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In this paper we present a study on the difficulties secondary school students experience in interpreting textbook images of elementary astronomical phenomena, namely, the changing of the seasons, Sun and lunar eclipses and Moon phases. Six images from a commonly used textbook in Italian secondary schools were selected. Interviews of 45?min about the astronomical concepts related to the images were carried out with eighteen students attending the last year of secondary school (aged 17?18). Students? responses were analyzed through a semiotic framework based on the different types of visual representation structures. We found that the wide range of difficulties shown by students come from na?ve or alternative ideas due to incorrect or inadequate geometric models of the addressed phenomena. As a primary implication of this study, we suggest that teachers should pay attention to specific iconic features of the discussed images, e.g., the compositional structure and the presence of real/symbolic elements.

The morphology of clusters of galaxies may be described with a set of parameters which contain information about the formation and evolutionary history of these systems. In this paper we present a preliminary study of the morphological parameters of a sample of 28 compact Abell clusters extracted from DPOSS data. The morphology of galaxy clusters is parameterized by their apparent ellipticity, position angle of the major axis, centre coordinates, core radius and beta-model power law index. Our procedure provides estimates of these parameters by simultaneously fitting them all, overcoming some of the difficulties induced by sparse data and low number statistics typical of this kind of analysis. The cluster parameters were fitted in a 3 x 3 h^-2 sqMpc region, measuring the background in a 2, Comment: 23 pages, 17 figures, accepted for publication in MNRAS. Full paper including full resolution figures 2 and 9 at http://www.eso.org/~vstrazzu/P/ME1030fv.pdf

The science education literature shows that students have difficulty understanding what causes the seasons. Incorrect explanations are often due to a lack of knowledge about the physical mechanisms underlying this phenomenon. To address this, we present a module in which the students engage in quantitative measurements with a photovoltaic panel to explain changes to the sunray flow on Earth’s surface over the year. The activities also provide examples of energy transfers between the incoming radiation and the environment to introduce basic features of Earth’s climate. The module was evaluated with 45 secondary school students (aged 17–18) and a pre-/post-test research design. Analysis of students’ learning outcomes supports the effectiveness of the proposed activities.

The Kilo-Degree Survey (KiDS) is an optical wide-field imaging survey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS will image 1500 square degrees in four filters (ugri), and together with its near-infrared counterpart VIKING will produce deep photometry in nine bands. Designed for weak lensing shape and photometric redshift measurements, the core science driver of the survey is mapping the large-scale matter distribution in the Universe back to a redshift of ~0.5. Secondary science cases are manifold, covering topics such as galaxy evolution, Milky Way structure, and the detection of high-redshift clusters and quasars. KiDS is an ESO Public Survey and dedicated to serving the astronomical community with high-quality data products derived from the survey data, as well as with calibration data. Public data releases will be made on a yearly basis, the first two of which are presented here. For a total of 148 survey tiles (~160 sq.deg.) astrometrically and photometrically calibrated, coadded ugri images have been released, accompanied by weight maps, masks, source lists, and a multi-band source catalog. A dedicated pipeline and data management system based on the Astro-WISE software system, combined with newly developed masking and source classification software, is used for the data production of the data products described here. The achieved data quality and early science projects based on the data products in the first two data releases are reviewed in order to validate the survey data. Early scientific results include the detection of nine high-z QSOs, fifteen candidate strong gravitational lenses, high-quality photometric redshifts and galaxy structural parameters for hundreds of thousands of galaxies. (Abridged), Comment: 26 pages, 26 figures, 2 appendices; two new figures, several textual clarifications, updated references; accepted for publication in A&A

The abundance of compact, massive, early-type galaxies (ETGs) provides important constraints to galaxy formation scenarios. Thanks to the area covered, depth, excellent spatial resolution and seeing, the ESO Public optical Kilo Degree Survey (KiDS), carried out with the VLT Survey Telescope (VST), offers a unique opportunity to conduct a complete census of the most compact galaxies in the Universe. This paper presents a first census of such systems from the first 156 square degrees of KiDS. Our analysis relies on g-, r-, and i-band effective radii ($R_{\rm e}$), derived by fitting galaxy images with PSF-convolved S��rsic models, high-quality photometric redshifts, $z_{\rm phot}$, estimated from machine learning techniques, and stellar masses, $M_{\rm \star}$, calculated from KiDS aperture photometry. After massiveness ($M_{\rm \star} > 8 \times 10^{10}\, \rm M_{\odot}$) and compactness ($R_{\rm e} < 1.5 \, \rm kpc$ in g-, r- and i-bands) criteria are applied, a visual inspection of the candidates plus near-infrared photometry from VIKING-DR1 are used to refine our sample. The final catalog, to be spectroscopically confirmed, consists of 92 systems in the redshift range $z \sim 0.2-0.7$. This sample, which we expect to increase by a factor of ten over the total survey area, represents the first attempt to select massive super-compact ETGs (MSCGs) in KiDS. We investigate the impact of redshift systematics in the selection, finding that this seems to be a major source of contamination in our sample. A preliminary analysis shows that MSCGs exhibit negative internal colour gradients, consistent with a passive evolution of these systems. We find that the number density of MSCGs is only mildly consistent with predictions from simulations at $z>0.2$, while no such system is found at $z < 0.2$., 11 pages, 6 figures, MNRAS in press, revised and improved version, figures and text have been updated

By means of CCD photometry in three bands (Gunn g, r, i) we investigate the existence of 12 candidate clusters extracted via a model independent peak finding algorithm (\cite{memsait}) from DPOSS data. The derived color-magnitude diagrams allow us to confirm the physical nature of 9 of the cluster candidates, and to estimate their photometric redshifts. Of the other candidates, one is a fortuitous detection of a true cluster at z~0.4, one is a false detection and the last is undecidable on the basis of the available data. The accuracy of the photometric redshifts is tested on an additional sample of 8 clusters with known spectroscopic redshifts. Photometric redshifts turn out to be accurate within z~0.01 (interquartile range)., A&A in press

The composite galaxy luminosity function (hereafter LF) of 39 Abell clusters of galaxies is derived by computing the statistical excess of galaxy counts in the cluster direction with respect to control fields. Due to the wide field coverage of the digitised POSS-II plates, we can measure field counts around each cluster in a fully homogeneous way. Furthermore, the availability of virtually unlimited sky coverage allows us to directly compute the LF errors without having to rely on the estimated variance of the background. The wide field coverage also allows us to derive the LF of the whole cluster, including galaxies located in the cluster outskirts. The global composite LF has a slope alpha ~ -1.1+/-0.2 with minor variations from blue to red filters, and M* ~ -21.7,-22.2,-22.4 mag (H_0=50 km/s/Mpc) in g, r and i filters, respectively. These results are in quite good agreement with several previous determinations and in particular with the LF determined for the inner region of a largely overlapping set of clusters, but derived making use of a completely different method for background subtraction. The similarity of the two LFs suggests the existence of minor differences between the LF in the cluster outskirts and in the central region, or a negligible contribution of galaxies in the cluster outskirts to the global LF., 15 pages, 14 figures, 4 tables; uses subfigure.sty; accepted for publication in Astronomy and Astrophysics

The multiplicity function (MF) of groups and clusters of galaxies is determined using galaxy catalogues extracted from a set of Digitized Palomar Sky Survey (DPOSS) plates. The two different types of structures (of low and high richness) were identified using two different algorithms: a modified version of the van Albada method for groups, and a peak finding algorithm for larger structures. In a 300 sq. deg. area up to z, 10 pages, 10 figures. Accepted by A&A