scholarly journals A PULSATING FLARE STAR IN THE NEW PLANETARY SYSTEM: KOI-258

2021 ◽  
Vol 57 (1) ◽  
pp. 39-55
Author(s):  
E. Yoldaş ◽  
H. A. Dal
Keyword(s):  
Radial Velocity ◽  
Small Amplitude ◽  
Main Sequence ◽  
Planetary System ◽  
Magnetic Activity ◽  
Main Sequence Star ◽  
Velocity Variation ◽  
Flare Activity ◽  
The Third ◽  
Radial Velocity Variation

We present findings about the nature of KOI-258. Its temperature was found to be 6500 ± 200 K from its spectrum, which also indicates that the target is a single main sequence star despite the existence of a radial velocity variation with a small amplitude. Ca II H, K lines indicate the existence of magnetic activity, though there is no remarkable excess or variation in the Hα line. We found 51 flares with a frequency of 0.00186 h−1, whose plateau value is 0.659 s. Apart from the flares, we found 420 frequencies due to solar-like oscillations at out-of-eclipses. Removing these 420 frequencies, we demonstrated three different transits caused by three exo-planets. Their radii were found to be 2.33 R_⊕ for the first planet, 0.53 R_⊕ for the second one, and 1.15 R_⊕ for the third planet. Consequently, KOI-258 is an oscillating, single, main sequence star, with in a planetary system and remarkable flare activity.

scholarly journals Activity-Induced Radial Velocity Variation of M Dwarf Stars

2012 ◽  
Vol 8 (S293) ◽  
pp. 197-200
Author(s):  
Jan Marie Andersen ◽  
Heidi Korhonen
Keyword(s):  
Radial Velocity ◽  
Magnetic Activity ◽  
Velocity Variation ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Highly Active ◽  
Radial Velocity Variation ◽  
Low Mass ◽  
M Dwarf Stars ◽  
M Dwarf

AbstractStellar magnetic activity manifests itself in a variety of ways including starspots–cool, dark regions on the stellar surface. Starspots can cause variations (‘jitter’) in spectral line-profiles which can mimic the radial velocity (RV) variations caused by an orbiting planet, or create RV noise that can drown out a planetary signature. Cool, low-mass M dwarf stars can be highly active, which can make detection of potentially habitable planets around these stars difficult. We investigate radial velocity variations caused by different activity (spot) patterns on M dwarf stars in order to determine the limits of detectability for small planets orbiting active M dwarfs. We report on our progress toward the aim of answering the following questions: What types of spot patterns are realistic for M dwarf stars? What effect will spots have on M dwarf RV measurements? Can jitter from M dwarf spots mimic planetary signals? What is the ideal observing wavelength to reduce M dwarf jitter?

scholarly journals Methods of the Long-term Radial-Velocity Variation Removal and their Application to Detect Duplicity of Several Be Stars

2011 ◽  
Vol 7 (S282) ◽  
pp. 319-320
Author(s):  
J. Nemravová ◽  
P. Harmanec ◽  
P. Koubský ◽  
A. Miroshnichenko
Keyword(s):  
Radial Velocity ◽  
Binary Stars ◽  
Orbital Motion ◽  
Continuous Functions ◽  
Velocity Variation ◽  
Be Stars ◽  
The Third ◽  
Radial Velocity Variation ◽  
Velocity Variations

AbstractThere are several types of binary stars which show non-periodical radial velocity variations with the amplitude larger than those connected with the orbital motion. The non-periodical changes have to be removed in order to study the orbital ones. We propose three removal techniques, two of which are based on the trend modeling with continuous functions and the third one that takes the orbital motion into account.

scholarly journals Spin–Orbit Alignment of the TrES-4 Transiting Planetary System and Possible Additional Radial-Velocity Variation

2010 ◽  
Vol 62 (3) ◽  
pp. 653-660 ◽  
Author(s):  
Norio Narita ◽  
Bun’ei Sato ◽  
Teruyuki Hirano ◽  
Joshua N. Winn ◽  
Wako Aoki ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Planetary System ◽  
Velocity Variation ◽  
Spin Orbit ◽  
Radial Velocity Variation

scholarly journals XO-2b: a Prograde Planet with Negligible Eccentricity and an Additional Radial Velocity Variation

2011 ◽  
Vol 63 (6) ◽  
pp. L67-L71 ◽  
Author(s):  
Norio Narita ◽  
Teruyuki Hirano ◽  
Bun'ei Sato ◽  
Hiroki Harakawa ◽  
Akihiko Fukui ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Velocity Variation ◽  
Radial Velocity Variation

scholarly journals WASP-4 transit timing variation from a comprehensive set of 129 transits

2020 ◽  
Vol 496 (1) ◽  
pp. L11-L15 ◽  
Author(s):  
R V Baluev ◽  
E N Sokov ◽  
S Hoyer ◽  
C Huitson ◽  
José A R S da Silva ◽  
...  
Keyword(s):  
Conservative Treatment ◽  
Radial Velocity ◽  
Decay Rate ◽  
High Accuracy ◽  
Light Curves ◽  
Velocity Variation ◽  
Radial Acceleration ◽  
Radial Velocity Variation ◽  
Non Linear ◽  
Doppler Data

ABSTRACT We homogeneously reanalyse 124 transit light curves for the WASP-4 b hot Jupiter. This set involved new observations secured in 2019 and nearly all observations mentioned in the literature, including high-accuracy GEMINI/GMOS transmission spectroscopy of 2011–2014 and TESS observations of 2018. The analysis confirmed a non-linear transit timing variation (TTV) trend with $P/|\dot{P}|\sim \hbox{17-30}$ Myr (1σ range), implying only half of the initial decay rate estimation. The trend significance is at least 3.4σ in the aggressively conservative treatment. Possible radial acceleration due to unseen companions is not revealed in Doppler data covering seven years 2007–2014, and radial acceleration of −15 m s−1 yr−1 reported in a recent preprint by another team is not confirmed. If present, it is a very non-linear radial velocity variation. Assuming that the entire TTV is tidal in nature, the tidal quality factor $Q_\star ^{\prime }\sim \hbox{(4.5-8.5)}\times 10^4$ does not reveal a convincing disagreement with available theory predictions.

scholarly journals Magnetic activity in HD 111456, a young F5–6 main-sequence star

2003 ◽  
Vol 413 (2) ◽  
pp. 657-667 ◽  
Author(s):  
R. Freire Ferrero ◽  
A. Frasca ◽  
E. Marilli ◽  
S. Catalano
Keyword(s):  
Main Sequence ◽  
Magnetic Activity ◽  
Main Sequence Star

scholarly journals Applegate mechanism in post-common-envelope binaries: Investigating the role of rotation

2018 ◽  
Vol 615 ◽  
pp. A81 ◽  
Author(s):  
F. H. Navarrete ◽  
D. R. G. Schleicher ◽  
J. Zamponi Fuentealba ◽  
M. Völschow
Keyword(s):  
Orbital Period ◽  
Rotation Rate ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Main Sequence Star ◽  
Common Envelope ◽  
Rotation Rates ◽  
Critical Rotation ◽  
Period Variations ◽  
Time Variations

Context. Eclipsing time variations are observed in many close binary systems. In particular, for several post-common-envelope binaries (PCEBs) that consist of a white dwarf and a main sequence star, the observed-minus-calculated (O–C) diagram suggests that real or apparent orbital period variations are driven by Jupiter-mass planets or as a result of magnetic activity, the so-called Applegate mechanism. The latter explains orbital period variations as a result of changes in the stellar quadrupole moment due to magnetic activity. Aims. In this work we explore the feasibility of driving eclipsing time variations via the Applegate mechanism for a sample of PCEB systems, including a range of different rotation rates. Methods. We used the MESA code to evolve 12 stars with different masses and rotation rates. We applied simple dynamo models to their radial profiles to investigate the scale at which the predicted activity cycle matches the observed modulation period, and quantifiy the uncertainty. We further calculated the required energies to drive the Applegate mechanism. Results. We show that the Applegate mechanism is energetically feasible in 5 PCEB systems. In RX J2130.6+4710, it may be feasible as well considering the uncertainties. We note that these are the systems with the highest rotation rate compared to the critical rotation rate of the main-sequence star. Conclusions. The results suggest that the ratio of physical to critical rotation rate in the main sequence star is an important indicator for the feasibility of Applegate’s mechanism, but exploring larger samples will be necessary to probe this hypothesis.

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