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\begin{document}
\IBVShead{6179}{5 August 2016}

\IBVStitle{Variability of the H\lowercase{e}\,I\,6678 emission in \boldmath{$\delta$} S\lowercase{co}}

\IBVSauth{Pollmann, Ernst}

\IBVSinsto{International Working Group ASPA, Emil-Nolde-Str. 12, 51375
Leverkusen, Germany}

\SIMBADobj{delta Sco}


\begintext


\section*{Introduction}

$\delta$ Scorpii (HD143275, HR5953) is a 2.3 magnitude Be binary
star whose binarity was discovered interferometrically by McAlister
(1978). But its binary nature was first reported by Innes (1901).
The star was first classified as a Be star when it showed an emission
profile on the wings of an absorption core of a spectrum taken in
1990 by Cot\'e \& van Kerkwijk (1993) and is now considered to be a
typical B0.3\,IV star.

This binary system with its large eccentric orbit ($e > 0.9$) (Tango
et~al. 2009) exhibits a strong mass loss that has resulted in a
circumstellar gaseous disk formation. He\,I\,lines are good tracers
of matter very close to the star, where temperature and density
are the highest and ionisation is the strongest. The He\,I\,6678 line
profile of $\delta$ Sco suggests that one sees some optically-thick
outflow and a lot of matter in the line of sight. The outflow should
add more mass to the disk and as a result, the disk will gradually
grow outwards. This is very interesting since the inclination angle
of the circumstellar disk is about 45\deg [36\deg, Miroshnichenko
et~al. (2013); 38\deg $\pm$ 5\deg Miroshnichenko et~al. (2001); 48.5\deg
$\pm$ 6.6\deg Hartkopf et~al. (1996); 70\deg, Bedding (1993)].

During each periastron (period = 10.8 years) some ring material
may flow from the primary's Roche lobe into the secondary's
Roche lobe. During that process the disk becomes denser and
single-, double- or triple peak profiles may be observable.
Outside of each periastron the He\,6678 line is emitted in an
extended rotating elliptical disk or ring around the central star,
where the ring is not centered on the central star.

The situation might be more complex since the companion is
triggering the disk/ring formation or destruction through tidal
effect on the circumstellar disk/ring. There seems to be two
physical effects going on in $\delta$ Sco: one is the ejection
of material from the photosphere, the other is the formation of
``blobs" of gas in the disk or ring(s) probably from viscosity
effects. The blobs rotate in a more or less Keplerian mode,
eventually to fall back closer to the star (Miroshnichenko,
personal communication 07/2004).

As to further studies of the physical properties of $\delta$
Sco's disk, I refer to the following important publications:
Properties of the $\delta$ Sco circumstellar disk from continuum
modelling, Carciofi et~al. (2006); Disk geometry and kinematics
before the 2011 periastron, Maillard et~al. (2011); Imaging disk
distortion of Be binary system $\delta$ Scorpii near periastron,
Che et~al. (2012); The circumstellar disk evolution after the
periastron, Meilland et~al. (2013).

\IBVSfig{8.5cm}{6179-f1.eps}{Correlation between the equivalent
width of He\,I\,6678 and H$\alpha$ from April 2005 to April 2016.}
\IBVSfigKey{6179-f1.eps}{delta Sco}{other}

\vspace*{+8mm}
\section*{Observation and results}

Following the generally accepted assumption that the disk of this
binary system is being fed due to outbursts of matter ejected
from the stellar surface (Miroshnichenko et~al., 2003), and since
the He\,I 6678 line forms near the photosphere of the primary
component one can expect a correlation between the equivalent width (EW)
of the H$\alpha$ and and He\,I 6678 lines (Fig.~1). Such a correlation
might be interpreted as a result of a disk feeding process. However we
cannot exclude that this reflects only contemporaneous density
variations within the line formation zones.

This study of a correlation between H$\alpha$ and He\,I 6678
EWs (Fig.~1) and of the behaviour of the He\,I  6678 line
profiles have been performed by the author at the
observatory of the Vereinigung der Sternfreunde K\"oln
(Germany) with a C14 40 cm Schmidt-Cassegrain-telescope, the
slit-grating-spectrograph LHIRES III with a spectral resolving
power $R \sim$ 17000 and a CCD-camera ($768 \times512$ pixel,
pixel size 9\,$\mu$m, this instrumental configuration provides
spectra within the range from 6500 to 6700 \AA), in collaboration
with observers of the ARAS
group\footnote{\tt http://www.astrosurf.com/aras} at
different locations, different telescopes (apertures between 20
and 40 cm) and different spectrographs with spectral resolving
powers of 10000 to 20000 (signal-to-noise ratios, S/N of these
spectra are ca.~200--300).

With exposure times of 300 to 350 sec for an individual
spectrum, the S/N in a sum spectrum of 10 individual spectra
reached values mostly more than 1000. The spectra have been
reduced manually with standard procedures (instr.~response,
normalisation, wavelength calibration) by using the programs
Maxim-DL\footnote{\tt http://www.cyanogen.com},
VSpec\footnote{\tt http://www.astrosurf.com/vdesnoux} and
MK32\footnote{\tt http://www.appstate.edu/~grayro/spectrum/spectrum276/}.  

Since April 2005, during every observing season, the observed
correlation impressively supports the existence of this
disk-feeding process, in which the slope of the linear fit
shown in Fig.~1 reflects the quantitative correlation.

\IBVSfig{8.5cm}{6179-f2.eps}{Long-term monitoring of the V/R ratio
from April 2005 to March 2016.}
\IBVSfigKey{6179-f2.eps}{delta Sco}{radial velocity curve}



In addition to the variability of the EWs (measured and analysed
in the same spectra) the He\,I 6678 line double-peaked profile
exhibits a variable V/R ratio that is the relative intensity of the
violet component $I_V$ to the red component $I_R$. For the first time
it was possible to analyse eleven complete cycles of the V/R
variations from April 2005 to March 2016 (Fig.~2). In the
earlier seasons, merely the descent could be measured. On this
occasion I emphasize that, among others, members of the ARAS group,
made a significant contribution to the frequent observations.

\IBVSfig{9cm}{6179-f3.eps}{The method of the PDM analysis
revealed a period of 553 d in the V/R data in Fig.~2.}
\IBVSfigKey{6179-f3.eps}{delta Sco}{other}

The V/R measurements of these eleven cycles presented here
permitted an analysis of possible periodicities. For the analysis
of the period (Fig.~3) and the phase diagram (Fig.~4) the method
of the PDM [phase dispersion minimization of Stellingwerf (1978)]
within the program package AVE\footnote{\tt http://astrogea.org/soft/ave/aveint.htm} was used.

\IBVSfig{9cm}{6179-f4.eps}{Phase diagram of the V/R data
folded on the period of 553 d with $T_0$ = 2453794 and the
marked phase sections of the triple-peak appearance (3pkd).}
\IBVSfigKey{6179-f4.eps}{delta Sco}{other}


As very clear result the period of 553 d ($\pm$ 2.3) with the
output epoch $T_0$ = JD 2453794 ($\pm$ 7.8) could be found.
The V/R ratio has been measured of course only in the spectra
for which the double peak profiles are apparent. In the light of
that result it is interesting to have a look on the cyclic behaviour
of the H$\alpha$ EW within our long-term monitoring of that star
from July 2000 to May 2015 (see Fig.~5). After subtracting the
long-term wave of approx. 9 years in the upper left panel of Fig.~5, I could derive a period
of 509 days (lower left, upper and lower right panels of Fig.~5), 
which is very close to the period of He\,I 6678 derived in this
paper.
These close coincidences of the periodic behaviour led to the
suspicion of identical physical causes. The long-term behaviour
of the H$\alpha$ emission of $\delta$ Sco might be studied in a further
paper.

\IBVSfig{11cm}{6179-f5.eps}{(Upper left) $\delta$ Sco H$\alpha$ monitoring and long-term variations (period approx. 9 years).
(Lower left) Long-term variation removed EW of Fig. 1 divided through the long-term variation.
(Upper right) Period analysis of the long-term removed data in the lower left panel.
(Lower right) Phase diagram of the 509~d period.}
\IBVSfigKey{6179-f5.eps}{delta Sco}{other}

An inspection of the spectra shown in Fig.~6 shows that the
third emission component (the triple-peak profile) was observed
within the phase intervals $\sim$ 0.06 to $\sim$ 0.3 (04-08/2006),
$\sim$ 0.75 (04/2007), $\sim$ 0.1 to $\sim$ 0.24 (05-07/2009)
and $\sim$ 0.03 to $\sim$ 0.13 (04-06/2015). 
marked (in red, as 3pkd) in Fig.~4. The last triple peak phase from
April to June 2016 (approx.~JD 2457114 to 2457175) was observed very
weakly as a consequence of the very low emission intensity.

%\newpage

\IBVSfig{18cm}{6179-f6.eps}{Three-dimensional plot to show the
appearance of the third emission component (the triple-peak profile),
observed within the phase interval $\sim$ 0.06 to $\sim$ 0.3
(04-08/2006), $\sim$ 0.75 (04/2007), $\sim$ 0.1 to $\sim$ 0.24
(05-07/2009) and $\sim$ 0.03 to $\sim$ 0.13 (04-06/2015).}
\IBVSfigKey{6179-f6.eps}{delta Sco}{other}

\newpage 

\IBVSfig{8cm}{6179-f7.eps}{Long-term monitoring of the
He\,I 6678 emission line EW from April 2005 to March 2016.}
\IBVSfigKey{6179-f7.eps}{delta Sco}{other}

The plot of the emission intensity long-term monitoring 
as EW of He\,I 6678 versus time  in
Fig.~7 confirms this fact with the EW being at minimum at that time. One
can state that there is no certain phase preference for the
appearance of this bizarre and mystery line profile
characteristics, in the He\,I 6678 emission of the spectra
of $\delta$ Sco. This might be due to the presence of a
density enhancement sometimes in front of the star and
sometimes hidden behind it at other phases.

%\newpage

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\endreferences

\IBVSCorrectedVersion{Aug 24 08:41:17 CEST 2016}

\end{document}
