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A&A 431, 307--319 (2005)
DOI: 10.1051/0004­6361:20041135
c
# ESO 2005
Astronomy
&
Astrophysics
Close binary companions of the HAeBe stars LkH# 198, Elias 1,
HK Ori and V380 Ori #
K. W. Smith 1 , Y. Y. Balega 2 , W. J. Duschl 3 , K.­H. Hofmann 1 , R. Lachaume 1 , T. Preibisch 1 ,
D. Schertl 1 , and G. Weigelt 1
1 Max­Planck­Institut fÝr Radioastronomie (MPIfR), Auf dem HÝgel 69, 53121 Bonn, Germany
e­mail: kester@mpifr­bonn.mpg.de
2 Special Astrophysical Observatory, Nizhnij Arkhyz, Zelenchuk region, Karachai­Cherkesia 357147, Russia
3 Institut fÝr Theoretische Astrophysik, Tiergartenstrasse 15, 69121 Heidelberg, Germany
Received 21 April 2004 / Accepted 19 October 2004
Abstract. We present di#raction­limited bispectrum speckle interferometry observations of four well­known Herbig Ae/Be
(HAeBe) stars, LkH# 198, Elias 1, HK Ori and V380 Ori. For two of these, LkH# 198 and Elias 1, we present the first
unambiguous detection of close companions. The plane of the orbit of the new LkH# 198 companion appears to be significantly
inclined to the plane of the circumprimary disk, as inferred from the orientation of the outflow. We show that the Elias 1
companion may be a convective star, and suggest that it could therefore be the true origin of the X­ray emission from this object.
In the cases of HK Ori and V380 Ori, we present new measurements of the relative positions of already­known companions,
indicating orbital motion. For HK Ori, photometric measurements of the brightness of the individual components in four bands
allowed us to decompose the system spectral energy distribution (SED) into the two separate component SEDs. The primary
exhibits a strong infrared excess which suggests the presence of circumstellar material, whereas the companion can be modelled
as a naked photosphere. The infrared excess of HK Ori A was found to contribute around two thirds of the total emission from
this component, suggesting that accretion power contributes significantly to the flux. Submillimetre constraints mean that the
circumstellar disk cannot be particularly massive, whilst the near­infrared data indicates a high accretion rate. Either the disk
lifetime is very short, or the disk must be seen in an outburst phase.
Key words. stars: circumstellar matter -- stars: formation -- stars: binaries -- ISM: Herbig­Haro objects
1. Introduction
Herbig Ae/Be stars (HAeBes) are young intermediate­mass
(2--8 M # ) pre­main­sequence stars first defined by Herbig
(1960). According to his definition, HAeBes should have emis­
sion lines in their spectra, an early spectral type and be asso­
ciated with dark cloud material as an indication of their youth.
Despite the similarities between HAeBes and the lower­mass
T Tauri stars, questions such as the existence of circumstellar
disks, the multiplicity and clustering of the objects, the origin
of X­ray emission (Zinnecker & Preibisch 1995), and the out­
flow activity are much less clarified in the case of HAeBes.
The frequency and properties of binary systems amongst
all stars are of great importance in understanding the star
formation process, since they can point to certain star for­
mation scenarios and rule out or strongly constrain others.
# Based on observations performed with the 6 m telescope of the
Special Astrophysical Observatory, Russia, the 2.2 m ESO/MPG tele­
scope at La Silla, and with the NASA/ESA Hubble Space Telescope,
obtained from the data archive at the Space Telescope Institute.
STScI is operated by the association of Universities for Research in
Astronomy, Inc. under the NASA contract NAS 5­26555.
The configuration of pre­main­sequence multiples is of spe­
cial importance because the binary properties of the objects
can be compared with their formation environment, for exam­
ple whether in a T association or massive star forming region.
There is also less scope for the system configuration to have
been altered by stellar interactions or continuing accretion. The
angular momentum of the binary can also be compared to that
of circumstellar or circumbinary disks which may still exist at
this stage. The coplanarity of the system orbit, the individual
disks of the components and a possible circumbinary disk are
all major constraints on viable formation mechanisms.
Numerous studies using a variety of techniques have es­
tablished that the majority of low­mass young stars are mem­
bers of binary systems (e.g. Ghez et al. 1993; Leinert et al.
1993; Simon et al. 1995). The T Tauri population in the nearby
Taurus­Auriga T­association displays a factor of 2 higher bi­
nary fraction than that seen amongst main­sequence stars. At
the high end of the stellar mass range, bispectrum speckle in­
terferometry of the massive stars in the Orion nebula cluster
revealed companions for 7 out of 13 target objects, which af­
ter correction for undetected systems was estimated to rep­
resent a binary frequency close to 100%, with an average

308 K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori
of >1.5 companions per primary (Preibisch et al. 1999). This
is about three times the multiplicity of low­mass stars, and may
suggest an alternative formation scenario for the high mass ob­
jects. Studies aimed specifically at intermediate mass stars have
been rare. Li et al. (1994) carried out an infrared imaging study
of 16 sources and reported companions for nine of them, al­
though of these many were widely separated and are proba­
bly not bound. Leinert et al. (1997, hereafter LRH97) studied
a larger sample of 31 stars using a speckle interferometry tech­
nique in the near­infrared, and found that 31% of the systems
were multiple with separations between 50 and 1300 AU. This
was estimated to represent an excess binarity among HAeBe
stars compared to main­sequence G dwarfs of a factor of two.
Pirzkal et al. (1997) used a speckle shift and add technique to
search for companions around 39 HAeBe stars. They detected
9 multiple systems, and estimated on statistical grounds that
this implied a true binary frequency amongst HAeBes of at
least 85%. A survey for spectroscopic binaries amongst HAeBe
stars by Corporon & Lagrange (1999) found a binary frequency
of 17%. For short periods (<100 days) the binary frequency
was found to be 10%, compared to the frequency amongst
WTTS spectroscopic binaries of 11±4% (Mathieu 1992) or the
frequency amongst main sequence solar­mass stars of 7 ± 2%
(Duquennoy & Mayor 1991).
In this paper, we present bispectrum speckle interferometry
at multiple epochs of four HAeBe systems. For two of these,
LkH# 198 and Elias 1, our di#raction­limited images show
unambiguously for the first time that they have close binary
companions. For the known binary HK Ori, we separate the
SEDs of the two companions and by considering the di#erent
colours show that the brighter object possesses a circumstel­
lar disk which the secondary lacks. For V380 Ori, we are able
to show relative motion compared to the position measured by
LRH97.
2. Observations and data reduction
The optical observations of HK Ori were made with the 2.2 m
ESO/MPG telescope on March 8, 1995. The speckle interfero­
grams were recorded through interference filters with central
wavelength/bandwidth of 550 nm/60nm and 656 nm/60nm.
The detector used for the visible observations was an image
intensifier (gain 500000) coupled optically to a fast CCD cam­
era (512 2 pixels/frame, frame rate 4 frames/s). All the other
speckle interferograms were recorded with the SAO 6 m tele­
scope in Russia between 1995 and 2003. The detector of our
speckle camera at SAO was either a Rockwell HAWAII ar­
ray (1998­2003; only one 512 â 512 Quadrant was used) or a
256 â 256 PICNIC array detector (1996 and 1997). The visible
data sets consist of about 700 to 1400 speckle interferograms
each with an exposure time of 50 msec. The infrared sets con­
sist of between 400 and 3200 speckle interferograms each with
an exposure time of between 150 and 250 msec.
The object power spectra were determined with the speckle
interferometry method (Labeyrie 1970). Speckle interfero­
grams of unresolved single stars were recorded just before
and after the object and served as references to determine
the speckle transfer function. Di#raction­limited images were
reconstructed using the bispectrum speckle interferometry
method (Weigelt 1977; Weigelt & Wirnitzer 1983; Lohmann
et al. 1983; Hofmann & Weigelt 1986).
For HK Ori, photometric calibration in the K # ­band
was carried out by observing the photometric standard stars
HD 18881 and Gl 105.5, chosen from Elias et al. (1982),
on October 19, 1997. For the photometric calibration in the
H­band the photometric standard star HD 40335 and the star
HD 31648 were observed on October 22 and 19, 1997. The
photometric calibration in the visible is based on our speckle
observations of NX Pup from March 10, 1995 (SchÆller et al.
1996). Simultaneously to our observations of NX Pup, CCD
photometry of the unresolved pair NX Pup A/B was carried out
at the Danish 1.5m telescope at La Silla. Observations of stan­
dard stars taken from the list by Landolt (1992) allowed for the
absolute photometric calibration.
3. Results
Each of the observed visibility functions clearly showed a pat­
tern suggestive of a binary system. The separation and position
angle of the system were measured directly from the two di­
mensional visibility function. Maps of the objects were made
and the flux ratios were also measured. The recovered param­
eters for the various systems are listed in Table 1. Below, we
discuss each object individually.
3.1. LkH# 198
LkH# 198 (SIMBAD coordinates: # = 00 h 11 m 25.97 s , # =
+58 # 49 # 29.1 ## , J2000) is a well­studied HAeBe located in the
dark cloud Lynds 1265 at a distance of about 600 pc. It is asso­
ciated with another well­known HAeBe star, V376 Cas, which
lies approximately 35 ## to the north. A schematic picture of the
complex environment around these two sources is given in the
paper by Koresko et al. (1997). We reproduce a previously un­
published HST image from the archives in Fig. 1, which shows
the inner 15 ## â 15 ## of the system. Other images of the in­
ner region of the system are shown in Koresko et al. (1997),
Fukagawa et al. (2002) and Perrin et al. (2004).
Lagage et al. (1993) detected an embedded source
(LkH# 198 B) 6 ## north of LkH# 198 in 10 #m images
which is also visible at 2.2 #m (Li et al. 1994) and in the
1.1 #m HST image shown here. A deeply embedded proto­
star (LkH# 198 MM) was found about 19 ## to the northwest
by Sandell & Weintraub (1994) using the JCMT at 800 #m.
This object dominates in the millimetre and submillimetre but
is not visible at all at shorter wavelengths. The most striking
extended feature in the optical is a large bubble­like elliptical
loop extending some 40 ## to the southeast at a position angle
of approximately 135 # (Corcoran et al. 1995). Coronagraphic
imaging in the near­infrared by Fukagawa et al. (2002) showed
in more detail the close environment of LkH# 198. Their image
showed the primary extended along a roughly north­south axis
(PA = 15 # ). This elongation was also reported by Koresko et al.
(1997), and is visible in the HST image in Fig. 1, but here the
issue is complicated by the presence of a di#raction spike along
the same axis.

K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori 309
Table 1. Summary of the observations. For each observation, the epoch and observing wavelength is shown, together with the recovered
binary separation (in both mas and AU for the assumed distance), position angle (measured anticlockwise from north), and flux ratio (typical
uncertainty 10--20%). Where photometric calibration was performed, the individual magnitudes of the components are also given.
LkH# 198
Epoch # c ## # # PA m A m B F s /F p
[nm] [nm] mas AU
1996.75 2191 411 66.3 ± 4 39.8 242 ± 2 0.25
1997.79 2165 328 66.6 ± 3 40.0 242 ± 2 0.20
1998.45 2110 192 65.8 ± 3 39.5 245 ± 2 0.20
1999.74 1648 317 63.9 ± 2 38.3 246 ± 1 0.17
2001.83 2115 214 58.4 ± 3 35.0 250 ± 1 0.16
2002.73 1648 317 50.4 ± 2 30.2 255 ± 2 0.16
2003.78 2115 214 48.6 ± 3 29.2 253 ± 2 0.27
Elias 1
1996.75 2191 411 50.5 ± 4 7.07 54 ± 3 0.69
2003.76 2115 214 60.4 ± 1 8.46 59 ± 1 1.00
HK Ori
1995.18 550 60 334.2 ± 11.5 153.72 44.1 ± 1.5 12.13 ± 0.2 13.01 ± 0.2 0.45
1995.18 656 60 333.4 ± 11.5 153.35 44.6 ± 1.5 11.62 ± 0.2 12.53 ± 0.2 0.43
1997.80 1613 304 339.2 ± 6.2 156.03 43.8 ± 0.5 8.55 ± 0.14 9.76 ± 0.16 0.33
1997.80 2165 328 343.1 ± 6.8 157.83 44.2 ± 0.5 7.42 ± 0.16 9.65 ± 0.17 0.13
2003.78 2115 214 347.7 ± 2.5 159.95 41.8 ± 0.7 0.17
V380 Ori
2003.78 2115 214 122.7 ± 2.5 56.44 224.0 ± 2.0 0.27
Numerous HH objects are found around LkH# 198 (see e.g.
Corcoran et al. 1995; Molinari et al. 1993; Goodrich 1993).
Corcoran et al. (1995) found knots of SII emission tracing both
sides of a jet from LkH# 198 at a position angle of around
160 # . a further knot of emission was seen along the same axis
on the opposite side of LkH# 198 at position angle 340 # . These
objects have been designated HH 164. Spectra of these emis­
sion knots revealed that they have a low radial velocity, and
therefore suggest that the jet lies close to the plane of the sky.
Another knot seems to trace the southeast part of a jet appar­
ently originating from the companion LkH# 198 B along the
axis of the loop. This knot, together with [SII] emission at the
loop apex, has been designated HH 161. The trail of nebulos­
ity that can be seen extending eastwards from the previously­
known companion LkH# 198 B may be the northern edge of
an outflow cavity caused by the flow from this source driving
HH 161. Nebulosity is also seen extending east from the main
object. This region contains ``streamer''­like structure with the
same position angle as HH 161 and this might indicate interac­
tion of the outflow from LkH# 198 Bwith material surrounding
the primary. Aspin & Reipurth (2000) discovered a further HH
object, HH 461, with a faint bowshock morphology, along the
axis of the LkH# 198 jet some 80 ## to the southeast. McGroarty
& Ray (2003) identified two further bowshock­shaped struc­
tures, designated HH 801 and HH 802, which lie along the line
of HH 164 with a total separation of 2.3 pc.
Polarization maps in the I band by Leinert et al. (1991) and
Piirola et al. (1992), and at V and I by Asselin et al. (1996) all
show a centrosymmetric polarization pattern extending in an
arc to the southeast. The map of Piirola et al. (1992), which was
taken under conditions of extremely good seeing, also shows
a similar centrosymmetric pattern extending to the northwest.
A region of polarization perpendicular to the centrosymmetric
pattern was seen within the central 0. ## 5. This was taken to be
the signature of a central, unresolved disk. Perrin et al (2004)
used laser guide star adaptive optics to obtain very high qual­
ity near­infrared J, H and K s band polarimetry of the central
part of the LkH# 198 system. They saw a polarized biconical
nebula aligned almost exactly north­south, with a dark unpo­
larized central region. This biconical nebula, which can be in­
terpreted as scattering from an evacuated bipolar cavity caused
by an outflow, is consistent with LkH# 198 being the source
of the outflow HH164, but the axis is apparently misaligned by
approximately 20 # .
Our speckle observations of LkH# 198 span seven years,
from 1996.75 to 2003.78. The two dimensional visibilities
show clear signatures of binarity, and the position of the com­
panion, which we designate LkH# 198 A2, relative to the pri­
mary (LkH# 198 A1) changes significantly over the period of
the observations. The track of the secondary relative to the pri­
mary is shown in Fig. 2. The trajectory shows signs of curva­
ture to the east, indicating that we are seeing a segment of an
orbit, although it appears a straight line trajectory cannot be
excluded. A map of the system reconstructed from the 1999
observations, is also shown in Fig. 2.
3.1.1. Orbital motion
With only seven points, spanning a short segment of the ap­
parent orbit, it is not possible to determine the true orbit with
any certainty. Nevertheless, we make some preliminary orbital
fits and explore the constraints which can be imposed on the
motion.

310 K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori
Fig. 1. HST image of LkH# 198, taken with the NICMOS camera at 1.1 #m. North is up and East to the left. The source approximately 6 ## due
north of LkH# 198 is the already known companion LkH# 198 B. A fan­shaped trail of emission is visible to the east of this companion. The
new speckle companion, LkH# 198 A2, lies within 60 mas of the primary and is not discernable in this image (see Fig. 2). The directions to
various associated HH objects and other structures are indicated. The various structures comprising HH 164 were identified by Corcoran et al.
(1995) as the jet of LkH# 198. The HH object HH 161 is believed to be powered by the companion LkH# 198 B, and the arrow pointing to
this object is shown originating from the position of this object. Interesting streamer­like structure can be seen to the east of LkH# 198 with the
same position angle as HH 161, perhaps indicating that the HH 161 flow interacts with the material around LkH# 198. The axis of the biconical
nebula mapped by Perrin et al. (2004) is indicated, running nearly exactly North­South. The opening angle of this structure is approximately
30 # , and so the outflow HH 164 emerges from within the supposed bipolar cavity, even though its direction is not exactly aligned with the axis.
The exact configuration of the orbit is particularly inter­
esting in the case of LkH# 198 because of the complex envi­
ronment of the system. The outflow has a low radial velocity,
suggesting that it lies in the plane of the sky and that the inner
disk should be seen nearly edge­on. This is also the impression
given by the polarization maps of Perrin et al. (2004). Long­
term photometric monitoring by Mel'nikov (1997) shows that
LkH# 198 lacks the strong photometric variations which define
UXOR sources, despite the supposed edge­on viewing angle of
any disk. According to the prevailing theories of UXOR vari­
ability, in which the deep photometric minima are caused by
obscuration by clumps in a disk, this makes the object some­
thing of an anomaly. The presence of the companion and the
details of the orbit are interesting in the context of the complex
environment, and we therefore make a more detailed discus­
sion of the orbit than would be justified for an isolated system
with such a short known orbital segment.
We made a number of fits to the observed relative motion
of the LkH# 198 companion. The fits were made numerically
by running a 2­body code multiple times and minimizing the
resulting deviations from the points. Conventional orbital pa­
rameters for the best fit, such as the major axis, eccentricity
and so on, can be recovered from a full simulation of the best­
fit orbit.
The mass of the primary was estimated by Hillenbrand
et al. (1992) to be 1.6 M # based on the luminosity estimated
from the dereddened V magnitude and a spectral type of A5.
However, Natta et al. (1992) estimated the luminosity to be
250 L # from far infrared measurements, which by comparison
with pre­main­sequence tracks from Palla & Stahler (1993),
suggests a mass of 3.5--4 M # , if the bulk of this luminosity
can be assumed to originate from the primary. If half this lumi­
nosity arises from accretion power, the estimated primary mass
would fall to 3.0#3.5 M # . For an orbit calculation, to the mass
of the primary must be added the mass of any compact circum­
stellar structure such as a disk. Leinert et al.'s (1991) estimate
of the mass of the immediate circumstellar material was only
0.01 M # , and so we neglect the possible mass of circumprimary

K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori 311
100 0 ­100
rel. position [mas]
­100
0
100
rel.
position
[mas]
100 0 ­100
rel. position [mas]
­100
0
100
rel.
position
[mas]
Fig. 2. Top: contour map of the LkH# 198 system constructed from
speckle observations on the 26th October 1999. Bottom: the position
of the LkH# 198 companion relative to the primary. The scale is given
in mas and AU for an assumed distance of 600 pc. The solid line is a
circle of radius 37 AU, for an assumed distance of 600 pc, centred on
the primary
and circumsecondary material. The flux ratio of the secondary
to the primary is measured to be 0.20 at K # and 0.16 at H (see
Table 1). If this is taken as a rough estimate of the luminosity
ratio, the mass of the secondary is estimated from evolution­
ary tracks to be either approximately 1.0 M # if the primary is
1.6 M # or 2--2.5 M # if the primary is around 3.5--4 M # . For the
sake of fitting the orbit, we have adopted two di#erent masses
for the system, one of 1.6 and 1.0 M # , following Hillenbrand
et al. (1992), and one of 4.0 and 2.5 M # , following Natta et al.
(1992).
The motion on the sky leads to tight constraints on the mo­
tion in the plane of the sky. Because such a short segment of
the orbit is observed, however, there is little constraint on the
possible initial position and velocity in the radial direction. On
the sky, the secondary covers an apparent distance of almost
12 AU in a time of six years. This implies a velocity in the plane
of the sky of 9.5 km s #1 . For a system comprising a 1.6 M #
and 1.0 M # components, the escape velocity would be approx­
imately 11 km s #1 . This implies that, if the system has such a
low mass, the orbit must lie close to the plane of the sky (as­
suming it is in fact bound). On the other hand, for a system
with a total mass of 6.5 M # , the escape velocity is approxi­
mately 17 km s #1 , so that the true velocity can be substantially
larger than the apparent velocity on the plane of the sky, and
the orbit can be significantly inclined to the line of sight.
In Fig. 3, we show four fitted orbits for various assumed
system parameters. The orbital parameters and fit # 2 values for
these are listed in Table 2. The top left panel shows the fit for
a system with masses 1.6/1.0 M # , and low values for the initial
value (i.e. before the fitting procedure) of the initial radial po­
sition and velocity. This leads to a quite eccentric orbit almost
in the plane of the sky. In the top right panel, we show a fit­
ted orbit with the same low values for the initial radial position
and velocity, for a system with masses 4/2.5 M # . The lower left
panel shows a fit for system with 4/2.5 M # , for which the initial
radial o#set and velocity were chosen to attempt to produce a
near­circular orbit. In fact, the eventual fit has an eccentricity of
about 0.3. Finally, a fit was made with a very large initial radial
velocity. The intention of this was to incline the fit as highly as
possible to the plane of the sky, so that it is as close as possible
to coplanar with the supposed edge­on disk at the heart of the
system. The inclination of this fit to the plane of the sky was
approximately 70 # . This fit is shown in the lower right panel
of Fig. 3. Finally, a fit was made with the secondary set a long
way back from the plane of the sky, and only the north­south
and east­west motion varied. This produces the best­fit straight­
line motion, the # 2 of which is listed in Table 2 for comparison
with the bound fits.
3.1.2. Results of orbit fitting
Although the straight line has the highest # 2 (because it can't
account for the apparent curvature), there is no significant
di#erence between the quality of the various fits. The most
edge­on orbit fits which could be made had an inclination of
approximately 20 # to the plane of the sky, and the long axis of
the projected orbit was tilted by at least 20 # to the east­west
direction. This contrasts with the Perrin et al. (2004) image
which shows a disk­like structure aligned almost exactly north­
south, and the jet velocity measurements of Corcoran et al.
(1995) which show low velocities for the jet material and there­
fore suggest that the jet lies very close to the plane of the sky.
Unfortunately, without tangential velocity measurements, it is
not possible to put firm limits on the inclination of the jet for
comparison with the model orbits. Interestingly, the orientation
of the axis of the projected orbit (d) is approximately aligned
with the direction of the HH 164 jet.
3.2. Elias 1
Elias 1, also known as V892 Tau (# = 04 h 18 m 40.60 s , # =
+28 # 19 # 16.7 ## , J2000) is located in the Taurus­Auriga complex
at a distance of approximately 140 pc (Elias 1978). Its spectral
type was estimated as A6 with AV = 3.9 mag and luminosity
of around 38 L # (Berrilli et al. 1992), but other authors have
assigned earlier spectral types of A0 (Elias 1978) or B9 (Strom
& Strom 1994). Elias 1 was classed as a type II HAeBe star by
Hillenbrand et al. (1992), having a very flat or even rising SED

312 K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori
Fig. 3. Orbit fits to the motion of the LkH# 198 companion for various choices of initial parameters. The main panel of each plot shows the
fitted orbit projected on the plane of the sky. North is up and east to the left. The measured data points are plotted as open squares and the
corresponding points in the fit are plotted with open triangles. A dash­dotted line marks the major axis, and a solid line marks the line of nodes
(i.e. the line of intersection between the orbital plane and the plane of the sky). The ascending and descending nodes are labelled ``a'' and ``d''.
In the inset at upper right in each figure, we show the segment of the orbit with the data points on a larger scale. The data points are shown with
errorbars, and the fitted points are again plotted as open triangles. The first and last points are labelled with the observing epoch. In the inset at
lower right, we show the projection in a plane perpendicular to the plane of the sky. North is up and the radial direction (pointing away from
the observer) is to the left. The coordinate systems are indicated in each panel of the top left­hand plot. a) Fit for an assumed primary mass of
1.6 M # and secondary mass 1.0 M # . The initial guess for the fit involves a low velocity in the R direction and a small displacement from the
plane of the sky. As a result, the fitted orbit lies close to the plane of the sky. b) The same low starting values for R position and velocity, but
for an assumed primary mass of 4.0 M # and secondary mass 2.5 M # . c) A fit with an assumed primary mass of 4.0 M # and secondary mass
2.5 M # , with starting conditions chosen to produce a near­circular orbit. d) This fit has masses of 4 and 2.5 M # and a high initial radial velocity,
which is intended to produce an orbital plane as highly inclined as possible to the plane of the sky.
in the NIR to FIR. This suggests the presence of a possible en­
velope as well as a circumstellar disk, or possibly a flared disk.
The polarization is 4.7% (Yudin 2000).
A T Tauri type companion lies approximately 4 ## to the
northeast (LRH97). Kataza & Maihara (1991) obtained one
dimensional speckle interferograms at K and L, with position
angles of zero and ninety degrees. They also obtained one­
dimensional speckle interferograms at L # with PA = 45 # , show­
ing the object was resolved in this direction. The object was
found to be resolved in the east­west direction, but unresolved
in the north­south direction. The preferred interpretation was
a flattened halo associated with a circumstellar accretion disk

K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori 313
Table 2. Parameters of the various fitted orbits shown in Fig. 3. The parameters shown are the mass of the primary, mass of the secondary, major
axis length, eccentricity, period, position angle of the ascending node (measured anticlockwise from north in the plane of the sky), inclination
between the orbital plane and the plane of the sky, and the longitude of periastron, defined as the angle between the ascending node and the
periastron measured in the plane of the true orbit and taken in the direction of the secondary's motion. All the orbits appear prograde on the
sky. The last line, labelled ``Straight Line'', shows the # 2 for the best straight­line fit.
Fit M 1 (M # ) M 2 (M # ) Major axis (AU) e P(yr) # i # # 2
(a) 1.6 1.0 164.2 0.90 462.7 31 0.3 344 1.32
(b) 4.0 2.5 58.8 0.90 62.7 33 0.4 14 1.37
(c) 4.0 2.5 117.9 0.31 178.0 48 70 300 1.34
(d) 4.0 2.5 206.3 0.69 412.1 243 70 63 1.15
Straight Line 1.56
and extending some 40 AU in K or 100 AU in L. Haas et al.
(1997) later obtained 1­D specklegrams at J, H, K and L with a
larger 3.5 m telescope. Their specklegrams were also oriented
north­south and east­west. Mostly on the basis of the relative
halo brightness at J and H, they rejected the disk hypothesis of
Kataza &Maihara (1991) and argued instead for a bipolar neb­
ula with east­west orientation. They also considered a possible
binary interpretation, noting that a binary with position angle
45 # or 135 # , separation <0. ## 1 and brightness ratio 0.08 at K or
0.2 at L was not ruled out by their data.
Elias 1 is unusual for HAeBe stars in being an X­ray source
(Zinnecker & Preibisch 1994). Giardino et al. (2004) observed
a strong X­ray flare from the system, and also smaller X­ray
variations which could be identified as originating on Elias 1
and not the companion Elias 1 NE. Spectral fits with a two
temperature model suggested a hot component of around kT #
2#3 keV. The time variability, and the hot plasma temperature,
point to magnetically confined plasma in the neighbourhood of
the star. Elias 1 is also a radio source, although its rising spec­
trum, though steep, is consistent with thermal emission from a
wind (Skinner et al. 1993).
Our data show that Elias 1 is a close binary with a separa­
tion of approximately 50 mas and position angle approximately
50 # (Fig. 4). Furthermore, the relative position of the secondary
with respect to the primary has changed in the seven years be­
tween the two observation epochs. The positions and flux ratios
are given in Table 1 and are shown in Fig. 5.
The binarity of Elias 1 is important for the interpretation of
the X­ray flux observed from this object. HAeBe stars should
lack the convective zone necessary to drive a conventional dy­
namo. Novel dynamo mechanisms have been developed to ex­
plain HAeBe activity, such as the di#erential rotation dynamo
model of Tout & Pringle (1995). Also, it has been suggested
that deuterium burning in a shell outside a radiative core powers
a surface convective layer (Palla & Stahler 1990). Such mod­
els are of course not necessary if a low­mass companion is in
fact the source of the X­ray emission. The spectral type of A6
and luminosity of Elias 1 suggest, from comparison with tracks
(Palla & Stahler 1993), that its mass is of order 2#2.5 M # .
The flux ratio of the system suggests a companion mass of
1.5#2 M # , which lies close to the boundary between fully ra­
diative and partially convective stars. Therefore, it is possible
that the companion has a normal convection­generated mag­
netic field and corona and is the source of the X­ray emission.
­12 ­8 ­4 0 4 8 12
cycles/arcsec
­12
­8
­4
0
4
8
12
cycles/arcsec
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2 4 6 8 10 12
Visibility^2
cycles/arcsec
visibility^2
cosine fit
Fig. 4. Top: the 2d power spectrum of Elias 1 from 2003.76. Bottom:
a cut across the fringes, with a cosine fit.
3.3. HK Ori
3.3.1. The data
HK Ori (# = 05 h 31 m 28. s 04, # = +12 # 09 # 10. ## 3, J2000) is an
A5 type star with AV = 1.2. It was found to be a binary by
LRH97, who designated the brighter NIR component to the
southwest A and the fainter northeastern component B. LRH97
found a binary separation of (0.34 ± 0.02) ## and position angle
(41.7 ± 0.5) # . Contour maps of the system in bands V , H and
K are shown in Fig. 6, together with 3­d plots illustrating the
brightness ratio. The track of component Bwith respect to com­
ponent A is shown in Fig. 7. Our data points trace a path from
southeast to northwest. The radial position of LRH97 is broadly

314 K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori
100 0 ­100
rel. position [mas]
­100
0
100
rel.
position
[mas]
100 0 ­100
rel. position [mas]
­100
0
100
rel.
position
[mas]
Fig. 5. Top: contour map of Elias 1 made from the 2003 observations.
Bottom: the position of the Elias 1 companion relative to the primary.
The primary position is marked with a dot.
consistent with our measured positions, but the azimuthal posi­
tion is not in agreement with the position suggested for epoch
1992.12 from our data.
Following LRH97, we can use our flux measurements to
disentagle the SEDs of the individual components of HK Ori.
LRH97 used observations at wavelengths of I # (0.917 #m), J,
H, and K, and had to rely on flux ratios alone. We have data
at four di#erent wavelengths, 550 nm (V), 656 nm (R), as
well as H and K. The optical points were not available to
LRH97, and we are therefore able to separate the SEDs of
the components over a significantly wider wavelength range.
Furthermore, our data is photometrically calibrated (except for
the 2003 point which we do not use in this analysis). There
remains the problem that our measurements are not simulta­
neous. However, independent measurements in October, 1997
show that the V­magnitude was the same as during our earlier
observations in 1995 (V = 11.7 ± 0.1 derived from speckle
observations in 1995, V = 11.6 ± 0.1 in 1997, Mel'nikov pri­
vate communication). This indicates that the system was in a
comparable state at both epochs and that it is therefore valid to
combine our data into one SED.
In Fig. 8 we present the separated SED (along with vari­
ous models described in Sect. 3.3.2). SEDs for the whole sys­
tem were taken from Hillenbrand et al. (1992) and Berrilli
et al. (1992). An upper limit at 1.3 mm was taken from
Henning et al. (1997). The error bars for U, B and V reflect
the measured variability as reported by Eiroa et al. (2002) in
the V­band. For R through K the measurement uncertainty was
used (typically of order 10%), and for wavelengths longer than
2.2 #m, an assumed 10% uncertainty was adopted.
The SEDs of the individual components A and B are con­
structed from points measured by us at V , R, H, and K, and
points measured by LRH97 at I J , J, H and K. Our points are
calibrated as described in Sect. 2. LRH97 obtained flux ratios
but not absolute fluxes. We therefore normalised their values
against the total flux given by Hillenbrand et al. (1992). In the
case of LRH97's I J point, the Cousins system flux of the com­
posite SED was converted to a supposed Johnson system I flux
using the information given in Bessell (1983).
All fluxes were corrected for the e#ect of interstellar red­
dening. The visual extinction, AV = 1.2 was determined by
Hillenbrand et al. (1992) from the (B # V) excess. The extinc­
tion law given by Cardelli et al (1989) was used to estimate the
wavelength dependency of the extinction, with the assumption
that R V = 3.1.
The SED is clearly dominated by component A (which
we designate the primary) at longer wavelengths. The bright­
ness ratio moves towards unity in the very near­infrared (I and
J bands). LRH97 considered one possible scenario in which the
brightest infrared component, A, might in fact be a low­mass IR
companion, and the fainter component the primary. This con­
jecture was apparently confirmed by Baines et al. (2004) who
used a spectroastrometry technique to show that the southwest­
ern component dominates the emission at H#, Their data also
suggested that the northeastern component might be the bright­
est optical source in the system. However, our data points at
550 nm and 656 nm now exclude this possibility, and show
clearly that the brighter IR component to the southwest also
dominates in the optical (see top panel of Fig. 7). Variability
of the T Tauri source is a possible but not convincing explana­
tion for this discrepency, since the photometrically calibrated
flux of component A matches the composite SED published
in Hillenbrand et al. (1992), whereas the flux of component B
does not.
The infrared colours of the two components are very dif­
ferent. The brightest component has H # K = 2.12, whereas
component B has H # K = 1.10. The implication is that com­
ponent A possesses significantly more circumstellar material
than component B, which resembles a naked photosphere of
around 4000 K. The positions of the two objects are shown
in a colour--colour diagram in Fig. 9. Comparing this figure
to colour--colour diagrams of young stars, for example Fig. 15
of Hillenbrand et al. (1992), it is clear that the primary (com­
ponent A, to the southwest) occupies a typical position for
an intermediate mass young star, whilst the companion (com­
ponent B, to the northeast) occupies a position typical for a
T Tauri star.
We have fitted a 4000 K photosphere, corresponding to a
mid­K spectral type, to the SED of component B. This fit rep­
resents the SED of component B very well, with the possible
exception of the B­band point. Where no resolved points were
available, we have subtracted this fit to determine points for A.
In practice, this model subtraction makes little di#erence to

K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori 315
600 400 200 0 ­200 ­400 ­600
rel. position [mas]
­600
­400
­200
0
200
400
600
rel.
position
[mas]
600 400 200 0 ­200 ­400 ­600
rel. position [mas]
­600
­400
­200
0
200
400
600
rel.
position
[mas]
600 400 200 0 ­200 ­400 ­600
rel. position [mas]
­600
­400
­200
0
200
400
600
rel.
position
[mas]
N
E
550nm/60nm; 1995.183; ESO/MPG 2.2m
B
A
­600 ­400 ­200 0 200 400 600
rel. position [mas]
­600
­400
­200
0
200
400
600
rel.
position
[mas]
­600 ­400 ­200 0 200 400 600
rel. position [mas]
­600
­400
­200
0
200
400
600
rel.
position
[mas]
­600 ­400 ­200 0 200 400 600
rel. position [mas]
­600
­400
­200
0
200
400
600
rel.
position
[mas]
N
E
H­band; 1997.799
­600 ­400 ­200 0 200 400 600
rel. position [mas]
­600
­400
­200
0
200
400
600
rel.
position
[mas]
­600 ­400 ­200 0 200 400 600
rel. position [mas]
­600
­400
­200
0
200
400
600
rel.
position
[mas]
­600 ­400 ­200 0 200 400 600
rel. position [mas]
­600
­400
­200
0
200
400
600
rel.
position
[mas]
N
E
K­band; 1997.799, SAO 6m
Fig. 6. Bispectrum speckle interferometry reconstructions of HK Ori. Contour plots on the left show the relative positions of the sources and
wire­frame plots on the right illustrate the relative brightnesses. The components A and B are identified in the topmost contour plot.
most of the fluxes measured for the composite system, and this
method is nearly equivalent to assuming that component A con­
tributes essentially all the flux at U, B and in the mid­infrared.
3.3.2. Modelling strategy
Component A is responsible for most of the IR­excess of the
system and presents a ``double­bumped'' SED. The first bump
peaks around 400nm and is produced by the central A­type
star. The second one, peaking around 3 #m, is a signature of the
presence of circumstellar matter and is usually interpreted as
emerging from an accretion disk (e.g. Hillenbrand et al. 1992).
Let us emphasise that the NIR­ and MIR­excesses are un­
usually strong for a Herbig star, with a flux intensity #F # peak­
ing as high as the stellar photosphere (see Fig. 8) while it is
one order of magnitude smaller in most HAeBes (see Fig. 1 in

316 K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori
Fig. 7. The position of the HK Ori companion B relative to the pri­
mary. The separate optical positions from 1995 and separate H and
K positions for epoch 1997.8 have each been averaged to produce one
position for each date. The solid line is a circle of radius 155 AU for
an assumed distance of 460 pc centred on the primary.
Natta et al. 2001). Making a simple three blackbody fit, we esti­
mate that the circumstellar flux accounts for fully two thirds of
the observed flux from component A. The low visual extinction
(AV = 1.2) hints that the star is not significantly shadowed by
circumstellar material, so that the circumstellar matter actually
emits twice as much flux as the star in the observer's direction.
Higher values of AV for the photosphere can be considered if
the extinction law is taken to be non­standard (R V # 5 leads to
AV # 3 for the measured E(B# V)), but we feel this is unlikely
since the the derived extinction is in agreement with the extinc­
tion from interstellar matter measured for nearby Herbig­Haro
objects (Goodrich et al. 1993). Though the reprocessing of stel­
lar light is widely accepted to be the main source of energy in
typical HAeBes (Chiang & Goldreich 1997; Natta et al. 2001;
Dullemond et al. 2001), it seems unable to account for so high
a IR­excess: an optically thin envelope would reprocess only a
fraction # # 1 of the stellar light, and an optically thick disk
#h/r # 0.05--0.5, where h is the thickness of the disk, and r
the distance to the star. So, we follow Hillenbrand et al. (1992)
in their assumption that viscous heating (i.e. accretion lumi­
nosity) is responsible for most of the observed flux. We use a
generalised version of the Chiang & Goldreich (1997) model
by Lachaume et al. (2003), that includes viscous dissipation in
addition to stellar irradiation, to fit the SED. Our approach has
the advantage of not excluding a priori the hypothesis of an ir­
radiated disk.
The fitted parameters are summarised in Table 3, and the
SED data and fit are displayed in Fig. 8. The large IR ex­
cess at # # 2 #m cannot be explained with irradiation only
(dash­dotted line in Fig. 8) and requires a high accretion rate
—
M = 2.5 â 10 #6 M # yr #1 (solid line). The depression in the
SED around 1 #m suggests that the inner, hot regions of the
disk should be depleted. which our model backs: the inner rim
of the disk is located at 31 R # = 20 R # = 0.15 AU from the star.
On one hand, the accretion rate and outer disk truncation
radius are in good agreement with those derived by Hillenbrand
et al. (1992). This could be expected, since these parameters
are sensitive to the mid­ and far­IR SED that was not a#ected
by our resolving the binary. On the other hand, the visible and
NIR SED for component A significantly di#ers from that of the
total system, so that our estimates for the stellar photosphere
(derived from the visible photometry) and the inner truncation
(sensitive to the depression at 1 #m) are quite di#erent from
their values.
3.3.3. Disk properties
The model was computed with the viscosity coe#cient # =
2 â 10 #2 (see Shakura & Sunyaev 1973), but choosing any #
above 10 #3 does not greatly a#ect the quality of the fit. The up­
per limit at 1.3 mm constrains the amount of material at larger
radii, and the mass of the disk is limited to about 0.06 M # .
Combined with the high accretion rate, this estimate leads to a
lifetime of the disk between a few 10 4 and a few 10 5 years, i.e.
less than the typical age of HAeBe stars. On one hand, the life­
time may be extended by replenishing of the disk with material
from some wider reservoir. The scenario of a circumbinary disk
is unlikely, since material with high angular momentum should
accrete on to the secondary instead of the primary, at least in
a coplanar system. This favors the hypothesis of mass infall
from a spherically symmetric envelope. This envelope should
however comprise at least a few solar masses, implying a sig­
nificant reddening, which is not observed. On the other hand,
HK Ori could be in a transitory high­accretion state of an oth­
erwise ``quiescent'', passive accretion disk.
More concerning is the presence of a large central gap
(20 R # ) in an intensively accreting disk. As pointed out by
Hartmann et al. (1993), a strongly accreting disk should not
present such a gap: the gap is either understood as a drop in
optical thickness beyond the dust sublimation radius, or as a
cleared region due to stellar magnetic fields which drive the
matter into accretion streams or into an outflow. However, the
large amount of material in this disk would ensure that the gas
remains optically thick, whilst the field strength required to
truncate the disk at 20R # would be of order tens of kilogauss.
Though these arguments plead for a moderately accreting disk,
we were not able to find a mechanism other than accretion that
could account for the very large IR­excess. In particular, the
reprocessing of the stellar light leads to IR fluxes of up to a
few tens of percent of that of the star, as previous simulations
by Chiang & Goldreich (1997) and Dullemond et al. (2001)
suggest.
3.4. V380 Ori
V380 Ori (# = 05 h 36 m 25.43 s , # = #06 # 42 # 57.7 ## , J2000) is a
B9 star in the Orion complex at a distance of 460 pc. It was
classified as a group I source by Hillenbrand et al. (1992),
meaning that its SED can be fitted by a geometrically thin,
optically thick accretion disk.

K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori 317
data for HK Ori A
this work
Leinert et al. (1997)
from A+B data
data for HK Ori B
this work
Leinert et al. (1997)
disc models for HK Ori A
irradiation + viscous heating
viscous heating only
irradiation only
model for HK Ori B
photosphere
1.0 10.0 100.0 1000.
10 -16
10 -14
10 -12

(µm)

F

(W.m
-2
)
Fig. 8. The SED of HK Ori's components. Data: open symbols stand for the primary and filled ones for the secondary. Separate photometric
measurements for HKOri A and HKOri B from this work are marked with squares. Flux ratios measured by LRH97 and normalised to separate
fluxes by reference to the composite photometry of Hillenbrand et al. (1992) are marked with triangles. For other points (diamonds), we have
subtracted the model fit to HK Ori B from the total system flux as measured by Hillenbrand et al. (1992) to obtain supposed values for the flux
of HK Ori A. We also show the 1.3 mm upper limit obtained by Henning et al. (1998), also with the flux of the HK Ori B model subtracted.
In U, B, and V , the uncertainties result from the reported variability. At NIR wavelengths, the measurement uncertainties are of order 10%
and are not plotted for the sake of clarity. Model for HK Ori A: a two­layer disk model by Lachaume et al. (2003), including irradiation by
the central star and heating by viscosity fits the data very well at all wavelengths (solid line). For comparison's sake similar models, in which
irradiation or viscous heating is turned o#, are displayed (dashed line is without irradiation and dash­dotted line is without viscous heating).
Model parameters are shown in Table 3. Model for HK Ori B: the SED of the secondary does not hint at an infrared excess, so a photosphere
model is fit to the data (dotted lines). It should be noted that excess emission from distant reprocessing material cannot be ruled out.
The system was resolved as a #150 mas binary by LRH97.
They attempted to divide the SED of the system into the con­
tributions of the two components. As with HK Ori, they con­
sidered two models; one in which the brightest source in the
IR continues to dominate in the optical, and one in which the
brighter IR source is an ``IR companion'' which is less bright
in the optical. Millan­Gabet et al. (2001) used long­baseline in­
terferometry to resolve V380 Ori A. Their uniform ring model
fit had an inner radius of 2.5 mas, corresponding to just over
1 AU.
In Fig. 10 we show a contour plot of the V380 Ori sys­
tem, and a plot of the position we obtained for the secondary in
2003, together with the position obtained by LRH97.
Based on the data presented, it would appear that there has
been orbital movement of the V380 Ori system. The relative
position of the secondary has changed by about 26 AU. This
apparent shift has been largely in a tangential sense, as can
be seen by comparison with the circle segment shown in the
figure.
The flux ratio at K # is measured by us to be 0.266 ± 0.008,
whereas LRH97 obtained 0.35 ± 0.08. These values are almost
compatible with each other to within 1#. Unfortunately, unlike
in the case of HK Ori, we have no optical observation and so
cannot resolve the ambiguity considered by these authors in the
SEDs.
4. Conclusions
We have used bispectrum speckle interferometry to resolve
for the first time the binary companions to the HAeBe stars

318 K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori
Fig. 9. (H#K) vs. (J#H) colour--colour diagram showing the positions
of the primary and secondary in the HK Ori system. Component A is
shown with a circular point and component B with a triangle. The
colours have been corrected for the e#ects of interstellar reddening.
The main sequence (from Bessell & Brett 1988) and the direction of
interstellar reddening are also shown.
Table 3. Fitted parameters for HK Ori. A disk mass of 0.06 M # is de­
rived from these parameters. The parameters obtained by Hillenbrand
et al. (1992) are given in italic when available.
Component A
stellar radius (R # ) 1.55 1.7 d
stellar mass (M # ) 2.0 2.0 d
stellar temperature (K) 8500 9700 d
Component B
stellar radius (R # ) 4.1
stellar mass a (M # ) 1.0
stellar temperature (K) 4000
Disk around A
disk inner radius (R # ) 31 17
disk outer radius (AU) 30 29
accretion rate (M # yr #1 ) 2.5 â 10 #6 1.7 â 10 #6
# 0.02 ---
disk inclination a (deg) 0 0
distance b (pc) 460 460
a Kept constant.
b Assumed.
c Derived from simulation.
d Both components.
LkH# 198 and Elias 1. We also resolved the known binaries
HK Ori and V380 Ori. In the case of LkH# 198, the new ob­
ject lies at a separation of approximately 60 mas, or 36 AU
from the brighter component. Our observations comprise seven
data points taken at intervals of approximately one year over a
seven year time period. Motion of the secondary with respect
to the primary is seen and the path is suggestive of an arc, al­
though a straight line cannot be excluded. Because the com­
panion may well have an important e#ect on the interesting
and well­studied circumstellar environment of LkH# 198, we
have fitted several possible orbits to these points and shown
200. 100. 0. ­100. ­200.
rel. position [mas]
­200.
­100.
0.
100.
200.
rel.
position
[mas]
200. 100. 0. ­100. ­200.
rel. position [mas]
­200.
­100.
0.
100.
200.
rel.
position
[mas]
1" 2.12 µm
Fig. 10. Top: contour plot of the V380 Ori system. Bottom: position
of the V380 Ori companion relative to the primary. The solid line is
a circle of radius 60 AU centred on the primary. The data point of
LRH97 is shown with an open diamond. This position was obtained
by LRH97 from data taken over a period of 3 years. Our data point is
marked with a filled symbol.
that the plane of the orbit cannot be viewed exactly edge­on
with an exactly east­west orientation. This may imply that the
binary is not coplanar with the inferred disk powering the out­
flow. The flux ratio of the Elias 1 system indicates that the new
companion has a mass of around 2 M # and therefore may be a
convective star. This opens the possibility that the X­ray emis­
sion of Elias 1 originates from the companion and is powered
by conventional mechanisms. The SED of HK Ori was sepa­
rated into the contributions of the primary and secondary com­
ponents. The IR excess of HK Ori A was found to contribute
around two thirds of the total emission from this component,
suggesting that accretion power contributes significantly to the
flux, in contrast to most HAeBe stars whose SEDs can often
be well fitted with passive disks. We fitted an accretion disk
model to the HK Ori A SED and determined the accretion rate
and disk mass. From these parameters, the inferred disk life­
time is found to be quite short compared to the suspected age
of HK Ori. It is possible that the disk could be replenished
from a wider reservoir of material, but there are problems with
such a picture; a spherical envelope should lead to extinction
which is not observed, whilst in a coplanar system, accretion

K. W. Smith et al.: Close binary companions of the HAeBe stars LkH# 198, Elias 1, HK Ori and V380 Ori 319
from a disk should proceed preferentially onto the secondary.
Another explanation could be that the HK Ori disk is seen
in an outburst phase. Such a phase need not a#ect the outer
disk, so that the accretion rate may not be uniform through­
out. Our relative positions for this system trace a path over the
eight years of observations which may be the segment of an
orbit. Future near­simultaneous multi­wavelength high resolu­
tion observations will allow a more detailed picture of the disk.
High­resolution observations in the mid­infrared could deter­
mine whether or not component B has a passive disk. Further
observations of all four stars will be necessary to build up re­
liable orbit determinations. LkH# 198 in particular should be
a fascinating subject for future study from this point of view,
since the close binary companion may be responsible for much
of the complexity in the circumstellar environment of this sys­
tem.
Acknowledgements. We would like to thank the anonymous referee
for constructive comments which have helped us to improve the
manuscript.
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