shell-model parameters of a star with the r coronae borealis type variability alexander e. rosenbush...
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Shell-model parameters of a star with the
R Coronae Borealis type variability
Alexander E. Rosenbush
Main Astronomical Observatory of the National Academy of Sciences of the Ukraine,
Zabolotnoho str. 27, 03680 Kyiv, Ukraine
e-mail: [email protected]
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INTRODUCTION
Against the spherical shell model of visual light minimum two basic arguments are put forward:
1 - absence of any correlation between variations in infra-red excess and visual light variation during a minimum (Forrest et al. 1972);
2 - decrease of color indexes of a star during a light minimum (Tatarnikov & Yudin 1998);
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It is proposed to return to the model of homogeneous circumstellar shell with one important addition:
the visual light minimum is caused by formation of one more shell, internal in relation to the permanent shell.
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The circumstellar environment of a star with the R Coronae
Borealis type variability out of a light minimum.
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The circumstellar environment of a star with the R Coronae Borealis type variability in a light minimum.
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A light curve of R CrB in 70-th years of XX century. The IR observations in 1976 according to Shenavrin & Khruzina (1979). (Some stars by data Feast et al. 1997.)
Δ t ~ 60-100 d
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Dependence of a polarization degree of radiation in the photometric V band at R CrB versus the light decline during light minima.Polarization during the light recovery is always less than by the decline.
I shell II shell
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Light V and color B-V and U-B indexes curves of R CrB in 1985 minimum. Data of Goncharova (1990) and Efimov (1988)).
Horizontal dashed lines –
an normal level of the V and, the B-V and the U-B. Vertical solid lines –
the moments of key changes in the stellar line spectrum.
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The scheme of the formation of a blue-shifted profile of a broad emission line in the permanent shell.The screening shell eclipses leaving parts of the permanent shell.
Profile of broad emission is superposition:1 – broad emission with the screening red wing; 2 – sharp emission; 3 – photospheric absorption; 4 – high-speed circumstellar absorption
The broad emissions are traced up to 1000 a.u. from a star as, for example, C II 133.5 nm in V854 Cen (Clayton & Ayres 2001)
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Profiles of cores of the IR triplet Са II line λ 854.2 nm in spectrum of R CrB in the 1998 minimum normalized to the continuum in a light maximum.
Sharp emission lines are formed between the screening and permanent shells.
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Very essential argument in favour of our model we consider consecutive development of the RCB phenomenon in FG Sge:
The increase of the IR excess in 1992 was a consequence of the formation of the screening shell.
FG Sge has allowed to define directly the optical thickness of a permanent shell after comparison of its brightness before and after 1992: τ ~ 0.7.
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Stellar environment Out of a light minimum In a light minimum
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Some physical parameters of a star with the R Coronae Borealis phenomenon
*) 25 km/s is the velocity of matter on the internal bound of the screening and permanent shells, i.e., before a dust condensation. The velocity of matter after the dust condensation is increased rapidly up to 200 km/s and more (previously it was present).
~ 25* 200 ~25* 200
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Observed light curve in 1998 – 2003 (the VSNET) and its approximation
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Observed light curve in 2007 and its approximation, as of September 8 (data by the VSNET)
First shell, τ =6.3
Second shell, τ = 5.7
If it will be not form the third shell
shell formationMax optical thickness
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Comparison of visual V and 38.6-days pulsations UV( 240 nm) brightness of visual (squares) of RY Sgr. and UV (plus) light of RY Sgr
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CONCLUSIONAt a result of my researches of stars with the R Coronae Borealis type
variability I came to understanding that it is necessary to investigate the phenomenon of R Coronae Borealis widespread among stars on final phases of evolution, novae, for example.
It is possible to give such definition of the R Coronae Borealis type variability or the R Coronae Borealis phenomenon.
The R Coronae Borealis phenomenon is
the phenomenon, which meets in stars on the late stages of
the stellar evolution possessing both the high mass-loss rate
by sub-Eddington luminosity, the overabundance of carbon and
the high enough abundance of hydrogen.
Enough of hydrogen in the atmosphere of a star is the necessary condition of processes which leads to light minima and the full exhaustion of hydrogen means disappearance of the RCB phenomenon in the star (Jurcsik 1996: the II Conference).
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One of two fundamental questions Answers: by Rao et al. (1999): what are the physical processes
that trigger and
control development
of the unpredictable minima?
<─ Pulsations of a star
<─ Maximum (Pugach 1977, ….) and<─ Minimum (RY Sgr: Feast 1996,
FG Sge: Arkhipova 1996) of pulsation (Göres, Woitke et al., 1996…)
<─ Activity of star controls by the 4284-days cycle(visual - Rosenbush 1997, 2001;confirmed in the infrared - Yudin et al. 2002 = 4342 days).
=>
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Synchronization of the 4284-days activity cycle of R CrB itself
and the H-def Conferences
Number
of
cycle
Duration of
Cycle
Month
year
V 4435 August
1983
VI 4291 October
1995
VII 4291 30 June
2007
VIII 4284:(±140)
20 March:
2019
Number
of
Conference
City,
country
Month
Year
I Maysor India
November
1985
II Bamberg
Germany
August
1995
III Tübingen
Germany
September
2007
IV ? October
2019
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This is all!
Thank you very much for your attention!