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| 3. |
- ERKENS, U, et al.
(author)
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MONITORING OF ACTIVE GALACTIC NUCLEI .6. THE QUASAR MKN-876
- 1995
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In: ASTRONOMY AND ASTROPHYSICS. - : SPRINGER VERLAG. - 0004-6361. ; 296:1, s. 90-98
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Journal article (other academic/artistic)abstract
- We present the results of a 6 month monitoring campaign of Mkn 876, a low luminosity quasar with M(abs) approximate to -24. High resolution spectroscopy and direct imaging in the Johnson filters B, V, R, I was carried out in the first half of 1990. Line a
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| 4. |
- Erkens, U., et al.
(author)
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Monitoring of active galactic nuclei. VI. The quasar Mrk 876
- 1995
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 296:1, s. 90-9898
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Journal article (peer-reviewed)abstract
- For pt. V see ibid., vol. 285, no. 3, p. 857-67 (1994). We present the results of a 6 month monitoring campaign of Mrk 876, a low luminosity quasar with M absap-24. High resolution spectroscopy and direct imaging in the Johnson filters B, V, R, I was carried out in the first half of 1990. Line and continuum light curves are presented. Mrk 876 showed a decrease of 17% in the continuum over the whole observing period whereas the line flux of Hbeta and Halpha stayed constant. This implies, that the radius of the broad line region is larger than 6 light months. Coadded spectra of Hbeta and Halpha are presented which confirm an extreme asymmetry of the line profiles to the red. With respect to much earlier spectra the line profiles changed considerably
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| 5. |
- Arft, M, et al.
(author)
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Responses of tundra plants to experimental warming : Meta-analysis of the international tundra experiment
- 1999
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In: Ecological Monographs. - 0012-9615 .- 1557-7015. ; 69:4, s. 491-511
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Journal article (peer-reviewed)abstract
- The International Tundra Experiment (ITEX) is a collaborative, multisite experiment using a common temperature manipulation to examine variability in species response across climatic and geographic gradients of tundra ecosystems. ITEX was designed specifically to examine variability in arctic and alpine species response to increased temperature. We compiled from one to four years of experimental data from 13 different ITEX sites and used meta-analysis to analyze responses of plant phenology, growth, and reproduction to experimental warming. Results indicate that key phenological events such as leaf bud burst and flowering occurred earlier in warmed plots throughout the study period; however, there was little impact on growth cessation at the end of the season. Quantitative measures of vegetative growth were greatest in warmed plots in the early years of the experiment, whereas reproductive effort and success increased in later years. A shift away from vegetative growth and toward reproductive effort and success in the fourth treatment year suggests a shift from the initial response to a secondary response. The change in vegetative response may be due to depletion of stored plant reserves, whereas the lag in reproductive response may be due to the formation of flower buds one to several seasons prior to flowering. Both vegetative and reproductive responses varied among life-forms; herbaceous forms had stronger and more consistent vegetative growth responses than did woody forms. The greater responsiveness of the herbaceous forms may be attributed to their more flexible morphology and to their relatively greater proportion of stored plant reserves. Finally, warmer, low arctic sites produced the strongest growth responses, but colder sites produced a greater reproductive response. Greater resource investment in vegetative growth may be a conservative strategy in the Low Arctic, where there is more competition for light, nutrients, or water, and there may be little opportunity for successful germination or seedling development. In contrast, in the High Arctic, heavy investment in producing seed under a higher temperature scenario may provide an opportunity for species to colonize patches of unvegetated ground. The observed differential response to warming suggests that the primary forces driving the response vary across climatic zones, functional groups, and through time.
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- Carpenter, KG, et al.
(author)
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Hubble Space Telescope spectroscopy of the carbon star TX Piscium
- 1997
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In: ASTROPHYSICAL JOURNAL. - : UNIV CHICAGO PRESS. - 0004-637X. ; 486:1, s. 457-470
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Journal article (peer-reviewed)abstract
- Ultraviolet spectra obtained with the Hubble Space Telescope of the carbon star TX Piscium (HR 9004) are presented, along with analysis providing information on its outer atmosphere, including flow and turbulent velocities, line formation mechanisms, and
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| 7. |
- Eglitis, P, et al.
(author)
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New techniques for auroral irregularity studies with COSCAT
- 1998
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In: ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES. - : SPRINGER VERLAG. - 0992-7689. ; 16:10, s. 1241-1250
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Journal article (other academic/artistic)abstract
- The COSCAT system enables the detection of E-region auroral backscatter with the EISCAT remote receivers at magnetic aspect angles close to 90 degrees. This is achieved by utilising a low-power transmitter stationed in Oulu, Finland. Many important observ
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| 9. |
- Koratkar, A, et al.
(author)
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The disappearing broad absorption lines and variable emission lines in NGC 3516
- 1996
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In: ASTROPHYSICAL JOURNAL. - : UNIV CHICAGO PRESS. - 0004-637X. ; 470:1, s. 378-393
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Journal article (other academic/artistic)abstract
- The Seyfert 1 galaxy NGC 3516 was monitored during 1993 February 16-May 13 by IUE every 4 days for the first month, and then every 2 days for 2 months giving a total of 40 observations. This paper gives the initial results from this campaign, (1) The broa
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