* Astronomy

Title: A spectroscopic analysis of the chemically peculiar star HD207561
Authors: S. Joshi (1), E.Semenko (2), P. Martinez (3), M. Sachkov (4), Y. C. Joshi (1), S. Seetha (5), N. K. Chakradhari (6), D. L. Mary (7), V. Girish (5), B. N. Ashoka (5) ((1) Aryabhatta Research Institute of Observational Sciences, Manora peak, Nainital, India,(2) Special Astrophysical Observatory RAS, Nizhny Arkhyz, Karachai-Cherkassian Republic, Russia, (3) South African Astronomical Observatory, Cape Town, South Africa, (4) Institute of Astronomy, Russian Academy of Sciences, Moscow, Russia, (5) ISRO Satellite Center, Airport Road, Bangalore, India, (6) School of Studies in Physics and Astrophysics, Pt. Ravishankar Shukla University, Raipur, India, (7) Laboratoire Lagrange, Universit'e de Nice Sophia-Antipolis, CNRS, Observatoire de la Cote d'Azur, France)

In this paper we present a high-resolution spectroscopic analysis of the chemically peculiar star HD207561. During a survey programme to search for new roAp stars in the Northern hemisphere, Joshi et al. (2006) observed significant photometric variability on two consecutive nights in the year 2000. The amplitude spectra of the light curves obtained on these two nights showed oscillations with a frequency of 2.79 mHz [P~6-min]. However, subsequent follow-up observations could not confirm any rapid variability. In order to determine the spectroscopic nature of HD207561, high-resolution spectroscopic and spectro-polarimetric observations were carried out. A reasonable fit of the calculated Hbeta line profile to the observed one yields the effective temperature (Teff) and surface gravity (log g) as 7300 K and 3.7 dex, respectively. The derived projected rotational velocity (vsin i) for HD207561 is 74 km/sec indicative of a relatively fast rotator. The position of HD207561 in the H-R diagram implies that this is slightly evolved from the main-sequence and located well within the delta-Scuti instability strip. The abundance analysis indicates the star has slight under-abundances of Ca and Sc and mild over-abundances of iron-peak elements. The spectro-polarimetric study of HD207561 shows that the effective magnetic field is within the observational error of 100 gauss (G). The spectroscopic analysis revealed that the star has most of the characteristics similar to an Am star, rather than an Ap star, and that it lies in the delta-Scuti instability strip; hence roAp pulsations are not expected in HD207561, but low-overtone modes might be excited.

Read more (339kb, PDF)