N‐body simulations of stars escaping from the Orion nebula (original) (raw)
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The FU Orionis Binary System RNO 1B/1C
The Astronomical Journal, 1995
Observations of CS {7-+6) emission reveal a ;;a.3A 0 core, 1.8X 10 4 AU in size, surrounding the FU Orionis binary system RNO 1B/1C. Fractional chemical abundances, calculated from LVG and LTE codes, are mostly similar to those in the cold core TMC 1. However, values for Si0/H 2 and CH 3 0H!H 2 are enhanced, possibly by sputtering reactions or grain-grain collisions in tile outflow associated with the young stars. Aperture syntllesis maps of tile 2.6 and 3.1 mm continuum emission at-5" and-9" resolution, respectively, reveal that RNO 1C is surrounded by a flattened, dusty envelope,-SOOOAU in size, witll mass ;;;.1.1 A 0. High spatial resolution (-3'1 interferometer observations of CS (2-+ 1) emission may trace the dense walls of ail outflow cavity comprised of two concentric arcs with dynamical ages of 4X10 3 and 1 X 10 4 yr. The velocity structure of lower density gas imaged in the CO (1-+0) transition is consistent witll the arcs being formed by two energetic FU Orionis outbursts. Each event may have imparted more tllan 4 A 0 km s-1 to the outflow, implying outburst mass loss rates of-10-4 A 0 yr-1 • It appears that RNO 1C is probably the driving source for the outflow and tllat, while pre-main sequence stars are in tile FU Orionis stage, outbursts may dominate botll outflow morphology and energetics. 1. INfRODUCTION tory, the results of which we describe below.
The Astrophysical Journal, 2012
Physical collisions and close approaches between stars play an important role in the formation of exotic stellar systems. Standard theories suggest that collisions are rare, occurring only via random encounters between stars in dense clusters. We present a different formation pathway, the triple evolution dynamical instability (TEDI), in which mass loss in an evolving triple star system causes orbital instability. The subsequent chaotic orbital evolution of the stars triggers close encounters, collisions, exchanges between the stellar components, and the dynamical formation of eccentric compact binaries (including Sirius like binaries). We demonstrate that the rate of stellar collisions due to the TEDI is approximately 10 −4 yr −1 per Milky-Way Galaxy, which is nearly 30 times higher than the total collision rate due to random encounters in the Galactic globular clusters. Moreover, we find that the dominant type of stellar collisions is qualitatively different; most collisions involve asymptotic giant branch stars, rather than main sequence, or slightly evolved stars, which dominate collisions in globular clusters. The TEDI mechanism should lead us to revise our understanding of collisions and the formation of compact, eccentric binaries in the field.
The Formation of a Bound Star Cluster: From the Orion Nebula Cluster to the Pleiades
Monthly Notices of The Royal Astronomical Society, 2000
(shortened) Direct N-body calculations are presented of the formation of Galactic clusters using GasEx, which is a variant of the code Nbody6. The calculations focus on the possible evolution of the Orion Nebula Cluster (ONC) by assuming that the embedded OB stars explosively drove out 2/3 of its mass in the form of gas about 0.4 Myr ago. A bound cluster forms readily and survives for 150 Myr despite additional mass loss from the large number of massive stars, and the Galactic tidal field. This is the very first time that cluster formation is obtained under such realistic conditions. The cluster contains about 1/3 of the initial 10^4 stars, and resembles the Pleiades Cluster to a remarkable degree, implying that an ONC-like cluster may have been a precursor of the Pleiades. This scenario predicts the present expansion velocity of the ONC, which will be measurable by upcoming astrometric space missions (DIVA and GAIA). These missions should also detect the original Pleiades members as an associated expanding young Galactic-field sub-population. The results arrived at here suggest that Galactic clusters form as the nuclei of expanding OB associations.
V1647 Orionis: Reinvigorated Accretion and the ReAppearance of McNeil's Nebula
Astrophysical Journal, 2009
In late 2003, the young eruptive variable star V1647 Orionis optically brightened by over 5 mag, stayed bright for around 26 months, and then declined to its pre-outburst level. In 2008 August, the star was reported to have unexpectedly brightened yet again and we herein present the first detailed observations of this new outburst. Photometrically, the star is now as bright as it ever was following the 2003 eruption. Spectroscopically, a pronounced P Cygni profile is again seen in Hα with an absorption trough extending to ∼700 km s −1 . In the near-infrared, the spectrum now possesses very weak CO overtone bandhead absorption in contrast to the strong bandhead emission seen soon after the 2003 event. Water vapor absorption is also much stronger than previously seen. We discuss the current outburst below and relate it to the earlier event.
Astrophysical Journal Supplement Series, 2004
We report the discovery of a double-lined, spectroscopic, eclipsing binary in the Orion star-forming region. We analyze the system spectroscopically and photometrically to empirically determine precise, distance-independent masses, radii, effective temperatures, and luminosities for both components. The measured masses for the primary and secondary, accurate to ∼ 1%, are 1.01 M ⊙ and 0.73 M ⊙ , respectively; thus the primary is a definitive pre-main-sequence solar analog, and the secondary is the lowestmass star yet discovered among pre-main-sequence eclipsing binary systems. We use these fundamental measurements to test the predictions of pre-main-sequence stellar evolutionary tracks. None of the models we examined correctly predict the masses of the two components simultaneously, and we implicate differences between the theoretical and empirical effective temperature scales for this failing. All of the models predict the observed slope of the mass-radius relationship reasonably well, though the observations tend to favor models with low convection efficiencies. Indeed, considering our newly determined mass measurements together with other dynamical mass measurements of pre-main-sequence stars in the literature, as well as measurements of Li abundances in these stars, we show that the data strongly favor evolutionary models with inefficient convection in the stellar interior, even though such models cannot reproduce the properties of the present-day Sun.
Monthly Notices of the Royal Astronomical Society
The kinematics of the plasma in 14 planetary nebulae (PNe) is analysed by measuring the expansion velocities (V exp) of different ions as derived from their collisionally excited lines (CELs) and optical recombination lines (ORLs). V exp is analysed as a function of the ionization potential of ions, which at a first approximation represents the distance of the ion from the central star. In most cases, the kinematics of ORLs is incompatible with the kinematics of CELs at the same ionization potential, especially if CELs and ORLs are considered for the same ion. In general, V exp from ORLs is lower than V exp from CELs, indicating that, if the gas is in ionization equilibrium, ORLs are emitted by a gas located closer to the central star. The velocity field derived from CELs shows a gradient accelerating outwards as predicted from hydrodynamic modelling of PNe ionization structures. The velocity field derived from ORLs is different. In many cases, the velocity gradient is flatter or non-existent and highly and lowly ionized species present nearly the same V exp. In addition, the full width at half-maximum (FWHM) for ORLs is usually smaller than FWHM(CEL). Our interpretation is that ORLs are mainly emitted by a plasma that coexists with the plasma emitting CELs, but does not fit the ionization structures predicted by models. Such a plasma should have been ejected in a different event from the plasma emitting CELs.
The Large-Scale Distribution and Motions of Older Stars in Orion
We review the current knowledge of the population of 'older' stars in the Orion OB1 association, specifically those in subgroups 1a and 1b. We briefly outline the history of the subject and then continue with a summary of the present state of knowledge of the early-type stars in Orion OB1. New results from the Hipparcos parallaxes and proper motions will be presented. The main result is that subgroup 1a is located at about 330 pc from the Sun, much closer than the previously determined distance, and about 100 pc distant from the other subgroups of the association and the Orion molecular clouds. Unfortunately, due to the unfavorable kinematics of the association with respect to the Galactic background, Hipparcos proper motions do not allow a clear kinematic separation of the association from the field. For this purpose accurate and homogeneous radial velocities are needed. Traditionally, the massive O and B stars have received most of the attention in the studies of OB associations. However, we will present results showing that significant numbers of low-mass stars are associated with Orion OB1. Unbiased, optically complete, spectroscopic and photometric surveys of areas within subgroups 1a and 1b have the potential to determine the complete low-mass stellar population, down to the brown dwarf limit. This will provide much insight into the overall initial mass function and studies of the kinematics of the low-mass stars will yield insights into the dispersal of the association.
Monthly Notices of the Royal Astronomical Society, 2003
Spherically symmetric equal mass star clusters containing a large amount of primordial binaries are studied using a hybrid method, consisting of a gas dynamical model for single stars and a Monte Carlo treatment for relaxation of binaries and the setup of close resonant and fly-by encounters of single stars with binaries and binaries with each other (three-and four-body encounters). What differs from our previous work is that each encounter is being integrated using a highly accurate direct few-body integrator which uses regularized variables. Hence we can study the systematic evolution of individual binary orbital parameters (eccentricity, semi-major axis) and differential and total cross sections for hardening, dissolution or merging of binaries (minimum distance) from a sampling of several ten thousands of scattering events as they occur in real cluster evolution including mass segregation of binaries, gravothermal collapse and reexpansion, binary burning phase and ultimately gravothermal oscillations. For the first time we are able to present empirical cross sections for eccentricity variation of binaries in close three-and four-body encounters. It is found that a large fraction of three-body and four-body encounters results in merging. Eccentricities are generally increased in strong three-and four-body encounters and there is a characteristic scaling law ∝ exp(4e fin ) of the differential cross section for eccentricity changes, where e fin is the final eccentricity of the binary, or harder binary for four-body encounters. Despite of these findings the overall eccentricity distribution remains thermal for all binding energies of binaries, which is understood from the dominant influence of resonant encounters. Previous cross sections obtained by Spitzer and Gao for strong encounters can be reproduced, while for weak encounters non-standard processes like formation of hierarchical triples occur.
Multiple star systems in the Orion nebula
Astronomy & Astrophysics
This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium cluster with the recently comissioned GRAVITY instrument. We observed a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for θ1 Ori B, θ2 Ori B, and θ2 Ori C. We determined a separation for the previously suspected companion of NU Ori. We confirm four companions for θ1 Ori A, θ1 Ori C, θ1 Ori D, and θ2 Ori A, all with substantially improved astrometry and photometric mass estimates. We refined the orbit of the eccentric high-mass binary θ1 Ori C and we are able to derive a new orbit for θ1 Ori D. We find a system mass of 21.7 M⊙ and a period of 53 days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about two, s...
Constraints on stellar-dynamical models of the Orion Nebula Cluster
New Astronomy, 2000
The results obtained by for specific models of young compact binary-rich clusters are generalised using dynamical scaling relations, to infer the candidate set of possible birth models leading to the Orion Nebula Cluster (ONC), of which the Trapezium Cluster is the core. It is found that candidate sets of solutions exist which allow the ONC to be in virial equilibrium, expanding or contracting. The range of possible solutions is quite narrow.