HBHA 4705-03: A new cataclysmic variable

Results of photometric and spectroscopic studies for the new eclipsing cataclysmic variable star HBHA 4705-03 with an orbital period of 0.1718 days are presented. Its spectrum exhibits hydrogen and helium emission lines. The Doppler maps constructed from hydrogen lines and the He II λ 4686 line show that the regions near the inner Lagrangian point are the main source of emission in these lines, while the maps constructed from He I lines suggest the presence of an accretion disk around the primary. The masses of the components (M _WD = 0.54 ± 0.10M _⊙ andM _RD = 0.45 ± 0.05 M _⊙) and the orbital inclination of the system (i = 71.8° ± 0.7°) have been determined from observational data using well-known relations for close binaries and cataclysmic variable stars.     

HR 7275: A new variable star

Differential photometry of the KI IV-III RS CVn-type binary HR 7275 in 1978, 1979, and 1980 at nine different observatories shows it definitely to be variable, thus confirming the suspicion of Herbst. The photometric period determined two ways was 27 _. ^d 91 or 27 _. ^d 65, thus about 3% shorter than the spectroscopically determined orbital period of 28 _. ^d 59. The total variation observed during the three years was 0 _. ^m 22 in theV. The light curve was always asymmetrical, with a stillstand on the rising branch in 1978 but on the falling branch in 1980.Kitt Peak National Observatory, operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation.Of the AAVSO.     

54 Cam: A new variable star

Differential photometry of the RS CVn-type binary 54 Cam in 1978, 1979, and 1980 shows its light to be variable with a period of 10 _. ^d 163±0 _. ^d 009 and an amplitude inV (max. to min.) which increased from 0 _. ^m 03 to 0 _. ^m 06 between 1979.19 and 1980.82. An epoch of light minimum was JD 2444529.7. The 9% difference betweenP(phtm.)=10 _. ^d 163 andP(orb.)=11 _. ^d 0764,a much larger difference than is characteristic of other RS CVn binaries, is suggested as an explanation for the radio emission.Guest Investigator, Kitt Peak National Observatory,which is operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation.Of the AAVSO.     

2MASS J01074282+4845188: A new nova-like cataclysmic star with a deep eclipse

We present V RI photometry and low-resolution spectroscopy of the object 2MASS J01074282+4845188. The V-shape of the eclipse, the phase variability of the colour indices as well as the presence of a pre-eclipse hump, standstill and flickering allow us to conclude that it is a nova-like cataclysmic star. This is supported by the observed broad emission Hα line. Its single profile with a relatively narrow FWHM but large FWZI is typical for a nova-like variable of SW Sex subtype. The observed deep eclipses make the newly discovered cataclysmic star 2MASS J01074282+4845188 an interesting object for future investigation.     

The age of cataclysmic variables: A kinematical study

Using available astrometric and radial velocity data, the space velocities of cataclysmic variables (CVs) with respect to Sun were computed and kinematical properties of various sub-groups of CVs were investigated. Although observational errors of systemic velocities (γ) are high, propagated errors are usually less than computed dispersions. According to the analysis of propagated uncertainties of the computed space velocities, available sample was refined by removing the systems with the largest propagated uncertainties so that the reliability of the space velocity dispersions was improved. Having a dispersion of $51\pm 7\mathrm{km}{\mathrm{s}}^{-1}$ for the space velocities, CVs in the current refined sample (159 systems) are found to have 5 ± 1 Gyr mean kinematical age. After removing magnetic systems from the sample, it is found that non-magnetic CVs (134 systems) have a mean kinematical age of 4 ± 1 Gyr. According to 5 ± 1 and 4 ± 1 Gyr kinematical ages implied by 52 ± 8 and 45 ± 7 km s^?1 dispersions for non-magnetic systems below and above the period gap, CVs below the period gap are older than systems above the gap, which is a result in agreement with the standard evolution theory of CVs. Age difference between the systems below and above the gap is smaller than that expected from the standard theory, indicating a similarity of the angular momentum loss time scales in systems with low-mass and high-mass secondary stars. Assuming an isotropic distribution, $\gamma$ velocity dispersions of non-magnetic CVs below and above the period gap are calculated ${\sigma }_{\gamma }=30\pm 5\mathrm{km}{\mathrm{s}}^{-1}$ and ${\sigma }_{\gamma }=26\pm 4\mathrm{km}{\mathrm{s}}^{-1}$. The small difference of $\gamma$ velocity dispersions between the systems below and above the gap may imply that magnetic braking does not operate in the detached phase, during which the system evolves from the post-common envelope orbit into contact.     

Population I Cepheids and understanding star formation history of the Small Magellanic Cloud

In this paper, we study the age and spatial distributions of Cepheids in the Small Magellanic Cloud(SMC) as a function of their ages using data from the OGLE III photometric catalogue. A period- age relation derived for Classical Cepheids in the Large Magellanic Cloud(LMC) has been used to find the ages of Cepheids. The age distribution of the SMC Classical Cepheids is found to have a peak at log(Age) = 8.40 ± 0.10 which suggests that a major star formation event might have occurred in the SMC about 250 ± 50 Myr ago. It is believed that this star forming burst had been triggered by close interactions of the SMC with the LMC and/or the Milky Way. A comparison of the observed spatial distributions of the Cepheids and open star clusters has also been carried out to study the star formation scenario in the SMC.     

Simultaneous UBVRI observations of the cataclysmic variable AE Aquarii: Temperatures and masses of fireballs

We report simultaneous multicolour observations in 5 bands (UBVRI) of the flickering variability of the cataclysmic variable AE Aqr. Our aim is to estimate the parameters (colours, temperature, size) of the fireballs that produce the optical flares. The observed rise times of the optical flares are in the interval 220‐440 s. We estimate the dereddened colours of the fireballs as (U ‐B)₀∼0.8‐1.4, (B ‐V)₀∼0.03‐0.24, and (V ‐I)₀∼0.26‐0.78. We find for the fireballs temperatures of 10000‐25000 K, masses of (7‐90)x10¹⁹ g, and sizes of (3‐7)x10⁹ cm (using a distance of d = 86 pc). These values refer to the peak of the flares observed in the UBVRI bands. The data are available upon request from the authors (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometric and spectroscopic observations of the variable star ET And. II

New spectroscopic and photometric observations of the variable Ap star ET And carried out 1982 and 1983 confirm once again the existence of short-time variations. For the radial velocity variations a period of 0.19771 days and for the light variations a period of 0.0989 days was found. Some spectrograms show a velocity progression of the Balmer lines. The gradient is of such a kind that the radial velocity values increase from the line H_γ to H₁₅. Different models for the interpreation of the velocity progression are discussed.     

Roche tomography of cataclysmic variables – I. Artefacts and techniques

Roche tomography is a technique used for imaging the Roche-lobe-filling secondary stars in cataclysmic variables (CVs). In order to interpret Roche tomograms correctly, one must determine whether features in the reconstruction are real, or the result of statistical or systematic errors. We explore the effects of systematic errors using reconstructions of simulated data sets, and show that systematic errors result in characteristic distortions of the final reconstructions that can be identified and corrected. In addition, we present a new method of estimating statistical errors on tomographic reconstructions using a Monte Carlo bootstrapping algorithm, and show this method to be much more reliable than Monte Carlo methods which 'jiggle' the data points in accordance with the size of their error bars.     

The orbital period and negative superhumps of the nova-like cataclysmic variable V378 Pegasi

A radial velocity study is presented of the cataclysmic variable V378 Pegasi (PG 2337 + 300). It is found to have an orbital period of 0.13858 ± 0.00004 d (3.32592 ± 0.00096 h). Its spectrum and long-term light curve suggest that V378 Peg is a nova-like variable, with no outbursts. We use the approximate distance and position in the Galaxy of V378 Peg to estimate E(B − V) = 0.095, and use near-infrared magnitudes to calculate a distance of 680 ± 90 pc and M_V = 4.68 ± 0.70, consistent with V378 Peg being a nova-like. Time-resolved photometry taken between 2001 and 2009 reveals a period of 0.1346 ± 0.0004 d (3.23 ± 0.01 h). We identify this photometric variability to be negative superhumps, from a precessing, tilted accretion disk. Our repeated measurements of the photometric period of V378 Peg are consistent with this period having been stable between 2001 and 2009, with its negative superhumps showing coherence over as many as hundreds or even thousands of cycles.     

Superhump and outburst activity of the cataclysmic variable RZ LMi in the $$- and optical passbands

An analysis of the new \(U,B,V,R_{C},I_{C}\)-photometry of the cataclysmic variable RZ LMi obtained in 2016–17 showed the largest \((U-B)\) colour excess in quiescence as well as during the decline of brightness, associated with the outbursts activity. The smallest \((U-B)\) colour excess was found during the brightness increase from the quiescence. In contrast to the \((U-B)\) colour index, the \((B-V),(V-R_{C}),(R_{C}-I_{C})\) colour indices exhibits the largest colour excesses near the maximum of the outburst and the smallest during the quiescence. The \((B-V)\) colour index showed also a large excess 1–2 days before a minimum. The detailed study of superhumps during the maximum of activity reveals the largest \((U-B)\) colour excess at the time of the minimum brightness of superhumps. The \((B-R_{C})\) colour index exhibits a similar behaviour, but with a phase shift of \(+0.1\mbox{--}{+}0.2\) period of superhumps. The tracks in two-colour and colour-magnitude diagrams during superoutbursts are compared with the data for other cataclysmic variables during their outbursts as well as with published theoretical calculations.     

The influence of selection effects on the observed cataclysmic variable population: modelling and application to the Palomar–Green sample

Large differences between the properties of the known sample of cataclysmic variable stars (CVs) and the predictions of the theory of binary star evolution have long been recognized. However, because all existing CV samples suffer from strong selection effects, observational biases must be taken into account before it is possible to tell whether there is an inconsistency. In order to address this problem, we have modelled the impact of selection effects on observed CV samples using a Monte Carlo approach. By simulating the selection criteria of the Palomar–Green (PG) Survey, we show that selection effects cannot reconcile the predictions of standard CV evolution theory with the observed sample. More generally, we illustrate the effect of the biases that are introduced by magnitude limits, selection cuts in U − B and restrictions in Galactic latitude.     

'Stokes imaging' of the accretion region in magnetic cataclysmic variables — I. Conception and realization

Modelling the polarized cyclotron emission from magnetic cataclysmic variables has been a pivotal technique for determining the structure of the accretion zones on the white dwarf. To date, model solutions have been obtained from trial fits to the intensity and polarization data, which have been constructed from emission regions (for example arcs and spots) put in by hand. These models were all inferred indirectly from arguments based on the polarization and X-ray light curves.   We present a more analytical and objective technique using optimization by a genetic algorithm, Tikhonov regularization and Powell's method that robustly models the details of polarized emission.   To demonstrate the success of this technique, we show the results of several simulations in which we calculated the intensity and polarization curves from arbitrarily shaped emission regions on the surface of a sphere and then applied our code to these curves to recover the original test data. We also show how adding artificial noise affects the outcome of the optimization technique.     

A multi-site campaign on the long period variable subdwarf b star PG 1627+017

We report on the outcome of the first major multi-site campaign on a long-period variable subdwarf B star. The target PG 1627+017 was observed for a total of 334 h during April/May/June 2003 from the lynchpin observatory at Mt. Bigelow, Arizona, with important contributions coming from co-observations at SAAO, Calar Alto and Siding Spring. Preliminary analysis indicates the presence of 8–10 probable periods in the range ～4500 to ～8900 s with relative amplitudes between 0.1 and 0.5%;. The range over which the periods are found is in qualitative agreement with theoretical predictions and the number of periods found shows potential for an in-depth asteroseismological analysis. Multi-colour observations show that the relative amplitudes of pulsation are larger in the U-band than in the R, which again is in agreement with theory. However, more multi-colour observations are needed to be able to make statements at the quantitative level.     

From the Oort cloud to observable short-period comets – I. The initial stage of cometary capture

We investigate the first stage of the dynamical evolution of Oort cloud comets entering the planetary region for the first time. To this purpose, we integrate numerically the motions of a large number of fictitious comets pertaining to two samples, both with perihelion distances up to 5.7 au and random inclinations; the first sample is composed of comets whose orbits have at least one node close to 5.2 au, while the second is not subject to this constraint. We examine the orbits when the comets come to aphelion after their first perihelion passage within the planetary region, and find that there is a clear statistical dependence of the energy perturbations on the Tisserand parameter. There appear to be two main processes, of comparable importance, governing the shortening of semimajor axes to values of less than 1000 au, i.e. planetary close encounters, especially with Jupiter, and indirect perturbations due to the shifting of the motion from barycentric to heliocentric and back; the former process mostly affects comets crossing the ecliptic at about 5.2 au, or on low-inclination orbits, while the latter mostly affects comets of small perihelion distance. This last result may help to understand the relative paucity of Halley-type comets with perihelion distances larger than about 1.5 au.     

Search for star clustering: methodology and application to the Two Micron Galactic Survey

A new approach to the study of the large-scale stellar cluster distribution in the Galaxy based on two-point correlation techniques is presented. The basic formalism for this method is outlined, and its applications are then investigated by the use of a simple model of cluster distribution in the Galaxy. This provides an estimate of the potentials of the two-point correlation function for indicating clustering in the measured star positions, which can be related to the presence of star clusters in the observed field. This technique is then applied to several areas of the Two Micron Galactic Survey catalogue, from which information is obtained on the distribution of clusters according to position in the Galaxy, as well as about age, density of stars, etc.