| 1. |
- Crenshaw, D. M., et al.
(author)
-
Multiwavelength observations of short-timescale variability in NGC 4151. I. Ultraviolet observations
- 1996
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 322-335335
-
Journal article (peer-reviewed)abstract
- Presents the results of an intensive ultraviolet monitoring campaign on the Seyfert 1 galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously with the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra every ~70 minutes, and during 4 hr periods for 4 days prior to and 5 days after the continuous-monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy. The continuum fluxes in bands from 1275 to 2688 Aring went through four significant and well-defined ldquoeventsrdquo of duration 2-3 days during the continuous-monitoring period. The authors find that the amplitudes of the continuum variations decrease with increasing wavelength, which extends a general trend for this and other Seyfert galaxies to smaller timescales (i.e., a few days). The continuum variations in all the UV bands are simultaneous to within an accuracy of ~0.15 days, providing a strict constraint on continuum models. The emission-line light curves show only one major event during the continuous monitoring (a slow rise followed by a shallow dip) and do not correlate well with continuum light curves over the short duration of the campaign, because the timescale for continuum variations is apparently smaller than the response times of the emission lines
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| 2. |
- Dietrich, M., et al.
(author)
-
Monitoring of active galactic nuclei. IV. The Seyfert 1 galaxy NGC 4593
- 1994
-
In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 284:1, s. 33-4343
-
Journal article (peer-reviewed)abstract
- Results of a five-month campaign of optical monitoring the Seyfert 1 galaxy NGC 4593 are presented. High resolution Halpha and Hbeta spectra and direct images in the Johnson U, B, V, R and I bands were obtained between January and June 1990. The emission lines and the continuum showed strong variations on time scales of weeks to days. The Halpha line varied by more than 30% within only 5 days. Cross-correlating the light curves of the Balmer lines with that of the optical continuum gives a lag of around 4 days. Therefore, this low luminosity Seyfert galaxy may have one of the smallest broad line regions known so far
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| 3. |
- Edelson, R. A., et al.
(author)
-
Multiwavelength observations of short-timescale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability
- 1996
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 364-377377
-
Journal article (peer-reviewed)abstract
- For pt.III see ibid., vol.470, no.1, p.349-63 (1996). Combines data from the three preceding papers in order to analyze the multi wave-band variability and spectral energy distribution of the Seyfert 1 galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths. The strongest variations were seen in medium-energy (~1.5 keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA=6%) variations (uncorrelated with those at lower energies) were seen at soft gamma-ray energies of ~100 keV. No significant variability was seen in softer (0.1-1 keV) X-ray bands. In the ultraviolet/optical regime, the NVA decreased from 9% to 1% as the wavelength increased from 1275 to 6900 Aring. These data do not probe extreme ultraviolet (1200 Aring to 0.1 keV) or hard X-ray (250 keV) variability. The phase differences between variations in different bands were consistent with zero lag, with upper limits of lsim0.15 day between 1275 Aring and the other ultraviolet bands, lsim0.3 day between 1275 Aring and 1.5 keV, and lsim1 day between 1275 and 5125 Aring. These tight limits represent more than an order of magnitude improvement over those determined in previous multi-wave-band AGN monitoring campaigns. The ultraviolet fluctuation power spectra showed no evidence for periodicity, but were instead well fitted with a very steep, red power law (ales-2.5)
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| 4. |
- Salamanca, I., et al.
(author)
-
Spectroscopic monitoring of active galactic nuclei. III. Size of the broad line region in NGC 3227
- 1994
-
In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 282:3, s. 742-752752
-
Journal article (peer-reviewed)abstract
- For pt.II see ibid., vol.269, no.1-2, p.39-53 (1993). The authors present the results of a five-month monitoring campaign of the active galactic nucleus in NGC 3227. The Hbeta and Halpha emission lines and the optical continuum have been analysed. The optical AGN continuum and the broad-line region (BLR) emission in NGC 3227 appear to vary by about 40% on a timescale of 1.5 month. The levels of the broad-line emission and the 675.0 nm continuum are well correlated, a fact consistent with the assumption that the BLR material is photoionised by the central continuum source. Cross-correlation analyses between the light curves of the 675.0 nm AGN continuum and the BLR H emission indicate that the lag of the BLR emission with respect to the continuum variations is 17plusmn7 days. This result suggests that the BLR clouds that are affected by the changes in the flux of the central ionising source lie about 17 light days away from it
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| 5. |
- Wanders, I., et al.
(author)
-
Spectroscopic monitoring of active galactic nuclei. II. The Seyfert-1 galaxy NGC 3516
- 1993
-
In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 269:1-2, s. 39-5353
-
Journal article (peer-reviewed)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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| 6. |
- Koratkar, A, et al.
(author)
-
The disappearing broad absorption lines and variable emission lines in NGC 3516
- 1996
-
In: ASTROPHYSICAL JOURNAL. - : UNIV CHICAGO PRESS. - 0004-637X. ; 470:1, s. 378-393
-
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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| 7. |
- Blauhut, Veit, et al.
(author)
-
Lessons from the 2018-2019 European droughts : a collective need for unifying drought risk management
- 2022
-
In: Natural hazards and earth system sciences. - : Copernicus Publications. - 1561-8633 .- 1684-9981. ; 22:6, s. 2201-2217
-
Journal article (peer-reviewed)abstract
- Drought events and their impacts vary spatially and temporally due to diverse pedo-climatic and hydrologic conditions, as well as variations in exposure and vulnerability, such as demographics and response actions. While hazard severity and frequency of past drought events have been studied in detail, little is known about the effect of drought management strategies on the actual impacts and how the hazard is perceived by relevant stakeholders. In a continental study, we characterised and assessed the impacts and the perceptions of two recent drought events (2018 and 2019) in Europe and examined the relationship between management strategies and drought perception, hazard, and impact. The study was based on a pan-European survey involving national representatives from 28 countries and relevant stakeholders responding to a standard questionnaire. The survey focused on collecting information on stakeholders' perceptions of drought, impacts on water resources and beyond, water availability, and current drought management strategies on national and regional scales. The survey results were compared with the actual drought hazard information registered by the European Drought Observatory (EDO) for 2018 and 2019. The results highlighted high diversity in drought perception across different countries and in values of the implemented drought management strategies to alleviate impacts by increasing national and sub-national awareness and resilience. The study identifies an urgent need to further reduce drought impacts by constructing and implementing a European macro-level drought governance approach, such as a directive, which would strengthen national drought management and mitigate damage to human and natural assets.
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| 8. |
- Blauhut, Veit, et al.
(author)
-
Lessons from the 2018–2019 European droughts: A collective need for unifying drought risk management
- 2021
-
In: Natural hazards and earth system sciences. - : Copernicus Publications. - 1561-8633 .- 1684-9981.
-
Journal article (other academic/artistic)abstract
- Drought events and their impacts vary spatially and temporally due to diverse pedo-climatic and hydrologic conditions, as well as variations in exposure and vulnerability, such as demographics and response actions. While hazardous severity and frequency of past drought events have been studied in detail, little is known about the effect of drought management strategies on the actual impacts, and how the hazard is perceived by relevant stakeholders for inducing action. In a continental study, we characterised and assessed the impacts and the perceptions of two recent drought events (2018 and 2019) in Europe and examined the relationship between management strategies and drought perception, hazard and impacts. The study was based on a pan-European survey involving national representatives from 28 countries and relevant stakeholders responding to a standard questionnaire. The survey focused on collecting information on stakeholders’ perceptions of drought, impacts on water resources and beyond, water availability and current drought management strategies at national and regional scales. The survey results were compared with the actual drought hazard information registered by the European Drought Observatory (EDO) for 2018 and 2019. The results highlighted high diversity in drought perceptions across different countries and in values of implemented drought management strategies to alleviate impacts by increasing national and sub-national awareness and resilience. The study concludes with an urgent need to further reduce drought impacts by constructing and implementing a European macro-level drought governance approach, such as a directive, which would strengthen national drought management and lessen harm to human and natural potentials.
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| 9. |
- Ciray, I., et al.
(author)
-
Effect of granulocyte colony-stimulating factor (G-CSF)-supported chemotherapy on MR imaging of normal red bone marrow in breast cancer patients with focal bone metastases
- 2003
-
In: Acta Radiol. - 0284-1851 .- 1600-0455. ; 44:5, s. 472-84
-
Journal article (peer-reviewed)abstract
- PURPOSE: To investigate the effect of granulocyte colony-stimulating factor (G-CSF)-supported chemotherapy on normal red bone marrow MR imaging in breast cancer patients with focal bone metastases. MATERIAL AND METHODS: Fifteen breast cancer patients who were examined before and after chemotherapy with T1-weighted-SE and long echo-time inversion-recovery turbo-spin-echo (long TE IR-TSE) sequences in the thoracolumbar spine and pelvis were retrospectively studied. Nine of them received G-CSF therapy after the administration of each chemotherapy course. Of these 9 patients, the MR follow-ups were performed during G-CSF in 4 patients and after G-CSF therapy in 5 patients. Six patients did not receive G-CSF. Signal intensity (SI) changes in normal bone marrow were evaluated visually in all patients and quantitatively in 13 patients. RESULTS: In all 4 patients investigated during G-CSF therapy a diffuse, homogeneous SI increase on long TE IR-TSE was observed visually and quantitatively in initially normal bone marrow. This change obscured some focal lesions in 2 patients. No such SI change was visible after G-CSF therapy (p = 0.008) or in patients not receiving G-CSF. On T1-weighted images an SI decrease was found both during and after G-CSF therapy, but an increase occurred in patients not receiving G-CSF. CONCLUSION: G-CSF-supported chemotherapy can induce diffuse SI changes in normal red bone marrow on MR imaging. On long TE IR-TSE, the changes are visible during G-CSF treatment and can lead to misinterpretations in the response evaluation of bone metastases to therapy.
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| 10. |
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| 11. |
- Dreilich, M., et al.
(author)
-
High-risk human papilloma virus (HPV) and survival in patients with esophageal carcinoma : a pilot study
- 2006
-
In: BMC Cancer. - : Springer Science and Business Media LLC. - 1471-2407. ; 6, s. 94-
-
Journal article (peer-reviewed)abstract
- BACKGROUND: Human papilloma virus (HPV) in patients with esophageal carcinoma has previously been studied with an average detection rate of 15%, but the role of HPV in relation to survival is less clear. In cervical cancer, lung cancer and tonsil cancer HPV viral load is a predictive factor for survival and outcome of treatment. The primary aim was to study the spectrum of high-risk HPV types in esophageal tumors. Secondary, as a pilot study we investigated the association between HPV status and the survival rates. METHODS: We compared both the presence and the viral load of high-risk HPV types 16, 18, 31, 33, 39, 45, 52, 58, and 67 in relation to clinical data from patients with esophageal carcinoma. Survival data and tumor samples were retrieved from 100 patients receiving treatment at the Department of Oncology, Uppsala Hospital, Uppsala, Sweden. The tumor samples were investigated for HPV viral load using real-time PCR. RESULTS: HPV 16 was detected in 16% of the patients; no other HPV type was detected. HPV 16 infection had no significant effect on survival (p = 0.72). Also, HPV 16 did not improve survival after treatment (radiotherapy or chemotherapy). CONCLUSION: Only HPV 16 was detected among the patients. HPV 16 in esophageal carcinoma patients did not influence survival or improve therapy response. However, given the size of the study there is a need to examine a larger cohort in order to understand in more detail the effect of high risk HPV types in esophageal carcinoma.
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| 12. |
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| 13. |
- Malmström, Per-Uno, et al.
(author)
-
AdCD40L immunogene therapy for bladder carcinoma--the first phase I/IIa trial
- 2010
-
In: Clinical Cancer Research. - : American Association for Cancer Research. - 1078-0432 .- 1557-3265. ; 16:12, s. 3279-3287
-
Journal article (peer-reviewed)abstract
- PURPOSE: Immunotherapy with Bacillus Calmette-Guerin (BCG) instillation is recommended for high-risk, non-muscle invasive bladder cancer. Bacillus Calmette-Guerin is not effective in advanced tumors, and better alternatives are warranted. Immunostimulating gene therapy with adenoviral vectors expressing CD40 ligand (AdCD40L) has shown efficacy in tumor models. CD40 ligand stimulates systemic immunity and may be effective in local and invasive human disease.EXPERIMENTAL DESIGN: Patients with invasive bladder cancer scheduled for cystectomy or patients with T(a) tumors were enrolled in a phase I/IIa trial. Patients were treated with three cycles of intrabladder Clorpactin WCS-90 prewash, followed by AdCD40L instillation 1 week apart. Safety, gene transfer, immune effects, and antitumor responses were monitored.RESULTS: All eight recruited patients were treated as scheduled, and therapy was well tolerated. The main adverse effect was transient local pain during prewash. Postoperatively, urinary tract infections and one case of late septicemia with elevated potassium were reported. No adverse events were ascribed to vector therapy. Gene transfer was detected in biopsies, and bladders were heavily infiltrated with T cells. The effector marker IFN-gamma increased in biopsies, whereas levels of circulating T regulatory cells were reduced. Histologic evaluation indicated that AdCD40L therapy reduced the load of malignant cells.CONCLUSIONS: To our knowledge, this is the first report on immunogene therapy in bladder cancer and the first using AdCD40L in vivo. Local AdCD40L gene therapy was safe, boosted immune activation, and should be further evaluated as a single or an adjuvant therapy for urothelial malignancies.
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| 14. |
- Perry, J. J., et al.
(author)
-
Hysteresis in broad-line regions of active galactic nuclei
- 1994
-
In: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 271:3, s. 561-572572
-
Journal article (peer-reviewed)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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| 15. |
- Ronnback, J., et al.
(author)
-
Host galaxies of intermediate redshift radio-loud and radio-quiet quasars
- 1996
-
In: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 283:1, s. 282-296296
-
Journal article (peer-reviewed)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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| 16. |
- van Groningen, E., et al.
(author)
-
An algorithm for the relative scaling of spectra
- 1992
-
In: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 104:678, s. 700-703703
-
Journal article (peer-reviewed)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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| 17. |
- van Kuilenburg, Andre B. P., et al.
(author)
-
Glutaminase Deficiency Caused by Short Tandem Repeat Expansion in GLS
- 2019
-
In: New England Journal of Medicine. - 0028-4793 .- 1533-4406. ; 380:15, s. 1433-1441
-
Journal article (peer-reviewed)abstract
- We report an inborn error of metabolism caused by an expansion of a GCA-repeat tract in the 5′ untranslated region of the gene encoding glutaminase (GLS) that was identified through detailed clinical and biochemical phenotyping, combined with whole-genome sequencing. The expansion was observed in three unrelated patients who presented with an early-onset delay in overall development, progressive ataxia, and elevated levels of glutamine. In addition to ataxia, one patient also showed cerebellar atrophy. The expansion was associated with a relative deficiency of GLS messenger RNA transcribed from the expanded allele, which probably resulted from repeat-mediated chromatin changes upstream of the GLS repeat. Our discovery underscores the importance of careful examination of regions of the genome that are typically excluded from or poorly captured by exome sequencing.
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| 18. |
- Van Loon, Anne F., et al.
(author)
-
Drought in a human-modified world : reframing drought definitions, understanding, and analysis approaches
- 2016
-
In: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 20:9, s. 3631-3650
-
Journal article (peer-reviewed)abstract
- In the current human-modified world, or Anthropocene, the state of water stores and fluxes has become dependent on human as well as natural processes. Water deficits (or droughts) are the result of a complex interaction between meteorological anomalies, land surface processes, and human inflows, outflows, and storage changes. Our current inability to adequately analyse and manage drought in many places points to gaps in our understanding and to inadequate data and tools. The Anthropocene requires a new framework for drought definitions and research. Drought definitions need to be revisited to explicitly include human processes driving and modifying soil moisture drought and hydrological drought development. We give recommendations for robust drought definitions to clarify timescales of drought and prevent confusion with related terms such as water scarcity and overexploitation. Additionally, our understanding and analysis of drought need to move from single driver to multiple drivers and from uni-directional to multi-directional. We identify research gaps and propose analysis approaches on (1) drivers, (2) modifiers, (3) impacts, (4) feedbacks, and (5) changing the baseline of drought in the Anthropocene. The most pressing research questions are related to the attribution of drought to its causes, to linking drought impacts to drought characteristics, and to societal adaptation and responses to drought. Example questions include (i) What are the dominant drivers of drought in different parts of the world? (ii) How do human modifications of drought enhance or alleviate drought severity? (iii) How do impacts of drought depend on the physical characteristics of drought vs. the vulnerability of people or the environment? (iv) To what extent are physical and human drought processes coupled, and can feedback loops be identified and altered to lessen or mitigate drought? (v) How should we adapt our drought analysis to accommodate changes in the normal situation (i.e. what are considered normal or reference conditions) over time? Answering these questions requires exploration of qualitative and quantitative data as well as mixed modelling approaches. The challenges related to drought research and management in the Anthropocene are not unique to drought, but do require urgent attention. We give recommendations drawn from the fields of flood research, ecology, water management, and water resources studies. The framework presented here provides a holistic view on drought in the Anthropocene, which will help improve management strategies for mitigating the severity and reducing the impacts of droughts in future.
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| 19. |
- Wanders, A., et al.
(author)
-
Nonsteroidal antiinflammatory drugs reduce radiographic progression in patients with ankylosing spondylitis : a randomized clinical trial
- 2005
-
In: Arthritis Rheum. ; 52:6, s. 1756-65
-
Journal article (peer-reviewed)abstract
- OBJECTIVE: A 2-year randomized controlled trial was performed to test the hypothesis that long-term, continuous treatment with nonsteroidal antiinflammatory drugs (NSAIDs), in comparison with NSAID treatment on demand only, influences radiographic progression in patients with ankylosing spondylitis (AS). METHODS: Patients with AS (n = 215), who had previously participated in a 6-week, randomized, double-blind clinical trial that compared celecoxib, ketoprofen, and placebo, were randomly allocated to receive either continuous treatment with NSAIDs or on-demand treatment with NSAIDs for a period of 2 years. All patients began treatment with celecoxib, at a starting dosage of 100 mg twice daily; patients could increase this dosage to 200 mg twice daily or could switch to another NSAID while maintaining the same treatment strategy. Structural changes were assessed by radiographs of the lumbar and cervical spine and scored according to the modified Stoke Ankylosing Spondylitis Spine Score by one observer who was blinded to the treatment strategy and temporal order of the radiographs. Statistical analyses included a between-group comparison of 1) radiographic progression scores (by Mann-Whitney U test), 2) time-averaged values of variables reflecting signs and symptoms of AS (by linear regression analysis), and 3) the frequency of reported site-specific adverse events (by chi-square test or Fisher's exact test, as appropriate). RESULTS: Complete sets of radiographs were available for 76 of the 111 patients in the continuous-treatment group and for 74 of the 104 patients in the on-demand group. The mean +/- SD scores for radiographic progression were 0.4 +/- 1.7 in the continuous-treatment group and 1.5 +/- 2.5 in the on-demand treatment group (P = 0.002). Parameters reflecting signs and symptoms were not statistically significantly different between groups. The between-group difference in radiographic progression did not disappear after adjusting for baseline values of radiographic damage or disease activity variables and for time-averaged values of disease activity variables, nor after input of missing data. Relevant adverse events tended to occur more frequently in the continuous-treatment group than in the on-demand group (for hypertension, 9% versus 3%; for abdominal pain, 11% versus 6%; for dyspepsia, 41% versus 38%), but the differences were not statistically significant. CONCLUSION: A strategy of continuous use of NSAIDs reduces radiographic progression in symptomatic patients with AS, without increasing toxicity substantially.
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| 20. |
- WANDERS, I
(author)
-
EVOLUTION OF THE BROAD-LINE REGION IN NGC-5548
- 1995
-
In: ASTRONOMY AND ASTROPHYSICS. - : SPRINGER VERLAG. - 0004-6361. ; 296:2, s. 332-338
-
Journal article (other academic/artistic)abstract
- In this paper I show that the broad-line region (BLR) of the Seyfert-1 galaxy NGC 5548 is an evolving entity on its dynamical time scale of a few years. The total observed H beta reprocessing of the BLR decreased by about 5% per year during four consecuti
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| 21. |
- Wanders, I., et al.
(author)
-
Seeing and aperture effects on [O III]-based flux calibration of AGN spectra. NGC 3516 : a case study
- 1992
-
In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 266:1, s. 72-7676
-
Journal article (peer-reviewed)abstract
- In variability studies of the broad emission lines in the spectra of active galactic nuclei, the narrow emission lines are generally used to flux calibrate spectra taken at different epochs to each other. In objects where the narrow-line region is resolved, seeing affects the ratio of narrow-line flux to broad-line and continuum flux entering the aperture since the broad-line region and the continuum source are unresolved. Thus observing under different seeing conditions introduces artificial correlated variations of the continuum and broad-line fluxes if one assumes the narrow lines to be constant in flux. The authors show that one can correct for this effect by simulating seeing variations using a narrow-band [O III] image, taken in good seeing conditions, of the nearby Seyfert 1 galaxy NGC 3516, in which the narrow-line region is clearly resolved and extends over more than 20". They also show that centring the aperture on the object consistently is very important and miscentring is also a source of artificial variability of the broad-line and continuum fluxes
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