On the effect of emission lines on UBVR photometry

We investigate the effect on the U, B, V, R_C and R_J magnitudes of the removal of emission lines from a spectrum. We determined Δm corrections from the ratio of fluxes with and without emission lines, transmitted from the object through a photometric filter. An exact and simplified approach for operative use was applied. The effect was demonstrated for classical symbiotic stars, symbiotic novae and the classical nova V1974 Cyg. It was found that about 20–30%, 30–40%, 10% and 26/20% of the observed flux in the U, B, V and R_C/R_J filters, respectively, are radiated in the emission lines of the investigated classical symbiotic stars. The largest effect was found for symbiotic novae (RR Tel and V1016 Cyg) and the classical nova V1974 Cyg at 210 days (an average of 74%, 79%, 56% and 66/60%), because of their very strong emission line spectrum. In all cases, the line corrected flux points fit the theoretical continuum well. The difference between Δm corrections obtained by the accurate calculation and that given by our approximate formula is less than 10%. Deviations up to 30% can exist only in the U passband. Examples for practical applications are suggested.     

UBVRI photometry and polarimetry of the young eclipsing binary EK Cep

Multicolor photometric and polarimetric observations of the eclipsing binary EK Cep at the Crimean Astrophysical Observatory in 1995 and 2006–2007 are reported. Polarimetric observations were made of stars in the neighborhood of EK Cep. It is shown that the observed linear polarization of EK Cep is determined by a variable circumstellar constituent, as well as by the interstellar component. Various possible mechanisms for formation of the intrinsic polarization of binary stars are discussed. Translated from Astrofizika, Vol. 52, No. 1, pp. 117–126 (February 2009).     

Optical photometry of GM Cep: evidence for UXor type of variability

Results from optical photometric observations of the pre-main sequence star GM Cep are reported in the paper. The star is located in the field of the young open cluster Trumpler 37—a region of active star formation. GM Cep shows a large amplitude rapid variability interpreted as a possible outburst from EXor type in previous studies. Our data from BVRI CCD photometric observations of the star are collected from June 2008 to February 2011 in Rozhen observatory (Bulgaria) and Skinakas observatory (Crete, Greece). A sequence of sixteen comparison stars in the field of GM Cep was calibrated in the BVRI bands. Our photometric data for a 2.5 years period show a high amplitude variations ($\Delta V \sim2\mbox{$\Delta V \sim2\mbox{) and two deep minimums in brightness are observed. The analysis of collected multicolor photometric data shows the typical of UX Ori variables a color reversal during the minimums in brightness. On the other hand, high amplitude rapid variations in brightness typical for the Classical T Tauri stars also present on the light curve of GM Cep. Comparing our results with results published in the literature, we conclude that changes in brightness are caused by superposition of both: (1) magnetically channeled accretion from the circumstellar disk, and (2) occultation from circumstellar clouds of dust or from features of a circumstellar disk.     

Edward Schoenfeld: Visual photometry of variable stars. 2. Variable stars

We describe the results of visual photometry of 111 variable stars observed by Schoenfeld in the 19th century. The entire body of data contains brightness curves in tabulated form, as well as certain additional useful information: graphs of changes in brightness of variable stars and identification tables of comparison stars and stars suspected of variation in brightness.     

BV photometry of the short-period variable UU Cam

First BV measures of the short period variable UU Cam are presented here. Though the GCVS classification of the star as an RR Lyr variable, based on the spectrographic measures of Bond (1978), is substantially confirmed, there remains some doubts about it, as suggested by the general aspect of theB-V colour index.     

Infrared photometry for three RV Tau variable stars

We have analyzed our long-term (1995–2008) JHKLM photometry for three variable RV Tau supergiants. It follows from this analysis that: the amplitude of the JHK brightness variations is approximately the same, 0 ^m . 9–1 ^m , for the three stars; a negative linear trend is noticeable in the variations of the mean J brightness for AC Her; and the mean J brightness of R Sct and V Vul remained constant. The observed J brightness fluctuations in the supergiants are shown to be consistent either only with the temperature pulsations (AC Her and V Vul) or with the temperature and radial pulsations (R Sct). We have detected long-term pulsations in the J brightness and J-H color variations of the supergiants with the following characteristic time scales: ∼1500 days (AC Her), ∼3500 days (R Sct), and ∼800 and ∼1500 days (V Vul). Our search for a periodic component in the infrared brightness variations of the three stars has revealed periods that differ from those obtained from optical observations. We show that relatively hot dust shells (T _d ∼ 700–800 K) exist around the supergiants under study; the densest and most massive shell was observed for V Vul. The ranges of optical-depth variations for the dust shells were τ(1.25 μm) ≈ 0.04–0.10 (AC Her), ≈0.02–0.12 (R Sct), and ≈0.18–0.32 (V Vul). The spectral types in the infrared varied over narrower ranges than those that followed from optical observations of these stars.     

BV photometry of the RRc variable star DH Pegasi

Revised light elements of the RR Lyrae variable star DH Pegasi are presented together with a newBV light curve.     

Infrared photometry for five close binary systems

We present the JHKLM photometry for five close (W Ser) binary systems obtained in the period 1996–2004. Positive phase shifts (with respect of the adopted ephemerides) have been found in the orbital infrared light curves for three binaries, RX Cas, KX And, and β Lyr; the rates of increase in their periods are ～3.5 × 10^?4, ～1.6 × 10^?3, and ～1.4 × 10^?4 days yr^?1, respectively. We have performed the spectral classification of the components of the binaries under study and estimated their parameters.     

UBV photometry of the Ap variable UZ Psc = HD 10783

NewUBV photometry, obtained between late 1965 and early 1969, is presented and combined with existing published photometry to derive an improved ephemeris for times of maximum brightness: 2439758.00+4 _d ^. .1328n. On leave from Dyer Observatory, Vanderbilt University, Nashville, Tennessee, U.S.A.     

On the interpretation of the photometry of irregular variable stars observed intermittently

This note is concerned with the inherent possibilities and limitations in the characterisation of irregular variables when, as is almost inevitably the case, the observations are not effectively continuous. The historical tendency to interpret almost everything in terms of strict periodicity is criticised. The basic logic of the situation is discussed, and it is emphasised that intermittency of observation inevitably blunts our knowledge of the spectrum of the variation. This can be restored to only a limited extent, depending on how reliably it is possible to presume missing observations by interpolation. Some applcation is made to a recent publication on 3C 345.A knowledge of formal Fourier theory is assumed, and the aim is to discuss critical principles rather than to recommend any fixed procedures of interpretation.     

Photometry and discussion of the classical Algol systems U Sge and U Cep

The (in many respects, similar) classical Algol-type eclipsing binary systems U Sge and U Cep are studied and compared against a background of photometric evidence, both broadhand and narrowband. Broadband photometry of the primary minimum of U Sge over a four year period fails clearly to confirm Olson's (1982b) finding of radial variations.On the other hand, the W-type pattern of variation indicated in Olson's (1976) H photometry of the primary eclipse of U Cep is also noticed for U Sge. These effects are analysed in terms of an emitting accretion disk, surrounding the primary components. Electron densities in these highly ionized structures are derived to be in the range 10¹⁰–10¹¹, for the H emitting region, with that of U Cep being 3 times greater than that of U Sge, though since the volume of the structure is 3 times bigger for U Sge, the overall masses are comparable.These findings can be placed in a Case B-type interacting binary context, which shows the studied accretion structures to be relatively tenuous; and, since the mean mass loss rate for U Cep is likely to be high than that of U Sge by more than an order of magnitude, suggests they are not so directly dependent on this mass-loss rate.     

Narrow-band photometry and differential effects in close binary systems

The application of narrow-band photometry to close binary systems is considered, with particular attention to the effects of eclipses. Models are examined, first in which two normal absorption spectra are superposed and then in which a third emission component is present. The purpose of these models is to relate to narrow-band observations of a kind similar to some preliminary results presented for U Sge in H. It is shown that, under the conditions obtaining for such observations, the role of Doppler effects should be small, but that the observations should be sensitive to any difference between the limb darkening in the line and surrounding continuum.In the three-component models, the emitting volume is pictured as (i) a chromospheric shell and (ii) an equational disk about the primary star. The expected modifications corresponding to such models of observations of primary eclipse are calculated. Possible applicability of the models to the preliminary observations is briefly considered.     

Near infrared photometry of some RS CVn systems and candidates

Infrared observations in the J, H, and K bands were made on eleven RS CVn systems. Infrared (IR) excess 0.3 mag in the J, H, and K bands was observed from the three systems UX Ari, HR 1099 and CrB. Similar observations were also made on the RS CVn candidates HD 26354, 39937, 42449, 51268, and 86005.The IR excess in the RS CVn systems for which near infrared photometric data are available is found to be correlated with the maximum of optical wave amplitude of these systems.The observed excess cannot be explained on the basis of a single process such as: (i) emission from cool spots on the photosphere; (ii) free-free emission from an optically thin circumstellar plasma; or (iii) dust grain emission from circumstellar material.On leave from TIFR, Bombay, India.     

Astrokit-an efficient program for high-precision differential CCD photometry and search for variable stars

Having a need to perform differential photometry for tens of thousands stars in a several square degrees field, we developed Astrokit program. The software corrects the star brightness variations caused by variations of atmospheric transparency: to this end, the program selects for each star an individual ensemble of reference stars having similar magnitudes and positions in the frame. With ten or more reference stars in the ensemble, the differences between their spectral types and the spectral type of the object studied become unimportant. A strokit searches for variable stars using Robust Median Statistics criterion, which allows candidate variables to be selected more efficiently than by analyzing the standard deviation of star magnitudes. The software allows very precise automatic analysis of long inhomogeneous sets of photometric observations of a large number of objects to be performed, making it possible to find “hot Jupiter” type exoplanet transits and low-amplitude variables. We describe the algorithm of the program and the results of its application to reduce the data of the photometric sky survey in Cygnus as well as observations of the open cluster NGC188 and the transit of the exoplanet WASP-11 b /HAT-P-10 b, performed with the MASTER-II-URAL telescope of the Kourovka Astronomical Observatory of the Ural Federal University.