\documentstyle[twoside]{article}

\input ibvs2.sty

\begin{document}
\IBVShead{4827}{15 January 2000}

\IBVStitletl{Triple System {\boldmath $\epsilon$} V\lowercase{ol} and Quadruple System {\boldmath $\eta$} M\lowercase{us}:}{ the Mass Ratio in Close Binary Systems }


\IBVSauth{Medici, A.; Hubrig, S.}

\IBVSinsto{Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany}

\SIMBADobjAlias{epsilon Vol}{HD 68520}
\SIMBADobjAlias{eta Mus}{HD 114911}

\begintext

In the course of our spectroscopic study aimed at searching the line Hg~II $\lambda$ 3984 in a sample of 28 spectroscopic binaries with late B primaries, 11 new double-lined spectroscopic binaries were discovered, 10 of which were previously known as single-lined systems: 3 Si stars (HD 35008, HD 61512, and HD 130081), one He-weak star (HD 139160), 5 stars with normal late B primary (HD 68520, HD 87191, HD 102010, HD 114911, and HD 162515) and two stars with HgMn anomaly (HD 75642 and HD 87751) (Hubrig \& Mathys 1996). The observations were carried out at the European Southern Observatory for five nights spanning from March 16 to March 20. We used the 1.5 m telescope and the Boller \& Chivens spectrograph, equipped with a Ford Aerospace chip. Spectra were recorded at a resolution of approximately 1 \AA\ over the wavelength range 3700--4600 \AA.

In two stars with known orbital parameters, HD~68520 ($=\varepsilon$~Vol,
spectral type B5, ${\rm V}=4.3$) and HD~114911 ($=\eta$~Mus, spectral type B8, ${\rm V}=4.8$), the lines issued from both components in binary systems are clearly separated in some phases. In this paper we report about the mass ratios of these systems.

\medskip
\noindent
{\bf HD 68520 ({\boldmath $\varepsilon$} Volantis)}

\noindent
This star is listed in the Eighth Catalogue of the Orbital Elements of
Spectroscopic Binary Systems (Batten et al.\ 1989) as a single-lined system. The orbital parameters for the primary component were calculated by Sanford (1914) using the method of Lehmann-Filhes. One of his spectrograms gives evidence of a secondary's spectrum which yielded the mass ratio ${\cal M}_{1}/{\cal M}_{2}=1.23$. From our observations we obtain ${\cal M}_{1}/{\cal M}_{2}=1.30$.

The catalogue of multiple stars (Tokovinin 1997) indicates $\varepsilon$ Vol to have one visual companion which is 2\fmm9 fainter and separated by 6\farcs1 at position angle 24$^{\circ}$. From the spectral type of the primary Tokovinin estimates the mass of the primary ${\cal M}_{1}=5.76$~M$_{\odot}$. Assuming a minimum secondary mass for the single-lined system, he obtains ${\cal M}_{2}=3.26$~M$_{\odot}$ for the secondary. Adopting these values the mass ratio for this system will be 1.77.

\medskip
\noindent
{\bf HD 114911 ({\boldmath $\eta$} Musc\ae)}

\noindent
This star is also listed in the Eighth Catalogue of the Orbital Elements of Spectroscopic Binary Systems (Batten et al.\ 1989) as a single-lined system. The orbital parameters for the primary component were calculated by Buscombe \& Morris (1961). Our observations yield a ratio ${\cal M}_{1}/{\cal M}_{2}=1.14$.

In the catalogue of multiple stars (Tokovinin 1997) $\eta$ Mus is mentioned as a triple star with a visual companion with common proper motion at the distance of 60\farcs00 and position angle of 332$^{\circ}$. This companion is 3\fmm4 fainter than $\eta$ Mus. From the spectral type of the primary Tokovinin estimates the mass of the primary ${\cal M}_{1}=4.48$~M$_{\odot}$. Assuming a minimum secondary mass for the single-lined system, he obtains ${\cal M}_{2}=2.63$~M$_{\odot}$
for the secondary. Adopting these values the mass ratio will be 1.70.

In fact, the triple system $\eta$ Mus is a quadruple system. In March 1999 we have observed $\eta$ Mus with the ESO adaptive optics system ADONIS at the 3.6-m telescope on La Silla. Our observations  revealed an additional faint companion separated by 2\farcs71 at position angle
125$^{\circ}$ (Hubrig \& Mignant 2000). The magnitude differences in the K, H and J bands are 4\fmm32, 4\fmm54 and 5\fmm25, respectively.

\references

Batten A. H., Fletcher J. M., MacCarthy D. G., 1989, Eighth Catalogue of the Orbital Elements of Spectroscopic Binary Systems, Publ. Dominion
Astrophys. Obs., {\bf 17}

Buscombe W., Morris P. M., 1961, MNRAS, {\bf 123}, 183

Hubrig S., Mathys G., 1996, A\&AS, {\bf 120}, 457

Hubrig S., Mignant D. L., 2000, in prep.

Sanford R. L., 1914, Lick O. Bull., {\bf 8}, 127

Tokovinin A. A., 1997, A\&AS, {\bf 124}, 75

\endreferences
\end{document}
