1,721,034 research outputs found
Long-term analysis of clear sky at astronomical sites: A comparison between polar and geostationary satellites
No full textThe astroclimatological comparison of the Paranal Observatory and El Roque de Los Muchachos Observatory
No full textThe new extremely large telescope projects need accurate evaluation of the candidate sites. In this paper, we present the astroclimatological comparison between the Paranal Observatory, located on the coast of the Atacama Desert (Chile), and the Observatorio del Roque de Los Muchachos (ORM), located in La Palma (Canary Islands). We apply a statistical analysis using long-term data bases from Paranal and Carlsberg Automatic Meridian Circle (CAMC) weather stations. The monthly, seasonal and annual averages of the main synoptical parameters in the two sites are computed. We compare the long-term trends in order to understand the main differences between the two sites. Significant differences between the two analysed sites have been found. Temperature has increasing trends in both observatories with somewhat higher evidence at the ORM. Seasonal variations of pressure at Paranal have been highly decreasing since 1989, and we do not see the same phenomenon at the ORM. The two sites are dominated by high pressure. In cold seasons, relative humidity (RH) is lower than 60 per cent at CAMC and 15 per cent at Paranal. In warm seasons, RH is lower than 40 per cent at CAMC and 20 per cent at Paranal. The analysis of the dew point has shown better conditions at Paranal with respect to CAMC in winter, autumn and spring before 2001, while the two sites are becoming similar afterwards. Winds at the ORM are subject to pronounced local variations
Spectroscopical confirmation of variability-selected active galactic nuclei
No full textThe cosmological evolution of active galactic nuclei (AGN) luminosity function is poorly known at the faint end, since active nuclei fainter than their host galaxies cannot be selected by color techniques. A sample of low luminosity AGN candidates has been selected on the basis of their variability. We carried out spectroscopic observations with the WYFFOS multi-fiber facility at the 4.2 m William Herschel Telescope. Preliminary results are presented, indicating the validity of the selection technique
Line and continuum variability of two intermediate-redshift, high-luminosity quasars
No full textContext. It has been shown that the luminosity of active galactic nuclei and the size of their broad line region obey a simple relation of the type R-BLR = aL(gamma), from faint Seyfert nuclei to bright quasars, allowing single-epoch determination of the central black hole mass M-BH = bL(gamma) Delta(2) H-beta from their luminosity L and width of H-beta emission line. Adopting this mass determination for cosmological studies requires the extrapolation to high redshift and luminosity of a relation whose calibration relies so far on reverberation mapping measurements performed for L less than or similar to 1046 erg s(-1) and redshift z less than or similar to 0.4. Aims. We initiated a campaign for the spectrophotometric monitoring of a few luminous, intermediate redshift quasars whose apparent magnitude, V < 15.7, allows observations with a 1.8 m telescope, aimed at proving that emission lines vary and respond to continuum variations even for luminosities less than or similar to 1047 erg s(-1), and determining eventually their MBH from reverberation mapping. Methods. We have repeatedly performed simultaneous spectrophotometric observations of quasars and reference stars to determine relative variability of continuum and emission lines. We describe the observations and methods of analysis. Results. For the quasars PG 1634+ 706 and PG 1247+ 268 we obtain light-curves respectively for CIII](lambda lambda 1909 angstrom), MgII(lambda lambda 2798 angstrom) and for CIV(lambda lambda 1549 angstrom), CIII](lambda lambda 1909 angstrom) emission lines with the relevant continua. During 3.2 years of observation, in the former case no continuum variability was detected and the evidence for line variability is marginal, while in the latter case both continuum and line variability are detected with high significance and the line variations appear correlated with continuum variations. Conclusions. The detection of the emission line variability in a quasar with L similar to 10(47) erg s(-1) encourages the continuation of the monitoring campaign which should provide a black hole mass estimate in another 5-6 years, constraining the mass-luminosity relation in a poorly explored range of luminosity
Continuum and emission-line variability of high-luminosity quasars
No full textWe report about our ongoing echo-mapping campaign of PG 1634+706 and PG 1247+268. While no significant variability is detected for the the former, we find both continuum and line variability for PG 1247+267
A New Echo-Mapping Campaign at Intermediate Redshift
No full textEdited by C. Martin Gaskell, Ian M. McHardy, Bradley M. Peterson and Sergey G. Sergee
Continuum and Emission-line Variability of High-luminosity Quasars
No full textEdited by Luis C. Ho and Jian-Min Wan
Detection of a 14-d atmospheric perturbation peak at Paranal associated with lunar cycles
No full textIn this paper we investigate the correlation between the atmospheric perturbations at Paranal Observatory and the Chilean coast tides, which are mostly modulated by the 14-d syzygy solar-lunar tidal cycle. To this aim, we downloaded 15 yr (2003-2017) of cloud coverage data from the Aqua satellite, in a matrix that includes also Armazones, the site of the European Extremely Large Telescope. By applying the Fast Fourier transform to these data we detected a periodicity peak of about 14 d. We studied the tide cycle at Chanaral De Las Animas, on the ocean coast, for the year 2017, and we correlated it with the atmospheric perturbations at Paranal and the lunar phases. We found a significant correlation (96{{per cent}}) between the phenomena of short duration and intensity (1-3 d) and the tidal cycle at Chanaral. We then show that an atmospheric perturbation occurs at Paranal in concomitance with the low tide, which anticipates the full (or the new) moon by 3-4 d. This result allows to improve current weather forecasting models for astronomical observatories by introducing a lunar variable
Analysis of the fraction of clear sky at the La Palma and Mt Graham sites
No full textThe amount of available telescope time is one of the most important requirements when selecting astronomical sites, as it affects the performance of ground-based telescopes. We present a quantitative survey of cloud coverage at La Palma and Mt Graham using both ground- and satellite-based data. The aim of this work is to derive clear nights for the satellite infrared channels and to verify the results using ground-based observations. At La Palma, we found a mean percentage of clear nights of 62.6 per cent from ground-based data and 71.9 per cent from satellite-based data. Taking into account the fraction of common nights, we found a concordance of 80.7 per cent of clear nights for ground- and satellite-based data. At Mt Graham, we found a 97 per cent agreement between the Columbine heliograph and the night-time observing log. From the Columbine heliograph and the Total Ozone Mapping Spectrometer-Ozone Monitoring Instrument (TOMS-OMI) satellite, we found that about 45 per cent of nights were clear, while satellite data (GOES, TOMS) are much more dispersed than those of La Palma. Setting a statistical threshold, we retried a comparable seasonal trend between the heliograph and satellite
Nuclear activity in galaxy pairs: a spectroscopic analysis of 48 UZC-BGPs
No full textContext: The role played by interaction on galaxy formation and evolution continues to be debated. Several questions remain open, among them whether, and to what extent, galaxy interaction induce nuclear activity, as theoretical predictions, so far, have not been adequately supported by observations. Part of the uncertainty affecting the observational results is likely to be due to the limited sizes and the inhomogeneity of the samples. Aims: Galaxy pairs are ideal sites in which to investigate the role of interaction on nuclear activity, since the proximity, in redshift and in projected separation, between members make interaction and encounters highly probable. For this reason we have undertaken a spectroscopic survey of a large homogeneous sample of galaxy pairs (UZC-BGP) selected applying an objective neighbour search algorithm to a 3D galaxy catalog (UZC). Methods: We present the results of the nuclear spectral classification, performed using standard diagnostic diagrams, of 48 UZC-BGPs, which represents more than half of the whole sample and has an excellent morphological match with it. Results: The fraction of emission line galaxies in our pair sample is large, especially among spirals where it reaches 84% and 95%, for early and late spirals. Star Burst (SB) is the most frequent type of nuclear activity encountered (30% of galaxies), while AGNs (Active Galactic Nuclei) make only 19%. The fractions increase to 45% and 22% when considering only spirals. Late spirals are characterized by both an unusual increase (35%) of AGN activity and high luminosity (44% have MB < -20.0 + 5 log h). LLAGNs (Low Luminosity AGNs) are only 8% of the total number of galaxies, but this kind of activity could be present in another 10% of the galaxies (LLAGN candidates). If confirmed, these candidates would make LLAGNs constitute a significant fraction of the whole AGN (LLAGN + AGN) population, and raise the AGN population as a whole to 37%. Absorption line galaxies reside mostly (61%) in S0 galaxies and display the lowest B luminosity in the sample; only 18% of them have MB < -20 + 5 log h, but together with LLAGNs (candidates included) they are the most massive galaxies in the sample. Intense-SB nuclei are found in galaxy pairs with galaxy-galaxy projected separation of up to 160 h-1 kpc suggesting that in bright isolated galaxy pairs interaction may be at work and effective up to that distance. Conclusions: AGNs are characterized by an advanced morphological type while the SB phenomenon occurs with the same frequency in early and late spirals. Whether and how these unusual characteristics relate to the pair environment needs to be further investigated. LLAGNs and LLAGN candidates do not always show similar properties; the former are more luminous in B, richer in early-type (E-S0s) galaxies, and half of them are hosted in galaxies showing visible signs of interaction with fainter companions. This last finding suggests that minor interactions might be a driving mechanism for a fraction of LLAGNs. The differences between LLAGNs and LLAGN candidates might confirm the heterogeneous nature of this class of objects
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