30 research outputs found
Photometric survey of stellar clusters in the outer part of M33. II. Analysis of HST/ACS images
We have used deep ACS/WFC images of M33 to check nature of extended objects
detected by the ground based survey of Zloczewski et al. (2008). A total of 24
candidates turned out to be genuine compact stellar clusters. In addition we
detected 91 new clusters. Equatorial coordinates, integrated magnitudes and
angular sizes are listed for all 115 objects. Fourty-two clusters have
sufficiently red colors to be candidates for old globulars. For four clusters
we extracted resolved stellar photometry. Object 33-3-018 located in the outer
disk of M33 turned out to be a young cluster with an age estimated at 200-350
Myr. Cluster ZK-90 has an age of 3-5 Gyr. The remaining two clusters have
intermediate ages ranging from one to a few Gyr.Comment: 22 pages, 9 figures, accepted to Acta Astronomica on 22.03.2009;
minor changes for ZK-90 and Figure 1
The 2003 and 2005 superhumps in V1113 Cygni
We report CCD photometry of the cataclysmic variable V1113 Cygni. During two
campaigns, lasting from May to August 2003 and from March to June 2005, we
recorded two superoutburst. In the obtained light curves we detected clear
superhumps with a mean period 0.07891(3) days (113.63(4) min). That fact
confirms that the star is a member of SU UMa class of dwarf novae. During the
first observed superoutburst the superhump period was decreasing with an
enormous rate of which is one of the highest
values ever observed in SU UMa systems.Comment: 9 pages, 5 figures, accepted for publication in Acta Astronomic
An Unusual Eclipsing Blue Straggler V8-NGC 6752
We report the analysis of a binary blue straggler in NGC 6752 with a short
orbital period of 0.315 d and a W UMA-type light curve. We use photometric data
spanning 13 years to place limits on the mass ratio (0.15<q<0.35), luminosity
ratio (L1/L2 about 4.0) and the ratio of the radii of the components (r1/r2
about 2.0). The effective temperatures of the components are nearly identical,
and the system is detached or semi-detached (in the latter case the component
filling its Roche lobe is the secondary). Such a configuration is unusual given
the shortness of the orbital period, and it must have resulted from substantial
mass exchange. We suggest that some secondaries of W UMa-type stars, normally
regarded as main sequence objects which fill their Roche lobes to different
degrees, in fact may be shell-burning cores of originally more massive
components.Comment: 13 pages, 5 figures, submitted to Acta Astronomic
Curious Variables Experiment (CURVE). CCD Photometry of Dwarf Nova V660 Herculis
We report extensive photometry of the dwarf nova V660 Herculis. During our
campaign, lasting from August 2003 to November 2004, we recorded one bright
eruption which turned out to be a superoutburst lasting about 15 days and
having amplitude of ~4.5 mag. Clear superhumps with a mean period of Psh =
0.080924(18) days were present during all nights of the superoutburst. The
period of the superhumps was not stable and in the interval covered by our
observations it decreased with a rate of -4.0(1.4) * 10^{-5}.
Basing on our data and the known orbital period of the binary (Thorstensen
and Fenton 2003) we calculate the period excess of 3.4 +/- 0.1%, which is
typical for an SU UMa star at this orbital period. This value indicates that
the mass ratio of the system is q=0.154.Comment: 11 pages, 7 figures, Acta Astronomica, in prin
Curious Variables Experiment (CURVE). Superhump Period Change Pattern in KS UMa and Other Dwarf Novae
We report extensive photometry of the dwarf nova KS UMa throughout its 2003
superoutburst till quiescence. During the superoutburst the star displayed
clear superhumps with a mean period of Psh = 0.070092(23) days. In the middle
stage of superoutburst the period was increasing with a rate of and later was decreasing with a rate of .
At the end of superoutburst and during first dozen days of quiescence the
star was showing late superhumps with a mean period of Plate = 0.06926(2) days.
This phenomenon was observed even 30 days after beginning of the superoutburst.
In quiescence the star shows quasi-periodic modulations with amplitude
reaching 0.5 mag. The most common structure observed during this stage was
sinusoidal wave characterized by a period of about 0.1 days.
Comparing KS UMa to other SU UMa stars we conclude that this group of dwarf
novae shows decreasing superhump periods at the beginning and the end of
superoutburst but increasing period in the middle phase.Comment: submitted to Acta Astronomica, 21 pages, 13 figure
The Cluster AgeS Experiment (CASE). Variable Stars in the Globular Cluster M55
We report time-series photometry for 55 variable stars located in the central
part of the globular cluster M55. The sample includes 28 newly identified
objects of which 13 are eclipsing binaries. Three of these are detached systems
located in the turn-off region on the cluster color-magnitude diagram. Two of
them are proper motion (PM) members of M55 and are excellent candidates for a
detailed follow-up study aimed at a determination of the cluster age and
distance. Other detached binaries are located along the unevolved part of the
cluster main sequence. Most of the variables are cluster blue straggler stars.
This group includes 35 SX Phe stars, two contact binaries, and one
semi-detached binary. V60 is a low mass, short period algol with the less
massive and cooler component filling its Roche lobe. The more massive component
is an SX Phe variable. The orbital period of V60 increases at a rate of
dP/P=3.0E-9. In addition to numerous variable blue stragglers we also report
the detection of two red stragglers showing periodic variability. Both of these
are PM members of M55. We note and discuss the observed paucity of contact
binaries among unevolved main sequence stars in M55 and NGC 6752. This apparent
paucity supports an evolution model in which the formation of contact binaries
is triggered by stellar evolution at the main-sequence turn off.Comment: 22 pages, 12 figures, published in Acta Astronomic
Curious Variables Experiment (CURVE). RZ LMi - the most active SU UMa star
We report extensive photometry of the frequently outbursting dwarf nova RZ
Leo Minoris. During two seasons of observations we detected 12 superoutbursts
and 7 normal outbursts. The V magnitude of the star varied in range from 16.5
to 13.9 mag. The superoutbursts occur quite regularly flashing every 19.07(4)
days and lasting slightly over 10 days. The average interval between two
successive normal outbursts is 4.027(3) days. The mean superhump period
observed during the superoutbursts is 0.059396(4) days (85.530(6) min). The
period of the superhumps was constant except for one superoutburst when it
increased with a rate of . Our
observations indicate that RZ LMi goes into long intervals of showing permanent
superhumps which are observed both in superoutbursts and quiescence. This may
indicate that decoupling of thermal and tidal instabilities play important role
in ER UMa systems. No periodic light variations which can be connected with
orbital period of the binary were seen, thus the mass ratio and evolutionary
status of RZ LMi are still unknown.Comment: 20 pages, 15 figures, accepted for publication in Acta Astronomic
The Clusters AgeS Experiment (CASE): Variable Stars in the Globular Cluster 47 Tucanae
Based on over 5400 BV images of 47 Tuc collected between 1998 and 2010 we
obtained light curves of 65 variables, 21 of which are newly detected objects.
New variables are located mostly just outside of the core in a region poorly
studied by earlier surveys of the cluster. Among them there are four detached
eclipsing binaries and five likely optical counterparts of X-ray sources. Two
detached systems are promising targets for follow-up observations. We briefly
discuss properties of the most interesting new variables.Comment: Accepted by Acta Astronomic
A proper motion study of the globular clusters M4, M12, M22, NGC 3201, NGC 6362 and NGC 6752
We derive relative proper motions of stars in the fields of globular clusters
M4, M12, M22, NGC 3201, NGC 6362 and NGC 6752 based on a uniform data set
collected between 1997 and 2008. We assign a membership class for each star
with a measured proper motion, and show that these membership classes can be
successfully used to eliminate field stars from color-magnitude diagrams of the
clusters. They also allow for the efficient selection of rare objects such as
blue/yellow/red stragglers and stars from the asymptotic giant branch. Tables
with proper motions and photometry of over 87000 stars are made publicly
available via the Internet.Comment: 9 pages, 18 figure
Curious Variables Experiment (CURVE). TT Bootis - superhump period change pattern confirmed
We report extensive multi-station photometry of TT Boo during its June 2004
superoutburst. The amplitude of the superoutburst was about 5.5 mag and its
length over 22 days. The star showed a small re-brightening starting around the
9th day of the superoutburst. During entire bright state we observed clear
superhumps with amplitudes from 0.07 to 0.26 mag and a mean period of Psh =
0.0779589(47) days (112.261 +/- 0.007 min). The period was not constant but
decreased at the beginning and the end of superoutburst yet increased in the
middle phase. We argue that the complicated shape of the O-C diagram is caused
by real period changes rather than by phase shifts. Combining the data from two
superoutbursts from 1989 and 2004 allowed us to trace the birth of the late
superhumps and we conclude that it is a rather quick process lasting about one
day.Comment: 14 pages, 6 figures, submitted to Acta Astronomic