The evolution of eccentricity in the eclipsing binary system AS Camelopardalis

In 2002,2004 and 2017 we conducted high precision CCD photometry observations of the eclipsing binary system AS Cam.By analysis of the light curves from 1967 to 2017(our data + data from the literature) we obtained photometric elements of the system and found a change in the system's orbital eccentricity of ?e = 0.03 ± 0.01.This change can indicate that there is a third companion in the system in a highly inclined orbit with respect to the orbital plane of the central binary,and its gravitational influence may cause the discrepancy between observed and theoretical apsidal motion rates of AS Cam.     

Pulsations in the eclipsing variable system AS Camelopardalis

We performed photoelectric observations of AS Cam in 2002–2004. Five new times of minima were obtained. Their positions are consistent with the previously found light equation for the system and with the hypothesis that the difference between the observed (15°/100 yr) and theoretical (44°/100 yr) rates of apsidal motion results from the presence of a third body in the system. A Fourier analysis of two observational data sets, 1968–1970 and 2002–2004, reveals, with a high significance, periodic light variations with a frequency of ω ₀ = 1.0950 ± 0.0001d^?1 and an amplitude of ～0 _. ^m 020, which are probably caused by the radial pulsations of one of the components. We found a seasonal phase shift of these oscillations that may be produced by other periodic processes in the system. We show that the fairly large scatter of observed times of minima about the theoretical curve of the light equation can be explained by the presence of pulsations. Using the 2002 and 2004 observations as an example, we show that including the pulsations reduces this scatter.     

Orbital elements of the RS CVn eclipsing binary,SV Camelopardalis

The extensiveUBV observations of SV Camelopardalis by Patkos (1982) have been analysed to derive the orbital elements of the system. The data were corrected for the effect of third body (Sarma, Sarma & Abhyankar 1985) and for the ‘RS CVn’ distortion wave (Sarma, Vivekanandarao & Sarma 1988). The cleaned data were used to obtain a preliminary solution by a modified version of Wellmann method (Sarma & Abhyankar 1979) from which we concluded that the primary eclipse is a transit. The final orbital elements of SV Cam were obtained by the modified version (Sarma 1988; Sarmaet al. 1987) of WINK program by Wood (1972). The colour and median brightness variation are discussed. From the spectroscopic mass functionf(m) = 0.118 M_⊙ (Hiltner 1953), the absolute dimensions of the components are found to be 0.826 M_bd & 0.592 M_⊙ and 1.236 R_⊙ & 0.778 R_⊙ for the primary and secondary components, respectively. The age of the binary system is estimated to be 6.0 ± 1.0 × 10⁸ years     

The eclipsing active star SV Camelopardalis

We present analysis and spot solutions based on yet unpublished B and V photoelectric observations on the active binary system SV Cam, carried out at Piszkéstető Mountain Station of Konkoly Observatory Budapest. The present spot solutions are based on the observed light curves in September 1993 and July 1994. Comparison of recent and older spot solutions – taken from the literature – suggests long term differences, but these divergences might be caused by some differences of the applied computational methods. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Period study of AL Camelopardalis

A detailed period study of the eclipsing binary system AL Cam is presented. A new period of 1^d.3283304 has been given. Period fluctuations are apparent around the years 1931, 1934, 1948, and 1965. Large scatter present in the early part of the O–C diagrams does not allow us to estimate the actual value of period changes present in different portions of O–C diagrams.     

The magnetic field and rotational period of 53 Camelopardalis

The magnetic Ap star 53 Cam has been described as the best object for testing theories of elemental diffusion in the presence of a stellar magnetic field. It is thus vital to determine the rotational period of this very important star as accurately as possible. An improved period (8.026 81±0.000 04 d) is derived here by combining new measurements of the effective magnetic field with previously published values.     

Variability Study of the SX Phoenicis Star BL Camelopardalis

New time-series photometric observations of BL Cam in the V band and white light were made during 2005 to 2007 at the Xinglong Station of China. The frequency analysis confirms two closely separated frequencies, 25.181 d-1 and 25.571 d-1, but the frequency of 31-32 d-1 reported in the literature was not detected in the new data. New times of maximum light were determined from both our light curves and those available on Internet, allowing a more comprehensive study of the O - C diagram, together with the times of maximum light in the literature. A new interpretation, including the period increasing before 1988 and decreasing since 1992 of BL Cam and the light-time effect in a binary system, looks plausible.     

The orbital and superhump periods of the dwarf nova HS 0417+7445 in Camelopardalis

We present the 2005–2010 outburst history of the SU UMa-type dwarf HS 0417+7445, along with a detailed analysis of extensive time-series photometry obtained in March 2008 during the second recorded superoutburst of the system. The mean outburst interval is 197 ± 59 d, with a median of 193 d. The March 2008 superoutburst was preceded by a precursor outburst, had an amplitude of 4.2 magnitudes, and the whole event lasted about 16 days. No superhumps were detected during the decline from the precursor outburst, and our data suggests instead that orbital humps were present during that phase. Early superhumps detected during the rise to the superoutburst maximum exhibited an unusually large fractional period excess of ? = 0.137 (P_sh = 0.0856(88) d). Following the maximum, a linear decline in brightness followed, lasting at least 6 days. During this decline, a stable superhump period of P_sh = 0.07824(2) d was measured. Superimposed on the superhumps were orbital humps, which allowed us to accurately measure the orbital period of HS 0417+7445, P_orb = 0.07531(8) d, which was previously only poorly estimated. The fractional superhump period excess during the main phase of the outburst was ? = 0.037, which is typical for SU UMa dwarf novae with similar orbital period. Our observations are consistent with the predictions of the thermal-tidal instability model for the onset of superoutbursts, but a larger number of superoutbursts with extensive time-series photometry during the early phases of the outburst would be needed to reach a definite conclusion on the cause of superoutbursts.     

New photoelectric observations and elements of the eclipsing W UMa-type system V839 Oph

The W UMa-type system V839 Oph was observed photoelectrically in two wavebands (B andV) during 1985 at the Kryonerion Astronomical Station of the National Observatory of Greece. The light curves of the system are analysed using the frequency-domain techniques and new geometric and photometric elements are given. The light variations of the system are also discussed.     

HT Camelopardalis: the simplest intermediate polar spin pulse

The intermediate polar (IP) HT Cam is unusual in that it shows no evidence for dense absorption in its spectrum. We analyse an XMM–Newton observation of this star, which confirms the absence of absorption and shows that the X-ray spin pulse is energy independent. The modulation arises solely from occultation effects and can be reproduced by a simple geometrical model in which the lower accretion footprint is fainter than the upper one.
We suggest that the lack of opacity in the accretion columns of HT Cam, and also of EX Hya and V1025 Cen, results from a low accretion rate owing to their being below the cataclysmic variable period gap.     

The McDonald photoelectric occultation observation program

Since 1968 an assiduous program of photoelectric observation of occultations of stars by the Moon has been pursued at McDonald Observatory. A total of about 600 events has been observed of which 254 have been published and a second list is in preparation. Timings derived from the reductions have errors of the order of 1 ms corresponding to a positional uncertainty in the lunar limb of typically 80 cm. Results are routinely communicated to the ephemerides offices.In about 140 events the fringe pattern due to diffraction by the lunar limb is sufficiently well defined to permit a determination of the slope near the point of occultation. A statistical discussion of these data is given. In all except a few cases, the slopes are numerically less than 15°, though 7 cases with slopes between 30° and 40° have been found. The relations between numbers of observations and contact angle, and between errors of slope determination and contact angle are discussed. The distribution of slope data with contact angle seems adequately explained. When slope data are collected by position angle consistently large and consistently small values show a tendency to group in a pattern suggesting a connection with observed large scale features on the lunar limb.The influence of lunar limb irregularities of a scale of a few meters on observed diffraction patterns and inferred timings is discussed. Multichannel observations should be of value in removing ambiguities. The use of occultation observations for the discovery of multiple stars and for the measurement of angular diameters of stars is mentioned. Future developments proposed for the project are considered.The project has involved contributions by a considerable number of individuals from the staff and student body at Austin, Texas, from the staff at McDonald Observatory, from visiting scientists and from the Laser Ranging Group. These contributions are acknowledged in the paper. The work has been supported by NSF Grants GP-21204 and GP-32263X.Communication presented at the conference on Lunar Dynamics and Observational Coordinate Systems held January 15–17, 1973 at the Lunar Science Institute, Houston, Tex., U.S.A.     

Spectrographic study of the eclipsing binary system SZ Camelopardalis

Thirteen high-dispersion spectrographs of the eclipsing binary star SZ Cam have been studied with a view of determining more accurate information on: (i) the spectral type and luminosity classifications, (ii) absolute parameters for the component stars, (iii) the stellar environment of SZ Cam. The main results in these categories are as follows: (i) O9.5 Vnk, (ii)m _g=19±2M _⊙,m _s=6.5±1M _⊙;r _g=9.7±3.6R _⊙,r _s=4.8±1.7R _⊙;T _e～30000 K,T _e～23000 K; (iii) there is a local concentration of absorbing material which may reach a density of 2M _⊙ pc^?3, and the distance of the star is found to be 600±150 pc. The determined overluminosity of the secondary star and the local concentration of absorbing material are two topics which provide the basis for a discussion section.     

The multifunction photoelectric photometer of Torino Observatory

The paper describes the design and the realization of a multiple-function photoelectric photometer made by Trieste Observatory for Torino Observatory. The system design shows a two-beam, sequential multiband photon counting and analog photoelectric photometer configuration based on a PDP8/E computer for the control and data acquisition and elaboration. The actual realization of the system and the use of it in the one-beam configuration operating now at torino Observatory shows the advantages of such a solution and the easiness in modifying and determining the system functions by software programs rather than by hardware specials. Work supported by Consiglio Nazionale delle Ricerche, Gruppo Nazionale di Astronomia, Settore Tecnologie Astronomiche. The realization of the machine was fully supported by Torino Observatory. Trieste Observatory-Instruments and Data Processing Group (5/76).     

Cyclic variations of the period and luminosity of SV Camelopardalis

New standardized V ‐band light curves (LCs) for the eclipsing binary SV Cam have been modeled using the PHOEBE program (v. 0.31a). Absolute parameters of the stellar components were then determined, enabling them to be positioned on the mass‐radius diagram. Analysis of eclipse minima timing data (O – C diagrams) indicated two cyclic periods of 48.0 and 23.3 yr. These cyclic variations of the orbital period are interpreted in terms of motion of a third body around the system and magnetic activity cycle modulating the orbital period of SV Cam via the Applegate (1992) mechanism. The use of the Applegate model for SV Cam has been checked by examining the long term brightness variation and calculating some important parameters of this system. The results of these calculations favor the modulation of the orbital period by the Applegate mechanism. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometric solution for the eclipsing binary system AO Camelopardalis

UBV light curves of AO Cam were analyzed with Wilson and Devinney's model. The system was found to be a contact configuration with a degree of overcontact of 1.4%. The mass ratio of the system is about 1.30, and the inclination is 75 _. ⁰ 9. The primary eclipse appears to be an occultation. Thus AO Cam has the characteristics of a W-type W UMa system. Its location in a period-spectral type diagram suggests that the system may be a zero-age contact system.     

Evidence for pole switching in the magnetic cataclysmic variable BY Camelopardalis

An analysis of X-ray and optical light curves of the magnetic cataclysmic variable (MCV) BY Cam is presented. This system is one of three MCVs in which the spin period of the white dwarf and the binary orbital period differ by ∼1 per cent. As such these 'BY Cam' stars are important objects with which to probe the field structure of the magnetic white dwarf and ultimately the nature of synchronization of AM Her binaries. We confirm asynchronous rotation of the magnetic white dwarf with respect to the binary. We find evidence that the accretion stream accretes directly on to the white dwarf as in AM Her systems, but further, the stream impacts on to different magnetic poles over the course of the beat period. We present evidence that the optical and hard X-ray light curves modulate in phase, but together they are out of phase with the soft X-ray light curve. We confirm the spin down of the white dwarf which is expected to lead to the synchronization of the spin and orbital periods of BY Cam.     

Multiple frequency analysis of the large-amplitude SX Phoenicis star BL Camelopardalis

A multifrequency analysis of the SX Phoenicis star BL Camelopardalis is presented on the basis of new high-speed photometry, along with fitting a total of 136 maxima. BL Cam is a multiple periodic pulsator. We find f ₀=25.5768, f ₁=25.2982, f ₂=25.8622, f ₃=31.5912, f ₄=25.1065, f ₅=25.5147 and f ₆=25.6188 cycle d⁻¹ together with the harmonics 51.1513 and 76.7268 cycle d⁻¹ and combination frequencies f ₀+ f ₁, f ₀+ f ₂ and f ₀+ f ₃. The new frequency solution represents the light curves of BL Cam quite well. The observed minus calculated (O-C) analysis indicates that the fundamental frequency is in good agreement with the results of Fourier analysis.     

High Effective Magnetic Field Strengths of the Magnetic Star 53 Camelopardalis

New measurements of the effective magnetic field strengths of 53 Cam yield essentially higher values than formerly published measurements. Three ZEEMAN -spectrograms yielded for the magnetic field +6800, – 11400 and – 7500 Gauß at the phases 0.17, 0.75 and 0.87 cycles after the positive crossover.     

Questions in photoelectric photometry

The paper reviews generally well-known, though still frequently overlooked, procedural points in photoelectric photometry. Some examples, which point up the value of high photometric precision, are included.     

A study of the distortion wave in the RS CVn eclipsing binary SV Camelopardalis

The light outside the eclipses of the totally eclipsing RS CVn binary SV Camelopardalis (SV Cam) is Fourier analysed and the amplitudes of the distortion waves have been derived. The distribution of the percentage contributions of these amplitudes inV, B andU colours with respect to the luminosities of the binary components indicates that the hotter component is the source of the distortion waves. These distortion waves, attributed to star spots, are modelled according to Budding (1977) and spot parameters like longitude, latitude, temperature and size are obtained. From this study it is noticed that while symmetric waves with two minima could be fitted satisfactorily, asymmetric waves with more than two minima could not be fitted well. From the longitudes of the minima of the best fitted curves, migration periods of four spot groups are determined. Assuming synchronism between rotation and orbital periods, the rotation periods of the four spot groups are derived from their migration periods. The period of rotation of one of the spot groups having direct motion is found to be 0^d.5934209 while the periods of the other three spot groups having retrograde motion are 0^d.5926588, 0^d.592607 and 0^d.5924688. As the latitudes of these spots are known from modelling parameters, the latitude having a rotation period equal to that of the orbital period (co-rotating latitude) is found to be about 30°