ABSTRACT
The transit method is a promising means of detecting exomoons, but few candidates have been identified. For planets close to their stars, the dynamical interaction between a satellite’s ...orbit and the star must be important in their evolution. Satellites beyond synchronous orbit spiral out due to the tide raised on their planet, and it has been assumed that they would likely escape the Hill sphere. Here we follow the evolution with a three-body code that accounts for tidal dissipation within both the planet and the satellite. We show that tidal dissipation in satellites often keeps them bound to their planet, making exomoons more observable than previously thought. The probability of escape depends on the ratio of tidal quality factors of the planet and satellite; when this ratio exceeds 0.5, escape is usually avoided. Instead, the satellite moves to an equilibrium in which the spin angular momentum of the planet is not transferred into the orbit of the satellite, but is transferred into the orbit of the planet itself. While the planet continues spinning faster than the satellite orbits, the satellite maintains a semi-major axis of approximately 0.41 Hill radii. These states are accompanied with modest satellite eccentricity near 0.1 and are found to be stable over long time-scales.
We report the discovery of a transiting, R sub(p) = 4.347 + or - 0.099R sub(+ in circle), circumbinary planet (CBP) orbiting the Kepler K + M eclipsing binary (EB) system KIC 12351927 (Kepler-413) ...every ~66 days on an eccentric orbit with a sub(p) = 0.355+ or -0.002 AU, e sub(p) = 0.118+ or -0.002. The orbital plane of the EB is slightly inclined to the line of sight (i sub(EB) = 87degrees.33 + or - 0degrees.06), while that of the planet is inclined by ~2degrees.5 to the binary plane at the reference epoch. Orbital precession with a period of ~11 yr causes the inclination of the latter to the sky plane to continuously change. As a result, the planet often fails to transit the primary star at inferior conjunction, causing stretches of hundreds of days with no transits (corresponding to multiple planetary orbital periods).
In the solar system, the planets' compositions vary with orbital distance, with rocky planets in close orbits and lower-density gas giants in wider orbits. The detection of close-in giant planets ...around other stars was the first clue that this pattern is not universal and that planets' orbits can change substantially after their formation. Here, we report another violation of the orbit-composition pattern: two planets orbiting the same star with orbital distances differing by only 10% and densities differing by a factor of 8. One planet is likely a rocky "super-Earth," whereas the other is more akin to Neptune. These planets are 20 times more closely spaced and have a larger density contrast than any adjacent pair of planets in the solar system.
The All Sky Automated Survey (ASAS) monitors bright stars (8 < V < 14 mag) south of declination +28°. The ASAS Catalogue of Variable Stars (ACVS) presently contains 50 099 objects; among them are ...2212 objects classified as RR Lyrae pulsating variables. We use ASAS photometric V-band data to search for multiperiodicity in those stars. We find that 73 of 1435 RRab stars and 49 of 756 RRc stars exhibit the Blazhko effect. We observe a deficiency of RRab Blazhko variables with main pulsation periods greater than 0.65 d. The Blazhko periods of RRc stars exhibit a strongly bimodal distribution. During our study we discovered the Blazhko effect with multiple periods in object ASAS 050747−3351.9 = SU Col. Blazhko periods of 89.3 and 65.8 d and a candidate of 29.5 d were identified with periodogram peaks near the first three harmonics of the main pulsation. These observations may inspire new models of the Blazhko effect, which has eluded a consistent theory since its discovery about one hundred years ago. Long-term light curve changes were found in 29 stars. We also found 19 Galactic double mode pulsators (RRd), of which four are new discoveries, raising the number of ASAS discoveries of such objects to 16, out of 27 known in the field of our Galaxy.
We present rotational velocities for individual components of 11 very low mass (VLM) binaries with spectral types between M7 and L7.5. These results are based on observations taken with the ...near-infrared spectrograph, NIRSPEC, and the Keck II laser guide star adaptive optics system. We find that the observed sources tend to be rapid rotators (v sin i > 10 km s super(-1)), consistent with previous seeing-limited measurements of VLM objects. The two sources with the largest v sin i, LP 349-25B and HD 130948C, are rotating at ~30% of their break-up speed, and are among the most rapidly rotating VLM objects known. Furthermore, five binary systems, all with orbital semimajor axes <, ~3.5 AU, have component v sin i values that differ by greater than 3sigma. To bring the binary components with discrepant rotational velocities into agreement would require the rotational axes to be inclined with respect to each other, and that at least one component is inclined with respect to the orbital plane. Alternatively, each component could be rotating at a different rate, even though they have similar spectral types. Both differing rotational velocities and inclinations have implications for binary star formation and evolution. We also investigate possible dynamical evolution in the triple system HD 130948A-BC. The close binary brown dwarfs B and C have significantly different v sin i values. We demonstrate that components B and C could have been torqued into misalignment by the primary star, A, via orbital precession. Such a scenario can also be applied to another triple system in our sample, GJ 569A-Bab. Interactions such as these may play an important role in the dynamical evolution of VLM binaries. Finally, we note that two of the binaries with large differences in component v sin i, LP 349-25AB and 2MASS 0746+20AB, are also known radio sources.
The multiple-planet systems discovered by the Kepler mission show an excess of planet pairs with period ratios just wide of exact commensurability for first-order resonances like 2:1 and 3:2. In ...principle, these planet pairs could have both resonance angles associated with the resonance librating if the orbital eccentricities are sufficiently small, because the width of first-order resonances diverges in the limit of vanishingly small eccentricity. We consider a widely held scenario in which pairs of planets were captured into first-order resonances by migration due to planet-disk interactions, and subsequently became detached from the resonances, due to tidal dissipation in the planets. In the context of this scenario, we find a constraint on the ratio of the planet's tidal dissipation function and Love number that implies that some of the Kepler planets are likely solid. However, tides are not strong enough to move many of the planet pairs to the observed separations, suggesting that additional dissipative processes are at play.
Kepler Object of Interest Network von Essen, C.; Ofir, A.; Dreizler, S. ...
Astronomy and astrophysics (Berlin),
07/2018, Letnik:
615
Journal Article
Recenzirano
Odprti dostop
During its four years of photometric observations, the
Kepler
space telescope detected thousands of exoplanets and exoplanet candidates. One of
Kepler
’s greatest heritages has been the confirmation ...and characterization of hundreds of multi-planet systems via transit timing variations (TTVs). However, there are many interesting candidate systems displaying TTVs on such long timescales that the existing
Kepler
observations are of insufficient length to confirm and characterize them by means of this technique. To continue with
Kepler
’s unique work, we have organized the “
Kepler
Object of Interest Network” (KOINet), a multi-site network formed of several telescopes located throughout America, Europe, and Asia. The goals of KOINet are to complete the TTV curves of systems where
Kepler
did not cover the interaction timescales well, to dynamically prove that some candidates are true planets (or not), to dynamically measure the masses and bulk densities of some planets, to find evidence for non-transiting planets in some of the systems, to extend
Kepler
’s baseline adding new data with the main purpose of improving current models of TTVs, and to build a platform that can observe almost anywhere on the northern hemisphere, at almost any time. KOINet has been operational since March 2014. Here we show some promising first results obtained from analyzing seven primary transits of KOI-0410.01, KOI-0525.01, KOI-0760.01, and KOI-0902.01, in addition to the
Kepler
data acquired during the first and second observing seasons of KOINet. While carefully choosing the targets we set demanding constraints on timing precision (at least 1 min) and photometric precision (as good as one part per thousand) that were achieved by means of our observing strategies and data analysis techniques. For KOI-0410.01, new transit data revealed a turnover of its TTVs. We carried out an in-depth study of the system, which is identified in the NASA Data Validation Report as a false positive. Among others, we investigated a gravitationally bound hierarchical triple star system and a planet–star system. While the simultaneous transit fitting of ground- andspace-based data allowed for a planet solution, we could not fully reject the three-star scenario. New data, already scheduled in the upcoming 2018 observing season, will set tighter constraints on the nature of the system.
Some short-period exoplanets ("hot Jupiters") are observed by their transits to have anomalously large radii. It has been suggested that these planets are in a resonance involving persistent ...misalignment and synchronous precession of their spin and orbital angular momenta (a Cassini state) and that the attendant tidal heating inflates the planet. We argue against this. Using explicit tidal integrations, we show that although an oblique Cassini state can dissipate many times the planet's rotational energy, the rate of dissipation must be much less than hypothesized. Dissipation causes the planetary spin to lie at an angle to the plane containing the orbital and total angular momenta. If dissipation is too rapid, this angle becomes so large that Cassini equilibrium is lost. A separate consideration limits the total energy that can be extracted from the orbit. The source of the torque on the orbit, either an oblique parent star or an inclined third body, aligns with the orbit as it absorbs the angular momentum shed by the planet. Alignment removes the orbital precession required by the Cassini state. In combination with observational bounds on the mass and semimajor axis of a possible second planet and with bounds on the stellar rotation and obliquity, these constraints make it very unlikely that obliquity tides can be the explanation for inflated hot Jupiters, especially HD 209458b.
ABSTRACT
We present a hierarchical triple star system (KIC 9140402) where a low‐mass eclipsing binary orbits a more massive third star. The orbital period of the binary (4.988 29 d) is determined by ...the eclipse times seen in photometry from NASA’s Kepler spacecraft. The periodically changing tidal field, due to the eccentric orbit of the binary about the tertiary, causes a change in the orbital period of the binary. The resulting eclipse timing variations provide insight into the dynamics and architecture of this system and allow the inference of the total mass of the binary (0.424 ± 0.017 M⊙) and the orbital parameters of the binary about the central star.
PDF
