Kinematics of nearby subdwarf stars

Abstract

Abstract.We present an analysis of the space motions of 742 subdwarf stars based on the sample of Carney et al. (1994, AJ, 107, 2240. Hipparcos parallaxes, TYC2+HIP proper motions and Tycho 2 proper motions were combined with radial velocities and metallicities from CLLA. The kinematical behavior is discussed in particular in relation to their metallicities. The majority of these sample stars have metal abundances of [Fe/H] > −1 and represent the thick disk population. The halo component, with [Fe/H] < −1.6, is characterized by a low mean rotation velocity and a radially elongated velocity ellipsoid. In the intermediate metallicity range (−1.6 ≤ [Fe/H] ≤ −1), we find a significant number of subdwarfs with disklike kinematics. We interpret this population of stars as a metal-weak thick disk (MWTD) population.

The Solar Neighborhood. XLII. Parallax Results from the CTIOPI 0.9 m Program—Identifying New Nearby Subdwarfs Using Tangential Velocities and Locations on the H–R Diagram

“…Thus, kinematically, HIP 117795 is very different from nearby disk M dwarfs (Hawley et al 1996) and it is about one magnitude below the center of the main sequence in Figure 6. As we discussed earlier, Arifyanto et al (2005) . The direction and velocity of HIP 117795ʼs V indicate that it has a retrograde motion and is much faster than the limit shown in Arifyanto et al (2005) for halo stars.…”

“…They use σ W values to separate over 770 FGKM stars from the NLTT catalog, among which they flagged 115 K and 4 M subdwarfs. A study by Arifyanto et al (2005), based on 742 nearby metal-poor stars from Carney et al (1994), reported that halo stars with [Fe/H]<−1.6 have a low mean rotational velocity around the Galaxy and a radially elongated velocity ellipsoid, while stars with −1.6<[Fe/H]<−1 have disk-like kinematics. Based on a limited sample of 69 subdwarfs with both parallaxes and radial velocities, Gizis (1997) found different mean Galactic rotation velocities between different sub-types of subdwarfs and noted that, overall, subdwarfs move faster than regular M dwarfs.…”

Signatures of star streams in the phase space distribution of nearby halo stars

“…In order to assess the reality of the overdensities we have performed Monte-Carlo simulations of a smooth velocity distribution of halo stars. We adopted a triaxial Schwarzschild distribution with the velocity dispersions determined by Arifyanto & Fuchs (2005). The size of the simulated sample was set equal to the observed number of stars with non-disk kinematics.…”

The Galactic Thick Disk: An Observational Perspective

“…An attempt was made to systematically search for MWTD and study their chemical abundance pattern in relation to the thin disk, thick disk and halo populations (Reddy & Lambert 2008). For this study they made use of the two catalogues (Arifyanto et al 2005;Schuster et al 2006) High resolution abundance analysis study showed no clear difference in any elemental abundance trends, among several elements examined, between stars of the MWTD, halo or the canonical thick disk (see Table 2). This raises three possibilities; a) MWTD is a metal-poor end of the thick disk and shows no distinguishable chemical abundance difference as the thick disk formed more rapidly, b) MWTD is a discrete entity with indistinguishable abundances either from the thick disk or halo populations.…”