A. M. Varela

Optical surface photometry of a sample of disk galaxies. II structural components

This work presents the structural decomposition of a sample of 11 disk galaxies, which span a range of different morphological types. The U, B, V, R, and I photometric information given in Paper I (color and color-index images and luminosity, ellipticity, and position-angle profiles) has been used to decide what types of components form the galaxies before carrying out the decomposition. We find and model such components as bulges, disks, bars, lenses and rings.

European Extremely Large Telescope Site Characterization I: Overview

ABSTRACT.The site for the future European Extremely Large Telescope (E-ELT) is already known to be Armazones, near Paranal (Chile). The selection was based on a variety of considerations, with an important one being the quality of the atmosphere for the astronomy planned for the ELT. We present an overview of the characterization of the atmospheric parameters of candidate sites, making use of standard procedures and instruments as carried out within the Framework Programme VI (FP6) of the European Union. We have achieved full characterization of the selected sites for the parameters considered. Further details on adaptive optics results and climatology will be the subject of two forthcoming articles. A summary of the results of the FP6 site-testing campaigns at the different sites is provided.

Astronomical site selection: On the use of satellite data for aerosol content monitoring

The main goal of this work is to analyse new approaches to the study of the properties of astronomical sites. In particular, satellite data measuring aerosols have recently been proposed as a useful technique for site characterization and searching for new sites to host future very large telescopes. Nevertheless, these data need to be critically considered and interpreted in accordance with the spatial resolution and spectroscopic channels used. In this paper, we have explored and retrieved measurements from satellites with high spatial and temporal resolutions and concentrated on channels of astronomical interest. The selected data sets are the Ozone Monitoring Instrument on board the NASA Aura satellite and the Moderate Resolution Imaging Spectroradiometer on board the NASA Terra and Aqua satellites. A comparison of remote-sensing and in situ techniques is discussed. As a result, we find that aerosol data provided by satellites up to now are not reliable enough for aerosol site characterization, and in situ data are required.

Atmosphere Extinction at the ORM on La Palma: A 20 yr Statistical Database Gathered at the Carlsberg Meridian Telescope

The Observatorio del Roque de los Muchachos (ORM), in the Canary Islands (Spain), was one of the candidates to host the future European Extremely Large Telescope (E-ELT) and is the site of the Gran Telescopio Canarias (GTC), the largest optical infrared facility to date. Sky transparency is a key parameter as it defines the quality of the photometry to be acquired in the astronomical observations. We present a study of the atmosphere extinction at the ORM, carried out after analysis of a database spanning more than 20 yr, 1 to our knowledge, the longest and most complete and homogeneous in situ database available for any observatory. It is based on photometric measurements in the V band and r 0 band (transformed to the V-band extinction coefficient kV) using the Carlsberg Meridian Telescope (CMT). Clear seasonal variations that repeat yearly are observed. The median value of kV is 0:13 mag airmass � 1 ; the mean value has a maximum in the summer months (June- September), corresponding to the season with maximum frequency of nights affected by dust or cirrus (∼29% in summer, but only ∼13% during the rest of the year). Two volcanic eruptions took place during the database baseline, which has enabled the study of the impact of volcanoes on the global atmosphere extinction. For the 5 yr of available information, we have estimated the average monthly weather downtime from the CMT data log, obtaining a result (20.7%) in reasonable agreement with earlier studies. The main conclusion of our study is that there is no significant evidence from the CMT data for any secular changes in kV over the 20 yr database baseline.

An hydrodynamical model of the barred galaxy NGC 5850

We present the results of hydrodynamical model calculations of the barred galaxy NGC 5850 and compare to HI observations. The models assume a mass distribution for the galaxy which was obtained from photometrical I band observations. A pure bar perturbation model reproduces the HI observations in the inner 80 00 of the galaxy. The reproduced morphological features are: the central gas concentration, the hole of gas in the bar region and the ring of HI located at the end of the bar. The spiral arms are not reproduced. The best model has the co-rotation located at 90 00 and the mass of the bulge, bar, disk and halo are respectively: 4:7 10 9 M, 4:6 10 9 M ,4 :9 10 10 M and 6:93 10 10 M.

Optical Surface Photometry of a Sample of Disk Galaxies. I. Observations and Data Reduction

We present accurate optical surface photometry in the U, B, V, R, and I passbands for 11 disk galaxies. The sample has been selected in order to study the different morphological structures present in disk galaxies and includes all morphological types. For each galaxy, we present surface brightness, ellipticity, and position angle radial profiles from ellipse fits to the isophotes. Color index images and color index profiles in U-B, B-V, and B-I are also shown. The photometric information obtained is crucial to understanding the different morphological structures presented in all these galaxies, and to obtain their mass distributions. The latter topic will be the subject of a forthcoming paper.

Homogeneity of image quality at the Roque de los Muchachos Observatory

Abstract Seeing statistics from several year-long site-testing campaigns carried out at different locations at the Roque de los Muchachos Observatory (ORM) are reviewed (this contribution contains results previously published by Munoz-Tunon et al. (1997) [Estudio de Sitio para el Gran Telescopio: Informe final; A&AS, 125, 183]). In particular, tests at the TNG, WHT, GTC1 and GTC2 sites are discussed. Routine measurements were taken with cross-calibrated differential image motion monitors. The values obtained for the two sites proposed for the Gran Telescopio de Canarias show excellent and similar results, with mean and median seeing values of 0.72 arcsec and 0.65 arcsec, consistent with those obtained in earlier campaigns at the ORM. Under typical seeing conditions, image quality does not depend on the particular location and shows a high degree of homogeneity over the whole Observatory. Differences may be more evident, up to 0.2 arcsec, for seeing poorer than 1.5 arcsec, which happens in less than 5% of cases. Seeing better than 1′′ occurs in about 80% of cases with an average of 25% meeting half-arcsecond conditions. This percentage can rise consistently to more than 50% in the best months at all the locations tested. A dependence of seeing with the season of the year is definitively established with the best values during the summer period, which is found to be correlated with the height and thickness of the inversion layer. From the analysis of surface-layer meteorological data taken simultaneously at two of the sites a possible relationship is found between the wind properties (direction and speed) and seeing behaviour. Other meteorological parameters do not seem to play any significant role as far as image quality is concerned.

European Extremely Large Telescope Site Characterization. II. High Angular Resolution Parameters

ABSTRACT.This is the second article of a series devoted to European Extremely Large Telescope (E-ELT) site characterization. In this article we present the main properties of the parameters involved in high angular resolution observations from the data collected in the site testing campaign of the E-ELT during the design study (DS) phase. Observations were made in 2008 and 2009, in the four sites selected to shelter the future E-ELT (characterized under the ELT-DS contract): Aklim mountain in Morocco, Observatorio del Roque de los Muchachos (ORM) in Spain, Macon range in Argentina, and Cerro Ventarrones in Chile. The same techniques, instruments, and acquisition procedures were taken on each site. A multiple aperture scintillation sensor (MASS) and a differential image motion monitor (DIMM) were installed at each site. Global statistics of the integrated seeing, the free atmosphere seeing, the boundary layer seeing, and the isoplanatic angle were studied for each site, and the results are presented here. ...

Bright stars and recent star formation in the irregular magellanic galaxy NGC 2366

This is an electronic version of an article published in The Astronomical Journal. Aparicio, A. et al. Bright stars and recent star formation in the irregular magellanic galaxy NGC 2366. The Astronomical Journal 110.1 (1995): 212-222

Non-correlation between atmospheric extinction coefficient and TOMS aerosol index at the Canarian Observatories

Satellite data measuring aerosols over the Canary Islands need to be correctly interpreted in accordance with the spatial resolution and spectroscopic channels used. In situ data are still a necessary reference for calibrating and interpreting the aerosol index provided by different spectrometers onboard satellites. A comparison of both techniques (in situ and remote) is discussed in this paper, showing there is no linear correlation between the aerosol index and the extinction coefficient. Here, we present an interpretation of different situations arising and discuss critically the correct interpretation of the aerosol index and images provided by the TOMS in accordance with the dust presence over the Observatories. The aerosol index measured at sectors centered at both Observatories (Observatorio del Roque de los Muchachos -ORM-, on La Palma and Observatorio del Teide -OT-, on Tenerife) is also compared.