Emre Işık

Emre Işık
Turkish-German University | TAU · Computer Science

PhD

About

47
Publications
2,039
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386
Citations
Introduction
My research focuses on the generation and transport of large-scale magnetic fields in the interiors of the Sun and other Sun-like stars. I use analytical and (mostly) computational tools to model the solar cycle (i.e., the sunspot cycle) and stellar activity cycles, in comparison with observational results.
Additional affiliations
August 2019 - present
Turkish-German University
Position
  • Professor (Associate)
September 2016 - September 2019
Max Planck Institute for Solar System Research
Position
  • Research Associate
April 2015 - present
Feza Gürsey Center for Physics and Mathematics, Bogazici University
Position
  • Member
Education
January 2005 - January 2008
Georg-August-Universität Göttingen
Field of study
  • Astrophysics
October 1999 - June 2002
Akdeniz University
Field of study
  • Physics
September 1994 - July 1998
Ege University
Field of study
  • Astronomy and Space Science

Publications

Publications (47)
Article
Surfaces of the Sun and other cool stars are filled with magnetic fields, which are either seen as dark compact spots or more diffuse bright structures like faculae. Both hamper detection and characterization of exoplanets, affecting stellar brightness and spectra, as well as transmission spectra. However, the expected facular and spot signals in s...
Article
A breakthrough in exoplanet detections is foreseen with the unprecedented astrometric measurement capabilities offered by instrumentation aboard the Gaia space observatory. Besides, astrometric discoveries of exoplanets are expected from the planned space mission, Small-JASMINE. In this setting, the present series of papers focuses on estimating th...
Preprint
Full-text available
Surfaces of the Sun and other cool stars are filled with magnetic fields, which are either seen as dark compact spots or more diffuse bright structures like faculae. Both hamper detection and characterisation of exoplanets, affecting stellar brightness and spectra, as well as transmission spectra. However, the expected facular and spot signals in s...
Preprint
A breakthrough in exoplanet detections is foreseen with the unprecedented astrometric measurement capabilities offered by instrumentation aboard Gaia space observatory. Besides, Earth-like planet discoveries are expected from the planned infrared astrometry space mission, Small-JASMINE. In this setting, the present series of papers focuses on estim...
Preprint
Full-text available
Ultra-precise astrometry from the Gaia mission is expected to lead to astrometric detections of more than 20,000 exoplanets in our Galaxy. One of the factors that could hamper such detections is the astrometric jitter caused by the magnetic activity of the planet host stars. In our previous study, we modeled astrometric jitter for the Sun observed...
Preprint
Full-text available
The plethora of photometric data collected by the Kepler space telescope has promoted the detection of tens of thousands of stellar rotation periods. However, these periods are not found to an equal extent among different spectral types. Interestingly, early G-type stars with near-solar rotation periods are strongly underrepresented among those sta...
Article
Observations and modelling of stars with near-solar masses in their early phases of evolution are critical for a better understanding of how dynamos of solar-type stars evolve. We examine the chemical composition and the spot distribution of the pre-main-sequence solar analogue EK Dra. Using spectra from the HERMES Spectrograph (La Palma), we obtai...
Preprint
Observations and modelling of stars with near-solar masses in their early phases of evolution is critical for a better understanding of how dynamos of solar-type stars evolve. We examine the chemical composition and the spot distribution of the pre-main-sequence solar analogue EK Dra. Using spectra from the HERMES Spectrograph (La Palma), we obtain...
Preprint
Kepler observations revealed that hundreds of stars with near-solar fundamental parameters and rotation periods have much stronger and more regular brightness variations than the Sun. Here we identify one possible reason for the peculiar behaviour of these stars. Inspired by solar nests of activity, we assume that the degree of inhomogeneity of act...
Article
Full-text available
Context. A comparison of solar and stellar brightness variations is hampered by the difference in spectral passbands that are used in observations, and also by the possible difference in the inclination of the solar and stellar rotation axes from the line of sight. Aims. We calculate the rotational variability of the Sun as it would be measured in...
Preprint
Comparing solar and stellar brightness variations is hampered by the difference in spectral passbands used in observations as well as by the possible difference in the inclination of their rotation axes from the line of sight. We calculate the rotational variability of the Sun as it would be measured in passbands used for stellar observations. In p...
Preprint
Full-text available
In G dwarfs, the surface distribution, coverage and lifetimes of starspots deviate from solar-like patterns as the rotation rate increases. We set up a numerical platform which includes the large-scale rotational and surface flow effects, aiming to simulate evolving surface patterns over an activity cycle for up to 8 times the solar rotation and fl...
Article
Context. The latitudinal distribution of starspots deviates from the solar pattern with increasing rotation rate. Numerical simulations of magnetic flux emergence and transport can help model the observed stellar activity patterns and the associated brightness variations. Aims. We set up a composite model for the processes of flux emergence and tra...
Preprint
Full-text available
The latitudinal distribution of starspots deviates from the solar pattern with increasing rotation rate. Numerical simulations of magnetic flux emergence and transport can help model the observed stellar activity patterns and the associated brightness variations. We set up a composite model for the processes of flux emergence and transport on Sun-l...
Preprint
Context. The latitudinal distribution of starspots deviates from the solar pattern with increasing rotation rate. Numerical simulations of magnetic flux emergence and transport can help model the observed stellar activity patterns and the associated brightness variations. Aims. We set up a composite model for the processes of flux emergence and tra...
Article
Surface flux transport (SFT) models have been successful in reproducing how magnetic flux at the solar photosphere evolves on large scales. SFT modelling proved to be useful in reconstructing secular irradiance variations of the Sun, and it can be potentially used in forward modelling of brightness variations of Sun-like stars. We outline our curre...
Preprint
Full-text available
Using a time series of high-resolution spectra and high-quality multi-colour photometry, we reconstruct surface maps of the primary component of the RS CVn type rapidly rotating eclipsing binary, SV Cam (F9V + K4V). We measure a mass ratio, q, of 0.641(2) using our highest quality spectra and obtain surface brightness maps of the primary component,...
Preprint
Full-text available
The tilt angle of a sunspot group is a critical quantity in the surface transport of magnetic flux and the solar dynamo. To contribute long-term databases of the tilt angle, we developed an IDL routine, which allows the user to interactively select and measure sunspot positions and areas on the solar disc. We measured the tilt angles of sunspot gro...
Preprint
Full-text available
Using high-precision photometry from the \textit{Kepler} mission, we investigate patterns of spot activity on the K1-type subgiant component of KIC 11560447, a short-period late-type eclipsing binary. We tested the validity of maximum entropy reconstructions of starspots by numerical simulations. Our procedure successfully captures up to three larg...
Article
The tilt angle of a sunspot group is a critical quantity in the surface transport of magnetic flux and the solar dynamo. To contribute long-term databases of the tilt angle, we developed an IDL routine, which allows the user to interactively select and measure sunspot positions and areas on the solar disc. We measured the tilt angles of sunspot gro...
Article
Using high-precision photometry from the Kepler mission, we investigate patterns of spot activity on the K1-type subgiant component of KIC 11560447, a short-period late-type eclipsing binary. We tested the validity of maximum entropy reconstructions of starspots by numerical simulations. Our procedure successfully captures up to three large spot cl...
Article
Full-text available
We present a detailed analysis of surface inhomogeneities on the K1-type sub-giant component of the rapidly rotating eclipsing binary KIC 11560447, using high-precision Kepler light curves spanning nearly four years, corresponding to about 2800 orbital revolutions. We precisely determine the system parameters using high-resolution spectra from the...
Data
Full-text available
Article
Full-text available
The average tilt angle of sunspot groups emerging throughout the solar cycle determines the net magnetic flux crossing the equator, which is correlated with the strength of the subsequent cycle. I suggest that a deep-seated, non-local process can account for the observed cycle-dependent changes in the average tilt angle. Motivated by helioseismic o...
Article
Full-text available
Within the Babcock-Leighton framework for the solar dynamo, the strength of a cycle is expected to depend on the strength of the dipole moment or net hemispheric flux during the preceding minimum, which depends on how much flux was present in each hemisphere at the start of the previous cycle and how much net magnetic flux was transported across th...
Article
Full-text available
Context: The Sun's polar fields and open flux around the time of activity minima have been considered to be strongly correlated with the strength of the subsequent maximum of solar activity. Aims: We aim to investigate the behavior of a Babcock-Leighton dynamo with a source poloidal term that is based on the observed sunspot areas and tilts. In par...
Conference Paper
Full-text available
We discuss possible mechanisms underlying the observed features of stellar activity cycles, such as multiple periodicities in very active stars, non-cyclic activity observed in moderately active stars, and spatial distribution of stellar magnetic regions. We review selected attempts to model the dependence of stellar activity cycles on stellar prop...
Article
Full-text available
We investigate the relations between tachocline-based dynamos and the surface flux transport mechanisms in stars with outer convection zones. Using our combined models of flux generation and transport, we demonstrate the importance of the buoyant rise of magnetic flux, which physically determines the emergence latitudes and tilt angles of bipolar m...
Article
Full-text available
The surface flux transport (SFT) model of solar magnetic fields involves empirically well-constrained velocity and magnetic fields. The basic evolution of the Sun's large-scale surface magnetic field is well described by this model. The azimuthally averaged evolution of the SFT model can be compared to the surface evolution of the flux transport dy...
Conference Paper
Full-text available
We present results from a model for magnetic flux generation and transport in cool stars and a qualitative comparison of models with observations. The method combines an αΩ-type dynamo at the base of the convection zone, buoyant rise of magnetic flux tubes, and a surface flux transport model. Based on a reference model for the Sun, numerical simula...
Article
Full-text available
The Sun and other cool stars harbouring outer convection zones manifest magnetic activity in their atmospheres. The connection between this activity and the properties of a deep-seated dynamo generating the magnetic flux is not well understood. By employing physical models, we study the spatial and temporal characteristics of the observable surface...
Article
Full-text available
We studied the effect of the perturbation of the meridional flow in the activity belts detected by local helioseismology on the development and strength of the surface magnetic field at the polar caps. We carried out simulations of synthetic solar cycles with a flux transport model, which follows the cyclic evolution of the surface field determined...
Article
Full-text available
Context: Flow-induced instabilities of magnetic flux tubes are relevant to the storage of magnetic flux in the interiors of stars with outer convection zones. The stability of magnetic fields in stellar interiors is of importance to the generation and transport of solar and stellar magnetic fields. Aims: We consider the effects of material flows on...
Article
Full-text available
We consider the effects of material flows on the dynamics of toroidal magnetic flux tubes located close to the base of the solar convection zone, initially within the overshoot region. The problem is to find the physical conditions in which magnetic flux can be stored for periods comparable to the dynamo amplification time, which is of the order of...
Conference Paper
Full-text available
The stability of magnetic fields in the solar interior is of critical importance for dynamo models. Instabilities induced by external flows are relevant for the storage of magnetic field in the stably stratified lower convective overshoot region. We have investigated the effects of finite perturbations and external flows on the stability and dynami...
Article
We present a combined model for magnetic field generation and transport in cool stars with outer convection zones. The mean toroidal magnetic field, which is generated by a cyclic thin-layer α Ω dynamo at the bottom of the convection zone is taken to determine the emergence probability of magnetic flux tubes in the photosphere. Following the nonlin...
Conference Paper
Full-text available
We present results of numerical simulations of magnetic flux transport on the surfaces of cool stars with radii of 1 Rm and 3.3 Rm. The effects of differential rotation and the tilt angle on the lifetimes of stellar bipolar magnetic regions are discussed. The existence of long-lasting polar spots can be explained by high-latitude persistent emergen...
Article
Full-text available
We carry out numerical simulations of the surface evolution of bipolar magnetic regions (BMRs) and magnetic spots on stars, which have radii and surface rotational shears of AB Doradus, the Sun, and the HR 1099 primary. The surface flux transport model is based on the magnetic induction equation for radial fields under the effects of surface differ...
Article
We have photometrically observed HD 112859, HD 144110, and HD 208472 using the 48-cm Cassegrain reflector with an SSP-5 photometer of Ege University Observatory during the 1996-1997 observing seasons. Observations were made between June 1996 and March 1997 using B, V, and R filters and light curves with color variations were obtained. The amplitude...
Article
We have photometrically observed HD 82443 and HD 29697 (= V834 Tau) using the 48-cm Cassegrain reflector with an SSP-5 photometer of Ege University Observatory during the 1996-1997 observing seasons. The observations were made between November 1996 and March 1997 in B, V, and R filters, and the light curves with color variations were obtained. The...
Article
Full-text available
DH Leo, a (K0V+K7V)/K5V type spectroscopic triple system consisting of an active close binary (Porb˜ 1.07 d) and a distant, slowly rotating tertiary has been observed spectroscopically in 2000 and 2002. The orbit of the tertiary has been estimated using long-term cross-correlation radial velocities and results from astrometric studies. Chromospheri...

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