Systematic Errors in the Estimation of Black Hole Masses by Reverberation Mapping

The mass of the central black hole in many active galactic nuclei has been estimated on the basis of the assumption that the dynamics of the broad emission line gas are dominated by the gravity of the black hole. The most commonly-employed method is to estimate a characteristic size-scale $r_*$ from reverberation mapping experiments and combine it with a characteristic velocity $v_*$ taken from the line profiles; the inferred mass is then estimated by $r_* v_*^2/G$. We critically discuss the evidence supporting the assumption of gravitational dynamics and find that the arguments are still inconclusive. We then explore the range of possible systematic error if the assumption of gravitational dynamics is granted. Inclination relative to a flattened system may cause a systematic underestimate of the central mass by a factor $\sim (h/r)^2$, where $h/r$ is the aspect ratio of the flattening. The coupled effects of a broad radial emissivity distribution, an unknown angular radiation pattern of line emission, and sub-optimal sampling in the reverberation experiment can cause additional systematic errors as large as a factor of 3 or more in either direction.Comment: 19 pages, 4 figures, AASLaTeX, accepted by Ap

The analysis of solar models: Neutrinos and oscillations

Tests of solar neutrino flux and solar oscillation frequencies were used to assess standard stellar structure theory. Standard and non-standard solar models are enumerated and discussed. The field of solar seismology, wherein the solar interior is studied from the measurement of solar oscillations, is introduced

Molecular footprint of drug-selective pressure in a human immunodeficiency virus transmission chain

Known human immunodeficiency virus (HIV) transmission histories are invaluable models for investigating the evolutionary and transmission dynamics of the virus and to assess the accuracy of phylogenetic reconstructions. Here we have characterized an HIV-1 transmission chain consisting of nine infected patients, almost all of whom were treated with antiviral drugs at later stages of infection. Partial pol and env gp41 regions of the HIV genome were directly sequenced from plasma viral RNA for at least one sample from each patient. Phylogenetic analyses in pol using likelihood methods inferred an evolutionary history not fully compatible with the known transmission history. This could be attributed to parallel evolution of drug resistance mutations resulting in the incorrect clustering of multidrug-resistant virus. On the other hand, a fully compatible phylogenetic tree was reconstructed from the env sequences. We were able to identify and quantify the molecular footprint of drug-selective pressure in pol using maximum likelihood inference under different codon substitution models. An increased fixation rate of mutations in the HIV population of the multidrug-resistant patient was demonstrated using molecular clock modeling. We show that molecular evolutionary analyses, guided by a known transmission history, can reveal the presence of confounding factors like natural selection and caution should be taken when accurate descriptions of HIV evolution are required.status: publishe

The End of the Lines for OX 169: No Binary Broad-Line Region

We show that unusual Balmer emission line profiles of the quasar OX 169, frequently described as either self-absorbed or double peaked, are actually neither. The effect is an illusion resulting from two coincidences. First, the forbidden lines are quite strong and broad. Consequently, the [N II]6583 line and the associated narrow-line component of H-alpha present the appearance of twin H-alpha peaks. Second, the redshift of 0.2110 brings H-beta into coincidence with Na I D at zero redshift, and ISM absorption in Na I D divides the H-beta emission line. In spectra obtained over the past decade, we see no substantial change in the character of the line profiles, and no indication of intrinsic double-peaked structure. The H-gamma, Mg II, and Ly-alpha emission lines are single peaked, and all of the emission-line redshifts are consistent once they are correctly attributed to their permitted and forbidden-line identifications. A systematic shift of up to 700 km/s between broad and narrow lines is seen, but such differences are common, and could be due to gravitational and transverse redshift in a low-inclination disk. Stockton & Farnham (1991) had called attention to an apparent tidal tail in the host galaxy of OX 169, and speculated that a recent merger had supplied the nucleus with a coalescing pair of black holes which was now revealing its existence in the form of two physically distinct broad-line regions. Although there is no longer any evidence for two broad emission-line regions in OX 169, binary black holes should form frequently in galaxy mergers, and it is still worthwhile to monitor the radial velocities of emission lines which could supply evidence of their existence in certain objects.Comment: 19 pages, 5 figures, accepted for publication in Ap.

Influence of s,p-d and s-p exchange couplings on exciton splitting in (Zn,Mn)O

This work presents results of near-band gap magnetooptical studies on (Zn,Mn)O epitaxial layers. We observe excitonic transitions in reflectivity and photoluminescence, that shift towards higher energies when the Mn concentration increases and split nonlinearly under the magnetic field. Excitonic shifts are determined by the s,p-d exchange coupling to magnetic ions, by the electron-hole s-p exchange, and the spin-orbit interactions. A quantitative description of the magnetoreflectivity findings indicates that the free excitons A and B are associated with the Gamma_7 and Gamma_9 valence bands, respectively, the order reversed as compared to wurtzite GaN. Furthermore, our results show that the magnitude of the giant exciton splittings, specific to dilute magnetic semiconductors, is unusual: the magnetoreflectivity data is described by an effective exchange energy N_0(beta-alpha)=+0.2+/-0.1 eV, what points to small and positive N_0 beta. It is shown that both the increase of the gap with x and the small positive value of the exchange energy N_0 beta corroborate recent theory describing the exchange splitting of the valence band in a non-perturbative way, suitable for the case of a strong p-d hybridization.Comment: 8 pages, 8 figure

Modeling Variable Emission Lines in AGNs: Method and Application to NGC 5548

We present a new scheme for modeling the broad line region in active galactic nuclei (AGNs). It involves photoionization calculations of a large number of clouds, in several pre-determined geometries, and a comparison of the calculated line intensities with observed emission line light curves. Fitting several observed light curves simultaneously provides strong constraints on model parameters such as the run of density and column density across the nucleus, the shape of the ionizing continuum, and the radial distribution of the emission line clouds. When applying the model to the Seyfert 1 galaxy NGC 5548, we were able to reconstruct the light curves of four ultraviolet emission-lines, in time and in absolute flux. This has not been achieved by any previous work. We argue that the Balmer lines light curves, and possibly also the MgII2798 light curve, cannot be tested in this scheme because of the limitations of present-day photoionization codes. Our fit procedure can be used to rule out models where the particle density scales as r^{-2}, where r is the distance from the central source. The best models are those where the density scales as r^{-1} or r^{-1.5}. We can place a lower limit on the column density at a distance of 1 ld, of N_{col}(r=1) >~ 10^{23} cm^{-2} and limit the particle density to be in the range of 10^{12.5}>N(r=1)>10^{11} cm^{-3}. We have also tested the idea that the spectral energy distribution (SED) of the ionizing continuum is changing with continuum luminosity. None of the variable-shape SED tried resulted in real improvement over a constant SED case although models with harder continuum during phases of higher luminosity seem to fit better the observed spectrum. Reddening and/or different composition seem to play a minor role, at least to the extent tested in this work.Comment: 12 pages, including 9 embedded EPS figures, accepted for publication in Ap

Los hongos de colombia - vii: leotiaceae - iv: hymenoscyphus caudatus and related species from colombia and adjacent regions

The present paper redescribes and illustrates five common species of Hymenoscyphus, H. caudatus, H. serotinus, H. affin. scutulus, H. Iasiopodtum  and amp; H.sclerogenus, from Colombia and adjacent regions in South America.  Emphasis is given to discussions of anatomical and morphological variability and host specificity of the species included.  Inoperculate Discomycetes are generally small Ascomycetes producing an apothecium as their sexual fruiting structure. The largest order, the Helotiales, contains 5 families: Dermateaceae, Hyaloscyphaceae, Orbiliaceae, Sclerotiniaceae and Leotiaceae, In recent years there have been several monographic and submonographic studies on selected genera within these families, but no definitive studies on the principal family, Leotiaceae (previously referred to as the Helotiaceae), has been prepared. These studies have resulted in a better understanding of some of the family limits, but most of the generic limits still remain vague and confused. This is especially true for Hymenoscyphus (previously referred to by most workers as Helotium), which for decades has been the depository for small Discomycetes of uncertain affinities.  White (1942, 1942-a, 1943, 1944) began to work systematically through the species of Hymenoscyphus and to bring order out of the existing chaos. His carefully prepared descriptions, meticulously drawn illustrations, and long  synonymies were the real important contribution to the understanding of the genus. The most recent attempts to studyHymenoscyphus have been by Dennis, who summarized his works in 1964 (Dennis, 1964). However, as Dennis himself points out, he was unable to come to a sound understanding and arrangement of the species because of the extent of the problems, and the resulting treatment is rather artificial. He relied heavily upon substrate and geographical relations, rather than true morphological similarities. We agree with Dennis, that this has resulted in the separation of closely related taxa and an "unnecessary proliferation of names".  Although Dennis contributions were extraordinary in terms of the number of described species he examined and in his literature searches, he did not have at his disposal necessary tropical collections for a complete comprehension of the individual species and/or the entire genus. Further, as pointed out by Dumont (1976), because of limited collections Dennis was unable to understand the full morphological and geographical variation of certain species and recognized several taxa, when in the final analysis only one existed. Many of these deficiencies are apparent in his monumental work on "The Fungus Flora of Venezuela and Adjacent Countries" (Dennis, 1970).  InHymenoscyphus for example, he included only seven species (in his 1964 treatment he included more than 70 species for the world), and of these three, H. crocatus , H. caracassensis and H.atrosubiculatum have been removed from the genus by Dumont (1974) and Dumont and Pal (1978). Arendholz (1979) has recently provided a very important contribution to the understanding of several species of leaf inhabiting species ofHymenoscyphus. Again, as with previous workers, his work stressed temperate collections and temperate species. The purpose of the present study is to report the findings of some of our tropical collecting, to expand the understanding of five species of Hymenoscyphus which appear to be common in northern South America, to discuss the morphological variability observed, and to comment on the host or substrate specificity (or lack of it) within certain taxa.  The materials and methods used during these studies are the same as those reported by Dumont (1972). The following is a key to the five species   reported herein.The present paper redescribes and illustrates five common species of Hymenoscyphus, H. caudatus, H. serotinus, H. affin. scutulus, H. Iasiopodtum  and amp; H. sclerogenus, from Colombia and adjacent regions in South America.  Emphasis is given to discussions of anatomical and morphological variability and host specificity of the species included.  Inoperculate Discomycetes are generally small Ascomycetes producing an apothecium as their sexual fruiting structure. The largest order, the Helotiales, contains 5 families: Dermateaceae, Hyaloscyphaceae, Orbiliaceae, Sclerotiniaceae and Leotiaceae, In recent years there have been several monographic and submonographic studies on selected genera within these families, but no definitive studies on the principal family, Leotiaceae (previously referred to as the Helotiaceae), has been prepared. These studies have resulted in a better understanding of some of the family limits, but most of the generic limits still remain vague and confused. This is especially true for Hymenoscyphus (previously referred to by most workers as Helotium), which for decades has been the depository for small Discomycetes of uncertain affinities.  White (1942, 1942-a, 1943, 1944) began to work systematically through the species of Hymenoscyphus and to bring order out of the existing chaos. His carefully prepared descriptions, meticulously drawn illustrations, and long  synonymies were the real important contribution to the understanding of the genus. The most recent attempts to study Hymenoscyphus have been by Dennis, who summarized his works in 1964 (Dennis, 1964). However, as Dennis himself points out, he was unable to come to a sound understanding and arrangement of the species because of the extent of the problems, and the resulting treatment is rather artificial. He relied heavily upon substrate and geographical relations, rather than true morphological similarities. We agree with Dennis, that this has resulted in the separation of closely related taxa and an "unnecessary proliferation of names".  Although Dennis contributions were extraordinary in terms of the number of described species he examined and in his literature searches, he did not have at his disposal necessary tropical collections for a complete comprehension of the individual species and/or the entire genus. Further, as pointed out by Dumont (1976), because of limited collections Dennis was unable to understand the full morphological and geographical variation of certain species and recognized several taxa, when in the final analysis only one existed. Many of these deficiencies are apparent in his monumental work on "The Fungus Flora of Venezuela and Adjacent Countries" (Dennis, 1970).  In Hymenoscyphus for example, he included only seven species (in his 1964 treatment he included more than 70 species for the world), and of these three, H. crocatus , H. caracassensis and H. atrosubiculatum have been removed from the genus by Dumont (1974) and Dumont and Pal (1978). Arendholz (1979) has recently provided a very important contribution to the understanding of several species of leaf inhabiting species of Hymenoscyphus. Again, as with previous workers, his work stressed temperate collections and temperate species. The purpose of the present study is to report the findings of some of our tropical collecting, to expand the understanding of five species of Hymenoscyphus which appear to be common in northern South America, to discuss the morphological variability observed, and to comment on the host or substrate specificity (or lack of it) within certain taxa.  The materials and methods used during these studies are the same as those reported by Dumont (1972). The following is a key to the five species   reported herein

Anisotropic Scaling in Layered Aperiodic Ising Systems

The influence of a layered aperiodic modulation of the couplings on the critical behaviour of the two-dimensional Ising model is studied in the case of marginal perturbations. The aperiodicity is found to induce anisotropic scaling. The anisotropy exponent z, given by the sum of the surface magnetization scaling dimensions, depends continuously on the modulation amplitude. Thus these systems are scale invariant but not conformally invariant at the critical point.Comment: 7 pages, 2 eps-figures, Plain TeX and epsf, minor correction

The Circumstellar Disk of HD 141569 Imaged with NICMOS

Coronagraphic imaging with the Near Infrared Camera and Multi Object Spectrometer on the Hubble Space Telescope reveals a large, ~400 AU (4'') radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected light image at 1.1 micron shows the disk oriented at a position angle of 356 +/- 5 deg and inclined to our line of sight by 51 +/- 3 deg; the intrinsic scattering function of the dust in the disk makes the side inclined toward us, the eastern side, brighter. The disk flux density peaks 185 AU (1.''85) from the star and falls off to both larger and smaller radii. A region of depleted material, or a gap, in the disk is centered 250 AU from the star. The dynamical effect of one or more planets may be necessary to explain this morphology.Comment: 4 pages, LaTeX with emulateapj.sty and epsfig.sty, 4 postscript figures, Accepted to ApJ Letter

Long-Term Profile Variability of Double Peaked Emission Lines in Active Galactic Nuclei

We present up to two decades of spectroscopic monitoring of the double-peaked broad Halpha emission lines of seven broad-line radio galaxies. These extremely broad, double-peaked lines are successfully modeled by emission from gas in the outer accretion disk, and their profiles vary on timescales of months to years. This variability is a valuable probe for understanding the structure and dynamics of the accretion disk. We characterize the long-term broad-line profile variability in detail, and compare the evolution of the line profiles with predictions from a few simple physical models for dynamical processes in the accretion disk. We find no evidence for persistent, periodic variability that would be indicative of a precessing elliptical disk, or a circular disk with a long-lived, single-armed spiral or warp. We do find transient, periodic variability on the orbital timescale, possibly resulting from shocks induced by tidal perturbations, and variability in the wings of the profile which suggests changes in the emissivity of the inner accretion flow. Dramatic but localized profile changes are observed during flares and high-states of broad-line flux. In 3C 332, these changes can be explained by a slow, smooth, secular change in disk illumination. In Arp 102B and 3C 390.3, however, a simple disk model cannot explain the asymmetric profile changes, suggesting a need for more sophisticated models. We also observe sharp, transient features that appear in the blue peak of the objects, which require a well-organized velocity field.Comment: 76 pages, 52 figures, 14 tables, Accepted for publication in ApJS, figures in Appendix are low resolutio