Time-resolved photometric and spectroscopic analysis of the luminous Ap star HD 103498

Abstract

We present the results of the photometric and spectroscopic monitoring of the luminous Ap star HD 103498. The time‐series photometric observations were carried out on 17 nights using a three‐channel fast photometer attached to the 1.04‐m optical telescope at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital. The photometric data from five nights in 2007 show a clear signature of 15‐min periodicity. However, the follow‐up observations during 2007–2009 did not reproduce any such periodicity. To confirm the photometric light variations, time‐series spectroscopic observations were carried out with the 2.56‐m Nordic Optical Telescope (NOT) at La Palma on 2009 February 2. No radial velocity variations were present in this data set, which is in full agreement with the photometric observations taken around the same date. Model atmosphere and abundance analysis of HD 103498 show that the star is evolved from the main sequence and its atmospheric abundances are similar to those of two other evolved Ap stars, HD 133792 and HD 204411: large overabundances of Si, Cr and Fe and moderate overabundances of the rare‐earth elements. These chemical properties and a higher effective temperature distinguish HD 103498 from any known roAp star.

Abundance and stratification analysis of the chemically peculiar star HD 103498

“…The classical abundance analysis in the approximation of chemically homogeneous atmosphere is based on the analysis of equivalent widths of the lines, which is performed using the updated version (Tsymbal 1996) of the width9 code (Kurucz 1993). We adopted υ sin i = 12 km s −1 (obtained by the best fit to the observed unblended line profiles) and microturbulent velocity ξ= 1.0 ± 0.2 km s −1 (derived from numerous lines of Cr i , Cr ii , Fe i and Fe ii ) from Joshi et al (2010). As the atmospheres of CP stars of type A are believed to be quiet in order to develop chemical peculiarities, a non‐zero microturbulence found in (Joshi et al 2010) probably results from the Zeeman broadening of spectral lines caused by a weak surface magnetic field.…”

“…We adopted υ sin i = 12 km s −1 (obtained by the best fit to the observed unblended line profiles) and microturbulent velocity ξ= 1.0 ± 0.2 km s −1 (derived from numerous lines of Cr i , Cr ii , Fe i and Fe ii ) from Joshi et al (2010). As the atmospheres of CP stars of type A are believed to be quiet in order to develop chemical peculiarities, a non‐zero microturbulence found in (Joshi et al 2010) probably results from the Zeeman broadening of spectral lines caused by a weak surface magnetic field. Since both in Joshi et al and in the present study we use non‐magnetic spectra synthesis, ξ= 1.0 km s −1 was still needed to mimic the effect of the star’s magnetic field and its value were kept constant during iterative abundance analysis described below.…”

“…The abundance analysis of the programme star is based on the average spectrum of time series spectroscopy. The finer details about the observations and data reduction procedure are given in Joshi et al (2010).…”

“…HD 103498 is a characteristic example of an evolved star belonging to the so‐called CP group of spectral type A (Ap) with a strong overabundance of Si, Fe and Cr in its atmosphere as follows from the recent analysis undertaken by Joshi et al (2010). The authors aimed at the pulsation analysis of the star’s atmosphere and performed only classical homogeneous abundance analysis based on scaled‐solar metallicity model atmosphere.…”

“…In this work we extend the study of Joshi et al (2010) and carry out a complex, self‐consistent analysis of the HD 103498 atmosphere. The main goal is to involve all the available observables to derive consistently the fundamental atmospheric parameters and abundance pattern of the star.…”