Funded by Programa Nacional
del Espacio (MEC-DGI)
For more information please contact A. Domingo (albert@laeff.esa.es)
Optically variable sources monitored by the OMC
A. Domingo, D. Rísquez, M.D. Caballero, J. M. Mas-Hesse, A. Giménez, R. Gutiérrez, E. Solano, L. Sarro
LAEFF-INTA. P.O. Box 50727, 28080 Madrid (Spain)
The Optical Monitoring Camera has observed serendipitously a large number of pre-selected optically variable sources (around 70.000 after
almost two years of operations). In this contribution we describe the main functionalities of the OMC scientific archive and present the optical
light-curves of some interesting objects. Included are different kind of variable stars but primarily binary systems whose optical monitoring had
been otherwise neglected. Other variables of previously unknown type and some new variables are also presented. We discuss the physical
parameters and implications that can be derived from the observed light-curves.
Main
Main results
results page
page
Name resolver
LAEFF (www.laeff.esa.es) has developed a
scientific archive (http://sdc.laeff.esa.es/omc/),
containing the data generated by the OMC, and an
access system capable of performing complex
searches. A remarkable point is the existence of
visualization and analysis tools, available from the
user's interface, aiming at optimizing the scientific
return of the OMC data.
Plot utility
More
More than
than
3,500,000
3,500,000
resolved
resolved names.
names.
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Input query form
Neural network
characterization
Future tools
Image:
Image:
visualization
visualization of
of the
the source
source image.
image.
Periodogram:
Periodogram: Fourier
Fourier analysis
analysis tools
tools to
to provide
provide
information
information in
in the
the frequency
frequency domain.
domain.
Query
Query by:
by:
•• Object
Object name
name // list
list of
of objects
objects
On-the-fly
On-the-fly data
data processing:
processing:
•• Object
Object Type
Type
•Re-sampling:
•Re-sampling:
on-the-fly
on-the-fly re-sampling
re-sampling of
of the
the
observation
observation data
data (originally
(originally sampled
sampled each
each 1,
1, 630
630 and
and
9000
9000 seconds).
seconds).
•• V-magnitude
V-magnitude range
range
•• Coordinates
Coordinates
•• Date
Date of
of observation
observation
•Window
•Window size:
size:
on-line
on-line modification
modification of
of the
the
extraction
extraction window
window size
size (originally
(originally of
of 5x5
5x5 pixels).
pixels).
•• Number
Number of
of points
points of
of the
the light
light curve
curve
Neural
Neural network:
network: search
search of
of the
the light
light curves
curves which
which are
are
similar
similar to
to one
one given
given by
by the
the user.
user.
These are close eclipsing binaries showing essentially flat maxima outside of eclipse. Among them we find well
detached systems with spherical or just slightly distorted components as well as semi-detached systems, like
the prototype Algol, where the highly distorted Roche-lobe filling component is much less luminous than the
almost spherical and hotter primary mate. These later cases are generally called classical Algols to distinguish
them from the detached systems, simply classified as Algols because of the shape of the light curve. In the
light curves of these systems it is possible to identify accurately the time when eclipses start and end. In cases
of large surface brightness differences between the two components, the secondary eclipse may be very
shallow or even undetectable. An extremely wide range of periods is observed, from 0.2 to > 10000 days and
light variations are also quite different and may reach several magnitudes.
These are eclipsing binaries with periods shorter than 1 day, consisting of highly distorted components in contact
and filling their inner Roche lobes. Their light curves do not allow to specify the exact times for the beginning or
end of the mutual eclipses. Moreover, the generally similar surface brightness of the components imply that the
depths of primary and secondary minima are almost equal or differ only slightly. Light amplitudes are usually
<0.8 mag in V. The components generally belong to spectral
types A-K; subclass A is used for early types (A-F), while
subclass W is kept for the classical W UMa binaries with
spectrum type G or K.
Eclipsing binaries of
W Ursae Majoris type
Eclipsing binaries of
Algol type
IOMC 2673000059 (GG Cyg)
is a semidetached system in
which the surface of the less
massive component fills its
inner Roche lobe. The period
we derive for this system is
2.0083758±0.0000002 days
with a best T0 of HJD
2452595.9771±0.0007. No
other measurement of the
period has been found in the
literature.
The proximity of both periods to integer values of days shows part of the
difficulties to get complete light curves with ground-based telescopes and
their status as neglected eclipsing binaries despite their relative brightness.
Eclipsing binaries
of β Lyrae type
IOMC 1861000027 (BV Tau) is a
contact system of early spectral
type (B9), both components
being close in size to their inner
critical surfaces. The computed
period is 0.9304532±0.0000002
days with a best T0 of HJD
2452687.6915±0.0004.
On the other hand, IOMC
2668000048 (V809 Cyg) is a
detached system in which both
components are main sequence
stars and do not fill their inner
Roche lobes. Our estimation of the
period is 1.9644570±0.0000001
days for a T0 of HJD
2452596.2342±0.0005.
These eclipsing systems are
generally semidetached, like the
classical Algols, but with much
stronger interaction. In some cases
they are close to contact systems
but with earlier type components
than classical W UMa-type
binaries. They present highly
distorted components as well as an
important contribution of mutual
reflection, and light curves do not
allow to specify the exact times of
beginning and end of the eclipses.
Secondary minimum is always
observed but in some cases is
found to be strongly distorted.
Periods are mainly longer than 1
day. The components generally
belong to early spectral types (BA). Light amplitudes are usually
<2 mag in V.
IOMC 0244000020 (FASTT 452) has been
recently classified by Greaves & Wils (2003)
as a classical W UMa binary system. Our
computed value for the orbital period of the
system is 0.42975±0.00001 days, with a
best T0 of HJD 2452600.625±0.001.
Variable stars of unknown
type before OMC
IOMC 5224000031 (FASTT 1534) shows
all the characteristics of an RR-Lyrae
type pulsating star. The period obtained
in this case is 0.5841±0.0008 days with
a best T0 of HJD 2452634.483±0.001.
Pulsating stars:
Cepheids and RR-Lyrae
IOMC 5228000021 (FY Aqr) is
probably a short period δ Cep variable
with asymmetric light curve and steep
ascending branches. A period of
1.0245670±0.0000005 days with a
best T0 of HJD 2452634.4648±0.0005
has been computed for this pulsating
star for which no previous value of the
period was available. The classical
bump at the end of the descending
branch is clearly visible.
IOMC 7634000040 (GZ Pup).
In this system an small
difference in the depth of the
primary and secondary can be
appreciated. A period of
0.320274343±0.000000005
days has been estimated, with
a best T0 of HJD
2452676.8141±0.0001.
IOMC 7634000039
(GY Pup) is a contact
system with distorted
components of G
spectral type close to
the zero-age main
sequence. The
estimated period is
0.41221146±0.00000001 days with a best T0 of HJD
2452676.8766±0.0002.
Radially-pulsating giant A-F
stars show periodic light curves
with continuous variations
having amplitudes from 0.2 to 2
magnitudes in V.
IOMC 5225000016 (GG Aqr). This is
probably an example of RRab-type
variable. These pulsating stars are very
similar to Cepheids but show periods
shorter than 1 day. The period is
estimated to be 0.6556±0.0005 days with
a best T0 of HJD 2452633.974±0.001.
Once again, no other previous value has
been found in the literature.
Several suspected, or unclassified, variable stars have also
been monitored by the OMC in its serendipitous capability.
Hints of the nature of these variable objects can be obtained using the
shape of the light curves as well as available information on colours and
periods. In the case of the OMC data, only light curves and periods are
available and classifications should
be considered as tentative.
IOMC 0559000027 (GI Aqr)
on the other hand was
erroneously classified as
eclipsing binary of β Lyrae
type. The shape of the new light curve nevertheless indicates
clearly a pulsating variable, most probably of the RR-Lyrae type.
The computed period of 0.6084±0.0009 days, with a best T0 of
HJD 2452634.124±0.002, favours this classification.
IOMC 7643000034 (NSV 17454,
HIP 35815). This star is classified
in the Hipparcos Catalogue as
unsolved variable, with a
variability range of 0.06 to 0.6
magnitudes. The variability is
clearly observed in the OMC data
with a semi-regular nature.
IOMC 7643000021 (GSC 07643-01178) is an OMC photometric
reference star. No flag related to variability was found in the
Tycho Catalogue, probably due to its intrinsic small amplitude
compared with the Tycho corresponding photometry accuracy.
The photometric reference
stars were selected to
avoid variability, according
to the available catalogues.
A detailed analysis of the
OMC light curves will
nevertheless identify
potential small amplitude
variability in these stars.
Stars not classified
as variables in
SIMBAD