Spectroscopic binary orbits and MK morphological studies of some AM stars

Abstract

The metallic-line A type stars (Am) on the main sequence are known to be largely the members of binary systems and therefore yield periods. Due to their small equatorial radial velocities, they display sharp spectral lines which facilitate an easy and accuracte measurement of their Doppler displacements as well as line profile studies. Their slow rotation (nu sin i less than 100 km/s) also causes surface abundance anomalies which are often represented by the distinct spectral characteristic Sp (K) less than Sp (H) less than Sp (ml). Such spectra require a third dimension specifying the metallic-line type for classification. Although, Am stars are cooler extensions of Ap stars, they are hitherto known to be exclusive to each other with respect to their magnetic fields and hence in the degree of display of abundance anomalies and associated spectrum variability. Therefore we have obtained well widened spectra of several Am stars with the Meinel spectrograph at the Nasmyth focus of the 1.2m telescope of the Japal-Rangapur Observatory with the aim to study: Spectroscopic orbits (HD 434, HR 3040, HR 903, 37 epsilon Ser and 41 Sex A at 33 A/mm); MK Morphology (28 Am stars and 39 MK standards at 66 A/mm); and Spectrum line variability (41 Sex A at 33 and 66 A/mm).