Triple Star Research Articles

HIGH ANGULAR RESOLUTION RADIO OBSERVATIONS OF THE HL/XZ TAU REGION: MAPPING THE 50 AU PROTOPLANETARY DISK AROUND HL TAU AND RESOLVING XZ TAU S INTO A 13 AU BINARY

We present new 7 mm and archive 1.3 cm high angular resolution observations of the HL/XZ Tau region made with the VLA. At 7 mm, the emission from HL Tau seems to be arising in a clumpy disk with radius of order 25 AU. The 1.3 cm emission from XZ Tau shows the emission from a binary system with 0"3 (42 AU) separation, known from previous optical/IR observations. However, at 7 mm, the southern radio component resolves into a binary with 0"09 (13 AU) separation, suggesting that XZ Tau is actually a triple star system. We suggest that the remarkable ejection of gas from the XZ Tau system observed with the HST may be related to a periastron passage of this newly discovered close binary system.

The Hill stability of inclined bound triple star and planetary systems

The dynamical stability of a triple system composed of a binary or planetary system and a bound third body moving on a orbit inclined to the system is discussed in terms of Hill stability for the full three-body problem. The situation arises in the determination of stability of triple star systems against disruption and component exchange and the determination of stability of planetary systems against disruption, component exchange or capture. It is found that increasing the inclination of the third body decreases the Hill regions of stability. Increasing the eccentricity of the binary also produces similar effects. These type of changes make exchange or disruption of the component masses more likely. Increasing the eccentricity of the third body initially increases the stability of the system then decreases stability as the eccentricity reaches higher values. The Hill stability criterion is applied to extrasolar planetary systems to determine the critical distances at which planets of the same mass as the observed extrasolar planet moving on a circular orbit could remain on a stable orbit. It was found that these distances were sufficiently short suggesting that the presence of further as yet unobserved stable extrasolar planets in observed systems was very likely.

ORBITAL PERIOD CHANGES AND THEIR EVOLUTIONARY STATUS FOR WEAK-CONTACT BINARIES. II. CC COMAE BERENICES AND BV DRACONIS

Based on O – C curves, we present detailed period investigations of two weak-contact binaries CC Com and BV Dra. It is found that the periods of these two binaries have varied in a cyclic variation way superposed on a secular period change. The periods and amplitudes of the cyclic variations are P 3 = 23.6(±0.4) yr and A = 00028(±00003) for CC Com and P 3 = 23.8(±0.6) yr and A = 00029(±00003) for BV Dra. The cyclic oscillations for these two stars may be attributed to the light-time effect via an unseen third body, which could extract angular momentum from the central system. If the existence of the additional body is true, CC Com and BV Dra may be triple system stars. For CC Com, the secular period decrease rate is dP/dt = –0.20 × 10–7 d yr–1, which suggests that the mass transfers from the more massive component to the less massive one, accompanied with the angular momentum loss due to mass outflow from L 2. A decrease in its orbital period will result in the shrinking of the inner and outer critical Roche lobes, and then cause the contact degree to increase. This kind of weak-contact binary with a long-term period decrease may evolve into a deep contact configuration. For BV Dra, the continuous period increase rate is dP/dt = +0.29 × 10–7 d yr–1, indicating that the mass transfers from the less massive component to the more massive one. An increase in its orbital period may cause the separation between both components to increase, and thus the contact configuration will break, as predicted by thermal relaxation oscillation theory. Therefore, this kind of weak-contact binary with a secular period increase will evolve into a broken-contact configuration.

Investigating the flyby scenario for the HD 141569 system

Context. HD 141569, a triple star system, has been intensively observed and studied because of its massive debris disk. Until recently, it was regarded as a gravitationally bound triple system but recent measurements of the HD 141569A radial velocity seem to invalidate this hypothesis. The flyby scenario therefore has to be further investigated to test its compatibility with the observed disk structures.Aims. We present a study of the flyby scenario for the HD 141569 system by considering 3 variants: a sole flyby, a flyby associated with one planet embedded in the disk and a flyby with two planets in the disk. We discuss the merits of each one to reproduce the scattered light observations of the disk.Methods. We first use analytical calculations to reduce the parameter space of the 2 stellar companion orbit and then perform N -body numerical simulations of the flyby encounter using symplectic integration, taking into account the gravitational influence of the stars and the planets on massless test particles.Results. The binary orbit is found to be almost fixed by the observational constraint on an edge-on plane with respect to the observers. If the binary had an influence on the disk structure, it should have a passing time at the periapsis between 5000 and 8000 years ago and a distance at periapsis between 600 and 900 AU. It also appears that the best scenario to reproduce the disk morphology is a flyby with 1 planet embedded in the disk. For a 2 M J planet, its orbital eccentricity must be around 0.2 while for a 8 M J planet, it must be below 0.1. In the two cases, its apoapsis is about 130 AU.Conclusions. Although the global disk shape is reasonably well reproduced, some observed features cannot be explained by the present model and the likehood of the flyby event remains an issue for the scenario explored in this paper. Dynamically speaking, HD 141569 is still a puzzling system.

A SURVEY FOR A COEVAL, COMOVING GROUP ASSOCIATED WITH HD 141569

We present results of a search for a young stellar moving group associated with the star HD 141569, a nearby, isolated Herbig AeBe primary member of a 5+/-3 Myr-old triple star system on the outskirts of the Sco-Cen complex. Our spectroscopic survey identified a population of 21 Li-rich, <30 Myr-old stars within 30 degrees of HD 141569 which possess similar proper motions with the star. The spatial distribution of these Li-rich stars, however, is not suggestive of a moving group associated with the HD 141569 triplet, but rather this sample appears cospatial with Upper Scorpius and Upper Centaurus Lupus. We apply a modified moving cluster parallax method to compare the kinematics of these youthful stars with Upper Scorpius and Upper Centaurus Lupus. Eight new potential members of Upper Scorpius and five new potential members of Upper Centaurus Lupus are identified. A substantial moving group with an identifiable nucleus within 15 degrees (~30 pc) of HD 141569 is not found in this sample. Evidently, the HD 141569 system formed ~5 Myr ago in relative isolation, tens of parsecs away from the recent sites of star formation in the Ophiucus-Scorpius-Centaurus region.

Milliarcsecond angular resolution of reddened stellar sources in the vicinity of the Galactic center

We present lunar occultation observations obtained in August 2006 with the recently demonstrated burst mode of the ISAAC instrument at the ESO VLT. The results presented here follow the previously reported observations carried out in March 2006 on a similar but unrelated set of sources. Interstellar extinction in the inner regions of the galactic bulge amounts to tens of magnitudes at visual wavelengths. As a consequence, the majority of sources in that area are poorly studied and large numbers of potentially interesting sources such as late-type giants with circumstellar shells, stellar masers, infrared stars, remain excluded from the typical investigations which are carried out in less problematic regions. Also undetected are a large numbers of binaries. By observing LO events in this region, we gain the means to investigate at least a selected number of sources with an unprecedented combination of sensitivity and angular resolution. The LO technique permits to achieve mas resolution with a sensitivity of K~12mag at a very large telescope. We have used the opportunity of a favorable passage of the Moon over a crowded region in the general direction of the Galactic Center to observe 78 LO events of heavily reddened stellar sources. We have detected six new binary and one triple star, with typical projected separation of ~0.01. We have also detected the compact circumstellar emission around one maser and one central star of a planetary nebula. Additionally we have measured the diameter and/or circumstellar shell of two carbon stars and other IR sources. In agreement with our previous result, we conclude that lunar occultations in fast read-out mode on a detector subwindow at an 8m-class telescope can achieve an angular resolution close to 0.001 with a sensitivity K~12mag.

Speckle interferometry of metal-poor stars in the solar neighborhood. II

The results of speckle interferometric observations of 115 metal-poor stars ([m/H] < −1) within 250 pc from the Sun and with proper motions µ ≳ 0.2″/yr, made with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, are reported. Close companions with separations ranging from 0.034″ to 1″ were observed for 12 objects—G76-21, G59-1, G63-46, G135-16, G168-42, G141-47, G142-44, G190-10, G28-43, G217-8, G130-7, and G89-14—eight of them are astrometrically resolved for the first time. The newly resolved systems include one triple star—G190-10. If combined with spectroscopic and visual data, our results imply a single:binary:triple:quadruple star ratio of 147:64:9:1 for a sample of 221 primary components of halo and thick-disk stars.

Milliarcsecond angular resolution of reddened stellar sources in the vicinity of the Galactic center

Context. We present lunar occultation (LO) observations obtained in August 2006 with the recently demonstrated burst mode of the ISAAC instrument at the ESO VLT. The results presented here follow the previously reported observations carried out in March 2006 on a similar but unrelated set of sources. Aims. Interstellar extinction in the inner regions of the galacti c bulge amounts to tens of magnitudes at visual wavelengths. As a consequence, the majority of sources in that area are poorly studied and large numbers of potentially interesting sources such as latetype giants with circumstellar shells, stellar masers, inf rared stars, remain excluded from the typical investigatio ns which are carried out in less problematic regions. Also undetected are a large numbers of binaries. By observing LO events in this region, we gain the means to investigate at least a selected number of sources with an unprecedented combination of sensitivity and angular resolution. Methods. The LO technique permits to achieve milliarcsecond resolution with a sensitivity of K≈12 mag at a very large telescope. We have used the opportunity of a favorable passage of the Moon over a crowded region in the general direction of the Galactic Center to observe 78 LO events of heavily reddened stellar sources. Results. We have detected six new binary and one triple star, with typical projected separation of≈ 0. 01. We have also detected the compact circumstellar emission around one maser and one central star of a planetary nebula. Additionally we have measured the diameter and/or circumstellar shell of two carbon stars and other IR sources. Conclusions. We have used the upper limits on the size of about 60 unresolved or marginally resolved sources to establish the performance of the method. In agreement with our previous result, we conclude that lunar occultations in fast read-out m ode on a detector subwindow at an 8 m-class telescope can achieve an angular resolution close to 0. ′′ 001 with a sensitivity K≈ 12 mag.

Comparative statistics and origin of triple and quadruple stars

The statistics of catalogued quadruple stars consisting of two binaries (hierarchy 2+2) is studied in comparison with triple stars, with respective sample sizes of 81 and 724. Seven representative quadruple systems are discussed in greater detail. The properties of multiple stars do not correspond to the products of dynamical decay of small clusters, hence the N-body dynamics is not the dominant process of their formation. On the other hand, rotationally-driven (cascade) fragmentation possibly followed by migration of inner and/or outer orbits to shorter periods is a promising scenario to explain the origin of triple and quadruple stars. Our main results are: (i) Quadruple systems of Epsilon Lyr type with similar masses and inner periods are common. (ii) The distributions of the inner periods in triple and quadruple stars are similar and bimodal. The inner mass ratios do not correlate with the inner periods. (iii) The statistics of outer periods and mass ratios in triples and quadruples are different. The median outer mass ratio in triples is 0.39 independently of the outer period, which has a smooth distribution. In contrast, the outer periods of 25% quadruples concentrate in the narrow range from 10yr to 100yr, the outer mass ratios of these tight quadruples are above 0.6 and their two inner periods are similar to each other. (iv) The outer and inner mass ratios in triple and quadruple stars are not mutually correlated. (v) The inner and outer orbital angular momenta and periods in triple and quadruple systems with inner periods above 30d show some correlation, the ratio of outer-to-inner periods is mostly comprised between 5 and 10^4. In the systems with small period ratios the directions of the orbital spins are correlated, while in the systems with large ratios they are not.

Predictions for triple stars with and without a pulsar in star clusters

Though about 80 pulsar binaries have been detected in globular clusters so far, no pulsar has been found in a triple system in which all three objects are of comparable mass. Here, we present predictions for the abundance of such triple systems, and for the most likely characteristics of these systems. Our predictions are based on an extensive set of more than 500 direct simulations of star clusters with primordial binaries, and a number of additional runs containing primordial triples. Our simulations employ a number Ntot of equal-mass stars from Ntot= 512 to 19 661 and a primordial binary fraction from 0 to 50 per cent. In addition, we validate our results against simulations with N= 19 661 that include a mass spectrum with a turn-off mass at 0.8 M⊙, appropriate to describe the old stellar populations of Galactic globular clusters. Based on our simulations, we expect that typical triple abundances in the core of a dense cluster are two orders of magnitude lower than the binary abundances, which in itself already suggests that we do not have to wait too long for the first comparable-mass triple with a pulsar to be detected.

CS 22964−161: A Double‐Lined Carbon‐ ands‐Process–Enhanced Metal‐Poor Binary Star

A detailed high-resolution spectroscopic analysis is presented for the carbon-rich low-metallicity Galactic halo object CS 22964–161. We have discovered that CS 22964–161 is a double-lined spectroscopic binary and have derived accurate orbital components for the system. From a model atmosphere analysis we show that both components are near the metal-poor main-sequence turnoff. Both stars are very enriched in carbon and in neutron-capture elements that can be created in the s-process, including lead. The primary star also possesses an abundance of lithium close to the value of the "Spite plateau." The simplest interpretation is that the binary members seen today were the recipients of these anomalous abundances from a third star that was losing mass as part of its AGB evolution. We compare the observed CS 22964–161 abundance set with nucleosynthesis predictions of AGB stars, discuss issues of envelope stability in the observed stars under mass transfer conditions, and consider the dynamical stability of the alleged original triple star. Finally, we consider the circumstances that permit survival of lithium, whatever its origin, in the spectrum of this extraordinary system.

Existence and minimizing properties of retrograde orbits to the three-body problem with various choices of masses

Poincare made the first attempt in 1896 on applying variational calculus to the three-body problem and observed that collision orbits do not necessarily have higher values of action than classical solutions. Little progress had been made on resolving this difficulty until a recent breakthrough by Chenciner and Montgomery. Afterward, variational methods were successfully applied to the JV-body problem to construct new classes of solutions. In order to avoid collisions, the problem is confined to symmetric path spaces and all new planar solutions were constructed under the assumption that some masses are equal. A question for the variational approach on planar problems naturally arises: Are minimizing methods useful only when some masses are identical? This article addresses this question for the three-body problem. For various choices of masses, it is proved that there exist infinitely many solutions with a certain topological type, called retrograde orbits, that minimize the action functional on certain path spaces. Cases covered in our work include triple stars in retrograde motions, double stars with one outer planet, and some double stars with one planet orbiting around one primary mass. Our results largely complement the classical results by the Poincare continuation method and Conley's geometric approach.

Speckle interferometry of nearby multiple stars. IV. Measurements in 2004 and new orbits

The results of speckle interferometric observations of 104 binary and 6 triple stars performed at the BTA 6 m telescope in 2004 October are presented. Nearby low-mass stars are mostly observed for the program, among which 59 there are new binaries recently discovered by the Hipparcos astrometric satellite. Concurrently with the diffraction-limited position measurements we obtained 154 brightness ratio measurements of binary and multiple star components in different bands of the visible spectrum. New, first-resolved binaries are the symbiotic star CH Cyg with a weak companion at 0.043″ separation and the pair of red dwarfs, GJ 913 = HIP 118212. In addition, we derived the orbital parameters for two interferometric systems: the CN-giant pair HD 210211 = HIP 109281 (P = 10.7 yr) and the G2V-K2V G2V-K2V binary GJ 9830 = HIP 116259 (P = 15.7 yr).

Planetary stability zones in hierarchical triple star systems

A symplectic integrator algorithm suitable for hierarchical triple systems is formulated and tested. The positions of the stars are followed in hierarchical Jacobi coordinates, whilst the planets are referenced purely to their primary. The algorithm is fast, accurate and easily generalised to incorporate collisions. There are five distinct cases -- circumtriple orbits, circumbinary orbits and circumstellar orbits around each of the stars in the hierarchical triple -- which require a different formulation of the symplectic integration algorithm. As an application, a survey of the stability zones for planets in hierarchical triples is presented, with the case of a single planet orbiting the inner binary considered in detail. Fits to the inner and outer edges of the stability zone are computed. Considering the hierarchical triple as two decoupled binary systems, the earlier work of Holman & Wiegert on binaries is shown to be applicable to triples, except in the cases of high eccentricities and close or massive stars. Application to triple stars with good data in the multiple star catalogue suggests that more than 50 per cent are unable to support circumbinary planets, as the stable zone is almost non-existent.

Micro-arcsecond relative astrometry by ground-based and single-aperture observations

AbstractWe present an observation method to obtain a relative astrometric precision of about 100 . . . 150 μas with ground-based and single-aperture observations. By measuring the separation of double or triple stars we want to determine the astrometric signal of an unseen substellar companion as a periodic change in the separation between the stellar components. Using an adaptive optics system we correct for atmospheric turbulences and furthermore by using a narrow band filter in the near infrared we can suppress differential chromatic refraction effects. To reach a high precision we use a statistical approach. Using the new observation mode “cube-mode” (where the frames were directly saved in cubes with nearly no loss of time during the readout), we obtain several thousand frames within half an hour. After the verification of the Gaussian distributed behaviour of our measurements (done with a Kolmogorov-Smirnov-Test) the measurement precision can be calculated as the standard deviation of our measurements divided by the square root of the number of frames.To monitor the stability of the pixel scale between our observations, we use the old globular cluster 47 Tuc as a calibration system.

Finding orbital motion of sub-stellar companions - the case of TWA 5B

AbstractTWA 5B is a brown dwarf companion of H=12 mag, 2″ off the ~5 mag brighter triple star CoD-33° 7795 (=TWA 5), a member of the TW Hydrae association of T Tauri stars at ~55 pc. This object is the first brown dwarf around a pre-main-sequence star (confirmed by common proper motion) ever found. In the last year we have newly reduced VLT NaCo data originally taken in 2003 and combined it with all the available astrometric data of the system to investigate possibly detectable orbital motion of the system. Indeed we were able to find linear orbital motion of the system combining data from HST, VLT and Gemini-North.

Numerical Evolution of Single, Binary and Triple Stars

AbstractI discuss my stellar evolution code Ev in the context of simulations of large clusters of stars. It has long been able to handle single stars, and also binary stars up to a point. That point is far beyond what other codes are able to do, but well short of what is necessary for believable simulations. A recent version, Ev(Twin), can in principle deal with the contact phase of binary evolution, but it is not yet clear what the physical interaction is that needs to be simulated.An upgrade, which I hope will be only a few lines, should allow it to follow Kozai cycles with tidal friction, a process that strongly influences the orbital period of close pairs that reside within wide, non-coplanar triples. However, there are many substantial gaps in the physics of even single stars, let alone binaries or triples.

The Problem of Three Stars: Stability Limit

AbstractThe problem of three stars arises in many connections in stellar dynamics: three-body scattering drives the evolution of star clusters, and bound triple systems form long-lasting intermediate structures in them. Here we address the question of stability of triple stars. For a given system the stability is easy to determine by numerical orbit calculation. However, we often have only statistical knowledge of some of the parameters of the system. Then one needs a more general analytical formula. Here we start with the analytical calculation of the single encounter between a binary and a single star by Heggie (1975). Using some of the later developments we get a useful expression for the energy change per encounter as a function of the pericenter distance, masses, and relative inclination of the orbit. Then we assume that the orbital energy evolves by random walk in energy space until the accumulated energy change leads to instability. In this way we arrive at a stability limit in pericenter distance of the outer orbit for different mass combinations, outer orbit eccentricities and inclinations. The result is compared with numerical orbit calculations.

Impact of Cultivar and Production Practices on Yield and Phytonutrient Content of Organically Grown Watermelon

Abstract Cultural practices can affect quality and phytonutrient content of watermelon [Citrullus lanatus var. lanatus (Thunb.) Matsum. & Nakai]. Knowing which cultivars perform well under various production systems, and how these systems affect quality, yield, and phytonutrient content is imperative to ensure high quality and yield. There is limited information on how watermelon cultivars perform when grown with organic practices. Production characteristics of six watermelon cultivars from certified organic seed sources were compared under high (black plastic and mechanical cultivation for weed control) and low input (no-till) organic culture. The high input production method almost doubled the number of fruit produced for all cultivars; producing greater yields and heavier average fruit weights, but fruit had decreased quality (lower Brix and lycopene content) compared with the low-input production. ‘Triple Star’ was the most productive seedless cultivar in terms of number of fruit in both organic field...

Planet dispersal in binary systems during transient multiple star phases

Aims. If a significant fraction of binary star systems spent some time as inclined triple systems, either during their formation process or as the outcome of several close dynamical encounters in a crowded stellar environemnt, then the number of planets in binaries would be significantly lower than around single stars. The stellar chaotic phase preceding the instability of the triple system and the wide oscillations in eccentricity and inclination of the companion star due to the high mutual inclination between the companion and the singleton would quickly eject planets orbiting the binary in S-type orbits. Methods. We perform numerical simulations of the dynamical evolution of hierarchical triple star systems with planets hosted around the primary star of the inner binary. Different values of mutual inclination, binary separation and singleton initial semimajor axis are explored in a statistical way. Results. We find that a significant mutual inclination i m between the singleton and the binary is a key factor for instability of the planetary system. When i m is larger than ~$40^{\circ}$ the fraction of planets in the binary surviving the chaotic phase of the triple declines dramatically. The combination of eccentricity and inclination oscillations of the binary companion induced by the secular perturbations of the singleton and the sequence of close encounters preceding the ejection of one star fully destabilize a planetary system extending beyond 1 AU from the star. For i m around $90^{\circ}$ the percentage of surviving planets is lower than 20% for all binaries with a semimajor axis smaller than 200 AU. Conclusions. The frequency of planets in binaries with low separation may be strongly reduced by the residence of the pair in the past in a temporary inclined hierarchical triple.