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Astron. Astrophys. 325, 1083-1087 (1997)

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2. Observations and results

The observations have been made in 1988-1992 with the middle resolution (R [FORMULA] 3000) echelle spectrograph "Zebra" (Gazhur et al. 1990; Klochkova & Panchuk 1991) mounted at the Nasmyth focus of the 6-m telescope (SAO RAS). The names of the objects and the data of the observations are listed in Table 1. According to our visual estimations neither of the stars were at a deep light minimum at the moment of the observations.


[TABLE]

Table 1. Main hydrogen emission characteristics of ALIVARS


The reduction of the numerical spectra from the images was achieved with a set of programmes elaborated in SAO RAS (Galazutdinov 1992). The final treatment of the spectra was performed using a software of the Main Astronomical Observatory of Ukraine. Scattered light and the spectral responce function of the detecting system were taken into account and a procedure of spectrum linearization was carried out. More details concerning the full treatment prosedure can be found in the preceding paper (Kovalchuk & Pugach, 1997, hereafter KP1). To obtain the correct equivalent widths of the observed [FORMULA] -emission lines, theoretical profiles of the [FORMULA] -absorption line were calculated in advance. We have used the effective temperatures, [FORMULA], and the gravity parameter lg g previously determined (KP1). The atmospheric model method of Kurucz (1979) was applied and the corresponding theoretical absorption profiles for hydrogen lines of each star were calculated. Then all theoretical profiles were convolved with the instrumental profile function as to make them comparable with the observations. The rotation effect of the star is considered to be negligible, because moderate rotation seems hardly effect broad hydrogen lines. Finally, profiles obtained in this way were shifted by [FORMULA] [FORMULA] defined as follows,

[EQUATION]

where: [FORMULA] and [FORMULA] are the observed wavelenghts of the hydrogen lines of each star.

The equivalent widths were expressed as a difference between the observed emission profiles and the corresponding calculated absorption ones. The same procedure was applied for the determination of the equivalent widths of [FORMULA] and [FORMULA] if available.

The conversion of the equivalent widths [FORMULA] into luminosities [FORMULA] is allowed by virtue of the coefficient [FORMULA]. The coefficient [FORMULA] gives a fraction of the total energy of the star which is radiated within a spectral interval of 1 [FORMULA] at the centre of [FORMULA] or the [FORMULA] lines. The [FORMULA] is roughly considered to be a function of [FORMULA] and corresponding values of [FORMULA] may be calculated using Planck's formulae. Then the total luminosities [FORMULA] for the given emission line was determined by means of:

[EQUATION]

where: [FORMULA], lg g) are luminosities of the stars depending on the effective temperature [FORMULA] and the parameter of gravity lg g. The values of L([FORMULA], lg g) were taken from the paper by de Jager & Nieuwenhuijzen (1987) and all the stars studied were considered to be giants.

Table 1 summarizes the results obtained. The following data are listed in this table:

  1. Designation of the star
  2. Date of observations
  3. Effective temperature (mean from KP1)
  4. Parameter of gravity (mean from KP1)
  5. Adopted luminosity of the stars [FORMULA] (from de Jager & Nieuwenhuijzen, 1987)
  6. Measured equivalent widths of [FORMULA]
  7. Measured equivalent widths of [FORMULA]
  8. Measured equivalent widths of [FORMULA] if possible
  9. [FORMULA] -emission envelope luminosities in erg s-1
  10. [FORMULA] -emission envelope luminosities in erg s-1
  11. Emission decrement [FORMULA]
  12. Form of the emission line profile

The values of [FORMULA] however should not be taken too seriously since their uncertainty is very great.

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998

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