Harmonic Analysis of the Line Profiles of an Oblique Rotator

view Abstract Citations (21) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Application of Fourier analysis to broadening of stellar line profiles. I. Three Mn stars. Smith, M. A. ; Parsons, S. B. Abstract This paper explores a modified form of Gray's technique of determiriing classical microturbulence (T) by Fourier analysis of line profiles. The technique entails the transformation of the functions defined by absorption-line scans to Fourier power spectra. Our instrumental resolution of 0.05 A does not reduce the strength in the first side- lobe of the power spectra appreciably. Thus the sidelobe power is suitable as a basic criterion in the comparison of computed and observed line profiles. Our study for three Mn Ap stars shows that the formal errors placed on the solution for T are most sensitive to limited photon statistics, to the choice of whether rotation (V) or macroturbulence (M) is dominant in broadening the line, and to the total amount of this broadening. On the other hand the solution for T is insensitive to the damping parameter, the model atmosphere, and the assumption of LTE. We demonstrate that the Fourier technique provides a more convenient and precisely defined test of the value of T than would be obtained from direct comparison of line profiles. For CrB we obtain T=0'iifV=4km s-1,orT= +ffM=3 km -1 ,wefind0 T 3, with V = 12. These results do not contradict the statement that both forms of turbulence may be zero. In themselves they do not exclude atmospheric difflision as the mechanism responsible for abundance anomalies in Mn stars. An unexpected discovery made in this study is that all three strong lines observed in L CrB show a depression in their blue wings displaced in velocity -91 1 km s: 1 from the centers. This effect is not instrumental, and it appears unlikely to be caused by a secondary star. The implication is that some hitherto unsuspected mass motions are occurring at the top of the atmospheres or over a small area of these stars. However, it is not yet clear how any such effect can be reconciled with the solutions obtained for low or zero turbulences in the line-formation regions of the atmospheres. Subject headings: atmospheres, stellar - line profiles - peculiar A stars - rotation, stellar - turbulence Publication: The Astrophysical Journal Supplement Series Pub Date: August 1975 DOI: 10.1086/190348 Bibcode: 1975ApJS...29..341S Keywords: A Stars; Fourier Analysis; Line Spectra; Manganese; Metallic Stars; Spectral Line Width; Absorption Spectra; Abundance; Atmospheric Diffusion; Continuous Spectra; Graphs (Charts); Power Spectra; Stellar Atmospheres; Stellar Rotation; Stellar Spectra; Astrophysics full text sources ADS | data products SIMBAD (3)

view Abstract Citations (38) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the interpretation of the magnetic curves of the Ap stars as determined by the photographic technique. Borra, E. F. Abstract Theoretical Zeeman-analyzed line profiles in magnetic stars have been computed for decentered dipole configurations of the magnetic field. It is found, on the basis of these profiles, that if the core of the lines are emphasized during the reduction of Zeeman-analyzed photographic plates, the longitudinal field obtained deviates from its true value. The deviations predicted are successful in producing the anharmonic variations observed in several Ap stars. Subject headings: line profiles - magnetic stars - peculiar A stars - Zeeman effect Publication: The Astrophysical Journal Pub Date: March 1974 DOI: 10.1086/152715 Bibcode: 1974ApJ...188..287B full text sources ADS | data products SIMBAD (4)

view Abstract Citations (23) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-resolution polarization observations inside the spectral lines of magnetic Ap stars. II. Observations of alpha 2Canum Venaticorum. Borra, E. F. ; Vaughan, A. H. Abstract We present observations, obtained with a photon-counting polarimeter and a Fabry-Perot interferometer, of the circular polarization and intensity profiles across the line Fe ii A4520.2 in the magnetic Ap star a2 Canum Venaticorum. We discuss briefly the He curve obtained from our data. Subject headings: polarization - stars: individual - stars: magnetic - stars: peculiar A - Zeeman effect Publication: The Astrophysical Journal Pub Date: March 1978 DOI: 10.1086/155981 Bibcode: 1978ApJ...220..924B Keywords: A Stars; Circular Polarization; Line Shape; Magnetic Stars; Zeeman Effect; Fabry-Perot Interferometers; High Resolution; Line Spectra; Polarimeters; Polarization Characteristics; Astronomy; Magnetic Fields:Peculiar A Stars; Magnetic Stars:Polarization full text sources ADS | data products SIMBAD (1) Related Materials (2) Part 1: 1977ApJ...216..462B Part 3: 1980ApJ...235..911B

view Abstract Citations (20) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Further comments on the effects of vacuum birefringence on the polarization of X-rays emitted from magnetic neutron stars. Chanan, G. A. ; Novick, R. ; Silver, E. H. Abstract The birefringence of the vacuum in the presence of strong (of the order of 1 teragauss) magnetic fields will in general affect the polarization of X-rays propagating through these fields. Two of the four Stokes parameters will vary so rapidly with wavelength as to be 'washed out' and unobservable, but the remaining two parameters will be unaffected. These results show that one conclusion of an earlier work is incorrect: Polarized X-ray emission from the surface of a magnetic neutron star will not in general be completely depolarized by the effects of vacuum birefringence. In particular, this birefringence has no effect on the linear polarization of cyclotron emission from the poles of magnetic neutron stars, and a similar result holds for synchrotron emission. More general cases of the propagation of polarized X-rays in magnetic fields are also discussed. Publication: The Astrophysical Journal Pub Date: March 1979 DOI: 10.1086/182906 Bibcode: 1979ApJ...228L..71C Keywords: Birefringence; Magnetic Stars; Neutron Stars; Polarization Characteristics; X Ray Sources; Cyclotron Radiation; Depolarization; Linear Polarization; Stellar Magnetic Fields; Synchrotron Radiation; Astrophysics; Magnetic Stars:Neutron Stars; Magnetic Stars:X Rays; Neutron Stars:X Rays; Polarization:X Rays full text sources ADS |

view Abstract Citations (38) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cyclotron self-absorption in accretion columns of magnetic degenerate stars. Chanmugam, G. ; Wagner, R. L. Abstract The maximum frequency is calculated up to which cyclotron radiation in the accretion columns of magnetic degenerate stars is self-absorbed, and the results are applied to the AM Herculis binaries. Attention is given to the emissivity for a plasma in a magnetic field, the importance of cyclotron cooling considering the effects of the strong magnetic fields in the AM Herculis binaries, and the probability that the broad-band nature of the observed polarized radiation is due to the inhomogeneity of the dipole magnetic field. Also discussed are binary X-ray systems containing magnetic neutron stars, in particular Her X-1. Publication: The Astrophysical Journal Pub Date: September 1979 DOI: 10.1086/157352 Bibcode: 1979ApJ...232..895C Keywords: Binary Stars; Cyclotron Radiation; Magnetic Stars; Neutron Stars; Self Absorption; Stellar Mass Accretion; X Ray Sources; Magnetic Dipoles; Optical Polarization; Polarized Radiation; Stellar Magnetic Fields; White Dwarf Stars; Astrophysics; Degenerate Stars:Polarization; Magnetic Stars:Polarization; Polarization:X-Ray Binaries full text sources ADS |

view Abstract Citations (192) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Accretion by rotating magnetic neutron stars. I. Flow of matter inside the magnetosphere and its implications for spin-up and spin-down of the star. Ghosh, P. ; Lamb, F. K. ; Pethick, C. J. Abstract We investigate the flow of accreting matter and the configuration of the magnetic field inside the magnetosphere of a rotating neutron star. We assume that the magnetic field of the star has a symmetry axis which is aligned with the rotation axis, that the accreting plasma becomes threaded by the stellar magnetic field near the magneto spheric boundary, and that the star is not a fast rotator. We show that for bright X-ray sources, flow within the Alfve'n surface is well described by the equations of magnetohydrodynamics and that the matter moves along field lines when viewed in the frame corotating with the star. In the case of slow rotators, matter inside the Alfve'n surface rotates in a sense opposite that of the net angular momentum flux toward the star. We also study the torque exerted on the star by the accreting matter and the flow of energy within the magnetosphere and the transition region at the magnetospheric boundary, when the star accretes matter from a disk. Finally, we comment briefly on the implications of our results for pulsating X-ray sources. Subject headings: hydromagnetics - stars: accretion - stars: magnetic - stars: neutron - stars: rotation Publication: The Astrophysical Journal Pub Date: October 1977 DOI: 10.1086/155606 Bibcode: 1977ApJ...217..578G Keywords: Magnetic Field Configurations; Magnetospheric Instability; Neutron Stars; Spin Dynamics; Stellar Magnetospheres; Stellar Mass Accretion; Stellar Rotation; Angular Momentum; Energy Transfer; Lines Of Force; Magnetic Stars; Stellar Magnetic Fields; Torque; X Ray Sources; Astrophysics full text sources ADS | Related Materials (2) Part 2: 1979ApJ...232..259G Part 3: 1979ApJ...234..296G

view Abstract Citations (62) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Evolution of Magnetic White Dwarfs Fontaine, Gilles ; Thomas, John H. ; van Horn, H. M. Abstract We show that the magnetic DC white dwarfs cannot have evolved from stars of spectral type DA. A separate origin is necessary, and a direct evolutionary connection between the magnetic DC stars and the nuclei of planetary nebulae seems plausible. Such a connection implies photospheric field strengths 10 -10 gauss in planetary nuclei, which may be large enough to be detectable. In addition, we find that magnetic white dwarfs must be hotter than some (weakly massdependent) limiting effective temperature. This prediction is potentially susceptible to observational verification. Subject headings: magnetic stars - stellar evolution - white dwarf stars Publication: The Astrophysical Journal Pub Date: September 1973 DOI: 10.1086/152381 Bibcode: 1973ApJ...184..911F full text sources ADS |

view Abstract Citations (66) References (49) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Theoretical photometric and spectroscopic properties of stellar accretion disks with application to cataclysmic variables. Herter, T. ; Lacasse, M. G. ; Wesemael, F. ; Winget, D. E. Abstract We present the results of an exploratory calculation of the theoretical photometric and spectroscopic properties of viscous accretion disks in cataclysmic variable systems. We use the theoretical α-model disks of Shakura and Sunyaev along with LTE model atmosphere calculations for plane-parallel geometry to obtain both continuum fluxes and hydrogen absorption line profiles for a variety of disk models. Our results are presented for mass-transfer rates ranging from 10-9 to 10-7 Msun yr-1, inclination angles ranging from 0° to 75°, and outer-disk radii ranging from 8.6 × 109 to 2.0 × 1010 cm. We tabulate line profiles and equivalent widths of Hα, Hβ, and Hγ the Balmer jump; bolometric correction; and both broad-band and Strömgren colors for most models. These results are then applied to a preliminary analysis of the Hγ absorption line profile in the nova-like variable CD 42°14462. The lack of agreement between the observed and theoretical profiles suggests that the observed line profile is predominantly pressure-broadened. This may possibly indicate that, in contrast to the results of our calculations, the observed profile originates in the innermost region of the disk and that this region contributes significantly to the visual light from the system. Publication: The Astrophysical Journal Supplement Series Pub Date: April 1979 DOI: 10.1086/190584 Bibcode: 1979ApJS...39..513H Keywords: Binary Stars; Stellar Mass Accretion; Stellar Spectrophotometry; Variable Stars; Balmer Series; Continuous Spectra; Dwarf Stars; H Lines; Novae; Spectral Line Width; Stellar Models; Astrophysics; Accretion Disks:Cataclysmic Variables; Accretion Disks:Close Binaries; Accretion Disks:Models full text sources ADS | data products SIMBAD (1)

view Abstract Citations (169) References (3) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Rotating Magnetosphere: a Simple Relativistic Model Michel, F. Curtis Abstract We solve exactly for the electromagnetic field configuration about an aligned rotating magnetic moment ("star") for the case that there is sufficient plasma about the object to "freeze in" the magnetic fields, but in the limit that the inertia and pressure of the plasma particles can be neglected. These solutions are expected to be valid except near the light cylinder, although there is no mathematical difficulty in solving the resultant equations at or even beyond the light cylinder. The solutions show quantitatively how the field lines make the transition from a closed (dipole-like) to an open configuration and provide a refined estimate of how much magnetic flux is available to open field lines (an important point in many pulsar theories). We find that if a flux from an unperturbed dipole closes outside the light cylinder, then for the perturbed field this flux is increased by a factor of about 1.592. The field lines in the dipole case exhibit a cusp at the light cylinder, and we can calculate the charge density there. This charge density is found to be insufficient to account for coherent radiation of radiofrequency waves from pulsars. Subject headings: hydromagnetics - magnetic stars - pulsars - relativity - rotation, stellar Publication: The Astrophysical Journal Pub Date: February 1973 DOI: 10.1086/151956 Bibcode: 1973ApJ...180..207M full text sources ADS |

view Abstract Citations (94) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Rotating Magnetosphere: Acceleration of Plasma from the Surface Michel, F. Curtis Abstract We solve for the space-charge field about a rotating object having a monopole magnetic field and a zero work-function surface. We generalize this result to obtain an approximate solution for the case of an axisymmetric dipole field, and find that electrons are accelerated from pulsar-like objects to an energy of the order of E (8ew2a3B /c)112 7 x 10 eV, where w is the rotation rate (estimated 6 rad 5-1), Bp is the polar surface field (estimated 1012 gauss), and a is the radius (estimated 10 m), with most of the acceleration taking place within a distance h (a3w/c)112 140 meters. The overall electromagnetic field structure is essentially unchanged from what one predicts by ignoring particle inertia. In the present work, the effect of a mass difference between the negative and positive particles is ignored. The above injection energy differs from that expected for a neutral stellar wind, and we account for this difference on the basis of the charge-separated nature of the plasma here. Incoherent radiation reaction is examined, and is found to play no important role. Subject headings: hydromagnetics - magnetic stars - plasmas - pulsars Publication: The Astrophysical Journal Pub Date: September 1974 DOI: 10.1086/153109 Bibcode: 1974ApJ...192..713M full text sources ADS |

view Abstract Citations (75) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High Time Resolution Observations of H alpha Line Profiles during the Impulsive Phase of a Solar Flare Wuelser, Jean-Pierre ; Marti, Hans Abstract H-alpha observations of the impulsive phase of a 1B/M1 solar flare on May 24, 1987, were carried out with high temporal resolution. A line center imaging system and an imaging spectrograph for line profile acquisition have been operated simultaneously with 0.3 s and 2.3 s temporal resolution, respectively. The temporal evolution at line center and in the blue and red wing have been correlated with hard X-ray data from HXRBS. The observed line profiles have been analyzed in terms of dynamic H-alpha line profile calculations by Canfield and Gayley. The combined H-alpha and hard X-ray signatures of two flare kernels are compatible with the theoretical predictions for strong nonthermal electron heating and the formation of a downward moving chromospheric condensation. A third kernel also shows the predicted downward moving chromospheric material, but its temporal evolution is not compatible with electron beam heating. Publication: The Astrophysical Journal Pub Date: June 1989 DOI: 10.1086/167567 Bibcode: 1989ApJ...341.1088W Keywords: H Alpha Line; Solar Flares; Solar Spectra; Spectrum Analysis; Temporal Resolution; Line Spectra; Solar X-Rays; X Ray Spectra; Solar Physics; LINE PROFILES; SUN: FLARES full text sources ADS |

view Abstract Citations (102) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Self-reversed CO profiles in collapsing molecular clouds. Snell, R. L. ; Loren, R. B. Abstract Observations of self-reversed CO line profiles in four dense molecular clouds (Mon R2, NGC 1333, W3, and Rho Oph) are discussed, and it is shown that these cases are readily explained by self-absorption in the outer layers of a nonhomologously collapsing cloud. Common features of the four clouds are reviewed, evidence is presented which indicates that the clouds are in a state of collapse rather than expansion, and it is demonstrated that the collapse is most likely nonhomologous with the collapse velocity varying as the inverse square root of cloud radius. CO line profiles are calculated with and without small amounts of turbulent broadening for a spherically symmetric nonhomologous collapsing cloud; these are compared with observed line-of-sight CO and (C-13)O line profiles. The general agreement between the line profiles given by the model with a small amount of turbulence and the observed line profiles is found to be quite good, with all the common features of the observed profiles present in the calculated profiles. An observational test of the model is proposed. Publication: The Astrophysical Journal Pub Date: January 1977 DOI: 10.1086/154909 Bibcode: 1977ApJ...211..122S Keywords: Carbon Monoxide; Gravitational Collapse; Interstellar Matter; Line Spectra; Molecular Spectra; Nebulae; Astronomical Models; Astronomical Spectroscopy; Cosmic Dust; Emission Spectra; Spectral Line Width; Astrophysics full text sources ADS |

view Abstract Citations (7) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Quadratic Zeeman effect in the hydrogen Balmer lines from magnetic white dwarfs. Surmelian, G. L. ; Oconnell, R. F. Abstract Motivated by Preston's suggestion of using the quadratic Zeeman effect to detect large magnetic fields in DA white dwarfs, we use a variational method for an accurate calculation of the total Zeeman wavelength shifts of the hydrogen Balmer absorption lines (Ha-H10) for magnetic fields from 106 to 5 x 106 gauss. Interference effects between upper values of the principal quantum number n become significant in that range. The quadratic shifts are smaller than those given by perturbation theory, leading to an increase in the estimated magnetic field. Subject headings: magnetic stars - white dwarf stars - Zeeman effect Publication: The Astrophysical Journal Pub Date: November 1974 DOI: 10.1086/153209 Bibcode: 1974ApJ...193..705S Keywords: Balmer Series; H Lines; Magnetic Stars; White Dwarf Stars; Zeeman Effect; Absorption Spectra; Frequency Shift; H Alpha Line; Hydrogen Atoms; Magnetic Flux; Stellar Spectra; Astrophysics full text sources ADS |

view Abstract Citations (265) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Accretion by magnetic neutron stars. I. Magnetospheric structure and stability. Elsner, R. F. ; Lamb, F. K. Abstract Results are presented of a detailed study of the magnetic neutron star model, taking into account the particular case in which the accretion flow is approximately radial and the star is slowly rotating. An investigation is conducted of the physical processes which occur in the neighborhood of the magnetospheric boundary and, in particular, on the manner in which accreting plasma enters the magnetosphere. Attention is given to the formation of a magnetosphere, the scale and structure of static magnetospheres, equilibrium shapes, the stability of the magnetospheric boundary, the plasma flow into the magnetosphere, the scale and structure of the magnetosphere, and the Alfven surface. The presented results imply that, for a wide range of conditions relevant to compact X-ray sources, the Rayleigh-Taylor instability is the most important plasma entry process. Publication: The Astrophysical Journal Pub Date: August 1977 DOI: 10.1086/155427 Bibcode: 1977ApJ...215..897E Keywords: Magnetic Stars; Neutron Stars; Stellar Atmospheres; Stellar Magnetospheres; Stellar Mass Accretion; Atmospheric Models; Stellar Models; Stellar Rotation; X Ray Sources; Astrophysics full text sources ADS | data products SIMBAD (11)

view Abstract Citations (16) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-resolution polarization observations inside spectral lines of magnetic AP stars. III. Observations of 78 Vir. Borra, E. F. Abstract Circular polarization and intensity profiles have been obtained across the Fe II λ4520.2 line throughout the magnetic cycle of the Ap star 78 Virginis. The Be curves obtained from the data are briefly discussed and compared to the Be curves obtained with other techniques. Publication: The Astrophysical Journal Pub Date: February 1980 DOI: 10.1086/157695 Bibcode: 1980ApJ...235..911B Keywords: A Stars; Chemical Composition; Circular Polarization; Line Spectra; Magnetic Stars; Stellar Spectra; Electrophotometers; H Alpha Line; High Resolution; Iron; Optical Scanners; Stellar Magnetic Fields; Astrophysics full text sources ADS | data products SIMBAD (1) Related Materials (2) Part 1: 1977ApJ...216..462B Part 2: 1978ApJ...220..924B