AM Herculis Systems Research Articles

The upper field-strength limit in AM Herculis systems

The recent proposal that most AM Her systems have essentially identical white dwarf masses (∼ 0.6−0.7 |$M_\odot$|⁠) implies a direct relation between their surface field-strengths B1 and magnetic moments. We show that for |$B_1\gt B_\text {max}\simeq 4\times 10^7 G$|⁠, magnetic braking via the white dwarf magnetic field may drive the binary evolution so rapidly as to cause the effective disappearance of these systems. They end as detached systems with low mass degenerate companions and orbital periods |$P\le 7$| hr. This may explain the existence of apparently isolated, rapidly rotating and highly magnetic white dwarfs. Very old systems may appear as non-magnetic white dwarfs with detached brown dwarf companions. We stress that the apparent lack of unpolarized but synchronously rotating CVs at short orbital periods is a serious problem unless most magnetic CVs have |$B_1\ge 10^7$|⁠. This limit is in rough agreement with that predicted by field-burying for 0.6−0.7 |$M_\odot$| white dwarfs.

EXO 033319-2554.2: an Eclipsing AM Herculis System Showing Cyclotron Emission Features

view Abstract Citations (68) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS EXO 033319-2554.2: an Eclipsing AM Herculis System Showing Cyclotron Emission Features Ferrario, Lilia ; Wickramasinghe, D. T. ; Bailey, Jeremy ; Tuohy, I. R. ; Hough, J. H. Abstract We report spectroscopic and circular polarization observations of the soft X-ray binary EXO 033319 - 2554.2 which confirm it as a member of the AM Herculis class with properties similar to VV Puppis. Circular polarization reaching 10% in the blue and less than or equal to 2% in the I band is seen during the bright phase which lasts for 70 minutes of the 126.5 minute orbital cycle. The optical light curve exhibits a narrow eclipse due to the companion star, lasting about 8 minutes and occurring toward the end of the bright phase. The radial velocity curves show a sharp discontinuity due to an eclipse of the line-forming region by the accretion funnel and the white dwarf. Broad resolvable and variable cyclotron harmonics are seen during the bright phase. At the center of the bright phase, the emission peaks are located near 4200 Å, 5200 Å, and 6550 Å, corresponding to a magnetic field B 5.6 × 107 gauss and a temperature T = 20 keV. Detailed theoretical models suggest the presence of a second emission region of field strength B ∼ 2.8 × 107 gauss which can be seen toward the end of the bright phase. We deduce a mass ratio of ∼0.1 and estimate an orbital inclination of ∼88° and a colatitude of ∼14° for the main emission region, assuming that it is a point source and that the duration of the bright phase is Δφ ∼ 0.55. Publication: The Astrophysical Journal Pub Date: February 1989 DOI: 10.1086/167153 Bibcode: 1989ApJ...337..832F Keywords: STARS: ECLIPSING BINARIES; POLARIZATION; STARS: INDIVIDUAL ALPHANUMERIC: EXO 033319-2554.2; STARS: MAGNETIC; STARS: WHITE DWARFS; X-RAYS: BINARIES full text sources ADS | data products SIMBAD (2)

The X-ray light curves of AM Herculis systems

The X-ray light curves of AM Herculis systems

Cyclotron spectra from inhomogeneous accretion columns

The cyclotron emission from infinite plasma cylinders with uniform magnetic fields, and temperatures, but with a variety of axially symmetric electron density profiles, is calculated. Such inhomogeneous plasmas are shown to be able to produce relatively flat spectra which cannot be produced by homogeneous models. Fits to the optical and infrared continua of the AM Herculis systems ST LMi, V834 Cen, and EF Eri are presented. For ST LMi and V834 Cen, good fits are obtained using a two-core model in which a dense inner cylindrical core with a temperature of 10 keV produces most of the observed X-rays, and both this core and the less dense outer shell produce the optical continuum. For EF Eri, the corresponding temperature is about 15 keV. The average value of the dimensionless plasma parameter Lambda is about 10 to the 6th - 10 to the 7th. 30 references.

The discovery of the 2 hour modulated X-ray source EXO 033319-2554.2, an AM Herculis system

view Abstract Citations (43) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Discovery of the 2 Hour Modulated X-Ray Source EXO 033319-2554.2, an AM Herculis System Osborne, J. P. ; Giommi, P. ; Angelini, L. ; Tagliaferri, G. ; Stella, L. Abstract The authors report the discovery of EXO 033319-2554.2, a soft X-ray source with 100% modulation of its soft X-ray flux, found during a systematic analysis of all of the EXOSAT soft X-ray data. The soft X-ray light curve, which has an on-off behavior, shows a period of 127.7±3.0 minutes. The bright part of the cycle lasts 0.55 in phase and is cut by an eclipse-like feature lasting 8 minutes. The optical counterpart has a magnitude of mv≈ 18.5. The characteristics of EXO 033319-2554.2 imply that it is an AM Her system. The companion star is probably responsible for the eclipse. Using the lengths of the bright phase and of the eclipse, the authors derive limits to the system geometry. Publication: The Astrophysical Journal Pub Date: May 1988 DOI: 10.1086/185157 Bibcode: 1988ApJ...328L..45O Keywords: Magnetic Stars; Stellar Mass Accretion; White Dwarf Stars; X Ray Binaries; X Ray Sources; Exosat Satellite; Modulation; Stellar Luminosity; Astrophysics; STARS: ACCRETION; STARS: INDIVIDUAL ALPHANUMERIC: EXO 033319-2554.2; STARS: MAGNETIC; STARS: WHITE DWARFS; X-RAYS: BINARIES; X-RAYS: SOURCES full text sources ADS | data products SIMBAD (5)

Phase-resolved IUE observations of AM Herculis system E1405-451

The first phase-resolved IUE observations of the AM Herculis system E1405-451 is reported. The spectra show bright emission lines from N V, C IV, and He II, whose centroids vary drastically during the 101.5 minute period. The radial velocities measured from the line centroids show a sinusoidal variation with a semiamplitude of 300 km/s. An explanation for the observed emission line velocities is considered using a model for the system having inclination i = 60 deg and magnetic colatitude Delta = 20 deg.

Absorption features from the accretion column in E1405-451

Phase-resolved circular spectropolarimetric observations of E1405-451 (V834 Cen) covering the wavelength region 3500-7800 A obtained using the Anglo-Australian Telescope are presented. The data show broad absorption features in a strongly polarized cyclotron-continuum present only near maximum light. Cyclotron harmonic and Zeeman line interpretations are investigated, and it is shown that the stronger features are consistent with a nonphotospheric Zeeman interpretation corresponding to a field range of 20-25 MG. The observations provide evidence of cool unshocked material surrounding accretion shocks in AM Herculis systems. 18 references.

2.3 metre multi-colour photometry of a new AM Herculis variable

AbstractWe present UBVRI photometry of the faint and highly erratic cataclysmic variable discovered by Hawkins (1983) from a sequence of U.K. Schmidt plates. Observations using the ANU 2.3 m telescope over two nights in September 1986 show pronounced and repeatable modulation at a binary period of 108.6 min. Dramatic colour differences are evident in the folded UBVRI light curves: in the U band, a single sinusoidal peak is present, while at longer wavelengths, a second red peak dominates at a phase separation of Δϕ = 0.5. This behaviour is strongly suggestive of cyclotron emission from two magnetic accretion funnels in an AM Herculis binary system. Furthermore, the binary period lies in the narrow range of 100-115 minutes that characterizes most of the AM Herculis variables lying on the short side of the 2-3 hour period gap. We conclude therefore that the object is almost certainly a new AM Herculis system, and develop a model in which the blue and red components originate from two non-diametrically opposed cyclotron regions that are characterized by differing electron temperatures and opacities. Predictions are made regarding the linear and circular polarization properties of this important new magnetic variable.

An Emission Line Model for AM Herculis Systems: Application to E1405-451

AbstractThe optical spectra of the AM Herculis binaries are characterized by extremely complex emission lines whose profiles can be resolved into at least three components which are formed in different regions of the accretion stream leading from the companion star towards the magnetic white dwarf. We present a theoretical model which localizes the formation region of the broad emission line component and provides information regarding the structure of this emitting region. In our model the particle trajectories are integrated in a Roche potential and the volume between the white dwarf and the companion has been divided into two different regimes of motion. In one region the gas escapes from the secondary near the inner Lagrange point and is accelerated along a straight line towards the white dwarf. In the other region the magnetic field is strong enought to divert the gas out of the orbital plane and to channel it towards the white dwarfs surface. The model has been used to interpret radial velocity and velocity dispersion data from the AM Herculis system E1405-451.

Time-resolved spectrophotometry of the AM Herculis system E2003 + 225

Time-resolved, medium-resolution photometry is reported for the binary system E2003 + 225 over a complete orbital period in 1984. The object was 1.5-2 mag fainter than when viewed earlier in 1984. The fluxes, equivalent widths and full widths at FWHM for dominant lines are presented for four points in the cycle. A coincidence of emission lines and a 4860 A continuum line was observed for the faster component, which had a 500 km/sec velocity amplitude that was symmetric around the zero line. An aberrant emission line component, i.e., stationary narrow emission lines displaced about 9 A from the rest wavelengths, is modeled as Zeeman splitting of emission from material close to the primary.

Absorption dips and the geometry of the AM Herculis systems

On explique ce phenomene observe dans les courbes de lumiere RX mou par le resultat d'occultations de la calotte polaire en accretion par des parties distantes (≥ 10 10 cm) du courant d'accretion

E2003 + 225 - A 3h 42m AM Herculis type binary system

The bright soft X-ray source E2003 + 225, originally discovered by the HEAO 1 low-energy detectors, has been found to be a new AM Herculis type binary. The optical counterpart shows a rich emission spectrum of He II, He I, and H as well as circular and linear polarization. Larger polarization in the near-infrared than in the ultraviolet argues for its origin as high harmonic cyclotron emission. Optical photometry, polarimetry, spectroscopy, and the X-ray light curves are all consistent with an orbital period of 222.51 m, the longest period known for AM Herculis systems, and only the second on the long side of the 2-3 hour cataclysmic variable period gap.

Identification of CW 1103+254 as a new magnetic variable

view Abstract Citations (47) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Identification of CW 1103+254 as a new magnetic variable. Stockman, H. S. ; Foltz, C. B. ; Schmidt, G. D. ; Tapia, S. Abstract The variations in linear and circular polarization are seen as suggesting a magnetically locked 114 min rotational period and resembling those of VV Pup in its one-pole state. Strong circular and linear polarization is seen during the entire bright phase, which lasts approximately 40 min. For the remainder of the period, the optical light is dominated by the unpolarized photospheric flux of the white dwarf primary and the high-excitation emission lines typical of AM Herculis systems. Linear and circular polarization data are presented, along with representative photometric data. In addition, time-resolved, high-resolution spectroscopic data are obtained for 1.6 periods of CW 1103+254. The emission line profiles are found to be complex and to be composed of a broad component, whose width varies from 350 km/s to 1400 km/s during the period, and one or two narrow components. The dramatic changes in line widths indicate strongly that converging flow velocities of approximately 1000 km/s are responsible for the observed radial velocities and line widths. Publication: The Astrophysical Journal Pub Date: August 1983 DOI: 10.1086/161239 Bibcode: 1983ApJ...271..725S Keywords: Magnetic Stars; Stellar Spectra; Variable Stars; White Dwarf Stars; Emission Spectra; Polarization Characteristics; Spectral Line Width; Stellar Mass Accretion; Astrophysics full text sources ADS |

IDENTIFICATION OF LANNING 90 AS A PREVIOUSLY UNCATALOGED CATACLYSMIC VARIABLE.

ABSTRACT Spectroscopic observations which reveal Lanning 90 to be a previously uncataloged cataclysmic variable are presented. Low-resolution spectra of the object display strong and broad emission lines of hydrogen and neutral helium superimposed on a continuum with roughly constant F-lambda. In addition to the Balmer and He I emision lines, the spectrum shows high excitation lines of He II, C II, C III, and N III. After a brief discussion of its general spectral character, it is argued that Lanning 90 is probably a nova-like variable. It is noted that the photometric and spectroscopic variability exhibited by the object is similar to the variability shown by the AM Herculis systems.

Recent Optical Observations of the X-Ray Source H0139-68; an AM-Herculis Type Binary System

The soft X-ray source HO 139-68 was originally detected with the low energy detectors of the HEAO A-2 experiment, and confirmed by later IPC observations (Agarwal et al. 1981). The X-ray observations show flux variations in the 0.15 – 0.4 keV band of a factor of two, or timescales of a few hours, with evidence for short time-scale flickering. Following communication of the source position to us by Agarwal and Riegler, we obtained time-resolved optical spectrophotometry of a star close to the X-ray position, using the IDPCA on the MSO 1.9m telescope. The spectrophotometry and later polarisation observations confirm the optical identification and that the source is an AM-Herculis type binary system, with a late type dwarf secondary overflowing its Roche lobe in a magnetically constrained funnel onto a magnetic white dwarf (WD) primary (Visvanathan and Pickles 1982).