Discovery and investigation of the spectral variability
of the high-latitude IR-source IRAS01005+7910

    The variability of the spectrum of the optical component of the IR-source IRAS01005+7910 was discovered for the first time in the BTA spectra [1]. Long-term monitoring of the object was carried out during 2002-2013 with a high spectral resolution (R=60000). The following fundamental parameters were determined: luminosity log L/L_☼=3.6 and effective temperature T_eff=21500K of the central star, and the chemical composition ([Fe/H]=-0.3, C/O>1) of its atmosphere. The spectral features include absorptions that form in near-photospheric layers, narrow envelope emissions, and emission-absorption profiles that form in photosphere-to-envelope transition layers (the wind). The presence of forbidden emissions [NII] and [SII] in the spectrum indicates the onset of the ionization of the circumstellar envelope and the nearing planetary nebula stage. We show that the deviations of the wind from spherical symmetry are small, which is in agreement with the shape of the circumstellar envelope according to HST images (Fig.1). Figs. 2 and 3 show examples of variations of the form and position of the profiles. The systemic velocity of the source, Vsys=-50.5 km/s, was determined for the first time from the positions of symmetric and stable profiles of forbidden emissions. The complex pattern of velocity-field variations (see example in Fig.4) is determined by pulsations, hidden binarity of the star, and variations of the absorption components of the profiles due to variations of the wind-base geometry and kinematics. The spectrum of the object is a unique natural laboratory for studying the physical and kinematic features of the atmosphere, expanding envelope, and intermediate structures. The relatively low wind velocity (27-74 km/s, based on different observations) and the high intensity of the long wavelength emission (up to 7 times higher than the continuum level, Fig.3) are typical of hypergiants rather than supergiants. IRAS01005+7910 is an example of a low-mass post-AGB star masquerading as a massive hypergiant.

Published:
1. V.G.Klochkova, M.V.Yushkin, A.S.Miroshnichenko, V.E.Panchuk, K.Bjorkman. Discovery of spectral variation in the optical counterpart of IRAS01005+7910. Astron.&Astrophys., 392, 143, 2002.
2. V.G.Klochkova, E.L.Chentsov, V.E.Panchuk, E.G.Sendzikas, M.V.Yushkin. Spectral variability of the IR-source IRAS01005+7910 optical component. Astrophys.Bull., 69, 439, 2014.

Fig.1. Images of IRAS01005+7910 obtained in different filters with the Hubble Space Telescope

Fig.2. Variations of the profiles of SiII 6347 Å, 4128+4130 Å in the spectrum of IRAS01005+7910. Dashed line - envelope curve of all the SiII 5979 Å profiles