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\IBVShead{5509}{12 March 2004}

\IBVStitletl{Discovery of the Secondary in the Spectrum of}{ the SB1 System HD\,861}

\IBVSauth{Budaj, J.$^{1,2}$; Iliev, I. Kh.$^{3}$; Fe\v{n}ov\v{c}\'{i}k, M.$^{4}$; Barzova, I.$^{3}$; Richards, M.T.$^{1}$; Geordzheva,~E.$^{5}$}

\IBVSinst{Dept. of Astronomy and Astrophysics, Penn State Univ., Davey Lab. 525, University Park, 16802 PA, USA}
\IBVSinst{Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatransk\'{a} Lomnica, Slovak Republic}
\IBVSinst{Institute of Astronomy, National Astronomical Observatory, P.O.B. 136, BG - 4700, Smolyan, Bulgaria}
\IBVSinst{Univ. of Pavol Jozef Safarik, Ko\v{s}ice,  Slovak Republic}
\IBVSinst{Technical University Sofia, Plovdiv Branch, Bulgaria\\
\indent e-mail: http://www.ta3.sk/\~{}budaj, iliani@astro.bas.bg, 
fenovcik@ta3.sk, mtr@astro.psu.edu} %email

\IBVSkey{spectroscopy}
\SIMBADobjAlias{HD 861}{HIP 1063}

\IBVSabs{We report the detection of the second spectrum in}
\IBVSabs{the SB1 system HD 861.}
\IBVSabs{The lines of the second spectrum are sharper than the primary}
\IBVSabs{spectrum and move}
\IBVSabs{in the opposite way as the lines of the primary. }
\IBVSabs{The most probable explanation is that they originate from}
\IBVSabs{the so far unseen secondary component of the binary system.}

\begintext

This star (HD 861, SAO 11044, HIP 1063, BD +61 16)
is a well known SB1 binary but has been rarely studied although it is 
quite bright and close.
Duflot \& Fehrenbach (1956a, 1956b) mentioned that it had variable
radial velocities.
The orbital elements were determined by Acker (1971) from 14 observations
combined with 3 additional older observations of Boulon (1956, 1957).
Its orbital elements are: $P_{\rm orb}=11\fday2153, K=43.8\, \rm km\,s^{-1}, 
e=0.22, V_{0}=-12.5\, \rm km\,s^{-1}, \omega=21\fdeg0$.
It was classified as A2 based on the CaIIK line and as F2 based on 
the metallic lines by Slettebak \& Nassau (1959). 
Calcium was found to be underabundant by about 0.4dex by 
K\"unzli \& North (1998) who also determined the following parameters:
$v \sin i=35\, \rm km\,s^{-1}, \xi_{\rm turb}=3.2\, \rm km\,s^{-1}, 
T_{\rm eff}=7715\,K, \log g=3.9$.
It is thus an Am star.
Hipparcos lists $V=6\fmm63, \pi=8.55 \pm0.63\, \rm mas$ (ESA 1997).
The photometric database of Mermilliod et al. (1997)
lists the UBV observations of Bouigue et al. (1961) $V=6.64, B-V=0.19$.
Geneva photometry can be found in Rufener (1980).

Our spectroscopic observations were carried out with the 2m RCC telescope of
the Bulgarian National Astronomical Observatory in the frame of our
observational program on Am stars in binary systems. The Photometrics AT200 
camera with a SITe SI003AB $1024 \times 1024$ CCD chip, 
($24\,\mu {\rm m}$ pixels) was used in the Third camera of the Coud\'e 
spectrograph to provide spectra in the 6400--6500 \AA~ region with R = 32000. 
The typical S/N ratio is about 300. IRAF standard procedures have been used 
for bias subtracting, flat-fielding and wavelength calibration. 
Telluric lines have been removed using spectra of hot, fast rotating stars. 
Wavelength calibration has the r.m.s. error of 0.005\,\AA. 
Three spectra of HD861 were used in this study.
The log of observations is listed in Table 1. 


\begin{table}[ht]
\caption[]{List of observations: Date, 
HJD of the beginning of the exposure, effective exposure and radial
velocity of the primary and secondary.}
\small
\begin{center}
\begin{tabular}{cccccc}
\hline
Sp.No.& Date [dd.mm.yyyy] &  HJD (2450000+) & Eff. exp. [sec] 
&  RV1 [km\,s$^{-1}$]    & RV2 [km\,s$^{-1}$]\\
\hline
1&  30.8.2001 & 2152.496 & 7230   &  -26.0 $\pm$ 1.5 & 62.3\\
2&  4.10.2003 & 2917.280 & 5400   &  -41.0 $\pm$ 1.2 & 92.6\\
3&  4.10.2003 & 2917.348 & 3980   &  -40.4 $\pm$ 1.0 & 91.8\\
\hline
\end{tabular}
\end{center}
\end{table}

Spectra No.2 and No.3 have very little time difference and were
coadded to increase their S/N ratio for the display in Fig.1.
The spectra are displayed over a range of wavelengths centered at
6430\AA\ in the vicinity of CaI~$\lambda$6439 line. 
We have chosen this line as it is almost free of blends. 
It is apparent that there are two systems of lines that shift
in opposite directions through the spectra. 
While the primary spectrum shifts towards the blue there are 
weak sharp features which move towards the red. The latter spectral lines
are illustrated by the arrows.
Moreover, these weak sharp lines are seen only in the vicinity of CaI and
FeI lines, although there are much stronger FeII lines from the primary
that are not accompanied by such sharp fine components.
The weak sharp lines thus form at a cooler place than the photosphere
of the primary.
The fact that the fine lines are sharper also rules out their origin
in the photosphere of the primary star.

We have calculated preliminary synthetic spectra and performed
an abundance analysis of the primary.
For this purpose we determined the effective temperature and gravity
($T_{\rm eff}=8130\,\rm K, \log g=3.97$) from the Geneva photometry 
using the calibration of Kobi \& North (1990).
Model atmospheres were interpolated from Kurucz (1993).
The VALD atomic line database (Kupka et al. 1999) also containing
Kurucz (1990) data was used to create a line list
for the spectrum synthesis.
A detailed spectrum synthesis of the spectral regions
was accomplished using the code SYNSPEC (Hubeny et al. 1994,
Krti\v{c}ka 1998).
The synthetic spectrum was convolved with
the 0.2 \AA\ instrumental profile and with the rotational profile.
We estimated the projected rotational velocity 
$v \sin i =37\, \rm km\,s^{-1}$.
Observed and synthetic spectra are compared in Fig.2.
Synthetic spectrum was shifted in wavelength to match the observed spectrum. 
There are no predicted theoretical lines at the points that we
identify with the secondary which strengthens our claims above. 
Radial velocities of the primary were then measured by means of the
cross-correlation with this synthetic spectrum. Radial velocities of the
secondary were measured from the corresponding components of
CaI~$\lambda$6439, CaI~$\lambda$6462 lines relative to their primary 
component lines which were assumed to have the velocity obtained from 
the cross-correlation of the whole spectrum. 
The estimated rms error of the radial velocity of the secondary star 
is about 2 km\,s$^{-1}$. 
The velocities obtained in this way are listed in Table 1.
They indicate a preliminary mass ratio of about 2. Also, we would like 
to point out that our radial velocities do not fit well on the predicted
RV curve and more observations are under way to improve the orbital 
elements and determine the precise mass ratio of the system.

In summary, several independent arguments were presented to demonstrate
convincingly that there are weak sharp features in the spectrum of HD861
which cannot be attributed to the primary star and that we have discovered
the spectrum of the secondary which is a cooler, fainter and less
massive star with considerably slower rotation than the primary.
 
\IBVSfig{10.cm}{5509-f1.eps}{Two successive spectra of HD\,861. 
While the strong lines of the primary are apparent and are shifted 
to the blue the fine and sharp components are sifted to the red
as indicated by the arrows.}
\IBVSfigKey{5509-f1.eps}{HD 861}{spectrum}

\IBVSfig{10.cm}{5509-f2.eps}{The observed spectrum No.1 (thin line) 
and the synthetic spectrum (thick line) of HD\,861. 
Arrows indicate the position of secondary lines.
There are no predicted theoretical lines at these points.}
\IBVSfigKey{5509-f2.eps}{HD 861}{spectrum}

This paper again underlines our feeling that our knowledge
of bright and nearby stars is still incomplete.
This is true especially for binary and multiple systems and when our 
knowledge is based on older photographic techniques only.
Particularly photographic data involving the longer orbital periods 
(where the orbital Doppler shift is less or comparable to the rotational 
broadening of the spectral lines) and early type stars (that have few and 
broad lines) need to be used with caution.
Our suspicion is that one might find more cases where the unresolved 
secondary lines and continuum may have led to previous misinterpretations 
of the data.
CCD observations with even small-medium telescopes can thus discover
the binary nature or secondary spectra in many currently unresolved 
SB1 systems and can thus provide us with important information 
such as mass ratios as demonstrated recently e.g. by
Faraggiana \& Gerbaldi (2003), Faraggiana et al. (2001),
Iliev et al. (2001a, 2001b), Budaj \& Iliev (2003), 
Budaj et al. (2003) and Ryabchikova (1998).

\vskip 2mm
\noindent
JB  gratefully acknowledges grant support from the Penn State university 
and wishes to thank Dr. K. Getman for his assistance with computer related 
problems.
This research was supported by the NSF-NATO fellowship (NSF DGE-0312144)
and partly by the VEGA grant No. 3014 from the Slovak Academy 
of Sciences and the Science and Technology Assistance agency under
the contract No. 51-000802.
This study made use of the Vienna Atomic Line Data Base (VALD)
services.



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