Article
Astronomy & Astrophysics
Tanayveer S. Bhatia, Robert H. Cameron, Sami K. Solanki, Hardi Peter, Damien Przybylski, Veronika Witzke, Alexander Shapiro
Summary: This study investigates changes in stratification and convection in the near-surface convection of different spectral types of cool main-sequence stars with the inclusion of small-scale dynamo (SSD) magnetic fields. The results show that the SSD efficiently produces magnetic fields and has a significant impact on thermodynamic stratification and convective velocities, especially for F-type stars.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Vindya Vashishth, Bidya Binay Karak, Leonid Kitchatinov
Summary: In the Sun and Sun-like stars, large-scale magnetic field cycles are believed to be produced due to differential rotation and helicity in plasma flows. Each star may have a critical dynamo number for the operation of a large-scale dynamo, and the study suggests the possible existence of a subcritical dynamo in some parameter regimes.
RESEARCH IN ASTRONOMY AND ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Vindya Vashishth, Bidya Binay Karak, Leonid Kitchatinov
Summary: Observations reveal that rapidly rotating (young) Sun-like stars exhibit a high level of activity with no Maunder-like grand minima and rarely display smooth regular activity cycles. On the other hand, slowly rotating old stars like the Sun have low activity levels and smooth cycles with occasional grand minima. We attempt to model these trends using flux transport dynamo models.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
E. L. Brown, S. Jeffers, S. C. Marsden, J. Morin, S. Boro Saikia, P. Petit, M. M. Jardine, V See, A. A. Vidotto, M. W. Mengel, M. N. Dahlkemper, BCool Collaboration
Summary: Spectropolarimetric data can monitor both chromospheric activity and magnetic field information of stars simultaneously, providing insights into the relationship between large-scale magnetic fields and chromospheric manifestations. The study finds a positive correlation between chromospheric activity and longitudinal magnetic field, with a possible change in G stars. Additionally, the research shows a decrease in chromospheric activity and toroidal field strength as rotation slows, and the disappearance of dominant toroidal fields at a certain level of chromospheric activity.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
V Skoutnev, J. Squire, A. Bhattacharjee
Summary: The study investigates the effects of stable stratification on mean-field dynamo theory, focusing on a non-helical large-scale dynamo (LSD) mechanism. The results show that the mechanism is robust to increasing stable stratification and capable of generating large-scale magnetic fields in stellar radiative zones.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Review
Astronomy & Astrophysics
Gopal Hazra, Dibyendu Nandy, Leonid Kitchatinov, Arnab Rai Choudhuri
Summary: The flux transport dynamo model is the most accepted model for the solar cycle. It originated from the traditional aO dynamo model, which was developed before the discovery of the Sun's meridional circulation. The model explains how the toroidal magnetic field is generated, with the poloidal field attributed to the Babcock-Leighton mechanism. The importance of the meridional circulation in transporting magnetic fields and its interaction with the dynamo process has been recognized.
SPACE SCIENCE REVIEWS
(2023)
Article
Astronomy & Astrophysics
S. K. Lander, P. Haensel, B. Haskell, J. L. Zdunik, M. Fortin
Summary: The study explores the thermal and magnetic field structure of a late-stage proto-neutron star, establishing a simplified equation of state for hot neutron stars and solving the stellar equilibrium equations numerically. The ellipticity increases with temperature for a fixed magnetic field strength, and the Keplerian velocity is considerably lower for hotter stars. Magnetic fields stronger than around 10^14 G have qualitatively similar equilibrium states in both hot and cold neutron stars, with the poloidal field component dominating over the toroidal one.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Thomas M. Boudreaux, Elisabeth R. Newton, Nicholas Mondrik, David Charbonneau, Jonathan Irwin
Summary: In this study, we use data from the Magellan Inamori Kyocera Echelle Spectrograph to analyze the relationship between Ca II H and K flux and rotation period for low-mass stars. We find consistent power-law and saturated regimes in the rotation-activity relationship, and observe a dependence on mass in R-HK'.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Q. Noraz, A. S. Brun, A. Strugarek, G. Depambour
Summary: Research suggests that solar-type stars with anti-solar differential rotation may sustain magnetic cycles through specific dynamo processes. This finding provides an interesting constraint in deciphering the actual dynamo mechanisms at work in solar-type stars.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
D. Evensberget, B. D. Carter, S. C. Marsden, L. Brookshaw, C. P. Folsom
Summary: By utilizing TOUPIES survey data and Alfven wave-driven stellar wind models, researchers conducted magnetic field simulations for five young stars in the Hyades cluster, finding that the unscaled field results indicate stellar wind mass-loss and angular momentum loss several times greater than that of the Sun today. Additionally, evidence of mass-loss saturation was observed in the Alfven wave-driven modeling.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
J. Betrisey, P. Eggenberger, G. Buldgen, O. Benomar, M. Bazot
Summary: Thanks to the photometry revolution brought about by space-based missions like CoRoT, Kepler, and TESS, asteroseismology has become a powerful tool in the study of stellar rotation. This study compared the rotation rate predicted by asteroseismology and starspot measurements of solar-type stars using different angular momentum (AM) transport prescriptions, and determined the observational constraints for these prescriptions.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
D. Evensberget, B. D. Carter, S. C. Marsden, L. Brookshaw, C. P. Folsom, R. Salmeron
Summary: We present wind models of 10 young Solar-type stars in different star clusters and find varied geometries and a greater spread in quantities such as the angular momentum loss. Our models show variation in wind angular momentum loss and wind mass-loss based on magnetic field geometry differences. We observe a tight correlation between unsigned open magnetic flux and angular momentum loss. The underreporting of the observed magnetic field strength is accounted for in a second series of wind models.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
F. Anzuini, A. Melatos, C. Dehman, D. Vigano, J. A. Pons
Summary: The dissipation of intense crustal electric currents can counterbalance fast cooling in neutron stars, making it difficult to infer the presence of hyperons from observed thermal luminosity. Models with and without hyperon cores both match the thermal luminosity of young and mature magnetars. Hyperon cores have little effect on the crustal temperature in magnetars, and the thermal luminosity of light and heavy magnetars are almost indistinguishable. Data from neutron stars with strong internal fields are not suitable for extracting information about the equation of state as long as hyperons are superfluid.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
F. Anzuini, A. Melatos, C. Dehman, D. Vigano, J. A. Pons
Summary: This study discusses the need for internal heating sources in neutron star models to reconcile theoretical cooling rates with observational data, focusing on moderately magnetized, isolated thermally emitting stars. By considering different internal heating mechanisms, the study finds that neutron star models can match observations of such stars through proper internal heating.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Sivan Ginzburg, Jim Fuller, Adela Kawka, Ilaria Caiazzo
Summary: Recent studies suggest that white dwarfs generate magnetic fields through convection driven by core crystallization and rotation. These crystallization-driven dynamos are mostly in a fast-rotating regime, where the magnetic field is enhanced by convective motion and can explain some observed magnetic field phenomena.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
H. V. Senavc, E. Bahar, D. Montes, S. Zola, G. A. J. Hussain, A. Frasca, E. Isik, O. Yorukoglu
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2018)
Article
Astronomy & Astrophysics
I. Ozavci, H. V. Senavci, E. Isik, G. A. J. Hussain, D. O'Neal, M. Yilmaz, S. O. Selam
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2018)
Article
Astronomy & Astrophysics
J. Jiang, R. H. Cameron, D. Schmitt, E. Isik
ASTRONOMY & ASTROPHYSICS
(2013)
Article
Astronomy & Astrophysics
R. H. Cameron, M. Dasi-Espuig, J. Jiang, E. Isik, D. Schmitt, M. Schuessler
ASTRONOMY & ASTROPHYSICS
(2013)
Article
Astronomy & Astrophysics
E. Isik, S. K. Solanki, N. A. Krivova, A. I. Shapiro
ASTRONOMY & ASTROPHYSICS
(2018)
Article
Astronomy & Astrophysics
N. -E. Nemec, E. Isik, A. I. Shapiro, S. K. Solanki, N. A. Krivova, Y. Unruh
ASTRONOMY & ASTROPHYSICS
(2020)
Article
Astronomy & Astrophysics
H. Senavci, T. Kilicoglu, E. Isik, G. A. J. Hussain, D. Montes, E. Bahar, S. K. Solanki
Summary: Observations and modeling of stars with near-solar masses in their early evolution phases are crucial for understanding how solar-type stars evolve. By examining the chemical composition and spot distribution of the pre-mainsequence solar analogue EK Dra, we have obtained insights into the age, mass, and abundance patterns of this star. Additionally, studying the surface brightness distributions and spot simulations have provided further understanding of the evolution and activity of this star.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
K. Sowmya, N-E Nemec, A. Shapiro, E. Isik, V Witzke, A. Mints, N. A. Krivova, S. K. Solanki
Summary: Ultra-precise astrometry from the Gaia mission is expected to detect over 20,000 exoplanets in our Galaxy, but astrometric jitter caused by the magnetic activity of planet host stars may hinder these detections. The study shows that stars observed out of their equatorial planes experience systematic shifts in their photocenters over the activity cycle, impacting planet detectability. Furthermore, an increase in metallicity and active-region nesting can enhance the amplitude of the photocenter jitter, potentially affecting detections by Gaia.
ASTROPHYSICAL JOURNAL
(2021)
Article
Astronomy & Astrophysics
K. Sowmya, N-E Nemec, A. Shapiro, E. Isik, N. A. Krivova, S. K. Solanki
Summary: This series of papers focuses on estimating the effect of the magnetic activity of G2V-type host stars on the astrometric signal. The simulations show that the contribution of magnetic activity becomes increasingly significant with increasing rotation rates. Furthermore, the study finds that the jitter for the most variable periodic Kepler stars is high enough to be detected by Gaia.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
N-E Nemec, A. Shapiro, E. Isik, K. Sowmya, S. K. Solanki, N. A. Krivova, R. H. Cameron, L. Gizon
Summary: The magnetic fields on the surfaces of stars affect the detection and characterization of exoplanets, and being able to differentiate between spots and faculae is important for correcting stellar data for magnetic activity.
ASTROPHYSICAL JOURNAL LETTERS
(2022)
Correction
Astronomy & Astrophysics
N. -E. Nemec, A. I. Shapiro, E. Isik, K. Sowmya, S. K. Solanki, N. . A. Krivova, R. H. Cameron, L. Gizon
ASTROPHYSICAL JOURNAL LETTERS
(2022)
Correction
Astronomy & Astrophysics
Emre Isik, Alexander I. Shapiro, Sami K. Solanki, Natalie A. Krivova
ASTROPHYSICAL JOURNAL LETTERS
(2020)
Article
Astronomy & Astrophysics
Emre Isik, Alexander I. Shapiro, Sami K. Solanki, Natalie A. Krivova
ASTROPHYSICAL JOURNAL LETTERS
(2020)
Article
Astronomy & Astrophysics
Emre Isik
ASTROPHYSICAL JOURNAL LETTERS
(2015)
Article
Astronomy & Astrophysics
Timo Reinhold, Alexander Shapiro, Veronika Witzke, Nina-E Nemec, Emre Isik, Sami K. Solanki
Summary: This study investigates the lack of solar-like stars with known near-solar rotation periods, attributing it to the difficulty of detecting periods due to the complexity and noise levels in photometric time series. The detectability is found to be influenced by the type of activity on the stellar surface and the level of photometric noise, complicating period detection and explaining the shortage of solar-like stars with known near-solar rotation periods. These findings suggest that the majority of solar-like stars with near-solar rotation periods remain undetected, prompting the use of new techniques to recover more rotation periods of near-solar rotators.
ASTROPHYSICAL JOURNAL LETTERS
(2021)