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High-Velocity Moving Groups in the Solar Neighborhood in Gaia DR2

Baluev R. V., Shaidulin V. Sh., Veselova A. V.

Acta Astronomica

2020

Vol. 70, No. 2

141--168

We use an improved wavelet analysis technique to reconstruct the (U,V,W) velocity distribution for ≈250 000 stars from Gaia DR2, located in the solar neighborhood of 200 pc. The 2D wavelet transforms for three bivariate distributions (U,V), (U,W), and (V,W) were investigated. Though most of currently known (low-velocity) stellar moving groups are densely overlapped in these diagrams, our analysis allowed us to detect and disentangle about twenty statistically significant 3D groups of stars with high velocities. Most of them appear to be new discoverirs. We also discuss the issue of correct noise thresholding in the wavelet transform and highlight the importance of using a global rather than local statistic for that. Using of a local significance measure may lead to an overstated statistical confidence for individual patterns due to the effect of multiple testing.

Ratio of the Mean Random Velocity Squares Revisited

Ninković S.

Acta Astronomica

2018

Vol. 68, No. 3

301--313

The paper aims at obtaining a new formula for the ratio of the mean squares of random velocity in the Galactic plane valid for nearly circular orbits. The formula is obtained by considering a more general case and then reducing it to that concerning low eccentricities. The formula usually referred to as "epicyclic one" is its special case. In addition to the ratio of the Oort constants moduli the ratio of the mean velocity squares depends on the distribution of stars in orbital phases which is presented by means of two parameters, including the asymmetry as well. Inclusion of asymmetry contributes to the increase of moduli of both parameters.

High Proper Motion Objects toward the Inner Milky Way: Characterization of Newly Identified Nearby Stars from the VISTA Variables in the Vía Láctea Survey

Gromadzki M., Kurtev R., Beamán J. C., Tekola A., Ramphul R., Ivanov V. D., Minniti D., Folkes S. L., Vaisanen P., Kniazev A. Y., Borissova J., Parsons S. G., Villanueva V.

Acta Astronomica

2016

Vol. 66, No. 3

293--306

The census of the Solar neighborhood is still incomplete, as demonstrated by recent discoveries of many objects within 5-10 pc from the Sun. The area around the mid-plane and bulge of the Milky Way presents the most difficulties in searches for such nearby objects, and is therefore deficient in the known population. This is largely due to high stellar densities encountered. Spectroscopic, photometric and kinematic characterization of these objects allows better understanding of the local mass function, the binary fraction, and provides new interesting targets for more detailed studies. We report the spectroscopic follow-up and characterization of twelve bright high proper motion objects, identified from the VISTA Variables in Vía Láctea survey (VVV). We used the 1.9-m telescope of the South African Astronomical Observatory (SAAO) for low-resolution optical spectroscopy and spectral classification, and the MPG/ESP 2.2-m telescope Fiber-fed Extended Range Optical Spectrograph (FEROS) high-resolution optical spectroscopy to obtain the radial and space velocities for three of them. Six of our objects have co-moving companions. We derived optical spectral types and photometric distances, and classified all of them as K and M dwarfs within 27-264 pc from the Sun. Finally, we found that one of the sources, VVV J141421.23-602326.1 (a co-moving companion of VVV J141420.55-602337.1), appears to be a rare massive white dwarf located close to the ZZ Cet instability strip in the CMD and CC diagrams. Many of the objects in our list are interesting targets for exoplanet searches.