To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Given the uncertainties in the derivation of the current and past SFR in galaxies of any kind, the SF regime in irregulars is subject of wide debate. Since the most direct information on the stellar populations and relative histories in any system can be derived from their CMD, we have undertaken a project for accurately studying the CMDs and luminosity functions (LF) of nearby, well resolved, irregulars. The method proceeds on two tracks: a) we have developed a numerical code for Montecarlo simulations of CMDs and b) we have taken deep and accurate CCD photometry of several galaxies and derived the corresponding CMDs and LFs. The comparison of the observational data with the corresponding theoretical expectations provides several constraints on the SF history and on the IMF of the analysed objects. We do not pretend to reach unique conclusions on the evolution of irregular galaxies, but we can sensibly reduce the range of possible interpretations.
All the irregulars in our sample were selected from the DDO Catalogue and were supposed to belong to the Local Group. Detailed descriptions of the data acquisition and reduction and of the simulation code can be found in Tosi et al. (1991). In the following we briefly summarize the results relative to Sextans B, NGC 3109 and DDO 210.
The process of star formation (SF) and the modalities with which it occurs in galaxies of different sizes are still poorly understood. On the other hand, interpretation of the chemical and photometric properties of galaxies requires the adoption of adequate laws for the SF rate and Initial Mass Function (IMF) in model computations. Dwarf irregular galaxies in the Local Group offer the chance to study their SF history through analysis of their HR diagrams, which can be derived down to V 25, corresponding to MV0, i.e. to main sequence stars of 2 M⊙. Therefore, for these galaxies, we can derive information on the star formation activity which has occurred over the last 1 Gyr approximately. In this framework, we have undertaken CCD observations of Dwarf irregular galaxies in the Local Group with ESO telescopes and briefly present here the results obtained for DDO 210, Sextans B and NGC 3109.
Archaeological excavations carried out at the sites of Laion/Lajen (Bolzano/Bozen) and Stufles-Oberegger (Bressanone/Brixen) in northern Italy uncovered well-preserved wooden samples in cultural layers archaeologically dated to the Iron Age. From the 2 sites, different wooden samples were recovered that were well preserved enough to allow clear identification of the tree species and of the ring structure. Among the different wooden samples, 2 were selected for radiocarbon analyses: from Laion/Lajen, a beam with an unbroken sequence of 158 rings; from Stufles-Oberegger, a combusted trunk with a sequence of 217 rings. Both samples were identified as Larix decidua species. From each sequence, single rings were selected and submitted for accelerator mass spectrometry (AMS) 14C dating analysis at CEDAD. Conventional 14C ages were then calibrated to calendar ages using the IntCal04 atmospheric data set, while the statistical constraints resulting from the defined ring sequence were used to develop a wiggle-matching approach by making use of the Bayesian analysis functions available in OxCal. The obtained results are an important contribution in refining the chronology of the studied sites.
We compare the theoretical and empirical PL relations in V and I bands for Cepheids in the LMC. We found that, within the current intrinsic dispersions, the theoretical predictions are in remarkable agreement with observational data. We also discuss the PLC relations in (V,B-V) and (V,V-I) as well as the dependence of distance determinations on uncertainties in colors, in reddening corrections and in metal content.
On the basis of a historical overview we outline the relevant results which allowed to approach on firm basis the physical mechanisms which govern the radial pulsation of RR Lyrae variables, revealing the astrophysical parameters which account for their limiting amplitude pulsational behavior.
Using observations from the Hubble Space Telescope archive, color-magnitude diagrams have been constructed for globular Cluster 4 in the Fornax dSph galaxy and its surrounding field. These diagrams extend below the main-sequence turnoffs and have yielded measurements of the ages of the populations. In particular, from our analysis Cluster 4 shows [Fe/H] ≃ 2.0, a value significantly lower than that derived for the Fornax field ([Fe/H] ≃ −1.40). Putting our results in the frame of the findings of Buonanno et al. (1998) for the Fornax clusters 1, 2, 3 and 5, a global analysis of the properties of Fornax stellar populations has been performed.
Nonlinear convective pulsation models representative of SMC Cepheids pulsating in the second overtone mode are presented. Model predictions are compared with observations and implications are derived for second overtone selection criteria. The role of overtone Cepheids as distance indicators is finally investigated and the derived distance scale is at odds with the so called short distance scale.
We present U, B, V, I (SUSI@NTT) and J,Ks (SOFI@NTT) photometry of the Large Magellanic Cloud (LMC) cluster Reticulum. The observing strategy and data reduction (DAOPHOTII/ALLFRAME) allowed us to reach an accuracy of the order of 0.01 – 0.03 mag in all the bands at limiting magnitudes typical of RR Lyrae stars. Reticulum hosts a sizable sample of RR Lyrae stars (32), and we supply an accurate distance estimate using the RR Lyrae K-band Period-Luminosity-Metallicity (PLZK) relation. This method presents several advantages when compared with the MV vs [Fe/H] relation, since it is only marginally affected by off-ZAHB evolutionary effects and reddening corrections.
We present the period-radius relations predicted by nonlinear convective models of Classical Cepheids and RR Lyrae stars. For the former variables we show that the metallicity effect is negligible for both fundamental and first overtone pulsators. This confirms the power of the period-radius relation to estimate Cepheid radii and in turn distances. For the latter class of variables we show that the dispersion of the period-radius relation of both fundamental and first overtone pulsators is significantly reduced once the metallicity dependence is taken into account. This provides a robust method to evaluate the radius of observed RR Lyrae with measured period and metal abundance.
We present new photoelectric observations of the Pre–Main-Sequence δ Scuti star, V351 Ori. These new data suggest that V351 Ori could be a multiperiodic variable. The comparison between observations and detailed pulsational models allows us to put independent constraints on the mass and luminosity of the star. The predicted distance is 210 pc, indicating that V351 Ori is much closer than the Orion star forming region. With an inferred mass of ∼1.8 M⊙ and an uncertain evolutionary stage, V351 Ori represents an excellent candidate for future asteroseismological studies that will assess whether it is a young PMS star (∼6 Myr) or an evolved object (∼1 Gyr) leaving the main-sequence.
We present some preliminary results based on new observations of the variable stars belonging to the Carina Dwarf Galaxy (DG). Photometric data were collected with the two wide field imagers available at ESO (WFI@2.2.) and CTIO (4m prime focus).
We report the discovery of periodicities in the light curve of the Herbig Ae star V346 Ori. We interpret these variations as the superposition of at least two signals with periods P1=42±6 min and P2=68±12 min resulting from stellar oscillations. The computation of linear non-adiabatic pulsation models for Pre-Main Sequence (PMS) stars reproduces these periods for a 1.5 M⊙ star with Teff= 7300 K and log L/L⊙= 0.74, pulsating in the fundamental and second overtones.
We present an overview of our study of the short period variable stars in the Large Magellanic Cloud, and in the dwarf galaxies Fornax, Leo I, and NGC 6822. Light curves are presented for RR Lyrae stars, Anomalous Cepheids and, for the first time, for Dwarf Cepheids in the field and in the globular cluster #3 of the Fornax galaxy.
We present some preliminary results of a Strömgren photometric survey searching for radially pulsating variables among Herbig Ae stars. These young objects are expected to show a characteristic δ Scuti variability when entering the instability strip along their pre-main sequence evolutionary tracks, according to the theoretical predictions by Marconi & Palla (1998). We identified at least five pulsating Herbig Ae stars with periods in the expected range. On the basis of these encouraging first results, we foresee both new more detailed observations and accurate comparisons with theoretical models.
We present the results of several numerical experiments aimed at testing the dependence of theoretical observables predicted by Cepheid hydrodynamical models on the equation of state (EOS). We focus our attention on nonlinear and time-dependent Cepheid convective models at solar chemical composition. We find that current predictions for both the blue and red edge of the instability strip present a mild dependence on the EOS. The same outcome applies to the morphology of the lightcurves.
We present first results concerning the detection of variable stars in the Carina dwarf Spheroidal from B, V images collected with the 4-m CTIO telescope. We show a sample of candidate variables spanning from the tip of the Red Giant Branch down to the Main Sequence turn off. Finally, we discuss the future photometric and spectroscopic developments of this project.
Many studies have reported that cannabis use increases the risk of a first episode of psychosis (FEP). However, only a few studies have investigated the nature of cannabis-related experiences in FEP patients, and none has examined whether these experiences are similar in FEP and general populations. The aim of this study was to explore differences in self-reported cannabis experiences between FEP and non-psychotic populations.
A total of 252 subjects, who met International Classification of Diseases (ICD)-10 criteria for FEP, and 217 controls who reported cannabis use were selected from the Genetics and Psychosis (GAP) study. The Medical Research Council Social Schedule and the Cannabis Experience Questionnaire were used to collect sociodemographic data and cannabis use information, respectively.
Both ‘bad’ and ‘enjoyable’ experiences were more commonly reported by FEP subjects than controls. Principal components factor analysis identified four components which explained 62.3% of the variance. Linear regression analysis on the whole sample showed that the type of cannabis used and beliefs about the effect of cannabis on health all contributed to determining the intensity and frequency of experiences. Linear regression analysis on FEP subjects showed that the duration of cannabis use and amount of money spent on cannabis were strongly related to the intensity and frequency of enjoyable experiences in this population.
These results suggest a higher sensitivity to cannabis effects among people who have suffered their first psychotic episode; this hypersensitivity results in them reporting both more ‘bad’ and ‘enjoyable’ experiences. The greater enjoyment experienced may provide an explanation of why FEP patients are more likely to use cannabis and to continue to use it despite experiencing an exacerbation of their psychotic symptoms.
The Magellanic System represents one of the best places to study the formation and evolution of galaxies. Photometric surveys of various depths, areas and wavelengths have had a significant impact on our understanding of the system; however, a complete picture is still lacking. VMC (the VISTA near-infrared YJKs survey of the Magellanic System) will provide new data to derive the spatially resolved star formation history and to construct a three-dimensional map of the system. These data combined with those from other ongoing and planned surveys will give us an absolutely unique view of the system opening up the doors to truly new science!
We present a project that aims to provide a complete theoretical and observational framework for an as yet unexplored class of variable stars, the ultralong-period Cepheids (P longer than 80–100 days). Given their very high luminosities (MV up to −7 mag), with the Hubble Space Telescope we will be able to observe them easily in stellar systems located at large distances (~ 100 Mpc). This limit will be further increased, out to the Hubble flow (~ 350 Mpc), using future ground-based facilities such as the European Extremely Large Telescope. The nature of their pulsation is as yet unclear, as is their evolutionary status, which seems different from the central helium-burning phase generally associated with classical Cepheids. These objects have been found to cover a very large metallicity range, from [Fe/H] ~ −2 dex to solar values, and they are located in heterogeneous stellar systems, from dwarf to spiral galaxies. Once completely characterized, they could provide a crucial test, since they have been found in all Type Ia supernova host spiral galaxies that have been monitored for variability over long periods and that currently offer sound constraints on the estimated value of the Hubble constant.