Zeeman Features from Accretion Columns in AM Herculis-Type Systems

AbstractAbsorption features seen in the bright phase spectra of E1405−451 are identified with Zeeman features of Hα originating from cool (T-104-105 °K) material surrounding the accretion shock. The presence of apparently unshocked material surrounding the cyclotron emission region is surprising and may indicate that accretion occurs onto a larger fraction of the stellar surface than had previously been thought possible.</jats:p

Detection of photospheric Zeeman features and cyclotron emission lines in V834 CEN in a low state

Copyright Royal Astronomical Society [Full text of this article is not available in the UHRA]Simultaneous spectroscopic and polarimetric observations of the AM Herculis system V834 Cen during a low state of accretion are reported. The polarization data show a reversal in the sign of the circular polarization when lambda is greater than about 5000 A, which lasts for about 0.1 in phase and which is not present during a high state. The reversal can be interpreted as the result of the dominance of photospheric radiation at these phases. The photometric observations show, for the first time, nearly sinusoidal UBV light curves with minima shifted by 0.5 in phase from previous high-state observations. This behavior is explained by assuming that the radiation in the blue bands is dominated by blackbody emission from the heated photosphere near the accretion region. The spectroscopic observations show broad, resolvable cyclotron harmonics and strong photospheric Zeeman features. Theoretical models suggest the presence of a dipole of polar field strength of about 31 MG offset by about -0.1 Rwd from the center of the white dwarf along the dipole axis. The cyclotron emission region is located about 10 deg from the pole and has B of about 23 MG.Peer reviewe

Detection of photospheric Zeeman features and cyclotron emission lines in V834 CEN in a low state

Simultaneous spectroscopic and polarimetric observations of the AM Herculis system V834 Cen during a low state of accretion are reported. The polarization data show a reversal in the sign of the circular polarization when lambda is greater than about 5000 A, which lasts for about 0.1 in phase and which is not present during a high state. The reversal can be interpreted as the result of the dominance of photospheric radiation at these phases. The photometric observations show, for the first time, nearly sinusoidal UBV light curves with minima shifted by 0.5 in phase from previous high-state observations. This behavior is explained by assuming that the radiation in the blue bands is dominated by blackbody emission from the heated photosphere near the accretion region. The spectroscopic observations show broad, resolvable cyclotron harmonics and strong photospheric Zeeman features. Theoretical models suggest the presence of a dipole of polar field strength of about 31 MG offset by about -0.1 Rwd from the center of the white dwarf along the dipole axis. The cyclotron emission region is located about 10 deg from the pole and has B of about 23 MG

New polarimetric observations and a 2 pole model for the cyclotron emission from AM Herculis

High signal-to-noise ratio phase dependent linear polarization and intensity data on AM Herculis which show the presence of structured linear pulses in the optical and near IR regions is presented. The data have been analyzed to construct a detailed model which reproduces closely the observed pulse structure and polarization angle variations and clearly demonstrates the presence of two interfering cyclotron emission regions located close to the foot points of a closed field line in an offset dipole field distribution. Both emission regions are linearly extended on the white dwarf surface. Th main region has a high-density edge at magnetic colatitude theta = 16 deg and extends up to theta to about 8 deg at almost constant magnetic longitude. The secondary region has a similar angular extent in theta but a larger width in magnetic longitude psi (Delta psi about 20-30 deg). The linear bright phase which, in the model corresponds to the phases of visibility of the secondary region, coincides with the X-ray bright phase of the anomalous state of AM Herculis. It is shown that the positions of the emission regions and their relative contributions to the total intensity change with time and that the linear pulses in different wavebands originate from different regions of structured shocks. The coupling region in the orbital plane extends from 18 R(wd) to 7 R(wd) with the distance of closest approach being about a third of the value that is calculated from standard theory for the magnetospheric radius

LYMAN : A New Window on the Universe

AbstractThis document is the final Phase A Science Report of the Australian LYMAN Science Working Group, and describes in detail the scientific objectives, technical feasibility, and engineering implementation of the LYMAN mission as developed in the Australian studies.</jats:p