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The temperature growth cessation of the hypergiant V1302 Aql (IRC+10420) is detected for the first time on the boundary of the Yellow Void

Russian version

    Evolutionary status of the high-luminous star V1302 Aql (associated with the powerful IR source IRC+10420) has not been determined for a long time. Figure 1 presents a high-spatial-resolution image of the star obtained with the Hubble Space Telescope. Based on spectral data from the 6-m telescope, Klochkova et al. (1997, 2002) drew decisive arguments to approve the status of V1302 Aql as a far evolved massive star, namely a considerable nitrogen excess in the atmosphere of V1302 Aql and its high luminosity Mbol= -9.5 mag. These results allowed us to refer V1302 Aql to an extremely rare stellar type - yellow hypergiants.
    In the Hertzsprung-Russell diagram (hereinafter H-R), these objects are located close to the luminosity limit in the instability region containing hypergiants of the spectral types from A to M. The typical luminosity of yellow hypergiants is log L/Lsun ~5.3-5.9. Progenitors of yellow hypergiants are massive (with initial weight of above 20 Msun) and absolutely brightest stars. In the course of their evolution, they lose much initial weight and fall into the red supergiants' region and then into the yellow supergiants'. The structured shells of hypergiants formed during several stellar-wind episodes (with the rate of up to 0.001 Msun/yr), are sources of infrared and maser radiation as well as radiation in the lines of numerous molecules.
    In the last decade of the XX century, the interest in V1302 Aql has increased due to the discovered fact of its effective temperature growth. While Humphreys et al. (Humphreys et al. 1973) classified V1302 Aql as a normal F supergiant using the spectra of 1970s, subsequent observations have revealed a change of spectral type to A5 (Oudmaijer et al. 1996; Klochkova et al. 1997; Klochkova et al. 2002). It is finally shown that the temperature of the star increases with the rate of about 120 K per year, consequently, the star cuts the H-R diagram approaching the Wolf-Rayet stage (Klochkova et al. 2002; Humphreys et al. 2002).
    As a result of the continued spectral monitoring V1302 Aql at the BTA in 2001-2014, we concluded on the fact that spectral types of V1302 Aql determined in 2001-2014 coincided with those from papers in 1997 and 2002. The homogeneity of the accumulated data and relative stability of the V1302 Aql spectrum in the last decade of observations allowed us to conclude that the hypergiant entered the deceleration phase (or termination phase) of effective temperature growth and in the H-R diagram is close to the high-temperature boundary of the Yellow Void. Further evolutionary loops are possible to follow the determined evolutionary stage of the hypergiant.
    For the purpose of determination of the hypergiant's velocity field, we derived radial velocities corresponding to lines of different types: forbidden and permitted emissions, absorption and emission components of the ionized lines, absorptions without obvious signs of emissions (HeI, SiII), and interstellar components of doublets of NaI, KI, and DIB (see Fig.2). Heliocentric radial velocities obtained from absorptions without obvious signs of emission components, from forbidden and permitted emissions are close to that of the system and are equal to: Vr=63.7+/- 0.3, 65.2+/-0.3, and 62.0+/-0.4 km/s respectively. We had not discovered velocity variability for a long period of observations that rejects the hypothesis on possible duality of the star.
    The position of the absorption components of lines with the inverse P Cyg profiles is stable and is indicative of the presence of accreting clumps of matter falling onto the star at a rate of about 20 km/s.
V.G.Klochkova, E.L.Chentsov, V.E.Panchuk, and M.V.Yushkin in collaboration with A.S.Miroshnichenko (University of North Carolina at Greensboro, Greensboro, USA)
V.G.Klochkova, E.L.Chentsov, A.S.Miroshnichenko, V.E.Panchuk, M.V.Yushkin. High-resolution optical spectroscopy of the yellow hypergiant V1302 Aql (=IRC+10420) in 2001-2014. MNRAS, v.459 p.4183-4190, 2016.
R.M.Humphreys, D.W.Strecker, T.L.Murdock and F.J.Low, ApJ, v.179, 49 (1973).
R.M.Humphreys, K.Davidson and N.Smith, AJ, v.124, 1026 (2002).
V.G.Klochkova, E.L.Chentsov and V.E.Panchuk, MNRAS, v.292, 19 (1997)
V.G.Klochkova, M.V.Yushkin, E.L.Chentsov, and V.E.Panchuk, Astron. Journ., v.79, 158 (2002).
V.G.Klochkova, E.L.Chentsov, A.S.Miroshnichenko, V.E.Panchuk, M.V.Yushkin. MNRAS, v.459, 4183, 2016.
R.D.Oudmaijer, M.A.T.Groenewegen, H.E.Matthews, et. al., MNRAS, v.280, 1062 (1996).

Contact - Klochkova V.G.
Fig.1. Image of the yellow hypergiant V1302 Aql (=IRC+10420) obtained with the HST telescope (Humphreys et al., 1997)
Fig.2. Radial velocities from the lines of different profiles: a) forbidden emissions; b) permitted double-peaked profiles; c) lines with P Cyg-type profiles; d) FeII and HeI absorptions; e) HI absorption components