The tip of the iceberg: the frequency content of the Delta Sct star HD 50844 from CoRoT space photometry

TL;DR

This study uses CoRoT space photometry to analyze the Delta Sct star HD 50844, revealing hundreds of low-amplitude modes and confirming the star's rich frequency content and high-degree modes, advancing understanding of stellar pulsations.

Contribution

The paper demonstrates the detection of hundreds of pulsation modes, including high-degree modes, in HD 50844 using space-based data, confirming the star's complex frequency spectrum.

Findings

Hundreds of frequency terms detected in HD 50844

High-degree modes up to ell=14 identified

Fundamental radial mode confirmed as f_1=6.92 d^{-1}

Abstract

It has been suggested that the detection of a wealth of very low amplitude modes in Delta Sct stars was only a matter of signal--to--noise ratio. Access to this treasure, impossible from the ground, is one of the scientific aims of the space mission CoRoT, developed and operated by CNES. This work presents the results obtained on HD 50844: the 140,016 datapoints allowed us to reach the level of 10^{-5} mag in the amplitude spectra. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0--30 d^{-1}. The initial guess that Delta Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high--degree modes (up to ell=14) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground--based observations indicate that HD 50844 is an evolved star that is slightly underabundant in heavy elements, located on the Terminal Age Main Sequence. The predominant term (f_1=6.92 d^{-1}) has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data. This work is based on observations made with ESO telescopes under the Large Programme LP 178.D-0361.