Dwarf Nova EM Research Articles

Quasi-periodic oscillations and long-term orbital period variation of the eclipsing dwarf nova EM Cyg

ABSTRACT EM Cyg is an eclipsing dwarf nova with an orbital period above the period gap of cataclysmic variables. Based on the whole outburst of EM Cyg observed by the Transiting Exoplanet Survey Satellite (TESS) from 2019 July 18–August 14, the evolution of quasi-periodic oscillations (QPOs) in EM Cyg was investigated. A QPO with a period of about 1000 s was found during both outburst and quiescence. In addition, we found another QPO with a period of about 500 s, which was present during the outburst but disappeared as the outburst ended. QPOs should be caused by the activity of the accretion disc. Using the data obtained during the outburst, we analysed the characteristics of the light curves and found that the eclipsing depth increased and the light-minimum moment earlier during the outburst. In addition, with the new eclipse times obtained by TESS and from our observations, an O − C diagram for this system was produced. According to the O − C analysis, the orbital period is increasing at a rate of $\dot{P} = 1.66(\pm 0.36) \times 10^{-8}\, \mathrm{d\,yr^{-1}}$. There is a cyclic variation in the O − C curve that might be caused by the light-traveltime effect. A third body may exist in the EM Cyg system with the mass $m_3\sin {i{^{\prime }}} = 0.097(\pm 0.000\,35) \, \mathrm{M}_{\odot }$.

On the accretion disc properties in eclipsing dwarf nova EM Cyg

In this paper we analyze the behavior of the unusual dwarf nova EM Cyg using the data obtained in April–October, 2007, at the Vyhorlat observatory (Slovak Republic) and in September, 2006, at the Crimean Astrophysical Observatory (Ukraine). During our observations, EM Cyg has shown outbursts in every 15–40 days. Because on the light curves of EM Cyg a partial eclipse of the accretion disc is observed, we applied the eclipse mapping technique to a reconstruction of the temperature distribution in the eclipsed parts of the disc. Calculations of the accretion rate for the system were made for the quiescent and the outburst states of activity for various distances.

A mystery solved: the mass ratio of the dwarf nova EM Cygni

We have discovered that the spectrum of the well-known dwarf nova EM Cyg is contaminated by light from a K2–5V star (in addition to the K-type mass donor star). The K2–5V star contributes approximately 16 per cent of the light from the system and if not taken into account has a considerable effect upon radial velocity measurements of the mass donor star. We obtain a new radial velocity amplitude for the mass donor star of K2=202±3 km s−1, compared with the value of K2=135±3 km s−1 obtained in Stover, Robinson & Nather's classic study of EM Cyg. The revised value of the amplitude, combined with a measurement of rotational broadening of the mass donor, v sin i=140±6 km s−1, leads to a new mass ratio of qM2M1=0.88±0.05. This solves a long-standing problem with EM Cyg, because Stover et al.'s measurements indicated a mass ratio q>1, a value that should have led to dynamically unstable mass transfer for the secondary mass deduced by Stover et al. The revised value of the mass ratio, combined with the orbital inclination i=67±2°, leads to masses of 0.99±0.12 M⊙ and 1.12±0.08 M⊙ for the mass donor and white dwarf respectively. The mass donor is evolved, because it has a later spectral type (K3) than its mass would imply. We discuss whether the K star could be physically associated with EM Cyg or not, and present the results of the spectroscopic study.

OBSERVATIONS OF THE RAPID OSCILLATIONS OF EM CYG.

ABSTRACT High-speed two-color photometric observations have been made of the dwarf nova EM Cyg and rapid coherent oscillations with periods between 14.6 and 16.5 sec have been found. The minimum period is less than the period of a Keplerian orbit at the surface of a carbon white dwarf. The color temperature of the oscillating component is much higher than that of the constant component of the luminosity. These results suggest that the source of the oscillations is the white dwarf or the inner part of the accretion disk.

Radial Velocity and Line Profile Variations in the Dwarf Nova Em-Cygni

view Abstract Citations (51) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radial velocity and line profile variations in the dwarf nova EM Cyg. Stover, R. J. ; Robinson, E. L. ; Nather, R. E. Abstract Spectroscopic observations of the dwarf nova EM Cygni are presented. From these spectra we measure the radial velocity variations of the accretion disk emission lines and the secondary star absorption lines. The emission line profiles show that the accretion disk was very unstable during the nights of observation, leading to uncertainties in the emission line radial velocities. In spite of the uncertainties we can estimate the masses of the accreting white dwarf and the mass-losing secondary star: Mwd = 0.56±00.5Msun and Msec =0.76 ± 0.1 Msun. We find that the secondary star is at least 10% larger than a zero-age main sequence star of the same mass. Publication: The Astrophysical Journal Pub Date: September 1981 DOI: 10.1086/159194 Bibcode: 1981ApJ...248..696S full text sources ADS | data products SIMBAD (3)

Infrared and optical light curves of the dwarf nova EM Cygni

Infrared and optical light curves of the dwarf nova EM Cygni

A PHOTOGRAPHIC STUDY OF EM CYGNI.

ABSTRACT A study of the dwarf nova EM Cyg is presented, based on 562 photographic observations, 1949-54. The nova-like variation shows, from time to time, relatively stable light curves up to 200-220 days as well as considerable seasonal changes of the light curve and the period. The mean cycle length may be around 24-25 days. An attempt has been made to detect the eclipsing light variation in the close binary system. Key words: photometry - dwarf novae - eclipsing binaries

The mass of the dwarf nova EM Cygni

view Abstract Citations (44) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The mass of the dwarf nova EM Cygni. Robinson, E. L. Abstract The fact that EM Cyg is simultaneously an eclipsing binary and a double-lined spectroscopic binary makes possible the direct determination of the masses of the white dwarf and the red star in this system. To this end the orbital inclination of the system was determined from photoelectric photometry carried out previously and used in conjunction with the calculated spectroscopic orbital elements. The white dwarf and the red star have masses of about 0.70 and 0.90 respectively. Publication: The Astrophysical Journal Pub Date: October 1974 DOI: 10.1086/153146 Bibcode: 1974ApJ...193..191R Keywords: Eclipsing Binary Stars; Novae; Stellar Mass; White Dwarf Stars; Electrophotometry; Orbital Elements; Radial Velocity; Stellar Luminosity; Stellar Spectrophotometry; Variable Stars; Astrophysics full text sources ADS | data products SIMBAD (2)