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.
Contact - Klochkova V.G.
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.
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