Sergei Zharikov

Subaru optical observations of the two middle-aged pulsars PSR B0656+14 and Geminga

Aims. We carried out a deep subarcsecond BRI imaging of the two middle-aged pulsars to establish their properties in the optical range Methods. Astrometry and photometry methods are applied to identify the pulsars and to measure their fluxes. We also reanalyze arch ival ESO/NTT and HST broadband data and find that some published fluxes f or Geminga were estimated inaccurately. The resulting dereddened broadband spectra in the near-IR-UV range are analyzed and compared with available data from the radio through gamma-rays. Results. Both pulsars are detected at>10σ level. Geminga is for the first time reliably detected in the I band with a magnitude of 25. 10±0.14. The dereddened spectra of both pulsars are remarkably similar to each other and show significant flux increases towards th e far-UV and near-IR, and a wide flux excess in V-I bands. This suggests a multicomponent structure of the optical emission. The nonthermal power law component of the pulsar magnetospheric origin dominates in the most part of the optical range. For PSR B0656+14 it is compatible with a low energy extension of the power law tail seen in hard X-rays. For Geminga the respective extension overshoots by a factor of 100 the nonthermal optical flux, which has a less steep spectral slope than in X-r ays. This implies a spectral break at a photon energy∼1 keV. The flux increases towards the far-UV are compatible with contributions of the Rayleigh-Jeans parts of the blackbody components from whole surfaces of the neutron stars dominating in soft X-rays. The V-I excess, which is most significant for PSR B0656+14, suggests a third spectral component of still unidentified origin. Faint, a few arcseconds in size ne bulae extended perpendicular to the proper motion directions of the pulsars, are seen around both objects in our deepest I band images. They can be optical counterparts of the bow-shock head of Geminga and of the tentative pulsar wind nebula of PSR B0656+14 observed in X-rays.

FS Aurigae: A New Class of Cataclysmic Variables or the Missing Link between Intermediate Polars and SW Sextantis Objects?

FS Aur is a known dwarf nova with an orbital period of about 85.7 minutes. It has been assumed to be a member of the SU UMa subclass of cataclysmic variables (CVs), but previous searches for superhumps and superoutburst have been unsuccessful. We conducted a series of photometric and spectroscopic observations of FS Aur during quiescence. We confirmed its short orbital period from radial velocity measurements. However, the long-term photometry revealed an unexpected result: the system also shows a distinct 0.24 mag modulation in the BVR photometric bands with a period of 205.5 min, which is 2.4 times longer than the orbital period. We discuss various possible causes for such a peculiar behavior.FS Aur is a known dwarf nova with an orbital period of about 85.7 minutes. It has been assumed to be a member of the SU UMa subclass of cataclysmic variables, but previous searches for superhumps and superoutbursts have been unsuccessful. We conducted a series of photometric and spectroscopic observations of FS Aur during quiescence. We confirmed its short orbital period from radial velocity measurements. However, the long-term photometry revealed an unexpected result: the system also shows a distinct 0.24 mag modulation in the BVR photometric bands with a period of 205.5 minutes, which is 2.4 times longer than the orbital period. We discuss various possible causes for such a peculiar behavior.

Composite Accretion Disk and White Dwarf Photosphere Analyses of the FUSE and Hubble Space Telescope Observations of EY Cygni

We explore the origin of FUSE and Hubble Space Telescope STIS far-UV spectra of the dwarf nova EY Cygni during its quiescence using combined high-gravity photosphere and accretion disk models, as well as model accretion belts. The best-fitting single-temperature white dwarf model to the FUSE plus STIS spectrum of EY Cyg has Teff = 24,000 K and log g = 9.0 with an Si abundance of 0.1 times solar and C abundance of 0.2 times solar, but the distance is only 301 pc. The best-fitting composite model consists of a white dwarf with Teff = 22,000 K and log g = 9, plus an accretion belt with Tbelt = 36,000 K covering 27% of the white dwarf surface with Vbelt sin i = 2000 km s-1. The accretion belt contributes 63% of the far-UV light and the cooler white dwarf latitudes contribute 37%. This fit yields a distance of 351 pc, which is within 100 pc of our adopted distance of 450 pc. EY Cyg has very weak C IV emission and very strong N V emission, which is atypical of the majority of dwarf novae in quiescence. We also conducted a morphological study of the surroundings of EY Cyg using direct imaging in narrow nebular filters from ground-based telescopes. We report the possible detection of nebular material associated with EY Cyg. Possible origins of the apparently large N V/C IV emission ratio are discussed in the context of nova explosions, contamination of the secondary star, and accretion of nova abundance-enriched matter back to the white dwarf via the accretion disk or as a descendant of a precursor binary that survived thermal-timescale mass transfer. The scenario involving pollution of the secondary by past novae may be supported by the possible presence of a nova remnant–like nebula around EY Cyg.

The orbital period of intermediate polar 1WGA J1958.2+3232

The detection of the orbital period of

The 2001 superoutburst of WZ Sge: Is there any connection with Nova Outbursts?

4\fh36

BV R c I c photometry of GRB 970508 optical remnant: May-August, 1997

is reported for the new Intermediate Polar 1 WGA J1958.2+3232. The orbital period was derived from time-resolved photometric and spectral observations. We also confirmed the 733 s spin period of the White Dwarf consistent with the X-ray pulsations and were able to distinguish the beat period in the light curve. Strong modulations with orbital period are detected in the emission lines from spectral observations. They show the presence of a bright hot spot on the edge of the accretion disk. The parameters of this recently discovered Intermediate Polar are determined.

On the orbital period of the Intermediate Polar 1WGA J1958.2+3232

We have observed WZ Sge with high resolution echelle spectroscopy during the 2001 superoutburst. The hot‐spot arising near the secondary star is again visible 15 days after its first detection. We have been able to measure its position as a function of orbital phase directly from individual spectra. We derive a a semiamplitude of Khs = 457 ± 16km s−1 and a systemic velocity of γ = 0 ± 14km s−1. We also show that the accretion disc has an ellipsoidal shape with a value around e = 0.75. Based on these facts we derive a phase shift of ΔΦ = −0.12 between the eclipse and the inferior conjuntion ephemeris. If this is the case, then the hot‐spot appears located at the trailing side of the red dwarf and must be the result of in‐falling material back to the donor star.