Details

Autor(en) / Beteiligte

• Gillet, D.
• Sefyani, F. L.
• Benhida, A.
• Mauclaire, B.
• El Youssoufi, D.
• de France, T.
• Benkhaldoun, Z.
• Lailly, P.

Titel

Atmospheric dynamics and shock waves in RR Lyr: I. The three H α emissions

Ist Teil von

• Astronomy and astrophysics (Berlin), 2023-12, Vol.680, p.A97

Erscheinungsjahr

2023

Quelle

EZB Free E-Journals

Beschreibungen/Notizen

• Context. Although spectroscopic observations of RR Lyrae stars have been underway for almost a century, the fact that the hydrogen line exhibits three successive emissions in each pulsation cycle is still a very recent discovery. Aims. The purpose of the present study is to clarify the physical origin of these three emissions and their connection to atmospheric dynamics and to examine the influence of Blazhko modulation on their intensity. Methods. We used 2437 high-resolution spectra over a total of 81 nights taken by the ELODIE spectrograph (Haute Provence Observatory, France) in the years 1994–1997, rounded out with a 2015 run from Oukaïmeden Observatory (Morocco). We performed a detailed analysis of the line profile variations over the whole pulsation cycle. Results. Based on the blueshift of the main H α emission, the velocity of the hypersonic shock front was estimated at between 100 and 150 ± 10 km s −1 (Mach number between 10 and 15). It has been established that the shock velocity increases from the minimum Blazhko to its maximum and afterward, it gradually decreases to the Blazhko minimum to start growing again. This observational result is consistent with the shock model proposed in 2013 to explain the Blazhko effect. The intensity of the H α emission increases with the shock velocity up to a maximum value around 137 km s −1 and then decreases as the shock velocity increases further. This effect would be the consequence of the increasingly important ionization of the atoms in the radiative shock wake. The second (blueshifted) H α emission is the consequence of an approximately constant supersonic compression (Mach number between 2 and 3) of the upper atmosphere falling onto the photospheric layers, during 3 to 16% of the pulsation period. Finally, the third H α emission (P-Cygni profile) would be the consequence of the expansion of the high atmosphere induced by the shock wave during its final weakening.