scholarly journals Episodes of Emission Lines in the Spectra of Red Giants as Signatures of Remnant Planetary Systems

2004 ◽  
Vol 202 ◽  
pp. 115-117
Author(s):  
G. M. Rudnitskij
Keyword(s):  
Solar System ◽  
Short Distance ◽  
Planetary System ◽  
Planetary Systems ◽  
Emission Lines ◽  
Circumstellar Envelope ◽  
Red Giants ◽  
Medium Effects ◽  
Solar Mass ◽  
Red Giant

When a star with a mass of about 1 solar mass enters the red giant stage of its evolution, the radius of its atmosphere reaches several astronomical units. If the star possessed during its mainsequence life a planetary system, similar to the solar system, the planets will be embedded into a rather dense and hot medium. Effects of a planet revolving around a red giant at a short distance (inside its circumstellar envelope) are discussed. Systematic monitoring of the spectra of red giants may reveal periodicities in the emergence of shock-induced emission lines and thus to detect probable remnant planetary systems around these stars.

scholarly journals Fly-by encounters between two planetary systems I: Solar system analogues

2019 ◽  
Vol 488 (1) ◽  
pp. 1366-1376 ◽  
Author(s):  
Daohai Li ◽  
Alexander J Mustill ◽  
Melvyn B Davies
Keyword(s):  
Solar System ◽  
Planetary System ◽  
Planetary Systems ◽  
Open Clusters ◽  
Giant Planets ◽  
Direct Imaging ◽  
Solar Mass ◽  
Close Encounters ◽  
Large Numbers

ABSTRACTStars formed in clusters can encounter other stars at close distances. In typical open clusters in the Solar neighbourhood containing hundreds or thousands of member stars, 10–20 per cent of Solar-mass member stars are expected to encounter another star at distances closer than 100 au. These close encounters strongly perturb the planetary systems, directly causing ejection of planets or their capture by the intruding star, as well as exciting the orbits. Using extensive N-body simulations, we study such fly-by encounters between two Solar system analogues, each with four giant planets from Jupiter to Neptune. We quantify the rates of loss and capture immediately after the encounter, e.g. the Neptune analogue is lost in one in four encounters within 100 au, and captured by the flying-by star in 1 in 12 encounters. We then perform long-term (up to 1 Gyr) simulations investigating the ensuing post-encounter evolution. We show that large numbers of planets are removed from systems due to planet–planet interactions and that captured planets further enhance the system instability. While encounters can initially leave a planetary system containing more planets by inserting additional ones, the long-term instability causes a net reduction in planet number. A captured planet ends up on a retrograde orbit in half of the runs in which it survives for 1Gyr; also, a planet bound to its original host star but flipped during the encounter may survive. Thus, encounters between planetary systems are a channel to create counter-rotating planets, This would happen in around 1 per cent of systems, and such planets are potentially detectable through astrometry or direct imaging.

scholarly journals Turning solar systems into extrasolar planetary systems in stellar clusters

2010 ◽  
Vol 6 (S276) ◽  
pp. 304-307
Author(s):  
Melvyn B. Davies
Keyword(s):  
Solar System ◽  
Planetary System ◽  
Large Fraction ◽  
Planetary Systems ◽  
Single Star ◽  
Solar Systems ◽  
Close Encounters ◽  
Eccentric Orbits ◽  
The Galaxy ◽  
Hostile Environments

AbstractMany stars are formed in some form of cluster or association. These environments can have a much higher number density of stars than the field of the galaxy. Such crowded places are hostile environments: a large fraction of initially single stars will undergo close encounters with other stars or exchange into binaries. We describe how such close encounters and exchange encounters will affect the properties of a planetary system around a single star. We define singletons as single stars which have never suffered close encounters with other stars or spent time within a binary system. It may be that planetary systems similar to our own solar system can only survive around singletons. Close encounters or the presence of a stellar companion will perturb the planetary system, leading to strong planet-planet interactions, often leaving planets on tighter and more eccentric orbits. Thus, planetary systems which initially resembled our own solar system may later more closely resemble the observed extrasolar planetary systems.

scholarly journals Molecular Masers in Variable Stars

2002 ◽  
Vol 19 (4) ◽  
pp. 499-504 ◽  
Author(s):  
Georgij M. Rudnitskij
Keyword(s):  
Line Emission ◽  
Variable Stars ◽  
Circumstellar Envelope ◽  
Red Giants ◽  
Circumstellar Envelopes ◽  
Emission Data ◽  
Physical Mechanisms ◽  
Stellar Pulsations ◽  
Red Giant ◽  
Maser Radio

AbstractWhen a star with a mass of one to a few solar masses enters the red giant stage of its evolution, the radius of its atmosphere reaches several astronomical units. Pulsational instability is typical for this stage. Most stars become Mira-type or semiregular variables with light cycles of a few hundred days. Red giants lose mass at a rate M = 10−7−10−5M⊙ yr−1. Extensive gas–dust circumstellar envelopes form. These envelopes contain various molecular species. Some of these molecules (OH, H2O, SiO, HCN) manifest themselves in maser radio emission. Data on the H2O maser variability and its connection with the stellar brightness variations are discussed. In the H2O line circumstellar masers can be divided into ‘stable’ (showing persistent emission — R Aql, U Her, S CrB, X Hya) and ‘transient’ (appearing in the H2O line once per 10–15 stellar light cycles — R Leo, R Cas, U Aur). Physical mechanisms of the maser variability are discussed. The most probable process explaining the observed visual–H2O correlation is the influence of shock waves on the masing region. Usually it is assumed that shocks in Mira atmospheres are driven by stellar pulsations. Here an alternative explanation is proposed. If a star during its main sequence life possessed a planetary system, similar to the solar system, the planets will be embedded in a rather dense and hot medium. Effects of a planet revolving around a red giant at a short distance (inside its circumstellar envelope) are discussed. A shock produced by the supersonic motion of a planet can account for the correlated variability of the Hα line emission and H2O maser. If the planetary orbit is highly eccentric, then the connected Hα–H2O flare episodes may be explained by the periastron passage of the planet. New tasks for the upgraded ATCA are discussed.

scholarly journals Conditions for the appearance of stars with a rotation opposite to the orbital rotation of their planets

2021 ◽  
pp. 22-25
Author(s):  
А.В. Тутуков ◽  
А.В. Федорова
Keyword(s):  
Molecular Clouds ◽  
Planetary System ◽  
Planetary Systems ◽  
Central Star ◽  
Giant Molecular Clouds ◽  
Relative Speed ◽  
Solar Mass ◽  
Orbital Rotation ◽  
Direction Opposite ◽  
Central Stars

Обнаружение планетной системы K2-290 A с двумя копланарными планетами, которые обращаются в направлении, обратном вращению центральной звезды, ставит задачу поиска адекватного сценария возникновения таких систем. В данной статье представленные нами ранее сценарии образования планетных систем пересматриваются для оценки возможности формирования в их рамках планет с орбитальным вращением, обратным вращению их центральных звезд. Оценки показывают, что аккреция холодного газа гигантских молекулярных облаков старыми звездами солнечной массы, движущимися в этих облаках с низкой относительной скоростью менее ∼ 1 км/с - это наиболее вероятный сценарий возникновения таких планетных систем. С другой стороны, обратное вращение только одной из нескольких планет системы может быть результатом взаимодействия близких массивных планет на неустойчивых орбитах. Detection of planetary system K2-290 A with two coplanar planets, which rotate in the direction opposite to the rotation of the central star, poses the problem of finding an adequate scenario for the emergence of such systems. In this article, the scenarios for the formation of planetary systems are revised to assess the possibility of forming within their framework planets with orbital rotation opposite to the rotation of their central stars. Estimates show that the accretion of cold gas from giant molecular clouds (GMOs) by old solar-mass stars moving in GMOs with a relative speed less than ∼ 1 km/s - this is the most probable scenario for the emergence of such planetary systems. On the other hand, the opposite rotation of only one of the several planets of the system can be the result of interaction of nearby massive planets in unstable orbits.

scholarly journals Close encounters with the Death Star: Interactions between collapsed bodies and the Solar System

2021 ◽  
Vol 648 ◽  
pp. L2 ◽  
Author(s):  
Václav Pavlík ◽  
Steven N. Shore
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Solar System ◽  
Planetary System ◽  
Planetary Systems ◽  
Symplectic Integrator ◽  
Orbital Parameters ◽  
Long Term Stability ◽  
Complete Disruption

Aims. We aim to investigate the consequences of a fast massive stellar remnant – a black hole (BH) or a neutron star (NS) – encountering a planetary system. Methods. We modelled a close encounter between the actual Solar System (SS) and a 2 M⊙ NS and a 10 M⊙ BH, using a few-body symplectic integrator. We used a range of impact parameters, orbital phases at the start of the simulation derived from the current SS orbital parameters, encounter velocities, and incidence angles relative to the plane of the SS. Results. We give the distribution of possible outcomes, such as when the SS remains bound, when it suffers a partial or complete disruption, and in which cases the intruder is able to capture one or more planets, yielding planetary systems around a BH or a NS. We also show examples of the long-term stability of the captured planetary systems.

scholarly journals Modelling differential rotation of red giants: the case of the evolved sun

2019 ◽  
Vol 490 (1) ◽  
pp. L71-L75
Author(s):  
Leonid Kitchatinov ◽  
Alexander Nepomnyashchikh
Keyword(s):  
Angular Momentum ◽  
Differential Rotation ◽  
Convective Transport ◽  
Rotational State ◽  
Red Giants ◽  
Solar Mass ◽  
Angular Momentum Transport ◽  
Stellar Convection ◽  
Order Of Magnitude ◽  
Red Giant

ABSTRACT Asteroseismology has revealed that cores of red giants rotate about one order of magnitude faster than their convective envelopes. This paper attempts an explanation for this rotational state in terms of the theory of angular momentum transport in stellar convection zones. A differential rotation model based on the theory is applied to a sequence of evolutionary states of a red giant of one solar mass. The model computations show a rotation of about ten times faster in the cores compared to the stellar surface. This rotational state is caused by the non-diffusive downward convective transport of angular momentum. The contrast in rotational rates between core and envelope increases with the radius (age) of the star. Seismologically detected scaling for the spin-down of the giants’ cores is also reproduced.

scholarly journals Is our Sun a Singleton?

2007 ◽  
Vol 3 (S246) ◽  
pp. 273-274
Author(s):  
D. Malmberg ◽  
M. B. Davies ◽  
J. E. Chambers ◽  
F. De Angeli ◽  
R. P. Church ◽  
...  
Keyword(s):  
Binary System ◽  
Solar System ◽  
Planetary System ◽  
Large Fraction ◽  
Planetary Systems ◽  
Number Density ◽  
Single Star ◽  
Close Encounters ◽  
Eccentric Orbits ◽  
Exoplanet Systems

AbstractMost stars are formed in a cluster or association, where the number density of stars can be high. This means that a large fraction of initially-single stars will undergo close encounters with other stars and/or exchange into binaries. We describe how such close encounters and exchange encounters can affect the properties of a planetary system around a single star. We define a singleton as a single star which has never suffered close encounters with other stars or spent time within a binary system. It may be that planetary systems similar to our own solar system can only survive around singletons. Close encounters or the presence of a stellar companion will perturb the planetary system, often leaving planets on tighter and more eccentric orbits. Thus planetary systems which initially resembled our own solar system may later more closely resemble some of the observed exoplanet systems.

Carbon and oxygen isotopes in AGB stars. From the cores of AGB stars to presolar dust

2018 ◽  
Vol 14 (S343) ◽  
pp. 447-448
Author(s):  
Thomas Lebzelter ◽  
Kenneth Hinkle ◽  
Oscar Straniero
Keyword(s):  
Solar System ◽  
Stellar Evolution ◽  
Galactic Evolution ◽  
Isotopic Ratios ◽  
Red Giants ◽  
Agb Stars ◽  
Carbon And Oxygen Isotopes ◽  
Different Types ◽  
Red Giant ◽  
Final Evolution

AbstractIsotopic ratios are a powerful tool for gaining insights into stellar evolution and nucleosynthesis. The isotopic ratios of the key elements carbon and oxygen are perfectly suited to investigate the pristine composition of red giants, the conditions in their interiors, and the mixing in their extended atmospheres. Of course the dust ejected from red giants in their final evolution also contains isotopically tagged material. This red giant dust is present in the solar system as presolar dust grains. We have measured isotopic ratios of carbon and oxygen in spectra from a large sample of AGB stars including both Miras and semiregular variables. We show how the derived ratios compare with expectations from stellar models and with measurements in presolar grains. Comparison of isotopes that are affected by different types of nucleosynthesis provides insights into galactic evolution.

scholarly journals SiO masers in red giants

2002 ◽  
Vol 206 ◽  
pp. 266-273
Author(s):  
E. M. L. Humphreys
Keyword(s):  
Structural Changes ◽  
Spatial Separation ◽  
Circumstellar Envelope ◽  
Red Giants ◽  
Giant Stars ◽  
Show Evidence ◽  
Complex Picture ◽  
Key Features ◽  
Red Giant ◽  
Inner Envelope

In recent years, it has become possible to trace rapid structural changes occurring in the extended atmospheres of red giant stars through VLBI monitoring of SiO masers. The observations reveal a complex picture. Firstly, material is predominantly outflowing, but also infalls towards the star, in a pulsating inner envelope periodically disrupted by shocks. Secondly, circular polarization measurements may indicate that the inner circumstellar envelope is permeated by a magnetic field strong enough to be of dynamical importance. Finally, towards a few stars, observations also show evidence for rotation of the SiO maser region. Current SiO maser models can reproduce many of the key features of circumstellar SiO maser emission, and have successfully predicted e.g. the infall of SiO masing gas and the observed spatial separation ofv= 1 andv= 2 43 GHz masers. However, both stellar hydrodynamical and maser codes need to increase in complexity in order to model fully these regions. In this review I will discuss the current developments in circumstellar SiO maser observations and models.

scholarly journals Effects of mass loss on the formation of planetary nebulae

1981 ◽  
Vol 59 ◽  
pp. 347-351 ◽  
Author(s):  
Sun Kwok
Keyword(s):  
Mass Loss ◽  
Planetary Nebulae ◽  
Open Clusters ◽  
Dominant Factor ◽  
Red Giants ◽  
Late Type ◽  
Solar Mass ◽  
Late Evolution ◽  
Nuclear Burning ◽  
Red Giant

The idea that planetary nebulae (PN) originated from outer layers of red giants goes back to Shlovskii (1956). This hypothesis was supported by Abell and Goldreich (1966) who argued convincingly that red giants are the most likely progenitors of PN. Although this is generally accepted today, the details of the transition from red giants to PN remain in controversy. It was pointed out by Paczyński (1971 a) that PN progenitors must have similar luminosities to central stars of PN, and therefore are likely to be late-type supergiants undergoing double-shell burning. The advent of infrared astronomy led to the discovery that most, if not all, late-type giants and supergiants are losing mass at rates of 10-6 - 10-5 Mʘyr-1 (Gehrz and Woolf 1971). Such mass loss rates greatly exceed the nuclear burning rate (6 x 10-8 - 5 x 10-7 Mʘyr-1 for stars with core masses between 0.6 and 1.2 Mʘ) and must be the dominant factor in the late evolution of intermediate mass stars. The observation of white dwarfs in open clusters implies that up to 6 Mʘ can be lost during the red-giant phase (Romanishin and Angel 1980). Since the observed masses of PN are no more than a few tenths of a solar mass, the existence of massive circumstellar envelopes formed by steady mass loss must have an effect on the formation of PN.

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