Domitilla de Martino

Far-Ultraviolet Spectroscopy of Magnetic Cataclysmic Variables*

Abstract HST and FUSE have provided high signal-to-noise, high-resolution spectra of a variety of cataclysmic variables and have allowed a detailed characterization of FUV emission sources in both high and low states. Here, I describe how this has advanced our understanding of non-magnetic CVs. In the high state, the FUV spectra are dominated by disk emission that is modified by scattering in high and low velocity material located above the disk photosphere. Progress is being made towards reproducing the high-state spectra using kinematic prescriptions of the velocity field and new ionization and radiative transfer codes. In conjunction with hydrodynamical simulations of the outflows, accurate estimates of the mass loss rates and determination of the launching mechanism are likely forthcoming. In quiescence, the FUV spectra reveal contributions from the WD and the disk. Quantitative analyses have lead to solid measurements of the temperatures and abundances of a number of WDs in CVs, and of a determination of the response of the WD to an outburst. Basic challenges exist in terms of understanding the other components of the emission in quiescence, however, and these are needed to better understand the structure of the disk and the physical mechanisms resulting in ongoing accretion in quiescence.

Anomalous Ultraviolet Line Flux Ratios in the Cataclysmic Variables 1RXS J232953.9+062814, CE 315, BZ Ursae Majoris, and EY Cygni, Observed with the Hubble Space Telescope Space Telescope Imaging Spectrograph*

Brief HST/STIS spectroscopic snapshot exposures of the cataclysmic variables 1RXSJ232953.9+062814, CE315, BZ UMa and EY Cyg reveal very large NV/CIV line flux ratios, similar to those observed in AE Aqr. Such anomalous line flux ratios have so far been observed in 10 systems, and presumably reflect a different composition of the accreted material compared to the majority of cataclysmic variables. We discuss the properties of this small sample in the context of the recent proposal by Schenker et al. (2002) that a significant fraction of the present-day population of cataclysmic variables may have passed through a phase of thermal time-scale mass transfer.Brief Hubble Space Telescope Space Telescope Imaging Spectrograph spectroscopic snapshot exposures of the cataclysmic variables 1RXS J232953.9+062814, CE 315, BZ UMa, and EY Cyg reveal very large N V/C IV line flux ratios, similar to those observed in AE Aqr. Such anomalous line flux ratios have so far been observed in 10 systems and presumably reflect a different composition of the accreted material compared to the majority of cataclysmic variables. We discuss the properties of this small sample in the context of the recent proposal by Schenker et al. that a significant fraction of the present-day population of cataclysmic variables may have passed through a phase of thermal timescale mass transfer.

Magnetic White Dwarfs

In this paper we review the current status of research on the observational and theoretical characteristics of isolated and binary magnetic white dwarfs (MWDs).Magnetic fields of isolated MWDs are observed to lie in the range 103–109xa0G. While the upper limit cutoff near 109xa0G appears to be real, the lower limit is more difficult to investigate. The incidence of magnetism below a few 103xa0G still needs to be established by sensitive spectropolarimetric surveys-conducted on 8xa0m class telescopes.Highly magnetic WDs tend to exhibit a complex and non-dipolar field structure with some objects showing the presence of higher order multipoles. There is no evidence that fields of highly magnetic WDs decay over time, which is consistent with the estimated Ohmic decay times scales of ∼1011xa0yrs. The slow rotation periods (∼100xa0yrs) inferred for a large number of isolated MWDs in comparison to those of non-magnetic WDs (a few days) suggest that strong magnetic fields augment the braking of the stellar core.MWDs, as a class, also appear to be more massive (0.784±0.047xa0M⊙) than their weakly or non-magnetic counterparts (0.663±0.136xa0M⊙).MWDs are also found in binary systems where they accrete matter from a low-mass donor star. These binaries, called magnetic Cataclysmic Variables (MCVs), comprise about 20–25xa0% of all known CVs. Zeeman and cyclotron spectroscopy of MCVs have revealed the presence of fields in the range ∼7–230xa0MG. Complex field geometries have been inferred in the high field MCVs (the polars) whilst magnetic field strength and structure in the lower field group (intermediate polars, IPs) are much harder to establish.The MCVs exhibit an orbital period distribution which is similar to that of non magnetic CVs. Polars dominate the distribution at orbital periods ≲4xa0h and IPs at longer periods. It has been argued that IPs above the 2–3xa0hr CV period gap with magnetic moments ≳u20095×1033xa0Gu2009cm3 may eventually evolve into polars. It is vital to enlarge the still incomplete sample of MCVs to understand not only their accretion processes but also their evolution.The origin of fields in MWDs is still being debated. While the fossil field hypothesis remains an attractive possibility, field generation within the common envelope of a binary system has been gaining momentum, since it would explain the absence of MWDs paired with non-degenerate companions and also the lack of relatively wide pre-MCVs.

Unambiguous Detection of Reflection in Magnetic Cataclysmic Variables: Joint NuSTAR–XMM-Newton Observations of Three Intermediate Polars

In magnetic cataclysmic variables (CVs), X-ray emission regions are located close to the white dwarf surface, which is expected to reflect a significant fraction of intrinsic X-rays above 10 keV, producing a Compton reflection hump. However, up to now, a secure detection of this effect in magnetic CVs has largely proved elusive because of the limited sensitivity of non-imaging X-ray detectors. Here we report our analysis of joint NuSTAR/XMM-Newton observations of three magnetic CVs, V709 Cas, NY Lup, and V1223 Sgr. The improved hard X-ray sensitivity of the imaging NuSTAR data has resulted in the first robust detection of Compton hump in all three objects, with amplitudes of ~1 or greater in NY Lup, and likely <1.0 in the other two. We also confirm earlier report of a strong spin modulation above 10 keV in V709 Cas, and report the first detection of small spin amplitudes in the others. We interpret this as due to different height of the X-ray emitting region among these objects. A height of ~0.2 white dwarf radii provides a plausible explanation for the low reflection amplitude of V709 Cas. Since emission regions above both poles are visible at certain spin phases, this can also explain the strong hard X-ray spin modulation. A shock height of ~0.05 white dwarf radii can explain our results on V1223 Sgr, while the shock height in NY Lup appears negligible.

X-ray observations of 4 Draconis : symbiotic binary or cataclysmic triple?

We present the first X-ray observations of the 4 Draconis system, consisting of an M3 III giant with a hot ultraviolet companion. It has been claimed that the companion is itself an AM Her-type binary system, an identification that places strong constraints on the evolution of cataclysmic variables. We find that the X-ray properties of 4 Draconis are consistent with the presence of an accreting white dwarf, but not consistent with the presence of an AM Her system. We conclude that 4 Draconis is therefore most likely a symbiotic binary containing a white dwarf accreting material from the wind of the red giant. n nThe X-ray spectrum of 4 Draconis is sometimes dominated by partially ionized photoelectric absorption, presumably due to the wind of the red giant. We note that X-ray monitoring of such systems would provide a powerful probe of the wind and mass-loss rate of the giant, and would allow a detailed test of wind accretion models.

Swift J2218.4+1925: a new hard-X-ray-selected polar observed with XMM–Newton

Swift J2218.4+1925, a hard X-ray source detected by Swift BAT, has been proposed as a candidate magnetic cataclysmic variable of the polar type from optical spectroscopy. Using XMM-Newton we perform detailed timing and spectral analysis with simultaneous X-ray (

Discovery of a Nova-like Cataclysmic Variable in the Kepler Mission Field

0.3-10

Building galaxies, stars, planets and the ingredients for life between the stars. The science behind the European Ultraviolet-Visible Observatory

keV) and optical B band data. We complement the spectral study with archival hard X-ray (14-70 keV) spectra collected by Swift BAT as well as with optical, near and mid-infrared photometry from

Stellar And Galactic Environment survey (SAGE)

SDSS

A universal relation for the propeller mechanisms in magnetic rotating stars at different scales

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