First observation of Hα redshifted emission in RR Lyr⋆
Evidence of a supersonic infalling motion of the atmosphere
1 Observatoire de Haute-Provence – CNRS/PYTHEAS/Université d’Aix-Marseille, 04870 Saint-Michel l’Observatoire France
2 Observatoire du Val de l’Arc, route de Peynier, 13530 Trets, France
3 Observatoire de Fontcaude, 19 Av. du Hameau du golf, 34990 Juvignac, France
4 Observatoire de Chelles, 23 Av. Hénin, 77500 Chelles, France
5 Observatoire Midi-Pyrénées, IRAP, Université de Toulouse, CNRS, UPS, CNES, Tarbes, 31400 Toulouse, France
6 Observatoire de Mèze, 5 Imp. des Tourterelles, 34140 Mèze, France
7 Observatoire OAV, 13 rue du Moulin, 34290 Alignan-du-Vent, France
8 115 Av. du général de Gaulle, 84450 Saint-Saturnin-les-Avignon, France
9 Les Trucs, 26420 Saint-Agnan en Vercors, France
10 42 chemin de la Beaume, 26190 Saint-Laurent-en-Royans, France
11 5 rue Edmond Gondinet, 75013 Paris, France
12 Observatoire de la Tourbière, 45 chemin du Lac, 38690 Chabons, France
13 Observatoire de Haute-Provence, 04870 Saint-Michel l’Observatoire, France
Received: 14 October 2016
Accepted: 22 August 2017
Context. The so-called Hα third emission occurs around pulsation phase ϕ = 0.30. It has been observed for the first time in 2011 in some RR Lyrae stars. The emission intensity is very weak, and its profile is a tiny persistent hump in the red side-line profile.
Aims. We report the first observation of the Hα third emission in RR Lyr itself (HD 182989), the brightest RR Lyrae star in the sky.
Methods. New spectra were collected in 2013−2014 with the AURELIE spectrograph (resolving power R = 22 700, T152, Observatoire de Haute-Provence, France) and in 2016−2017 with the eShel spectrograph (R = 11 000, T035, Observatoire de Chelles, France). In addition, observations obtained in 1997 with the ELODIE spectrograph (R = 42 000, T193, Observatoire de Haute-Provence, France) were reanalyzed.
Results. The Hα third emission is clearly detected in the pulsation phase interval ϕ = 0.188−0.407, that is, during about 20% of the period. Its maximum flux with respect to the continuum is about 13%. The presence of this third emission and its strength both seem to depend only marginally on the Blazhko phase. The physical origin of the emission is probably due to the infalling motion of the highest atmospheric layers, which compresses and heats the gas that is located immediately above the rising shock wave. The infalling velocity of the hot compressed region is supersonic, almost 50 km s-1, while the shock velocity may be much lower in these pulsation phases.
Conclusions. When the Hα third emission appears, the shock is certainly no longer radiative because its intensity is not sufficient to produce a blueshifted emission component within the Hα profile. At phase ϕ = 0.40, the shock wave is certainly close to its complete dissipation in the atmosphere.
Key words: stars: variables: RR Lyrae / stars: atmospheres / shock waves
© ESO, 2017