bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observations of the Triple Star ETA Virginis with a Long Baseline Optical Interferometer
Authors: Hummel C.A. 
Published: June 2019

AbstractWe observed the hierarchical triple star Eta Virginis with the Navy Prototype Optical Interferometer and present the first images resolving all three components. The stars in the close pair have a separation between 4 and 9 milliarcseconds. The orbital motions of the stars were followed during the winter and spring of 2002. Preliminary, astrometrically determined orbits of the two components in the close pair by reference to the tertiary were derived, thus enabling the estimation of the mass ratio (1.27) of the components in the close pair. We also determined the relative orbital inclination to be 31 degrees. We describe the model-fitting process to interferometrie and spectroscopic data, and discuss some astrophysical component parameters.
Increased Multiplicity of 77 Cygni, V815 Herculis, and HD 140122
Authors: Fekel Francis C. 
Published: June 2019

AbstractHigh-dispersion spectroscopic observations of 77 Cygni, V815 Herculis, and HD 140122 have resulted in the detection of at least one additional component in each system. The newly identified component of 77 Cyg has a period of 35.48 days. V815 Her is a triple system with periods of 1.810 and 2300 days or 6.3 yr. The two visual binary components of HD 140122 are short-period spectroscopic binaries with periods of 10.879 and 15.770 days.
The Distribution of Separations of Wide Binaries of Different Ages
Authors: Poveda Arcadio , Allen Christine 
Published: June 2019

AbstractFor the purpose of understanding how the distribution of major semiaxes of double and multiple stars has evolved from the earliest ages up to the ages of the oldest systems, we have studied a number of different groups of such systems. We review and expand our previous work on the following groups of stars: (a) The wide binaries in the IDS; (b) Luyten’s common proper motion pairs (the LDS catalogue), (c) Our catalogue of nearby wide binaries divided into two groups: the youngest and the oldest; (d) The common proper motion pairs in the Orion Nebula cluster; (e) Our sample of high velocity, low metallicity binaries that represents a population of very old systems. From the very young binaries (Orion Nebula Cluster) to the oldest (thick disk and halo), all groups show a distribution of major semiaxes following Oepik, i.e., f(a) da ∝ da/a (where a is the major semiaxis), valid over an interval of a between 60 AU and am(t), am(t) being a maximum semiaxis which depends on the age of the binaries as well as on the number density and velocities of the massive objects they encounter as they travel in the Galaxy. Strong gravitational encounters in recently formed multiple systems were found to produce an Oepik distribution, which at small separations (a ≤ 40 − 60 AU) gets truncated by circumstellar disks and close binaries, and at large separations gets depleted by encounters with massive objects.
Photometry of the δ Scuti Star DG Leo: Preliminary Results
Authors: Lampens P. , Garrido R. , Parrao L. , Peña J.H. , Arentoft T. , Frémat Y. 
Published: June 2019

AbstractNew uvby photoelectric photometry has been acquired for the triple star DG Leo at two different observatories equipped with analogous instrumentation. A preliminary period analysis indicates the presence of at least 3 close δ Scuti frequencies (10-12 c/d, 3-6 mmag) and a slow variation. This slow variation fits quite well with half the orbital period of the spectroscopic binary; the noise level in the amplitude spectrum is only 3–4 mmag (after prewhitening).
The Double-Lined Spectroscopic Binary HR 6046
Authors: Scarfe C.D. , Griffin R.F. , Griffin R.E.M. 
Published: June 2019

AbstractHR 6046 has long been known as a single-lined binary with a late-K-giant primary star. The long period of just over six years and the large mass function led to several, so far unsuccessful, attempts to resolve the system interferometrically. However, we have detected the secondary spectroscopically, and present here the spectroscopic orbital elements. The secondary is nearly as massive as the primary, despite being much fainter. Comparison with late-type standard spectra suggests that it is also an evolved star.
Orbital Motions in Binary Protostellar Systems
Authors: Rodríguez L.F. 
Published: June 2019

AbstractUsing high-resolution (~ 01), multi-epoch Very Large Array observations, we have detected orbital motions in several low-luminosity protobinary systems in the Taurus and ρ Ophiuchus molecular complexes. The masses obtained from Kepler’s third law are of the order of 0.5 to 2 M⊙, as expected for such low-mass protostars. The relatively large bolometric luminosities of these young systems corroborates the notion that protostars obtain most of their luminosity from accretion and not from nuclear reactions. In addition, in one of the sources studied (a multiple system in Taurus), a low-mass young star has shown a drastic change in its orbit after a close approach with another component of the system, presumed to be a double star. The large proper motion achieved by this low mass protostar (20 km s−1), suggests an ejection from the system.
What Causes the Low Binary Frequency in the Orion Nebula Cluster?
Authors: Köhler R. 
Published: June 2019

AbstractWe report on the results of a binary survey in the outer parts of the Orion Nebula Cluster, 0.7 to 2 pc from the cluster center. The results should help to decide if the binary formation rate was lower in Orion than in Taurus-Auriga, or if many binaries formed initially, but were destroyed in close stellar encounters. We find that the binary frequency of low-mass stars does not depend on the distance to the cluster center. The companion star frequency of intermediate- to high-mass stars shows a trend to decrease with cluster radius, but the statistical significance of this trend is rather weak.
Young Stars far from the Galactic Plane: Runaways from Clusters
Authors: Allen Christine , Kinman T.D. 
Published: June 2019

AbstractQuite recently, a significant number of OB stars far from the galactic plane have been found, situated at z- distances ranging from several hundreds of pc to several kpc. The short lifetimes of these stars pose problems for their interpretation in terms of the standard picture of star formation. Different mechanisms have been put forward to explain the existence of these stars, either within the conventional view, or postulating star formation in the galactic halo itself. These mechanisms range from arguing that they are misidentified evolved or abnormal stars, to postulating powerful ejection mechanisms for young disk stars; in situ formation also admits several variants. We have collected from the literature a list of young stars far from the plane, for which the evidence of youth seems convincing. We discuss two possible formation mechanisms for these stars: ejection from the plane as the result of dynamical evolution of small clusters (Poveda et al. 1967) and in situ formation, via induced shocks created by spiral density waves (Martos et al. 1999). We compute galactic orbits for these stars, and identify the stars that could be explained by one or the other mechanism. We find that about 90 percent of the stars can be accounted for by the cluster ejection mechanism, that is, they can be regarded as runaway stars in the galactic halo.
Formation and Evolution of Hierarchical Systems
Authors: Aarseth Sverre J. 
Published: June 2019

AbstractInitial distributions of primordial binaries used in realisticN-body simulations give rise to bound subsystems of different multiplicity. An examination of the formation process shows that the most compact triples arise via binary-binary collisions, whereas higher-order systems have diverse origins. Low formation rates are compensated by long life-times, leading to a significant population building up. Being fairly energetic, the outer orbit tends to shrink by further encounters. In addition, external perturbations also modify the eccentricity and may create conditions for instability. Onecharacteristic outcome is internal disruption by the sling-shot mechanism. Such interactions are often sufficiently energetic to produce high-velocityescapers and it is not uncommon for triples and quadruples to be ejected. For high inclinations, the eccentricity growth induced by the Kozai effect may lead to significant shrinkage of the inner binary orbit by tidal circularization. If some of the components were spit into a dynamically inactive ultra-hard binary, the hierarchies would be attributed an even higher multiplicity. One implication of these results is that a proportion of multiple systems observed in the field may have been formed in a dynamical environment.
The Interaction of Binary Systems with Accretion Disks
Authors: Ortega-Rodríguez Manuel 
Published: June 2019

AbstractWe study the (time) fluctuations in the outgoing radiation of accretion disks in binary systems in order to obtain properties of those systems (via comparison with observations), such as the angular momentum of the compact star within the disk. The effects of the companion star are discussed, and a prediction is made on the frequency of the outgoing (modulated) X-ray radiation.
Guieloa: Adaptive Optics System for the 2.1-M SPM UNAM Telescope
Authors: Cuevas S. , Iriarte A. , Martínez L.A. , Garfias F. , Sánchez L. , Chapa O. , Ruelas R.A. 
Published: June 2019

AbstractGuieloa is the adaptive optics system project for the 2.1-m SPM telescope. This is a 19 sub-apertures curvature-type system. It corrects 8 Zernike terms. Guieloa is very similar to PUEO, the CFHT adaptive optics system and compensates the atmospheric turbulence from the R band to the K band. Among the planned applications of Guieloa are the study of OB binary systems, the detection of close binary stars, and the study of disks, jets and other phenomena associated with young stars.
Interferometry and Lunar Occultations: Status and Prospects of Ground-Based Milliarcsecond Resolution Observations
Authors: Richichi A. 
Published: June 2019

AbstractLunar occultations and long-baseline interferometry are two direct observational methods capable of delivering milliarcsecond resolution of binary stars. We will review the status of these two techniques, particularly with reference to their respective advantages, limitations, and accessibility for binary star research programs. We will also illustrate the near-term prospects, in connection with the availability of large modern interferometric facilities such as the VLTI.
Observational Properties of Synthetic Visual Binary
Authors: Nurmi P. 
Published: June 2019

AbstractForthcoming astrometric missions will observe a huge number of new binaries from which a large fraction will be visual binaries. Detailed planning of optimal detection procedures requires pre-launch information about the observational properties of expected visual binaries. Hence, a synthetic binary catalog is created and analyzed for observational properties of visual binary stars. These results help to understand what kind of binaries we expect to find in the final output catalogs of astrometric missions. These results represent ‘true’ binary distributions if all of them would be observed. All real observational projects or astrometric satellites sample only small fractions of these populations depending on the observational capabilities of the missions. In this study we consider only relative numbers with respect to the total number of binary stars assumed to exist in the sky down to the magnitude limit depending on the astrometric mission.
Nine Years of VLBI Imaging of Supernova 1993J
Authors: Bietenholz M.F. , Bartel N. , Rupen M.P. , Beasley A.J. , Graham D.A. , V.I. Altunin , Venturi T. , Umana G. , Cannon W.H. , Conway J.E. 
Published: June 2019

SummaryWe present a selection of our VLBI images of SN 1993J, along with our latest results on its expansion and its shell structure.
Optical, Ultraviolet, and Infrared Observations of SN 1993J
Authors: Filippenko Alexei V. , Matheson Thomas 
Published: June 2019

SummaryWe review the existing set of optical/UV/IR observations of Supernova 1993J, concentrating heavily on optical data because these are by far the most plentiful. Some results from theoretical modeling of the observations are also discussed. SN 1993J has provided the best observational evidence for the transformation of a SN from one spectral type to another, thereby providing a link between Type II and Type Ib supernovae (SNe). This has strengthened the argument that SNe Ib (and, by extension, SNe Ic) are core-collapse events. SN 1993J has remained relatively bright for 10 years; its late-time emission comes from the collision of supernova ejecta with circumstellar gas that was released by the progenitor prior to the explosion. The circumstellar material shows strong evidence of CNO processing.
Simulated Radio Images and Light Curves of SN 1993J
Authors: Dwarkadas Vikram V. , Mioduszewski Amy J. , Ball Lewis T. 
Published: June 2019

SummaryWe present calculations of the radio images and light curves from supernovae, based on high-resolution numerical simulations of the hydrodynamics and radiation transfer in a spherically symmetric medium. As a specific example we model the emission from SN1993J. This supernova does not appear to be expanding in a self-similar fashion, and cannot be adequately fitted with the often-used analytic mini-shell model. We present a good fit to the radio evolution at a single frequency. Both free-free absorption and synchrotron self-absorption are needed to fit the light curve at early times, and a circumstellar density profile of ρ ~ r−1.7 provides the best fit to the later data. Comparisons of VLBI images of SN1993J with synthetic model images suggest that internal free-free absorption completely obscures emission at 8.4 GHz passing through the center of the supernova for the first few tens of years after explosion.
The Early Spectroscopy of Supernovae
Authors: Yamaoka Hitoshi , Ayani Kazuya , Hashimoto Tetsuya 
Published: June 2019

SummaryThe spectroscopy of a supernova (SN) just after its discovery is quite important not only for the spectral type classification but also for the planning further follow-up observations or the target-of-opportunity observations (ToOs). The early spectroscopy is needed also because the information from the outermost envelope of such exploding objects as SNe cannot be obtained in the later phase. In order to obtain the early spectrum, the quick circulation of the discovery information is important. We introduce our contributions with the public astronomical observatories in Japan, including the case of “hypernova” SN 2002ap discovered by a Japanese amateur astronomer. We summarize the time interval between the discoveries, the announcements, and the first spectral classifications of recent SNe, and discuss what would be required for the early spectroscopy.
Photometric Observations of Recent Supernovae
Authors: Tsvetkov D.Yu. 
Published: June 2019

SummaryRegular photometric observations of sufficiently bright northern supernovae are carried out at Sternberg Astronomical Institute’s observatories. Since 1998 the observations of more than 60 supernovae were obtained on about 150 nights with different telescopes and detectors. We present the data of the observation program, the parameters of light curves for 18 SNe and the light curves for SNe 1999aa, 2001B, 2002bo.
Radio Observations of Supernova Remnants in the M82 Starburst
Authors: Pedlar Alan , Muxlow Tom , Riley Jon 
Published: June 2019

SummaryWe report on recent MERLIN, VLA and VLBI observations of the compact radio sources in the nearby starburst M82, with angular resolutions ranging from arcseconds to milliarcseconds. The spectral properties of the compact sources have been investigated by 15 GHz VLA-Pie Town observations which show that 16 of the less luminous compact sources are, in fact, HII regions. However the steep non-thermal spectrum, parsec size and small variability of the remaining sources is consistent with their being supernova remnants. Several show clear shell structures at MERLIN resolution (~50 mas) and 5 have been resolved further using VLBI. Measurements of the most compact source (41.95+575) shows an expansion velocity of ~ 2000 km s-1, and one of the best defined SNR shells (43.31+592) shows an expansion velocity of ~ 104 km s-1. Recent VLBI and MERLIN measurements confirm this expansion velocity and show little evidence for deceleration. We comment on the discrepancy between this measured expansion velocity and the low expansion velocities predicted theoretically for remnants in M82.
Understanding Type II Supernovae
Authors: Zampieri L. , Ramina M. , Pastorello A. 
Published: June 2019

SummaryWe present the results of a systematic analysis of a group of Type II plateau supernovae that span a large range in luminosities, from faint objects like SN 1997D and 1999br to very luminous events like SN 1992am. The physical properties of the supernovae appear to be related to the plateau luminosity or the expansion velocity. The simultaneous analysis of the observed light curves, line velocities and continuum temperatures leads us to robust estimates of the physical parameters of the ejected envelope. We find strong correlations among several parameters. The implications of these results regarding the nature of the progenitor, the central remnant and the Ni yield are also addressed.
Magnetorotational Mechanism of Supernova Type II Explosion
Authors: Moiseenko S.G. , Bisnovatyi-Kogan G.S. , Ardeljan N.V. 
Published: June 2019

SummaryResults of 2D simulations of the magnetorotational mechanism of supernova type II are presented. Amplification of toroidal magnetic field of the star due to differential rotation of the star leads to the transformation of the rotational (gravitational) energy to the energy of the supernova explosion. In our simulation the energy of the explosion is 1.12 - 1051 erg. The explosion ejects about 0.11 M⊙.
Explosion Models for Thermonuclear Supernovae Resulting from Different Ignition Conditions
Authors: Bravo Eduardo , García-Senz Domingo 
Published: June 2019

SummaryWe have explored in three dimensions the fate of a white dwarf of mass of 1.38 M⊙ as a function of different initial locations of carbon ignition, with the aid of a SPH code. The calculated models cover a variety of possibilities ranging from the simultaneous ignition of the central volume of the star to the off-center ignition in multiple scattered spots. In the former case, the possibility of a transition to a detonation when the mean density of the nuclear flame decreases to ρ ≃ 2 × 107 g cm−3 and its consequences are discussed. In the last case, the dependence of the results as a function of the number of initial igniting spots and the chance of some of these models to evolve to the pulsating delayed detonation scenario are also outlined.
Using Multi-Band Photometry to Classify Supernovae
Authors: Poznanski Dovi , Gal-Yam Avishay , Maoz Dan , Filippenko Alexei V. , Leonard Douglas C. , Matheson Thomas 
Published: June 2019

SummaryLarge numbers of supernovae (SNe) have been discovered in recent years, and many more will be found in the near future. Once discovered, further study of a SN and its possible use as an astronomical tool (e.g., as a distance estimator) require knowledge of the SN type. Current classification methods rely almost solely on the analysis of SN spectra to determine their type. However, spectroscopy may not be possible or practical. We present a classification method for SNe based on the comparison of their observed colors with synthetic ones, calculated from a large database of multi-epoch optical spectra of nearby events. Broadband photometry at optical wavelengths allows classification of SNe up to z = 0.75, and the use of infrared bands extends it further to z = 2.5. We demonstrate the applicability of this method, outline the observational data required to further improve the usefulness of the method, and discuss prospects for its use on future SN samples. Community access to the tools developed is provided by a dedicated website.
Optical Bumps in Cosmological GRBs as Supernovae
Authors: Bloom J.S. 
Published: June 2019

SummaryFrom both photometric and broadband spectral monitoring of γ-ray burst (GRB) lightcurve “bumps,” particularly in GRB 011121, a strong case grew for a supernova (SN) origin. The GRB-SN connection was finally solidified beyond a reasonable doubt with the discovery that the bump in GRB 030329 was spectroscopically similar to a bright Type Ic SN. In light of this result, I re-assess the previous SN bump claims and conclude that: 1) the distribution of GRB-SN bump peak magnitudes is consistent with the local Type Ib/c SNe peak distribution and 2) the late-time bumps in all long-duration GRBs are likely supernovae.
Cosmic Gamma-Ray Bursts: The Big Picture
Authors: Hurley Kevin 
Published: June 2019

SummaryA “typical” GRB occurs in a star-forming region of a galaxy at a redshift z~1. In currently popular models, it is caused by the collapse of a massive star which has exhausted its nuclear fuel supply. The star collapses to a black hole threaded by a strong magnetic field, and possibly fed by an accretion torus. Through a variety of processes, electrons are accelerated and gamma-rays, X-rays, optical light, and radio emission ensue, with durations from seconds to years. In this talk, I will review the general observational properties of bursts, their afterglows and host galaxies, and some of the open questions about them.
Physical Restrictions to Cosmological Gamma-Ray Burst Models
Authors: Bisnovatyi-Kogan G.S. 
Published: June 2019

SummaryThe present common view about GRB origin is related to cosmology, and is based on statistical analysis, and on measurements of the redshifts in the GRB optical afterglows of long GRB. No correlation is found between redshifts, GRB spectrum, and total GRB fluence. Comparison of KONUS and BATSE data about statistics and hard X-ray lines is done, and some differences are noted. Hard gamma-ray afterglows, prompt optical spectra, hard X-ray lines, polarization measurements could be very important for farther insight into GRB origin. Possible connection of short GRB with soft gamma repeaters is discussed.
Observations of Type Ia Supernovae and Challenges for Cosmology
Authors: Li Weidong , Filippenko Alexei V. 
Published: June 2019

SummaryObservations of Type Ia supernovae (SNe Ia) reveal correlations between their luminosities and light-curve shapes, and between their spectral sequence and photometric sequence. Assuming SNe Ia do not evolve at different redshifts, the Hubble diagram of SNe Ia may indicate an accelerating Universe, the signature of a cosmological constant or other forms of dark energy. Several studies raise concerns about the evolution of SNe Ia (e.g., the peculiarity rate, the rise time, and the color of SNe Ia at different redshifts), but all these studies suffer from the difficulties of obtaining high-quality spectroscopy and photometry for SNe Ia at high redshifts. There are also some troubling cases of SNe Ia that provide counter examples to the observed correlations, suggesting that a secondary parameter is necessary to describe the whole SN Ia family. Understanding SNe Ia both observationally and theoretically will be the key to boosting confidence in the SN Ia cosmological results.