Magnetic fields are hypothesized to inflate the radii of low-mass stars—defined as less massive than 0.8 M ☉—in detached eclipsing binaries (DEBs). We investigate this hypothesis using the recently introduced magnetic Dartmouth stellar evolution code. In particular, we focus on stars thought to have a radiative core and convective outer envelope by studying in detail three individual DEBs: UV Psc, YY Gem, and CU Cnc. Our results suggest that the stabilization of thermal convection by a magnetic field is a plausible explanation for the observed model-radius discrepancies. However, surface magnetic field strengths required by the models are significantly stronger than those estimated from observed coronal X-ray emission. Agreement between model predicted surface magnetic field strengths and those inferred from X-ray observations can be found by assuming that the magnetic field sources its energy from convection. This approach makes the transport of heat by convection less efficient and is akin to reduced convective mixing length methods used in other studies. Predictions for the metallicity and magnetic field strengths of the aforementioned systems are reported. We also develop an expression relating a reduction in the convective mixing length to a magnetic field strength in units of the equipartition value. Our results are compared with those from previous investigations to incorporate magnetic fields to explain the low-mass DEB radius inflation. Finally, we explore how the effects of magnetic fields might affect mass determinations using asteroseismic data and the implication of magnetic fields on exoplanet studies.

https://iopscience.iop.org/article/10.1088/0004-637X/779/2/183/pdf

Magnetic inhibition of convection and the fundamental properties of low-mass stars. i. stars with a radiative core

W UMa-type stars are contact systems where both cool components fill the critical Roche lobes and share a common convective envelope. Long and unbroken time-series photometry is expected to play an important role in their origin and activity. The newly discovered short-period W UMa-type star, CSTAR 038663, was monitored continuously by Chinese Small Telescope ARray (CSTAR) in Antarctica during the winters of 2008 and 2010. There were 15 optical flares recorded in the i band during the winter of 2010. This was the first time such flares were detected from a W UMa-type star. By analyzing the nearly unbroken photometric data from 2008, it is discovered that CSTAR 038663 is a W-type shallow contact binary system (f = 10.6(+/- 2.9)%) with a high mass ratio of q = 1.12(+/- 0.01), where the less massive component is slightly hotter than the more massive one. The asymmetric light curves are explained by the presence of a dark spot on the more massive component. Its temperature is about 800 K lower than the stellar photosphere and it covers 2.1% of the total photospheric surface. The lifetime of the dark spot is longer than 116 days. Using 725 eclipse times, we found that the observed-calculated (O-C) curve may show a cyclic variation that is explained by the presence of a close-in third body. Both the shallow contact configuration and the extremely high mass ratio suggest that CSTAR 038663 is presently evolving into a contact system with little mass transfer. The formation and evolution is driven by the loss of angular momentum via magnetic braking, and the close-in companion star is expected to play an important role, removing angular momentum from the central eclipsing binary.

Optical flares and a long-lived dark spot on a cool shallow contact binary

About 3196 EA-type binaries (EAs) were observed by LAMOST by 2017 June 16 and their spectral types were derived. Meanwhile, the stellar atmospheric parameters of 2020 EAs were determined. In this paper, those EAs are cataloged and their physical properties and evolutionary states are investigated. The period distribution of EAs suggests that the period limit of tidal locking for the close binaries is about 6 days. It is found that the metallicity of EAs is higher than that of EW-type binaries (EWs), indicating that EAs are generally younger than EWs and they are the progenitors of EWs. The metallicities of long-period EWs (0.4

https://iopscience.iop.org/article/10.3847/1538-4365/aaa601/pdf

Physical Properties and Evolutionary States of EA-type Eclipsing Binaries Observed by LAMOST

The phenomenon of quasi-periodic pulsations (QPPs) in solar and stellar flares has been known for over 50 years and significant progress has been made in this research area. It has become clear that QPPs are not rare—they are found in many flares and, therefore, robust flare models should reproduce their properties in a natural way. At least fifteen mechanisms/models have been developed to explain QPPs in solar flares, which mainly assume the presence of magnetohydrodynamic (MHD) oscillations in coronal structures (magnetic loops and current sheets) or quasi-periodic regimes of magnetic reconnection. We review the most important and interesting results on flare QPPs, with an emphasis on the results of recent years, and we present the predicted and prominent observational signatures of each of the fifteen mechanisms. However, it is not yet possible to draw an unambiguous conclusion as to the correct underlying QPP mechanism because of the qualitative, rather than quantitative, nature of most of the models and also due to insufficient observational information on the physical properties of the flare region, in particular the spatial structure of the QPP source. We also review QPPs in stellar flares, where progress is largely based on solar-stellar analogies, suggesting similarities in the physical processes in flare regions on the Sun and magnetoactive stars. The presence of QPPs with similar properties in solar and stellar flares is, in itself, a strong additional argument in favor of the likelihood of solar-stellar analogies. Hence, advancing our understanding of QPPs in solar flares provides an important additional channel of information about stellar flares. However, further work in both theory/simulations and in observations is needed.

Quasi-Periodic Pulsations in Solar and Stellar Flares: A Review of Underpinning Physical Mechanisms and Their Predicted Observational Signatures

We analyze and interpret the oscillatory signal in the decay phase of the U-band light curve of a stellar megaflare observed on 2009 January 16 on the dM4.5e star YZ CMi. The oscillation is well approximated by an exponentially decayingharmonicfunction.Theperiodoftheoscillationisfoundtobe32minutes,thedecaytimeabout46minutes, and the relative amplitude 15%. As this observational signature is typical of the longitudinal oscillations observed in solar flares at extreme ultraviolet and radio wavelengths, associated with standing slow magnetoacoustic waves, we suggest that this megaflare may be of a similar nature. In this scenario, macroscopic variations of the plasma parameters in the oscillations modulate the ejection of non-thermal electrons. The phase speed of the longitudinal (slow magnetoacoustic) waves in the flaring loop or arcade, the tube speed, of about 230 km s −1 would require a

The decaying long-period oscillation of a stellar megaflare

In this paper, we report on the discovery of an optical flare observed in the R band from the red-dwarf eclipsing binary CU Cancri, whose component stars are at the upper boundary of full convection (M1= 0.43 M? and M2= 0.4 M?, where M? is the solar mass). The amplitude of the flare is the largest among those detected in the R band (similar to 0.52 mag) and the duration time is about 73 min. Like flares observed on the Sun, quasi-periodic oscillations were seen during and after the flare. Three more R-band flares were found by follow-up monitoring. In total, this binary was monitored photometrically by using an R filter for 79.9 h, which has revealed an R-band flare rate of about 0.05 flares per hour. Together with other strong chromospheric and coronal activities (i.e. very strong Ha and H beta emission features and an extreme ultraviolet and X-ray source), these detections indicate that it has very strong magnetic activity. Therefore, the apparent faintness (similar to 1.4 mag in the V band) of CU Cnc, compared with other single red dwarfs of the same mass, can be plausibly explained by the high coverage of dark spots.

Optical flares and flaring oscillations on the M-type eclipsing binary CU Cancri

TY UMa is an F-type eclipsing binary star. Four-color light curves and radial velocities of this system were presented and simultaneously analyzed using the W-D code. It is found that TY UMa is a W-subtype shallow contact binary system (f = 13.4%) with a mass ratio of q = 2.523. In order to explain the asymmetric light curve of this binary, a dark spot on the less massive component was employed. Our newly determined 31 times of minimum light, including those collected from the literature, have been used to analyze orbital period changes of TY UMa. The complicated period variation could be sorted into a secular period increase at a rate of dp/dt = +5.18(+/- 0.21) x 10(-7) days yr(-1), a 51.7 yr periodic modulation (A(3) = 0.0182 days), and a very small amplitude cyclic oscillation with a period of 10.0 yr (A(4) = 0.0015 days). The long-term increase of the period can be explained by mass transfer from the less massive component to the more massive one. The Applegate mechanism may impossibly explain the two cyclic components in the period. The two cyclic variations are very likely caused by the light travel time effect of third and fourth components, suggesting that TY UMa is a quadruple system.

http://iopscience.iop.org/article/10.1088/0004-6256/149/4/120/pdf

The Active Contact Binary Ty UMa Revisited: is It a Quadruple Star?

New photometric data of EQ Tau observed in 2010 and 2013 are presented. Light curves obtained in 2000 and 2004 by Yuan & Qian and 2001 by Yang & Liu, together with our two newly determined sets of light curves, were analyzed using the Wilson-Devinney code. The five sets of light curves exhibit very obvious variations, implying that the light curves of EQ Tau show a strong O'Connell effect. We found that EQ Tau is an A-type shallow contact binary with a contact degree of f = 11.8%; variable dark spots on the primary component of EQ Tau were also observed. Using 10 new times of minimum light, together with those collected from the literature, the orbital period change of EQ Tau was analyzed. We found that its orbital period includes a secular decrease (dP/dt = -3.63 x 10(-8) days yr(-1)) and a cyclic oscillation (A(3) = 0.0058 days and P-3 = 22.7 yr). The secular increase of the period can be explained by mass transfer from the more massive component to the less massive one or/and angular momentum loss due to a magnetic stellar wind. The Applegate mechanism cannot explain the cyclic orbital period change. A probable transit-like event was observed in 2010. Therefore, the cyclic orbital period change of EQ Tau may be due to the light time effect of a third body.

http://iopscience.iop.org/article/10.1088/0004-6256/147/5/98/pdf

The triple binary star eq tau with an active component

With the explosive increase of big data, it is necessary to apply large-scale data processing systems to analysis Big Data. Arguably, Spark is state of the art in large-scale data computing systems nowadays, due to its good properties including generality, fault tolerance, high performance of in-memory data processing, and scalability. Spark adopts a flexible Resident Distributed Dataset(RDD) programming model with a set of provided transformation and action operators whose operating functions can be customized by users according to their applications. It is originally positioned as a fast and general data processing system. A large body of research efforts have been made to make it more efficient(faster) and general by considering various circumstances since its introduction. In this survey, we aim to have a thorough review of various kinds of optimization techniques on the generality and performance improvement of Spark. We introduce Spark programming model and computing system, discuss the pros and cons of Spark, and have an investigation on various solving techniques in the literature. Moreover, we also introduce various data management and processing systems, machine learning algorithms and applications supported by Spark. Finally, we make a discussion on the open issues and challenges for Spark.

A Survey on Spark Ecosystem: Big Data Processing Infrastructure, Machine Learning, and Applications

New multi-color CCD photometric light curves of the eclipsing binary EP And were obtained over six nights in 2006, 2011, and 2012 Using the Wilson-Devinney code, we computed the photometric elements of this system It was discovered that EP And is a W-type W UMa contact binary system with a mass ratio of q = 2685 and a degree of contact factor f = 249%, rather than an A-type system Combining 28 newly determined times of minimum light derived from 1999 to 2012 with others collected from the literature, a long-term increase (dP/dt = +522 x 10(-8) days yr(-1)) with a sinusoidal variation (A = 00109 days; T = 4089 yr) in the orbital period was found The orbital period secular increases may be interpreted as conservative mass transfer from the less massive component to the more massive one, and cyclic variations of the orbital period may be caused by the light-travel time effect through the presence of a third body The evolutionary status and the age of the system are also discussed

http://iopscience.iop.org/article/10.1088/0004-6256/146/4/79/pdf

K. Li

Papers

Optical flares and flaring oscillations on the M-type eclipsing binary CU Cancri

The Active Contact Binary Ty UMa Revisited: is It a Quadruple Star?

The triple binary star eq tau with an active component

A Survey on Spark Ecosystem: Big Data Processing Infrastructure, Machine Learning, and Applications

THE MULTI-COLOR LIGHT CURVES OF THE W UMa TYPE CONTACT BINARY EP ANDROMEDAE