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 High-Level Magnetic Activity on a Low-Mass Close Binary: GSC 02038-0293

2012 ◽  
Vol 29 (2) ◽  
pp. 150-160 ◽  
Author(s):  
H. A. Dal ◽  
E. Sipahi ◽  
O. Özdarcan
Keyword(s):  
Light Curve ◽  
Active Component ◽  
Magnetic Activity ◽  
Curve Analysis ◽  
Light Curves ◽  
Close Binary ◽  
Physical Parameters ◽  
Light Curve Analysis ◽  
Low Mass ◽  
High Level

AbstractTaking into account results obtained from light-curve analysis and out-of-eclipse analyses, we discuss the nature of GSC 02038-00293 and also its magnetic activity behaviour.We obtained light curves of the system during observing seasons 2007, 2008 and 2011. We obtained its secondary minimum clearly in I-band observations in 2008 for the first time. Analysing this light curve, we found the physical parameters of the components. The light-curve analysis indicates that the possible mass ratio of the system is 0.35. We obtained the remaining V-band light curves, extracting the eclipses. We modelled these remaining curves using the SPOTMODEL program and found possible spot configurations of the magnetically active component for each observing season. The models demonstrated that there are two active longitudes for the active component. The models reveal that both active longitudes migrate in the direction of decreasing longitude. We also examined the light curves in out-of-eclipse phases with respect to minimum and maximum brightness, amplitude, etc. The amplitude of the curves during out-of-eclipse phases varies in a sinusoidal way with a period of ∼8.9 yr; the mean brightness of the system is dramatically decreasing. The phases of the deeper minimum during out-of-eclipse periods exhibit a migration toward decreasing phase.

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 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 High-resolution spectroscopy of detached solar-type eclipsing binaries observed during the Kepler K2 mission

2020 ◽  
Vol 493 (2) ◽  
pp. 2329-2338
Author(s):  
B Hoyman ◽  
Ö Çakırlı
Keyword(s):  
Theoretical Models ◽  
Eclipsing Binaries ◽  
High Resolution Spectroscopy ◽  
Physical Parameters ◽  
Evolutionary Status ◽  
Low Mass Stars ◽  
Ongoing Effort ◽  
Stellar Parameter ◽  
Solar Type ◽  
Low Mass

ABSTRACT Solar-type stars in eclipsing binaries are proving to be a remarkable resource of knowledge for testing models of stellar evolution, as spectroscopic and photometric studies have opened up a window into their interiors. Until recently, many cases have been worked out with Kepler data. In an ongoing effort to elucidate this research, we examine five detached eclipsing binaries, selected from the Kepler catalogue. There is a well-known stellar parameter discrepancy for low-mass stars, in that the observed radii and masses are often larger and stars overluminous than predicted by theory by several per cent. In our samples, we found five double-lined binaries, with solar-type stars dominating the spectrum. The orbital and light-curve solutions were found for them, and compared with isochrones, in order to estimate absolute physical parameters and evolutionary status of the components. An important aspect of this work is that the calculated stellar radii and masses are consistent with theoretical models within the uncertainties, whereas the estimated temperatures from the disentangled spectra of the components are no different than predicted.

scholarly journals CM Draconis: Masses and Radii of Very Low Mass Stars

2006 ◽  
Vol 2 (S240) ◽  
pp. 628-630
Author(s):  
J.C. Morales ◽  
I. Ribas ◽  
C. Jordi ◽  
G. Torres ◽  
E.F. Guinan ◽  
...  
Keyword(s):  
Magnetic Activity ◽  
Time Span ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
Low Mass Stars ◽  
Fundamental Properties ◽  
Low Mass ◽  
Effective Temperatures ◽  
Better Than

AbstractIn this work we have studied CM Draconis, one of the least massive eclipsing binaries known. Its components are very similar, with masses and radii of about 0.23 M⊙ and 0.25 R⊙. We have analysed light curves in the R and I bands to calculate the fundamental properties of this system with accuracies better than 1%. With these results we plan to carry out a thorough test of the models, which have been found to predict smaller radii and larger effective temperatures than observed for these low-mass stars. This will also be especially interesting in the case of CM Dra since the mechanism driving magnetic activity is thought to be different from that of more massive stars. In addition, the extended time-span of the observations has led to the detection of apsidal motion. This provides a further check on models through the determination of the internal structure of the stars.

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.

scholarly journals Magnetic Activity and Rotation in Brown Dwarfs and Low Mass Stars

2003 ◽  
Vol 211 ◽  
pp. 427-435 ◽  
Author(s):  
Gibor Basri ◽  
Subanjoy Mohanty
Keyword(s):  
Theoretical Work ◽  
Magnetic Activity ◽  
Stellar Rotation ◽  
Low Mass Stars ◽  
Strong Activity ◽  
Substellar Objects ◽  
Substantial Progress ◽  
Solar Type ◽  
Low Mass ◽  
M Stars

One of the triumphs of the last 2 decades has been the establishment of the relation between stellar rotation and magnetic activity in solar-type stars. Rapid rotation produces strong activity, which in turn provides magnetic braking to reduce rotation. A solar-type dynamo cannot operate in fully convective stars, so it is of interest to study mid and late M stars. Hints that a dramatic change occurs in very low-mass stars and substellar objects appeared in 1995. The past 7 years have seen substantial progress on this question, with the conclusion that the rotation-activity connection indeed breaks down. As one goes to the bottom of the main sequence and below, the amount of magnetic activity takes a sudden fall, with a concomitant increase in the spindown times of the objects. We summarize these results, and some theoretical work which helps explain them. We also present some remaining mysteries, such as why very young objects seem excessively active, and flaring in objects with no other signs of magnetic activity.

scholarly journals Ground-Based and Space Observations of Interacting Binaries

2011 ◽  
Vol 7 (S282) ◽  
pp. 21-26
Author(s):  
Panagiotis G. Niarchos
Keyword(s):  
Binary Systems ◽  
Accurate Determination ◽  
Space Missions ◽  
Light Curves ◽  
Physical Parameters ◽  
Multi Wavelength ◽  
Low Mass ◽  
Space Observations

AbstractMulti-wavelength observational data, obtained from ground-based and space observations are used to compute the physical parameters of the observed Interacting Binaries (IBs) and study the interactions and physical processes in these systems. In addition, the database of IBs from ground-based surveys and space missions will provide light curves for many thousands of new binary systems for which extensive follow up ground-based observations can be carried out. In certain cases, light curves of superior quality will allow studies of fine effects of stellar activity and very accurate determination of stellar parameters. Moreover, many new discoveries of interesting systems are expected from ground-based all-sky surveys and space missions, including low mass binaries and star-planet binary systems. The most important current and future programs of observations of IBs from ground and space are presented.

scholarly journals Stellar cycles: general properties and future directions

2011 ◽  
Vol 7 (S286) ◽  
pp. 257-267
Author(s):  
Mark S. Giampapa
Keyword(s):  
Differential Rotation ◽  
Magnetic Activity ◽  
Scaling Relation ◽  
Cycle Frequency ◽  
Future Directions ◽  
General Properties ◽  
Empirical Relations ◽  
Solar Type ◽  
The Mean

AbstractWe discuss the general properties of stellar cycles with emphasis on their amplitudes as a function of stellar parameters, particularly those stellar characteristics relevant to dynamo-driven magnetic activity. We deduce an empirical scaling relation between cycle frequency and differential rotation based on previously established empirical relations. We also compare the recent Cycle 23 to cycles in solar-type stars. We find that the extended minimum of Cycle 23 resembled in its Ca II H & K emission at minimum the mean levels of activity seen in stars with no cycles.

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