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Sökning: WFRF:(van Groningen E.)

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  • Föregående 1[2]3Nästa
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11.
  • Wanders, I., et al. (författare)
  • Spectroscopic monitoring of active galactic nuclei. II. The Seyfert-1 galaxy NGC 3516
  • 1993
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 269:1-2, s. 39-5353
  • Tidskriftsartikel (refereegranskat)abstract
    • The authors present the results of a five month spectroscopic monitoring campaign of the Seyfert-1 galaxy NGC 3516. Using a new calibration method and applying a correction for seeing differences during the various observations they can scale the spectra to each other with a much higher accuracy than hitherto achieved. NGC 3516 shows large amplitude variations on a time scale of several weeks. Asymmetric profile variations occur on the same time scale as the continuum variations. The authors show the presence of a varying dip on the blue wing of the Hbeta profile, which is not present on the Halpha profile, and which corresponds to the absorption features previously seen in the UV emission lines of NGC 3516. From cross-correlation analysis they find a time lag of 14plusmn2 days for the Halpha and 7plusmn3 days for the Hbeta emission-line response to continuum variations
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12.
  • Ronnback, J., et al. (författare)
  • Host galaxies of intermediate redshift radio-loud and radio-quiet quasars
  • 1996
  • Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 283:1, s. 282-296296
  • Tidskriftsartikel (refereegranskat)abstract
    • In a search for host galaxies associated with quasars, the authors present results from deep CCD imaging using the European Southern Observatory 3.5-m New Technology Telescope. Altogether 21 targets, 12 radio-loud and nine radio-quiet quasars, were observed in R, and additional V and Gunn i images were collected for a subgroup of these. The quasar redshifts are between 0.4 and 0.8, a range largely unexplored in previous studies. At these redshifts the R band corresponds to a rest-frame wavelength between 4600 and 3600 Aring. Thus, the authors are primarily probing the light from young stellar components of the presumed host galaxies. To separate out the light originating from the host object the authors remove the quasar contribution by scaling the point spread function (PSF). The PSF is a combination of an empirical PSF model, derived from stars lying in the same field as the quasars (used for the core of the PSF), and an analytical model for the wings of the PSF. After PSF subtraction of the QSO image the authors identify extended residual objects in 17 targets (nine in radio-loud and eight in radio-quiet quasars), of which a few are only marginal detections. These objects are large and luminous and their colours are relatively blue. Their V-R colours are consistent with a stellar population typical of late-type spirals and irregular galaxies. The blue colours could be caused by recent star formation events or by scattering of the QSO light
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13.
  • van Genderen, A. M., et al. (författare)
  • A discussion on new VBLUW observations of the X-ray binary Sk. 160=SMC X-1
  • 1981
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 101:1, s. 101-104104
  • Tidskriftsartikel (refereegranskat)abstract
    • VBLUW photometry (Walraven system) of Sk. 160=SMC X-1 made in 1973, 1975, and 1977 are discussed. They are compared with those of van Paradijs (1977) made in 1976. Using all available photometric and X-ray mid-eclipse data, a period is determined by a weighted least-squares solution: P=3.89235 dplusmn0.00002 d m.e
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14.
  • van Genderen, A. M., et al. (författare)
  • VBLUW photometry of the association Sco OB1 (containing the open cluster NGC 6231). A discussion on the evolutionary status of the hypergiant zeta 1 Sco (B1 Ia +)
  • 1984
  • Ingår i: Astronomy and Astrophysics Supplement Series. - 0365-0138 .- 1286-4846. ; 58:3, s. 537-548548
  • Tidskriftsartikel (refereegranskat)abstract
    • VBLUW photometry of nearly 190 stars in the very young association Sco OB1, including the cluster NGC 6231, is presented and discussed. Temperature and surface gravity are determined with the aid of theoretical colours. Individual reddenings are also obtained. The distance modulus ( m- M) 0=11.00plusmn0.25 is similar to the value found by Shobbrook (1983). It appears that the reddening is not uniformly distributed across the association (~2degtimes1deg), but that areas of low and high reddening, varying from E( B- V) J=0.35 up to 0.67, can be distinguished. Practically all reddening is caused by dust in the local spiral arm up to a distance of at most 700 pc from the Sun. The Sagittarius-Carina arm where Sco OB1 is situated is practically transparent over a distance of ~0.5 kpc. The kinematical age of ~10 6 yr is in reasonable agreement with the average evolutionary age of ~(3.6plusmn0.6)times10 6 yr of the 12 brightest stars. The evolutionary status of the hypergiant zeta 1 Sco (B1 Ia +) is discussed
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15.
  • Perry, J. J., et al. (författare)
  • Hysteresis in broad-line regions of active galactic nuclei
  • 1994
  • Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 271:3, s. 561-572572
  • Tidskriftsartikel (refereegranskat)abstract
    • The response of emission-line luminosities to changes in the observed continuum in active galaxies is commonly used for reverberation mapping (RM) of the emission-line region. The method assumes regularity in the continuum source and linearity in the line response to the continuum, and that the phase-space distribution of the line-emitting gas is constant in time. The wealth of information contained in the detailed line profiles is under-utilized in current methods of RM. The authors propose a new method to improve this situation. The authors define normalized profiles and show how their use enables one to explore details of the emission-line region that have hitherto eluded detection. Furthermore, the authors investigate the possibility of testing the validity of the assumptions as used in the standard application of RM. The authors present new methods, the hysteresis test and the Q concept - also based on the line profiles - to test the basic assumptions of RM. The test fails when applied to NGC 4151. The authors show that there is good evidence either for significantly extended and complex emission-line regions, or for changes in the mass distribution over time-scales of months or more - i.e. on time-scales comparable to the length of typical observing campaigns
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16.
  • Stirpe, G. M., et al. (författare)
  • Broad emission line variability in the Seyfert 1 galaxies NGC 5548 and NGC 3783
  • 1988
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 200:1-2, s. 9-1616
  • Tidskriftsartikel (refereegranskat)abstract
    • High quality spectra are presented for the Seyfert 1 galaxies NGC 5548 and NGC 3783. Halpha and Hbeta were observed at different epochs, with time intervals between 4 and 13 months. The spectra have been scaled to each other by normalizing the flux of the narrow lines. The difference spectra show that the broad emission lines have varied not only in flux, but also in shape. The authors compare their data with those published by Peterson (1987) and Peterson et al. (1987) and conclude that the supermassive binary scenario proposed by the latter is not unique. The observed variations can be interpreted in an accretion disk scenario. The whole data-set also provides evidence against models based on outflowing motion. The He II lambda4686 line discussed together with N III lambda4640 Bowen emission. A limit to the results is given by the long time intervals separating the observations, which do not allow the authors to set as strong constraints on the BLR as high quality, frequent monitoring of Seyfert 1 spectra would
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17.
  • Stirpe, G. M., et al. (författare)
  • Emission line variation in the Seyfert galaxy Fairall 9 and the presence of broad [O III] emission
  • 1989
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 211:2, s. 310-314314
  • Tidskriftsartikel (refereegranskat)abstract
    • The authors present two high quality spectra of the Hbeta region in the Seyfert 1 galaxy Fairall 9, separated by a period of 4 years. The variation of the broad lines is discussed, and in particular that of the Fe II lines of multiplet 42. The difference spectrum shows clearly Fe II (42) lambda 5018 and lambda 5169 with equal intensity. There is a strong, broad (4000 km s -1) wing present under the [O III] lambda 5007 line, which varied only by a small amount. The authors show that this variation is entirely due to the variation of Fe II lambda 5018 and that the remainder of the [O III]-wing has not varied. On this basis the authors argue that the wing is not caused by the Fe II (42) lambda 5018 line, nor by any other Fe II lines, but that they are observing high velocity [O III]-emitting material. From the lack of variation in this component a minimum distance to the source can be set of 1.3 pc. Other features of the difference spectrum are also discussed
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18.
  • van Groningen, E. (författare)
  • Accretion disks in Seyfert nuclei : broad line profiles and asymmetries
  • 1983
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 126:2, s. 363-371371
  • Tidskriftsartikel (refereegranskat)abstract
    • Keplerian rotation around a massive object in the centre of a Seyfert galaxy is considered as the main broadening mechanism for the broad emission lines. The resultant line profiles are shown to be of power-law form in the wings and are compared with recently published high quality observations. Several possible solutions are given for the [O III]-problem raised by Shields (1978). Asymmetries in the line profiles are explained by anisotropically radiating filaments in two oppositely directed jets emanating from the centre of the disk and by radial motions in or above the disk
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19.
  • van Groningen, E., et al. (författare)
  • An algorithm for the relative scaling of spectra
  • 1992
  • Ingår i: Publications of the Astronomical Society of the Pacific. - 0004-6280 .- 1538-3873. ; 104:678, s. 700-703703
  • Tidskriftsartikel (refereegranskat)abstract
    • A method is described for the automatic relative scaling of spectra in which one or more lines with constant flux are present. The algorithm takes into account differences in spectral resolution, flux factors, and spectral shifts. It was developed for the relative calibration of series of optical spectra obtained in variability studies of active galactic nuclei but it also can be used for other purposes, e.g., the subtraction of an underlying stellar continuum in AGN with a template spectrum. Tests show that a high degree of accuracy is obtained, and that the method is superior to scaling the spectra by eye or measuring narrow-band fluxes
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20.
  • van Groningen, E. (författare)
  • An analysis of the spectra of 3 Seyfert-1 galaxies with strong Ca II emission
  • 1993
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 272:1, s. 25-3636
  • Tidskriftsartikel (refereegranskat)abstract
    • High resolution spectroscopy is presented of three Seyfert-1 galaxies-I Zw 1, Akn 564 and Mkn 231. The spectra cover the optical wavelength region and the regions with the Ca II triplet and the [Ca II] lines. The broad lines in I Zw 1 and Akn 564 are relatively narrow (FWHM<1000 km s -1); and in both objects the Ca II triplet lines are considerably broader than the Balmer lines. These lines are formed at large column densities in the line emitting region; electron scattering by thermal electrons in the broad line clouds may explain the larger widths of the Ca II lines. I Zw 1 has three emission line regions. In addition to the broad line region there are two kinematically separated narrow line regions: a high excitation region with relatively broad lines (FWHM~1100 km s -1), blue shifted with regard to the systemic velocity by ~700 km s -1; and a region with very low excitation at the systemic velocity and much narrower lines (FWHM~400 km s -1)
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  • Resultat 11-20 av 25
  • Föregående 1[2]3Nästa

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