The Nainital-Cape Survey

II. Report for pulsation in five chemically peculiar A-type stars and presentation of 140 null results

¹ Inter-University Centre for Astronomy and Astrophysics (IUCAA), Post Bag 4, Ganeshkhind, Pune 411007, India e-mail: santosh@iucaa.ernet.in
² Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital-263129, India e-mail: santosh@aries.ernet.in
³ Astronomisches Rechen-Institut am Zentrum fuer Astronomie, Moenchhofstrasse 12-14, 69120, Heidelberg, Germany e-mail: dmary@ari.uni-heidelberg.de
⁴ South African Astronomical Observatory (SAAO), PO Box 9, Observatory 7935, South Africa e-mail: peter@saao.ac.za
⁵ Centre for Astrophysics, University of Central Lancashire, Preston PR1 2HE, UK e-mail: dwkurtz@uclan.ac.uk
⁶ Tata Institute of Fundamental Research (TIFR), Homi Bhabha Road, Mumbai-400 005, India e-mail: giri@tifr.res.in
⁷ ISRO Satellite Center, Airport Road, Bangalore-560 017, India e-mail: seetha@isac.ernet.in

Received: 6 February 2006
Accepted: 25 April 2006

Abstract

Aims.We search for photometric variability in chemically peculiar A type stars in the northern hemisphere.

Methods.High-speed photometric observations of Ap and Am star candidates have been carried out from ARIES (Manora Peak, Nainital) using a three-channel fast photometer attached to the ARIES 104-cm Sampurnanand telescope.

Results.This paper presents three new variables: HD 113878, HD 118660 and HD 207561. During the time span of the survey (1999 December to 2004 January) pulsations of the δ Sct type were also found for the two evolved Am stars HD 102480 and HD 98851, as reported in Joshi et al. (2002, 2003). Additionally, we present 140 null results of the survey for this time span.

Conclusions.The star HD 113878 pulsates with a period of 2.31 h, which is typical of δ Sct stars. HD 118660 exhibits multi-periodic variability with a prominent period of nearly 1 h. These periods need to be investigated and make HD 118660 a particularly interesting target for further observations. For HD 207561, a star classified as Am, a probable pulsation with a period of 6 min was found in the light curves obtained on two consecutive nights. Both HD 102480 and HD 98851 exhibit unusual alternating high and low amplitude maxima, with a period ratio of 2:1. The analysis of the null results confirms the photometric quality of the Nainital site.