Browsing by Author "Aslan, Zeki"

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    On the K-term and dispersion ratios of semi-regular variables
    (1981) Aslan, Zeki; Fen Fakültesi
    Optical velocities of semi-regular (SR) and irregular (Lb) variables are analysed for a K-term. There is evidence for a dependence upon stellar period. Absorption lines in shorter period non-emission SR variables are blue-shifted relative to the centre-of-mass velocity by about 6±3 km s−1. Emission-line SR variables give a non-negative absorption K-term and Lb variables give no K-terms other than zero. Comparison is made with the K-terms implied by the OH velocity pattern in long-period variables. Dispersion ratios are also calculated. They are σv/σu=0.69±0.16 for non-emission, and 0.74±0.20 for emission variables (from absorption lines). Kinematics suggest that the sequence Lb–SR (non-emission)–SR (emission)–Mira is a sequence of increasing age. It is suggested that this sequence may also be the sequence indicating the direction of evolution.