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Speckle interferometry of two low­mass triple
systems in the solar neighbourhood
E.V. Malogolovets 1 , Y.Y. Balega 2 , K.­H. Hofmann 3 , D.A. Rastegaev 4 and
G. Weigelt 5
1 Special Astrophysical Observatory Russian Academy of Sciences evmag@sao.ru
2 Special Astrophysical Observatory Russian Academy of Sciences balega@sao.ru
3 Max­Planck­Institut fuer Radioastronomie khh@mpifr­bonn.mpg.de
4 Special Astrophysical Observatory Russian Academy of Sciences leda@sao.ru
5 Max­Planck­Institut fuer Radioastronomie weigelt@mpifr­bonn.mpg.de
1 Introduction
Multiple systems with low levels of hierarchy are important targets for the
study of formation, evolution, and dynamical stability of multiple stars. Two
such triple stars with low mass components, GJ 900 and KUI 99, have been
observed during the last six years at the 6 m BTA telescope (Zelenchuk).
The first object is a young system with projected distances between the
components in the range of 200­700 mas. The second one is a group of middle­
aged K dwarfs.
In the V and I bands, the observations were performed using the speckle
camera described in [7]. In the K­band the data were obtained with the
speckle camera of the Max­Planck­Institut fuer Radioastronomie in Bonn.
The mean square error of the speckle measurements is 2­4 mas, depending
on seeing conditions. The speckle images were reconstructed using the triple
correlation method [6]. Below, we present the results of the relative motion
study in the systems and give conclusions about their hierarchy.
2 GJ 900
GJ 900 is a young nearby (# hip =51.8 mas) K7 star. It was first resolved
as a triple system with speckle interferometry at the 6 m BTA telescope in
November 2000. The bispectrum reconstruction of the K­band image is shown
in Fig. 1. Later, the system was observed in the H and K bands with the 8 m
Subaru telescope using adaptive optics [8]. From the apparent configuration
of the components, it was supposed that it could be a low­mass Trapezium­
type system. If this is the case, GJ 900 is the first known Trapezium­type star
at the bottom of the main sequence.
Presently, 4 speckle interferometric observations and 2 adaptive op­
tics measurements allow us to follow the relative motion of the compo­
nents. Speckle photometry gives the following magnitude di#erences be­
tween the stars: #IAB =2.42±0.08, #IAC =3.67±0.22, #KAB =1.92±0.18,

2 E.V. Malogolovets et al.
Fig. 1. The bispectrum reconstruction of the GJ 900 image in the K­band.
#KAC =2.55±0.30. These di#erences are approximately 0.2 mag larger than
those given by adaptive optics. With magnitude di#erences in the I­band and
Hipparcos parallaxes in hand, we obtain the following absolute magnitudes
for the components: M IA =10.5, M IB =12.9, M IC =14.2. The corresponding
spectral types of the individual stars are: K7, M5 and M7.
The relative positions of the AB pair changed linearly during the period
2000­2004, showing a mean value of 48 mas/yr (Fig. 2). The angular sepa­
ration in the AC pair remains constant within the errors of measurements.
These observations are represented in Fig. 3. We expect that the period of
the AB pair lies between 50 and 100 yrs, while for the AC subsystem it can
be over 1000 yrs. It looks as if the GJ 900 apparent configuration is caused
by a chance projection.
Fig. 2. Relative positions for GJ 900 AB between 2000.8754 and 2004.8208. Filled
circles are from the 6 m BTA speckle measurements; open circles are the adaptive
optics data from Martin [8].

Speckle interferometry of two low­mass triple systems 3
Fig. 3. Relative positions for GJ 900 AC between 2000.8754 and 2004.8208.
3 KUI99=GJ 795
KUI 99 is a late­type K star from the solar neighbourhood (# hip =53.82 mas).
In 1943, Kuiper [5] first resolved KUI 99 as a visual binary star. Duquennoy [3]
found that the brighter component of KUI 99 is itself a spectroscopic binary.
Orbital solutions for the outer pair were proposed by Baize [1], Heintz [4] and
Soderhjelm [10]. In 1998, KUI 99 was directly resolved as a triple star for the
first time using the speckle interferometer at the 6 m BTA telescope [2]. The
di#erential magnitude speckle measurements showed that the components B
and C have similar brightness: #mAB =0.94±0.03, #mAC =1.14±0.03. Di#er­
ential speckle photometry and Hipparcos parallax give the following absolute
magnitudes and spectral types for the stars: M V A =7.2, M V B =8.1, M V C =8.3
and K4, K7 and K8.
Interferometric orbits for the AB and AC pair can be derived from the
1998­2004 data. The apparent ellipses of the KUI 99 AC and KUI 99 AB pair
are shown in Fig. 4
KUI 99 AC KUI 99 AB
Fig. 4. Speckle interferometric orbits for the inner (KUI 99 AC) and the outer
(KUI 99 AB) pair. The line of nodes is shown by the dash­dotted line. The arrow
shows the direction of motion. North is up, east is to the left. The dashed circle has
a radius of 20 mas.

4 E.V. Malogolovets et al.
For the inner AC pair the speckle orbit parameters are in good agreement
with the spectroscopic orbit of Duquennoy [3]. The orbital elements for the
inner and outer subsystems are given in Table 1.
Table 1. Orbital elements for the inner (KUI 99 AC) and outer (KUI 99 AB) pair.
Comp. P(yr) T e a(##) i
## # # #
AC 2.51 2000.55 0.620 0.120 18.2 173.6 87.1
± ± ± ± ± ± ±
0.01 0.01 0.006 0.002 2.5 10.9 10.3
AB 39.55 2001.83 0.161 0.690 85.9 128.6 92.0
± ± ± ± ± ± ±
0.37 0.07 0.075 0.074 0.8 0.4 0.8
We can state from the orbital solutions that KUI 99 is a low­hierarchical
system with an angle between the two orbital planes of about 70 # . It is
necessary to continue the monitoring of the relative motion in the systems in
order to detect possible oscillations of the orbital parameters, which can be
caused by the Kozai mechanizm [9].
References
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(2002)
3. A. Duquennoy: Astron. Astrophys. 178, 114 (1987)
4. W.D. Heintz: Astron. Astrophys. Suppl. Ser. 56, 5 (1984)
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6. A.W. Lohmann, G. Weigelt, B. Wirnitzer: Applied Optics 22, 4028 (1983)
7. A.F. Maksimov, Y.Y. Balega, U. Beckmann et al: Bull. Special Astrophys.
Obs. 56, 25 (2003)
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10. S. Soderhjelm: Astron. Astrophys. 341, 121 (1999)