The Architecture of the GW Ori Young Triple Star System and Its Disk: Dynamical Masses, Mutual Inclinations, and Recurrent Eclipses

The Architecture of the GW Ori Young Triple Star System and Its Disk: Dynamical Masses, Mutual Inclinations, and Recurrent Eclipses 

Authors: 

Czekala et al 

Abstract: 

We present spatially and spectrally resolved Atacama Large Millimeter/submillimeter Array (ALMA) observations of gas and dust orbiting the pre-main sequence hierarchical triple star system GW Ori. A forward-modeling of the 13CO and C18O J=2--1 transitions permits a measurement of the total stellar mass in this system, 5.29±0.09M⊙, and the circum-triple disk inclination, 137.6±2.0∘. Optical spectra spanning a 35 year period were used to derive new radial velocities and, coupled with a spectroscopic disentangling technique, revealed that the A and B components of GW Ori form a double-lined spectroscopic binary with a 241.50±0.05 day period; a tertiary companion orbits that inner pair with a 4218±50 day period. Combining the results from the ALMA data and the optical spectra with three epochs of astrometry in the literature, we constrain the individual stellar masses in the system (MA≈2.7M⊙, MB≈1.7M⊙, MC≈0.9M⊙) and find strong evidence that at least one (and likely both) stellar orbital planes are misaligned with the disk plane by as much as 45∘. A V-band light curve spanning 30 years reveals several new ∼30 day eclipse events 0.1-0.7 mag in depth and a 0.2 mag sinusoidal oscillation that is clearly phased with the AB-C orbital period. Taken together, these features suggest that the A-B pair may be partially obscured by material in the inner disk as tertiary approaches apoastron. Lastly, we conclude that stellar evolutionary models are consistent with our measurements of the masses and basic photospheric properties if the GW Ori system is ∼1 Myr old.

Proxima's orbit around Alpha Centauri

Proxima's orbit around Alpha Centauri

Authors:

Kervella et al

Abstract:

Proxima and Alpha Centauri AB have almost identical distances and proper motions with respect to the Sun. Although the probability of such similar parameters is in principle very low, the question whether they actually form a single gravitationally bound triple system has been open since the discovery of Proxima one century ago. Owing to recent high precision radial velocity measurements and the revision of the parameters of the Alpha Cen pair, we show that Proxima and Alpha Cen are gravitationally bound with a high degree of confidence. The orbital period of Proxima is approximately 600 000 years, with a moderate excentricity of 0.42 +0.07 -0.08. Proxima comes within 5.3 -0.9 +1.2 kAU of Alpha Cen at periastron, and the apastron occurs at 12.9 +0.3 -0.1 kAU. This orbital motion may have influenced the formation or evolution of the recently discovered planet orbiting Proxima as well as circumbinary planet formation around Alpha Cen.

94 Ceti: a triple star with a planet and dust disk

94 Ceti: a triple star with a planet and dust disc

Authors:

Wiegert et al

Abstract:

94 Ceti is a triple star system with a circumprimary gas giant planet and far-infrared excess. Such excesses around main sequence stars are likely due to debris discs, and are considered as signposts of planetary systems and, therefore, provide important insights into the configuration and evolution of the planetary system. Consequently, in order to learn more about the 94 Ceti system, we aim to precisely model the dust emission to fit its observed SED and to simulate its orbital dynamics. We interpret our APEX bolometric observations and complement them with archived Spitzer and Herschel bolometric data to explore the stellar excess and to map out background sources in the fields. Dynamical simulations and 3D radiative transfer calculations were used to constrain the debris disc configurations and model the dust emission. The best fit dust disc model for 94 Ceti implies a circumbinary disc around the secondary pair, limited by dynamics to radii smaller than 40 AU and with a grain size power-law distribution of ~a^-3.5. This model exhibits a dust-to-star luminosity ratio of 4.6+-0.4*10^-6. The system is dynamically stable and N-body symplectic simulations results are consistent with semi-analytical equations that describe orbits in binary systems. In the observations we also find tentative evidence of a circumtertiary ring that could be edge-on.

HD 131399Ab: a Directly Imaged 4 Jupiter Mass Gas Giant in a Trinary System

Direct imaging discovery of a Jovian exoplanet within a triple-star system

Authors:

Wagner et al

Abstract:

Direct imaging allows for the detection and characterization of exoplanets via their thermal emission. We report the discovery via imaging of a young Jovian planet in a triple star system and characterize its atmospheric properties through near-infrared spectroscopy. The semi-major axis of the planet is closer relative to that of its hierarchical triple star system than for any known exoplanet within a stellar binary or triple, making HD 131399 dynamically unlike any other known system. The location of HD 131399Ab on a wide orbit in a triple system demonstrates that massive planets may be found on long and possibly unstable orbits in multi-star systems. HD 131399Ab is one of the lowest mass (4 ± 1 MJup) and coldest (850 ± 50 K) exoplanets to have been directly imaged.

pop sci links 1st, 2nd, 3rd.

Retrograde Orbits for Hot Jupiters is VERY Hard to Form in Hierarchical Trinary Systems

Difficulty in Formation of Counter-orbiting Hot Jupiters from Near-coplanar Hierarchical Triple Systems: A Sub-stellar Perturber

Authors:

Xue et al

Abstract:

Among a hundred transiting planets with a measured projected spin-orbit angle {\lambda}, several systems are suggested to be counter-orbiting. While they may be due to the projection effect, the mechanism to produce a counter-orbiting planet is not established. A promising scenario for the counter-orbiting planets is the extreme eccentricity evolution in near-coplanar hierarchical triple systems with eccentric inner and outer or- bits. We examine this scenario in detail by performing a series of systematic numerical simulations, and consider the possibility of forming hot Jupiters, especially counter- orbiting one under this mechanism with a distant sub-stellar perturber. We incorporate quadrupole and octupole secular gravitational interaction between the two orbits, and also short-range forces (correction for general relativity, star and inner planetary tide and rotational distortion) simultaneously. We find that most of systems are tidally disrupted and that a small fraction of survived planets turns out to be prograde. The formation of counter-orbiting hot Jupiters in this scenario is possible only in a very restricted parameter region, and thus very unlikely in practice.

KELT-4Ab is a hot Jupiter in a Trinary System

A team of researchers working at the Harvard-Smithsonian Center for Astrophysics has announced the finding of a triple-star system—one that also as has a stable orbit planet in it. In their paper published in The Astronomical Journal, the team describes how they came to see that a binary system once thought to be a single star, was actually a pair of stars orbiting one another, and how that led to the revelation of the triple-star system.

Known planets with three stars appearing in their sky are rare, this new discovery is just the fourth, and it has caused excitement in the space community because it is the closest one yet, allowing for a better look than has been possible with the other finds. The main star is also brighter than the other stars that serve as suns for their planets, making it easier to study both the star and the planet.

The objects under study in the new system are KELT-4Ab, a gas giant planet, similar in size to Jupiter—it takes approximately three days to make its way around the star KELT-A, which serves as its sun. The other two stars, named KELT-B and C, are much farther away and orbit one another over the course of approximately 30 years. It takes the pair approximately four thousand years to orbit KELT-A. The researchers suggest that the view from KELT-4Ab would likely be one where its sun, KELT-A, would appear roughly forty times as big as our sun does to us due to its close proximity. The two other orbiting stars, on the other hand, would appear much dimmer due to their great distance, shining no brighter than our moon.

Space scientists have known of the existence of the KELT system for several years, but it was thought that the binary stars were actually just one star. The researchers on this new effort were able to see that they were actually a binary system courtesy of two robotically controlled telescopes on two different continents—one is in Arizona, the other in South Africa. Together they are known as the Kilodegree Extremely Little Telescope (KELT), which is of course how the KELT system got its name.

The triple-star system offers a unique opportunity for scientists working to try to understand how it is that gas giants, such as KELT-4Ab, manage to orbit so close to their star. Theory suggests that they should be more distant, as is the case with Jupiter. One possibility, at least for this new discovery, is that it might have something to do with the nearby binary system.

link.

A Hidden M Dwarf star in the Circumstellar Disk of Herbig HD 142527 System

An M-dwarf star in the transition disk of Herbig HD142527; Physical parameters and orbital elements

Authors:

Lacour et al

Abstract:

HD 142527A is one of the most studied Herbig Ae/Be stars with a transitional disk, as it has the largest imaged gap in any protoplanetary disk: the gas is cleared from 30 to 90 AU. The HD 142527 system is also unique in that it has a stellar companion with a small mass compared to the mass of the primary star. This factor of ≈20 in mass ratio between the two objects makes this binary system different from any other YSO. The HD142527 system could therefore provides a valuable testbed for understanding the impact of a lower mass companion on disk structure. This low-mass stellar object may be responsible for both the gap and the dust trapping observed by ALMA at longer distances. We have observed this system with the NACO and GPI instruments using the aperture masking technique. Aperture masking is ideal for providing high dynamic range even at very small angular separations. We present here the SEDS for HD 142527A and B from the R band up to the M band as well as the orbital motion of HD 142527B over a period of more than 2 years. The SED is compatible with a T=3000±100K object in addition to a 1700\,K black body environment (likely a circum-secondary disk). From evolution models, we find that HD142527B is compatible with an object of mass 0.13±0.03Msun, radius 0.90±0.15Rsun and age 1.0+1.0−0.75Myr. This age is significantly younger than the age previously estimated for HD142527A. Computations to constrain the orbital parameters found a semi-major axis of 140+120−70\,mas, an eccentricity of 0.5±0.2, an inclination of 125±15 degrees, and a position angle of the right ascending node of −5±40 degrees. Despite its high eccentricity, it is unlikely that HD142527B is responsible for truncating the inner edge of the outer disk.

GG Tauri A triple System: A System With a Circumtrinary (?) Protoplanetary Disk Around Stars With Disks

CO Gas orbiting around the GG Tauri A triple System: rings beyond the ring ?

Authors:

Tang et al

Abstract:

We aim at unveiling the observational imprint of physical mechanisms that govern planetary formation in the young, multiple system GG Tau A. We present ALMA observations of 12CO and 13CO 3-2 and continuum at 0.9 mm at 0.35" resolution. The 12CO gas, found in the cavity of the dust ring where no 13CO gas is detected, confirms the existence of a CO accretion shock near the circumstellar disk of GG Tau Aa. The outer disk and the hot spot lying at the outer edge of the dust ring are observed both in 12CO and 13CO. The gas emission in the outer disk can be radially decomposed in a series of slightly overlapping gaussian rings, suggesting the presence of unresolved gaps. The dip closest to the disk center lies at a radius very close to the CO hot spot location (∼250−260~au). Studies of the CO excitation conditions reveal that the outer disk remains in the shadow of the ring. The hot spot probably results from local heating processes. The two latter points strongly support the hypothesis making the hot spot an embedded proto-planet shepherding the outer disk and accreting surrounding material which may be traced by the the redshifted component observed in the spectra around the hot spot.

VHS 1256-1257 is the Only Known Trinary Brown Dwarf System

Adaptive Optics imaging of VHS 1256-1257: A Low Mass Companion to a Brown Dwarf Binary System

Authors:

Stone et al

Abstract:

Recently, Gauza et al. (2015) reported the discovery of a companion to the late M-dwarf, VHS J125601.92-125723.9 (VHS 1256-1257). The companion's absolute photometry suggests its mass and atmosphere are similar to the HR 8799 planets. However, as a wide companion to a late-type star, it is more accessible to spectroscopic characterization. We discovered that the primary of this system is an equal-magnitude binary. For an age ∼300 Myr the A and B components each have a mass of 64.6+0.8−2.0 MJup, and the b component has a mass of 11.2+9.7−1.8, making VHS 1256-1257 only the third brown dwarf triple system. There exists some tension between the spectrophotometric distance of 17.2±2.6 pc and the parallax distance of 12.7±1.0 pc. At 12.7 pc VHS1256-1257 A and B would be the faintest known M7.5 objects, and are even faint outliers among M8 types. If the larger spectrophotmetric distance is more accurate than the parallax, then the mass of each component increases. In particular, the mass of the b component increases well above the deuterium burning limit to ∼35 MJup and the mass of each binary component increases to 73+20−17 MJup. At 17.1 pc, the UVW kinematics of the system are consistent with membership in the AB~Dor moving group. The architecture of the system resembles a hierarchical stellar multiple suggesting it formed via an extension of the star-formation process to low masses. Continued astrometric monitoring will resolve this distance uncertainty and will provide dynamical masses for a new benchmark system.

KELT-4Ab: an Inflated hot Jupiter in a Hierarchical Trinary System

KELT-4Ab: An inflated Hot Jupiter transiting the bright (V~10) component of a hierarchical triple

Authors:

Eastman et al

Abstract:

We report the discovery of KELT-4Ab, an inflated, transiting Hot Jupiter orbiting the brightest component of a hierarchical triple stellar system. The host star is an F star with Teff=6206±75 K, logg=4.108±0.014, [Fe/H]=−0.116+0.065−0.069, M∗=1.201+0.067−0.061 M⊙, and R∗=1.610+0.078−0.068 R⊙. The best-fit linear ephemeris is BJDTDB=2456193.29157±0.00021+E(2.9895936±0.0000048). With a magnitude of V∼10, a planetary radius of 1.699+0.046−0.045 RJ, and a mass of 0.902+0.060−0.059 MJ, it is the brightest host among the population of inflated Hot Jupiters (RP>1.5RJ), making it a valuable discovery for probing the nature of inflated planets. In addition, its existence within a hierarchical triple and its proximity to Earth (210 pc) provides a unique opportunity for dynamical studies with continued monitoring with high resolution imaging and precision radial velocities. In particular, the motion of the binary stars around each other and of both stars around the primary star relative to the measured epoch in this work should be detectable when it rises in October 2015.

The V471 Tauri System: a White Dwarf- Red Dwarf Eclipsing Binary With a Brown Dwarf at 12 AU

The V471 Tauri System: A Multi-datatype Probe

Authors:

Vaccaro et al

Abstract:

V471 Tauri, a white dwarf--red dwarf eclipsing binary in the Hyades, is well known for stimulating development of common envelope theory, whereby novae and other cataclysmic variables form from much wider binaries by catastrophic orbit shrinkage. Our evaluation of a recent imaging search that reported negative results for a much postulated third body shows that the object could have escaped detection or may have actually been seen. The balance of evidence continues to favor a brown dwarf companion about 12 AU from the eclipsing binary. A recently developed algorithm finds unified solutions from three datatypes. New radial velocities (RVs) of the red dwarf and BV RCIC light curves are solved simultaneously along with white dwarf and red dwarf RVs from the literature, uvby data, the MOST mission light curve, and 40 years of eclipse timings. Precision-based weighting is the key to proper information balance among the various datasets. Timewise variation of modeled starspots allows unified solution of multiple data eras. Light curve amplitudes strongly suggest decreasing spottedness from 1976 to about 1980, followed by approximately constant spot coverage from 1981 to 2005. An explanation is proposed for lack of noticeable variation in 1981 light curves, in terms of competition between spot and tidal variations. Photometric spectroscopic distance is estimated. The red dwarf mass comes out larger than normal for a K2V star, and even larger than adopted in several structure and evolution papers. An identified cause for this result is that much improved red dwarf RVs curves now exist.

Several Kepler Eclipsing Binaries are Really Trinaries, Some With Brown Dwarfs

Ten Kepler Eclipsing Binaries Containing the Third Components

Authors:

Zasche et al

Abstract:

Analyzing the available photometry from the Kepler satellite and other databases, we performed detailed light curve modeling of 10 eclipsing binary systems that were found to exhibit a periodic modulation of their orbital periods. All of the selected systems are detached Algol type, with orbital periods from 0.9 to 2.9 days. In total, 9448 times of minimum for these binaries were analyzed in an attempt to identify the period variations caused by the third bodies in these systems. The well-known method of the light-travel time effect was used for the analysis. The orbital periods of the outer bodies were found to be between 1 and 14 years. This hypothesis makes such systems interesting for future prospective detections of these components, despite their low predicted masses. Considering the dynamical interaction between the orbits, the system KIC 3440230 seems to be the most interesting, in which one would expect the detection of some effects (i.e., changing the inclination) even after a few years or decades of observations.

Kepler Compact Binary Stellar Systems With Exoplanets may be False Positives, Really Trinary Systems

No circumbinary planets transiting the tightest Kepler binaries - a fingerprint of a third star

Authors:

Martin et al

Abstract:

The Kepler mission has yielded the discovery of eight eclipsing binaries, within period range of 7 - 40 d, hosting circumbinary planets. This is longer than the typical eclipsing binary period found by Kepler, and hence there is a dearth of planets around the closest binaries. In this paper we demonstrate how this dearth may be explained by the presence of a distant stellar tertiary companion, which shrunk the inner binary orbit by the process of Kozai cycles and tidal friction, a mechanism that has been implicated for producing most binaries with periods below 7 d. We show that the geometry and orbital dynamics of these evolving triple-star systems are highly restrictive for a circumbinary planet, which is subject itself to Kozai modulation, on one hand, and can shield the two inner stars from their Kozai cycle and subsequent shrinking, on the other hand. Only small planets on wide and inclined orbits may form, survive and allow for the inner binary shrinkage. Those are difficult to detect.

Updated: Brown Dwarf LHS 6343 C's Physical Properties

Characterizing the Cool KOIs. VII. Refined Physical Properties of the Transiting Brown Dwarf LHS 6343 C

Authors:

Montet et al

Abstract:

We present an updated analysis of LHS 6343, a triple system in the Kepler field which consists of a brown dwarf transiting one member of a widely-separated M+M binary system. By analyzing the full Kepler dataset and 34 Keck/HIRES radial velocity observations, we measure both the observed transit depth and Doppler semiamplitude to 0.5% precision. With Robo-AO and Palomar/PHARO adaptive optics imaging as well as TripleSpec spectroscopy, we measure a model-dependent mass for LHS 6343 C of 62.1 +/- 1.2 M_Jup and a radius of 0.783 +/- 0.011 R_Jup. We detect the secondary eclipse in the Kepler data at 3.5 sigma, measuring e cos omega = 0.0228 +/- 0.0008. We also derive a method to measure the mass and radius of a star and transiting companion directly, without any reliance on stellar models. The mass and radius of both objects depend only on the orbital period, stellar density, reduced semimajor axis, Doppler semiamplitude, eccentricity, and inclination, as well as the knowledge that the primary star falls on the main sequence. With this method, we calculate a model-independent mass and radius for LHS 6343 C to a precision of 3% and 2%, respectively.

older version here.

KIC 5621294: an Algol Type Eclipsing Binary With a Circumbinary Brown Dwarf

The Kepler Eclipsing System KIC 5621294 and its Substellar Companion

Authors:

Lee et al

Abstract:

We present the physical properties of KIC 5621294 showing light and timing variations from the Kepler photometry. Its light curve displays partial eclipses and O'Connell effect with Max II fainter than Max I, which was fitted quite well by applying third-body and spot effects to the system. The results indicate that the eclipsing pair is a classical Algol-type system with parameters of q=0.22, i=76∘.8, and Δ(T1--T2)=4,235 K, in which the detached primary component fills about 77\% of its limiting lobe. Striking discrepancies exist between the primary and secondary eclipse times obtained with the method of Kwee \& van Woerden. These are mainly caused by surface inhomogeneities due to spot activity detected in our light-curve synthesis. The 1,253 light-curve timings from the Wilson-Devinney code were used for a period study. It was found that the orbital period of KIC 5621294 has varied due to a periodic variation overlaid on a downward parabola. The sinusoidal variation with a period of 961 d and a semi-amplitude of 22.5 s most likely arise from a light-time effect due to a third component with a mass of M3sini3=46.9 MJup, which is in good agreement with that calculated from the light curve itself. If its orbital inclination is larger than about 40∘, the mass of the circumbinary object would possibly match a brown dwarf. The parabolic variation could not be fully explained by either a mass transfer between the binary components or an angular momentum via magnetic braking. It is possible that the parabola may only be the observed part of a period modulation caused by the presence of another companion in a wider orbit.

Circum Trinary Stable Orbits

Secular dynamics of hierarchical quadruple systems: the case of a triple system orbited by a fourth body

Authors:

Hamers et al

Abstract:

We study the secular gravitational dynamics of quadruple systems consisting of a hierarchical triple system orbited by a fourth body. These systems can be decomposed into three binary systems with increasing semimajor axes, binaries A, B and C. The Hamiltonian of the system is expanded in ratios of the three binary separations, and orbit-averaged. Subsequently, we numerically solve the equations of motion. We study highly hierarchical systems that are well described by the lowest-order terms in the Hamiltonian. We find that the qualitative behaviour is determined by the ratio 0 of the initial Kozai-Lidov (KL) time-scales of the binary pairs AB and BC. If 0≪1, binaries AB remain coplanar if this is initially the case, and KL eccentricity oscillations in binary B are efficiently quenched. If 0≫1, binaries AB become inclined, even if initially coplanar. However, there are no induced KL eccentricity oscillations in binary A. Lastly, if 0∼1, complex KL eccentricity oscillations can occur in binary A that are coupled with the KL eccentricity oscillations in B. Even if binaries A and B are initially coplanar, the induced inclination can result in very high eccentricity oscillations in binary A. These extreme eccentricities could have significant implications for strong interactions such as tidal interactions, gravitational wave dissipation, and collisions and mergers of stars and compact objects. As an example, we apply our results to a planet+moon system orbiting a central star, which in turn is orbited by a distant and inclined stellar companion or planet, and to observed stellar quadruples.

Brown Dwarf LHS 6343 C's Physical Properties

Characterizing the Cool KOIs. VII. Refined Physics Properties of the Eclipsing Brown Dwarf LHS 6343 C

Authors:

Montet et al

Abstract:

We present an updated analysis of LHS 6343, a triple system in the Kepler field which consists of a brown dwarf eclipsing one member of a widely-separated M+M binary system. By analyzing the full Kepler dataset and 34 Keck/HIRES radial velocity observations, we measure both the observed eclipse depth and Doppler semiamplitude to 0.5% precision. With Robo-AO and Palomar/PHARO adaptive optics imaging as well as TripleSpec spectroscopy, we measure a model-dependent mass for LHS 6343 C of 62.1 +/- 1.2 M_Jup and a radius of 0.783 +/- 0.011 R_Jup. We detect the secondary eclipse in the Kepler data at 3.5 sigma, measuring e cos omega = 0.0228 +/- 0.0008. We also derive a method to measure the mass and radius of a star and transiting/eclipsing companion directly, without any reliance on stellar models. The mass and radius of both objects depend only on the orbital period, stellar density, reduced semimajor axis, Doppler semiamplitude, eccentricity, and inclination. With this method, we calculate a model-independent mass and radius for LHS 6343 C to a precision of 3% and 2%, respectively.

Circumstellar Disk/Host Star Interaction may be the Source of Tight Trinary Star Systems

Stellar orbit evolution in close circumstellar disc encounters

Authors:

Muñoz et al

Abstract:

The formation and early evolution of circumstellar discs often occurs within dense, newborn stellar clusters. For the first time, we apply the moving-mesh code AREPO, to circumstellar discs in 3-D, focusing on disc-disc interactions that result from stellar fly-bys. Although a small fraction of stars are expected to undergo close approaches, the outcomes of the most violent encounters might leave an imprint on the discs and host stars that will influence both their orbits and their ability to form planets. We first construct well-behaved 3-D models of self-gravitating discs, and then create a suite of numerical experiments of parabolic encounters, exploring the effects of pericenter separation r_p, disc orientation and disc-star mass ratio (M_d/M_*) on the orbital evolution of the host stars. Close encounters (2r_p<~ disc radius) can truncate discs on very short time scales. If discs are massive, close encounters facilitate enough orbital angular momentum extraction to induce stellar capture. We find that for realistic primordial disc masses M_d<~0.1M_*, non-colliding encounters induce minor orbital changes, which is consistent with analytic calculations of encounters in the linear regime. The same disc masses produce entirely different results for grazing/colliding encounters. In the latter case, rapidly cooling discs lose orbital energy by radiating away the energy excess of the shock-heated gas, thus causing capture of the host stars into a bound orbit. In rare cases, a tight binary with a circumbinary disc forms as a result of this encounter.

Sources of Eccentricity in Trinary Systems

Eccentricity generation in hierarchical triple systems with non-coplanar and initially circular orbits

Authors:

Georgakarakos et al

Abstract:

In a previous paper, we developed a technique for estimating the inner eccentricity in coplanar hierarchical triple systems on initially circular orbits, with comparable masses and with well separated components, based on an expansion of the rate of change of the Runge-Lenz vector. Now, the same technique is extended to non-coplanar orbits. However, it can only be applied to systems with I0 less than 39.23∘ or I0 greater than 140.77∘, where I is the inclination of the two orbits, because of complications arising from the so-called 'Kozai effect'. The theoretical model is tested against results from numerical integrations of the full equations of motion.

Using HD 181068 to Study Multistellar Exoplanet Systems

A multiwavelength study of the hierarchical triple HD 181068: A test bed for studying star-planet-interaction?

Authors:

Czesla et al

Abstract:

HD 181068 is the only compact, triply eclipsing, hierarchical triple system containing a giant star known to date. With its central, highly-active G-type giant orbited by a close pair of main-sequence dwarfs, the system is ideal to study tidal interactions. We carried out a multiwavelength study to characterize the magnetic activity of the HD 181068 system. To this end, we obtained in- and out-of-eclipse X-ray snapshots with XMM-Newton and an optical spectrum, which we analyzed along with the Kepler light-curve. The primary giant shows strong quiescent X-ray emission at a level of 2e31 ergs, an S-index of 0.41 +/- 0.01, and marked white-light flares releasing up to 6e38 erg in the Kepler-band. During the second X-ray observation, we found a three-times elevated -- yet decaying -- level of X-ray emission, which might be due to an X-ray flare. The high level of magnetic activity is compatible with the previously reported absence of solar-like oscillations in the giant, whose atmosphere, however, undergoes tidally-induced oscillations imposed by the changing configuration of the dwarf-binary. We found that the driving force exciting these oscillations is comparable to the disturbances produced by a typical hot Jupiter, making the system a potential test bed to study the effects of tidal interactions also present in planetary systems.