V405 Aur Research Articles

ULTRAVIOLET SPECTROSCOPY OF PQ Gem AND V405 Aur FROM THEHSTANDIUESATELLITES

Ultraviolet spectra of two intermediate polars (IPs), PQ Gem and V405 Aur, observed with Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph and Faint Object Spectrograph and International Ultraviolet Explorer (IUE) satellites were analyzed during the period between 1994–2000. We estimated the reddening of the two systems from the 2200 A feature. Six spectra of the two systems revealing modulations of line fluxes at different times are presented. PQ Gem and V405 Aur are featured by spectral lines in different ionization states. This paper focuses on the third ionized carbon emission line at 1550 A and the first ionized helium emission line at 1640 A produced in the optically thin outer region of the accretion curtain for the two systems by calculating spectral line fluxes. From HST and IUE data, we deduced ultraviolet luminosities and ultraviolet accretion rates for the two binary stars. The average temperature of the accretion streams for PQ Gem and V405 Aur are ~4500 K and 4100 K, respectively. The results reveal that there are modulations in fluxes of spectral lines, ultraviolet luminosities, and ultraviolet accretion rates with time for both systems. These modulations are referred to the changes of both density and temperature as a result of the variations of mass transfer rate from the secondary star to the primary star. The current results are consistent with an accretion curtain model for IPs.

The Magnetospheric Boundary in Cataclysmic Variables

The magnetic cataclysmic variables (MCVs) present a wealth of observational diagnostics for studying accretion flows interacting with a magnetosphere. Spin-period pulsations from the rotation of the white dwarf are seen in optical light, in the UV and X-ray bands, and in polarimetry, and modelling these can constrain the size and location of the accretion footprints on the white-dwarf surface. Tracing these back along field lines can tell us about the transition region between the stream or disk and the magnetosphere. Further, optical emission lines give us velocity information, while analysis of eclipses gives spatial information. I discuss MCVs (particularly FO Aqr, V405 Aur, XY Ari and EX Hya, but also mentioning PQ Gem, GK Per, V2400 Oph, HT Cam, TX Col, AO Psc, AE Aqr, WZ Sge, V1223 Sgr and DQ Her), reviewing what observations tell us about the disk-magnetosphere boundary. The spin-period variations are caused by a mixture of geometric effects and absorption by the accretion flow, and appear to show that the accretion disk feeds onto field lines differently in different systems, being sometimes along field lines ahead of the magnetic pole and sometimes behind the pole. During outbursts, when the accretion flow increases by orders of magnitude, the disk pushes the magnetosphere inwards, and appears to feed field lines over a much greater range of magnetic azimuth. The non-equilibrium outburst behaviour shows an even richer phenomenology than in quiescence, adding DNOs and QPOs into the mix.

Variability of the spin period of the white dwarf in the intermediate polar v405 aur: low-mass third body or precession?

We present the results of photometric CCD observations of the magnetic cataclysmic variable V405 Aurigae (RX J0558.0+5353 = 1RXS J055800.7+535358) obtained using different instruments. We analysed variability of the spin period of the white dwarf in the V405 Aur (RX J0558.0+5353) system using our observations and previously published maxima timings. The spin period of the system in 2010-2012 is $P=545.4558163(94)$s. As we have gaps in observational data, we present 2 hypotheses of the spin period variability of this system - a cubic ephemeris which may be interpreted by a precession of the magnetic white dwarf or a periodic change with a period of 6.2 years and semi-amplitude of $17.2\pm1.8$ sec. The periodic variations may be interpreted by a light-time effect caused by a low-mass star ($M_3\ge0.09M_\odot$). In this case, the system belongs to a rare class of cataclysmic variables with a third body.

Pure cyclotron spectra of V405 Aur

In this study we investigate the pure cyclotron spectra of an Intermediate Polar (IP), V405 Aur, which has the highest magnetic field strength in its class. Recent studies have shown that cyclotron harmonics are seen in the spectra of V405 Aur. We assume that cyclotron harmonics are produced by electrons having a streaming bi-Maxwellian velocity profile found in the lower portions of the accretion column connecting to the magnetic poles of the white dwarf in V405 Aur system. Then we applied the Green function for a dispersive medium such as the one found in V405 Aur. Further we assume that the cyclotron radiation is produced at Ordinary and Extraordinary wave modes. We find the general solution of the Green function for the Extraordinary wave mode and a dispersive medium and we derived the pure cyclotron spectra from the Green function. This function enabled us to calculate energy radiated per unit wavelength per unit solid angle as a function of wavelength which revealed the sixth, seventh and the eighth harmonics which correspond to the observed values. Our model produces the observed cyclotron spectrum of V405 Aur.

V405 Aurigae: A High Magnetic Field Intermediate Polar

Our simultaneous multicolor (UBVRI) circular polarimetry has revealed nearly sinusoidal variation over the WD spin cycle, and almost symmetric positive and negative polarization excursions. Maximum amplitudes are observed in the B and V bands (±3%). This is the first time that polarization peaking in the blue has been discovered in an intermediate polar (IP), and suggests that V405 Aur is the highest magnetic field IP found so far. The polarized flux spectrum is similar to those found in polars with magnetic fields in the range B ~ 25-50 MG. Our low-resolution circular spectropolarimetry has given evidence of transient features which can be fitted by cyclotron harmonics n = 6, 7, and 8, at a field of B = 31.5 ± 0.8 MG, consistent with the broadband polarized flux spectrum. Timings of the circular polarization zero crossovers put strict upper limits on WD spin period changes, and indicate that the WD in V405 Aur is currently accreting closely at the spin equilibrium rate, with very long synchronization timescales, Ts > 109 yr. For the observed spin to orbital period ratio, Pspin/Porb = 0.0365, and Porb ~ 4.15 hr, existing numerical accretion models predict spin equilibrium condition with B ~ 30 MG if the mass ratio of the binary components is q1 ~ 0.4. The high magnetic field makes V405 Aur a likely candidate as a progenitor of a polar.

Far Ultraviolet Spectroscopic Explorer Spectroscopy of the Transitional Magnetic Cataclysmic Variable V405 Aurigae11Based on observations made with the NASA‐CNES‐CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by the Johns Hopkins University under NASA contract NAS5‐32985.

ABSTRACTWe present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the magnetic cataclysmic variable V405 Aurigae. Together with four other DQ Her–type binaries, V405 Aur forms a small subclass of intermediate polars that are likely to evolve into low magnetic field strength polars, similar to AM Her. Our co‐added FUSE spectrum exhibits broad O vi and C iii emission lines, in addition to a narrow O vi emission‐line component that likely forms near the white dwarf surface. The O vi λ1032/λ1038 narrow emission‐line flux ratio is near 2.0 throughout the orbit, which is indicative of its formation in an optically thin gas. Radial velocity measurements of the narrow O vi emission lines restrict any orbital modulation to a very low amplitude (KWD = 2.5 ± 0.5 km s−1), indicating, along with other single‐peaked broad disk emission lines in the UV and optical, that the binary system is at low inclination.

Why does the intermediate polar V405 Aurigae show a double-peaked spin pulse?

V405 Aurigae is an intermediate polar showing a double-peaked pulsation in soft X-rays and a single-peaked pulsation in harder X-rays. From XMM‐Newton observations, we find that the soft band is dominated by blackbody emission from the heated white dwarf surface. Such emission is at a maximum when either magnetic pole points towards us, explaining the doublepeaked pulsation. The symmetry of the pulses requires that the angle between the magnetic and spin axes be high. The single-peaked pulsation in harder X-rays is explained in the usual way, as a result of opacity in the accretion curtains. However, the high dipole inclination means that the accretion curtains are nearly in the plane. Thus the outer regions of the curtains do not cross the line of sight to the accretion footprints, explaining the absence of the deep absorption dip characteristic of many intermediate polars. The sawtooth profile of this pulsation requires that the magnetic axis be offset from the white dwarf centre. We remark also on the double-peaked optical emission in this star. We suggest that the difference between the spin pulse of V405 Aur and those of other intermediate polars is the result of its high dipole inclination. Ke yw ords: accretion, accretion discs ‐ stars: individual: V405 Aur (RX J0558.0+5353) ‐ novae, cataclysmic variables ‐ X-rays: binaries.

BeppoSAX observations of soft X-ray intermediate polars

We present broad-band (0.1-90 keV) spectral and temporal properties of the three Intermediate Polars, RE 0751+144 (PQ Gem), RX J0558.0+5353 (V405 Aur) and RX J1712.6 2414 (V2400 Oph) based on simultaneous soft and hard X-ray observations with the BeppoSAX satellite. The analysis of their spectra over the wide energy range of BeppoSAX instruments allows us to identify the soft and hard X-ray components and to determine simultaneously their temperatures. The black-body temperatures of the irradiated poles of the white dwarf atmosphere are found to be 60-100 eV, much higher than those found in their synchronous analogues, the Polars. The temperature of the optically thin post-shock plasma is well con- strained in RX J1712.6 2414 and in RE 0751+144 (13 and 17 keV) and less precisely determined in RX J0558.0+5353. In the first two systems evidence of subsolar abundances is found, similarly to that estimated in other magnetic Cataclysmic Variables. A Compton reflection component is present in RX J0558.0+5353 and in RE 0751+144 and it is favoured in RX J1712.6 2414. Its origin is likely at the irradiated white dwarf surface. Although these systems share common properties (a soft X-ray compo- nent and optical polarized radiation), their X-ray power spectra and light curves at dierent energies suggest accretion geome- tries that cannot be reconciled with a single and simple configuration.

RX J0944.5+0357: A Probable Intermediate Polar

From optical photometry the cataclysmic variable RX J0944.5+0357 is shown to have a double-peaked pulse profile with a period ∼ 2160 s. The two peaks vary rapidly in relative amplitude. Often most of the optical power is concentrated in the first harmonic of the 2160 s modulation; RX J0944.5+0357therefore probably belongs to the relatively rare class of two-pole accreting intermediate polars exemplified by YY Dra and V405 Aur.

Extreme Ultraviolet Explorer and Optical Observations of the Magnetic Cataclysmic Variables RX J1015.5+0904 and V405 Auriga (RX J0558+5353)11Based on observations with the Apache Point Observatory (APO) 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium (ARC).

ABSTRACTWe present simultaneous Extreme Ultraviolet Explorer (EUVE) and optical observations of one of the shortest orbital period AM Herculis systems (RX J1015.5+0904) and of one of the intermediate polars which shows a soft X‐ray flux (V405 Aur=RX J0558+5353). RX J1015.5+0904 shows a very typical geometry of the accretion area for a one‐pole system. The count rate is consistent with a column at the low end of the ROSAT determinations and, therefore, a relatively high temperature for the heated area. Thus, there is every indication that heating operates efficiently even at low accretion rates onto very cool white dwarfs. V405 Aur has a very low count rate, which does not allow a good determination of the spin variation at EUVE wavelengths, although it is obvious in the optical photometry. Doppler tomography of the optical spectra shows a trend of decreasing disk structure and increasing spot structure with increasing excitation, with a change in the location of the primary emitting zone from previous years.