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\IBVShead{5063}{25 April 2001}

\IBVStitle{A Spectrum of R C\lowercase{r}B During Recovery from 2000 Minimum}

\IBVSauth{Kipper, T.}

\IBVSinsto{Tartu Observatory, T\~oravere, 61602, Estonia, e-mail: tk@aai.ee}

\SIMBADobj{R CrB}
\IBVStyp{ R CrB }
\IBVSkey{spectroscopy}
\IBVSabs{The spectra of R~CrB obtained on recovery phase from brightness}
\IBVSabs{decline in 2000 are described. The radial velocities of sharp}
\IBVSabs{emission lines, absorption lines and absorption components of}
\IBVSabs{emission lines are determined.} 

\begintext

The eponym of the R~Coronae Borealis stars was observed by
V.~Klochkova, V.~Panchuk and M.~Yush\-kin with the prime focus echelle
spectrometer of a 6-m telescope (Panchuk et al.\ 1998) on 7 January, 2001
during a program not directly devoted to R~CrB stars. At the moment of
these observations the star happened to be in the recovery state after
a quite deep ($V\sim 13$ in minimum) brightness decline which started
53 days earlier according to AFOEV (2001) data.

The spectra were obtained with a spectropolarimetric device attached
before the slit and each set of exposures consists of two exposures
with different position of the analyser of linear polarization. In this
note, however, the polarization measurements are not addressed. The
spectra cover the wavelength region $\lambda\lambda$ 5000--6600 with the
resolution $R\approx12000$.  The reduction of the spectra  was
performed using the image reduction system IRAF\IBVSfm. \IBVSfoot{IRAF is
distributed by the National Optical Astronomy Observatories, which are
operated by the Association of Universities for research in Astronomy,
Inc., under cooperative agreement with the National Science
Foundation.}

The 2000 decline started only about 260 days after the recovery from
the previous very deep decline and therefore it is not clear whether
some residual effects of that decline were present. Before the
1995--1996 decline which was thoroughly discussed by 
Kameswara Rao et al.\ (1999)
the star stayed at its maximum brightness for much longer time.

Our spectra reveal most of the spectroscopic components found in earlier
accounts:

{\bf 1. Sharp emission lines.} The low excitation lines of Sc~II,
Ti~II, Fe~II, Fe~I, Mg~I, Y~II and Ba~II were observed in emission.
These are the lines belonging to the type E2 according to Alexander et
al.\ (1972). The radial velocity measured from those lines is
$16.8\pm2.5$~km\,s$^{-1}$.

The mean systemic velocities published for different observations
differ more than the stated errors. We adopt the mean value of
22.5~km\,s$^{-1}$ (Kameswara Rao et al.\ 1999).  In that case  the sharp
emission lines show a blueshift around 6~km\,s$^{-1}$ which is very
close to the value of 4~km\,s$^{-1}$ reported by Kameswara Rao et al.\ (1999)
and this supports their suggestion that the sharp emission lines are
the permanent features.

The onset of the decline on JD~2451863 started at maximum light of the
pulsational variations, or more precisely, the brightness smoothly
followed the cosine curve from its maximum to decline.
Photometrically, the last cycle before the onset of decline is better
distinguishable than the previous ones.

Here raises a question how the systemic velocity compares with the
photospheric velocity.  If the photospheric radial velocity at the
onset of decline had its maximum value as for the 1995--1996 decline
and the radial velocity has the period of about 43 days with the range
of 6~km\,s$^{-1}$ (Kameswara Rao et al.\ 1999) we could expect that at the 
moment of our observations ($\phi=1.23$) the photospheric radial velocity
should have been at its mean value. This assumption is, however, not
fully justified. The fadings of R~CrB and its radial velocity
variations are not found to be locked to photometric phases (Fernie
2000).

Many authors have found that the pulsational period in the photometric
variation of R~CrB is itself variable (e.g.\ Lawson \& Kilkenny 1996).
Now, more data on R~CrB photometry is available. We analysed for
periodicities the photometry from the full time interval covered by
AAVSO Monographs (1963--1995) (Mattei et al.\ 1991 \& 1996) and AFOEV
Database (1995--2000), excluding obvious light declines.  As a tool a
set of codes ISDA for irregularly spaced data analysis developed by
Pelt(1992) was used. The mean period of 45.5 days was found for
1993--2000.  The shorter intervals  limited by the fadings gave very
much different periods spanning from 35.3 to 51.4 days confirming the
earlier results by other authors. The time dependence of those periods
was also studied.  There is a slight indication that these periods
themselves vary cyclically with a timescale around 3.3 years or its
multiples.

All sharp emission lines show an inverse P~Cygni profile. In Fig.~1.
some of these lines are shown. The mean differential velocity between
the emission core and the redshifted absorption minimum is $\Delta
v_{\rm r}=42.0\pm 2.5$~km\,s$^{-1}$.

\IBVSfig{10.0cm}{5063-f1.ps}{The group of sharp emission lines at 
$\lambda$ 5190. Note the large (42~km\,s$^{-1}$) redshift of the absorption
components}

{\bf 2. Photospheric absorption lines.} Along with the emission lines
the star showed a rich absorption spectrum. The strongest lines
belonged to C~I\@. Other lines included Fe~I, Fe~II, Cr~I, O~I, Mg~I,
Na~I, and Si II\@. The mean radial velocity found from these lines is
$38.4\pm3.2$~km\,s$^{-1}$ without any noticeable dependence from the line
strength and excitation potential.  Compared with the mean systemic
velocity this corresponds to the redshift of around 16~km\,s$^{-1}$.
The explanation of this redshift was proposed by Kameswara Rao et al.\ (1999) as
the effect of multiple scattering of the photospheric photons by the
circumstellar dust moving out from the star. The effect was in details
studied by Van~Blerkom \& Van~Blerkom (1978) and shown to depend both
on the optical and geometrical parameters of that cloud. Therefore from
this single datum the expansion velocity of the cloud could not be
determined.

Returning to the redshifted absorption components of the sharp emission
lines one could expect that those are the absorption lines
corresponding to the emission lines and are also redshifted  due to
the  scattering.  Vanture \& Wallerstein (1995) explained the similar
pseudo-P~Cygni profiles in the spectrum of RY~Sgr on the recovery phase
as the superposition of blueshifted emission lines and photospheric
lines at the systemic velocity. However, in our case the redshift of
these absorption components compared to the photospheric velocity is
much larger (around 36~km\,s$^{-1}$) than the other absorption lines
(16~km\,s$^{-1}$).  Therefore the scattering in the same clouds could
not explain these results.

{\bf 3. Molecular emission.} The emission in C$_2$ (0,0) $\lambda$
5165, (0,1) $\lambda$ 5635 and (0,2) $\lambda$ 6191 bands was visible
but too weak for radial velocity measurements.

\IBVSfig{10.0cm}{5063-f2.ps}{Na~I doublet in the spectrum of R~CrB in
velocity scale.  The sharp and broad emission components and
interstellar and high speed absorptions are visible and their radial
velocities indicated}

{\bf 4. Broad emission lines.} From the category of broad emission
lines only the broad components of Na~I doublet were observed. Fig.~2.
shows the Na~I doublet.  The full width at its base of D$_1$ is almost
400~km\,s$^{-1}$. The width of D$_2$ is about a half of that due to
blending with the absorption in D$_1$.  The radial velocity of the
blueshifted absorption component of D$_2$ is $-174$~km\,s$^{-1}$
measured at the deepest point of the profile.  The full width at the
continuum level is 133~km\,s$^{-1}$. The He~I $\lambda$ 5876 line,
which showed broad emission during the 1995--1996 decline (Kameswara Rao et al.\
1999), was present in absorption.

\bigskip

{\it Acknowledgements.} This note was prepared with the financial support by
Estonian Science Foundation grant 3166. I am grateful to V.~Klochkova,
V.~Panchuk and M.~Yushkin for obtaining the spectra used here.  In this
note, I have used, and acknowledge with thanks, the data from the AAVSO
International Database and the AFOEV Database, operated at CDS,
France.

\references

AFOEV, 2001, ftp://cdsarc.u-strasbg.fr/pub/afoev

Alexander, J.B., Andrews, P.J., Catchpole, R.M., et al., 1972, {\it MNRAS},
{\bf 158}, 305

Fernie, J.D., 2000, in: {\it The Carbon Star Phenomenon}, ed.\ R.F. Wing, 191

Kameswara Rao, N., Lambert, D., Adams, M.T., Doss, D.R., et al., 1999, {\it MNRAS},
{\bf 310}, 717

Lawson, W., Kilkenny, D., 1996, {\it ASP Conf.\ Series}, {\bf 96}, 349

Mattei, J.A., Waagen, E.O., Foster, E.G., 1991, {\it AAVSO Monograph}, 4

Mattei, J.A., Waagen, E.O., Foster, E.G., 1996, {\it AAVSO Monograph}, 4,
Suppl.\ 1

Panchuk, V.E., Najdenov, I.D., Klochkova, V.G., et al., 1998, {\it Bull.\
Spec.\ Astrophys.\ Obs.}, {\bf 44}, 127

Pelt, J., 1992, {\it Irregularly Spaced Data Analysis, User Manual},\\
http://www.aai.ee/\~{}pelt/soft.htm

Van Blerkom, J., Van Blerkom, D., 1978, {\it ApJ}, {\bf 225}, 482

Vanture, A.D., Wallerstein G., 1995, {\it PASP}, {\bf 107}, 244

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