Refining the asteroseismic model for the young δ Scuti star HD 144277 using HARPS spectroscopy⋆
1 Instituut voor Sterrenkunde, K. U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
2 Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya Str. 48, 109017 Moscow, Russia
3 Copernicus Astronomical Centre, Bartycka 18, 00-716 Warsaw, Poland
4 University of Vienna, Institute of Astronomy, Türkenschanzstrasse 17, 1180 Vienna, Austria
5 Argelander-Institut für Astronomie der Universität Bonn, auf dem Hügel 71, 53121 Bonn, Germany
6 Moscow M.V. Lomonosov State University, Sternberg Astronomical Institute, Universitetskii pr. 13, 119992 Moscow, Russia
7 Dept. of Astronomy, University of Texas at Austin, Austin TX 78712, USA
8 INAF – Osservatorio Astronomico di Brera, Merate, Italy
Received: 31 October 2013
Accepted: 5 May 2014
Context. HD 144277 was previously discovered by Microvariability and Oscillations of Stars (MOST) space photometry to be a young and hot δ Scuti star showing regular groups of pulsation frequencies. The first asteroseismic models required lower than solar metallicity to fit the observed frequency range based on a purely photometric analysis.
Aims. The aim of the present paper is to determine, by means of high-resolution spectroscopy, fundamental stellar parameters required for the asteroseismic model of HD 144277, and subsequently, to refine it.
Methods. High-resolution, high signal-to-noise spectroscopic data obtained with the HARPS spectrograph were used to determine the fundamental parameters and chemical abundances of HD 144277. These values were put into context alongside the results from asteroseismic models.
Results. The effective temperature, Teff, of HD 144277 was determined as 8640 +300-100 K, log g is 4.14 ± 0.15 and the projected rotational velocity, υsini, is 62.0 ± 2.0 km s-1. As the υsini value is significantly larger than previously assumed, we refined the first asteroseimic model accordingly. The overall metallicity Z was determined to be 0.011 where the light elements He, C, O, Na, and S show solar chemical composition, but the heavier elements are significantly underabundant. In addition, the radius of HD 144277 was determined to be 1.55 ± 0.65 R⊙ from spectral energy distribution fitting, based on photometric data taken from the literature.
Conclusions. From the spectroscopic observations, we could confirm our previous assumption from asteroseismic models that HD 144277 has less than solar metallicity. The fundamental parameters derived from asteroseismology, Teff, log g, L/L⊙ and R/R⊙ agree within one sigma to the values found from spectroscopic analysis. As the υsini value is significantly higher than assumed in the first analysis, near-degeneracies and rotational mode coupling were taken into account in the new models. These suggest that HD 144277 has an equatorial rotational velocity of about 80 km s-1 and is seen equator-on. The observed frequencies are identified as prograde modes.
Key words: stars: variables: delta Scuti / stars: oscillations / stars: individual: HD 144277 / stars: fundamental parameters / techniques: photometric / asteroseismology
© ESO, 2014