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]
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);
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.
The circumstellar environment of a star with the R Coronae
Borealis type variability out of a light minimum.
The circumstellar environment of a star with the R Coronae Borealis type variability in a light minimum.
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
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
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.
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)
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.
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.
Stellar environment Out of a light minimum In a light minimum
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
Observed light curve in 1998 – 2003 (the VSNET) and its approximation
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
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
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).
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).
=>
=>
=>
=>
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
This is all!
Thank you very much for your attention!
