A spectroscopic search for nonradial pulsations in the Delta Scuti stars Delta Delphini and Epsilon Cephei

Details A spectroscopic search for nonradial pulsations in the Delta Scuti stars Delta Delphini and Epsilon Cephei A spectroscopic search for nonradial pulsations in the Delta Scuti stars Delta Delphini and Epsilon Cephei

Mar 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...269..195b&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 269, no. 1-2, p. 195-200.

Astronomy and Astrophysics

Astrophysics

3

A Stars, Binary Stars, Hertzsprung-Russell Diagram, Stellar Oscillations, Giant Stars, Radial Velocity, Vibration Mode

Scientific paper

In high-resolution observations of the reported 40.5-day binary Delta Del, the spectra of the two almost identical components were found to be well separated. However, in over 40 percent of the primary pulsation period of 0.135 days no significant line profile variations or asymmetries were detected in either component. The line widths of about 30 km/s are too small for the detection of higher-order nonradial modes. The latter goal was clearly achieved in Epsilon Cep, in spite of 20-minute exposures. The nonradial mode order inferred from the line profiles is 6-8; corotating surface features are not probably a viable alternative explanation. The timescale agrees with the photometrically dominating 61-minute period to within the errors whereas no evidence of radial or low-order nonradial pulsation was found. This is surprising as such a relatively high-order mode is not expected to be prominent in integrated-light observations such as photometry. An identity of these spectroscopic and photometric modes would provide a drastic renewal of warnings against the usage of period ratios for mode identification. The existence of higher-order modes raises questions about the nature of the photometrically constant stars in the Delta Scuti strip and the true boundaries of the latter.

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