scholarly journals GSC 4019 3345: An A-Type Twin Binary

2013 ◽  
Vol 30 ◽  
Author(s):  
V. Bakış ◽  
H. Bakış ◽  
Z. Eker
Keyword(s):  
Circular Orbit ◽  
Time Scale ◽  
Rotation Velocity ◽  
Young Age ◽  
Synthetic Spectrum ◽  
Evolutionary Status ◽  
Age Difference ◽  
The Sun ◽  
Synchronization Time ◽  
Orbit Modeling

AbstractPhysical dimensions and evolutionary status of the A-type twin binary GSC 4019 3345 are presented. Located at a distance of ~1.1 kpc from the Sun, the system was found to have two components with identical masses (M1,2 = 1.92 M⊙), radii (R1,2 = 1.76 R⊙), and luminosities (log L1,2 = 1.1 L⊙) revolving in a circular orbit. Modeling the components with theoretical evolutionary tracks and isochrones implies a young age (t = 280 Myr) for the system, which is bigger than the synchronization time scale but smaller than the circularization time scale. Nevertheless, synthetic spectrum models revealed components’ rotation velocity of Vrot12 = 70 km s−1, that is about three times higher than their synchronization velocity. No evidence is found for an age difference between the components.

scholarly journals Astrometry of Galactic Star-Forming Regions ON1 and ON2N with VERA

2012 ◽  
Vol 8 (S287) ◽  
pp. 391-395 ◽  
Author(s):  
Takumi Nagayama ◽  
Keyword(s):  
Three Dimensional ◽  
Rotation Velocity ◽  
Galactic Rotation ◽  
The Sun ◽  
Angular Rotation ◽  
Star Forming ◽  
Star Forming Regions ◽  
Circular Rotation

AbstractWe conducted the astrometry of H2O masers in the Galactic star-forming regions ON1 and ON2N with the VLBI Exploration of Radio Astrometry (VERA). The measured distances to ON1 and ON2N are 2.47±0.11 kpc and 3.83±0.13 kpc, respectively. In the case that ON1 and ON2N are on a perfect circular rotation, we estimate the angular rotation velocity of the Galactic rotation at the Sun (the ratio of the Galactic constants) to be 28 ± 2 km s−1 kpc−1 using the measured distances and three-dimensional velocity components of ON1 and ON2N. This value is larger than the IAU recommended value of 25.9 km s−1 kpc−1, but consistent with other results recently obtained with the VLBI technique.

scholarly journals Surface Abundances of Light Elements as Diagnostics of Transport Processes in the Sun and Solar-type stars

1990 ◽  
Vol 121 ◽  
pp. 437-448
Author(s):  
A. Baglin ◽  
Y. Lebreton
Keyword(s):  
Solar Surface ◽  
Rotation Velocity ◽  
Transport Processes ◽  
Physical Parameters ◽  
The Sun ◽  
Light Elements ◽  
Cosmic Abundance ◽  
Solar Type ◽  
The Moment ◽  
Slow Transport

AbstractObservations of the surface abundances of lithium, beryllium and helium-3 in the Sun and in solar-type stars of different ages should be interpreted in a coherent way. The abundance of lithium at the surface of a star decreases slowly with age; for stars of the same age it decreases with mass and a dependence on the rotation velocity is suggested. The solar surface lithium is depleted by a factor of 100 relative to the cosmic abundance while an He-3 enrichment of 15% at the solar surface during evolution is suggested.Observations favour the hypothesis of a slow transport process at work between the outer convective zone and the radiative interior of these stars. Orders of magnitude of the transport coefficient as well as its dependence upon the physical parameters can be inferred from surface abundances of light elements, but at the moment we are far from producing a completely consistent modelization.

scholarly journals IPS Observations of Short-Time Scale Interplanetary Activity

1996 ◽  
Vol 154 ◽  
pp. 225-228
Author(s):  
Pradeep Gothoskar ◽  
A. Pramesh Rao
Keyword(s):  
Time Scale ◽  
Solar Maximum ◽  
Component Model ◽  
Scintillation Index ◽  
Short Time Scale ◽  
High Time Resolution ◽  
The Sun ◽  
X Ray ◽  
Average Mass ◽  
Short Time

AbstractWe have carried out a program of continuous Interplanetary Scintillation (IPS) monitoring of the interplanetary activity using Ooty Radio Telescope (ORT). From May 1990 to March 1991, during the 22nd solar maximum, a few radio sources were monitored to provide long stretches of IPS data with a high-time resolution of few minutes. These observations covered 0.3 to 0.8 AU region (12° to 70° elongations) around the sun at several heliographic latitudes. During the observation, we detected 33 short-time scale IPS events which had significant variation in the scintillation index and solar wind velocity. These were considered to be due to travelling interplanetary disturbances.A multi-component model of plasma density enhancement was developed to estimate the geometry and physical properties of these IPS events. Detailed analysis of 20 of these events suggests, 1. fast IPS events were interplanetary signatures of Coronal Mass Ejections (CMEs), 2. the average mass and energy of these events was ~ 1016 gm and 1033 erg respectively, 3. 80% of IPS events were associated with X-ray flares on the sun and 50% were associated with geomagnetic activity at earth. Detailed study of the multi-component model suggests IPS observations at smaller elongations (hence at higher radio frequencies) are more suited to detect fast-moving interplanetary disturbances such as produced by CMEs.

scholarly journals Effects of a Time Varying Moment on a Large Tethered Satellite in Circular or Elliptical Orbit

2019 ◽  
Author(s):  
Narayan Iyer
Keyword(s):  
Circular Orbit ◽  
Rotation Angle ◽  
Orbital Plane ◽  
Rotation Velocity ◽  
Elliptical Orbit ◽  
Time Varying ◽  
Angular Rotation ◽  
Tethered Satellite ◽  
Different Types

The purpose of this paper is to investigate the effect of a varying moment on the rotation angle of a large tethered satellite that is orbiting a planet. Two different types of orbits were investigated: a simple circular orbit and an elliptical orbit. Cases with zero and non-zero initial angular rotation velocity were investigated as well. This investigation will assist satellite docking missions. The large rigid tethered satellite is a futuristic concept, and this investigation is meant to assist possible docking missions to the satellite. To simplify the problem, the rotation is constrained to the orbital plane.

scholarly journals The near-synchronous polar V1432 Aql (RX J1940.1–1025): Accretion geometry and synchronization time scale

2003 ◽  
Vol 407 (3) ◽  
pp. 987-998 ◽  
Author(s):  
R. Staubert ◽  
S. Friedrich ◽  
K. Pottschmidt ◽  
S. Benlloch ◽  
S. L. Schuh ◽  
...  
Keyword(s):  
Time Scale ◽  
Synchronization Time

City-Strata of the Anthropocene

2017 ◽  
Vol 72 (2) ◽  
pp. 225-245
Author(s):  
Jan Zalasiewicz ◽  
Colin Waters ◽  
Mark Williams
Keyword(s):  
Time Scale ◽  
Future Generations ◽  
Urban Metabolism ◽  
Waste Materials ◽  
The Sun ◽  
Geological Time ◽  
Waste Products ◽  
Fossil Energy ◽  
Geological Materials ◽  
Planetary Scale

The fabric of a city represents a transformation of raw geological materials into a complex assemblage of new, human-made minerals and rocks such as steel, glass, plastics, concrete, brick, and ceramics. This activity has been considered in terms of an “urban metabolism,” with day-to-day inflows and outflows of people, food, water, and waste materials. Here we adopt a longer time-scale spanning years to millennia, related to geological time-scales but still meaningful for present and future generations of humans, and consider cities as sedimentary systems. In natural sedimentary systems, flows of materials are governed by natural forces such as climate and gravity, and leave physical records in, for instance, river-strata. In cities, the flows of geological materials needed for construction and reconstruction are directed by humans, and are largely powered by the fossil energy stored in hydrocarbons rather than by gravity or the sun. The resultant assemblages of anthropogenic rocks and minerals may be thought of as sedimentary (and/or trace-fossil) systems that can undergo fossilization and now exist on a planetary scale. Far more diverse than natural geological strata, they are also evolving much more rapidly, not least in terms of their growing waste products. Considering cities through such a perspective may become increasingly useful as they come to be influenced by, and need to adapt to, the changing conditions of the emerging Anthropocene epoch.

scholarly journals Measurements of annual parallaxes and proper motions of the red supergiant S Per

2007 ◽  
Vol 3 (S242) ◽  
pp. 378-380 ◽  
Author(s):  
Yoshiharu Asaki ◽  
Shuji Deguchi ◽  
Hirishi Imai ◽  
Kazuya Hachisuka ◽  
Makoto Miyoshi ◽  
...  
Keyword(s):  
Water Vapor ◽  
Proper Motion ◽  
Galactic Center ◽  
Rotation Velocity ◽  
Galactic Rotation ◽  
The Sun ◽  
Proper Motions ◽  
Right Ascension

AbstractVLBI phase-referencing monitoring of water vapor masers around the red supergiant, S Per, was conducted over four years. We successfully obtained proper motions and an annual parallax of the masers and determined the distance to S Per of 2.51±0.09 kpc. The proper motion of the star itself was inferred from the maser proper motions, and it was −0.38 and −1.54 mas/yr for right ascension and declination, respectively. Assuming the distance from the sun to the Galactic center, R0, of 8.5 kpc and the rotation velocity around the sun, Θ0, of 220 km/s, the Galactic rotation velocity around S Per is 200 km/s.

scholarly journals A naked-eye triple system with a nonaccreting black hole in the inner binary

2020 ◽  
Vol 637 ◽  
pp. L3 ◽  
Author(s):  
Th. Rivinius ◽  
D. Baade ◽  
P. Hadrava ◽  
M. Heida ◽  
R. Klement
Keyword(s):  
Time Series ◽  
Black Hole ◽  
Neutron Star ◽  
Circular Orbit ◽  
Triple System ◽  
The Sun ◽  
Be Stars ◽  
Naked Eye ◽  
Be Star ◽  
Triple Star

Several dozen optical echelle spectra demonstrate that HR 6819 is a hierarchical triple. A classical Be star is in a wide orbit with an unconstrained period around an inner 40 d binary consisting of a B3 III star and an unseen companion in a circular orbit. The radial-velocity semi-amplitude of 61.3 km s−1 of the inner star and its minimum (probable) mass of 5.0 M⊙ (6.3 ± 0.7 M⊙) imply a mass of the unseen object of ≥4.2 M⊙ (≥5.0 ± 0.4 M⊙), that is, a black hole (BH). The spectroscopic time series is stunningly similar to observations of LB-1. A similar triple-star architecture of LB-1 would reduce the mass of the BH in LB-1 from ∼70 M⊙ to a level more typical of Galactic stellar remnant BHs. The BH in HR 6819 probably is the closest known BH to the Sun, and together with LB-1, suggests a population of quiet BHs. Its embedment in a hierarchical triple structure may be of interest for models of merging double BHs or BH + neutron star binaries. Other triple stars with an outer Be star but without BH are identified; through stripping, such systems may become a source of single Be stars.

scholarly journals About the Luminous Blue Variable He3-519

2010 ◽  
Vol 6 (S272) ◽  
pp. 87-88
Author(s):  
Anthony Hervé ◽  
Jean-Claude Bouret
Keyword(s):  
Stellar Evolution ◽  
Time Scale ◽  
Massive Stars ◽  
Model Atmosphere ◽  
Transition Phase ◽  
Evolutionary Status ◽  
Stellar Winds ◽  
Luminous Blue Variables ◽  
Luminous Blue Variable

AbstractLuminous Blue Variables (LBVs) are massive stars, in a transition phase, from being O-type stars and rapidly becoming Wolf-Rayet objects. LBVs possess powerful stellar winds, high luminosities and show photometric and spectroscopic variability. We present the stellar and wind parameters of He3-519 obtained by the modeling of UVES observations with the model atmosphere code CMFGEN. We compare our results to previous studies in order to find mid-time scale variability of the stellar parameters and finally, we use stellar evolution models to determine the evolutionary status of this star.

scholarly journals A Method for Calibrating, in Absolute Flux Units, Ca II H Profiles of Late Type Stars Observed at ESO

1988 ◽  
Vol 132 ◽  
pp. 153-161 ◽  
Author(s):  
F. Castelli ◽  
P. Gouttebroze ◽  
J. Beckman ◽  
L. Crivellari ◽  
B. Foing
Keyword(s):  
Solar Flux ◽  
Calibration Factor ◽  
Synthetic Spectrum ◽  
The Sun ◽  
The Moon ◽  
Late Type ◽  
Equilibrium Models ◽  
Collisional Broadening ◽  
Absolute Flux ◽  
Fitting In

In this paper we have applied to the Sun a method for calibrating, in absolute flux units, Ca II H profiles of late-type stars. After comparing, in the region 3948-3882 A, an LTE synthetic spectrum with the data of the solar flux Atlas by Kurucz et al. (1984), we have defined the wavelength ranges where observations agree with computations, based on specific radiative equilibrium models and collisional broadening parameters. By fitting in these regions the spectrum of the moon observed at ESO with the corresponding synthetic spectrum, we derived a calibration factor that enables us to calibrate, in absolute flux units, the whole observed range.

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