Stability, chaos and entrapment of stars in very wide pairs

ABSTRACT Distribution of eccentricities of very wide (up to 10 kau) low-mass binaries in the solar neighbourhood is studied using the catalogue of El-Badry and Rix (2018) based on Gaia. Direction and speed of relative motions in wide pairs contain statistical information on the eccentricity distribution, otherwise inaccessible owing to very long orbital periods. It is found that the eccentricity distribution is close to the linear (thermal) one f(e) = 2e. However, pairs with projected separations <200 au have less eccentric orbits, while f(e) for wide pairs with s > 1 kau appears to be slightly superthermal, with an excess of very eccentric orbits. Eccentricity of any wide binary can be constrained statistically using direction and speed of its motion. The thermal eccentricity distribution signals an important role of the stellar dynamics in the formation of wide binaries, although disc-assisted capture also can produce such pairs with eccentric orbits.

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Statistical Modeling and Analysis of Wide Binary Star Systems

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307006230 ◽

2006 ◽

Vol 2 (S240) ◽

pp. 686-689

Author(s):

K.B. Johnston ◽

T.D. Oswalt ◽

D. Valls-Gabaud

Keyword(s):

Mass Loss ◽

Main Sequence ◽

Galactic Disk ◽

Binary Star ◽

Wide Binary ◽

Robust Test ◽

Modeling And Analysis ◽

Tidal Interactions ◽

Wide Pairs ◽

Binary Separations

AbstractPost-main-sequence (MS) mass loss causes orbital separation amplification in fragile (i.e. common proper motion) binary star systems. Components typically have separations around ∼1000 AU. Such wide pairs experience negligible tidal interactions and mass transfer between companions; thus they evolve as two separate but coeval stars. In this paper we compute the rate of mass loss during the components' lifetimes and attempt to model how it will statistically distort a frequency distribution of fragile binary separations. Understanding this process provides a robust test of current theories of stellar evolution and sets constraints on the dynamics of the Galactic disk.

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The evolution of the stars

Mathematical Proceedings of the Cambridge Philosophical Society ◽

10.1017/s0305004100021368 ◽

1939 ◽

Vol 35 (4) ◽

pp. 592-609 ◽

Cited By ~ 35

Author(s):

F. Hoyle ◽

R. A. Lyttleton

Keyword(s):

Binary Stars ◽

Total Angular Momentum ◽

Interstellar Matter ◽

Low Velocity ◽

Double Stars ◽

Accretion Process ◽

Wide Pairs ◽

Massive Component ◽

Low Mass ◽

Direct Results

Difficulties associated with the evolution of stars by radiation alone are briefly discussed. It is clear that some other process is also affecting the stars and it is shown that the stars are capable of adding to their mass by the process of accretion of the cosmical cloud. The gravitation of a moving star causes additional collisions of the atoms of the interstellar matter and the motions become randomized to such an extent that the star probably captures all material passing within the distance at which the velocity of the star relative to the cloud is the parabolic velocity. This rate of accretion of mass of a star is 4πγ2ρM2/ν3, and is accordingly of great importance for stars of low velocity. Stars of high velocity are least affected by accretion and therefore in general remain of low mass, while stars of low velocity must attain great mass. The periods of time involved in bringing about appreciable changes in the mass of a star are of the order of 5 × 1010 years and are in agreement with independent estimates of the time scale, as deduced, for example, from the companion of Sirius. The evolution of the components and orbits of binary stars are consequences of the accretion process. The more massive component increases in mass more rapidly than the less massive component in the case of wide pairs, and may therefore in general continue to emit more ergs per gram. The orbit evolves in such a way that the total angular momentum remains constant. For equal masses the separation is proportional to the inverse cube of the mass, and the period to the inverse fifth power, so that great changes of separation and period occur. The evolution of the stars is governed almost entirely by their velocities relative to the cosmical cloud. In the case of double stars the evolution takes the form of decreasing period and decreasing separation. Such features as galactic concentration and the correlation between spectral type and velocity are direct results of accretion.

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Multiplicity and clustering in Taurus star forming region

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833042 ◽

2018 ◽

Vol 620 ◽

pp. A27 ◽

Cited By ~ 13

Author(s):

Isabelle Joncour ◽

Gaspard Duchêne ◽

Estelle Moraux ◽

Frédérique Motte

Keyword(s):

Star Formation ◽

Nearest Neighbor ◽

Spatial Clustering ◽

Mean Value ◽

K Nearest Neighbor ◽

Star Forming ◽

Star Forming Regions ◽

Wide Pairs ◽

A Chain ◽

The One

Context. Multiplicity and clustering of young pre-main sequence stars appear as critical clues to understand and constrain the star formation process. Taurus is the archetypical example of the most quiescent star forming regions that may still retain primeval signatures of star formation. Aims. This work identifies local overdense stellar structures as a critical scale between wide pairs and loose groups in Taurus. Methods. Using the density-based spatial clustering of applications with noise (dbscan) algorithm, and setting its free parameters based on the one-point correlation function and the k-nearest neighbor statistics, we have extracted reliably overdense structures from the sky-projected spatial distribution of stars. Results. Nearly half of the entire stellar population in Taurus is found to be concentrated in 20 very dense, tiny and prolate regions called NESTs (for Nested Elementary STructures). They are regularly spaced (≈2 pc) and mainly oriented along the principal gas filaments axes. Each NEST contains between four and 23 stars. Inside NESTs, the surface density of stars may be as high as 2500 pc−2 and the mean value is 340 pc−2. Nearly half (11) of these NESTs contain about 75% of the class 0 and I objects. The balance between Class I, II, and, III fraction within the NESTs suggests that they may be ordered as an evolutionary temporal scheme, some of them getting infertile with time, while other still giving birth to young stars. We have inferred that only 20% of stars in Taurus do not belong to any kind of stellar groups (either multiple system, ultra wide pairs or NESTs). The mass-size relation for stellar NESTs is very close to the Bonnor–Ebert expectation. The range in mass is about the same as that of dense molecular cores. The distribution in size is bimodal peaking at 12.5 and 50 kAU and the distribution of the number of YSOs in NESTs as a function of size exhibits two regimes. Conclusions. We propose that the NESTs in their two size regimes represent the spatial imprints of stellar distribution at birth as they may have emerged within few millions years from their natal cloud either from a single core or from a chain of cores. We have identified them as the preferred sites of star formation in Taurus. These NESTs are the regions of highest stellar density and intermediate spatial scale structures between ultra-wide pairs and loose groups.

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A new take on the low-mass brown dwarf companions on wide orbits in Upper-Scorpius

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935732 ◽

2020 ◽

Vol 633 ◽

pp. A124 ◽

Cited By ~ 5

Author(s):

S. Petrus ◽

M. Bonnefoy ◽

G. Chauvin ◽

C. Babusiaux ◽

P. Delorme ◽

...

Keyword(s):

Physical Properties ◽

Evolutionary Model ◽

Brown Dwarfs ◽

Emission Lines ◽

Medium Resolution ◽

Wide Pairs ◽

Hydrogen Emission Lines ◽

Mechanisms Of Formation ◽

Bayesian Inference Method ◽

Low Mass

Context. The Upper-Scorpius association (5–11 Myr) contains a unique population of low-mass (M ≤ 30MJup) brown dwarfs either free-floating, forming wide pairs, or on wide orbits around solar-type and massive stars. The detailed relative characterization of their physical properties (mass, radius, temperature, composition, and ongoing accretion) offers the opportunity to potentially explore their origin and mechanisms of formation. Aims. In this study, we aim to characterize the chemical and physical properties of three young, late-M brown dwarfs claimed to be companions of the Upper-Scorpius stars USco 161031.9-16191305, HIP 77900, and HIP 78530 using medium-resolution spectroscopy at UV (0.30−0.56μm; Rλ ~ 3300), optical (0.55−1.02μm; Rλ ~ 5400), and NIR (1.02−2.48μm; Rλ ~ 4300) wavelengths. The spectra of six free-floating analogs from the same association are analyzed for comparison and to explore the potential physical differences between these substellar objects found in different configurations. We also aim to examine and analyze hydrogen emission lines at UV and optical wavelengths to investigate the presence of ongoing accretion processes. Methods. The X-shooter spectrograph at VLT was used to obtain the spectra of the nine young brown dwarfs over the 0.3−2.5μm range simultaneously. Performing a forward modeling of the observed spectra with the ForMoSA code, we infer the Teff, log (g), and radius of our objects. The code compares here the BT-SETTL15 models to the observed spectra using the Nested Sampling Bayesian inference method. Mass is determined using evolutionary models, and a new analysis of the physical association is presented based on Gaia-DR2 astrometry. Results. The Teff and log (g) determined for our companions are compatible with those found for free-floating analogs of the Upper-Scorpius association and with evolutionary model predictions at the age of the association. However the final accuracy on the Teff estimates is strongly limited by nonreproducibility of the BT-SETTL15 models in the range of Teff corresponding to the M8–M9 spectral types. We identified Hα, Hβ, Hγ, and Ca II H and K emission lines in the spectrum of several objects. We attribute these lines to chromospheric activity except for the free-floating object USco 1608-2315 for which they are indicative of active accretion (M˙ ≤ 10−10.76 M⊙ yr−1). We confirm the four-fold over-luminosity of USco 161031.9-16191305 B down to 0.3 μm, which could be explained in part by the activity of this object and if the companion is an unresolved multiple system.

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Binary Star Formation Simulations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311027955 ◽

2011 ◽

Vol 7 (S282) ◽

pp. 409-416

Author(s):

C. J. Clarke

Keyword(s):

Star Formation ◽

Magnetic Fields ◽

Binary Stars ◽

Binary Star ◽

Statistical Properties ◽

Future Research ◽

Mass Ratio ◽

Theoretical Comparison ◽

Wide Pairs ◽

Binary Formation

AbstractBinary stars provide an excellent calibration of the success or otherwise of star formation simulations, since the reproduction of their statistical properties can be challenging. Here, I summarise the direction that the field has taken in recent years, with an emphasis on binary formation in the cluster context, and discuss which observational diagnostics are most ripe for meaningful theoretical comparison. I focus on two issues: the prediction of binary mass ratio distributions and the formation of the widest binaries in dissolving clusters, showing how in the latter case the incidence of ultra-wide pairs constrains the typical membership number of natal clusters to be of order a hundred. I end by drawing attention to recent works that include magnetic fields and which will set the direction of future research in this area.

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The Importance of Wide-System Studies for Stellar Evolution and Galactic Dynamics

International Astronomical Union Colloquium ◽

10.1017/s0252921100088382 ◽

1984 ◽

Vol 80 ◽

pp. 23-28

Author(s):

J. Dommanget

Keyword(s):

Double Star ◽

Galactic Dynamics ◽

Time Interval ◽

Short Time Interval ◽

Main Task ◽

Multiple Star ◽

Multiple Systems ◽

Wide Pairs ◽

Wide System ◽

Short Time

AbstractWide pairs and wide multiple systems have been too much neglected during many years by visual double star astronomers with the argument that only close visual pairs (short periods) may lead to mass-determinations in a relatively short time interval. But mass-determination should not be considered as the only interest of double star astronomy, even if it is of a fundamental nature.Today, it appears that researches on the origin and the evolution of the wide systems are urgently wanted, not only for the understanding of the evolution of the stellar medium, but also for a better knowledge of galactic dynamics. Some examples are given.Presently, the main task for double star specialists will be an important improvement in double and multiple star census for all kind of systems: close, medium, and wide. The Hipparcos satellite will probably add some important informations in that respect but ground-based observations also remain of the highest importance (radial velocities, photometry, astrometry, etc.).

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L’Astronomie des Etoiles Doubles face a la Mission Astrometrique du Satellite Hipparcos

International Astronomical Union Colloquium ◽

10.1017/s0252921100010137 ◽

1983 ◽

Vol 62 ◽

pp. 260-260 ◽

Cited By ~ 2

Author(s):

J. Dommanget

Keyword(s):

Optical Design ◽

Double Star ◽

Scanning Process ◽

Wide Pairs

SummaryThe Hipparcos satellite is described as well as the scanning process of the sky by its optical design, as a consequence of the satellite’s motion. From these data, the possibilities of the mission is deduced and applied in the case of the binaries.Discussion is made of what may be expected for different double star categories including spectroscopic, astrometric, close visual and wide pairs. Information are given on how proposals should be made for lists of binaries that should be observed.

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