Poster abstract details

Do hybrid stars comprise a distinct group of variables?
Markus Hareter & Werner W. Weiss


Investigation of main sequence A and F stars have shown that gamma Dor - delta Scuti hybrid stars do not significantly concentrate in the overlapping region within the HRD of the respective instability strips, but rather populate the delta Scuti Instability strip.

High order g mode pulsation of g Dor stars require a certain depth of the base of the convective envelope in order to drive those g modes. This condition is fulfilled near the red border of the delta Scuti Instability strip, where the gamma Doradus stars are located. Hybrids exhibit as well g modes, but their frequencies cannot easily be explained by the same mechanism as the gamma Doradus stars.

A comparison of the p mode pulsation of delta Scuti and hybrid stars shows a different behaviour. When plotting
1) the strongest pulsation mode of each of these two groups against their effective
temperature, the delta Scuti stars show a correlation of their main pusation period with Teff, but hybrids do not.
2) If the average of the three modes with largest amplitudes is considered we see the same tendency, both relations are not followed by Hybrids.

Hybrid stars are known, which exhibit three distinct groups of frequencies (e.g. HD 8801, HD 114839, BD +18 4914) with a narrow range of excited modes and with gaps in between. The intermediate frequency group could probably be explained by low-order g modes in contrast to gamma Dor stars,
which have high-order g modes excited.

Are hybrid stars a distinct class of pulsators within the delta Scuti instability strip?

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