
magnetic field
life (durability)
estimates
magnetic fields
temperature

Keywords

  • Binaries: eclipsing
  • Stars: activity
  • Stars: evolution
  • Stars: fundamental parameters
  • Stars: late-type
  • Starspots

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Eclipsing spotted giant star with K2 and historical photometry. / Oláh, K.; Rappaport, S.; Borkovits, T.; Jacobs, T.; Latham, D.; Bieryla, A.; Bíró, I. B.; Bartus, J.; Kővári, Z.; Vida, K.; Vanderburg, A.; Lacourse, D.; Csányi, I.; Bakos, G. A.; Bhatti, W.; Csubry, Z.; Hartman, J.; Omohundro, M.

In: Astronomy and Astrophysics, Vol. 620, A189, 01.12.2018.

Research output: Contribution to journalArticle

Oláh, K, Rappaport, S, Borkovits, T, Jacobs, T, Latham, D, Bieryla, A, Bíró, IB, Bartus, J, Kővári, Z, Vida, K, Vanderburg, A, Lacourse, D, Csányi, I, Bakos, GA, Bhatti, W, Csubry, Z, Hartman, J & Omohundro, M 2018, 'Eclipsing spotted giant star with K2 and historical photometry', Astronomy and Astrophysics, vol. 620, A189. https://doi.org/10.1051/0004-6361/201834106
Oláh, K. ; Rappaport, S. ; Borkovits, T. ; Jacobs, T. ; Latham, D. ; Bieryla, A. ; Bíró, I. B. ; Bartus, J. ; Kővári, Z. ; Vida, K. ; Vanderburg, A. ; Lacourse, D. ; Csányi, I. ; Bakos, G. A. ; Bhatti, W. ; Csubry, Z. ; Hartman, J. ; Omohundro, M. / Eclipsing spotted giant star with K2 and historical photometry. In: Astronomy and Astrophysics. 2018 ; Vol. 620.
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abstract = "Context. Stars can maintain their observable magnetic activity from the pre-main sequence (PMS) to the tip of the red giant branch. However, the number of known active giants is much lower than active stars on the main sequence (MS) since the stars spend only about 10{\%} of their MS lifetime on the giant branch. Due to their rapid evolution it is difficult to estimate the stellar parameters of giant stars. A possibility for obtaining more reliable stellar parameters for an active giant arises when it is a member of an eclipsing binary system. Aims. We have discovered EPIC 211759736, an active spotted giant star in an eclipsing binary system during the Kepler K2 Campaign 5. The eclipsing nature allows us to much better constrain the stellar parameters than in most cases of active giant stars. Methods. We have combined the K2 data with archival HATNet, ASAS, and DASCH photometry, new spectroscopic radial velocity measurements, and a set of follow-up ground-based BVRCIC photometric observations, to find the binary system parameters as well as robust spot models for the giant at two different epochs. Results. We determined the physical parameters of both stellar components and provide a description of the rotational and long-term activity of the primary component. The temperatures and luminosities of both components were examined in the context of the Hertzsprung-Russell diagram. We find that both the primary and the secondary components deviate from the evolutionary tracks corresponding to their masses in the sense that the stars appear in the diagram at lower masses than their true masses. Conclusions. We further evaluate the proposition that traditional methods generally result in higher masses for active giants than what is indicated by stellar evolution tracks in the HR diagram. A possible reason for this discrepancy could be a strong magnetic field, since we see greater differences in more active stars.",
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AU - Latham, D.

AU - Bieryla, A.

AU - Bíró, I. B.

AU - Bartus, J.

AU - Kővári, Z.

AU - Vida, K.

AU - Vanderburg, A.

AU - Lacourse, D.

AU - Csányi, I.

AU - Bakos, G. A.

AU - Bhatti, W.

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KW - Stars: fundamental parameters

KW - Stars: late-type

KW - Starspots

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