Kinematics and ellipsoidal motion of the mid to late M-type stars

Abstract

Truly, kinematics in the Solar neighborhood has provided important information both for the structure and for the evolution of the Galaxy since the early 20th century. The relationship between Oort constants and the ratio of the velocity dispersion are important quantities in stellar kinematics. In the present paper, we calculated the kinematical parameters and the Oort constants of various samples of late to intermediate M-type stars. We calculated the velocity dispersion <mfenced open="(" close=")" separators="">σ1,σ2,σ3</mfenced> in units of km s⁻¹ for the samples under study. The longitude of the vertex <mfenced open="(" close=")" separators="">l2</mfenced> having negative values with our analysis; that is, the program I (538 stars), l2=−0.5410°; program II (100 stars), l2=−0.4937°; and program III (60 stars), l2=−0.9495°. We calculate the Oort constants as A=14.69±0.61 km s⁻¹ kpc⁻¹ and B=−16.70±0.67 km s^−-1 kpc⁻¹, and the rotational velocity Vo=257.38±9.40 km s−1. A possible explanation for the overestimated values of the second Oort constants has been presented.