A&A 386, 548-557 (2002)
DOI: 10.1051/0004-6361:20020239
D. P. Kjurkchieva1 - D. V. Marchev1 - S. Zola2,3
1 - Department of Physics, Shoumen University, 9700 Shoumen, Bulgaria
and Isaac Newton Institute of Chile, Bulgarian Branch
;
2 - Astronomical Observatory, Jagiellonian University, ul. Orla 171,
30-244 Cracow, Poland
3 -
Mt. Suhora Observatory of the Pedagogical University,
ul. Podchorazych 2, 30-094 Cracow, Poland
Received 25 September 2001 / Accepted 12 February 2002
Abstract
Spectroscopic observations of the eclipsing,
short-period RS CVn-star SV Cam in the range 6500-6700 Å,
covering the whole orbital period are presented. The absorption
profiles of the lines H
and FeI 6678 are doubled out of
the eclipses. The relative contribution of the secondary star is
stronger in the FeI 6678 line than in H
.
We determined
kms-1 and
kms-1 by measurements of the Doppler shifts of these lines.
The resulting masses of the components are:
and
.
From the radial velocity
solution and photometrically obtained relative stellar radii we determined
the absolute radii of the components:
and
.
The equatorial velocities
kms-1 and
kms-1 corresponding
to the measured rotational broadenings of the investigated lines
coincide with the velocities calculated from the obtained stellar radii.
The phase
behavior of both H
and FeI 6678 profiles of the primary
star shows the presence of two cool spots with maximum
visibilities at phases 0.27 and 0.86.
The analysis of the two lines in the middle of
the primary eclipse allows us to illustrate the excess
of the H
emission of the secondary star.
The parameters of the stellar components of SV Cam derived from
our spectroscopy and photometry are in very good agreement. The
final result of our investigation is that there are three
sources of activity in SV Cam: local active regions (photospheric
spots) on its primary component, enhanced chromospheric emission
from the secondary star and some additional emission originating
from circumstellar gas.
Key words: stars: activity - binaries: eclipsing - binaries: spectroscopic - stars: chromospheres - stars: individual: SV Cam - stars: starspots
Stars which are forced into rapid rotation through tidal interaction in binary systems exhibit high levels of activity. A large number of observations have demonstrated the fundamental importance of stellar rotation for the generated activity level. Studies which relate the characteristics of star activity to basic star parameters are a natural way to test dynamo theories.
The strong photospheric, chromospheric, transition region and
coronal activity in RS CVn stars are generally attributed to the
deep convection zone and the fast rotation that drives the dynamo
mechanism. Enhanced emission cores in the CaII H and K as well as
the H
lines are the primary optical indicators of the
chromospheric activity (Fernandez-Figueroa et al. 1994).
Analysis of the spectra at different orbital phases allows us to
establish which star is the source of the emission. If the
activity of RS CVn stars is linked to the stellar dynamo then the
short-period RS CVn stars have a proportionally larger supply of
rotational energy to be converted into magnetic energy.
The eclipsing binary star SV Cam (G2-3V+K4V) belongs to the subgroup
of short-period RS CVn systems and it is one of the closest binaries
among them (
days) with an orbital inclination
.
The star shows remarkable changes out of the eclipses.
Variations of the light
curve shape by as much as 0.1 mag on time scales as short as one
month have been observed. Extensive observations from 1973 until
1980 led Patkos (1982a,b) to the conclusion that cool spots on the
surface of the primary component and sporadic gas streams are
present in the system.
Hempelmann et al. (1997) found evidence for chromospheric activity
of the secondary star of SV Cam by an analysis of the strength of the
H
absorption line during the primary and secondary
eclipses.
SV Cam does not show all of the signatures of RS CVn-type activity: there
is no apparent H
emission, neither radio emission nor
flare activity have been reported.
Results from X-ray observations of SV Cam are contradictory.
Agrawal et al. (1980) and Welty
Ramsey (1995) reported high
X-ray luminosity and surprisingly large X-ray surface flux
compared to that observed in semi-detached, Algol-type systems
(Singh et al. 1980). On the other hand, Hempelmann et al. (1997)
found the total X-ray output from SV Cam to be on a level
typical of single Main Sequence stars, i.e. the observed coronal
activity of this system is not enhanced compared to single stars.
In semi-detached systems the mass transfer through the inner
Lagrangian point is responsible for the higher X-ray flux. In case
of SV Cas, however, due to its low Roche lobe filling factor this
explanation is not valid. Hempelmann et al. (1997) modelled the
X-ray light curve of SV Cam with two localized coronal emission
regions rather than by global emission coming either from a
homogeneously radiating stellar corona or from a common envelope
surrounding the two stars.
Although SV Cam is photometrically a well-studied star,
only the primary's radial velocity curve was known until Pojmanski
(1998), thus making any inferences from analysis of the
data unreliable.
In order to search for a presence of the secondary star's lines in
the spectrum of SV Cam and to investigate the phase behavior of
the H
line which is a spectroscopic indicator of stellar
chromospheric activity (Zarro
Rogers 1983; Herbig 1985; Frasca
Catalano 1994; Strassmeier et al. 1990), we decided to observe
SV Cam in the spectral range around this line. An additional reason for
undertaking these spectral observations was to compare the derived
star parameters with those obtained from the light curve modeling. The multicolor
light curve of SV Cam in 1997 was modeled with two circular cool spots
having an angular size of 20
located in the middle latitudes
above and below the star equator, on opposite hemispheres of the
primary star surface (Kjurkchieva et al. 2000a, hereafter Paper I).
Spectroscopic observations are described in the next section. In
Sect. 3 we present the new radial velocity solution. The
evidence of the enhanced H
emission of the secondary star is shown
by an analysis of the line profiles in the middle of the primary
eclipse. In Sect. 4 we discuss our spectral data in the framework
of the dynamo theory of stellar activity and show a good
agreement of the values of the parameters of stars determined both from
our spectral and photometric data.
SV Cam was observed in the spectral range 6500-6700 Å with
resolution 0.19 Å/pixel on 3 consecutive nights from November
30 to Dec. 2, 1999. We used a CCD camera mounted on the Coude
spectrograph (grating
)
of the 2m telescope
operated by the National Astronomical Observatory in Rozhen
(Bulgaria). The seeing during the observations did not exceed 2
arcsec (FWHM). The exposure time was 20 min. The bias frames and
flat-field integrations were obtained at the beginning and end of
each night. All stellar integrations were alternated with Fe
comparison source exposures. The data were processed in a standard
way using the PCIPS (Smirnov et al. 1992) and Rewia (Borkowski
1988) software packages. The S/N ratio was around 120-160. The
spectra were reduced by bias substraction, flat-field division and
wavelength calibration. The normalization of the continuum was
made to the whole line-free spectral range.
Apart from the H
line, in the range 6500-6700 Å there
are several weaker Fe lines, whose radial velocities change with
the orbital period of SV Cam. However, only the H
and FeI
6678 Å lines show apparent double profiles out of the
eclipses. For instance, the FeI 6593 line is stronger than FeI
6678 but it is blended with surrounding lines whose contribution
is difficult to separate.
An appropriate Fourier noise filter was applied to the weaker FeI
6678 line in order to remove the high-frequency noise. This
procedure causes some smoothing of the profiles without loss of
their important details (Gray 1992).
The data were phased using the ephemeris of Kreiner (2001):
![]() |
(1) |
The measurements of the lines of the short-period RS CVn systems
are difficult for several reasons. First, the lines arising
from each component are rotationally broadened and blended with
the surrounding metal lines of itself and the companion star.
Second, the profiles are distorted by the presence of emission
features.
The absorption H
and FeI 6678 lines show double
profiles outside the eclipses. Although the FeI 6678
line is significantly weaker than H
its doubling is
better pronounced.
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Figure 1: An illustration of the fitting procedure. |
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Figure 2: Radial velocity curves of SV Cam. |
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Figure 3:
H![]() |
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Figure 4:
H![]() |
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Figure 5:
H![]() |
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Figure 6:
H![]() |
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Figure 7:
H![]() |
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Figure 8: FeI 6678 profiles of SV Cam from Nov. 30. |
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Figure 9: FeI 6678 profiles of SV Cam from Dec. 1. |
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Figure 10: FeI 6678 profiles of SV Cam from Dec. 1, continued. |
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Figure 11: FeI 6678 profiles of SV Cam from Dec. 1, continued. |
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Figure 12: FeI 6678 profiles of SV Cam from Dec. 2. |
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Phase | RV1(H![]() |
![]() ![]() |
RV2(H![]() |
![]() ![]() |
RV1(FeI) |
![]() |
RV2(FeI) |
![]() |
0.105 |
-60.4 | 7.60 | -69.6 | 24.78 | 121.3 | 11.70 | ||
0.130 | -74.0 | 10.60 | -73.0 | 19.13 | 134.0 | 15.20 | ||
0.153 | -90.0 | 3.42 | -96.6 | 23.04 | 164.0 | 28.00 | ||
0.177 | -94.6 | 6.09 | -105.6 | 20.86 | 191.0 | 28.00 | ||
0.200 | -96.9 | 6.66 | -114.5 | 20.86 | 195.0 | 25.80 | ||
0.225 | -99.2 | 8.53 | -116.8 | 26.95 | ||||
0.250 | -101.5 | 11.26 | 205.0 | 27.50 | -119.0 | 28.69 | 218.0 | 50.40 |
0.270 | -106.0 | 10.66 | -123.5 | 23.04 | 195.4 | 21.06 | ||
0.295 | -103.7 | 9.13 | 200.0 | 25.00 | -105.6 | 19.13 | 183.0 | 18.66 |
0.320 | -101.5 | 7.93 | 195.0 | 27.40 | -105.6 | 30.43 | 173.0 | 33.60 |
0.590 | 81.4 | 10.93 | 62.9 | 26.52 | -123.0 | 30.13 | ||
0.613 | 92.8 | 8.00 | 78.6 | 24.78 | -132.5 | 26.66 | ||
0.637 | 104.2 | 6.06 | 96.5 | 11.73 | ||||
0.660 | 111.1 | 5.80 | 110.0 | 22.60 | ||||
0.668 | 118.0 | 4.93 | -193.0 | 22.00 | 119.0 | 27.40 | ||
0.700 | 122.5 | 4.80 | -199.7 | 17.80 | 128.0 | 28.20 | -195.4 | 49.06 |
0.720 | 145.3 | 4.92 | 134.7 | 20.80 | ||||
0.740 | 151.0 | 6.26 | 137.0 | 27.39 | -213.9 | 49.06 | ||
0.766 | 145.3 | 6.27 | -201.0 | 20.30 | 130.0 | 23.40 | -213.0 | 41.86 |
0.790 | 140.3 | 6.26 | -197.0 | 21.65 | 123.0 | 23.47 | -204.0 | 45.33 |
0.814 | 137.0 | 5.93 | -193.0 | 24.20 | 114.0 | 27.40 | -198.0 | 30.93 |
0.840 | 105.0 | 29.13 | ||||||
0.860 | 96.5 | 21.30 | -186.0 | 19.20 |
Our
value is almost the same as that determined by
Rainger et al. (1991)
(122.3 kms-1) and that of Hiltner (1953)
(123 kms-1) but it is slightly bigger than that of Hempelmann et al.
(1997) (117 kms-1) and that of Pojmanski (1998) (118.3 kms-1). Our
value of
is close to the only value known so far,
published by Pojmanski (211.5 kms-1) and obtained from the
analysis of near IR CaII spectral lines.
Assuming the photometrically determined value of
(Hilditch
et al. 1979; Kjurkchieva et al. 2000a)
and using our values for
and
the resulting
values of the mass ratio and masses of the components are
,
and
.
On the basis of our radial velocity solution and photometrically
obtained fractional radii
and
(Paper I),
we determined the absolute star's radii
and
.
It should be noted that the values of
and
determined by
different authors lie in the ranges 0.32-0.4 and 0.19-0.25 (Budding
Zeilik 1987; Zeilik et al. 1988; Patkos
Hempelmann 1994;
Djurasevic 1998; Heckert et al. 1998).
The radii of the components of SV Cam corresponding to their masses calculated
from the mass-radius relation for MS stars are
and
for the primary and secondary, respectively.
This means that the masses and the radii of the two components almost obey
the mass-radius relation for MS stars in spite of their gravity
distortions.
We determined the rotational broadenings of the two profiles of
the investigated lines by measurements of the widths at the continuum
level of the 6th order polynomial fit (Fig. 1).
The mean values of the full width of the broadened profiles
are almost the same for the H
and
FeI 6678 lines:
Å for the primary
profiles and
Å for the secondary
ones. The corresponding equatorial velocities to these rotational
broadenings (
)
are
kms-1 and
kms-1. For comparison, assuming synchroneous rotation of the
components and the obtained stars' radii the calculated equatorial
velocities of the stars (
)
are
kms-1 and
kms-1. Hence, in spite of the fact that the spectral lines
are distorted by different
effects their widths agree with the expected rotational broadenings.
The normalized H
and FeI 6678 profiles are shown in
Figs. 3-12 together with the corresponding orbital phases.
We established the following pecularities in the phase behavior of
the H
profile of the primary star:
(1) The profile has a central pseudo-emission bump in the middle of the primary eclipse. We attribute this distortion to the obscuration of the primary star by the cooler secondary that causes masking of a part of the primary's absorption line. The width of the central bump is 3.4 Å and corresponds precisely to the secondary star's radius (see the previous section).
(2) The profile is deeper around the second quadrature than
around the first one. The shape of the H
profile is
symmetrical at the second quadrature and distorted at the
first quadrature.
(3) Some emission feature at the end of the left wing of the profile appears at phase range 0.95-0.98 that repeats on two dates (Figs. 3 and 5). One can also note a similar, weaker emission feature almost half orbital cycle later (in the phase range 0.54-0.56) at the end of the right wing. This feature may be due to the emission from circumstellar matter, perhaps ejected from the component(s) whose contribution is most apparent in the spectra around the eclipses. The presence of circumstellar matter in SV Cam was suspected a long time ago on the basis of its optical light curves (Patkos 1982a,b) and the X-ray data (Hempelmann et al. 1997). Another reason for the emission feature can be the increased contribution of the trailing and leading part of the secondary star chromosphere in the corresponding phase ranges.
(4) The profile has a nearly flat core at phases 0.86, 0.105
and 0.79. The first two phases are almost symmetric relative to
the primary eclipse. We found the same behavior in the
H
line of the primary star in the short-period RS
CVn-type star RT And (Kjurkchieva et al. 2001).
(5) The profile is distorted and filled-in in the phase ranges
0.2-0.34 and 0.84-0.91. The distortions of the profile are
variable and seem to be caused by features that moves through the
stellar disk during the above phases (see Figs. 4 and 6). They could
be attributed, at least partially, to the effects of cool spots.
The phases 0.27 and 0.86 of the biggest distortions (flat cores)
of the H
profile almost coincide with phases of the
maximum spot visibility determined by modeling of the SV Cam light
curves (Paper I). It should be stressed out that the strong
decrease of the profiles depths at the phase range 0.225-0.295 is
difficult to explain only by spots with a reasonable size.
We established the following similarities in the phase behavior of
the FeI 6678 and H
profiles of the primary star: (i)
the depth of the FeI 6678 line is also greater around the second
quadrature than around the first one but the difference between
them is smaller for FeI 6678; (ii) there is also an emission
feature at the end of the left wing of the profile at the phases
0.95-0.98; (iii) in the middle of the primary eclipse, the FeI 6678
profile also has a central pseudo-emission bump with the same
width (about 3.4 Å), but its relative height is somewhat
less than in H
.
We found additional peculiarities of the FeI 6678 profile of the primary star:
(1) Apparent central emission features are visible at phases 0.25,
0.84 and 0.564. The first two of them almost coincide with the
phases of maximum visibility of the two spots on the primary star
reproducing the distortion light curve of SV Cam from 1997 (Paper I). We may calculate the angular size
of the spots
from the equation (Kjurkchieva 1995):
![]() |
(2) |
(2) A strong increase of the depth of the profile is seen at phase 0.98 that repeats on two dates.
Consequently, the phase behavior of the H
and FeI 6678
profiles show the presence of two cool spots on the primary star
of SV Cam. The Doppler image of SV Cam obtained by Hempelmann et al. (1997) also shows a distinct spot on the primary star whose
location coincides with the spot found by modeling of the optical
light curve.
Our observations out of the eclipses show a weak Habsorption profile from the secondary star that is deeper around
the second quadrature than around the first one similarly to the
behavior of the H
line of the primary star. For
comparison, the H
profiles obtained by Hempelmann et al. (1997) revealed no features that could be attributed to the
secondary star at the out-of-eclipse phases and they determined
the contribution of the secondary star by an analysis of the single
H
profile during both eclipses.
Our observations of the FeI 6678 line outside the eclipses show
also an absorption line from the secondary star. This line is
shallower at quadratures than in the phases around them.
The central intensities (
)
of the primary's and secondary's
H
profiles change during the orbital cycle in the
ranges 0.2-0.38 and 0.02-0.07 while intensities for the
FeI 6678 line vary in the ranges 0.015-0.04 and 0.005-0.01.
Because we have no observations of standard, non-active stars we
cannot apply the widespread method of substraction of comparison
spectrum from that of the active star (Strassmeier et al. 1990;
Frasca
Catalano 1994; Pojmanski 1998;
Frasca et al. 2000, etc.).
However, in order to obtain some information about the emission
from the stellar components of SV Cam we analyzed the
profiles at the primary eclipse. The line profile in the middle of
this eclipse (adopting
)
is described roughly by
the expressions:
![]() |
(3) |
![]() |
(4) |
![]() |
(5) |
![]() |
(6) |
The expressions (3) and (4) describe the line profile with two-wave or W-like shape, i.e. a line profile with a central bump. The main parameters of this profile are:
(a) width of the bump
;
(b) width of the whole profile
;
(c) depth of the center of the bump
(d) depths of the ends of the bump
Line | ![]() |
![]() |
![]() |
![]() |
H![]() |
0.380 | 0.060 | 0.120 | 0.175 |
FeI 6678 | 0.085 | 0.012 | 0.034 | 0.048 |
For the H
profile the measured and calculated values of
are respectively 0.316 and 0.38,
i.e. the calculated value is about
bigger than the
observed one. The measured and calculated values of
(e)/
are respectively 0.46 and 0.55, i.e. the
calculated value is also about
bigger than the observed
one. Consequently, the observed bump of the H
profile
in the middle of the primary eclipse is higher than one
would expect. We attribute this to the H
emission from
the secondary star.
For the FeI 6678
line, the measured and calculated values of
(0) are 0.4 and 0.36, respectively. Therefore, the calculated value
for this parameter is smaller than the measured one. The
measured and calculated values of
(e)/
(0),
0.55 and 0.56, respectively agree very well. Thus the calculated
profile of FeI 6678 in the middle of the primary eclipse is
slightly above the observed one.
In this way, our spectral observations show an enhanced
emission of the secondary star of SV Cam in the
H
line but not in the FeI 6678 line. The result of
our analysis supports the conclusion of Ozeren et al. (2001)
about the H
emission excess from the secondary star of
SV Cam obtained by spectral substraction technique as well as the more
general conclusion of Frasca
Catalano (1994) about the H
emission in late-type active binaries.
Montes et al. (1995) found that systems with H
emission
above the continuum are all cooler than 5000 K. The temperature of
the primary star of SV Cam is above this limit and there should be no
emission excess expected from it. Our spectral observations show
some weak H
emission from the primary star that is
connected with its large spots. Rainger et al. (1991) obtained 8
spectra of SV Cam in H
(with S/N=40) that displayed an
apparently undisturbed line without any signature of emission.
The analysis of our spectral and photometric data shows that the
activity of the primary star is connected with its local surface
structures (photospheric spots). Because of the small contribution
of the secondary star to the total light (around ), it is
difficult to find evidence for its spots by photometry
as well as by spectroscopy. That is why we do not
exclude the presence of active regions on the secondary's surface
distributed relatively uniformly and close to each other, in
contrast to the large spots on the primary star. But the quality of
our spectral data allows us to conclude only that the secondary
star shows some H
emission excess.
Finally we would like to point out the good agreement between the values for parameters of stars determined by analysis of the spectral data (this paper) and the photometric data (Paper I):
(1) The photometric ratio of the star radii k=0.685 is precisely the same as that determined by the rotational broadenings of their spectral lines k=0.68.
(2) The obtained value of the mass of the primary star corresponds
to a F5V star. This value is in good agreement with the color
index B-V=0.42 obtained on the basis of our multicolor photometry (Paper I).
The mass of the primary star is significantly greater than
previously assumed (
)
based on its adopted spectral
type (Budding
Zeilik 1987; Rainger et al. 1991; Patkos
Hempelmann 1994). The G2-3V classification of Hilditch et al.
(1979) was based on photometric observations in the DDO system and
in the ubvy Stromgren system and would not give a reliable
mass value if the primary star's surface were covered with large
cool spots or if there was circumstellar matter present in the
system. Our determination of the primary star mass is very close
to the value (
)
obtained by Pojmanski (1998) from
the near IR spectroscopic observations. We conclude that according
to both our photometric and spectroscopic data the spectral types
of the SV Cam components are F5 and K4.
(3) It is worth noting that the photometric ratio of the
luminosities of the two components in the R band (the range of the
two investigated spectral lines) l=0.136 is close to the ratio
of the fluxes in the FeI 6678 line (equal to the ratio
)
of 0.143 while the ratio of the fluxes in the
H
profiles (0.085) is quite smaller. This fact also
confirms the H
emission excess from the secondary star.
The results from the analysis of our spectral data of SV Cam could be summarized as follows:
Acknowledgements
The authors are grateful to the referee for very useful remarks which allowed us to significantly improve this work.