Article

Discovery of unusual pulsations in the cool, evolved Am stars HD 98851 and HD 102480

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.52). 08/2003; 344(2):431 - 438. DOI: 10.1046/j.1365-8711.2003.06823.x
Source: arXiv

ABSTRACT The chemically peculiar (CP) stars HD 98851 and HD 102480 have been discovered to be unusual pulsators during the ‘Naini Tal–Cape Survey’ programme to search for pulsational variability in CP stars. Time series photometric and spectroscopic observations of these newly discovered stars are reported here. Fourier analyses of the time series photometry reveal that HD 98851 is pulsating mainly with frequencies 0.208 and 0.103 mHz, and HD 102480 is pulsating with frequencies 0.107, 0.156 and 0.198 mHz. The frequency identifications are all subject to 1 d−1 cycle count ambiguities. We have matched the observed low-resolution spectra of HD 98851 and HD 102480 in the range 3500–7400 Å with theoretical synthetic spectra using Kurucz models with solar metallicity and a micro-turbulent velocity of 2 km s−1. These yield Teff= 7000 ± 250 K, log g= 3.5 ± 0.5 for HD 98851 and Teff= 6750 ± 250 K, log g= 3.0 ± 0.5 for HD 102480. We determined the equivalent H-line spectral class of these stars to be F1 IV and F3 III/IV, respectively. A comparison of the location of HD 98851 and HD 102480 in the HR diagram with theoretical stellar evolutionary tracks indicates that both stars are about 1-Gyr-old, 2-M⊙ stars that lie towards the red edge of the δ Sct instability strip. From comparison between the observed and calculated physical parameters, we conclude that HD 98851 and HD 102480 are cool, evolved Am pulsators. The light curves of these pulsating stars have alternating high and low amplitudes, nearly harmonic (or subharmonic) period ratios, high pulsational overtones and Am spectral types. This is unusual for both Am and δ Sct pulsators, making these stars interesting objects for further observational and theoretical studies.

0 Bookmarks
 · 
72 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: The discovery of a new rapidly oscillating Ap star, HD 116114, with a pulsation period of 21 min, using high-resolution spectra obtained with the Ultraviolet-Visual Echelle Spectrograph at the European Southern Observatory's Very Large Telescope, is presented. The highest amplitudes of the radial velocity variations are between 50 and 125 m s−1 visible in the Eu ii lines. The spectral lines of La ii and the core of the H line have amplitudes of about 30 m s−1. The frequency obtained for the oscillations is in good agreement with theoretical predictions of longer-period, evolved roAp stars. The distinction in luminosity between the roAp and noAp stars, and the suggestion that in all roAp stars the abundance of the second ions of Pr and Nd, relative to the abundance of the first ions, is anomalously high, need to be revised in the light of this discovery.
    Monthly Notices of the Royal Astronomical Society 03/2005; 358(2):665 - 670. · 5.52 Impact Factor
  • Source
    Astronomy & Astrophysics - ASTRON ASTROPHYS. 01/2009; 507(3):1763-1784.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Recently, Tiwari, Chaubey & Pandey detected the bright component of the visual binary HD 151878 to exhibit rapid photometric oscillations through a Johnson B filter with a period of 6 min (2.78 mHz) and a high, modulated amplitude up to 22 mmag peak-to-peak, making this star by far the highest amplitude rapidly oscillating Ap (roAp) star known. As a new roAp star, HD 151878 is of additional particular interest as a scarce example of the class in the northern sky, and only the second known case of an evolved roAp star – the other being HD 116114. We used the FIbre-fed Echelle Spectrograph at the Nordic Optical Telescope to obtain high time-resolution spectra at high dispersion to attempt to verify the rapid oscillations. We show here that the star at this epoch is spectroscopically stable to rapid oscillations of no more than a few tens of m s−1. The high-resolution spectra furthermore show the star to be of type Am rather than Ap and we show the star lacks most of the known characteristics for roAp stars. We conclude that this is an Am star that does not pulsate with a 6-min period. The original discovery of pulsation is likely to be an instrumental artefact.
    Monthly Notices of the Royal Astronomical Society 10/2008; 390(1):257 - 264. · 5.52 Impact Factor

Full-text

Download
0 Downloads
Available from