Search

The prototype star for the γ Doradus class of pulsating variables was studied employing photometric and spectroscopic observations to determine the frequencies and modes of pulsation. The four frequencies found are self-consistent between the observation types and almost identical to those found in previous studies (1.3641 d-1, 1.8783 d-1, 1.4742 d-1, and 1.3209 d-1). Three of the frequencies are classified as l, m = (1, 1) pulsations and the other is ambiguous between l, m = (2, 0) and (2, -2) modes. Two frequencies are shown to be stable over 20 yr since their first identification. The agreement in ground-based work makes this star an excellent calibrator between high-precision photometry and spectroscopy with the upcoming TESS observations and a potential standard for continued asteroseismic modelling. [ABSTRACT FROM AUTHOR]

We present a spectroscopic survey of known and candidate γ Doradus stars. The high-resolution, high signal-to-noise spectra of 52 objects were collected by five different spectrographs. The spectral classification, atmospheric parameters (Teff, logg, ξ), vsini and chemical composition of the stars were derived. The stellar spectral and luminosity classes were found between G0-A7 and IV-V, respectively. The initial values for Teff and logg were determined from the photometric indices and spectral energy distribution. Those parameters were improved by the analysis of hydrogen lines. The final values of Teff, logg and ξ were derived from the iron lines analysis. The Teff values were found between 6000K and 7900K, while logg values range from 3.8 to 4.5 dex. Chemical abundances and vsini values were derived by the spectrum synthesis method. The vsini values were found between 5 and 240 km s-1. The chemical abundance pattern of γ Doradus stars were compared with the pattern of non-pulsating stars. It turned out that there is no significant difference in abundance patterns between these two groups. Additionally, the relations between the atmospheric parameters and the pulsation quantities were checked. A strong correlation between the vsini and the pulsation periods of γ Doradus variables was obtained. The accurate positions of the analysed stars in the Hertzsprung-Russell diagram have been shown. Most of our objects are located inside or close to the blue edge of the theoretical instability strip of γ Doradus. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the mode identification of frequencies found in spectroscopic observations of the γ Doradus star HD 135825. Four frequencies were successfully identified: 1.3150 ± 0.0003, 0.2902 ± 0.0004, 1.4045 ± 0.0005 and 1.8829 ± 0.0005 d−1. These correspond to ( l, m) modes of (1, 1), (2, −2), (4, 0) and (1, 1), respectively. Additional frequencies were found but they were below the signal-to-noise ratio limit of the Fourier spectrum and not suitable for mode identification. The rotational axis inclination and v sin i of the star were determined to be 87° (nearly edge-on) and 39.7 km s−1 (moderate for γ Doradus stars), respectively. A simultaneous fit of these four modes to the line profile variations in the data gives a reduced χ2 of 12.7. We confirm, based on the frequencies found, that HD 135825 is a bona fide γ Doradus star. [ABSTRACT FROM AUTHOR]

ABSTRACT Gravity modes present in γ Doradus stars probe the deep stellar interiors and are thus of particular interest in asteroseismology. Mode identification will improve the knowledge of these stars considerably and allow an understanding of the issues with current pulsational models. A frequency analysis followed by a mode identification were done based on the high-resolution spectroscopic data of two γ Doradus stars: HD 189631 and HD 40745. Extensive spectroscopic data sets are obtained by three instruments: HARPS, FEROS and HERCULES. We obtained 422 spectra for HD 189631 and 248 spectra for HD 40745. The pulsational frequencies were determined by four methods: analysis of the variation in equivalent width, variation in radial velocity, asymmetry of the line profile and the pixel-by-pixel frequency analysis. The mode identification was done using the recently developed Fourier Parameter Fit method. Without achieving the same degree of confidence for all results, we report the identification of four pulsational modes in HD 189631: ( ℓ= 1; m =+1) at f1= 1.67 d−1; (3; −2) at f2= 1.42 d−1; (2; −2) at f3= 0.07 d−1; and (4; +1) at f4= 1.82 d−1; and two modes in HD 40745: (2; −1) at f1= 0.75 d−1 and (3; −3) at f2= 1.09 d−1. This study provides the first pulsational analysis based on spectroscopy of HD 189631 and HD 40745. We discuss the performance of current methods of analysis and outline the difficulties presented by γ Doradus stars. [ABSTRACT FROM AUTHOR]

In this paper we examine the problems of phasing using light curves and offer an alternate technique using the changes in acceleration to establish the zero point. We give astrophysical justification as to why this technique is useful and apply the technique to a selection of Type II Cepheids. We then examine some limitations of the technique which qualify its use. [ABSTRACT FROM AUTHOR]