1,194 research outputs found

    Time Variable Faraday Rotation Measures of 3C-273 and 3C-279

    Full text link
    Multifrequency polarimetry with the VLBA confirms the previously reported time-varying Faraday rotation measure (RM) in the quasar 3C-279. Variability in the RM and electric vector position angle (EVPA) of the jet component (C4) is seen making it an unreliable absolute EVPA calibrator. 3C-273 is also shown to vary its RM structure on 1.5 year time-scales. Variation in the RM properties of quasars may result from a Faraday screen which changes on time-scales of a few years, or from the motion of jet components which sample spatial variations in the screen. A new component emerging from the core of 3C-279 appears to be starting to sample such a spatial variation. Future monitoring of this component and its RM properties is suggested as a diagnostic of the narrow line region in 3C-279. We also present a new method of EVPA calibration using the VLA Monitoring Program.Comment: Accepted to ApJ Letters. 12 pages, 5 figure

    Dynamical mass of the O-type supergiant in Zeta Orionis A

    Full text link
    A close companion of Zeta Orionis A was found in 2000 with the Navy Precision Optical Interferometer (NPOI), and shown to be a physical companion. Because the primary is a supergiant of type O, for which dynamical mass measurements are very rare, the companion was observed with NPOI over the full 7-year orbit. Our aim was to determine the dynamical mass of a supergiant that, due to the physical separation of more than 10 AU between the components, cannot have undergone mass exchange with the companion. The interferometric observations allow measuring the relative positions of the binary components and their relative brightness. The data collected over the full orbital period allows all seven orbital elements to be determined. In addition to the interferometric observations, we analyzed archival spectra obtained at the Calar Alto, Haute Provence, Cerro Armazones, and La Silla observatories, as well as new spectra obtained at the VLT on Cerro Paranal. In the high-resolution spectra we identified a few lines that can be associated exclusively to one or the other component for the measurement of the radial velocities of both. The combination of astrometry and spectroscopy then yields the stellar masses and the distance to the binary star. The resulting masses for components Aa of 14.0 solar masses and Ab of 7.4 solar masses are low compared to theoretical expectations, with a distance of 294 pc which is smaller than a photometric distance estimate of 387 pc based on the spectral type B0III of the B component. If the latter (because it is also consistent with the distance to the Orion OB1 association) is adopted, the mass of the secondary component Ab of 14 solar masses would agree with classifying a star of type B0.5IV. It is fainter than the primary by about 2.2 magnitudes in the visual. The primary mass is then determined to be 33 solar masses

    Current definitions of “transdiagnostic” in treatment development: A search for consensus

    Full text link
    Research in psychopathology has identified psychological processes that are relevant across a range of Diagnostic and Statistical Manual (DSM) mental disorders, and these efforts have begun to produce treatment principles and protocols that can be applied transdiagnostically. However, review of recent work suggests that there has been great variability in conceptions of the term “transdiagnostic” in the treatment development literature. We believe that there is value in arriving at a common understanding of the term “transdiagnostic.” The purpose of the current manuscript is to outline three principal ways in which the term “transdiagnostic” is currently used, to delineate treatment approaches that fall into these three categories, and to consider potential advantages and disadvantages of each approachFirst author draf

    Multitechnique testing of the viscous decretion disk model I. The stable and tenuous disk of the late-type Be star β\beta CMi

    Full text link
    The viscous decretion disk (VDD) model is able to explain most of the currently observable properties of the circumstellar disks of Be stars. However, more stringent tests, focusing on reproducing multitechnique observations of individual targets via physical modeling, are needed to study the predictions of the VDD model under specific circumstances. In the case of nearby, bright Be star β\beta CMi, these circumstances are a very stable low-density disk and a late-type (B8Ve) central star. The aim is to test the VDD model thoroughly, exploiting the full diagnostic potential of individual types of observations, in particular, to constrain the poorly known structure of the outer disk if possible, and to test truncation effects caused by a possible binary companion using radio observations. We use the Monte Carlo radiative transfer code HDUST to produce model observables, which we compare with a very large set of multitechnique and multiwavelength observations that include ultraviolet and optical spectra, photometry covering the interval between optical and radio wavelengths, optical polarimetry, and optical and near-IR (spectro)interferometry. Due to the absence of large scale variability, data from different epochs can be combined into a single dataset. A parametric VDD model with radial density exponent of nn = 3.5, which is the canonical value for isothermal flaring disks, is found to explain observables typically formed in the inner disk, while observables originating in the more extended parts favor a shallower, nn = 3.0, density falloff. Modeling of radio observations allowed for the first determination of the physical extent of a Be disk (35−5+10^{+10}_{-5} stellar radii), which might be caused by a binary companion. Finally, polarization data allowed for an indirect measurement of the rotation rate of the star, which was found to be W≳0.98W \gtrsim 0.98, i.e., very close to critical.Comment: 19 pages (35 including online material), 17 figures, 2 online figures, 2 online tables with dat

    VLBI Polarimetry of 177 Sources from the Caltech-Jodrell Bank Flat-spectrum Survey

    Get PDF
    We present VLBA observations and a statistical analysis of 5 GHz VLBI polarimetry data from 177 sources in the Caltech-Jodrell Bank flat-spectrum (CJF) survey. The CJF survey, a complete, flux-density-limited sample of 293 extragalactic radio sources, gives us the unique opportunity to compare a broad range of source properties for quasars, galaxies and BL Lacertae objects. We focus primarily on jet properties, specifically the correlation between the jet axis angle and the polarization angle in the core and jet. A strong correlation is found for the electric vector polarization angle in the cores of quasars to be perpendicular to the jet axis. Contrary to previous claims, no correlation is found between the jet polarization angle and the jet axis in either quasars or BL Lac objects. With this large, homogeneous sample we are also able to investigate cosmological issues and AGN evolution.Comment: Accepted to the Astrophysical Journal: 37 pages, 14 figure
    • …
    corecore