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  • ASTROPHYSICS  (6)
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  • 1
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    The Mg II line profile in the Seyfert galaxy NGC 4151 - A new outflowing component (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: This paper examines the Mg II 2795-2802 A doublet in the Seyfert galaxy NGC 4151 at a higher resolution than has previously been used, searching for velocity systems in absorption and emission. Evidence is presented for a new, narrow, outflowing absorption system in Mg II having a velocity of 825 km/s relative to the sun, and -165 km/s relative to the systemic velocity of NGC 4151. This feature is not present in Ly-alpha or C IV and possible explanations for this are considered. For the Mg II and C IV lines, a model decomposition of the line profile is presented.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Montly Notices (ISSN 0035-8711); 225; 837-849
    Format: text
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  • 2
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    The missing UV absorption lines of NGC 4151 (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Near simultaneous high dispersion long and short wavelength International Ultraviolet Explorer (IUE) observations of the Seyfert galaxy NGC 4151 are discussed. Previous observations revealed a narrow absorption system in Mg II not present in Ly alpha or C IV. The new observations confirm the presence of this system in Mg II and its absence in the other lines. Possible reasons for this are discussed. Future Hubble Space Telescope studies of NGC 4151 are discussed.
    Keywords: ASTROPHYSICS
    Type: ESA, Evolution in Astrophysics: IUE Astronomy in the Era of New Space Missions; p 523-525
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  • 3
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    IUE observations of Fe 2 galaxies (1981)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Repeated observations of the Seyfert 1 galaxies I Zw 1 and II Zw 136, which have very strong Fe II emission lines in the optical region, were made at low resolution with the IUE Satellite. The ultraviolet spectra are very similar: both are variable and show broad emission features of Fe II (especially the UV multiplets 1, 33, 60, 62, and 63) as well as the emission lines usually strong in Seyferts and quasars. The data strongly support the hypothesis that the optical Fe II emission lines are primarily due to collisional excitation and that resonance fluorescence makes only a minor contribution to the excitation of these lines.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 757-766
    Format: application/pdf
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  • 4
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    Further observations of the Orion Nebula cluster (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: New spectral types for 16 stars, UBVRI photometry for 13 stars and UBVRIHKL photometry for 35 stars in the Orion Nebula cluster are presented. Analysis of these data together with those of Penston (1973) shows that the reddening law in the cluster is normal. Previous claims for high ratios of total to selective absorption are caused by mistaking infrared emission for a hole in the absorption at that wavelength. The distance modulus of M42 is 8.0 + or - 0.1 mag. Star formation in the cluster has been in progress over the last 10 million yr. The infrared colors of cluster stars are correlated with their range of variation in the optical region.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society; vol. 171
    Format: text
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  • 5
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    The Lambda Orionis association (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The Lambda Orionis association has the photometric properties of a typical young cluster with an age of about 4 million yr. Its distance is 400 + or - 40 pc. Attention is drawn to the lack of a dense molecular cloud and associated infrared sources in this young grouping
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society; vol. 181
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  • 6
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    On the nature of the broad line region clouds (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The possibility that the broad line region (BLR) clouds in quasars and AGN may be irradiated stellar chromospheres is examined. This possibility is supported by the fact that stars are known to have peak densities in galactic nuclei and by data from symbiotic stars which show that cool stars irradiated by an ultraviolet source yield spectra with line ratios similar to those of AGN. Other evidence in favor of the theory includes the fact that stellar chromospheres do not require an external confining medium and the way in which line profiles can be accounted for by emission from parabolically orbiting objects of constant cross section. The main problem with this theory is that irradiated stars possess much more mass than traditional BLR models because only a small proportion of the stellar mass actually lies in the irradiated chromosphere. It is suggested that the irradiated stars must be dwarfs which have 'bloated' in response to the radiation field rather than normal giants.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 233; 601-609
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