Detection of Surface Brightness Fluctuations in Elliptical Galaxies imaged with the Advanced Camera for Surveys. B- and I-band measurements

Taking advantage of the exceptional capabilities of ACS on board of HST, we derive Surface Brightness Fluctuation (SBF) measurements in the B and I bands from images of six elliptical galaxies with $1500 \leq cz \leq 3500$. Given the low S/N ratio of the SBF signal in the blue band images, the reliability of the measurements is verified both with numerical simulations and experimental data tests. This paper presents the first published B- and I-band SBF measurements for distant ($\geq$ 20 Mpc) galaxies, essential for the comparisons of the models to observations of normal ellipticals. By comparing I-band data with our new Simple Stellar Population (SSP) models we find an excellent agreement and we confirm that I-band SBF magnitudes are mainly sensitive to the metallicity of the dominant stellar component in the galaxy, and are not strongly affected by the contribution of possible secondary stellar components. As a consequence I-band fluctuations magnitudes are ideal for distance studies. On the other hand, we show that standard SSP models do not reproduce the B-band SBF magnitudes of red ((B-I)_0 \gsim 2.1) galaxies in our sample. We explore the capability of two non--canonical models in properly reproducing the high sensitivity of B SBF to the presence of even small fractions of bright, hot stars (metal poor stars, hot evolved stars, etc.). The disagreement is solved both by taking into account hot (Post--AGB) stars in SSP models and/or by adopting Composite Stellar Population models. Finally, we suggest a limit value of the S/N for the B-band SBF signal required to carry out a detailed study of stellar population properties based on this technique.Comment: ApJ accepte

WFPC2 Observations of Massive and Compact Young Star Clusters in M31

We present color magnitude diagrams of four blue massive and compact star clusters in M31: G38, G44, G94, and G293. The diagrams of the four clusters reveal a well-populated upper main sequence and various numbers of supergiants. The U-B and B-V colors of the upper main sequence stars are used to determine reddening estimates of the different lines of sight in the M31 disk. Reddening values range from E(B-V) = 0.20 +/- 0.10 to 0.31 +/- 0.11. We statistically remove field stars on the basis of completeness, magnitude and color. Isochrone fits to the field-subtracted, reddening-corrected diagrams yield age estimates ranging from 63 +/- 15 Myr to 160 +/- 60 Myr. Implications for the recent evolution of the disk near NGC 206 are discussed.Comment: 17 pages, Latex, ApJ, in Pres

Eccentric Ellipsoidal Red Giant Binaries in the LMC: Complete Orbital Solutions and Comments on Interaction at Periastron

Modelling ellipsoidal variables with known distances can lead to exact determination of the masses of both components, even in the absence of eclipses. We present such modelling using light and radial velocity curves of ellipsoidal red giant binaries in the LMC, where they are also known as sequence E stars. Stars were selected as likely eccentric systems on the basis of light curve shape alone. We have confirmed their eccentric nature and obtained system parameters using the Wilson-Devinney code. Most stars in our sample exhibit unequal light maxima as well as minima, a phenomenon not observed in sequence E variables with circular orbits. We find evidence that the shape of the red giant changes throughout the orbit due to the high eccentricity and the varying influence of the companion. Brief intervals of pulsation are apparent in two of the red giants. We determine pulsation modes and comment on their placement in the period-luminosity plane. Defining the parameters of these systems paves the way for modelling to determine by what mechanism eccentricity is maintained in evolved binaries.Comment: 14 pages, 11 figures. Accepted to MNRAS 2012 January

The spatial and age distribution of stellar populations in DDO 190

The spatial distribution of stellar populations, the star formation history, and other properties of the dIrr galaxy DDO 190 have been analyzed using color--magnitude diagrams (CMDs) of about 3900 resolved stars and the Ha fluxes of HII regions. From the mean color index of the red giant branch, a mean metallicity [Fe/H]=-2.0 is obtained. The I magnitude of the TRGB has been used to estimate the distance. DDO 190 is 2.9+/-0.2 Mpc from the Milky Way, 2.1 Mpc from the M 94 group (CnV-I), 2.4 Mpc from the M 81 group and 2.9 Mpc from the barycenter of the Local Group, all indicating that it is an isolated, field galaxy. The surface-brightness distribution of the galaxy is well fitted by ellipses of ellipticity e=1-a/b=0.1 and P.A.=82deg. The radial star density distribution follows an exponential law of scale length a=43."4, corresponding to 611 pc. The Holmberg semi-major axis to mu_B=26.5 is estimated to be r^B_(26.5)=3.'0. Stellar populations of different ages in DDO 190 show strong spatial decoupling, the oldest population appearing much more extended than the youngest. Stars younger than 0.1 Gyr occupy only the central 40'' (0.55 kpc); stars younger than a few (~4) Gyr extend out to ~80'' (125 kpc), and for larger galactocentric distances only older stars seem to be present. This behavior is found in all the dIrr galaxies for which spatially extended studies have been performed and could be related with the kinematical history of the galaxy.Comment: To be published in the AJ. 29 pages, 13 figure

Esperienze di didattica della fisica in diversi livelli del sistema educativo

The growing interest of people in science events, the projects supported by the Italian Ministry of Education, University and Research to foster STEM teaching in different levels of the education system and the introduction of modern physics in some Italian high schools, contributed to the strengthening of interaction between schools, universities and research centers. This interaction realized in dedicated activities characterized by innovative communication and education strategies.This paper presents the events of science dissemination organized in the last years by the University of Ferrara and the National Institute for Nuclear Physics taking into account some case study differentiated by contents, recipients and education strategies.Comment: The article is written in Italia

Due casi carmelitani. L'intricata vicenda di Santo Stefano e Santa Teresa e la sconosciuta San Pietro d'Ungheria

Inserito nel nono numero dei "Quaderni di San Lorenzo", collana dedicata alle chiese mantovane (e nel caso specifico alle chiese carmelitane), il contributo ricostruisce la storia di tre chiese di Mantova: Santo Stefano, Santa Teresa, San Pietro d'Ungheria, delle quali sopravvivono solo pochi resti. Accanto alle notizie storiche ed artistiche vi \ue8 anche l'inserimento di ampie trascrizioni di inventari d'archivio, il tutto accompagnato da un aggiornamento globale dei titoli e delle fonti pertinenti

The White Dwarf Cooling Age of M67

A deep imaging survey covering the entire 23\arcmin diameter of the old open cluster M67 to $V = 25$ has been carried out using the mosaic imager (UHCam) on the Canada-France-Hawaii Telescope. The cluster color-magnitude diagram (CMD) can be traced from stars on its giant branch at $M_{V} = +1$ down through main sequence stars at least as faint as $M_{V} = 13.5$. Stars this low in luminosity have masses below $0.15 M_{\odot}$. A modest white dwarf (WD) cooling sequence is also observed commencing slightly fainter than $M_V = 10$ and, after correction for background galaxy and stellar field contamination, terminating near $M_V = 14.6$. The observed WDs follow quite closely a theoretical cooling sequence for $0.7 M_{\odot}$ pure carbon core WDs with hydrogen-rich atmospheres (DA WDs). The cooling time to an $M_V$ of 14.6 for such WDs is 4.3 Gyr which we take as the WD cooling age of the cluster. A fit of a set of isochrones to the cluster CMD indicates a turnoff age of 4.0 Gyr. The excellent agreement between these results suggests that ages derived from white dwarf cooling should be considered as reliable as those from other dating techniques. The WDs currently contribute about 9% of the total cluster mass but the number seen appears to be somewhat low when compared with the number of giants observed in the cluster.Comment: 15 pages plus 3 diagrams, minor corrections, Accepted for publication in the Astrophysical Journal Letters, to be published September 10, 199

Ognissanti, da \uabspedale\ubb benedettino a parrocchia

Inserito nell'ottavo dei "Quaderni di San Lorenzo", collana dedicata alle chiese mantovane (e nel caso specifico alle chiese di conventi benedettini), il contributo ricostruisce la storia della chiesa di Ognissanti in Mantova. Accanto alle notizie storiche ed artistiche vi \ue8 anche la lettura attuale del monumento con le opere d'arte, accompagnata da un aggiornamento globale dei titoli e delle fonti pertinenti