The First Orbits of Six Wide Double Stars in the Solar Neighborhood Based on Gaia DR2 Observations

2020 ◽  
Vol 46 (8) ◽  
pp. 555-571
Author(s):  
O. V. Kiyaeva ◽  
L. G. Romanenko
Keyword(s):  
Solar Neighborhood ◽  
Double Stars ◽  
Gaia Dr2

scholarly journals Determination of the local dark matter density using K-dwarfs from Gaia DR2

2020 ◽  
Vol 240 ◽  
pp. 04002
Author(s):  
M. Dafa Wardana ◽  
Hesti Wulandari ◽  
Sulistiyowati ◽  
Akbar H. Khatami
Keyword(s):  
Dark Matter ◽  
Galactic Disk ◽  
Matter Density ◽  
Solar Neighborhood ◽  
Stellar Disk ◽  
Vertical Position ◽  
Dark Halo ◽  
Detection Rates ◽  
Dark Matter Density ◽  
Gaia Dr2

Local dark matter density, ρdm, is one of the crucial astrophysical inputs for the estimation of detection rates in dark matter direct search experi- ments. Knowing the value also helps us to investigate the shape of the Galactic dark halo, which is of importance for indirect dark matter searches, as well as for various studies in astrophysics and cosmology. In this work, we performed kinematics study of stars in the solar neighborhood to determine the local dark matter density. As tracers we used 95,543 K-dwarfs from Gaia DR2 inside a heliocentric cylinder with a radius of 150 pc and height 200 pc above and below the Galactic mid plane. Their positions and motions were analyzed, assum- ing that the Galaxy is axisymmetric and the tracers are in dynamical equilib- rium. We applied Jeans and Poisson equations to relate the observed quantities, i.e. vertical position and velocity, with the local dark matter density. The tilt term in the Jeans equation is considered to be small and is therefore neglected. Galactic disk is modelled to consist of a single exponential stellar disk, a thin gas layer, and dark matter whose density is constant within the volume consid- ered. Marginalization for the free parameters was performed with Bayesian theorem using Markov Chain Monte Carlo (MCMC) method. We find that ρdm = 0.0116 ± 0.0012 MO/pc or ρdm = 0.439 ± 0.046 GeV/cm3, in agreement within the range of uncertainty with results of several previous studies.

scholarly journals New ultra-cool and brown dwarf candidates in Gaia DR2

2018 ◽  
Vol 619 ◽  
pp. L8 ◽  
Author(s):  
C. Reylé
Keyword(s):  
Brown Dwarfs ◽  
Mass Range ◽  
Solar Neighborhood ◽  
Proper Motions ◽  
Brown Dwarf ◽  
Expected Number ◽  
Data Release ◽  
Low Mass ◽  
Fine Structures ◽  
Gaia Dr2

Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources. The resulting Hertzsprung–Russel diagram reveals fine structures throughout the mass range. Aims. This paper aims to investigate the content of Gaia DR2 at the low-mass end and to characterize ultra-cool and brown dwarfs. Methods. We first retrieved the sample of spectroscopically confirmed ultra-cool and brown dwarfs in Gaia DR2. We used their locus in the precise Hertzsprung–Russel diagram to select new candidates and to investigate their properties. Results. The number of spectroscopically confirmed objects recovered in Gaia DR2 corresponds to 61% and 74% of the expected number of objects with an estimated Gaia magnitude G est ≤ 21.5 and 20.3, respectively. This fills much of the gap to Gaia DR1. Furthermore, Gaia DR2 contains Ȉ13 000 ≥ M7 and 631 new L candidates. A tentative classification suggests that a few hundred of them are young or subdwarf candidates. Their distance distribution shows that the solar neighborhood census is still incomplete. Conclusions. Gaia DR2 offers a great wealth of information on low-mass objects. It provides a homogeneous and precise catalog of candidates that is worthwhile to be further characterized with spectroscopic observations.

scholarly journals A comparison of the local spiral structure from Gaia DR2 and VLBI maser parallaxes

2018 ◽  
Vol 616 ◽  
pp. L15 ◽  
Author(s):  
Y. Xu ◽  
S. B. Bian ◽  
M. J. Reid ◽  
J. J. Li ◽  
B. Zhang ◽  
...  
Keyword(s):  
Spiral Structure ◽  
Young Stars ◽  
Solar Neighborhood ◽  
Proper Motions ◽  
Data Set ◽  
Ob Stars ◽  
Three Samples ◽  
Significant Distance ◽  
Gaia Dr2 ◽  
Spiral Arm

Context. The Gaia mission has released the second data set (Gaia DR2), which contains parallaxes and proper motions for a large number of massive, young stars. Aims. We investigate the spiral structure in the solar neighborhood revealed by Gaia DR2 and compare it with that depicted by VLBI maser parallaxes. Methods. We examined three samples with different constraints on parallax uncertainty and distance errors and stellar spectral types: (1) all OB stars with parallax errors of less than 10%; (2) only O-type stars with 0.1 mas errors imposed and with parallax distance errors of less than 0.2 kpc; and (3) only O-type stars with 0.05 mas errors imposed and with parallax distance errors of less than 0.3 kpc. Results. In spite of the significant distance uncertainties for stars in DR2 beyond 1.4 kpc, the spiral structure in the solar neighborhood demonstrated by Gaia agrees well with that illustrated by VLBI maser results. The O-type stars available from DR2 extend the spiral arm models determined from VLBI maser parallaxes into the fourth Galactic quadrant, and suggest the existence of a new spur between the Local and Sagittarius arms.

scholarly journals CCD Astrometry and Photometry of Visual Double Stars: Northern Hipparcos Wide Pairs Measured in the Years 2003-2005

2006 ◽  
Vol 2 (S240) ◽  
pp. 613-618
Author(s):  
D. Sinachopoulos ◽  
P. Gavras ◽  
Th. Medupe ◽  
Ch. Ducourant ◽  
O. Dionatos
Keyword(s):  
Angular Separation ◽  
Double Star ◽  
Solar Neighborhood ◽  
Common Origin ◽  
Double Stars ◽  
The North ◽  
Visual Double Stars ◽  
Wide Pairs ◽  
Stellar Formation ◽  
Formation And Evolution

AbstractThe relative positions of Hipparcos visual double star components are currently known with a precision around fifty mas. Modern CCD astrometric observations of these objects achieve an accuracy of their angular separation between ten and twenty mas per observation. New CCD measurements have been obtained at Kryonerion Observatory in the north hemisphere. They provide current relative positions of visual double stars which are at least twice as accurate as the ones provided by Hipparcos. The new measurements will permit us to extract the physical pairs from the sample, and the double stars, which have components of common origin. Final statistics of these systems will improve our understanding of stellar formation and evolution rates of wide binaries in the solar neighborhood.

scholarly journals Challenging a Newtonian prediction through Gaia wide binaries

2019 ◽  
Vol 28 (08) ◽  
pp. 1950101 ◽  
Author(s):  
X. Hernandez ◽  
R. A. M. Cortés ◽  
Christine Allen ◽  
R. Scarpa
Keyword(s):  
Dark Matter ◽  
Relative Velocity ◽  
Binary Star ◽  
Dynamical Evolution ◽  
Small Sample ◽  
Solar Neighborhood ◽  
Newtonian Gravity ◽  
Orientation Effects ◽  
Newtonian Dynamics ◽  
Gaia Dr2

Under Newtonian dynamics, the relative motion of the components of a binary star should follow a Keplerian scaling with separation. Once orientation effects and a distribution of ellipticities are accounted for, dynamical evolution can be modeled to include the effects of Galactic tides and stellar mass perturbers, over the lifetime of the solar neighborhood. This furnishes a prediction for the relative velocity between the components of a binary and their projected separation. Taking a carefully selected small sample of 81 solar neighborhood wide binaries from the Hipparcos catalog, we identify these same stars in the recent Gaia DR2, to test the prediction mentioned using the latest and most accurate astrometry available. The results are consistent with the Newtonian prediction for projected separations below 7000 AU, but inconsistent with it at larger separations, where accelerations are expected to be lower than the critical [Formula: see text][Formula: see text]m.s[Formula: see text] value of MONDian gravity. This result challenges Newtonian gravity at low accelerations and shows clearly the appearance of gravitational anomalies of the type usually attributed to dark matter at galactic scales, now at much smaller stellar scales.

scholarly journals On the Stellar Velocity Distribution in the Solar Neighborhood in Light of Gaia DR2

2018 ◽  
Vol 863 (2) ◽  
pp. L37 ◽  
Author(s):  
Tatiana A. Michtchenko ◽  
Jacques R. D. Lépine ◽  
Angeles Pérez-Villegas ◽  
Ronaldo S. S. Vieira ◽  
Douglas A. Barros
Keyword(s):  
Velocity Distribution ◽  
Solar Neighborhood ◽  
Stellar Velocity ◽  
Gaia Dr2

Spectroscopic Observations of Visual Double Stars

1965 ◽  
Vol 5 ◽  
pp. 109-111
Author(s):  
Frederick R. West
Keyword(s):  
Radial Velocity ◽  
High Dispersion ◽  
Velocity Difference ◽  
Spectrograph Slit ◽  
Spectroscopic Observations ◽  
Double Stars ◽  
Visual Double Stars ◽  
Relative Orbit ◽  
Two Component ◽  
Star Images

There are certain visual double stars which, when close to a node of their relative orbit, should have enough radial velocity difference (10-20 km/s) that the spectra of the two component stars will appear resolved on high-dispersion spectrograms (5 Å/mm or less) obtainable by use of modern coudé and solar spectrographs on bright stars. Both star images are then recorded simultaneously on the spectrograph slit, so that two stellar components will appear on each spectrogram.

Discovery and Measurement of Double Stars by Lunar Occultations

1965 ◽  
Vol 5 ◽  
pp. 28-37
Author(s):  
R. Edward Nather ◽  
David S. Evans
Keyword(s):  
The Moon ◽  
Double Stars ◽  
Stellar Diameters ◽  
Diffraction Effects

When a star is occulted by the dark limb of the Moon its apparent intensity drops to zero very quickly. MacMahon (1909) proposed that the time of disappearance would measure the diameter of the star, but Eddington (1909) demonstrated that diffraction effects at the lunar limb would lengthen the apparent time of disappearance to about 20 msec, and suggested that these effects would greatly limit the usefulness of the technique. MacMahon’s paper indicates that he was aware that stellar duplicity could be detected from occultation observations, but he did not amplify the point and Eddington did not comment on it. While it has been demonstrated theoretically by Williams (1939) and experimentally by Whitford (1939) and others that stellar diameters of a few arcmsec can be measured by this technique, its use for the discovery and measurement of double stars has been only incidental to other programs (O’Keefe and Anderson, 1952; Evanset al., 1954). Properly exploited, the method can contribute materially to the study of double stars.

A Search for Dyson Spheres around Late-Type Stars in the Solar Neighborhood II

1997 ◽  
Vol 161 ◽  
pp. 707-709 ◽  
Author(s):  
Jun Jugaku ◽  
Shiro Nishimura
Keyword(s):  
Solar Neighborhood ◽  
The Sun ◽  
Late Type ◽  
Solar Type

AbstractWe continued our search for partial (incomplete) Dyson spheres associated with 50 solar-type stars (spectral classes F, G, and K) within 25 pc of the Sun. No candidate objects were found.

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