arXiv subjects

A. Olech

Publications and source records attributed to A. Olech.

At least 37 records · Page 2Linked to original sources

arXiv2010

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 $\dot P = -4.5(8)\times 10^{-4}$ which is one of the highest values ever observed in SU UMa systems.

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arXiv2009

SDSS J210014.12+004446.0 - dwarf nova with negative and positive superhumps

We report the results of 67h of CCD photometry of the recently discovered dwarf nova SDSS J210014.12+004446.0. The data were obtained on 24 nights spanning a month. During this time we observed four ordinary outbursts lasting about 2-3 days and reaching an amplitude of ~1.7 mag. On all nights our light curve revealed persistent modulation with the stable period of 0.081088(3) days. These humps were already observed on one night by Tramposch et al. (2005), who additionally observed superhumps during a superoutburst. Remarkably, from scant evidence at their disposal they were able to discern them as negative and positive (common) superhumps, respectively. Our period in quiescence clearly different from their superhump period confirmed this. Our discovery of an additional modulation, attributed by us to the orbital wave, completes the overall picture. Lack of superhumps in our data indicates that all eruptions we observed were ordinary outbursts. The earlier observation of the superhumps combined with the presence of the ordinary outbursts in our data enables classification of SDSS J2100 as an active SU UMa dwarf nova. Additionally, we have promoted SDSS J2100 to the group of cataclysmic variables exhibiting three periodic modulations of light from their accretion discs. We updated available information on positive and negative superhumps and thus provided enhanced evidence that their properties are strongly correlated mutually as well as with the orbital period. By recourse to these relations we were able to remove an alias ambiguity and to identify the orbital period of SDSS J2100 of 0.083304(6) days. SDSS J21000 is only third SU UMa dwarf nova showing both positive and negative superhumps. Their respective period excess and deficit equal to 4.99(3)% and -2.660(8)%, yielding the mass ratio q=0.24.

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arXiv2009

Curious Variables Experiment (CURVE). CCD photometry of active dwarf nova DI UMa

We report an analysis of photometric behaviour of DI UMa, an extremely active dwarf nova. The observational campaign (completed in 2007) covers five superoutbursts and four normal outbursts. We examined principal parameters of the system to understand peculiarities of DI UMa, and other active cataclysmic variables. Based on precise photometric measurements, temporal light curve behaviour, O-C analysis, and power spectrum analysis, we investigated physical parameters of the system. We found that the period of the supercycle now equals 31.45 +/-0.3 days. Observations during superoutbursts infer that the period of superhumps equals P_sh = 0.055318(11) days (79.66 +/- 0.02 min). During quiescence, the light curve reveals a modulation of period P_orb = 0.054579(6) days (78.59 +/- 0.01 min), which we interpret as the orbital period of the binary system. The values obtained allowed us to determine a fractional period excess of 1.35% +/- 0.02%, which is surprisingly small compared to the usual value for dwarf novae (2%-5%). A detailed O-C analysis was performed for two superoutbursts with the most comprehensive coverage. In both cases, we detected an increase in the superhump period with a mean rate of dot_P/P_sh = 4.4(1.0)*10^{-5}. Based on these measurements, we confirm that DI UMa is probably a period bouncer, an old system that reached its period minimum a long time ago, has a secondary that became a degenerate brown dwarf, the entire system evolving now toward longer periods. DI UMa is an extremely interesting object because we know only one more active ER UMa star with similar characteristics (IX Dra).

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arXiv2008

Double mode RR Lyrae stars in Omega Centauri

Aim: The aim of this work was to search for double mode pulsators among RR Lyr variables of globular cluster Omega Cen. Methods: We conducted a systematic frequency analysis of CASE photometry of Omega Cen RR Lyr stars. We searched for periodicities using Fourier and ANOVA periodograms, combined with consecutive prewhitening technique. Results: We discovered six double mode pulsators, with the first overtone and a secondary mode of higher frequency simultaneously excited. These are the first double mode RR Lyr stars identified in Omega Cen. In variable V10 period ratio of the two modes is 0.80, which corresponds to pulsations in the first and second radial overtones. In V19 and V105 we found unexpected period ratio of 0.61. Three other stars display period ratios of either ~0.80 or ~0.61, depending on the choice of aliases. Conclusions: While the period ratio of ~0.80 is easy to interpret in terms of two lowest radial overtones, the value of ~0.61 cannot be explained by any two radial modes. Thus, V19 and V105 are the first members of a new class of double mode RR Lyr pulsators.

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arXiv2008

Multiperiodic RR Lyrae Stars in Omega Centauri

We have conducted a systematic search for multiperiodic pulsations in the RR Lyrae-type stars of the galactic globular cluster Omega Cen. Secondary periodicities close to the primary pulsation frequency have been detected in 17 out of 70 studied fundamental mode (RRab) pulsators and in 35 out of 81 overtone (RRc) pulsators. Because of the observed period ratios, these newly detected periodicities must correspond to nonradial modes. Their beating with the primary radial pulsation leads to a slow amplitude and phase modulation, commonly referred to as the Blazhko effect. The incidence rate of Blazhko modulation in Omega Cen RRab stars (24 +/- 5%) is similar to that observed in the Galactic Bulge. In the case of Omega Cen RRc stars, the incidence rate of Blazhko effect is exceptionally high (38 +/- 5%), more than 3 times higher than in any other studied population. In addition to Blazhko variables, we have also identified two RR Lyr variables exhibiting first overtone/second overtone double-mode pulsations, and a triple-mode High Amplitude Delta Scuti variable.

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arXiv2008

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 $\dot P/P_{\rm sh} = 7.6(1.9)\cdot 10^{-5}$. 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.

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arXiv2008

CURiuos Variables Experiment (CURVE): Variable Stars in the metal-poor Globular Cluster M56

We have surveyed a 6.5' x 6.5' field centered on the globular cluster M56 (NGC 6779) in search for variable stars. We have detected seven variables, among which two objects are new identifications. One of the new variables is an RR Lyrae star, the third such star in M56. Comparison of the new observations and old photometric data for an RV Tauri variable V6 indicates a likely period change in the star. Its slow and negative rate of -0.005+/-0.003 d/yr would disagree with post-AGB evolution, however this could be a result of blue-loop evolution and/or random fluctuations of the period.

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arXiv2008

Curious Variables Experiment (CURVE). Three Periodicities of BF Ara

We report CCD photometry of the dwarf nova BF Ara throughout fifteen consecutive nights in quiescence. Light curve in this interval is dominated by a large amplitude around 0.8 mag modulation consisting two periods. Higher amplitude signal is characterized by period of 0.082159(4) days, which was increasing at the rate of dotP/Psh = 3.8(3)* 10^{-5}. Weaker and stable signal has period of 0.084176(21) days. Knowing the superhump period of BF Ara determined by Kato et al. (2003) and equal to 0.08797(1) days, the first modulation is interpreted as quiescent negative superhump arising from retrograde precesion of titled accretion disk and the latter one as an orbital period of the binary. The respective period excess and defect are epsilon_+ = 4.51% +/- 0.03% and epsilon_- = -2.44% +/- 0.02%. Thus BF Ara is yet another in-the-gap nova with mass ratio q of around 0.21.

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arXiv2007

Curious Variables Experiment (CURVE). CCD Photometry of V419 Lyr in its 2006 July Superoutburst

We report extensive photometry of the dwarf nova V419 Lyr throughout its 2006 July superoutburst till quiescence. The superoutburst with amplitude of ~3.5 magnitude lasted at least 15 days and was characterized by the presence of clear superhumps with a mean period of Psh=0.089985(58) days (129.58+-0.08 min). According to the Stolz-Schoembs relation, this indicates that the orbital period of the binary should be around 0.086 days i.e. within the period gap. During the superoutburst the superhump period was decreasing with the rate of dotP/Psh=-24.8(2.2)*10^-5, which is one of the highest values ever observed in SU UMa systems. At the end of the plateau phase, the superhump period stabilized at a value of 0.08983(8) days. The superhump amplitude decreased from 0.3 mag at the beginning of the superoutburst to 0.1 mag at its end. In the case of V419 Lyr we have not observed clear secondary humps, which seems to be typical for long period systems.

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arXiv2007

Variable stars in the field of the old open cluster Melotte 66

We report the results of photometric monitoring of the Melotte 66 field in BVI filters. Ten variables were identified with nine being new discoveries. The sample includes eight eclipsing binaries of which four are W UMa type stars, one star is a candidate blue straggler. All four contact binaries are likely members of the cluster based on their estimated distances. Ten blue stars with U-B<-0.3 were detected inside a 14.8 x 22.8 arcmin^2 field centred on the cluster. Time series photometry for 7 of them showed no evidence for any variability. The brightest object in the sample of blue stars is a promising candidate for a hot subdwarf belonging to the cluster. We show that the anomalously wide main sequence of the cluster, reported in some earlier studies, results from a combination of two effects: variable reddening occuring across the cluster field and the presence of a rich population of binary stars in the cluster itself. The density profile of the cluster field is derived and the total number of member stars with 16<V<21 or 2.8<M_{V}<7.8 is estimated conservatively at about 1100.

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arXiv2006

CURious Variables Experiment (CURVE). CCD Photometry and Variable Stars in the field of open cluster NGC 637

We present VI photometry for the open cluster NGC 637 which is located in the Cassiopeia region. Morphology of cluster color-magnitude diagram indicates that it is a young object with age of a few million years. The apparent distance modulus of the cluster is 13.9<(m-M)_V<14.3, while reddening is 0.69<E(V-I)<0.73. We estimated the heliocentric distance as 2.6<d<3.3 kpc. We also report the identification of two variable stars in NGC 637. One of the variables is a non-radial pulsating beta Cep-type star. Other one is a likely ellipsoidal variable, however its pulsating nature can not be excluded.

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arXiv2006

Curious Variables Experiment (CURVE). Variable properties of the dwarf nova SS UMi

We report on extensive photometry of the dwarf nova SS Ursae Minoris throughout nine months of 2004. In total, we recorded two superoutbursts and 11 normal outbursts of the star. SS UMi has been known to show frequent superoutbursts with a mean interval of 84.7 days. Our data suggest that the interval between successive superoutbursts lengthened to 197 days, indicating that SS UMi entered a period of untypical behavior manifested by a growth in the quiescent magnitude of the star and a series of frequent, low-amplitude, normal outbursts observed from July to September 2004. The mean superhump period derived for the April 2004 superoutburst of SS UMi is 0.070149(16) days (101.015 min). Combining this value with an earlier orbital period determination, we were able to derive the period excess, which is equal to 3.5 +/- 1.6%, and estimate the mass ratio of the binary system as equal to q=0.16 +/- 0.07. During the entire superoutburst, the period decreased at a rate of $\dot P/P_{\rm sh} = -6.3(1.4) \times 10^{-5}$. However, detailed analysis of the timings of superhump maxima seem to suggest a more complex period change, with a decrease in the period during the first and last stages of the superoutburst but an increase in the middle interval.

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arXiv2005

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.

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arXiv2005

Cluster AgeS Experiment (CASE): SX Phe stars from the globular cluster Omega Centauri

We present an analysis and interpretation of oscillation spectra for all 69 SX Phoenicis stars discovered in the field of the cluster. For most of the stars we have reliable absolute magnitudes and colors. Except of one, or perhaps two, objects, the stars are cluster members. Their pulsational behaviour is very diversified. Multiperiodic variability with at least part of the excited modes being nonradial is most common but there are also many cases of high amplitude, presumably radial mode, pulsators. In a number of such cases we have evidence for two radial modes being excited. Parameters of radial mode pulsators are in most cases consistent with standard evolutionary models for stars in the mass range 0.9-1.15 Mo. However, in four cases we have evidence that the masses are significantly lower than expected. Three objects show frequency triplets that may be interpreted in terms of rotational frequency splitting of l=1 modes. Implied equatorial velocities of rotation are from 10 to over 100 km/s. Nearly all measured frequencies fall in the ranges predicted for unstable modes. Two cases of low frequency variability are interpreted as being caused by tidal distortion induced by close companions.

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arXiv2004

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.

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arXiv2004

Cluster AgeS Experiment. Catalog of Variable Stars in the Globular Cluster Omega Centauri

We present results of a photometric survey for variable stars in the field of the globular cluster Omega Centauri. The observed region was centered roughly on the cluster core and covered 644 arcmin^2. The cluster was monitored on 59 nights in 1999 and 2000. A total of 117 new variables were identified. Among them there are 16 RR Lyr-type stars, 35 SX Phe variables and 26 eclipsing binaries. A comprehensive catalog including all variable stars so far reported from the cluster field is presented. We list basic photometric properties and provide finding charts for a total of 392 objects. For 313 of them new BV light curves were obtained. The presented sample includes several interesting variables, such as SX Phe stars with extremely short periods of pulsation and several candidates for pulsating K giants. Optical counterparts to 9 X-ray sources detected by XMM and Chandra telescopes were identified: all of them are likely to be foreground variables not related to the cluster.

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arXiv2004

Curious Variables Experiment (CURVE). IX Draconis - a Clue for Understanding Evolution of Cataclysmic Variable Stars

We report extensive photometry of frequently outbursting dwarf nova IX Draconis. During five months of observations the star went into three superoutbursts and seven ordinary outbursts. This allowed us to determine its supercycle and cycle lengths as equal to 54 +/- 1 and 3.1 +/- 0.1 days, respectively. During the Sep 2003 superoutburst, which had the best observational coverage, IX Dra displayed clear superhumps with a period of Psh=0.066968(17) days. This period was constant during the whole superoutburst. Another period, which was clearly present in the light curve of IX Dra in superoutburst, had a value of 0.06646(6) days and we interpret it as the orbital period of the binary. Thus IX Dra is the first SU UMa star showing orbital modulation during the entire superoutburst. The beat between these two periods is the main cause of an unusual phase reversal of superhumps - a phenomenon which was previously observed in ER UMa. If our interpretation of the second periodicity is correct, IX Dra has an extremely low period excess $ε$ equal to only 0.76% +/- 0.03%. This implies very low mass ratio q=0.035 +/- 0.003, which strongly suggests that the system contains a brown dwarf-like degenerate secondary of mass ~0.03 Mo and that IX Dra is the most evolved dwarf nova known. Such a very low mass ratio results in the outer edge of the accretion disk reaching 80% of the distance between the components of the system. In turn, this allows the disk particles to enter a 2:1 resonance and leads to the appearance of the orbital period in the light curve of the entire superoutburst.The high level of activity and brightness of IX Dra indicate that very old cataclysmic variables go through episodes of increased activity leading to loss of angular momentum through mass loss from the system.

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arXiv2003

Curious Variables Experiment (CURVE). CCD Photometry of QW Serpentis in Superoutburst and Quiescence

We report extensive photometry of the dwarf nova QW Ser throughout its 2003 February superoutburst till quiescence. During the superoutburst the star displayed clear superhumps with a mean period of Psh = 0.07703(4) days. In the quiescence we observed a double humped wave characterized by a period of P=0.07457(2) days. As both periods obey the Stolz-Schoembs relation with a period excess equal to 3.30+/-0.06% the latter period is interpreted as the orbital period of the binary system.

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