Asteroseismology of HD 23734, HD 68703, and HD 73345 using K2–TESS space-based photometry and high-resolution spectroscopy

Abstract

In this paper, we present a comprehensive study of three stars, HD 23734, HD 68703, and HD 73345, which were previously observed as chemically peculiar candidates within the Nainital-Cape survey and reported as null results for the pulsational variability. Frequency analyses of K2 and TESS time-series photometric data reveal the co-existence of rotational modulation and pulsation. We use the spectrum synthesis technique to determine fundamental parameters and chemical composition, which shows that all the three stars are likely to be chemically normal. The evolutionary status of the target stars corresponds to the main-sequence phases and places them within the δ Scuti instability strip of the Hertzsprung–Russell diagram. The line profile variability is observed in all three stars, especially intriguing in HD 68703 and a typical signature of the non-radial pulsation, demands further detailed examination. Using TESS photometry, we identified the radial modes of orders n = 3 and 4 for HD 23734, n = 1, 3, and 4 for HD 68703, and n = 3, 4, and 5 for HD 73345. In addition to the presence of pulsation and rotation, HD 73345 exhibits a steady increase in radial velocity that we interpret as the star being likely to be part of a long-period binary system. Finally, we propose an extended campaign aimed for the in-depth spectroscopic and spectropolarimetric study of selected pulsating stars monitored under the Nainital-Cape survey project.