Journal articles: 'Stellar astronomy and planetary systems'

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Kouwenhoven, M. B. N., Francesco Flammini Dotti, Qi Shu, Xiuming Xu, Kai Wu, Xiaoying Pang, and Wei Hao. "Planetary systems in dense stellar environments." Journal of Physics: Conference Series 1523 (April 2020): 012011. http://dx.doi.org/10.1088/1742-6596/1523/1/012011.

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Terzian, Yervant. "Distances of Planetary Nebulae." Symposium - International Astronomical Union 155 (1993): 109–21. http://dx.doi.org/10.1017/s0074180900170287.

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One of the most fundamental physical parameter in astronomy is the distance to the objects we detect in the universe. For many classes of astronomical objects, accurate and proven methods have been developed to determine their distances. Such classes of objects include stars within ∼100 pc from the sun, binary stellar systems, variable stars, stellar clusters, main sequence stars, and other galaxies. It has been, however, more difficult to develop satisfactory methods to determine accurate distances to the more than 1000 planetary nebulae that have been discovered in our galaxy.

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Fukushima, Toshio, Jan Vondrák, Nicole Capitaine, George A. Krasinsky, Andrea Milani, Imants Platais, Veronique Dehant, and Demetrios N. Matsakis. "DIVISION I: FUNDAMENTAL ASTRONOMY." Proceedings of the International Astronomical Union 3, T26B (December 2007): 71–73. http://dx.doi.org/10.1017/s1743921308023673.

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Division I provides a focus for astronomers studying a wide range of problems related to fundamental physical phenomena such as time, the inertial reference frame, positions and proper motions of celestial objects, and precise dynamical computation of the motions of bodies in stellar or planetary systems in the Universe.

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Vondrák, Jan, Dennis D. McCarthy, Toshio Fukushima, Aleksander Brzezinski, Joseph A. Burns, Pascale Defraigne, Dafydd Wyn Evans, et al. "DIVISION I: FUNDAMENTAL ASTRONOMY." Proceedings of the International Astronomical Union 4, T27A (December 2008): 1–4. http://dx.doi.org/10.1017/s1743921308025222.

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Division I provides a focus for astronomers studying a wide range of problems related to fundamental physical phenomena such as time, the inertial reference frame, positions and proper motions of celestial objects and precise dynamical computation of the motions of bodies in stellar or planetary systems in the Universe.

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Milani, Andrea, Joseph A. Burns, J. Hadjidemetriou, Z. Knežević, C. Beaugé, B. Erdi, T. Fukushima, et al. "COMMISSION 7: Celestial Mechanics and Dynamical Astronomy." Proceedings of the International Astronomical Union 1, T26A (December 2005): 7–16. http://dx.doi.org/10.1017/s1743921306004297.

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The orbital fits of multi-planetary systems from radial velocity data has proved to be a complex task. In some cases, different orbital solutions provide similarly good fits, especially when two planets are near mean-motion resonances. Ferraz-Melloet al(2005) and Goździewskiet al(2005) showed that the published best fits of systemsHD82932andHD160691are dynamically unstable, and re-determined their orbital parameters with Monte Carlo and genetic algorithms. In both cases dynamically stable orbits were found with RMS similar to the published orbits. It was also shown that uncertainties in the stellar mass Ferraz Melloet al(2005) and the stellar jitter Gozdziewskiet al(2005) can significantly affect the orbital determination. Ford (2005) used a Markov chain Monte Carlo technique to quantify the orbit uncertainties. For some planetary systems he found a strong correlation between the orbital elements and/or significant non-Gaussian error distribution in the parameter space. As a consequence, the actual uncertainties in the orbital fits can be much larger (or smaller) than those published.

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Mal’nev, A. G., V. V. Orlov, and A. V. Petrova. "The dynamical evolution of stellar-planetary systems." Astronomy Reports 50, no. 5 (May 2006): 405–10. http://dx.doi.org/10.1134/s106377290605009x.

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Niedzielski, Andrzej, Grzegorz Nowak, and Paweł Zieliński. "The PSU/TCfA search for planets around evolved stars. Stellar parameters and activity indicators of targets." Proceedings of the International Astronomical Union 3, S249 (October 2007): 49–52. http://dx.doi.org/10.1017/s1743921308016359.

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AbstractThe main objective of the Penn State/Toruń Centre for Astronomy search for planets around evolved stars is the detection of planetary systems around massive, evolved stars. We are also interested in the evolution of these systems on stellar evolution timescales. In this paper we present our approach to determine the basic physical parameters of our targets GK-giants. We also discuss the stellar activity indicators used in our survey: line bisector and curvature, and Hα variability.

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Le Bars, M., L. Lacaze, S. Le Dizès, P. Le Gal, and M. Rieutord. "Tidal instability in stellar and planetary binary systems." Physics of the Earth and Planetary Interiors 178, no. 1-2 (January 2010): 48–55. http://dx.doi.org/10.1016/j.pepi.2009.07.005.

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Adibekyan, V., N. C. Santos, O. D. S. Demangeon, J. P. Faria, S. C. C. Barros, M. Oshagh, P. Figueira, et al. "Stellar clustering and orbital architecture of planetary systems." Astronomy & Astrophysics 649 (May 2021): A111. http://dx.doi.org/10.1051/0004-6361/202040201.

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Context. Revealing the mechanisms shaping the architecture of planetary systems is crucial for our understanding of their formation and evolution. In this context, it has been recently proposed that stellar clustering might be the key in shaping the orbital architecture of exoplanets. Aims. The main goal of this work is to explore the factors that shape the orbits of planets. Methods. We performed different statistical tests to compare the properties of planets and their host stars associated with different stellar environments. Results. We used a homogeneous sample of relatively young FGK dwarf stars with radial velocity detected planets and tested the hypothesis that their association to phase space (position-velocity) over-densities (“cluster” stars) and under-densities (“field” stars) impacts the orbital periods of planets. When controlling for the host star properties on a sample of 52 planets orbiting around cluster stars and 15 planets orbiting around field stars, we found no significant difference in the period distribution of planets orbiting these two populations of stars. By considering an extended sample of 73 planets orbiting around cluster stars and 25 planets orbiting field stars, a significant difference in the planetary period distributions emerged. However, the hosts associated with stellar under-densities appeared to be significantly older than their cluster counterparts. This does not allow us to conclude as to whether the planetary architecture is related to age, environment, or both. We further studied a sample of planets orbiting cluster stars to study the mechanism responsible for the shaping of orbits of planets in similar environments. We could not identify a parameter that can unambiguously be responsible for the orbital architecture of massive planets, perhaps, indicating the complexity of the issue. Conclusions. An increased number of planets in clusters and in over-density environments will help to build large and unbiased samples which will then allow to better understand the dominant processes shaping the orbits of planets.

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Flammini Dotti, Francesco, M. B. N. Kouwenhoven, Maxwell Xu Cai, and Rainer Spurzem. "Planetary systems in a star cluster I: the Solar system scenario." Monthly Notices of the Royal Astronomical Society 489, no. 2 (August 23, 2019): 2280–97. http://dx.doi.org/10.1093/mnras/stz2346.

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ABSTRACTYoung stars are mostly found in dense stellar environments, and even our own Solar system may have formed in a star cluster. Here, we numerically explore the evolution of planetary systems similar to our own Solar system in star clusters. We investigate the evolution of planetary systems in star clusters. Most stellar encounters are tidal, hyperbolic, and adiabatic. A small fraction of the planetary systems escape from the star cluster within 50 Myr; those with low escape speeds often remain intact during and after the escape process. While most planetary systems inside the star cluster remain intact, a subset is strongly perturbed during the first 50 Myr. Over the course of time, $0.3\!-\!5.3{{\ \rm per\ cent}}$ of the planets escape, sometimes up to tens of millions of years after a stellar encounter occurred. Survival rates are highest for Jupiter, while Uranus and Neptune have the highest escape rates. Unless directly affected by a stellar encounter itself, Jupiter frequently serves as a barrier that protects the terrestrial planets from perturbations in the outer planetary system. In low-density environments, Jupiter provides protection from perturbations in the outer planetary system, while in high-density environments, direct perturbations of Jupiter by neighbouring stars is disruptive to habitable-zone planets. The diversity amongst planetary systems that is present in the star clusters at 50 Myr, and amongst the escaping planetary systems, is high, which contributes to explaining the high diversity of observed exoplanet systems in star clusters and in the Galactic field.

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Wang, Yi-Han, Rosalba Perna, and Nathan W. C. Leigh. "Planetary architectures in interacting stellar environments." Monthly Notices of the Royal Astronomical Society 496, no. 2 (June 9, 2020): 1453–70. http://dx.doi.org/10.1093/mnras/staa1627.

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ABSTRACT The discovery of exoplanetary systems has challenged some of the theories of planet formation, which assume unperturbed evolution of the host star and its planets. However, in star clusters the interactions with fly-by stars and binaries may be relatively common during the lifetime of a planetary system. Here, via high-resolution N-body simulations of star–planet systems perturbed by interlopers (stars and binaries), we explore the reconfiguration to the planetary system due to the encounters. In particular, via an exploration focused on the strong scattering regime, we derive the fraction of encounters that result in planet ejections, planet transfers, and collisions by the interloper star/binary, as a function of the characteristics of the environment (density, velocity dispersion), and for different masses of the fly-by star/binary. We find that binary interlopers can significantly increase the cross-section of planet ejections and collisions, while they only slightly change the cross-section for planet transfers. Therefore, in environments with high binary fractions, floating planets are expected to be relatively common, while in environments with low binary fractions, where the cross-sections of planet ejection and transfer are comparable, the rate of planet exchanges between two stars will be comparable to the rate of production of free-floating planets.

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Iorio, Lorenzo. "Frame-Dragging in Extrasolar Circumbinary Planetary Systems." Universe 8, no. 10 (October 21, 2022): 546. http://dx.doi.org/10.3390/universe8100546.

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Extrasolar circumbinary planets are so called because they orbit two stars instead of just one; to date, an increasing number of such planets have been discovered with a variety of techniques. If the orbital frequency of the hosting stellar pair is much higher than the planetary one, the tight stellar binary can be considered as a matter ring current generating its own post-Newtonian stationary gravitomagnetic field through its orbital angular momentum. It affects the orbital motion of a relatively distant planet with Lense-Thirring-type precessional effects which, under certain circumstances, may amount to a significant fraction of the static, gravitoelectric ones, analogous to the well known Einstein perihelion precession of Mercury, depending only on the masses of the system’s bodies. Instead, when the gravitomagnetic field is due solely to the spin of each of the central star(s), the Lense-Thirring shifts are several orders of magnitude smaller than the gravitoelectric ones. In view of the growing interest in the scientific community about the detection of general relativistic effects in exoplanets, the perspectives of finding new scenarios for testing such a further manifestation of general relativity might be deemed worth of further investigations.

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Dotti, F. Flammini, Maxwell Xu Cai, Rainer Spurzem, and M. B. N. Kouwenhoven. "Planetary Systems in Star Clusters: the dynamical evolution and survival." Proceedings of the International Astronomical Union 14, S345 (August 2018): 293–94. http://dx.doi.org/10.1017/s174392131900142x.

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AbstractMost stars form in crowded stellar environments. Such star forming regions typically dissolve within ten million years, while others remain bound as stellar groupings for hundreds of millions to billions of years, and then become the open clusters or globular clusters that are present in our Milky Way galaxy today. A large fraction of stars in the Galaxy hosts planetary companions. To understand the origin and dynamical evolution of such exoplanet systems, it is necessary to carefully study the effect of their environments. Here, we combine theoretical estimates with state-of-the-art numerical simulations of evolving planetary systems similar to our own solar system in different star cluster environments. We combine the planetary system evolution code, and the star cluster evolution code, integrated in the multi-physics environment. With our study we can constrain the effect of external perturbations of different environments on the planets and debris structures of a wide variety of planetary systems, which may play a key role for the habitability of exoplanets in the Universe.

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Lueftinger, Theresa, Manuel Güdel, Sudeshna Boro Saikia, Colin Johnstone, Beatrice Kulterer, Oleg Kochukhov, and Kristina Kislyakova. "Stellar activity and winds shaping the atmospheres of Earth-like planets." Proceedings of the International Astronomical Union 14, S345 (August 2018): 181–84. http://dx.doi.org/10.1017/s174392131900293x.

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AbstractPlanets orbiting young, active stars are embedded in an environment that is far from being as calm as the present solar neighbourhood. They experience the extreme environments of their host stars, which cannot have been without consequences for young stellar systems and the evolution of Earth-like planets to habitable worlds. Stellar magnetism and the related stellar activity are crucial drivers of ionization, photodissociation, and chemistry. Stellar winds can compress planetary magnetospheres and even strip away the outer layers of their atmospheres, thus having an enormous impact on the atmospheres and the magnetospheres of surrounding exoplanets. Modelling of stellar magnetic fields and their winds is extremely challenging, both from the observational and the theoretical points of view, and only ground breaking advances in observational instrumentation and a deeper theoretical understanding of magnetohydrodynamic processes in stars enable us to model stellar magnetic fields and their winds – and the resulting influence on the atmospheres of surrounding exoplanets – in more and more detail. We have initiated a national and international research network (NFN): ‘Pathways to Habitability – From Disks to Active Stars, Planets to Life’, to address questions on the formation and habitability of environments in young, active stellar/planetary systems. We discuss the work we are carrying out within this project and focus on how stellar evolutionary aspects in relation to activity, magnetic fields and winds influence the erosion of planetary atmospheres in the habitable zone. We present recent results of our theoretical and observational studies based on Zeeman Doppler Imaging (ZDI), field extrapolation methods, wind simulations, and the modeling of planetary upper atmospheres.

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Takeda, Genya, Ryosuke Kita, and Frederic A. Rasio. "Induced Kozai Migration and Formation of Close-in Planets in Binaries." Proceedings of the International Astronomical Union 4, S253 (May 2008): 181–87. http://dx.doi.org/10.1017/s1743921308026392.

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AbstractMany recent observational studies have concluded that planetary systems commonly exist in multiple-star systems. At least ~20%, and presumably a larger fraction, of the known extrasolar planetary systems are associated with one or more stellar companions. These stellar companions normally exist at large distances from the planetary systems (typical projected binary separations are 102–104AU) and are often faint (ranging from F to T spectral types). Yet, secular cyclic angular momentum exchange with these distant stellar companions can significantly alter the orbital configuration of the planets around the primaries. One of the most interesting and fairly common outcomes seen in numerical simulations is the opening of a large mutual inclination angle between the planetary orbits, forced by differential nodal precessions caused by the binary companion. The growth of the mutual inclination angle between planetary orbits induces additional large-amplitude eccentricity oscillations of the inner planet due to the quadrupole gravitational perturbation by the outer planet. This eccentricity oscillation may eventually result in the orbital decay of the inner planet through tidal friction, as previously proposed as Kozai migration or Kozai cycles with tidal friction (KCTF). This orbital decay mechanism induced by the binary perturbation and subsequent tidal dissipation may stand as an alternative formation channel for close-in extrasolar planets.

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Fregeau, John M., Sourav Chatterjee, and Frederic A. Rasio. "Dynamical Interactions of Planetary Systems in Dense Stellar Environments." Astrophysical Journal 640, no. 2 (April 2006): 1086–98. http://dx.doi.org/10.1086/500111.

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Duchêne, Gaspard. "Prospects for planet formation in multiple stellar systems." Proceedings of the International Astronomical Union 5, H15 (November 2009): 764–65. http://dx.doi.org/10.1017/s1743921310011488.

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AbstractAs I review here, planet formation in multiple stellar systems is far from exceptional. However, it appears that binaries with projected separation in the 5–100 AU range have different initial conditions and end result properties than wider systems, probably because they undergo different physical processes. In addition, very tight binaries, with projected separation less than a few AU, seem to fulfill all the known requirements to form planetary systems, suggesting that circumbinary planets are very likely to exist.

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Galera-Rosillo, Rebeca, Romano L. M. Corradi, Bruce Balick, Karen Kwitter, Antonio Mampaso, and Jorge García-Rojas. "The origin of the most luminous Planetary Nebulae." Proceedings of the International Astronomical Union 12, S323 (October 2016): 386–87. http://dx.doi.org/10.1017/s1743921317003465.

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AbstractAs part of a systematic effort to characterize the properties and progenitors of the most luminous planetary nebulae (PNe), we obtained a sample among the brightest PNe in two stellar systems of different metallicities: LMC (Z/Z⊙~0.5) and M31 (Z/Z⊙~1) by means of a combined effort with the VLT and the 10mGTC. Modelling of these data will allow us to infer the masses of the stellar progenitors, gaining insights into the controversial origin of the universal cutoff of the Planetary Nebulae Luminosity Function (PNLF).

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Eberle, Jason, Manfred Cuntz, and Zdzislaw E. Musielak. "Orbital stability of Earth-type planets in stellar binary systems." Proceedings of the International Astronomical Union 5, H15 (November 2009): 691–92. http://dx.doi.org/10.1017/s1743921310010987.

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AbstractAn important factor in estimating the likelihood of life elsewhere in the Universe is determining the stability of a planet's orbit. A significant fraction of stars like the Sun occur in binary systems which often has a considerable effect on the stability of any planets in such a system. In an effort to determine the stability of planets in binary star systems, we conducted a numerical simulation survey of several mass ratios and initial conditions. We then estimated the stability of the planetary orbit using a method that utilizes the hodograph to determine the effective eccentricity of the planetary orbit. We found that this method can serve as an orbital stability criterion for the planet.

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Bonfanti, A., L. Fossati, D. Kubyshkina, and P. E. Cubillos. "Constraining stellar rotation and planetary atmospheric evolution of a dozen systems hosting sub-Neptunes and super-Earths." Astronomy & Astrophysics 656 (December 2021): A157. http://dx.doi.org/10.1051/0004-6361/202142010.

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Context. Planetary atmospheric evolution modelling is a prime tool for understanding the observed exoplanet population and constraining formation and migration mechanisms, but it can also be used to study the evolution of the activity level of planet hosts. Aims. We constrain the planetary atmospheric mass fraction at the time of the dispersal of the protoplanetary disk and the evolution of the stellar rotation rate for a dozen multi-planet systems that host sub-Neptunes and/or super-Earths. Methods. We employ a custom-developed PYTHON code that we have dubbed PASTA (Planetary Atmospheres and Stellar RoTation RAtes), which runs within a Bayesian framework to model the atmospheric evolution of exoplanets. The code combines MESA stellar evolutionary tracks, a model describing planetary structures, a model relating stellar rotation and activity level, and a model predicting planetary atmospheric mass-loss rates based on the results of hydrodynamic simulations. Results. Through a Markov chain Monte Carlo scheme, we retrieved the posterior probability density functions of all considered parameters. For ages older than about 2 Gyr, we find a median spin-down (i.e. P(t)∝ty) of ȳ = 0.38−0.27+0.38, indicating a rotation decay slightly slower than classical literature values (≈0.5), though still within 1σ. At younger ages, we find a median spin-down (i.e. P(t)∝tx) of x̄ = 0.26−0.19+0.42, which is below what is observed in young open clusters, though within 1σ. Furthermore, we find that the x probability distribution we derived is skewed towards lower spin-down rates. However, these two results are likely due to a selection bias as the systems suitable to be analysed by PASTA contain at least one planet with a hydrogen-dominated atmosphere, implying that the host star has more likely evolved as a slow rotator. We further look for correlations between the initial atmospheric mass fraction of the considered planets and system parameters (i.e. semi-major axis, stellar mass, and planetary mass) that would constrain planetary atmospheric accretion models, but without finding any. Conclusions. PASTA has the potential to provide constraints to planetary atmospheric accretion models, particularly when considering warm sub-Neptunes that are less susceptible to mass loss compared to hotter and/or lower-mass planets. The TESS, CHEOPS, and PLATO missions are going to be instrumental in identifying and precisely measuring systems amenable to PASTA’s analysis and can thus potentially constrain planet formation and stellar evolution.

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Adams, Fred C., Kassandra R. Anderson, and Anthony M. Bloch. "Evolution of planetary systems with time-dependent stellar mass-loss." Monthly Notices of the Royal Astronomical Society 432, no. 1 (April 19, 2013): 438–54. http://dx.doi.org/10.1093/mnras/stt479.

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Ballantyne, Harry A., Tore Espaas, Bethan Z. Norgrove, Bethany A. Wootton, Benjamin R. Harris, Isaac L. Pepper, Richard D. Smith, Rosie E. Dommett, and Richard J. Parker. "Long-term stability of planets in and around binary stars." Monthly Notices of the Royal Astronomical Society 507, no. 3 (August 19, 2021): 4507–20. http://dx.doi.org/10.1093/mnras/stab2324.

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ABSTRACT Planets are observed to orbit the component star(s) of stellar binary systems on so-called circumprimary or circumsecondary orbits, as well as around the entire binary system on so-called circumbinary orbits. Depending on the orbital parameters of the binary system, a planet will be dynamically stable if it orbits within some critical separation of the semimajor axis in the circumprimary case, or beyond some critical separation for the circumbinary case. We present N-body simulations of star-forming regions that contain populations of primordial binaries to determine the fraction of binary systems that can host stable planets at various semimajor axes, and how this fraction of stable systems evolves over time. Dynamical encounters in star-forming regions can alter the orbits of some binary systems, which can induce long-term dynamical instabilities in the planetary system and can even change the size of the habitable zone(s) of the component stars. However, the overall fraction of binaries that can host stable planetary systems is not greatly affected by either the assumed binary population or the density of the star-forming region. Instead, the critical factor in determining how many stable planetary systems exist in the Galaxy is the stellar binary fraction – the more stars that are born as singles in stellar nurseries, the higher the fraction of stable planetary systems.

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Niedzielski, A., E. Villaver, M. Adamów, K. Kowalik, A. Wolszczan, and G. Maciejewski. "Tracking Advanced Planetary Systems (TAPAS) with HARPS-N." Astronomy & Astrophysics 648 (April 2021): A58. http://dx.doi.org/10.1051/0004-6361/202037892.

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Context. We present the current status of and new results from our search for exoplanets in a sample of solar-mass evolved stars observed with the HARPS-N and the 3.6 m Telescopio Nazionale Galileo (TNG), and the High-Resolution Spectrograph (HRS) and the 9.2 m Hobby-Eberly Telescope (HET). Aims. The aim of this project is to detect and characterize planetary-mass companions to solar-mass stars in a sample of 122 targets at various stages of evolution from the main sequence to the red giant branch, mostly subgiants and giants, selected from the Pennsylvania-Toruń Planet Search sample, and to use this sample to study relations between stellar properties, such as metallicity, luminosity, and the planet occurrence rate. Methods. This work is based on precise radial velocity (RV) measurements. We have observed the program stars for up to 14 yr with the HET/HRS and the TNG/HARPS-N. Results. We present the analysis of RV measurements with the HET/HRS and the TNG/HARPS-N of four solar-mass stars, HD 4760, HD 96992, BD+02 3313, and TYC 0434-04538-1. We found that HD 4760 hosts a companion with a minimum mass of 13.9 MJ (a = 1.14 au, e = 0.23); HD 96992 is a host to a m sin i = 1.14 MJ companion on an a = 1.24 au and e = 0.41 orbit, and TYC 0434-04538-1 hosts an m sin i = 6.1 MJ companion on an a = 0.66 au and e = 0.08 orbit. In the case of BD+02 3313 we found a correlation between the measured RVs and one of the stellar activity indicators, suggesting that the observed RV variations may either originate in stellar activity or be caused by the presence of an unresolved companion. We also discuss the current status of the project and a statistical analysis of the RV variations in our sample of target stars. Conclusions. In our sample of 122 solar-mass stars, 49 ± 5% of them appear to be single and 16 ± 3% spectroscopic binaries. The three giants hosting low-mass companions presented in this paper join the six previously identified giants in the sample.

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Kovacs, Geza. "More planetary candidates from K2 Campaign 5 using TRAN_K2." Astronomy & Astrophysics 643 (November 2020): A169. http://dx.doi.org/10.1051/0004-6361/202038726.

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Context. The exquisite precision of space-based photometric surveys and the unavoidable presence of instrumental systematics and intrinsic stellar variability call for the development of sophisticated methods that distinguish these signal components from those caused by planetary transits. Aims. Here, we introduce the standalone Fortran code TRAN_K2 to search for planetary transits under the colored noise of stellar variability and instrumental effects. We use this code to perform a survey to uncover new candidates. Methods. Stellar variability is represented by a Fourier series and, when necessary, by an autoregressive model aimed at avoiding excessive Gibbs overshoots at the edges. For the treatment of systematics, a cotrending and an external parameter decorrelation were employed by using cotrending stars with low stellar variability as well as the chip position and the background flux level at the target. The filtering was done within the framework of the standard weighted least squares, where the weights are determined iteratively, to allow a robust fit and to separate the transit signal from stellar variability and systematics. Once the periods of the transit components are determined from the filtered data by the box-fitting least squares method, we reconstruct the full signal and determine the transit parameters with a higher accuracy. This step greatly reduces the excessive attenuation of the transit depths and minimizes shape deformation. Results. We tested the code on the field of Campaign 5 of the K2 mission. We detected 98% of the systems with all their candidate planets as previously reported by other authors. We then surveyed the whole field and discovered 15 new systems. An additional three planets were found in three multiplanetary systems, and two more planets were found in a previously known single-planet system.

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Swastik, C., Ravinder K. Banyal, Mayank Narang, P. Manoj, T. Sivarani, S. P. Rajaguru, Athira Unni, and Bihan Banerjee. "Galactic Chemical Evolution of Exoplanet Hosting Stars: Are High-mass Planetary Systems Young?" Astronomical Journal 164, no. 2 (July 19, 2022): 60. http://dx.doi.org/10.3847/1538-3881/ac756a.

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Abstract The imprints of stellar nucleosynthesis and chemical evolution of the galaxy can be seen in different stellar populations, with older generation stars showing higher α-element abundances and the later generations becoming enriched with iron-peak elements. The evolutionary connections and chemical characteristics of circumstellar disks, stars, and their planetary companions can be inferred by studying the interdependence of planetary and host star properties. Numerous studies in the past have confirmed that high-mass giant planets are commonly found around metal-rich stars, while the stellar hosts of low-mass planets have a wide range of metallicity. In this work, we analyzed the detailed chemical abundances for a sample of >900 exoplanet hosting stars drawn from different radial velocity and transit surveys. We correlate the stellar abundance trends for α- and iron-peak elements with the planets’ mass. We find the planet mass–abundance correlation to be primarily negative for α-elements and marginally positive or zero for the iron-peak elements, indicating that stars hosting giant planets are relatively younger. This is further validated by the age of the host stars obtained from isochrone fitting. The later enrichment of protoplanetary material with iron and iron-peak elements is also consistent with the formation of the giant planets via the core accretion process. A higher metal fraction in the protoplanetary disk is conducive to rapid core growth, thus providing a plausible route for the formation of giant planets. This study, therefore, indicates that the observed trends in stellar abundances and planet mass are most likely a natural consequence of Galactic chemical evolution.

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Hopkins, Philip F., Norman Murray, Eliot Quataert, and Todd A. Thompson. "A maximum stellar surface density in dense stellar systems." Monthly Notices of the Royal Astronomical Society: Letters 401, no. 1 (January 2010): L19—L23. http://dx.doi.org/10.1111/j.1745-3933.2009.00777.x.

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Coccato, Lodovico. "Planetary nebulae as kinematic tracers of galaxy halos." Proceedings of the International Astronomical Union 11, A29B (August 2015): 20–25. http://dx.doi.org/10.1017/s1743921316004361.

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AbstractThe kinematics and dynamical properties of galaxy stellar halos are difficult to measure, given the faint surface brightness that characterizes these regions. Gas-rich systems such as spiral galaxies can be probed using the radio Hi emission. Early-type galaxies contain less gas, therefore alternative kinematic tracers need to be used. Planetary Nebulae (PNe) can be easily detected far out in the halo thanks to their bright [O iii] emission at 5007 Å. It is therefore possible to map the halo kinematics also in early-type galaxies, typically out to 5 effective radii or beyond. Thanks to the recent spectroscopic surveys targeting extra-galactic PNe, we can now rely on few tens of galaxies where the kinematics of the stellar halos are measured. I will discuss the most important results: (a) the relation of the stellar surface brightness and the PNe number density; (b) the velocity and velocity dispersion two-dimensional fields; (c) the radial profiles of angular momentum; and (d) the relation between the derived kinematics physical properties of the host galaxies.

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Li, Daohai, Alexander J. Mustill, and Melvyn B. Davies. "Flyby encounters between two planetary systems II: exploring the interactions of diverse planetary system architectures." Monthly Notices of the Royal Astronomical Society 496, no. 2 (June 9, 2020): 1149–65. http://dx.doi.org/10.1093/mnras/staa1622.

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ABSTRACT Planetary systems formed in clusters may be subject to stellar encounter flybys. Here, we create a diverse range of representative planetary systems with different orbital scales and planets’ masses and examine encounters between them in a typical open cluster. We first explore the close-in multisuper Earth systems ≲0.1 au. They are resistant to flybys in that only ones inside a few au can destabilize a planet or break the resonance between such planets. But these systems may capture giant planets on to wide orbits from the intruding star during distant flybys. If so, the original close-in small planets’ orbits may be tilted together through Kozai–Lidov mechanism, forming a ‘cold’ system that is significantly inclined against the equator of the central host. Moving to the intermediately placed planets around solar-like stars, we find that the planets’ mass gradient governs the systems’ long-term evolution post-encounter: more massive planets have better chances to survive. Also, a system’s angular momentum deficit, a quantity describing how eccentric/inclined the orbits are, measured immediately after the encounter, closely relates to the longevity of the systems – whether or not and when the systems turn unstable in the ensuing evolution millions of years post-encounter. We compare the orbits of the surviving planets in the unstable systems through (1) the immediate consequence of the stellar fly or (2) internal interplanetary scattering long post-encounter and find that those for the former are systematically colder. Finally, we show that massive wide-orbit multiplanet systems like that of HR 8799 can be easily disrupted and encounters at a few hundreds of au suffice.

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Cuntz, M., G. E. Luke, M. J. Millard, L. Boyle, and S. D. Patel. "An Early Catalog of Planet-hosting Multiple-star Systems of Order Three and Higher." Astrophysical Journal Supplement Series 263, no. 2 (December 1, 2022): 33. http://dx.doi.org/10.3847/1538-4365/ac9302.

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Abstract We present a catalog (status 2022 July 1) of triple and higher-order systems identified containing exoplanets based on data from the literature, including various analyses. We explore statistical properties of the systems with a focus on both the stars and the planets. So far, about 30 triple systems and one to three quadruple systems, including (mildly) controversial cases, have been found. The total number of planets is close to 40. All planet-hosting triple-star systems are highly hierarchic, consisting of a quasi-binary complemented by a distant stellar component, which is in orbit about the common center of mass. Furthermore, the quadruple systems are in fact pairs of close binaries (“double–doubles”), with one binary harboring a planet. For the different types of star–planet systems, we introduce a template for the classifications of planetary orbital configurations in correspondence to the hierarchy of the system and the planetary host. The data show that almost all stars are main-sequence stars, as expected. However, the stellar primaries tend to be more massive (i.e., corresponding to spectral types A, F, and G) than expected from single-star statistics, a finding also valid for stellar secondaries but less pronounced. Tertiary stellar components are almost exclusively low-mass stars of spectral type M. Almost all planets have been discovered based on either the Radial Velocity method or the Transit method. Both gas giants (the dominant type) and terrestrial planets (including super-Earths) have been identified. We anticipate the expansion of this database in the light of future planetary search missions.

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Kubyshkina, Daria, Aline A. Vidotto, Carolina Villarreal D’Angelo, Stephen Carolan, Gopal Hazra, and Ilaria Carleo. "Atmospheric mass-loss and stellar wind effects in young and old systems – I. Comparative 3D study of TOI-942 and TOI-421 systems." Monthly Notices of the Royal Astronomical Society 510, no. 2 (December 11, 2021): 2111–26. http://dx.doi.org/10.1093/mnras/stab3594.

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ABSTRACT At young ages, when radiation from the host star is high, and the planet is hot and inflated after formation, planetary atmospheric mass-loss can be extremely strong compared to older planets. In turn, stellar winds are faster and denser for young stars compared to evolved main-sequence stars. Their interaction with escaping planetary atmospheres can substantially affect atmospheric mass-loss rates, as well as the observable signatures of escaping atmospheres, with both effects expected to occur differently for young and evolved planets. We perform a comparative study of two systems around stars of similar masses but very different ages (50 Myr and 9 Gyr): TOI-942 and TOI-421. Both stars host two sub-Neptune-like planets at similar orbits and in similar mass ranges, which allows a direct comparison of the atmospheric escape and interactions with the stellar winds in the young and old systems. We perform the 3D atmospheric modelling of the four planets in TOI-942 and TOI-421 systems and make the theoretical predictions of possible observational signatures in Ly α absorption. We find that accounting for the stellar wind interacting with planetary atmospheres is crucial for the interpretation of the observations for young planets. Additionally, we show that a particular energy distribution along the XUV spectra has a minor effect on the atmospheric mass-loss rates, but it is of crucial importance for modelling the Ly α absorption and therefore for interpretation of observations.

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31

Johnstone, C. P., E. Pilat-Lohinger, T. Lüftinger, M. Güdel, and A. Stökl. "Stellar activity and planetary atmosphere evolution in tight binary star systems." Astronomy & Astrophysics 626 (June 2019): A22. http://dx.doi.org/10.1051/0004-6361/201832805.

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Context. In tight binary star systems, tidal interactions can significantly influence the rotational and orbital evolution of both stars, and therefore their activity evolution. This can have strong effects on the atmospheric evolution of planets that are orbiting the two stars. Aims. In this paper, we aim to study the evolution of stellar rotation and of X-ray and ultraviolet (XUV) radiation in tight binary systems consisting of two solar mass stars and use our results to study planetary atmosphere evolution in the habitable zones of these systems. Methods. We have applied a rotation model developed for single stars to binary systems, taking into account the effects of tidal interactions on the rotational and orbital evolution of both stars. We used empirical rotation-activity relations to predict XUV evolution tracks for the stars, which we used to model hydrodynamic escape of hydrogen dominated atmospheres. Results. When significant, tidal interactions increase the total amount of XUV energy emitted, and in the most extreme cases by up to factor of ~50. We find that in the systems that we study, habitable zone planets with masses of 1 M⊕ can lose huge hydrogen atmospheres due to the extended high levels of XUV emission, and the time that is needed to lose these atmospheres depends on the binary orbital separation. For some orbital separations, and when the stars are born as rapid rotators, it is also possible for tidal interactions to protect atmospheres from erosion by quickly spinning down the stars. For very small orbital separations, the loss of orbital angular momentum by stellar winds causes the two stars to merge. We suggest that the merging of the two stars could cause previously frozen planets to become habitable due to the habitable zone boundaries moving outwards.

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Spalding, Christopher, and Konstantin Batygin. "MAGNETIC ORIGINS OF THE STELLAR MASS-OBLIQUITY CORRELATION IN PLANETARY SYSTEMS." Astrophysical Journal 811, no. 2 (September 24, 2015): 82. http://dx.doi.org/10.1088/0004-637x/811/2/82.

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Montet, Benjamin T., and John Asher Johnson. "MODEL-INDEPENDENT STELLAR AND PLANETARY MASSES FROM MULTI-TRANSITING EXOPLANETARY SYSTEMS." Astrophysical Journal 762, no. 2 (December 20, 2012): 112. http://dx.doi.org/10.1088/0004-637x/762/2/112.

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34

Albrecht, Simon H., Rebekah I. Dawson, and Joshua N. Winn. "Stellar Obliquities in Exoplanetary Systems." Publications of the Astronomical Society of the Pacific 134, no. 1038 (August 1, 2022): 082001. http://dx.doi.org/10.1088/1538-3873/ac6c09.

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Abstract The rotation of a star and the revolutions of its planets are not necessarily aligned. This article reviews the measurement techniques, key findings, and theoretical interpretations related to the obliquities (spin–orbit angles) of planet-hosting stars. The best measurements are for stars with short-period giant planets, which have been found on prograde, polar, and retrograde orbits. It seems likely that dynamical processes such as planet–planet scattering and secular perturbations are responsible for tilting the orbits of close-in giant planets, just as those processes are implicated in exciting orbital eccentricities. The observed dependence of the obliquity on orbital separation, planet mass, and stellar structure suggests that in some cases, tidal dissipation damps a star’s obliquity within its main-sequence lifetime. The situation is not as clear for stars with smaller or wider-orbiting planets. Although the earliest measurements of such systems tended to find low obliquities, some glaring exceptions are now known in which the star’s rotation is misaligned with respect to the coplanar orbits of multiple planets. In addition, statistical analyses based on projected rotation velocities and photometric variability have found a broad range of obliquities for F-type stars hosting compact multiple-planet systems. The results suggest it is unsafe to assume that stars and their protoplanetary disks are aligned. Primordial misalignments might be produced by neighboring stars or more complex events that occur during the epoch of planet formation.

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35

Palmer, P. L., and J. Papaloizou. "Instability in spherical stellar systems." Monthly Notices of the Royal Astronomical Society 224, no. 4 (February 1, 1987): 1043–53. http://dx.doi.org/10.1093/mnras/224.4.1043.

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36

Shapiro, Stuart L., and Saul A. Teukolsky. "Relativistic Stellar Systems with Rotation." Astrophysical Journal 419 (December 1993): 636. http://dx.doi.org/10.1086/173514.

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37

Merritt, David, and J. A. Sellwood. "Bending instabilities in stellar systems." Astrophysical Journal 425 (April 1994): 551. http://dx.doi.org/10.1086/174005.

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Gurzadyan, V. G., and A. A. Kocharyan. "Relative chaos in stellar systems." Astrophysics and Space Science 135, no. 2 (1987): 307–24. http://dx.doi.org/10.1007/bf00641567.

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39

Lau, Jun Yan, and James Binney. "Relaxation of spherical stellar systems." Monthly Notices of the Royal Astronomical Society 490, no. 1 (September 19, 2019): 478–90. http://dx.doi.org/10.1093/mnras/stz2567.

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ABSTRACTA total of 10 000 simulations of 1000 particle realizations of the same cluster are computed by direct force summation. After three crossing times self-gravity has amplified the original Poisson noise more than tenfold on large scales, and the amplification is still far from complete. The cluster’s fundamental dipole mode is strongly excited by Poisson noise, and this mode makes a major contribution to driving diffusion of stars in energy. The diffusive flow through action space is computed for the simulations and compared with the predictions of both Chandrasekhar’s local-scattering theory and the Balescu–Lenard (BL) equation. The predictions of local-scattering theory are qualitatively wrong because the latter neglects self-gravity. These results imply that local-scattering theory can account for only a fraction of a cluster’s relaxation. Future work on cluster evolution should employ either N-body simulation or the BL equation. However, significant code development will be required to make use of the BL equation practicable and the way forward may be to merge BL theory with local scattering theory so fluctuations of every scale are efficiently handled.

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40

Dejonghe, Herwig. "On entropy and stellar systems." Astrophysical Journal 320 (September 1987): 477. http://dx.doi.org/10.1086/165565.

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41

Evans, N. W., and J. An. "Hypervirial models of stellar systems." Monthly Notices of the Royal Astronomical Society 360, no. 2 (June 21, 2005): 492–98. http://dx.doi.org/10.1111/j.1365-2966.2005.09078.x.

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42

Ciotti, L. "Tomography of collisionless stellar systems." Celestial Mechanics & Dynamical Astronomy 60, no. 4 (December 1994): 401–7. http://dx.doi.org/10.1007/bf00692024.

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Roberts, Paul H. "Planetary dynamos: from equipartition to asymptopia." Proceedings of the International Astronomical Union 4, S259 (November 2008): 259–70. http://dx.doi.org/10.1017/s1743921309030609.

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AbstractThis review focuses on three topics relevant to naturally-occurring dynamos. The first considers how a common belief, that states of equipartition of magnetic and kinetic energy are preferred in nonrotating systems, is modified when Coriolis forces are influential, as in the Earth's core. The second reviews current difficulties faced by planetary and stellar dynamo theories, particularly in representing the sub-grid scales. The third discusses recent attempts to extract scaling laws from numerical integrations of the Boussinesq dynamo equations.

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44

Rodet, Laetitia, and Dong Lai. "The impact of stellar clustering on the observed multiplicity of super-earth systems: outside–in cascade of orbital misalignments initiated by stellar flybys." Monthly Notices of the Royal Astronomical Society 509, no. 1 (October 21, 2021): 1010–23. http://dx.doi.org/10.1093/mnras/stab3046.

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ABSTRACT A recent study suggests that the observed multiplicity of super-Earth (SE) systems is correlated with stellar overdensities: field stars in high phase-space density environments have an excess of single-planet systems compared to stars in low-density fields. This correlation is puzzling as stellar clustering is expected to influence mostly the outer part of planetary systems. Here, we examine the possibility that stellar flybys indirectly excite the mutual inclinations of initially coplanar SEs, breaking their co-transiting geometry. We propose that flybys excite the inclinations of exterior substellar companions, which then propagate the perturbation to the inner SEs. Using analytical calculations of the secular coupling between SEs and companions, together with numerical simulations of stellar encounters, we estimate the expected number of ‘effective’ flybys per planetary system that lead to the destruction of the SE co-transiting geometry. Our analytical results can be rescaled easily for various SE and companion properties (masses and semimajor axes) and stellar cluster parameters (density, velocity dispersion, and lifetime). We show that for a given SE system, there exists an optimal companion architecture that leads to the maximum number of effective flybys; this results from the trade-off between the flyby cross-section and the companion’s impact on the inner system. Subject to uncertainties in the cluster parameters, we conclude that this mechanism is inefficient if the SE system has a single exterior companion, but may play an important role in ‘SE + two companions’ systems that were born in dense stellar clusters. Whether this effect causes the observed correlation between planet multiplicity and stellar overdensities remains to be confirmed.

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45

Martin, Rebecca G., Mario Livio, Jeremy L. Smallwood, and Cheng Chen. "Asteroid belt survival through stellar evolution: dependence on the stellar mass." Monthly Notices of the Royal Astronomical Society: Letters 494, no. 1 (February 13, 2020): L17—L21. http://dx.doi.org/10.1093/mnrasl/slaa030.

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ABSTRACT Polluted white dwarfs are generally accreting terrestrial-like material that may originate from a debris belt like the asteroid belt in the Solar system. The fraction of white dwarfs that are polluted drops off significantly for white dwarfs with masses $M_{\rm WD}\gtrsim 0.8\, \rm M_\odot$. This implies that asteroid belts and planetary systems around main-sequence (MS) stars with mass $M_{\rm MS}\gtrsim 3\, \rm M_\odot$ may not form because of the intense radiation from the star. This is in agreement with current debris disc and exoplanet observations. The fraction of white dwarfs that show pollution also drops off significantly for low-mass white dwarfs $(M_{\rm WD}\lesssim 0.55\, \rm M_\odot)$. However, the low-mass white dwarfs that do show pollution are not currently accreting but have accreted in the past. We suggest that asteroid belts around MS stars with masses $M_{\rm MS}\lesssim 2\, \rm M_\odot$ are not likely to survive the stellar evolution process. The destruction likely occurs during the AGB phase and could be the result of interactions of the asteroids with the stellar wind, the high radiation, or, for the lowest mass stars that have an unusually close-in asteroid belt, scattering during the tidal orbital decay of the inner planetary system.

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Stock, Katja, Maxwell X. Cai, Rainer Spurzem, M. B. N. Kouwenhoven, and Simon Portegies Zwart. "On the survival of resonant and non-resonant planetary systems in star clusters." Monthly Notices of the Royal Astronomical Society 497, no. 2 (July 13, 2020): 1807–25. http://dx.doi.org/10.1093/mnras/staa2047.

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ABSTRACT Despite the discovery of thousands of exoplanets in recent years, the number of known exoplanets in star clusters remains tiny. This may be a consequence of close stellar encounters perturbing the dynamical evolution of planetary systems in these clusters. Here, we present the results from direct N-body simulations of multiplanetary systems embedded in star clusters containing N = 8k, 16k, 32k, and 64k stars. The planetary systems, which consist of the four Solar system giant planets Jupiter, Saturn, Uranus, and Neptune, are initialized in different orbital configurations, to study the effect of the system architecture on the dynamical evolution of the entire planetary system, and on the escape rate of the individual planets. We find that the current orbital parameters of the Solar system giants (with initially circular orbits, as well as with present-day eccentricities) and a slightly more compact configuration, have a high resilience against stellar perturbations. A configuration with initial mean-motion resonances of 3:2, 3:2, and 5:4 between the planets, which is inspired by the Nice model, and for which the two outermost planets are usually ejected within the first 105 yr, is in many cases stabilized due to the removal of the resonances by external stellar perturbation and by the rapid ejection of at least one planet. Assigning all planets the same mass of 1 MJup almost equalizes the survival fractions. Our simulations reproduce the broad diversity amongst observed exoplanet systems. We find not only many very wide and/or eccentric orbits, but also a significant number of (stable) retrograde orbits.

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Arbab, Behzad Bojnordi, and Sohrab Rahvar. "Close stellar encounters kicking planets out of habitable zone in various stellar environments." International Journal of Modern Physics D 30, no. 09 (May 19, 2021): 2150063. http://dx.doi.org/10.1142/s0218271821500632.

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Continuous habitability of a planet is a critical condition for advanced forms of life to appear, but it can be endangered by astronomical events such as stellar encounters. The purpose of this study is to analyze close stellar encounters able to change planetary orbits initially in circumstellar habitable zones and to investigate the expected encounter rates in a variety of stellar environments. Using gravitational simulations for three-body systems, this study analyzed the dependencies of encounter impact-parameters with kinematic, geometric, and habitability parameters of the system. We also used kinematic properties of various stellar regions and estimated encounter rates of the events. The expected number of threatening stellar encounters in the Solar neighborhood is [Formula: see text] in 4 billion years, while for the Galactic bulge environment, we expect approximately 5.5 times the value. The encounter rates for other stellar environments are calculated and spheroidal dwarf galaxies and globular clusters encounter rates are estimated. The results show that in contrast with the solar neighborhood, close stellar encounters can play a significant role in the expected number of planets with continuous habitability in dense stellar environments. Another notable result shows that threatening stellar encounter rate follows the number density of stars, and is not strongly dependent of the region’s velocity dispersion. Further investigations are needed to study long-term multiple planetary systems and how they can change the overall expected value of continuously habitable planets.

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Pillitteri, Ignazio, S. J. Wolk, A. Maggio, and T. Matsakos. "Star-Planet Interaction: The Curious Case of the Planet Spoon-feeding Its Host Star (and Other Amenities)." Proceedings of the International Astronomical Union 10, S314 (November 2015): 262–63. http://dx.doi.org/10.1017/s174392131500592x.

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AbstractWe report two cases of Star-Planet Interaction (SPI) in two systems with hot Jupiters: HD 189733 and HD 17156. We used HST-COS to study the FUV variability of HD 189733 after the planetary eclipse. With the support of MHD simulations, we evince that material is likely evaporating from the planet and accreting onto the parent star. This produces a hot spot on the stellar surface, co-moving with the planetary motion and responsible of the X-ray and FUV variability at peculiar planetary phases. In HD 17156, which hosts a hot Jupiter in an eccentric orbit, we observed an enhancement of the X-ray activity at the passage of its planet at the periastron. The origin can be due to magnetic reconnection between the planetary and stellar magnetic fields, or due to material tidally stripped from the planet and accreting onto the star.

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Flammini Dotti, Francesco, M. B. N. Kouwenhoven, Qi Shu, Wei Hao, and Rainer Spurzem. "Planetary systems in a star cluster II: intermediate-mass black holes and planetary systems." Monthly Notices of the Royal Astronomical Society 497, no. 3 (July 27, 2020): 3623–37. http://dx.doi.org/10.1093/mnras/staa2188.

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ABSTRACT Most stars form in dense stellar environments. It is speculated that some dense star clusters may host intermediate-mass black holes (IMBHs), which may have formed from runaway collisions between high-mass stars, or from the mergers of less massive black holes. Here, we numerically explore the evolution of populations of planets in star clusters with an IMBH. We study the dynamical evolution of single-planet systems and free-floating planets, over a period of 100 Myr, in star clusters without an IMBH, and in clusters with a central IMBH of mass $100\, \mathrm{M}_\odot$ or $200\, \mathrm{M}_\odot$. In the central region ($r\lesssim 0.2$ pc), the IMBH’s tidal influence on planetary systems is typically 10 times stronger than the average neighbour star. For a star cluster with a $200\, \mathrm{M}_\odot$ IMBH, the region in which the IMBH’s influence is stronger within the virial radius (∼1 pc). The IMBH quenches mass segregation, and the stars in the core tend to move towards intermediate regions. The ejection rate of both stars and planets is higher when an IMBH is present. The rate at which planets are expelled from their host star rate is higher for clusters with higher IMBH masses, for t < 0.5trh, while remains mostly constant while the star cluster fills its Roche lobe, similar to a star cluster without an IMBH. The disruption rate of planetary systems is higher in initially denser clusters, and for wider planetary orbits, but this rate is substantially enhanced by the presence of a central IMBH.

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Niraula, Prajwal, Avi Shporer, Ian Wong, and Julien de Wit. "Revisiting Kepler Transiting Systems: Unvetting Planets and Constraining Relationships among Harmonics in Phase Curves." Astronomical Journal 163, no. 4 (March 15, 2022): 172. http://dx.doi.org/10.3847/1538-3881/ac4f64.

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Abstract Space-based photometric missions widely use statistical validation tools for vetting transiting planetary candidates, particularly when other traditional methods of planet confirmation are unviable. In this paper, we refute the planetary nature of three previously validated planets—Kepler-854 b, Kepler-840 b, and Kepler-699 b—and possibly a fourth, Kepler-747 b, using updated stellar parameters from Gaia and phase-curve analysis. In all four cases, the inferred physical radii rule out their planetary nature given the stellar radiation the companions receive. For Kepler-854 b, the mass derived from the host star’s ellipsoidal variation, which had not been part of the original vetting procedure, similarly points to a nonplanetary value. To contextualize our understanding of the phase curve for stellar-mass companions in particular and extend our understanding of high-order harmonics, we examine Kepler eclipsing binaries with periods between 1.5 and 10 days. Using a sample of 20 systems, we report a strong power-law relation between the second cosine harmonic of the phase-curve signal and the higher cosine harmonics, which supports the hypothesis that those signals arise from the tidal interaction between the binary components. We find that the ratio between the second- and third-harmonic amplitudes is 2.24 ± 0.48, in good agreement with the expected value of 2.4 from the classical formalism for the ellipsoidal distortion.

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Journal articles on the topic 'Stellar astronomy and planetary systems'

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