共查询到20条相似文献，搜索用时 219 毫秒
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D. C. Gabuzda T. V. Cawthorne 《Monthly notices of the Royal Astronomical Society》2000,319(4):1056-1066
Global VLBI images in intensity and linear polarization at of the BL Lacertae objects 0235+164, 0300+470, 0735+178, 0954+658, 1803+784, 1823+568, and BL Lac and OVV quasar 3C 279 are presented and analysed. These are the highest resolution polarization images currently available for several of these sources. On the whole, the tendencies observed at longer centimetre wavelengths are also exhibited in these 1.3-cm images. When core polarization is detected, the corresponding polarization angles χ tend to lie either parallel or perpendicular to the direction of the inner jet. The core degrees of polarization are usually comparable to those typical at 6 cm, but somewhat lower in several cases, suggesting that the higher resolution data are better separating the contributions of intrinsically weakly polarized cores and highly polarized emerging knots. The observed χ vectors in the jets of 0735+178, 0954+658, 1823+568, BL Lac and 3C 279 are aligned with the jet, implying the presence of transverse magnetic fields. In 0300+470 and BL Lac, there are regions where the direction of χ seems to be neither parallel nor perpendicular to the jet; it is not clear whether this is due to genuine obliquity of the magnetic field structure or to inadequate knowledge of the local flow direction. 相似文献
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Peter Martinez C. Koen G. Handler & E. Paunzen 《Monthly notices of the Royal Astronomical Society》1998,301(4):1099-1103
We present spectroscopic and multisite time series photometric observations of the star HD 105759 which confirm that this is a new pulsating λ Bootis star. Our spectroscopy indicates an overall metallicity of [Z] = log Z − log Z⊙ = −1 and that T eff = 8000 ± 300 K and log g = 4.0 ± 0.2. The photometric data reveal that this star pulsates with at least five frequencies: 8.62, 12.69, 20.15, 21.27 and 23.66 d−1 . These frequencies do not all match those found in an earlier single-site study, indicating that the pulsation spectrum changes with time. 相似文献
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Sergei M. Andrievsky Ernst Paunzen 《Monthly notices of the Royal Astronomical Society》2000,313(3):547-552
Having analysed the accretion-based model of the dust–gas separation, which is regarded to be the most promising for the explanation of the anomalous properties of λ Bootis-type stars, we can conclude that: (i) for any reasonable density profiles of the shell, dust grains appear to be decoupled from the gaseous background within the region where the temperature drops to a value that is less than the condensation temperature of heavy elements such as Mg, Ca, Fe, etc; (ii) most likely, in the shell of λ Bootis-type stars only small dust particles (of less than ≈10−6 cm in size) can be created; (iii) significant alteration of the initial atmospheric chemical composition can take place in the case when the density in the shell changes as ∼ r −2 . 相似文献
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David M. Russell Sara L. Ellison Chris R. Benn 《Monthly notices of the Royal Astronomical Society》2006,367(1):412-422
We present a sample of 33 damped Lyman α systems (DLAs) discovered in the Sloan Digital Sky Survey (SDSS) whose absorption redshifts ( z abs ) are within 6000 km s−1 of the quasi-stellar object's (QSO) systemic redshift ( z sys ). Our sample is based on 731 2.5 < z sys < 4.5 non-broad absorption line (non-BAL) QSOs from Data Release 3 (DR3) of the SDSS. We estimate that our search is ≈100 per cent complete for absorbers with N (H i ) ≥ 2 × 1020 cm−2 . The derived number density of DLAs per unit redshift, n ( z ), within Δ v < 6000 km s−1 is higher (3.5σ significance) by almost a factor of 2 than that of intervening absorbers observed in the SDSS DR3, i.e. there is evidence for an overdensity of galaxies near the QSOs. This provides a physical motivation for excluding DLAs at small velocity separations in surveys of intervening 'field' DLAs. In addition, we find that the overdensity of proximate DLAs is independent of the radio-loudness of the QSO, consistent with the environments of radio-loud and radio-quiet QSOs being similar. 相似文献
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We present the results of microlens ray-tracing simulations showing the effect of absorbing material between a source quasar and a lensing galaxy in a gravitational lens system. We find that, in addition to brightness fluctuations due to microlensing, the strength of the absorption line relative to the continuum varies with time, with the properties of the variations depending on the structure of the absorbing material. We conclude that such variations will be measurable via ultraviolet spectroscopy of image A of the gravitationally lensed quasar Q2237+0305 if the Lyman α clouds between the quasar and the lensing galaxy possess structure on scales smaller than ∼0.1 pc. The time-scale for the variations is on the order of years to decades, although very short-term variability can occur. While the Lyman α lines may not be accessible at all wavelengths, this approach is applicable to any absorption system, including metal lines. 相似文献
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Paul J. Francis Sunsanee McDonnell 《Monthly notices of the Royal Astronomical Society》2006,370(3):1372-1378
We use integral field spectroscopy with the Gemini North Telescope to detect probable fluorescent Lyman α (Lyα) emission from gas lying close to the luminous QSO PSS 2155+1358 at redshift 4.28. The emission is most likely coming not from primordial gas, but from a multiphase, chemically enriched cloud of gas lying about 50 kpc from the QSO. It appears to be associated with a highly ionized associated absorber seen in the QSO spectrum. With the exception of this gas cloud, the environment of the QSO is remarkably free of neutral hydrogen. We also marginally detect Lyα emission from a foreground subdamped Lyα absorption-line system. 相似文献
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Minfeng Gu Zhaoyu Chen Xinwu Cao 《Monthly notices of the Royal Astronomical Society》2009,397(3):1705-1710
The relationship between the black hole mass and velocity dispersion indicated with [O iii ] linewidth is investigated for a sample of 87 flat-spectrum radio quasars selected from the Sloan Digital Sky Survey Data Release 3 quasar catalogue. We found that the M BH −σ[O III] relation is different from the Tremaine et al. relation for nearby inactive galaxies, with a larger black hole mass at given velocity dispersion. There is no strong evidence of cosmology evolution in the M BH −σ[O III] relation up to z ∼ 0.8 . A significant correlation between the [O iii ] luminosity and broad-line region (BLR) luminosity is found. When transferring the [O iii ] luminosity to narrow-line region (NLR) luminosity, the BLR luminosity is, on average, larger than the NLR one by about one order of magnitude. We found a strong correlation between the synchrotron peak luminosity and NLR luminosity, which implies a tight relation between the jet physics and accretion process. 相似文献
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We present three seasons of photometric observations and one season of intensive high-dispersion spectroscopic observations of the Be star λ Eridani. We show that only one period, P =0.70173 d , is present in the photometry, although there are large light amplitude variations from season to season. We confirm a suspicion that light outbursts repeat at intervals of about 475 d. A total of 348 echelle spectra of the star were obtained over a 2-week observing run. We show that the periodic variations are present in the emission wings of the helium lines, in the emission wings of the H α line and in the absorption cores of H β and H γ . Together with the fact that the periodic variations appear outside the projected rotational velocity limit, this indicates that they are associated with circumstellar material immediately above the photosphere and supports the idea of corotating gas clouds. We present evidence in support of a true rotational period of 2 P =1.40346 d and suggest that the mass loss in Be stars is caused by centrifugal magnetic acceleration. 相似文献
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X. Hernandez Changbom Park B. Cervantes-Sodi Yun-Young Choi 《Monthly notices of the Royal Astronomical Society》2007,375(1):163-170
Using simple dimensional arguments for both spiral and elliptical galaxies, we present formulae to derive an estimate of the halo spin parameter λ for any real galaxy, in terms of common observational parameters. This allows a rough estimate of λ, which we apply to a large volume-limited sample of galaxies taken from the Sloan Digital Sky Survey data base. The large numbers involved (11 597) allow the derivation of reliable λ distributions, as signal adds up significantly in spite of the errors in the inferences for particular galaxies. We find that if the observed distribution of λ is modelled with a lognormal function, as often done for this distribution in dark matter haloes that appear in cosmological simulations, we obtain parameters λ0 = 0.04 ± 0.005 and σλ = 0.51 ± 0.05 , interestingly consistent with values derived from simulations. For spirals, we find a good correlation between empirical values of λ and visually assigned Hubble types, highlighting the potential of this physical parameter as an objective classification tool. 相似文献