arXiv subjects

Andrei Tokovinin

Publications and source records attributed to Andrei Tokovinin.

At least 37 records · Page 2Linked to original sources

arXiv2024

A comparison of next-generation turbulence profiling instruments at Paranal

A six-night optical turbulence monitoring campaign has been carried at Cerro Paranal observatory in February and March, 2023 to facilitate the development and characterisation of two novel atmospheric site monitoring instruments - the ring-image next generation scintillation sensor (RINGSS) and 24-hour Shack Hartmann image motion monitor (24hSHIMM) in the context of providing optical turbulence monitoring support for upcoming 20-40m telescopes. Alongside these two instruments, the well-characterised Stereo-SCIDAR and 2016-MASS-DIMM were operated throughout the campaign to provide data for comparison. All instruments obtain estimates of optical turbulence profiles through statistical analysis of intensity and wavefront angle-of-arrival fluctuations from observations of stars. Contemporaneous measurements of the integrated turbulence parameters are compared and the ratios, bias, unbiased root mean square error and correlation of results from each instrument assessed. Strong agreement was observed in measurements of seeing, free atmosphere seeing and coherence time. Less correlation is seen for isoplanatic angle, although the median values agree well. Median turbulence parameters are further compared against long-term monitoring data from Paranal instruments. Profiles from the three small-telescope instruments are compared with the 100-layer profile from the stereo-SCIDAR. It is found that the RINGSS and SHIMM offer improved accuracy in characterisation of the vertical optical turbulence profile over the MASS-DIMM. Finally, the first results of continuous optical turbulence monitoring at Paranal are presented which show a strong diurnal variation and predictable trend in the seeing. A value of 2.65" is found for the median daytime seeing.

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arXiv2023

Spectroscopic Orbits of Subsystems in Multiple Stars. X (Summary)

Results of a large program of spectroscopic monitoring of nearby solar-type stellar hierarchical systems using the CHIRON echelle spectrograph at the 1.5 m telescope are summarized. Ten papers of this series contain 102 spectroscopic orbits and substantially contribute to the knowledge of periods and eccentricties, providing input for the study of their formation and early evolution. Radial velocities of additional 91 targets without CHIRON orbits (members of wide physical pairs) are published here. Our results are compared to the recent Gaia Non-Single Star (NSS) catalog, revealing its strengths and weaknesses. The NSS provides orbital periods for 31 objects of the CHIRON sample (about one third). Of the 22 spectroscopic NSS orbits in common, 14 are in good agreement with CHIRON, the rest have reduced velocity amplitudes or other problems. Hence ground-based monitoring gives, so far, a more accurate and complete picture of nearby hierarchies than Gaia. The distribution of inner periods in hierarchical systems is non-monotonic, showing a shallow minimum in the 30-100 days bin and a strong excess at shorter periods, compared to the smooth distribution of simple binaries in the field. The period-eccentricity diagram of inner subsystems updated by this survey, recent literature, and Gaia, displays an interesting structure.

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arXiv2023

Spectroscopic Orbits of Subsystems in Multiple Stars. IX

New spectroscopic orbits of inner subsystems in 14 hierarchies are determined from long-term monitoring with the optical echelle spectrometer, CHIRON. Their main components are nearby solar-type stars belonging to nine triple systems (HIP 3645, 14307, 36165, 79980, 103735, 103814, 104440, 105879, 109443) and five quadruples of 2+2 hierarchy (HIP 41171, 49336, 75663, 78163, and 117666). The inner periods range from 254 days to 18 yr. Inner subsystems in HIP 3645, 14313, 79979, 103735, 104440, and 105879 are resolved by speckle interferometry, and their combined spectro-interferometric orbits are derived here. Astrometric orbits of HIP 49336 Aa,Ab and HIP 117666 Aa,Ab are determined from wobble in the observed motion of the outer pairs. Comparison with three spectroscopic orbits found in the Gaia DR3 archive reveals that Gaia under-estimated the amplitudes (except for HIP 109443), while the periods match approximately. This work contributes new data on the architecture of nearby hierarchical systems, complementing their statistics.

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arXiv2023

Dynamics of Four Triple Systems

Orbital motions in four hierarchical stellar systems discovered by speckle interferometry are studied. Their inner orbits are relatively well constrained, while the long outer orbits are less certain. The eccentric and misaligned inner orbits in the early-type hierarchies Epsilon Cha (B9V, central star of the 5 Myr old association, P=6.4 yr, e=0.73), and I~385 (A0V, P~300 yr, e~0.8) suggest past dynamical interactions. Their nearly equal masses could be explained by a dynamical decay of a 2+2 quadruple progenitor consisting of four similar stars. However, there is no evidence of the associated recoil, so similar masses could be just a consequence of accretion from the same core. The other two hierarchies, HIP 32475 (F0IV, inner period 12.2 yr) and HIP 42910 (K7V, inner period 6.8 yr), have smaller masses and are double twins where both inner and outer mass ratios are close to one. A double twin could either result from a merger of one inner pair in a 2+2 quadruple or can be formed by a successive fragmentation followed by accretion.

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arXiv2023

Exploring Thousands of Nearby Hierarchical Systems with Gaia and Speckle Interferometry

There should be about 10,000 stellar hierarchical systems within 100 pc with primary stars more massive than 0.5 Msun, and a similar amount of less massive hierarchies. A list of 8000 candidate multiples is derived from wide binaries found in the Gaia Catalog of Nearby Stars where one or both components have excessive astrometric noise or other indicators of inner subsystems. A subset of 1243 southern candidates were observed with high angular resolution at the 4.1 m telescope, and 503 new pairs with separations from 0.03" to 1" were resolved. These data allow estimation of the inner mass ratios and periods and help to quantify the ability of Gaia to detect close pairs. Another 621 hierarchies with known inner periods come from the Gaia catalog of astrometric and spectroscopic orbits. These two non-overlapping groups, combined with existing ground-based data, bring the total number of known nearby hierarchies to 2754, reaching a completeness of ~22% for stars above 0.5 Msun. Distributions of their periods and mass ratios are briefly discussed, and the prospects of further observations are outlined.

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arXiv2022

Speckle Interferometry at SOAR in 2021

The speckle interferometry program at the the 4.1 m Southern Astrophysical Research Telescope (SOAR), started in 2008, now accumulated over 30,300 individual observations of 12,700 distinct targets. Its main goal is to monitor orbital motion of close binaries, including members of high-order hierarchies and low-mass dwarfs in the solar neighborhood. The results from 2021 are published here, totaling 2,623 measurements of 2,123 resolved pairs and non-resolutions of 763 targets. The median measured separation is 0.21", and 75 pairs were closer than 30 mas. The calibration of scale and orientation is based on the observations of 103 wide pairs with well-modeled motion. These calibrators are compared to the latest Gaia data release, and minor (0.5%) systematic errors were rectified, resulting in accurate relative positions with typical errors on the order of 1 mas. Using these new measurements, orbits of 282 binaries are determined here (54 first determinations and 228 corrections). We resolved for the first time 50 new pairs, including subsystems in known binaries. A list of 94 likely spurious pairs unresolved at SOAR (mostly close Hipparcos binaries) is also given.

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arXiv2022

The Solar Neighborhood XLIX: New Discoveries and Orbits of M Dwarf Multiples with Speckle Interferometry at SOAR

We present the first results of a multi-year program to map the orbits of M dwarf multiples within 25 parsecs. The observations were conducted primarily during 2019 - 2020 using speckle interferometry at the Southern Astrophysical Research (SOAR) Telescope in Chile, using the High-Resolution Camera mounted on the adaptive optics module (HRCam+SAM). The sample of nearby M dwarfs is drawn from three sources: multiples from the RECONS long-term astrometric monitoring program at the SMARTS 0.9m, known multiples for which these new observations will enable or improve orbit fits, and candidate multiples flagged by their astrometric fits in Gaia Data Release 2 (DR2). We surveyed 333 of our 338 M dwarfs via 830 speckle observations, detecting companions for 63% of the stars. Most notably, this includes new companions for 76% in the subset selected from Gaia DR2. In all, we report the first direct detections of 97 new stellar companions to the observed M dwarfs. Here we present the properties of those detections, the limits of each non-detection, and five orbits with periods 0.67 - 29 yr already observed as part of this program. Companions detected have projected separations of 0.024 - 2.0 arcsec (0.25 - 66 AU) from their primaries and have $ΔI \lesssim 5.0$ mag. This multi-year campaign will ultimately map complete orbits for nearby M dwarfs with periods up to 3 yr, and provide key epochs to stretch orbital determinations for binaries to 30 yr.

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arXiv2022

Spectroscopic orbits of subsystems in multiple stars. VIII

Periods, eccentricities, and masses in hierarchical stellar systems inform us on the formation and early evolution of these fascinating objects. To complement the multiplicity statistics of nearby solar-type stars, 19 new spectroscopic orbits of inner subsystems in 15 hierarchies (10 triples and 5 quadruples) are determined based on high-resolution echelle spectra collected during several years. While previous papers of this series contained mostly short-period orbits, here most periods are on the order of a year. The main components of these hierarchies are HIP 7852, 9148, 12548, 21079, 24320, 27970, 34212, 56282, 57860, 76400, 76816, 81394, 96284, 100420, and HD 108938. Noteworthy systems are HIP 12548 and 24230 (hierarchies of 2+2 architecture with low-mass spectroscopic secondaries), HIP 56282 (a planetary-type 3+1 hierarchy), and HIP 27970 (a compact triple with periods of 15 and 1049 days).

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arXiv2022

The family of V1311 Ori: a young sextuple system or a mini-cluster?

A compact bound group of four active M-type dwarfs containing V1311 Ori is identified in the Gaia catalog of nearby stars. Located at a distance of 39 pc, it is likely related to the beta Pictoris and 32 Ori moving groups by kinematics, isochronal age, and other indicators of youth (Halpha emission, presence of lithium, and fast rotation). The brightest star A is a known close binary, for which a preliminary 80-yr visual-spectroscopic orbit is determined. Star B is resolved here into a 0.08" pair, and the faintest stars C and D are probably single. Considering the non-hierarchical configuration with projected separations of ~10 kau, this could be either a young sextuple system or a bound but dynamically unstable mini-cluster (trapezium) that avoided disruption so far. This pre-main-sequence system bridges the gap between moving groups and wide hierarchies.

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arXiv2021

Resolved Gaia Triples

A sample of 392 low-mass hierarchical triple stellar systems within 100 pc resolved by Gaia as distinct sources is defined. Owing to the uniform selection, the sample is ideally suited to study unbiased statistics of wide triples. The median projected separations in their inner and outer pairs are 151 and 2569 au, respectively, the median separation ratio is close to 15. Some triples appear in non-hierarchical configurations, and many are just above the dynamical stability limit. Internal motions in these systems are known with sufficient accuracy to determine the orbital motion sense of the outer and inner pairs and to reconstruct the eccentricity distributions. The mean inner and outer eccentricities are 0.66+-0.02 and 0.54+-0.02, respectively; the less eccentric outer orbits are explained by dynamical stability. The motion sense of the inner and outer pairs is almost uncorrelated, implying a mean mutual inclination of 83.1+-4.5deg. The median mass of the most massive component is 0.71 Msun, the median system mass is 1.53 Msun. In a 0.69 fraction of the sample the primary belongs to the inner binary, while in the remaining systems it is the tertiary. A 0.21 fraction of the inner subsystems are twins with mass ratios >0.95. The median outer mass ratio is 0.41; it decreases mildly with increasing outer separation. Presumably, these wide hierarchies were formed by collapse and fragmentation of isolated cores in low-density environments and represent a small fraction of initial systems that avoided dynamical decay. Wide pre-main sequence multiples in Taurus could be their progenitors.

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arXiv2021

Mysterious Dust-emitting Object Orbiting TIC 400799224

We report the discovery of a unique object of uncertain nature -- but quite possibly a disintegrating asteroid or minor planet -- orbiting one star of the widely separated binary TIC 400799224. We initially identified the system in data from TESS Sector 10 via an abnormally-shaped fading event in the light curve (hereafter 'dips'). Follow-up speckle imaging determined that TIC 400799224 is actually two stars of similar brightness at 0.62" separation, forming a likely bound binary with projected separation of ~300 au. We cannot yet determine which star in the binary is host to the dips in flux. ASAS-SN and Evryscope archival data show that there is a strong periodicity of the dips at ~19.77 days, leading us to believe that an occulting object is orbiting the host star, though the duration, depth, and shape of the dips vary substantially. Statistical analysis of the ASAS-SN data shows that the dips only occur sporadically at a detectable threshold in approximately one out of every three to five transits, lending credence to the possibility that the occulter is a sporadically-emitted dust cloud. The cloud is also fairly optically thick, blocking up to 37% or 75% of the light from the host star, depending on the true host. Further observations may allow for greater detail to be gleaned as to the origin and composition of the occulter, as well as to a determination of which of the two stars comprising TIC 400799224 is the true host star of the dips.

astro-ph.EP↗

arXiv2021

Architecture of Hierarchical Stellar Systems and their Formation

Accumulation of new data on stellar hierarchical systems and the progress in numerical simulations of their formation open the door to genetic classification of these systems, where properties of a certain group (family) of objects are tentatively related to their formation mechanisms and early evolution. A short review of the structure and statistical trends of known stellar hierarchies is given. Like binaries, they can be formed by the disk and core fragmentation events happening sequentially or simultaneously and followed by the evolution of masses and orbits driven by continuing accretion of gas and dynamical interactions between stars. Several basic formation scenarios are proposed and associated qualitatively with the architecture of real systems, although quantitative predictions for these scenarios are still pending. The general trend of increasing orbit alignment with decreasing system size points to the critical role of the accretion-driven orbit migration, which also explains the typically comparable masses of stars belonging to the same system. The architecture of some hierarchies bears imprints of chaotic dynamical interactions. Characteristic features of each family are illustrated by several real systems.

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arXiv2021

SOAR TESS Survey. II: The impact of stellar companions on planetary populations

We present the results of the second year of exoplanet candidate host speckle observations from the SOAR TESS survey. We find 89 of the 589 newly observed TESS planet candidate hosts have companions within 3\arcsec, resulting in light curve dilution, that if not accounted for leads to underestimated planetary radii. We combined these observations with those from paper I to search for evidence of the impact binary stars have on planetary systems. Removing the quarter of the targets observed identified as false-positive planet detections, we find that transiting planet are suppressed by nearly a factor-of-seven in close solar-type binaries, nearly twice the suppression previously reported. The result on planet occurrence rates that are based on magnitude limited surveys is an overestimation by a factor of two if binary suppression is not taken into account. We also find tentative evidence for similar close binary suppression of planets in M-dwarf systems. Lastly, we find that the high rates of widely separated companions to hot Jupiter hosts previously reported was likely a result of false-positive contamination in our sample.

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arXiv2021

TIC 454140642: A Compact, Coplanar, Quadruple-lined Quadruple Star System Consisting of Two Eclipsing Binaries

We report the discovery of a compact, coplanar, quadruply-lined, eclipsing quadruple star system from TESS data, TIC 454140642, also known as TYC 0074-01254-1. The target was first detected in Sector 5 with 30-min cadence in Full-Frame Images and then observed in Sector 32 with 2-min cadence. The light curve exhibits two sets of primary and secondary eclipses with periods of PA = 13.624 days (binary A) and PB = 10.393 days (binary B). Analysis of archival and follow-up data shows clear eclipse-timing variations and divergent radial velocities, indicating dynamical interactions between the two binaries and confirming that they form a gravitationally-bound quadruple system with a 2+2 hierarchy. The Aa+Ab binary, Ba+Bb binary, and A-B system are aligned with respect to each other within a fraction of a degree: the respective mutual orbital inclinations are 0.25 degrees (A vs B), 0.37 degrees (A vs A-B), and 0.47 degrees (B vs A-B). The A-B system has an orbital period of 432 days - the second shortest amongst confirmed quadruple systems - and an orbital eccentricity of 0.3.

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arXiv2021

Speckle Interferometry at SOAR in 2020

The results of speckle interferometric observations at the 4.1 m Southern Astrophysical Research Telescope (SOAR) in 2020, as well as earlier unpublished data, are given, totaling 1735 measurements of 1288 resolved pairs and non-resolutions of 1177 targets. We resolved for the first time 59 new pairs or subsystems in known binaries, mostly among nearby dwarf stars. This work continues our long-term speckle program. Its main goal is to monitor orbital motion of close binaries, including members of high-order hierarchies and Hipparcos pairs in the solar neighborhood. We also report observations of 892 members of young moving groups and associations, where we resolved 103 new pairs.

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arXiv2021

TIC 168789840: A Sextuply-Eclipsing Sextuple Star System

We report the discovery of a sextuply-eclipsing sextuple star system from TESS data, TIC 168789840, also known as TYC 7037-89-1, the first known sextuple system consisting of three eclipsing binaries. The target was observed in Sectors 4 and 5 during Cycle 1, with lightcurves extracted from TESS Full Frame Image data. It was also previously observed by the WASP survey and ASAS-SN. The system consists of three gravitationally-bound eclipsing binaries in a hierarchical structure of an inner quadruple system with an outer binary subsystem. Follow-up observations from several different observatories were conducted as a means of determining additional parameters. The system was resolved by speckle interferometry with a 0."42 separation between the inner quadruple and outer binary, inferring an estimated outer period of ~2 kyr. It was determined that the fainter of the two resolved components is an 8.217 day eclipsing binary, which orbits the inner quadruple that contains two eclipsing binaries with periods of 1.570 days and 1.306 days. MCMC analysis of the stellar parameters has shown that the three binaries of TIC 168789840 are "triplets", as each binary is quite similar to the others in terms of mass, radius, and Teff. As a consequence of its rare composition, structure, and orientation, this object can provide important new insight into the formation, dynamics, and evolution of multiple star systems. Future observations could reveal if the intermediate and outer orbital planes are all aligned with the planes of the three inner eclipsing binaries.

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arXiv2021

Inner and Outer Orbits in 13 Resolved Hierarchical Stellar Systems

Orbits of inner and outer subsystems in 13 triple or higher-order stellar systems are computed or updated using position measurements and, in three cases, radial velocities. The goal is to determine mutual orbital inclinations, period ratios, and masses to complement the statistics of hierarchical systems. Effect of the subsystems on the motion in the outer orbits (wobble) is explicitly modeled to determine inner mass ratios. Stars studied here (HD 5408, 8036, 9770, 15089, 29310, 286955, 29316, 140538, 144362, 154621, 156034, 185655, and 213235) are bright and nearby (from 15\,pc to 150\,pc). Their inner periods range from 1.7 yr to 49 yr, and the outer periods from 83 to 2400 yr. Some long-period outer orbits are poorly constrained. Four astrometric inner orbits and one outer orbit are computed for the first time.

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arXiv2020

Measurement of turbulence profile from defocused ring images

A defocused image of a bright single star in a small telescope contains rich information on the optical turbulence, i.e. the seeing. The concept of a novel turbulence monitor based on recording sequences of ring-like intrafocal images and their analysis is presented. It can be implemented using standard inexpensive telescopes and cameras. Statistics of intensity fluctuations in the rings and their radial motion allow measurement of the low-resolution turbulence profile, the total seeing, and the atmospheric time constant. The algorithm of processing the images and extracting the turbulence parameters is developed and extensively tested by numerical simulation. Prescriptions to correct for finite exposure time and partially saturated scintillation are given. A prototype instrument with a 0.13-m aperture was tested on the sky. The RINGSS (Ring-Image Next Generation Scintillation Sensor) can be used as a portable turbulence monitor for site testing and as an upgrade of existing seeing monitors.

astro-ph.IM↗