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Description
A high resolution optical spectrum of the post-red supergiant candidate IRC +10420 is presented. The Utrecht Echelle Spectrograph observations, with a total integration time of more than 9 hours provide a spectral coverage from 3850 A to 1micron, and a spectral resolution of 9km/s. The spectrum is shown, and an identification list of lines in the spectrum is provided. From a preliminary analysis of the spectrum we find that the spectral type of IRC+10420 has changed from F8I+ in 1973 to mid- to early A type now, confirming the results of Oudmaijer et al. (1996MNRAS.280.1062O), who claimed a change in temperature based on photometric changes. It is shown that most of the emission lines in the spectrum of IRC +10420 are blue-shifted with respect to the systemic velocity traced by circumstellar rotational CO emission, while the (few) absorption lines - with the exception of some high excitation lines - are red-shifted by 25km/s, which may suggest infall of material onto the star. Finally, it is found that the interstellar extinction towards IRC +10420, as traced by the Diffuse Interstellar Bands is very large, with an inferred E(B-V) of 1.4+/-0.5 compared to a total E(B-V) of 2.4. This table provides the line identifications for the measured spectral lines from atomic species. Listed in the table are respectively the laboratory wavelength (in air) taken from Moore (1945, in A multiplet table of astrophysical interest, Contribution from the Princeton University Observatory No. 20.), the line identification (ion and multiplet), the energies of the lower levels of the transitions in eV, and the log(gf). The latter two values are taken from Wiese et al. (1966, Nat. Stand. Ref. Data Ser. 20 and 1969, Nat. Stand. Ref. Data Ser. 22), Martin et al. (1988, Cat. <VI/72>) and Fuhr et al. (1988, Cat. <VI/72>). The spectral lines that are marked `UN' were not identified, the wavelength given for these lines is the observed wavelength. Then next entries in the table are the velocity shift of the centres of spectral lines (in LSR), the equivalent width in milli-Angstrom, and the full-width-at-half maximum of the fit in Angstrom. The velocity shifts have been measured by fitting Gaussian profiles through the lines, the equivalent widths have been measured by integrating the line over the continuum. In the case of overlapping lines, the lines were de-composed by fitting multiple Gaussian components to the profiles. In these cases (marked with `deb.' in the table) the equivalent widths are the areas under the Gaussian fits. Equivalent widths for lines that could not be deblended, are given between brackets. These values represent the total equivalent width of the lines concerned.
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