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26 pages, 1081 KiB

Open AccessArticle

The “Drake Equation” of Exomoons—A Cascade of Formation, Stability and Detection

by Gyula M. Szabó, Jean Schneider, Zoltán Dencs and Szilárd Kálmán

Universe 2024, 10(3), 110; https://doi.org/10.3390/universe10030110 - 28 Feb 2024

Cited by 1 | Viewed by 1868

Abstract

After 25 years of the prediction of the possibility of observations, and despite the many hundreds of well-studied transiting exoplanet systems, we are still waiting for the announcement of the first confirmed exomoon. We follow the “cascade” structure of the Drake equation but [...] Read more.

After 25 years of the prediction of the possibility of observations, and despite the many hundreds of well-studied transiting exoplanet systems, we are still waiting for the announcement of the first confirmed exomoon. We follow the “cascade” structure of the Drake equation but apply it to the chain of events leading to a successful detection of an exomoon. The scope of this paper is to reveal the structure of the problem, rather than to give a quantitative solution. We identify three important steps that can lead us to discovery. The steps are the formation, the orbital dynamics and long-term stability, and the observability of a given exomoon in a given system. This way, the question will be closely related to questions of star formation, planet formation, five possible pathways of moon formation; long-term dynamics of evolved planet systems involving stellar and planetary rotation and internal structure; and the proper evaluation of the observed data, taking the correlated noise of stellar and instrumental origin and the sampling function also into account. We highlight how a successful exomoon observation and the interpretations of the expected further measurements prove to be among the most complex and interdisciplinary questions in astrophysics. Full article

(This article belongs to the Special Issue The Royal Road: Eclipsing Binaries and Transiting Exoplanets)

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17 pages, 6172 KiB

Open AccessArticle

Alpha Centauri: Disc Dynamics, Planet Stability, Detectability

by Nicolás Cuello and Mario Sucerquia

Universe 2024, 10(2), 64; https://doi.org/10.3390/universe10020064 - 31 Jan 2024

Cited by 2 | Viewed by 1613 | Correction

Abstract

Alpha Centauri is a triple stellar system, and it contains the closest star to Earth (Proxima Centauri). Over the last decades, the stars in Alpha Cen and their orbits have been investigated in great detail. However, the possible scenarios for planet formation and [...] Read more.

Alpha Centauri is a triple stellar system, and it contains the closest star to Earth (Proxima Centauri). Over the last decades, the stars in Alpha Cen and their orbits have been investigated in great detail. However, the possible scenarios for planet formation and evolution in this triple stellar system remain to be explored further. First, we present a 3D hydrodynamical simulation of the circumstellar discs in the binary Alpha Cen AB. Then, we compute stability maps for the planets within Alpha Cen obtained through N-body integrations. Last, we estimate the radial velocity (RV) signals of such planets. We find that the circumstellar discs within the binary cannot exceed 3 au in radius and that the available dust mass to form planets is about 30

M_{\oplus}

. Planets around A and B are stable if their semimajor axes are below 3 au, while those around C are stable and remain unperturbed by the binary AB. For rocky planets, the planetary mass has only a mild effect on the stability. Therefore, Alpha Cen could have formed and hosted rocky planets around each star, which may be detected with RV methods in the future. The exoplanetary hunt in this triple stellar system must continue. Full article

(This article belongs to the Special Issue The Royal Road: Eclipsing Binaries and Transiting Exoplanets)

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15 pages, 1181 KiB

Open AccessArticle

Update on WASP-19

by Judith Korth and Hannu Parviainen

Universe 2024, 10(1), 12; https://doi.org/10.3390/universe10010012 - 27 Dec 2023

Cited by 3 | Viewed by 1619

Abstract

Tidal interaction between a star and a close-in massive exoplanet causes the planetary orbit to shrink and eventually leads to tidal disruption. Understanding orbital decay in exoplanetary systems is crucial for advancing our knowledge of planetary formation and evolution. Moreover, it sheds light [...] Read more.

Tidal interaction between a star and a close-in massive exoplanet causes the planetary orbit to shrink and eventually leads to tidal disruption. Understanding orbital decay in exoplanetary systems is crucial for advancing our knowledge of planetary formation and evolution. Moreover, it sheds light on the broader question of the long-term stability of planetary orbits and the intricate interplay of gravitational forces within stellar systems. Analyzing Transiting Exoplanet Survey Satellite (TESS) data for the ultra-short period gas giant WASP-19, we aim to measure orbital period variations and constrain the stellar tidal quality parameter. For this, we fitted the TESS observations together with two WASP-19 transits observed using the Las Cumbres Observatory Global Telescope (LCOGT) and searched for orbital decay in combination with previously published transit times. As a result, we find a deviation from the constant orbital period at the

7 σ

level. The orbital period changes at a rate of

\dot{P} = - 3.7 \pm 0.5 ms {year}^{- 1}

, which translates into a tidal quality factor of

Q_{★}^{'} = (7 \pm 1) \times 10^{5}

. We additionally modeled WASP-19 b’s phase curve using the new TESS photometry and obtained updated values for the planet’s eclipse depth, dayside temperature, and geometric albedo. We estimate an eclipse depth of

520 \pm 60

ppm, which is slightly higher than previous estimates and corresponds to a dayside brightness temperature of

2400 \pm 60

K and geometric albedo of

0.20 \pm 0.04

. Full article

(This article belongs to the Special Issue The Royal Road: Eclipsing Binaries and Transiting Exoplanets)

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17 pages, 637 KiB

Open AccessArticle

The Apparent Tidal Decay of WASP-4 b Can Be Explained by the Rømer Effect

by Jan-Vincent Harre and Alexis M. S. Smith

Universe 2023, 9(12), 506; https://doi.org/10.3390/universe9120506 - 5 Dec 2023

Cited by 4 | Viewed by 1494

Abstract

Tidal orbital decay plays a vital role in the evolution of hot Jupiter systems. As of now, this has only been observationally confirmed for the WASP-12 system. There are a few other candidates, including WASP-4 b, but no conclusive result could be obtained [...] Read more.

Tidal orbital decay plays a vital role in the evolution of hot Jupiter systems. As of now, this has only been observationally confirmed for the WASP-12 system. There are a few other candidates, including WASP-4 b, but no conclusive result could be obtained for these systems as of yet. In this study, we present an analysis of new TESS data of WASP-4 b together with archival data, taking the light–time effect (LTE) induced by the second planetary companion into account as well. We make use of three different Markov chain Monte Carlo models: a circular orbit with a constant orbital period, a circular orbit with a decaying orbit, and an elliptical orbit with apsidal precession. This analysis is repeated for four cases. The first case features no LTE correction, with the remaining three cases featuring three different timing correction approaches because of the large uncertainties of the ephemeris of planet c. Comparison of these models yields no conclusive answer to the cause of WASP-4 b’s apparent transit timing variations. A broad range of values of the orbital decay and apsidal precession parameters are possible, depending on the LTE correction. However, the LTE caused by planet c can explain on its own—in full—the observed transit timing variations of planet b, with no orbital decay or apsidal precession being required at all. This work highlights the importance of continued photometric and spectroscopic monitoring of hot Jupiters. Full article

(This article belongs to the Special Issue The Royal Road: Eclipsing Binaries and Transiting Exoplanets)

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44 pages, 1998 KiB

Open AccessArticle

Photodynamical Modeling of the Compact, Multiply Eclipsing Systems KIC 5255552, KIC 7668648, KIC 10319590, and EPIC 220204960

by Jerome A. Orosz

Universe 2023, 9(12), 505; https://doi.org/10.3390/universe9120505 - 2 Dec 2023

Cited by 2 | Viewed by 1471

Abstract

We present photodynamical models of four eclipsing binary systems that show strong evidence of being members of higher-order multiple systems via their strong eclipse timing variations and/or via the presence of extra eclipse events. Three of these systems are from the main Kepler [...] Read more.

We present photodynamical models of four eclipsing binary systems that show strong evidence of being members of higher-order multiple systems via their strong eclipse timing variations and/or via the presence of extra eclipse events. Three of these systems are from the main Kepler mission, and the other is from the K2 mission. We provide some ground-based radial velocities measurements for the three Kepler systems and make use of recent light curves from the TESS mission. Our sample consists of two 2 + 1 systems and two 2 + 2 systems. The first 2 + 1 system, KIC 7668648, consists of an eclipsing binary (

P_{bin}

= 27.8 days) with late-type stars (

M_{1} = 0.8403 \pm 0.0090

M_{⊙}

,

R_{1} = 1.0066 \pm 0.0036 R_{⊙}

and

M_{2} = 0.8000 \pm 0.0085 M_{⊙}

,

R_{2} = 0.8779 \pm 0.0032 R_{⊙}

) with a low-mass star (

M_{3} = 0.2750 \pm 0.0029 M_{⊙}

,

R_{3} = 0.2874 \pm 0.0010 R_{⊙}

) on a roughly coplanar outer orbit (

P_{3} = 208

days). There are several eclipse events involving the third star that allow for the precise determination of the system parameters. The second 2 + 1 system, KIC 10319590, consists of a binary (

P_{bin} = 21.3

days) with late-type stars (

M_{1} = 1.108 \pm 0.043 M_{⊙}

,

R_{1} = 1.590 \pm 0.019 R_{⊙}

and

M_{2} = 0.743 \pm 0.023 M_{⊙}

,

R_{2} = 0.7180 \pm 0.0086 R_{⊙}

) that stopped eclipsing about a third of the way into the nominal Kepler mission. We show here that the third star in this system is a Sun-like star (

M_{3} = 1.049 \pm 0.038 M_{⊙}

,

R_{3} = 1.39 \pm 0.11 R_{⊙}

) on an inclined outer orbit (

P_{3} = 456

days). In this case, there are no extra eclipse events. We present the first comprehensive solution for KIC 5255552 and demonstrate that it is a 2 + 2 system consisting of an eclipsing binary (

P_{bin, 1} = 32.5

days) with late-type stars (

M_{1} = 0.950 \pm 0.018 M_{⊙}

,

R_{1} = 0.9284 \pm 0.0063 R_{⊙}

and

M_{2} = 0.745 \pm 0.014 M_{⊙}

,

R_{2} = 0.6891 \pm 0.0051 R_{⊙}

) paired with a non-eclipsing binary (

P_{bin, 2} = 33.7

days) with somewhat lower-mass stars (

M_{3} = 0.483 \pm 0.010 M_{⊙}

,

R_{3} = 0.4640 \pm 0.0036 R_{⊙}

and

M_{4} = 0.507 \pm 0.010 M_{⊙}

,

R_{4} = 0.4749 \pm 0.0031 R_{⊙}

). The two binaries, which have nearly coplanar orbits, orbit their common barycenter on a roughly aligned outer orbit (

P_{out} = 878

days). There are extra eclipse events involving the component stars of the non-eclipsing binary, which leads to relatively small uncertainties in the system parameters. The second 2 + 2 system, EPIC 220204960, consists of a pair of eclipsing binaries (

P_{bin, 2} = 13.3

days,

P_{bin, 2} = 14.4

days) that both consist of two low-mass stars (

M_{1} = 0.54 M_{⊙}

,

R_{1} = 0.46 R_{⊙}

,

M_{2} = 0.46 M_{⊙}

,

R_{2} = 0.37 R_{⊙}

and

M_{3} = 0.38 M_{⊙}

,

R_{3} = 0.40 R_{⊙}

,

M_{4} = 0.38 M_{⊙}

,

R_{4} = 0.37 R_{⊙}

) that orbit their common barycenter on a poorly determined outer orbit. Because of the relatively short time span of the observations (≈80 days for the photometry and ≈70 days for the radial velocity measurements), the masses and radii of the four stars in EPIC 220204960 can only be determined with accuracies of ≈10% and ≈5%, respectively. We show that the most likely period of the outer orbit is 957 days, with a

1 σ

range of 595 to 1674 days. We can only place weak constraints on the mutual inclinations of the orbital planes, and additional radial velocity measurements and/or additional eclipse observations would allow for much tighter constraints on the properties of the outer orbit. Full article

(This article belongs to the Special Issue The Royal Road: Eclipsing Binaries and Transiting Exoplanets)

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31 pages, 4838 KiB

Open AccessArticle

Observational Detection of Higher-Order Secular Perturbations in Tight Hierarchical Triple Stars

by Tamás Borkovits and Tibor Mitnyan

Universe 2023, 9(11), 485; https://doi.org/10.3390/universe9110485 - 20 Nov 2023

Cited by 6 | Viewed by 1335

Abstract

In this work, we search for observational evidence of higher-order secular perturbations in three eclipsing binaries. These are slightly eccentric binaries, and they form the inner pairs of tight, compact, hierarchical triple star systems. Simultaneously, we analyze the high-precision satellite (Kepler and [...] Read more.

In this work, we search for observational evidence of higher-order secular perturbations in three eclipsing binaries. These are slightly eccentric binaries, and they form the inner pairs of tight, compact, hierarchical triple star systems. Simultaneously, we analyze the high-precision satellite (Kepler and TESS) light curves; eclipse timing variations; combined spectral energy distributions (through catalog passband magnitudes); and, where available, radial velocities of KICs 9714358, 5771589, and TIC 219885468. Besides the determination of the robust astrophysical and dynamical properties of the three systems, we find evidence that the observed unusual eclipse timing variations of KIC 9714358 are a direct consequence of the octupole-order secular eccentricity perturbations forced by unusual, resonant behavior between the lines of the apsides of the inner and outer orbital ellipses. We also show that, despite its evident cyclic eclipse depth variations, KIC 5771589 is an almost perfectly coplanar system (to within

0 . 3^{\circ}

), and we explain the rapid eclipse depth variations with the grazing nature of the eclipses. Finally, we find that the inner pair of TIC 219885468 consists of two twin stars; hence, in this triple there are no octupole-order three-body perturbations. Moreover, we show that this triple is also coplanar on the same level as the former one, but due to its deep eclipses, it does not exhibit eclipse depth variations. We intend to follow this work up with further analyses and a quantitative comparison of the theoretical and the observed perturbations. Full article

(This article belongs to the Special Issue The Royal Road: Eclipsing Binaries and Transiting Exoplanets)

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Review

Jump to: Research, Other

28 pages, 1006 KiB

Open AccessReview

The EBLM Project—From False Positives to Benchmark Stars and Circumbinary Exoplanets

by Pierre F. L. Maxted, Amaury H. M. J. Triaud and David V. Martin

Universe 2023, 9(12), 498; https://doi.org/10.3390/universe9120498 - 29 Nov 2023

Cited by 4 | Viewed by 1748

Abstract

The EBLM project aims to characterise very-low-mass stars that are companions to solar-type stars in eclipsing binaries. We describe the history and motivation for this project, the methodology we use to obtain the precise mass, radius, and effective temperature estimates for very-low-mass M [...] Read more.

The EBLM project aims to characterise very-low-mass stars that are companions to solar-type stars in eclipsing binaries. We describe the history and motivation for this project, the methodology we use to obtain the precise mass, radius, and effective temperature estimates for very-low-mass M dwarfs, and review the results of the EBLM study and those from related projects. We show that radius inflation in fully convective stars is a more subtle effect than what was previously thought based on less precise measurements, i.e., the mass–radius–effective temperature relations we observe for fully convective stars in single-line eclipsing binaries show reasonable agreement with the theoretical models, particularly if we account for the M-dwarf metallicity, as inferred from the analysis of the primary star spectrum. Full article

(This article belongs to the Special Issue The Royal Road: Eclipsing Binaries and Transiting Exoplanets)

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16 pages, 3070 KiB

Open AccessReview

Transiting Circumbinary Planets in the Era of Space-Based Photometric Surveys

by Veselin B. Kostov

Universe 2023, 9(10), 455; https://doi.org/10.3390/universe9100455 - 21 Oct 2023

Cited by 1 | Viewed by 1546

Abstract

Planets orbiting binary stars—circumbinary planets—play a paramount role in our understanding of planetary and stellar formation and evolution, dynamical interactions in many-body systems, and the potential for habitable environments beyond the Solar System. Each new discovery holds immense value and inherent fascination both [...] Read more.

Planets orbiting binary stars—circumbinary planets—play a paramount role in our understanding of planetary and stellar formation and evolution, dynamical interactions in many-body systems, and the potential for habitable environments beyond the Solar System. Each new discovery holds immense value and inherent fascination both for the astronomical community and for the general public. This is perhaps best demonstrated by the 1500+ citations of the discovery papers for the 14 known transiting circumbinary planets and the dozens of related press-releases in major news outlets. This article reviews the observational and theoretical aspects related to the detection and confirmation of transiting circumbinary planets around main-sequence binaries from space-based surveys, discusses the associated challenges, and highlights some of the recent results. Full article

(This article belongs to the Special Issue The Royal Road: Eclipsing Binaries and Transiting Exoplanets)

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