scholarly journals Signatures of Magnetic Activity in the Seismic Data of Solar-type Stars Observed by Kepler

2018 ◽  
Vol 237 (1) ◽  
pp. 17 ◽  
Author(s):  
A. R. G. Santos ◽  
T. L. Campante ◽  
W. J. Chaplin ◽  
M. S. Cunha ◽  
M. N. Lund ◽  
...  
Keyword(s):  
Seismic Data ◽  
Magnetic Activity ◽  
Solar Type

scholarly journals Seismic signatures of magnetic activity in solar-type stars observed by Kepler

2018 ◽  
Vol 13 (S340) ◽  
pp. 225-228
Author(s):  
A. R. G. Santos ◽  
T. L. Campante ◽  
W. J. Chaplin ◽  
M. S. Cunha ◽  
M. N. Lund ◽  
...  
Keyword(s):  
Seismic Data ◽  
Magnetic Activity ◽  
Acoustic Properties ◽  
Acoustic Modes ◽  
Solar Type ◽  
Magnetic Cycles

AbstractThe properties of the acoustic modes are sensitive to magnetic activity. The unprecedented long-term Kepler photometry, thus, allows stellar magnetic cycles to be studied through asteroseismology. We search for signatures of magnetic cycles in the seismic data of Kepler solar-type stars. We find evidence for periodic variations in the acoustic properties of about half of the 87 analysed stars. In these proceedings, we highlight the results obtained for two such stars, namely KIC 8006161 and KIC 5184732.

scholarly journals Stellar activity and rotation of the planet host Kepler-17 from long-term space-borne photometry

2019 ◽  
Vol 626 ◽  
pp. A38 ◽  
Author(s):  
A. F. Lanza ◽  
Y. Netto ◽  
A. S. Bonomo ◽  
H. Parviainen ◽  
A. Valio ◽  
...  
Keyword(s):  
Maximum Entropy ◽  
Differential Rotation ◽  
Activity Cycle ◽  
Magnetic Activity ◽  
Model Parameters ◽  
The Sun ◽  
Level Of Activity ◽  
Spot Model ◽  
Rotational Evolution ◽  
Solar Type

Context. The study of young Sun-like stars is fundamental to understanding the magnetic activity and rotational evolution of the Sun. Space-borne photometry by the Kepler telescope provides unprecedented datasets to investigate these phenomena in Sun-like stars. Aims. We present a new analysis of the entire Kepler photometric time series of the moderately young Sun-like star Kepler-17 accompanied by a transiting hot Jupiter. Methods. We applied a maximum-entropy spot model to the long-cadence out-of-transit photometry of the target to derive maps of the starspot filling factor versus the longitude and the time. These maps are compared to the spots occulted during transits to validate our reconstruction and derive information on the latitudes of the starspots. Results. We find two main active longitudes on the photosphere of Kepler-17, one of which has a lifetime of at least ∼1400 days although with a varying level of activity. The latitudinal differential rotation is of solar type, that is, with the equator rotating faster than the poles. We estimate a minimum relative amplitude ΔΩ/Ω between ∼0.08 ± 0.05 and 0.14 ± 0.05, our determination being affected by the finite lifetime of individual starspots and depending on the adopted spot model parameters. We find marginal evidence of a short-term intermittent activity cycle of ∼48 days and an indication of a longer cycle of 400−600 days characterized by an equatorward migration of the mean latitude of the spots as in the Sun. The rotation of Kepler-17 is likely to be significantly affected by the tides raised by its massive close-by planet. Conclusion. We confirm the reliability of maximum-entropy spot models to map starspots in young active stars and characterize the activity and differential rotation of this young Sun-like planetary host.

scholarly journals Dynamo Action in Evolved Stars

1991 ◽  
Vol 130 ◽  
pp. 336-341
Author(s):  
David F. Gray
Keyword(s):  
Angular Momentum ◽  
Magnetic Fields ◽  
Rotation Rate ◽  
Magnetic Activity ◽  
Dynamo Action ◽  
Rotation Rates ◽  
Evolved Stars ◽  
Solar Type ◽  
Limiting Value

AbstractEvolved stars tell us a great deal about dynamos. The granulation boundary shows us where solar-type convection begins. Since activity indicators also start at this boundary, it is a good bet that solar-type convection is an integral part of dynamo activity for all stars. The rotation boundary tells us where the magnetic fields of dynamos become effective in dissipating angular momentum, and rotation beyond the boundary tells us the limiting value needed for a dynamo to function. The observed uniqueness of rotation rates after the rotation boundary is crossed can be understood through the rotostat hypothesis. Quite apart from the reason for the unique rotation rate, its existence can be used to show that magnetic activity of giants is concentrated to the equatorial latitudes, as it is in the solar case. The coronal boundary in the H-R diagram is probably nothing more than a map of where rotation becomes too low to sustain dynamo activity.

scholarly journals Magnetic Activity of Two Similar Subgiants in Binaries with Very Different Mass Ratios: EI Eri and V711 Tau

2011 ◽  
Vol 7 (S282) ◽  
pp. 478-479 ◽  
Author(s):  
Katalin Oláh ◽  
Zsolt Kővári ◽  
Krisztián Vida ◽  
Klaus G. Strassmeier
Keyword(s):  
Differential Rotation ◽  
Activity Patterns ◽  
Magnetic Activity ◽  
Light Curves ◽  
Physical Parameters ◽  
Remarkable Difference ◽  
High Latitudes ◽  
Solar Type ◽  
Low Mass ◽  
Fast Rotating

AbstractWe use more than three decades-long photometry to study the activity patterns on the two fast-rotating subgiant components in EI Eri (G5IV) and V711 Tau (K1IV). From yearly mean rotational periods from the light curves, we find that EI Eri, with well-measured solar-type differential rotation, always has spots from the equator to high latitudes. The measured differential rotation of V711 Tau is controversial, and in any case is very small. The spots on the K1IV star in V711 Tau seem to be tidally locked. The physical parameters of the two systems are similar, with one remarkable difference: EI Eri has a low mass M4-5 dwarf companion, whereas V711 Tau has a G5V star in the system, thus their mass centers are in very different positions. This may modify the whole internal structure of the active stars, causing marked differences in their surface features.

scholarly journals How the planetary research helps to the stellar dynamo understanding

2012 ◽  
Vol 8 (S294) ◽  
pp. 471-475
Author(s):  
I. Boisse ◽  
M. Oshagh ◽  
C. Lovis ◽  
N. C. Santos ◽  
X. Dumusque ◽  
...  
Keyword(s):  
Planetary System ◽  
Magnetic Activity ◽  
Doppler Imaging ◽  
Habitable Zone ◽  
Stellar Activity ◽  
Term Variation ◽  
Solar Type ◽  
Low Mass ◽  
Stellar Dynamo

AbstractMost of the exoplanet science is dependent on the stellar knowledge. One of them that has to be understood is the magnetic activity when we search for planets with radial velocity or photometry measurements. The main shape of stellar activity and spots properties have to be understood, for example, to choose the best targets to search for low-mass planets in the habitable zone or to derive the accurate parameters of a planetary system. With that aim, we show in this presentation how these studies lead to give clues on spots latitudes and on the long term variation of stellar activity. The properties of magnetic activity on the low rotators solar-type stars are not easily reachable by other techniques (spectropolarimetry or Doppler imaging) and these studies should be used to constrain theories of stellar dynamo.

scholarly journals The Solar-Stellar Connection and Disconnection

2004 ◽  
Vol 219 ◽  
pp. 11-28 ◽  
Author(s):  
Klaus G. Strassmeier
Keyword(s):  
Magnetic Field ◽  
Meridional Circulation ◽  
Magnetic Activity ◽  
Driving Mechanism ◽  
The Sun ◽  
Dynamo Action ◽  
Convective Envelope ◽  
Surface Rotation ◽  
Single Process ◽  
Solar Type

The study of stellar activity is now an almost classical astronomical topic. The first Ca ii-H&K observations were made a hundred years ago by Eberhard & Schwarzschild1 and many thousand papers were published after its rediscovery some three decades ago by O. C. Wilson. The complexity of the atmospheric and interior magnetic activity as observed on the Sun is hard, if not impossible, to extrapolate to solar-type stars. So far there is no solar twin found, despite that it appears that just a single process acts as the driving mechanism for activity in all atmospheric layers and partially even in the convective envelope: the dynamodriven magnetic field. In this paper, I will try to give examples where the solar analogy holds and where it is clearly not appropriate, putting some emphases on differential surface rotation and meridional circulation. I stress the importance of mapping stellar surfaces as fingerprints of the underlying dynamo action and directly measure surface magnetic fields.

Solar Rotation, Irradiance Changes and Climate

1994 ◽  
Vol 143 ◽  
pp. 244-251
Author(s):  
Elizabeth Nesme-Ribes ◽  
Dmitry Sokoloff ◽  
Robert Sadourny
Keyword(s):  
Magnetic Fields ◽  
Internal Rotation ◽  
Solar Rotation ◽  
Total Solar Irradiance ◽  
Magnetic Activity ◽  
Convective Envelope ◽  
Surface Rotation ◽  
Solar Type ◽  
Activity Cycles ◽  
The Impact

Magnetic activity cycles for solar-type stars are believed to originate from non-uniform internal rotation. To determine this depthwise angular velocity distribution, helioseismology is a valuable source of information. Surface rotation, as traced by sunspot motion, is a well-observed parameter with data going back to the beginning of the telescopic era. This long sunspot series can be used in understanding the behaviour of the Sun’s surface rotation, the connection with its internal rotation, and thereby its magnetic activity. Apparent solar diameter is another important parameter. This is related to the structure of the convective envelope and how it reacts to the presence of magnetic fields. Both these parameters are related to the solar output, and can provide a surrogate for total solar irradiance, by way of a theoretical modeling of the response of the convective zone to the emergence of periodic magnetic fields. The impact of solar variability on the terrestrial climate is also addressed.

scholarly journals The Sun in time: age, rotation, and magnetic activity of the Sun and solar-type stars and effects on hosted planets

2008 ◽  
Vol 4 (S258) ◽  
pp. 395-408 ◽  
Author(s):  
Edward F. Guinan ◽  
Scott G. Engle
Keyword(s):  
Main Sequence ◽  
High Energy ◽  
Magnetic Activity ◽  
The Sun ◽  
X Ray ◽  
Multi Wavelength ◽  
Solar Type ◽  
Rotation Age ◽  
Energy Emissions ◽  
Solar Analogs

AbstractMulti-wavelength studies of solar analogs (G0–5 V stars) with ages from ~50 Myr to 9 Gyr have been carried out as part of the “Sun in Time” program for nearly 20 yrs. From these studies it is inferred that the young (ZAMS) Sun was rotating more than 10× faster than today. As a consequence, young solar-type stars and the early Sun have vigorous magnetohydrodynamic (MHD) dynamos and correspondingly strong coronal X-ray and transition region/chromospheric FUV–UV emissions (up to several hundred times stronger than the present Sun). Also, rotational modulated, low amplitude light variations of young solar analogs indicate the presence of large starspot regions covering ~5–30% of their surfaces. To ensure continuity and homogeneity for this program, we use a restricted sample of G0–5 V stars with masses, radii, Teff, and internal structure (i.e. outer convective zones) closely matching those of the Sun. From these analogs we have determined reliable rotation-age-activity relations and X-ray–UV (XUV) spectral irradiances for the Sun (or any solar-type star) over time. These XUV irradiance measures serve as input data for investigating the photo-ionization and photo-chemical effects of the young, active Sun on the paleo-planetary atmospheres and environments of solar system planets. These measures are also important to study the effects of these high energy emissions on the numerous exoplanets hosted by solar-type stars of different ages. Recently we have extended the study to include lower mass, main-sequence (dwarf) dK and dM stars to determine relationships among their rotation spin-down rates and coronal and chromospheric emissions as a function of mass and age. From rotation-age-activity relations we can determine reliable ages for main-sequence G, K, M field stars and, subsequently, their hosted planets. Also inferred are the present and the past XUV irradiance and plasma flux exposures that these planets have endured and the suitability of the hosted planets to develop and sustain life.

scholarly journals Dynamo Processes Constrained by Solar and Stellar Observations

2018 ◽  
Vol 13 (S340) ◽  
pp. 275-280
Author(s):  
Maria A. Weber
Keyword(s):  
Differential Rotation ◽  
Meridional Circulation ◽  
Mean Field ◽  
Magnetic Activity ◽  
Flux Emergence ◽  
Dynamo Theory ◽  
M Dwarfs ◽  
Dynamo Action ◽  
Solar Type ◽  
Stellar Dynamo

AbstractOur understanding of stellar dynamos has largely been driven by the phenomena we have observed of our own Sun. Yet, as we amass longer-term datasets for an increasing number of stars, it is clear that there is a wide variety of stellar behavior. Here we briefly review observed trends that place key constraints on the fundamental dynamo operation of solar-type stars to fully convective M dwarfs, including: starspot and sunspot patterns, various magnetism-rotation correlations, and mean field flows such as differential rotation and meridional circulation. We also comment on the current insight that simulations of dynamo action and flux emergence lend to our working knowledge of stellar dynamo theory. While the growing landscape of both observations and simulations of stellar magnetic activity work in tandem to decipher dynamo action, there are still many puzzles that we have yet to fully understand.

scholarly journals Rotation and Magnetic Activity in Brown Dwarfs

2004 ◽  
Vol 215 ◽  
pp. 248-257 ◽  
Author(s):  
Gibor Basri
Keyword(s):  
Angular Momentum ◽  
Recent Work ◽  
Brown Dwarfs ◽  
Magnetic Activity ◽  
New Work ◽  
History Of ◽  
Solar Type ◽  
Low Mass ◽  
Magnetic Braking

Brown dwarfs and very low mass (VLM) stars are the last frontier on the map of the angular momentum histories of star-like objects. Until the advent of 8-m class telescopes, it was impossible to obtain spectra with enough resolution to detect their rotation. The very existence of brown dwarfs was only established then. It was immediately apparent that there are differences between VLM objects and their heftier stellar cousins. Field VLM objects were found to be very rapidly rotating, yet they did not display the strong magnetic activity that would be expected of convective objects in that case. We now have a good preliminary understanding of the situation near the substellar boundary. I summarize the rotational data (both spectroscopic and photometric) on VLM objects, and how rotation and temperature fit into the production of magnetic activty. I also report more recent work on VLM objects when they are very young. There is increasing evidence that they form much like stars, beginning (when they become visible) as relatively slow rotators for the most part, followed by spin-up as they contract. Their disk lifetimes may be shorter, and they are more magnetically active when they are young. The subsequent angular momentum history of VLM objects is different from solar-type stars, as the usual magnetic braking mechanisms do not operate as in the stellar case. Much of the new work reported here is from the thesis of Subanjoy Mohanty, and was supported by NSF/AST-0098468.

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