Eclipsing binary system R Canis Majoris

Problems raised by R CMa are revisited. The theoretical significance of observable period changes is noted. Some recent observations are presented and briefly considered against this background.     

A spectrographic study of R Canis Majoris

New spectroscopic elements of R Canis Majoris are given in this paper, computed from 17 plates secured at the Astronomical Observatory of Merate. A new orbit has also been computed with the program by Bertiau, from 81 observations covering a period of about 40 years.Two models of this binary system are proposed, based on two different assumptions and on a newly determined mass function. It is confirmed that the main peculiarity of this binary with regard to the mass-luminosity relation is real; there is also an evidence of mass loss from the Lagrangian pointL ₂ as suggested by Kitamura.A suspected variation of the velocityV ₀ of the center of mass seems to indicate the presence of a third body. The evidnece is, however, not yet conclusive.     

Orbital period of the dwarf nova HL Canis Majoris

We present a small sample of time-resolved optical spectroscopy of the dwarf nova HL CMa during an outburst state. By combining radial velocity measurements with published data we show that the previously quoted value is not the only candidate for the orbital period of this system. We reduce the significance of daily aliasing but cannot distinguish between two periods at 0.2146±0.0004 and 0.2212±0.0005 d. We show that the low-excitation emission lines are composites from an accretion disc and the companion star, and that high-excitation emission originates in the disc or outflowing material associated with the accreting white dwarf.     

On the relation between the amplitude of light and radial velocity variations of β Canis Majoris stars

The relation between the amplitude of light m and the amplitude of the radial velocity 2K for Canis Majoris stars is investigated. A linear relationship between m and 2K is found. However, the two stars BW Vul and Sco, which have the largest radial velocity variations, do not seem to share this relationship.     

Preliminary results of the spectral analysis of Suzaku data of SW Ursae Majoris and BZ Ursae Majoris

Herein, we present the preliminary results of the spectral analysis of the Suzaku data of SW Ursae Majoris (SW UMa) and BZ Ursae Majoris (BZ UMa) which were obtained in their quiescent states. The aim of this study was to analyse 0.5–6.0 keV energy range X-ray photons of the Suzaku satellite and to determine their emission mechanisms and the areas where they were radiated from these two dwarf novae. No study on this energy range for BZ UMa has been reported in the literature. We analysed the Suzaku data in the (0.5–6.0) keV and in (0.5–2.5) keV energy bands of the systems separatelly to search for possible differences between the emission mechanisms in the energy ranges; however, none were found. We obtained the best-fitted spectral models, flux, luminosity, temperature and mass accretion rate values for the systems. The white dwarf radius of BZ UMa, which has not been reported in the literature, was found to be 6.88 × 10⁸ cm. From this study, we concluded that the mass accretion rate values for both systems were lower than the critical mass accretion rate value in the boundary layers of cataclysmic variables, which indicates that the boundary layers are composed of optically thin thermal X-ray emitting gas in their quiescent state; these results support those of previous studies regarding SW UMa and some studies regarding BZ UMa. Another result was that there can be a coronal structure above the boundary layer which act as soft X-ray emitter for SW UMa.     

The SU Ursae Majoris Star TU Crateris

We have established that the cataclysmic variable TU Crateris is an SU UMa star. Superhumps were observed after 3 days of the 1998 March-April supermaximum, repeating with a mean period of P_s = 0d.08535(5). Timings of superhump maxima revealed a period decrease of P = 7.2 × 10^-5. Based on an empirical relationship, we estimated an orbital period of 0d.0810(25), just in the lower limit of the reported quiescence photometric period. H emission lines during quiescence vary with the orbital period with radial velocity half amplitude of 70 ± 19 km s^-1, evidencing a hotspot located in front of the standard position.     

The Detection of Multimodal Oscillations on alpha Ursae Majoris

We have used the star camera on the Wide-Field Infrared Explorer satellite to observe the K0 III star alpha UMa, and we report the apparent detection of 10 oscillation modes. The lowest frequency mode is at 1.82 μHz, and it appears to be the fundamental mode. The mean spacing between the mode frequencies is 2.94 μHz, which implies that all detected modes are radial. The mode frequencies are consistent with the physical parameters of a K0 III star, if we assume that only radial modes are excited. Mode amplitudes are 100-400 μmag, which is consistent with the scaling relation of Kjeldsen & Bedding.     

New absolute magnitude calibrations for WUrsa Majoris type binaries

Parallaxes of W UMa stars in the Hipparcos catalogue have been analyzed. 31 W UMa stars, which have the most accurate parallaxes (σ_π /π < 0.15) which are neither associated with a photometric tertiary nor with evidence of a visual companion, were selected for re‐calibrating the Period‐Luminosity‐Color (PLC) relation of W UMa stars. Using the Lutz‐Kelker (LK) bias corrected (most probable) parallaxes, periods (0.26 < P < 0.87, P in days), and colors (0.04 < (B – V)₀ < 1.28) of the 31 selected W UMa, the PLC relation have been revised and re‐calibrated. The difference between the old (revised but not bias corrected) and the new (LK bias corrected) relations are almost negligible in predicting the distances of W UMa stars up to about 100 pc. But, it increases and may become intolerable as distances of stars increase. Additionally, using (J – H)₀ and (H – K_s)₀ colors from 2MASS (TwoMicron All Sky Survey) data, a PLC relation working with infrared data was derived. It can be used with infrared colors in the range –0.01 < (J – H)₀ < 0.58, and –0.10 < (H – K_s)₀ < 0.18. Despite of the fact that the 2MASS data refer to single epoch observations which are not guaranteed to be taken at maximum brightness of theWUMa stars, the established relation has been found surprisingly consistent and reliable in predicting LK corrected distances of W UMa stars (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The variation of the light curve of W Ursae Majoris

A new set of photoelectric B and V observations of W Ursae Majoris obtained during a period of one week in 1968 is presented.From the measurements it can be concluded that in general the light curve in both colors is free from complications. In particular, no systematic brightness differences between consecutive periods can be found.The observations made during total eclipse in two different periods yield flat minima fitting almost perfectly together, the mean error of the single measurement beeing of the order of 0.^m003. The duration of the phase of totality is estimated to 0.036P=17.3 m thus confirming the value given by Cester and Gridelli.From a plot of the square deviations of the single observations (I/I)² from the mean intensity curve vs phase it can be shown that the scattering decreases strongly during primary eclipse thus indicating that the source producing these fluctuations is essentially confined to the space between the two components. A comparison with earlier photoelectric observations also supports the assumption that the variational behavior of the light curve is caused by a gaseous cloud between the two components rather than by an envelope surrounding the whole system.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Multicolor Photometry of the SU Majoris Dwarf Nova V1504 Cygni

On the basis of multicolor observations of the dwarf nova V1504 Cyg, made from 1988 to 2001 at the Crimean Astrophysical Observatory and at the Crimean Laboratory of the P. K. Shternberg State Astronomical Institute in bands of the standard BVR photometric system, the brightness characteristics and color indices were obtained for a superoutburst and normal outbursts of the star. At an outburst maximum V1504 Cyg is bluer than at a minimum, with the ascending branch of an outburst being characterized by redder color indices than the descending branch. A detailed analysis of the behavior of two outbursts is consistent with Smak's model A, in which an outburst is caused by temperature instability developing first in the outer parts of the accretion disk around the compact component of the binary system and propagating into the inner parts. The characteristics of the other outburst are consistent with Smak's model B, in which instability develops first in the inner parts of the disk. It is suggested that type A outbursts are typical of V1504 Cyg, while type B outbursts are rare.     

uvbyβ photometry of the short-period binary VV Ursae Majoris

We present well-sampled uvby light curves, supplemented by a few β filter measurements, of the Algol binary VV UMa. The light curves are analysed using two different codes to derive the orbital and absolute stellar parameters of this binary. We find reasonably good fits to the light curves and determine the stellar effective temperatures T _eff,1≃9000–9600 K , and T _eff,2≃5300–5600 K with a mass ratio q ≃0.35 . From the light-curve fits we discard the possibility of an anomalous gravity-darkening exponent for the secondary star of this system, as previously suggested.
We find evidence of short-term, small-amplitude variations in the brightness of the system. Two periodicities of about 1.10 and 0.51 h seem to be present in the data for at least two different nights, even within the secondary eclipse. This suggests that VV UMa may be a new Algol binary with a low-amplitude variable primary star, but new data collected during longer observing runs are necessary to confirm the pulsating nature of the brightness variations.     

W Ursae Majoris stars: Period-spectral type relation and period changes

The relation between period and spectral type is examined for 33 W Ursae Majoris stars for which accurate observations have enabled us to clearly classify their eclipse types at the primary minimum (transit (A) or occultation (W)). About a half of the examined stars are of A-type, and the rest correspond to W-type. Periods of W-type systems are found to fall within 0.25–0.5 days, while periods of A-type systems range between 0.25–0.9 days. For A-type systems certain period-spectral type relations seem to hold, but for W-type systems no definite relation could be found. Statistically, a W Ursae Majoris star will undergo a period change every ～17000 cycles, on the average, and a time scale for the period change (d lnP/dt)^?1 is estimated to be about 10⁶ years.     

A multicolor photometric study of the neglected eclipsing binary FT Ursae Majoris

The multicolor photometric observations of the neglected eclipsing binary FT Ursae Majoris (FT UMa) were obtained in 2010. The 2003 version of the Wilson-Devinney code was used to analyze the light curves in the B, V and R bands simultaneously. Based on the spectroscopic mass ratio q = 0.984 published by Pribulla et al., it is found that FT UMa is an evolved contact binary with a contact degree of 15.3%. The low amplitude of light variations, ～ 0.15 mag, arises mainly from a moderately low inclination angle...     

Superhumps in a Peculiar SU Ursae Majoris-Type Dwarf Nova, ER Ursae Majoris

We report the photometry of a peculiar SU Ursae Majoris-type dwarf nova, ER Ursae Majoris, for 10 nights during 1998 December and 1999 March, covering a complete rise to the supermaximum and a normal outburst cycle. Superhumps have been found during the rise to the superoutburst. A negative superhump appeared in the December 22 light curve, while the superhump on the next night became positive and had a large-amplitude waveform distinct from that of the previous night. In the normal outbursts we captured, superhumps with larger or smaller amplitudes seem to always exist, although it is not necessarily true for every normal outburst. These results show great resemblance to V1159 Ori. It is more likely that superhumps occasionally exist at essentially all phases of the eruption cycles of ER UMa stars, which should be considered in modeling.     

New CCD photometry for the extreme lower mass-ratio binary AW Ursae Majoris

This paper presents charge-couple device (CCD) photometric observations for the eclipsing binary AW UMa. The V-band light curve in 2007 was analyzed using the 2003 version of the Wilson–Devinney code. It is confirmed that AW UMa is a total eclipsing binary with a higher degree of contact f=80.2% and a lower mass ratio of q=0.076. From the (O−C) curve, the orbital period shows a continuous period decrease at a rate of dP/dt=−2.05×10⁻⁷ d yr⁻¹. The long-term period decrease suggested that AW UMa is undergoing the mass transfer from the primary component to the secondary one, accompanied by angular momentum loss due to mass outflow L ₂. Weak evidence indicates that there exists a cyclic variation with a period of 17.6 yr and a small amplitude of A=0. ^d 0019, which may be attributed to the light-time effect via the third body. If the existence of an additional body is true, it may remove a great amount of angular momentum from the central system. For this kind of contact binary, as the orbital period decreases, the shrinking of the inner and outer critical Roche lobes will cause the contact degree f to increase. Finally, this kind of binary will merge into a single rapid-rotation star.