scholarly journals The Short-Period Binary Frequency Among Low-Mass Pre-Main Sequence Stars

1992 ◽  
Vol 135 ◽  
pp. 30-40
Author(s):  
Robert D. Mathieu
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Main Sequence ◽  
Early Period ◽  
Dynamical Evolution ◽  
Orbital Evolution ◽  
Semi Major Axis ◽  
Single Star ◽  
Binary Formation ◽  
Short Period

The pre-main sequence (PMS) binary frequency is a fundamental datum in the study of binary formation. It reflects on numerous basic issues, such as:• The formation process. Binary stars are the primary branch of the star-formation process, and thus their frequency is an essential challenge to star-formation theories. (Indeed, the infrequency of single-star formation is likely as significant as the binary frequency.)• The epoch of binary formation. Assessing whether the binary population exists in total by the pre-main sequence phase sets an upper limit on the binary formation timescale.• Early period evolution. The frequency distribution as a function of period of PMS binaries, when compared to the distribution at the zero-age main sequence, can shed light on early orbital evolution.• The interaction of binaries with disks. The formation and consequent dynamical evolution of a binary with semi-major axis less than typical disk radii must substantially modify disk structures and accretion flows. Thus the binary frequency might differ between PMS stars with and without associated disks.

scholarly journals The Origin of the RS CVn Binaries

1976 ◽  
Vol 73 ◽  
pp. 381-387 ◽  
Author(s):  
P. Biermann ◽  
D. S. Hall
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Total Mass ◽  
Total Angular Momentum ◽  
Main Sequence ◽  
Be Stars ◽  
Large Space ◽  
Single Star ◽  
The Core ◽  
Thermal Phase

We consider six possible origins for the RS CVn binaries based on the following possibilities. RS CVn binaries might now be either pre-main-sequence or post-main-sequence. A pre-main-sequence binary might not always have been a binary but might have resulted from fission of a rapidly rotating single pre-main-sequence star. The main-sequence counterparts might be either single stars or binaries.To decide which of the six origins is possible, we consider the following observed data for the RS CVn binaries: total mass, total angular momentum, lack of observed connection with regions of star formation, large space density, kinematical age, and the visual companion of WW Dra. In addition we consider lifetimes and space densities of single stars and other types of binaries.The only origin possible is that the RS CVn binaries are in a thermal phase following fission of a main-sequence single star. In this explanation the single star had a rapidly rotating core which became unstable due to the core contraction which made it begin to evolve off the main sequence. The present Be stars might be examples of such parent single stars.

scholarly journals The Dynamical Evolution of Young Clusters and Associations

1986 ◽  
Vol 7 ◽  
pp. 481-488 ◽  
Author(s):  
Robert D. Mathieu
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Initial Conditions ◽  
Dynamical Evolution ◽  
Short Review ◽  
Stellar Systems ◽  
Galactic Field ◽  
Dynamical State ◽  
Orbital Mixing ◽  
Formation Efficiency

A young cluster or association bears the imprint of the conditions at its birth for perhaps ten million years, after which the initial conditions are lost to either dilution in the galactic field or erasure by orbital mixing and stellar encounters. In its youngest years, however, the dynamical state of the system can provide valuable information concerning the structure and energetics of the parent gas, the star-formation efficiency and the star-formation process itself. This short review discusses recent theoretical and observational progress in the study of the very youngest of stellar systems.

scholarly journals TESS observations of pulsating subdwarf B stars: extraordinarily short-period gravity modes in CD−28° 1974

2020 ◽  
Vol 493 (4) ◽  
pp. 5162-5169 ◽  
Author(s):  
M D Reed ◽  
K A Shoaf ◽  
P Németh ◽  
J Vos ◽  
M Uzundag ◽  
...  
Keyword(s):  
Main Sequence ◽  
Orbital Motion ◽  
Proper Motions ◽  
Reflection Effect ◽  
Echelle Spectrograph ◽  
Single Star ◽  
B Stars ◽  
Subdwarf B Stars ◽  
Short Period ◽  
Typical Period

ABSTRACT Transiting Exoplanet Survey Satellite (TESS) observations show CD−28° 1974 to be a gravity(g)-mode-dominated hybrid pulsating subdwarf B (sdBV) star. It shows 13 secure periods that form an ℓ = 1 asymptotic sequence near the typical period spacing. Extraordinarily, these periods lie between 1500 and 3300 s, whereas typical $\ell = 1\, g$ modes in sdBV stars occur between 3300 and 10 000 s. This indicates a structure somewhat different from typical sdBV stars. CD−28° 1974 has a visually close F/G main-sequence companion 1.33 arcsec away, which may be a physical companion. Gaia proper motions indicate a comoving pair with the same distance. A reanalysis of Ultraviolet and Visual Echelle Spectrograph (UVES) spectra failed to detect any orbital motion and the light curve shows no reflection effect or ellipsoidal variability, making an unseen close companion unlikely. The implication is that CD−28° 1974 has become a hot subdwarf via single star or post-merger evolution.

scholarly journals The multiplicity of massive stars: a 2016 view

2016 ◽  
Vol 12 (S329) ◽  
pp. 110-117 ◽  
Author(s):  
Hugues Sana
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Massive Star ◽  
Main Sequence ◽  
Initial Conditions ◽  
Massive Stars ◽  
Massive Star Formation ◽  
Future Evolution

AbstractMassive stars like company. Here, we provide a brief overview of progresses made over the last 5 years by a number of medium and large surveys. These results provide new insights on the observed and intrinsic multiplicity properties of main sequence massive stars and on the initial conditions for their future evolution. They also bring new interesting constraints on the outcome of the massive star formation process.

scholarly journals Dynamical evolution of objects on highly elliptical orbits near high-order resonance zones

2014 ◽  
Vol 9 (S310) ◽  
pp. 168-169
Author(s):  
Eduard D. Kuznetsov ◽  
Stanislav O. Kudryavtsev
Keyword(s):  
Dynamical Evolution ◽  
Major Axis ◽  
Orbital Evolution ◽  
High Order ◽  
Semi Major Axis ◽  
Order Resonance ◽  
High Order Resonance ◽  
Elliptical Orbits ◽  
Pass Through

AbstractBoth analytical and numerical results are used to study high-order resonance regions in the vicinity of Molnya-type orbits. Based on data of numerical simulations, long-term orbital evolution are studied for objects in highly elliptical orbits depending on their area-to-mass ratio. The Poynting–Robertson effect causes a secular decrease in the semi-major axis of a spherically symmetrical satellite. Under the Poynting–Robertson effect, objects pass through the regions of high-order resonances. The Poynting–Robertson effect and secular perturbations of the semi-major axis lead to the formation of weak stochastic trajectories.

scholarly journals What Can Pre-Main Sequence Binary Star Populations Tell Us about Binary Formation Mechanisms?

2001 ◽  
Vol 200 ◽  
pp. 210-218 ◽  
Author(s):  
Andrea M. Ghez
Keyword(s):  
Star Formation ◽  
Binary Stars ◽  
Main Sequence ◽  
Binary Star ◽  
Open Clusters ◽  
Formation Mechanisms ◽  
Primary Star ◽  
Binary Formation ◽  
Review Current ◽  
Made In

We review current observations of binary star populations with particular attention to what insight these populations can give us into the problem of how binary stars form. Significant progress has been made in the past few years, revealing variations as a function of site, primary star mass, and binary star separations. The variations in the binary star population with type of star formation site in comparison with the field, suggests that ∼30% of the field binaries formed in loose T associations and ∼70% formed in the dense progenitors of open clusters. Variations with mass and separation on the whole are well matched by the predictions of fragmentation followed by competitive accretion. However, there remains much work to be done on both the observational and theoretical end before a complete picture of binary star formation can be developed.

scholarly journals Spectropolarimetric follow-up of 8 rapidly rotating, X-ray bright FK Comae candidates

2020 ◽  
Vol 496 (1) ◽  
pp. 295-308
Author(s):  
J Sikora ◽  
J Rowe ◽  
S B Howell ◽  
E Mason ◽  
G A Wade
Keyword(s):  
Evolutionary History ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Single Star ◽  
X Ray ◽  
Spectroscopic Binary ◽  
Short Period ◽  
Show Evidence ◽  
Red Giant

ABSTRACT Our understanding of the evolved, rapidly rotating, magnetically active, and apparently single FK Comae stars is significantly hindered by their extreme rarity: only two stars in addition to FK Com itself are currently considered to be members of this class. Recently, a sample of more than 20 candidate FK Comae type stars was identified within the context of the Kepler–Swift Active Galaxies and Stars (KSwAGS) survey. We present an analysis of high-resolution Stokes V observations obtained using ESPaDOnS@CFHT for 8 of these candidates. We found that none of these targets can be considered members of the FK Comae class based primarily on their inferred rotational velocities and on the detection of spectroscopic binary companions. However, 2 targets show evidence of magnetic activity and have anomalously high projected rotational velocities (vsin i) relative to typical values associated with stars of similar evolutionary states. EPIC 210426551 has a $v\sin {i}=209\, {\rm km\, s}^{-1}$, an estimated mass of $1.07\, \mathrm{ M}_\odot$, and, based in part on its derived metallicity of [M/H] = −0.4, it is either an evolved main sequence (MS) star or a pre-MS star. KIC 7732964 has a mass of $0.84\, \mathrm{ M}_\odot$, lies near the base of the red giant branch, and exhibits a $v\sin {i}=23\, {\rm km\, s}^{-1}$. We find that these two objects have similar characteristics to FK Com (albeit less extreme) and that their rapid rotation may be inconsistent with that predicted for a single star evolutionary history. Additional observations are necessary in order to better constrain their evolutionary states and whether they have short-period binary companions.

scholarly journals Statistical and numerical studies of the orbital evolution of short-period comets

1985 ◽  
Vol 83 ◽  
pp. 261-278
Author(s):  
A. Carusi ◽  
G.B. Valsecchi
Keyword(s):  
Dynamical Evolution ◽  
Orbital Evolution ◽  
Special Role ◽  
Outer Solar System ◽  
Orbital Elements ◽  
Numerical Work ◽  
Numerical Studies ◽  
Short Period ◽  
Evolutionary Paths ◽  
Work Done

AbstractThe evolutionary paths connecting cometary reservoirs in the outer solar system and the population of periodic comets involve stellar and planetary perturbations. Close planetary encounters play a special role, making the dynamical evolution slow or fast depending on the orbital elements of the comet at various stages of the process. In this paper numerical work done in the last decades on this subject, using both real and fictitious objects, is reviewed.

scholarly journals Orbital evolution of short-period comets with high values of the Tisserand constant

2006 ◽  
Vol 2 (S236) ◽  
pp. 35-42 ◽  
Author(s):  
N.Yu. Emel'yanenko
Keyword(s):  
Dynamical Evolution ◽  
Orbital Evolution ◽  
Giant Planets ◽  
Time Interval ◽  
Short Period

AbstractThe orbital evolution of comets with high values of the Tisserand constant is studied for a time interval of 800 years. Scenarios of dynamical evolution are obtained for 85 comets. Particular features of the orbital evolution of the comets of this class are singled out. The orbits of all comets are tangent to the orbit of Jupiter and have a steadily low inclination. For 80% of comets, the evolution scenario includes a timespan in which the comets move in low-eccentricity orbits. The possibility is analyzed of a change in the Tisserand constant and of a transition of the comet to be controlled by other giant planets.

Star-Disc Interactions and Binary Formation

1992 ◽  
Vol 135 ◽  
pp. 176-184
Author(s):  
Cathie Clarke
Keyword(s):  
Mass Exchange ◽  
Main Sequence ◽  
Orbital Evolution ◽  
Body System ◽  
Tidal Effects ◽  
Orbital Parameters ◽  
Binary Formation

By the time a binary arrives on the main sequence, its dynamics have essentially become those of a simple two-body system, so that its orbital parameters are constants of the motion thereafter. This statement of course needs to be modified under several circumstances, such as where tidal effects, mass exchange or interactions with field stars come into play. For the majority of binaries, however, orbital evolution is all but over by the main sequence. Therefore, in order to explain the distribution of binary orbital parameters one has to look to earlier times (prior to 107 years) when the more complicated dynamics can drive the orbital evolution that establishes these parameters.

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