Issue |
A&A
Volume 514, May 2010
|
|
---|---|---|
Article Number | A34 | |
Number of page(s) | 8 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361/201013992 | |
Published online | 07 May 2010 |
Orionis C - A triple system?
H. Lehmann1 - E. Vitrichenko2 - V. Bychkov3 - L. Bychkova3 - V. Klochkova3
1 - Thüringer Landessternwarte Tautenburg, Karl-Schwarzschild-Observatorium,
07778 Tautenburg, Germany
2 -
Space Research Institute, Russian Academy of Sciences,
117880 Moscow, Russia
3 -
Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnij Arkhyz, Zelenchuk region,
357147 Karachai-Cherkesia, Russia
Received 4 January 2010 / Accepted 26 January 2010
Abstract
Context. As the brightest star in the Trapezium cluster,
Ori C
is the youngest and nearest to us among O-stars. It is considered to be
a multiple system where the main component is an oblique magnetic
rotator.
Aims. Here, we aim at explaining the structure of the
Ori C
system. We check for a new hypothesis about the presence of a third
component and try to derive the corresponding orbital solutions and the
absolute masses of the components.
Methods. We measured new radial velocities (RVs) of
Ori C
and and combined them with data from literature. For the analysis, we
used multiple frequency search and iterative calculations of orbits
based on the method of differential corrections, applying successive
prewhitening to the data in both methods. Results are compared with
those obtained from speckle observations.
Results. We detected the impact of the known distant companion
in the RVs of the primary and can now calculate a spectroscopic orbital
solution that is consistent with the observed astrometric positions. We
find evidence that
Ori C
is at least a triple system consisting of the primary, the known
astrometric companion in a wide eccentric orbit with a period of
11 yr, and a second companion in a close eccentric orbit with a
period of 61
5. We assign the additionally found period of 15
4 d to the rotation of the primary, which is in a 1:4 resonance with the close orbit. Derived masses are 31
for the primary, 12
for the distant, and 1
for the close companion.
Key words: stars: early-type - binaries: general - stars: individual:
Ori C
- binaries: spectroscopic - binaries: visual
1 Introduction
Two of the four brightest Orion Trapezium stars, BM Ori =
Ori B and
V1016 Ori =
Ori A, are eclipsing. The
brightest star
Ori C exhibits brightness variations with an
amplitude of
= 0
06 (Kukarkin et al. 1982). Genderen et al. (1989), on the other hand,
claim that the magnitude of
this star is constant with an accuracy up to a few mmag.
Radial velocities (RVs) of the star were measured for the first time by Frost et al.
(1926) who discovered its variability. Struve &
Titus (1944) obtained a dense series of RV observations, but did not search for
variability. Sparse, but highly accurate data was obtained by Conti (1972), who concluded that the RV is constant.
Based on a dense series of precise RV measurements using
the photospheric C IV 5801 Å line, Stahl et al. (1993) conclude that it varies. The authors
did not derive an orbital solution, however. Vitrichenko (2002) analyzed the RVs measured from the IUE
spectra (Folker 1994) along with all available data from other observations. He concludes that
Ori C is a
triple system where three companions orbit its common center of mass. The periods of the two companions were
determined to about 120 yr and probably 61 or 66 days.
Stahl et al. (2008) present 206 RV measurements and convincingly show that the
RV is variable. Again, the authors do not derive an orbital solution.
Multicolor photoelectric observations of the combined stellar fluxes indicate that the observed radiation
is emitted by three sources with temperatures of 37 500 K, 4000 K, and 190 K (Vitrichenko 2000) where
the first source is the main star.
The third, cold source could be a dust cloud with emission from interstellar silicate grains, while the
second source is definitely a star located at the very beginning (near the birth line) of the track of a
15
star in the Hertzsprung-Russell diagram.
The star
Ori C exhibits a multitude of variations.
Spectral variations were discovered for the first time by Conti (1972) who observed that the
He II 4686 Å line profile varied on a time scale of a few days showing the appearance and
disappearance of a blue-shifted emission line component. A systematic variation in the spectral class of the
star from O6 to O4 within seven days was observed by Walborn (1981). Stahl et al. (1993)
studied the H
emission component and discovered its variability with a 15
4 period. Walborn &
Nichols (1994) discovered the variability in the C IV 1548 and 1550 Å line profiles with
a period of (15.41
0.02) d. This period agrees with the period of the H
emission.
Gagne et al. (1997) found that the X-ray flux from the star is variable with a period of (16
4) d
which does not contradict the previously mentioned periods. The authors suggest that the variations are
caused by an oblique magnetic rotator with a large-scale magnetic field modulating the stellar wind. Babel &
Montmerle (1997) propose a dipole with a surface field strength
of at least 300 Gauss for the structure of such magnetic field.
Stahl et al. (1996) analyzed the spectrum variability of
Ori C and confirm the results by Walborn &
Nichols (1994). When investigating the behavior of the equivalent widths of the H
and
C IV 1548 and 1550 Å lines, they found a period of (
) d.They attributed this
periodicity to the rotation of the star rather than to its binary nature, however.
Strong evidence that the 15
4 period is the rotation period of
Ori C comes from
Simon-Diaz et al. (2006) who determined the
of the primary and find the value to be in good agreement with the assumed rotation period.
Based on speckle interferometry, Weigelt et al. (1999) discovered the companion
(star C2 in our designation) at an angular distance of
from the primary. The authors measured
the K-magnitude of the companion to 5
95 and its color index
H-K to 0
24. An upper limit of
was derived for the mass of the companion according
to its expected position in the Hertzsprung-Russell diagram.
The orbit of the secondary has been determined in a later work by Kraus et al. (2009) using near IR
long-baseline and speckle interferometry. The derived orbital elements imply a high-eccentric orbit (e = 0.6)
and an orbital period of 11
3. They estimate the system mass to (44
7)
and find a dynamical
distance of (410
20) pc. Comparing the RVs given by Stahl et al. (2008) with the found orbital
solution, the authors derived a mass ratio M2/M1 of 0.23.
Table 1: Journal of observations.
Table 2: Line list for the determination of the RVs of the primary.
Table 3: New RV measurements (in km s-1).1
Table 4: Fe V lines measured in the IUE spectra.
Table 5: RVs measured from the IUE spectra.
2 Radial velocities
We used the spectra received by the IUE satellite (camera SWP, Folker 1994) as listed in
Vitrichenko (2002), the data from Stahl et al. (2008), the spectra from the Elodie
Archive, the spectra received by Stetsenko et al. (2007) and kindly provided to us, and
our newly obtained spectra as described in Table 1.
The reduction of the newly obtained spectra included bias and straylight subtraction, filtering of cosmic rays, flat-fielding, optimum extraction of echelle orders, wavelength calibration using a Th-Ar lamp, normalization to the assumed local continuum, and weighted merging of orders. TLS spectra were additionally corrected for instrumental zero point shifts using a large number of telluric O2 lines in each spectrum. As a measure of the effectively achieved spectral resolution, we measured the mean half-width of the telluric lines from Gaussian fits, which is given in the last column of Table 1.
The RVs were measured by determining the positions of the spectral lines using a Gaussian fit of the line profiles. The complete line list is given in Table 2. Three of the lines, C III 5826, Si IV 6701, and O III 6508 Å, could only be measured from the TLS spectra. Table 3 lists the sources and observation dates of our spectra together with the determined RVs. They were also measured from the IUE spectra using the Fe V lines. The highest observed ionization stage is Fe V, and no line of Fe VI was observed in any spectrum. Table 4 lists the Fe V lines used. To improve the signal-to-noise ratio, all spectra were filtered using a sliding window with a width corresponding to 12 kms-1. Table 5 lists the determined RVs.
3 The orbital solution assuming one wide orbit
The orbit of the primary was calculated from the RVs given in Tables 3 and 5
and from the RVs taken from Stahl et al. (2008).
The derived period and orbital elements are listed in
Table 6, together with the orbital solution derived by Vitrichenko
in 2002.
The -velocity and
-values of both solutions coincide within the limits of errors, although
the periods are completely different. We assume that
Vitrichenko (2002) derived a multiple of the true orbital period.
These RVs are shown in Fig. 1.
The large scatter of the measured values around the
calculated curve can probably be reduced by assuming additional components in the
Ori C system.
Table 6: Elements of the spectroscopic orbit of the primary.
![]() |
Figure 1: RVs of the primary folded with the period of 10.5 yr. RVs shown by plus signs without circles have been rejected from the calculation of the orbital solution and the corresponding plotted curve. |
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According to Kraus et al. (2007), the mean ratio of the fluxes in the V band for the
primary C, and its astrometric companion C2 is
.
In this case,
the luminosities of the stars relative to the system luminosity are
,
.
The relative luminosity of the primary can be roughly determined from
where








4 The close companion C1
4.1 Frequency analysis
For the frequency analysis of the RVs of the primary we used the program
PERIOD04, together with a
successive prewhitening of the data. After each step of prewhitening, we optimized all the frequencies
found so far,
together with the corresponding amplitudes and phases, to search in the next step for other frequencies.
In this way we found significant contributions at periods of 4082, 15.416, 61.557, 30.723, and
155.33 d, corresponding to the frequencies f1 to f5 listed in Table 7 (model 1)
in the order of detection. Both f2 and f4 seem to be multiples of f3, and f1 corresponds to
the period of the wide orbit, which is known to be highly eccentric.
For these reasons we tried to establish a two-frequency model (F1, F2, see
Table 7), including
the 4082 d period and its first two
harmonics counting for the wide orbit and its eccentricity and the 61.557 d period plus its first three harmonics.
In the result the previously found 155 d period vanished and no other period could be found in
the data. Figure 2 shows the finding periodograms for F1 and F2.
![]() |
Figure 2: Periodograms (power spectra). Top: Original data, indicating F1. Bottom: After prewhitening for F1 and its harmonics, indicating F2. |
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4.2 Orbital solutions
The existence of the close companion C1 has already been suspected by Vitrichenko (2002), and two possible periods of 60.8 or 66.3 d have been suggested. We assume that F2 is related to the orbital period of such a companion. To check this assumption, we used the method of differential corrections to the orbital elements and computed optimized orbital solutions, where we iteratively prewhitened the RVs for the contributions found from the wide orbit and, vice versa, from the close orbit.
![]() |
Figure 3: Periodograms (power spectra). Top: After subtracting the contributions from the wide and close orbits, indicating the frequency of rotation. Bottom: Residuals after subtracting also the contribution due to rotation. |
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Table 7:
Frequencies and amplitudes found in the RVs of
Ori C.
Finally, we checked the residuals after subtracting both orbital solutions from the RVs for further periodicity. We found only one period, namely the 15.4 d period (Fig. 3) corresponding to f2 in Table 7. This period was also found by Stahl et al. (2008) and interpreted as the rotational period. If this holds true, the rotation of the primary must be well synchronized with the close orbit in a 1:4 resonance.
Table 8: Orbital elements including two orbits and rotation.
We extended our model accordingly, now counting for the RV contributions from the close and the wide orbit and from
the rotation of the primary. The optimized elements were calculated iteratively by prewhitening the
data for the found contributions as described above. Additionally, we checked in each step for outliers
that have been rejected using a
criterion. These outliers do not concern a special source of RVs,
but are evenly distributed over the different observational sites.
Table 8 lists the derived elements.
In the case of the RV variations due to rotation, the calculated ``orbital solution'' gives the
rotational period and RV amplitude, whereas the calculated eccentricity counts for some slight deviation
from a sinusoidal curve.
Figures 4 to 6 illustrate the results. We fixed the elements to its finally derived values
and applied the solutions to the complete data set. Then we prewhitened the RVs for two of the three contributions
and folded the resulting RVs with the period of the third one.
The difference in periods compared to those derived in Sect. 4.1 results mainly from two reasons: first, from applying two different methods, the prewhitening for two frequencies and a limited number of harmonics, and the subtraction of optimized orbits; second, from the insufficient orbital phase coverage of data with respect to the highly eccentric wide orbit (Fig. 4), which causes a high sensitivity of the orbital elements with respect to the applied method and the selection of outliers.
![]() |
Figure 4: RVs of the primary prewhitened for the C-C1 orbit and for rotation, folded with the period of the wide orbit of 10.98 years. |
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![]() |
Figure 5: RVs of the primary prewhitened for the C-C2 orbit and for rotation, folded with the period of the close orbit of 61.49 days. |
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![]() |
Figure 6: RVs of the primary prewhitened for the two orbits, folded with the rotation period of 15.42 days. |
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4.3 The close orbit
The remaining scatter in the different phase plots is still remarkable.
The 61
49 period can be regarded as an orbital period only if it is stable, i.e. if it can be found in all epochs of
observation. To check for this, we split the data (without the rejected outliers) into four subsets and did a frequency analysis
on each of them.
Table 9 lists the frequencies f and amplitudes A found both from a single frequency search and by a search for a
frequency and its first harmonic (frequency
,
amplitudes A1, A2).
and
are the number of days (range in JD) and the number of included data
points, respectively.
Whereas in most cases the search for the dominating single frequency
does not reproduce the previously derived orbital period, including
the first harmonic that counts for the high eccentricity let us find
this period in all the data sets. The resulting amplitudes
vary strongly, however. The reason for this can be seen from the
orbital phase diagrams plotted for the four subsets
in Fig. 7, based on the derived orbital solution as listed in Table 8.
Subset 1 shows a convincing phase diagram, and it is the only one that reproduces the orbital frequency directly. The other
three subsets contain fewer data points, not enough with respect to the highly noisy data to allow for such a
finding without counting for the non-sinusoidal shape of variation.
![]() |
Figure 7: RVs of the primary prewhitened for the C-C2 orbit and for rotation, folded with the period of the close orbit of 61.49 days. Mean JD of 2 448 970 (top left), 2 449 590 (right), 2 451 370 (bottom left), and 2 454 620 (right). The solid curves correspond to the solution for the C-C1 orbit as listed in Table 8. |
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![]() |
Figure 8:
Mean deviation
|
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Table 9: Results of the frequency search in four subsets prewhitened for the wide orbit and for rotation for different mean epochs of observation.
In a next step, we applied a running mean to the residuals after subtracting all the solutions
from the observed RVs, using a bandwidth of 200 d.
Figure 8 shows the result. From a linear regression (solid line in
Fig. 8), we obtain an increase of the -velocity by 0.26 km s-1 y-1 on average. Taking
the slight increase in the frequency
with the epoch of observation that can be seen from Table 9
into account, we
checked for a possible variable period of
the close orbit allowing for a linear trend in period length in the
calculation of differential corrections to the orbital elements.
We obtained a rate of period decrease of (
) min y-1. Because of the large error and because
the scatter of the residuals of the orbital solution is downsized by the new solution by less than 1%, we argue
that both the trend in
and the trend derived from the orbital solution are non-significant.
Because of the influence of the third body C2 in its highly eccentric
orbit, an advance of the apsidal line of the close orbit could also be a possible
source of the observed scatter. Thus we checked for apsidal motion in the
complete set of RVs of the primary by allowing for a linear trend in
in the differential corrections to the orbital elements. We obtained a rate of
(
)
yr-1 for the apsidal advance. We do not think that this is a significant finding, not only because there is the large
error but also because the scatter of the residuals of the
new solution was reduced by only 1% compared to the previous one. Observations
on a longer time base and high-accuracy RV measurements are necessary for appropriate studies.
5 The distant companion C2
In the astrometric solution derived by Kraus et al. (2009) from VLT/Amber and speckle observations,
the orbital period P and the elements T and e are found from a grid search or from some nonlinear
optimization method to minimize the
of the solution. From these three parameters, normalized
coordinates are obtained from which the Thiele-Innes elements can be derived by a linear regression
with the observed rectangular coordinates (Hartkopf & McAlister 1989). All other
orbital elements like
,
,
i, and a can then be directly computed from the
Thiele-Innes elements (Heintz 1978).
We used our spectroscopically obtained P, T, and e with the astrometric positions observed by Kraus et al. (2009) to do the same. Table 10 compares the results with those from Kraus et al. (2009). Based on the good agreement, there should be no doubt that the RVs measured from the lines of the primary reflect the orbit with its astrometric companion. Figure 9 shows the astrometric orbit calculated from our orbital elements and compares it with the speckle positions measured by Kraus et al. (2009).
Table 10: Elements of the astrometric orbit obtained from our spectral analysis (first row) and by Kraus et al. (2009).
![]() |
Figure 9:
Speckle positions of
|
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6 Absolute parameters
In Table 8 we gave the mass functions and projected
semi-major axes calculated from
f(M) | = | ![]() |
|
![]() |
= | ![]() |
(2) |
where K is in km s-1, P in d, and a in AU. The large errors of the obtained mass functions of 30% for the C-C1 orbit and 60% for the C-C2 orbit mainly result from the insufficient accuracy in determining the eccentricities and K-values of the orbits.
In the following we assume that the components C, C1, and C2 of
Ori C build a hierarchical system where the
components C and C1 of the close system orbit around their center of mass and that this center, representing the
total mass of C1 plus C2, orbits with C2 around the center of mass of the wide system.
6.1 The distant companion C2
Kraus et al. (2009) determined a dynamical mass of the
Ori C system of (44
7)
.
By combining
this, the known inclination of the C-C2 orbit (Table 10), and
the spectroscopic mass function of C2 (Table 8),
we can derive the mass of C2 to (
)
.
I follows that he mass of C+C1 is
(
)
and the mass ratio between C2 and C+C1 is
.
The latter value agrees with the value of
derived by Kraus et al. (2007) by modeling the wavelength-dependent binary flux ratio of the
Ori C system, whereas
Kraus et al. (2009) determine
by analyzing the RVs from Stahl et al. without applying
any cleaning for additional components.
Kraus et al. (2009) estimate a dynamical distance of
Ori C of (
) pc, in agreement with
the value of 414 pc given by Menten et al. (2007). From this distance and a=44 mas (Table 10),
the semi-major axis of the relative orbit follows to 18 AU. The spectroscopically derived value of the semi-major axis of
the orbit of the primary is of 5 AU (Table 8). The deduced mass ratio of 0.45 gives a semi-major axis of
the relative orbit of a=17 AU, in good agreement with the astrometric value.
6.2 The close companion C1
From the mass function of C1 of
(Table 8) and the mass of C+C1 of
(
)
we obtain a projected mass (or lower limit) of C1 of (
)
so that
an upper limit of (31
3)
follows for the mass of the primary. This gives a mass ratio of
.
With this mass ratio and the projected semi-major axis of the primary of (
) AU
(Table 8), the projected semi-major axis of the relative orbit follows to (
) AU.
The projected values are very close to the absolute values if we assume that the C1 and C2 orbits are coplanar
(
). In this case the close companion would be a solar mass star revolving around the primary in a
highly eccentric orbit, and the smallest distance between the components during periastron passage would be (
) AU.
6.3 The rotational period of the primary
Our model assumes that the period of 61











Assuming that the rotation axis of the primary is aligned with the orientation of the wide orbit (
),
= 15
417, and R = 11
,
we get
= 36 km s-1, a value that corresponds to the order of values
obtained by Simon-Diaz et al. (2006) from the FWHM method.
On the other hand, if we reject the hypothesis that the found 61
5
period and its harmonics arise from RV variations caused by
orbital motion because of the unlikely high eccentricity, we have to
ask for some physical process that acts on this time scale. In that
case, the 61
5 period and all its observed harmonics have to be assigned to the same process - the 15
4 period cannot be the
rotation period anymore.
A nearby assumption would be that the 61
5 period itself is the rotation period and its harmonics describe
surface or near-to-surface inhomogeneities. In that case, however, the
should be smaller than 9 km s-1 for
R = 11
or, in case of
= 24 km s-1, the radius of the primary should be larger than 29
.
Neither is compatible with the observations.
7 Conclusions
By combining new RV measurements of
Ori C with data from the literature, we deduced two fundamental periods of 11 yr and 61
49.
The first one is the period of the wide orbit with the known
astrometric companion. The second one occurs with
significant contributions from its first and third harmonics. By
cleaning the RVs for the shorter fundamental period and its harmonics,
we were able to derive an improved orbital solution
for the wide orbit that can reproduce the observed astrometric
positions. By combining the astrometric and spectroscopic findings,
we derived the absolute masses of the primary of (32
3)
and of its companion of (12
3)
,
corresponding to a mass ratio of 0.41
0.12. This mass ratio is significantly greater than estimated by
Kraus et al. (2009) from the uncleaned RVs measured by Stahl et al. (2008) but agrees well with the
value of 0.45
0.15 derived
by Kraus et al. (2007) from modeling the wavelength-dependent binary flux ratio of the
Ori C system. All other derived
system parameters agree with the astrometric findings.
Assuming that the second period of 61
49 is the orbital period of a close companion, we end up with an eccentric orbit of
e = 0.49. In this case, the third harmonic, 15
42,
can be found again in the residuals after subtracting the solutions
for the close and the wide orbit, and we assign it to the rotation of
the primary that is in a 1:4 resonance with the orbital period.
The interpretation of the 15
42 as the rotational period agrees with Stahl et al. (2008) who found this
period without counting for the 61
49 period and with the
measurements by Simon-Diaz et al. (2006).
The high eccentricity of the close orbit causes some doubt about our interpretation of the 61
49
as an orbital period because
one normally expects that the tidal forces of the much more massive
primary should have circularized the orbit. We therefore had a closer
look at the observational data with respect to the close orbit C-C1.
The analysis of separated subsets of RVs showed that the period of 61
49
can be found in each of them and that the data are compatible with the
derived orbital
solution in each epoch of observation. On the other hand, this analysis
was hampered by the fact that in most of the subsets the number
of data points and its distribution in time were not sufficient to come
to a precise conclusion about the behavior of the scatter of
the RVs around the orbital solution. It seems, however, that this
scatter is more or less evenly distributed over all epochs of
observation. In the residuals there remains a trend of increasing
velocity with time. We tried to explain it by a decrease in the
period of the C-C1 orbit but could not get significant results.
Presently, we cannot definitely say if the interpretation of the 61
49
period as an orbital period is correct. Either the close companion
exists and the RVs are distorted by photospheric or magnetospheric
activity or we observe the effects of such activity on different
time scales with some underlying quasi-periodicity with a typical time
scale of 61
49. In the latter case, the existence of the 15
42 period
can hardly be explained as the rotational period, it will be simply an overtone of the basic time scale of 61
49. We can exclude
61
49 as the rotational period because it is not compatible with the
as measured by Simon-Diaz et al. (2006).
However, there are a lot of findings that favor the 15
42 period as the rotational period. It is compatible with the measured
,
and with the suggested model of an oblique magnetic rotator for
Ori C (Stahl et al. 1996) that is also agrees
with the X-ray observations. Based on observations with the ROSAT satellite, Gagne et al. (1997) came to the conclusion that
the observed X-ray variability can be explained either by an
absorption of magnetospheric X-rays in a corotating wind or by magnetosphere eclipses. Both explanations assume a very extended
magnetosphere of the star and are based on the 15
42 period.
Assuming that our model of a triple star is valid and that the
close and wide orbits are coplanar, we end up with absolute masses of
the
primary of (31 3)
and of the close companion of (1.01
0.16)
.
The semi-major axis of the
close orbit is of (0.82
0.26) AU.
Although the scatter in the residuals of the orbital solution could be reduced by cleaning the RVs for the 61
49 period
and, independent of its nature, for its harmonics, the remaining scatter exceeds the estimated errors of measurement. An
apsidal advance of the close orbit due to the tidal interaction with the distant companion could be excluded as the main
reason for this scatter. On the other hand, its detection could help to confirm the assumed structure of a triple system.
The still too short time base of our observations and the RV variations of
Ori C caused by additional processes prevent us
from a certain statement, however.
The Nyquist frequency of the time sampling of our data is about 0.5 c d-1. Up to this frequency, we can exclude additional RV variations due to strongly periodic processes. We assume that the remaining scatter in the residuals comes from quasi-periodic as well as from irregular variations on different time scales. We do not want to speculate about the underlying processes based on our observations in the visual range but refer to the model by Babel & Montmerle (1997) derived from the X-ray variability and to the wide range of effects that can be expected from the interaction of the large-scale, oblique, magnetic field with the stellar wind.
The star
Ori C
has been studied for about 90 years and about a hundred of papers have
been dedicated to it. However, lines of the satellites could not be
detected in its spectrum until now. It seems that there is no
chance to detect the lines of the assumed close companion. The light
contribution of a one solar mass star compared to that of the
30 times more massive primary should be negligible, at least in the
visual range. Although we have so far not found any contribution from
the distant companion in the spectra of
Ori C, the V-band flux ratio of 0.32 deduced by Kraus et al. (2007)
let us
hope to find such lines in the future, based on the actual findings and
by applying more advanced methods of spectral decomposing
like KOREL (Hadrava 1995,2006).
We are grateful to V. Tsymbal and I. Bikmaev for useful discussions and to J. Lancaster, E. Brevnova, A. Serber, N. Bondar, and Z. Scherbakova, who supported us in preparing this paper. We want to thank the referee, O. Stahl, for his useful comments that helped us to improve the article.
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Footnotes
- ...
Archive
- http://atlas.obs-hp.fr/elodie/common.css
- ... PERIOD04
- Copyright (©) 2004-2008 Patrick Lenz, Institute of Astronomy, University of Vienna
All Tables
Table 1: Journal of observations.
Table 2: Line list for the determination of the RVs of the primary.
Table 3: New RV measurements (in km s-1).1
Table 4: Fe V lines measured in the IUE spectra.
Table 5: RVs measured from the IUE spectra.
Table 6: Elements of the spectroscopic orbit of the primary.
Table 7:
Frequencies and amplitudes found in the RVs of
Ori C.
Table 8: Orbital elements including two orbits and rotation.
Table 9: Results of the frequency search in four subsets prewhitened for the wide orbit and for rotation for different mean epochs of observation.
Table 10: Elements of the astrometric orbit obtained from our spectral analysis (first row) and by Kraus et al. (2009).
All Figures
![]() |
Figure 1: RVs of the primary folded with the period of 10.5 yr. RVs shown by plus signs without circles have been rejected from the calculation of the orbital solution and the corresponding plotted curve. |
Open with DEXTER | |
In the text |
![]() |
Figure 2: Periodograms (power spectra). Top: Original data, indicating F1. Bottom: After prewhitening for F1 and its harmonics, indicating F2. |
Open with DEXTER | |
In the text |
![]() |
Figure 3: Periodograms (power spectra). Top: After subtracting the contributions from the wide and close orbits, indicating the frequency of rotation. Bottom: Residuals after subtracting also the contribution due to rotation. |
Open with DEXTER | |
In the text |
![]() |
Figure 4: RVs of the primary prewhitened for the C-C1 orbit and for rotation, folded with the period of the wide orbit of 10.98 years. |
Open with DEXTER | |
In the text |
![]() |
Figure 5: RVs of the primary prewhitened for the C-C2 orbit and for rotation, folded with the period of the close orbit of 61.49 days. |
Open with DEXTER | |
In the text |
![]() |
Figure 6: RVs of the primary prewhitened for the two orbits, folded with the rotation period of 15.42 days. |
Open with DEXTER | |
In the text |
![]() |
Figure 7: RVs of the primary prewhitened for the C-C2 orbit and for rotation, folded with the period of the close orbit of 61.49 days. Mean JD of 2 448 970 (top left), 2 449 590 (right), 2 451 370 (bottom left), and 2 454 620 (right). The solid curves correspond to the solution for the C-C1 orbit as listed in Table 8. |
Open with DEXTER | |
In the text |
![]() |
Figure 8:
Mean deviation
|
Open with DEXTER | |
In the text |
![]() |
Figure 9:
Speckle positions of
|
Open with DEXTER | |
In the text |
Copyright ESO 2010
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