Spectral Investigations of Cepheids in Southern Hemisphere Scientifical Seminar KOLOS

Authors: I.A. Usenko, Dpt. Of Astronomy, Odessa National University, Odessa, Ukraine A.Yu. Knyazev, SAAO, CapeTown, 7925 South Africa L.N. Berdnikov, Sternberg Astronomical Institute, Moscow, Russia V.V. Kravtsov, Instituto de Astronomia, Universidad Catolica del Norte, Antofagasta, Chile A.B. Fokin, Institute of Astronomy, Russian Academy of Sciences, Moscow Russia

The Main Tasks: 1. To obtain as many as possible spectra of Cepheids during its pulsational period. 2. To estimate the peculiar properties of absorptinal lines in these spectra. 3 To determine their atmosphere parametrs and chemical composition.

Three unusual Cepheids: 1. X Sgr P = days, = 4.56 mag; Spec. Type = F7 II, DCEP. 2. W Sgr P = days, = 4.66 mag; Spec. Type = F7.2 Ib, DCEP. 3. BG Cru P = days, = 5.49 mag; Spec. Type = F7.2 Ib, DCEPS.

Observations: 1.9-m telescope of South African Astronomical Observatory, High Karoo, South Africa.

Observations: Echelle-spectrograph GIRAFFEGIRAFFE (Grating Instrument for Radiation Analysis with a Fibre Fed Echelle); R=39000; Specral ranges: AA

Radial Velocity Curve for X Sgr

Fe I line in X Sgr Atmosphere (SAAO)

Fe I line in X Sgr Atmosphere (MDO)

Hβ line profiles for X Sgr

Hα line profiles for X Sgr

Atmosphere parameters for X Sgr HJD Teff log g Vt Phase (K) (km/s) ± ± ± ± ± ±

Elemental abundances for X Sgr «Key Elements» Element [El/H] σ NL C I O I Na I Mg I Al I Fe I Fe II

Elemental abundances for X Sgr «α-Elements» Element [El/H] σ NL Si I Si II S I Ca I Sc II

Elemental abundances for X Sgr «Fe- group Elements» Element [El/H] σ NL Ti I Ti II V I V II Cr I Cr II Mn I Co I Ni I

Elemental abundances for X Sgr «r- and s- process Elements» Element [El/H] σ NL Cu I Zn I Sr I Y II Zr II La II Ce II Pr II Nd II Sm II Eu II Gd II

Radial Velocity Curve for W Sgr

Hβ line profiles for W Sgr

Hα line profiles for W Sgr

Atmosphere parameters for W Sgr HJD Teff log g Vt Phase (K) (km/s) ± ± ± ± ± ±

Elemental abundances for W Sgr «Key Elements» Element [El/H] σ NL C I O I Na I Mg I Al I Fe I Fe II

Elemental abundances for W Sgr «α-Elements» Element [El/H] σ NL Si I Si II S I Ca I Sc I Sc II

Elemental abundances for W Sgr «Fe- group Elements» Element [El/H] σ NL Ti I Ti II V I V II Cr I Cr II Mn I Co I Ni I

Elemental abundances for W Sgr «r- and s- process Elements» Element [El/H] σ NL Cu I Zn I Sr I Y II Zr II La II Ce II Pr II Nd II Sm II Eu II Gd II

Radial Velocity Curve for BG Cru

Fe I line in BG Cru Atmosphere (SAAO)

Fe I line in BG Cru Atmosphere (VLT)

Lines of Ions Fe II and Si II in the Spectra of BG Cru (SAAO)

Lines of Ions Fe II and Si II in the Spectra of BG Cru (VLT)

Hα line profiles for BG Cru

Atmosphere parameters for BG Cru HJD Teff log g Vt Phase (K) (km/s) ± ± ± ± ± ±

Elemental abundances for BG Cru «Key Elements» Element [El/H] σ NL C I O I Na I Mg I Al I Fe I Fe II

Elemental abundances for BG Cru «α-Elements» Element [El/H] σ NL Si I Si II S I Ca I Sc II

Elemental abundances for BG Cru «Fe- group Elements» Element [El/H] σ NL Ti I Ti II V I V II Cr I Cr II Mn I Co I Ni I

Elemental abundances for BG Cru «r- and s- process Elements» Element [El/H] σ NL Cu I Zn I Sr I Y II Zr II La II Ce II Pr II Nd II Sm II Eu II Gd II

Circumstellar envelopes around the Cepheids 1 ) Cepheids with periods more than days: absorptional lines of metals demonstrate the usual character, therefore Hα line undergoes the complicated changes (see X Cyg (Gillet, 1993)); 2) The main reason of this effect is the presence of circumstellar envelope around the Cepheid atmosphere (see Nardetto et al. 2008); 3) The observations of RS Pup and l Car confirmthis hypothesis ( see Krevella et al. 2009)

Circumstellar envelopes around the Cepheids 4) The main problem: this envelope should be «optically thick» in Hα line core, but to be «clear» for the absorptional lines of metals. 5) In this case the Hα line represents the radial velocity of this envelope, therefore the lines of metals represent the Doppler velocities of pulsating layers.

The Cases of X Sgr and BG Cru 1 ) This pecuilar character of metals absorptional lines and absence of these onesfor hydrogen lines should be explained by the presence of multiple shock waves combined with non-radial pulsations, producing the extensive hydrogen shell around the Cepheid. 2) This shell promoted itself to form these shock waves in the Cepheids atmospheres

The Cases of X Sgr and BG Cru 3 ) The presence of close hot companion could be promote to non-radial pulsations in the high levels of Cepheids atmospheres. X Sgr has a companion with an orbital period days (Szabados 1989), thereas BG Cru is a spectroscopical binary too.

The Case of W Sgr 1) Emission features in the core of hydrogen lines are not typical for Population I Cepheids, but they are present in the W Vir type variables (Population II). These emission features are an evidence of so called «highlighting» behind the front of shock wave after its passing.

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