713 research outputs found
The VMC survey - XV : The Small Magellanic Cloud-Bridge connection history as traced by their star cluster populations
Date of Acceptance: 19/03/2015We present results based on YJKs photometry of star clusters located in the outermost, eastern region of the Small Magellanic Cloud (SMC). We analysed a total of 51 catalogued clusters whose colour-magnitude diagrams (CMDs), having been cleaned from field-star contamination, were used to assess the clusters' reality and estimate ages of the genuine systems. Based on CMD analysis, 15 catalogued clusters were found to be possible non-genuine aggregates. We investigated the properties of 80 per cent of the catalogued clusters in this part of the SMC by enlarging our sample with previously obtained cluster ages, adopting a homogeneous scale for all. Their spatial distribution suggests that the oldest clusters, log(t/yr) ≥ 9.6, are in general located at greater distances to the galaxy's centre than their younger counterparts - 9.0 ≤ log(t/yr) ≤ 9.4 - while two excesses of clusters are seen at log(t/yr) ~9.2 and log(t yr-1) ˜ 9.7. We found a trail of younger clusters which follow the wing/bridge components. This long spatial sequence does not only harbour very young clusters, log(t yr-1) ~7.3, but it also hosts some of intermediate ages, log(t/yr) ~9.1. The derived cluster and field-star formation frequencies as a function of age are different. The most surprising feature is an observed excess of clusters with ages of log(t/yr) < 9.0, which could have been induced by interactions with the LMC.Peer reviewedFinal Accepted Versio
Representative galaxy age-metallicity relationships
The ongoing surveys of galaxies and those for the next generation of
telescopes will demand the execution of high-CPU consuming machine codes for
recovering detailed star formation histories (SFHs) and hence age-metallicity
relationships (AMRs). We present here an expeditive method which provides
quick-look AMRs on the basis of representative ages and metallicities obtained
from colour-magnitude diagram (CMD) analyses. We have tested its perfomance by
generating synthetic CMDs for a wide variety of galaxy SFHs. The representative
AMRs turn out to be reliable down to a magnitude limit with a photometric
completeness factor higher than 85 per cent, and trace the chemical
evolution history for any stellar population (represented by a mean age and an
intrinsic age spread) with a total mass within ~ 40 per cent of the more
massive stellar population in the galaxy.Comment: 12 pages, 11 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
The age-metallicity relationship in the Fornax spheroidal dwarf galaxy
We produce a comprehensive field star age-metallicity relationship (AMR) from
the earliest epoch until ~ 1 Gyr ago for three fields in the Fornax dSph galaxy
by using VI photometric data obtained with FORS1 at the VLT. We find that the
innermost one does not contains dominant very old stars (age > 12 Gyr), whereas
the relatively outer field does not account for representative star field
populations younger than ~ 3 Gyr. When focusing on the most prominent stellar
populations, we find that the derived AMRs are engraved by the evidence of a
outside-in star formation process. The studied fields show bimodal metallicity
distributions peaked at [Fe/H] = (-0.95 +- 0.15) dex and (-1.15 or -1.25 +-
0.05) dex, respectively, but only during the first half of the entire galaxy
lifetime. Furthermore, the more metal-rich population appears to be more
numerous in the outer fields, while in the innermost Fornax field the
contribution of both metallicity populations seems to be similar. We also find
that the metallicity spread ~ 6 Gyr ago is remarkable large, while the
intrinsic metallicity dispersion at ~ 1-2 Gyr results smaller than that for the
relatively older generations of stars. We interpret these outcomes as a result
of a possible merger of two galaxies that would have triggered a star formation
bursting process that peaked between ~ 6 and 9 Gyr ago, depending on the
position of the field in the galaxy.Comment: 7 pages, 5 figures, MNRAS, in pres
Sure to rise: reading the Edmonds cookery book as a popular icon
Cookbooks are one of a variety of written forms that can be read as historical documents, functioning as testaments to individual, familial and cultural development. In the recipe, one can find a sense of culinary preference which simultaneously shapes and is shaped by a sense of belonging and identity. The (post-) colonial past of countries such as New Zealand and Australia allows a particular view into reading cookery books as chronicles of everyday life as well as an archive of cultural memory, uses and popular customs. Starting from the premise that cookbooks can function as a site for heritage and identity, this paper addresses the status of the Edmonds cookery kook as a popularised national icon. Now an established presence within New Zealand’s culinary culture, the Edmonds collection – first published in 1908 as The sure to rise cookery book – has evolved over the decades to include new and updated recipes, mirroring the cultural and socio-historical moment in which it was placed. With this in mind, I analyse how cookbook writing can be interpreted as a national practice which owes a lot of its success to pervasive links to popular culture. My paper also offers a critical framework which highlights the material conditions – historical, aesthetico-political and socio-cultural – that encouraged the rise and popularity of the Edmonds cookbook within an expanding national readership
Magnetic, electrical, and GPR waterborne surveys of moraine deposits beneath a lake: A case history from Turin, Italy
Bathymetry and bottom sediment types of inland water basins provide meaningful information to estimate water reserves and possible connections between surface and groundwater. Waterborne geophysical surveys can be used to obtain several independent physical parameters to study the sediments. We explored the possibilities of retrieving information on both shallow and deep geological structures beneath a morainic lake by means of waterborne nonseismic methods. In this respect, we discuss simultaneous magnetic, electrical, and groundpenetrating radar (GPR) waterborne surveys on the Candia morainic lake in northerly Turin (Italy).We used waterborne GPR to obtain information on the bottom sediment and the bathymetry needed to constrain the magnetic and electrical inversions. We obtained a map of the total magnetic field (TMF) over the lake from which we computed a 2D constrained compact magnetic inversion for selected profiles, along with a laterally constrained inversion for one electrical profile. The magnetic survey detected some deep anomalous bodies within the subbottom moraine. The electrical profiles gave information on the more superficial layer of bottom sediments. We identify where the coarse morainic material outcrops from the bottom finer sediments from a correspondence between high GPR reflectivity, resistivity, and magnetic anomalie
New quasars behind the Magellanic Clouds. Spectroscopic confirmation of near-infrared selected candidates
Context. Quasi-stellar objects (quasars) located behind nearby galaxies provide an excellent absolute reference system for astrometric studies, but they are difficult to identify because of fore- and background contamination. Deep wide-field, high angular resolution surveys spanning the entire area of nearby galaxies are needed to obtain a complete census of such quasars. Aims. We embarked on a program to expand the quasar reference system behind the Large and the Small Magellanic Clouds, the Magellanic Bridge, and the Magellanic Stream that connects the Clouds with the Milky Way. Methods. Hundreds of quasar candidates were selected based on their near-infrared colors and variability properties from the ongoing public ESO VISTA Magellanic Clouds survey. A subset of 49 objects was followed up with optical spectroscopy. Results. We confirmed the quasar nature of 37 objects (34 new identifications): four are low redshift objects, three are probably stars, and the remaining three lack prominent spectral features for a secure classification. The bona fide quasars, identified from their broad emisison lines, are located as follows: 10 behind the LMC, 13 behind the SMC, and 14 behind the Bridge. The quasars span a redshift range from z ~ 0.5 to z ~ 4.1. Conclusions. Upon completion the VMC survey is expected to yield a total of ~1500 quasars with Y< 19.32 mag, J< 19.09 mag, and Ks< 18.04 mag
Probing the LMC age gap at intermediate cluster masses
The LMC has a rich star cluster system spanning a wide range of ages and
masses. One striking feature of the LMC cluster system is the existence of an
age gap between 3-10 Gyrs. But this feature is not as clearly seen among field
stars. Three LMC fields containing relatively poor and sparse clusters whose
integrated colours are consistent with those of intermediate age simple stellar
populations have been imaged in BVI with the Optical Imager (SOI) at the
Southern Telescope for Astrophysical Research (SOAR). A total of 6 clusters, 5
of them with estimated initial masses M < 10^4M_sun, were studied in these
fields. Photometry was performed and Colour-Magnitude Diagrams (CMD) were built
using standard point spread function fitting methods. The faintest stars
measured reach V ~ 23. The CMD was cleaned from field contamination by making
use of the three-dimensional colour and magnitude space available in order to
select stars in excess relative to the field. A statistical CMD comparison
method was developed for this purpose. The subtraction method has proven to be
successful, yielding cleaned CMDs consistent with a simple stellar population.
The intermediate age candidates were found to be the oldest in our sample, with
ages between 1-2 Gyrs. The remaining clusters found in the SOAR/SOI have ages
ranging from 100 to 200 Myrs. Our analysis has conclusively shown that none of
the relatively low-mass clusters studied by us belongs to the LMC age-gap.Comment: 9 pages, 8 figures. Accepted to MNRA
Analysis of the chemical evolution of the Galactic disk via dynamical simulations of the open cluster system
For several decades now, open clusters have been used to study the structure and chemical evolution of the disk of our Galaxy. Due to the fact that their ages and metallicities can be determined with relatively good precision, and since they can be observed even at great distances, they are excellent tracers of the variations in the abundance of heavy chemical elements with age and position in the Galactic disk. In the present work we analyze the star formation history and the chemical evolution of the disk of the Galaxy using numerical simulations of the dynamical evolution of the system of open clusters in the Milky Way. Starting from hypotheses on the history of cluster formation and the chemical enrichment of the disk, we model the present properties of the Galactic open cluster system. The comparison of these models with the observations allows us to examine the validity of the assumed hypotheses and to improve our knowledge about the initial conditions of the chemical evolution of the Galactic disk
Notes on the diet of seven terrestrial frogs in three agroecosystems and forest remnants in Northwestern São Paulo State, Brazil.
Anurans are predators of a great diversity of invertebrates, but studies on agroecosystems are very scarce. Herein we described the diet composition of seven species of terrestrial anurans captured in three different agroecosystems (corn, soybean and rubber tree) and in forest remnants of the Northwestern region of São Paulo state, Brazil. Ten prey categories were identified in the stomachs of 80 specimens belonging to the families Bufonidae, Leptodactylidae and Microhylidae. Hymenoptera (Formicidae) was consumed by all species. Coleoptera was the most frequent item, consumed by six of the even species followed by Araneae and Isoptera. Isoptera was the most abundant item followed by Formicidae, Coleoptera and Araneae. Adults and juveniles of Physalaemus nattereri, the most abundant species in our study, consumed Formicidae and Isoptera more than other food items and there is not a significant difference in the abundance of consumed prey items between the age categories. In summary, the majority of the studied species can be considered generalists predators and, probably, consumed the prey items available in the environment. The most abundant species found in our study can be considered here as having a specialized diet, by consuming social insects in great frequency.Published online on 12 August 2015
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