Abstract
We present new spectroscopic observations of the peculiar supergiant IRC+10420. In 1997–2000, we obtained three high signal-to-noise ratio spectra of the object at 4300–8000 A with a spectral resolution of 15 000 (20 km/ s) using the 6-m telescope of the Special Astrophysical Observatory. From our 2000 spectrum, we estimate the spectral type of IRC+10420 to be A2, corresponding to a temperature of ∼9200 K. Many emission lines were detected, identified with lines of Fe I; Fe II, Ti II, Cr II, and Sc II ions; and [O I], [Fe II], and [Ca II] forbidden lines. The radial velocity derived from absorption lines without obvious emission components (He I λ5876, O I, N I, Si II) and from absorption components of the Balmer lines is 93±1 km/s. The redshift of photospheric lines relative to the star’s center-of-mass velocity is interpreted as a consequence of scattering in the expanding, optically thick dust envelope. Both emission and absorption lines show a correlation between radial velocity and oscillator strength. We found variability in the relative intensities of the H α and H β emission components. We conclude that IRC+10420 is rapidly evolving towards a Wolf-Rayet stage; the current rate of the photospheric temperature increase is ∼120 K per year. Based on the intensity of the O I (λ7773) triplet, we estimate the star’s luminosity to be M bol=−9.5m. In all 1997–2000 spectra of IRC+10420, the He I λ5876 line has a significant equivalent width of at least 200 mA; this may be possible in the presence of such a low temperature due to the star’s high luminosity and the enhanced helium abundance in the supergiant’s atmosphere.
Published Version
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