arXiv subjects

Andrei Tokovinin

Publications and source records attributed to Andrei Tokovinin.

At least 73 records · Page 4Linked to original sources

arXiv2019

Near-resonance in a system of sub-Neptunes from TESS

We report the Transiting Exoplanet Survey Satellite ($TESS$) detection of a multi-planet system orbiting the $V=10.9$ K0 dwarf TOI 125. We find evidence for up to five planets, with varying confidence. Three high signal-to-noise transit signals correspond to sub-Neptune-sized planets ($2.76$, $2.79$, and $2.94\ R_{\oplus}$), and we statistically validate the planetary nature of the two inner planets ($P_b = 4.65$ days, $P_c = 9.15$ days). With only two transits observed, we report the outer object ($P_{.03} = 19.98$ days) as a high signal-to-noise ratio planet candidate. We also detect a candidate transiting super-Earth ($1.4\ R_{\oplus}$) with an orbital period of only $12.7$ hours and a candidate Neptune-sized planet ($4.2\ R_{\oplus}$) with a period of $13.28$ days, both at low signal-to-noise. This system is amenable to mass determination via radial velocities and transit timing variations, and provides an opportunity to study planets of similar size while controlling for age and environment. The ratio of orbital periods between TOI 125 b and c ($P_c/P_b = 1.97$) is slightly smaller than an exact 2:1 commensurability and is atypical of multiple planet systems from $Kepler$, which show a preference for period ratios just $wide$ of first-order period ratios. A dynamical analysis refines the allowed parameter space through stability arguments and suggests that, despite the nearly commensurate periods, the system is unlikely to be in resonance.

astro-ph.EP↗

arXiv2019

Spectroscopic orbits of subsystems in multiple stars. V

Spectroscopic orbits are determined for inner subsystems in nine stellar hierachies (HIP 2863, 4974, 8353, 28796, 35261, 92929, 115272, 115552, and 117596). Their periods range from 2.5 to 312 days. For each system, estimates of masses, orbital inclination and other parameters are given.

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arXiv2018

Observations of Binary Stars with the Differential Speckle Survey Instrument. VIII. Measures of Metal-Poor Stars and Triple Stars from 2015 to 2018

We present 248 speckle observations of 43 binary and 19 trinary star systems chosen to make progress in two main areas of investigation: the fundamental properties of metal poor stars and star formation mechanisms. The observations were taken at the Gemini North and South telescopes during the period 2015 July to 2018 April, mainly with the Differential Speckle Survey Instrument (DSSI), but also with a few early results from the new 'Alopeke speckle camera at Gemini North. We find that the astrometry and photometry of these observations as a whole are consistent with previous work at Gemini. We present five new visual orbits for systems important in understanding metal-poor stars, three of which have orbital periods of less than 4 years, and we indicate the degree to which these and future observations can impact our knowledge of stellar properties and star formation. In particular, we find a decrease in mass at fixed spectral type for metal poor stars versus their solar-metallicity analogues that is consistent with predictions that are made from current stellar models.

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arXiv2018

Spectroscopic orbits of subsystems in multiple stars. IV. Double-lined pairs

Spectroscopic orbits are computed for inner pairs in 9 hierarchical multiple systems (HIP 19639, 60845, 75663, 76816, 78163, 78416, 80448, 84789, and HD 105080) and for one simple binary HIP 61840. All subsystems are double-lined, and their periods range from 2.27 to 30.4 days. Five spectroscopic binaries are twins with equal masses. Each hierarchical system is discussed individually, providing estimates of outer periods, masses, orbital inclination, and axial rotation. For systems with three resolved visual components (HIP 60845 and 80448), the outer and inner visual orbits are determined, complementing the description of their architecture. The radial velocities of HIP 75663A, 76816B, and 78163B are found to be variable with long periods, implying that these hierarchies are 2+2 quadruples. The period-eccentricity relation for spectroscopic subsystems is discussed.

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arXiv2018

Yes, multi-periodic dwarfs in Upper Scorpius are binaries

We found that multi-periodic low-mass stars discovered by Kepler K2 in the Upper Scorpius association are close binaries with typical separations of the order of 10 au and large mass ratios. These stars were surveyed by speckle interferometry at the SOAR telescope with spatial resolution of 0.04". Out of 129 observed targets, we resolved 70 pairs (including 16 previously known ones and three new triple systems). The distribution of projected separations of binaries with primary stars less massive than the Sun corresponds to a log-normal with median of 11.6 au and logarithmic dispersion of 0.60 dex, similar to M dwarfs in the field. Future orbits of newly discovered binaries will provide accurate measurements of masses to calibrate pre-main sequence evolutionary tracks; a tentative orbit of one previously known binary is determined here.

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arXiv2018

Young and eccentric: the quadruple system HD 86588

High-resolution spectroscopy and speckle interferometry reveal the young star HD 86588 as a quadruple system with a 3-tier hierarchy. The 0.3" resolved binary A,B with an estimated period around 300 years contains the 8-year pair Aa,Abc (also potentially resolvable), where Ab,Ac is a double-lined binary with equal components, for which we compute the spectroscopic orbit. Despite the short period of 2.4058 day, the orbit of Ab,Ac is eccentric (e=0.086+-0.003). It has a large inclination, but there are no eclipses; only a 4.4 mmag light modulation apparently caused by star spots on the components of this binary is detected with Evryscope. Assuming a moderate extinction of A_V = 0.5 mag and a parallax of 5.2 mas, we find that the stars are on or close to the main sequence (age >10 Myr) and their masses are from 1 to 1.3 solar. We measure the strength of the Lithium line in the visual secondary B which, together with rotation, suggests that the system is younger than 150 Myr. This object is located behind the extension of the Chamaeleon I dark cloud (which explains extinction and interstellar Sodium absorption), but apparently does not belong to it. We propose a scenario where the inner orbit has recently acquired its high eccentricity through dynamical interaction with the outer two components; it is now undergoing rapid tidal circularization on a time scale of ~1 Myr. Alternatively, the eccentricity could be excited quasi-stationary by the outer component Aa.

astro-ph.SR↗

arXiv2018

Spectroscopic orbits of subsystems in multiple stars. III

Spectroscopic orbits are computed for inner pairs in six nearby hierarchical multiple systems (HIP 35733, 95106/95110, 105441, 105585/105569, 105947, and 109951). Radial velocities and resolved measurements, when available, are used to derive combined sets of outer orbital elements for three systems. Each multiple system is discussed individually. Additionally, HIP 115087 is a simple 7.9 day single-lined binary. Although the minimum companion mass is sub-stellar (in the brown dwarf desert regime), it appears to be a 0.2 solar-mass star in a low-inclination orbit.

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arXiv2018

Speckle interferometry at SOAR in 2016 and 2017

The results of speckle interferometric observations at the 4.1 m SOAR telescope in 2016 and 2017 are given, totaling 2483 measurements of 1570 resolved pairs and 609 non-resolutions. We describe briefly recent changes in the instrument and observing method and quantify the accuracy of the pixel scale and position angle calibration. Comments are given on 44 pairs resolved here for the first time. Orbital motion of the newly resolved subsystem BU~83 Aa,Ab roughly agrees with its 36 year astrometric orbit proposed by J.~Dommanget. Most Tycho binaries examined here turned out to be spurious.

astro-ph.SR↗

arXiv2018

Dancing twins: stellar hierarchies that formed sequentially?

This paper attracts attention to the class of resolved triple stars with moderate ratios of inner and outer periods (possibly in a mean motion resonance) and nearly circular, mutually aligned orbits. Moreover, stars in the inner pair are twins with almost identical masses, while the mass sum of the inner pair is comparable to the mass of the outer component. Such systems could be formed either sequentially (inside-out) by disk fragmentation with subsequent accretion and migration or by a cascade hierarchical fragmentation of a rotating cloud. Orbits of the outer and inner subsystems are computed or updated in four such hierarchies: LHS 1070 (GJ 2005, periods 77.6 and 17.25 years), HIP 9497 (80 and 14.4 years), HIP 25240 (1200 and 47.0 years), and HIP 78842 (131 and 10.5 years).

astro-ph.SR↗

arXiv2018

Ten years of speckle interferometry at SOAR

Since 2007, close binary and multiple stars are observed by speckle interferometry at the 4.1 m Southern Astrophysical Research (SOAR) telescope. The HRCam instrument, observing strategy and planning, data processing and calibration methods, developed and improved during ten years, are presented here in a concise way. Thousands of binary stars were measured with diffraction-limited resolution (29mas at 540nm wavelength) and a high accuracy reaching 1mas; two hundred new pairs or subsystems were discovered. To date, HRCam has performed over 11000 observations with a high efficiency (up to 300 stars per night). An overview of the main results delivered by this instrument is given.

astro-ph.IM↗

arXiv2017

The Updated Multiple Star Catalog

The catalog of hierarchical stellar systems with three or more components is an update of the original 1997 version of the MSC. For two thousand hierarchies, the new MSC provides distances, component's masses and periods, as well as supplementary information (astrometry, photometry, identifiers, orbits, notes). The MSC content and format are explained, its incompleteness and strong observational selection are stressed. Nevertheless, the MSC can be used for statistical studies and it is a valuable source for planning observations of multiple stars. Rare classes of stellar hierarchies found in the MSC (with 6 or 7 components, extremely eccentric orbits, planar and possibly resonant orbits, hosting planets) are briefly presented. High-order hierarchies have smaller velocity dispersion compared to triples and are often associated with moving groups. The paper concludes by the analysis of the ratio of periods and separations between inner and outer subsystems. In wide hierarchies, the ratio of semimajor axes, estimated statistically, is distributed between 3 and 300, with no evidence of dynamically unstable systems.

astro-ph.SR↗

arXiv2017

New binaries in the epsilon Cha association

We present Adaptive Optics-aided speckle observations of 47 young stars in the $ε$ Cha association, made at the 4-m Southern Astrophysical Research Telescope in the $I$-band. We resolved 10 new binary pairs, 5 previously known binaries and two triple systems, also previously known. In the separation range between 4 and 300 AU, the 30 association members of spectral types G0 and later host 6 binary companions, leading to the raw companion frequency of $0.010\pm0.04$ per decade of separation, comparable to the main sequence dwarfs in the field. On the other hand, all 5 massive association members of spectral types A and B have companions in this range. We discuss the newly resolved and known binaries in our sample. Observed motions in the triple system $ε$ Cha, composed of three similar B9V stars, can be described by tentative orbits with periods 13 and $\sim 900$ years, and a large mutual inclination.

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arXiv2017

New orbits based on speckle interferometry at SOAR. II

Orbits of 44 close and fast visual binaries are computed using the latest speckle observations; 23 orbits are determined for the first time, the rest are revisions, some quite substantial. Six combined orbits use radial velocities. The median period is 15.6 years, the shortest period is one year. Most stars are nearby late-type dwarfs. Dynamical parallaxes and estimates of the masses are derived from the orbital elements and the photometry of the components.

astro-ph.SR↗

arXiv2017

Orbit alignment in triple stars

Statistics of the angle Φbetween orbital angular momenta in hierarchical triple systems with known inner visual or astrometric orbits are studied. Correlation between apparent revolution directions proves partial orbit alignment known from earlier works. The alignment is strong in triples with outer projected separation less than ~50 AU, where the average Φis about 20 degrees. In contrast, outer orbits wider than 1000 AU are not aligned with the inner orbits. It is established that the orbit alignment decreases with increasing mass of the primary component. Average eccentricity of inner orbits in well-aligned triples is smaller than in randomly aligned ones. These findings highlight the role of dissipative interactions with gas in defining the orbital architecture of low-mass triple systems. On the other hand, chaotic dynamics apparently played a role in shaping more massive hierarchies. Analysis of projected configurations and triples with known inner and outer orbits indicates that the distribution of Φis likely bimodal, where 80% of triples have Φ<70 degrees and the remaining ones are randomly aligned.

astro-ph.SR↗

arXiv2017

Formation of wide binary stars from adjacent cores

Wide gravitationally bound pairs of stars can be formed from adjacent prestellar cores that happen to move slowly enough relative to each other. These binaries are remnants of the primordial clustering. It is shown that the expected fraction of wide bound pairs in low-density star formation regions can be larger than the fraction of wide pairs in the field. On the other hand, wide binaries do not form or survive in dense clusters. Recent works on the separation distribution of young binaries, summarized here, confirm these expectations. Alternative formation mechanisms of wide binaries such as cluster dissolution or unfolding of triple stars cannot explain the large observed fraction of young wide pairs and therefore are not dominant. The fact that more than a half of wide pairs contain subsystems matches the general multiplicity statistics and does not imply that hierarchical multiplicity and wide binaries are genetically related.

astro-ph.SR↗

arXiv2017

Relative orbit orientation in several resolved multiple systems

This work extends the still modest number of multiple stars with known relative orbit orientation. Accurate astrometry and radial velocities are used jointly to compute or update outer and inner orbits in three nearby triple systems HIP 101955 (orbital periods 38.68 and 2.51 years), HIP 103987 (19.20 and 1.035 years), HIP 111805 (30.13 and 1.50 years) and in one quadruple system HIP 2643 (periods 70.3, 4.85 and 0.276 years), all composed of solar-type stars. The masses are estimated from the absolute magnitudes and checked using the orbits. The ratios of outer to inner periods (from 14 to 20) and the eccentricities of the outer orbits are moderate. These systems are dynamically stable, but not very far from the stability limit. In three systems all orbits are approximately coplanar and have small eccentricity, while in HIP 101955 the inner orbit with e=0.6 is highly inclined.

astro-ph.SR↗

arXiv2017

Continued Kinematic and Photometric Investigations of Hierarchical Solar-Type Multiple Star Systems

We observed 15 of the solar-type binaries within 67 pc of the Sun previously observed by the Robo-AO system in the visible, with the PHARO near-IR camera and the PALM-3000 adaptive optics system on the 5 m Hale telescope. The physical status of the binaries is confirmed through common proper motion and detection of orbital motion. In the process we detected a new candidate companion to HIP 95309. We also resolved the primary of HIP 110626 into a close binary making that system a triple. These detections increase the completeness of the multiplicity survey of the solar-type stars within 67 pc of the Sun. Combining our observations of HIP 103455 with archival astrometric measurements and RV measurements, we are able to compute the first orbit of HIP 103455 showing that the binary has a 68 yr period. We place the components on a color-magnitude diagram and discuss each multiple system individually.

astro-ph.SR↗

arXiv2016

The triple system Zeta Aquarii

Zeta Aquarii is a bright and nearby (28 pc) triple star with a 26-year astrometric subsystem. Almost a half of the outer 540-year visual orbit has been covered in 238 years of its observations. Both inner and outer orbits are revised here taking into account recent direct resolution of the inner pair Aa,Ab. The inner orbit has a high eccentricity of 0.87 and is inclined to the outer orbit by 140+-10 degrees, suggesting that Kozai-Lidov cycles take place. The masses of the stars Aa, B, and Ab are 1.4, 1.4, and 0.6 solar. The age of the system is about 3 Gyr, and the two main components have just left the main sequence. Hypothetically, this system could have formed by a dynamical capture of the small star Ab in the twin binary Aa,B.

astro-ph.SR↗