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29 March 2024 |
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Photometric and Spectroscopic Study of the Supergiant with an Infrared Excess V1027 Cygni | V.P. Arkhipova
; O.G. Taranova
; N.P. Ikonnikova
; V.F. Esipov
; G.V. Komissarova
; V.I. Shenavrin
; M.A. Burlak
; | Date: |
29 Sep 2016 | Abstract: | We present the results of our $UBV$ and $JHKLM$-photometry for the
semiregular pulsating variable V1027~Cyg, a supergiant with an infrared excess,
over the period from 1991 to 2015. Our search for a periodicity in the $UBV$
brightness variations has led to several periods from $P=212^{d}$ to
$P=320^{d}$ in different time intervals. We have found the period $P=237^{d}$
based on our infrared photometry. The variability amplitude, the light-curve
shape, and the magnitude of V1027~Cyg at maximum light change noticeably from
cycle to cycle. An ambiguous correlation of the $B-V$ and $U-B$ colors with the
brightness has been revealed. The spectral energy distribution for V1027~Cyg
from our photometry in the range 0.36 ($U$)-5.0 ($M$) $mu$m corresponds to
spectral types from G8I to K3I at different phases of the pulsation cycle.
Low-resolution spectra of V1027 Cyg in the range $lambda$4400--9200 AA were
taken during 16 nights over the period 1995--2015. At the 1995 and 2011
photometric minima the star’s spectrum exhibited molecular TiO bands whose
intensity corresponded to spectral types M0--M1, while the photometric data
point to a considerably earlier spectral type. We hypothesize that the TiO
bands are formed in the upper layers of the extended stellar atmosphere. We
have measured the equivalent widths of the strongest absorption lines, in
particular, the infrared Ca~II triplet in the spectrum of V1027~Cyg. The
calcium triplet (Ca T) with $W_{lambda}(mathrm{Ca~T})=20.3pm1.8$ AA as a
luminosity indicator for supergiants places V1027 Cyg in the region of the
brightest G--K supergiants. V1027 Cyg has been identified with the infrared
source IRAS~20004+2955 and is currently believed to be a candidate for post-AGB
stars. The evolutionary status of the star and its difference from other
post-AGB objects are discussed. | Source: | arXiv, 1609.9279 | Services: | Forum | Review | PDF | Favorites |
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