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: aeros@mao.kiev.ua

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!