The role of chemical composition in RR Lyrae pulsationalproperties – I. Periods

We analyse the periods of theoretical radial pulsators, covering the range of total masses, luminosities, effective temperatures and chemical compositions expected for RR Lyrae variables in both galactic fields and globular clusters.
We show that for fixed values of the structural parameters (mass, luminosity and effective temperature), the period of fundamental and first-overtone pulsators is independent of the helium content ( Y ), whereas it slightly increases as the amount of metals ( Z ) increases. Furthermore, we find that the period along the blue edge for first-overtone pulsation is a function of mass, luminosity and helium content, with a marginal dependence on Z .
On these grounds, new linear relations connecting the periods to stellar parameters are derived. Such new relations should allow a more accurate interpretation of the RR Lyrae observed periods and, in particular, they should help in ascertaining the calibration of the mean absolute magnitude of RR Lyrae stars in terms of metal content.     

Reconstructing long-term changes in Daphnia's body size from subfossil remains in sediments of a small lake in the Himalayas

A combined analysis of modern zooplankton and fossil Cladocera assemblages from a Himalayan lake, Lake 40, revealed that the endemic Daphnia tibetana disappeared in the late-1980s, after persisting as the only Daphnia species for almost 3000 years. Daphnia head shields, which are rarely recovered from the sediments, were the most abundant Daphnia remains in the lake. The remains were of the Ctenodaphnia type; the smaller ones had a large central hole. Head shields of the same type were also found in zooplankton water samples, rich in exuviae as well as of intact specimens of D. tibetana, from a nearby lake. Small individuals had a distinct nuchal organ in the dorsal region of the head. We therefore postulated that the head shields with the hole were from young (newborn or individuals in the two first moults). Up to now, the nuchal organ has been described in laboratory populations of D. (Ctenodaphnia) magna, where it disappears quite early in life. It probably functions as an osmoregulatory organ, essential for the survivorship of late embryos and early juveniles. On the other hand, as far as we know, head shields with a hole have never been recorded in plankton or in sediments. In view of the fact that head shields were representative of Daphnia abundance, we used them to reconstruct changes in density and body size during ca. 3000 years. In fishless mountain lakes, mean Daphnia body size tends to increase toward the end of the productive season. The number of moults and maximum body size depend mainly on the duration of the ice-free period, and on summer temperatures. In cold years, when the productive season is short, the number of moults will be low, and the range of Daphnia body size will be narrow. We used Daphnia body size and abundance estimates, in addition to an analysis of changes in the Cladocera assemblage, to reconstruct past environmental conditions.     

Sardinia Coastal Uplift and Volcanism

The low variability of MIS 5.5 sea level (M.I.S = Marine Isotopic Stage) with respect to the present day sea level, allows the Sardinian coast to be used as an eustatic reference for the entire Mediterranean region. This level is generally at 7 ± 2 m above current sea level along the Sardinian coast. One sector along the Orosei Gulf (eastern Sardinia) includes a characteristic and well conserved tidal notch that changes in elevation from 7.6 to 11.5 m over only 30 km, tilting upwards towards the north. Generally, height deviations of such a tidal notch would be due to tectonic or volcanic activity. The Sardinia coast however, is considered to have too little tectonic activity, and also too small post-glacial rebound in order to explain the anomaly. The remaining possibility is Neogene-Quaternary continental and/or submarine volcanic activity, which we investigate as a possible cause for the observed anomalies. In this paper, our goal is to explain the anomaly by modelling recent volcanic loading or updoming related to magmatic intrusion emplacement. We review the literature on the recent volcanic deposits, both on-shore and off-shore, and investigate to what extent volcanic loads can influence the coastline from a theoretical standpoint, using the isostatic flexure model and a range of loads. We find that the observed notch height anomaly cannot be explained by volcanic loading, but must be produced by an upward welling due to the emplacement of volcanic material, as produced for instance by a laccolith or batholith. The upward movement could be related to the submarine volcano only recently detected, or to a source located on the eastern Sardinia coast near Orosei.     

Organochlorine compounds in tissues of swordfish (Xiphias gladius) from Mediterranean Sea and Azores islands

Polychlorobiphenyls (PCB) and organochlorine (OC) pesticides are endocrine-disrupting chemicals (EDCs). The Italian Ministry of Environment has undertaken a program (1999-2001) to measure levels of contaminants in top marine predators and to develop sensitive biomarkers for the evaluation of toxicological risk in these species. In 1999, 15 swordfishes (Xiphias gladius) taken from the Mediterranean Sea along the Sicilian coast (Strait of Messina, Italy) and in the Atlantic Ocean along the Azores Islands, and analysed for 34 congeners of PCBs and 27 organochlorine (OC) pesticides in gonad, muscle, liver and blubber tissues. In the tissues of Mediterranean swordfishes the sum of the determined PCBs congeners ranged from 4.61 to 4651.17 ng g(-1) on fresh tissue basis. Among organochlorine pesticides DDE, DDT and DDD (TDE) predominated with an overall range of 2.37-4734.56 ng(-1) w.w. In particular p,p'-DDE had concentrations appearing up to 3900 ng(-1), with the highest values found in fatty tissues, such as blubber. In the liver of Azores Island swordfishes lower levels of summation PCBs (8.43-294.17 ng/g w.w.) and summation DDTs (<0.01-217.44 ng/g w.w.) were determined.