scholarly journals Physics of the Applegate mechanism: Eclipsing time variations from magnetic activity

2018 ◽  
Vol 620 ◽  
pp. A42 ◽  
Author(s):  
M. Völschow ◽  
D. R. G. Schleicher ◽  
R. Banerjee ◽  
J. H. M. M. Schmitt
Keyword(s):  
Binary Systems ◽  
Theoretical Work ◽  
Magnetic Activity ◽  
Close Binary ◽  
Magnetic Fluctuations ◽  
Common Envelope ◽  
Stellar Parameter ◽  
Low Mass ◽  
Time Variations ◽  
Binary Separations

Since its proposal in 1992, the Applegate mechanism has been discussed as a potential intrinsical mechanism to explain transit-timing variations in various types of close binary systems. Most analytical arguments presented so far focused on the energetic feasibility of the mechanism while applying rather crude one- or two-zone prescriptions to describe the exchange of angular momentum within the star. In this paper, we present the most detailed approach to date to describe the physics giving rise to the modulation period from kinetic and magnetic fluctuations. Assuming moderate levels of stellar parameter fluctuations, we find that the resulting binary period variations are one or two orders of magnitude lower than the observed values in RS-CVn like systems, supporting the conclusion of existing theoretical work that the Applegate mechanism may not suffice to produce the observed variations in these systems. The most promising Applegate candidates are low-mass post-common-envelope binaries with binary separations ≲1 R⊙ and secondary masses in the range of 0.30 M⊙ and 0.36 M⊙.

scholarly journals Evolution of Low-Mass Helium Dwarfs in Interacting Binaries: Application to 4U1820-30

1989 ◽  
Vol 114 ◽  
pp. 469-472
Author(s):  
Lorne A. Nelson ◽  
Paul C. Joss ◽  
Saul Rappaport
Keyword(s):  
Effective Temperature ◽  
Binary Systems ◽  
Mass Transfer Rate ◽  
Rate Of Change ◽  
Close Binary ◽  
Common Envelope ◽  
Elapsed Time ◽  
Evolved Stars ◽  
History Of ◽  
Low Mass

A number of evolutionary scenarios have been proposed that lead to the formation of binary systems consisting of a degenerate dwarf in orbit with a neutron star. In fact, most degenerate dwarfs in close-binary systems are probably the cores of evolved stars whose envelopes have been stripped by one or more episodes of common-envelope evolution. Once the envelope has been removed, the newly exposed core of the giant will have an effective temperature and radius that are considerably larger than the corresponding quantities in an older, highly degenerate dwarf. It is important for at least two reasons to evaluate the subsequent cooling history of such objects: (i) For detached binaries, we want to be able to infer from the current effective temperature and luminosity of the degenerate dwarf the elapsed time since the core of its progenitor giant was exposed, (ii) For semi-detached binaries, we must know the evolution of the radius of the degenerate dwarf in order to compute important relationships among the orbital period and its rate of change, the mass of the degenerate dwarf, and the mass-transfer rate.

scholarly journals X-ray and UV emission of the ultrashort-period, low-mass eclipsing binary system BX Trianguli

2018 ◽  
Vol 619 ◽  
pp. A138
Author(s):  
V. Perdelwitz ◽  
S. Czesla ◽  
J. Robrade ◽  
T. Pribulla ◽  
J. H. M. M. Schmitt
Keyword(s):  
Binary System ◽  
Light Curve ◽  
Binary Systems ◽  
Uv Light ◽  
Close Binary ◽  
Eclipsing Binary ◽  
X Ray ◽  
Uv Emission ◽  
Low Mass ◽  
Orbital Modulation

Context.Close binary systems provide an excellent tool for determining stellar parameters such as radii and masses with a high degree of precision. Due to the high rotational velocities, most of these systems exhibit strong signs of magnetic activity, postulated to be the underlying reason for radius inflation in many of the components. Aims.We extend the sample of low-mass binary systems with well-known X-ray properties. Methods.We analyze data from a singular XMM-Newton pointing of the close, low-mass eclipsing binary system BX Tri. The UV light curve was modeled with the eclipsing binary modeling tool PHOEBE and data acquired with the EPIC cameras was analyzed to search for hints of orbital modulation. Results.We find clear evidence of orbital modulation in the UV light curve and show that PHOEBE is fully capable of modeling data within this wavelength range. Comparison to a theoretical flux prediction based on PHOENIX models shows that the majority of UV emission is of photospheric origin. While the X-ray light curve does exhibit strong variations, the signal-to-noise ratio of the observation is insufficient for a clear detection of signs of orbital modulation. There is evidence of a Neupert-like correlation between UV and X-ray data.

scholarly journals The Influence of Binarity on Stellar Activity

2006 ◽  
Vol 2 (S240) ◽  
pp. 442-452 ◽  
Author(s):  
Katalin Oláh
Keyword(s):  
Binary Systems ◽  
Magnetic Energy ◽  
Theoretical Calculations ◽  
Deep Convection ◽  
Magnetic Activity ◽  
Close Binary ◽  
Convective Envelope ◽  
Flux Tubes ◽  
Gravitational Forces ◽  
Magnetic Flux Tubes

AbstractActivity of late type stars is enhanced by fast rotation, which is maintained in nearly synchronized close binary systems. Magnetic activity originates in the deep convection zones of stars from where magnetic flux tubes emerge to their surfaces. The gravitational forces in binaries help the clustering of activity features giving rise to active longitudes. These preferred longitudes are observed in binaries from dwarfs to giants. Differential rotation is found in many active stars that are components of binary systems. If these binaries are circularized and nearly synchronized, then there will be a corotation latitude in their surfaces, and its position can be determined by observations and by theoretical calculations. Enhanced activity in binaries could have a reverse effect as well: strong magnetism in a binary component can modify the orbital period by the cyclic exchange of kinetic and magnetic energy in its convective envelope.

scholarly journals V392 Orionis: Observations and Evolutionary State of a Low-Mass System

1998 ◽  
Vol 11 (1) ◽  
pp. 371-371
Author(s):  
S. Narusawa ◽  
A. Yamasaki ◽  
Y. Nakamura
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Circumstellar Matter ◽  
Small Mass ◽  
Primary Component ◽  
Close Binary ◽  
Mass System ◽  
Future Evolution ◽  
Short Period ◽  
Low Mass

Although the evolution of binary systems has been qualitatively interpreted with the evolutionary scenario, the quantitative interpretation of any observed system is still unsatisfactory due to the difficulty of the quantitative treatment of mass and angular momentum transfer/loss. To reach a true understanding of the evolution of binary systems, we have to accumulate more observational evidence. So far, we have observed several binaries that are short-period and noncontact, and found the existence of extremely small-mass systems. In the present paper, we study another short-period (P=0.659d), noncontact, eclipsing binary system, V392 Ori. We have made photometric and spectroscopic observations of V392 Ori. The light curves are found to vary, suggesting the existence of circumstellar matter around the system. Combining the photometric and spectroscopic results, we obtain parameters describing the system; we find the mass of the primary component is only 0.6Mʘ- undermassive for its spectral and luminosity class A5V, suggesting that a considerable amount of its original mass has been lost from the system during the course of evolution. The low-mass problem is very important for investigation of the evolution of close binary systems: largemass loss within and/or after the main-sequence will have a significant influence on the future evolution of binary systems.

scholarly journals The MUCHFUSS photometric campaign

2018 ◽  
Vol 614 ◽  
pp. A77 ◽  
Author(s):  
V. Schaffenroth ◽  
S. Geier ◽  
U. Heber ◽  
R. Gerber ◽  
D. Schneider ◽  
...  
Keyword(s):  
Brown Dwarfs ◽  
Close Binary ◽  
Red Giants ◽  
Reflection Effect ◽  
Common Envelope ◽  
Sdb Stars ◽  
Solar Type ◽  
Low Mass ◽  
Substellar Companions ◽  
Almost All

Hot subdwarfs (sdO/Bs) are the helium-burning cores of red giants, which have lost almost all of their hydrogen envelope. This mass loss is often triggered by common envelope interactions with close stellar or even substellar companions. Cool companions like late-type stars or brown dwarfs are detectable via characteristic light-curve variations like reflection effects and often also eclipses. To search for such objects, we obtained multi-band light curves of 26 close sdO/B binary candidates from the MUCHFUSS project with the BUSCA instrument. We discovered a new eclipsing reflection effect system (P = 0.168938 d) with a low-mass M dwarf companion (0.116 M⊙). Three more reflection effect binaries found in the course of the campaign have already been published; two of them are eclipsing systems, and in one system only showing the reflection effect but no eclipses, the sdB primary is found to be pulsating. Amongst the targets without reflection effect a new long-period sdB pulsator was discovered and irregular light variations were found in two sdO stars. The found light variations allowed us to constrain the fraction of reflection effect binaries and the substellar companion fraction around sdB stars. The minimum fraction of reflection effect systems amongst the close sdB binaries might be greater than 15% and the fraction of close substellar companions in sdB binaries may be as high as 8.0%. This would result in a close substellar companion fraction to sdB stars of about 3%. This fraction is much higher than the fraction of brown dwarfs around possible progenitor systems, which are solar-type stars with substellar companions around 1 AU, as well as close binary white dwarfs with brown dwarf companions. This might suggest that common envelope interactions with substellar objects are preferentially followed by a hot subdwarf phase.

scholarly journals Starspot Activity on Short-period RS CVn Stars

1991 ◽  
Vol 130 ◽  
pp. 370-372
Author(s):  
Michael Zeilik
Keyword(s):  
Binary Stars ◽  
Binary Systems ◽  
Magnetic Activity ◽  
Close Binary ◽  
Tidal Interactions ◽  
Rs Cvn Stars ◽  
Short Period ◽  
Basic Physics ◽  
Synchronous Rotation ◽  
Orbital Periods

We have yet to understand the magnetic activity cycles of cool close binary systems of sunlike stars. Mutual tidal interactions, as well as magnetic ones, may result from a regime of dynamo models not yet tested, because these have been developed for single stars. To arrive at the basic physics, though, requires that we first examine the phenomenology of magnetic activity for binary systems. In particular, we would like to discover if such activity has a clearly-defined cycle, such as the sun exibits.Among the proxy indicators of magnetic activity are the Ca II H and K lines. Strassmeier et al. (1988) used the strength of these lines as the primary criterion for the inclusion of systems in The Catalog of Chromospherically Binary Stars. Of the RS CVn stars in the catalog, 12 have orbital periods of one day or shorter; 9 are eclipsing systems. As part of a decade-long program, we have focussed our observations and models on eight of the short-period group (Hall, 1976): XY UMa, UV Psc, SV Cam, RT And, CG Cyg, ER Vul, BH Vir, and WY Cnc. These close systems are tidally-locked in synchronous rotation and tidally-distorted into Roche lobe configurations.

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