arXiv subjects

M. Marconi

Publications and source records attributed to M. Marconi.

At least 181 records · Page 10Linked to original sources

arXiv2007

Updated pulsation models for BL Herculis stars

Population II pulsatingvariables play a relevant role both as distance indicators and as tracers of the properties of old stellar populations. In this paper we present an update and homogeneous pulsational scenario for a wide range of stellar parameters typical of BL Her stars i.e., Population II Cepheids with periods shorter than 8 days. To this purpose, we adopt a nonlinear convective hydrodinamical code evaluate the stability and full amplitude behaviour of an extensive set of BL Her pulsation models. Various assumptions of mass, luminosity and metallicity consistent with the most recent evolutionary prescriptions, are adopted. We obtain the theoretical instability strip for both fundamental and first overtone pulsators and present a detailed atlas of light/radial-velocity curves. Some relations for the boundaries of the instability strip and for the dependence of the absolute magnitude on period, mass and color, as well as the fundamental period-amplitude relations are derived.Finally, we provide the theoretical period-radius relation for BL Her and find that it is in excellent agreement with the empirical relation by Burki & Meylan and consistent with the one holding for shorter periods for RR Lyrae stars.

astro-ph↗

arXiv2006

Variable stars in the newly discovered Milky Way satellite in Bootes

We present $V,I$ light curves for 12 variable stars identified in the newly discovered satellite of the Milky Way in the Bootes constellation (Belokurov et al. 2006).Our sample includes 11 RR Lyrae stars (5 first overtone, 5 fundamental mode and 1 double mode pulsator),and one long period variable close to the galaxy red giant branch tip. The RR Lyrae stars trace very well the average $V$ luminosity of the galaxy horizontal branch, leading to a true distance modulus for the galaxy of $μ_0$=19.11 $\pm$ 0.08 mag for an assumed metal abundance of [Fe/H]=-2.5 (Monoz et al. 2006), and for $E(B-V)$=0.02 mag. Average periods are =0.69 d and =0.37 d for {\it ab-} and {\it c-} type RR Lyrae stars, respectively, making of Bootes the second pure Oosterhoff type II (OoII) dSph after Ursa Minor. The location of the double mode RR Lyrae (RRd) in the Petersen diagram is consistent with RRd stars in OoII clusters, and corresponds to an intrinsic luminosity of $log L/logL\odot$=1.72 (for Z=10$^{-4}$ and M=0.80 M$\odot$) according to Bono et al. (1996) pulsation models.

astro-ph↗

arXiv2006

The Galactic Halo density distribution from photometric survey data: results of a pilot study

Our goal is to recover the Galactic Halo spatial density by means of field stars. To this aim, we apply a new technique to the Capodimonte Deep Field (OACDF, Alcala' et al. 2004), as a pilot study in view of the VLT Survey Telescope (VST) stellar projects. Considering the unique chance to collect deep and wide-field photometry with the VST, our method may represent a useful tool towards a definitive mapping of the Galactic Halo. In the framework of synthetic stellar populations, turn-off stars are used to reconstruct the spatial density. The determination of the space density is achieved by comparing the data with synthetic color-magnitude diagrams (CMDs). The only assumptions involve the IMF, age and metallicity of the synthetic halo population. Stars are randomly placed in the solid angle. The contributions of the various Monte Carlo distributions (with a step of 4 kpc) along the line of sight are simultaneously varied to reproduce the observed CMD. Our result on the space density is consistent with a power-law exponent n~3 over a range of Galactocentric distances from 8 to 40 kpc.

astro-ph↗

arXiv2006

Discovery of $δ$ Scuti pulsation in the Herbig Ae star VV Ser

A new observational study of the Herbig Ae star VV Ser has been performed in order to detect and accurately measure pulsation frequencies in the $δ$ Scuti range. As it belongs to the continuous field of view of the asteroseismological satellite COROT, this study also aims at characterizing the properties of VV Ser as a potential ``COROT additional program'' candidate. CCD time series photometry in the Johnson V filter has been obtained during three consecutive years. The resulting light curves have been subject to detailed frequency analysis and the derived frequencies have been compared to model predictions. Seven pulsation frequencies have been measured on the basis of the best dataset obtained in 2004, ranging from $\sim$ 31 to $\sim$ 118 $μHz$, with an accuracy of the order of 0.5 $μHz$. The comparison with an extensive set of asteroseismological models shows that all the observed periodicities can be reproduced if the stellar mass is close to $4 M_{\odot}$. Conversely, the measured frequencies can be associated to $p$ modes only if the effective temperature is significantly lower than that obtained from the spectral type conversion. The present results seem to suggest that more accurate spectral type determination is necessary in order to discriminate the best fit model solution. In any case, the stellar mass of VV Ser is close to the upper mass limit ($\sim 4 M_{\odot}$) for this class of pulsators.

astro-ph↗

arXiv2006

Synthetic properties of bright metal-poor variables. I. "Anomalous" Cepheids

We present new grids of evolutionary models for the so-colled ``Anomalous'' Cepheids (ACs), adopting Z=0.0001 and various assumptions on the progenitor mass and mass-loss efficiency. These computations are combined with the results of our previous set of pulsation models and used to build synthetic populations of the predicted pulsators as well as to provide a Mass-Luminosity relation in the absence of mass-loss. We investigate the effect of mass-loss on the predicted boundaries of the instability strip and we find that the only significant dependence occurs in the Period-Magnitude plane, where the synthetic distribution of the pulsators is, on average, brighter by about 0.1 mag than the one in absence of mass-loss. Tight Period-Magnitude relations are derived in the K band for both fundamental and first overtone pulsators, providing a useful tool for distance evaluations with an intrinsic uncertainty of about 0.15 mag, which decreases to about 0.04 mag if the mass term is taken into account. The constraints provided by the evolutionary models are used to derive evolutionary (i.e, mass-independent) Period-Magnitude-Color relations which provide distance determinations with a formal uncertainty of the order of about 0.1 mag, once the intrinsic colors are well known. We also use model computations from the literature to investigate the effect of metal content both on the instability strip and on the evolutionary Period-Magnitude-Color relations. Finally, we compare our theoretical predictions with observed variables and we confirm that a secure identification of actual ACs requires the simultaneous information on period, magnitude and color, that also provide constraints on the pulsation mode.

astro-ph↗

arXiv2006

Predicted properties of RR Lyrae stars in the SDSS photometric system

The luminosities and effective temperatures, as well as the whole bolometric lightcurves of nonlinear convective RR Lyrae models with 0.0001<Z<0.006 are transformed into the SDSS photometric system. The obtained ugriz lightcurves, mean magnitudes and colors, pulsation amplitudes and color-color loops are shown and analytical relations connecting pulsational to intrinsic stellar parameters, similarly to the ones currently used in the Johnson-Cousins filters, are derived. Finally the behaviour in the color-color planes is compared with available observations in the literature and possible systematic uncertainties affecting this comparison are discussed.

astro-ph↗

arXiv2006

Report on the CoRoT Evolution and Seismic Tools Activity

We present the work undertaken by the Evolution and Seismic Tools Activity (ESTA) team of the CoRoT Seismology Working Group. We have focused on two main tasks: Task 1 - now finished - has aimed at testing, comparing and optimising seven stellar evolution codes which will be used to model the internal structure and evolution of the CoRoT target stars. Task 2, still underway, aims at testing, comparing and optimising different seismic codes used to calculate the oscillations of models for different types of stars. The results already obtained are quite satisfactory, showing minor differences between the different numerical tools provided the same assumptions on the physical parameters are made. This work gives us confidence on the numerical tools that will be available to interpret the future CoRoT seismic data.

astro-ph↗

arXiv2005

A multisite photometric campaign on the Pre-Main-Sequence delta Scuti pulsator IP Per

We present the results of a photometric multisite campaign on the $δ$ Scuti Pre-Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 190 hours of observations over 38 nights. Present data confirms the multiperiodic nature of this star and leads to the identification of at least nine pulsational frequencies. Comparison with the predictions of linear non-adiabatic radial pulsation models allowed us to identify only five of the nine observed frequencies, and to constrain the position of IP Per in the HR diagram. The latter is in good agreement with the empirical determination of the stellar parameters obtained by Miroshnichenko et al. (2001). An initial interpretation of the observed frequencies using the Aarhus non-radial pulsation code suggests that three frequencies could be associated with non-radial ($l$=2) modes. Finally, we present new evolutionary and pulsation models at lower metallicity (Z=0.008) to take into account the possibility that IP Per is metal deficient, as indicated by Miroshnichenko et al. (2001).

astro-ph↗

arXiv2005

RR Lyrae-based calibration of the Globular Cluster Luminosity Function

We test whether the peak absolute magnitude Mv(TO) of the Globular Cluster Luminosity Function (GCLF) can be used for reliable extragalactic distance determinations. Starting with the luminosity function of the Galactic Globular Clusters listed in Harris catalog, we determine Mv(TO) either using current calibrations of the absolute magnitude Mv(RR) of RR Lyrae stars as a function of the cluster metal content [Fe/H] and adopting selected cluster samples. We show that the peak magnitude is slightly affected by the adopted Mv(RR)-[Fe/H] relation, while it depends on the criteria to select the cluster sample. As for the GCLFs in other external galaxies, using Surface Brightness Fluctuations (SBF) measurements we give evidence that the luminosity functions of the blue (metal-poor) Globular Clusters peak at the same luminosity within ~0.2 mag, whereas for the red (metal-rich) samples the agreement is within ~0.5 mag even accounting for the theoretical metallicity correction expected for clusters with similar ages and mass distributions. Then, using the SBF absolute magnitudes provided by a Cepheid distance scale calibrated on a fiducial distance to LMC (m(LMC)=18.50 mag), we show that the Mv(TO) value of the metal-poor clusters in external galaxies(-7.67+/-0.23 mag) is in excellent agreement with the value of both Galactic (-7.66+/-0.11 mag) and M31 (-7.65+/-0.19 mag)ones.

astro-ph↗

arXiv2005

Near-Infrared Observations of RR Lyrae Variables in $ω$ Centauri

We present Near-Infrared (NIR) $J$ and $K_s$-band observations for 181 RR Lyrae stars in the Galactic Globular Cluster $ω$ Cen. The comparison between predicted and empirical slopes of NIR Period-Luminosity (PL) relations indicates a very good agreement. Cluster distance estimates based on NIR PL relations agree quite well with recent determinations based on different standard candles, giving a true mean distance modulus $μ= 13.71\pm0.05$, and $d=5.52\pm0.13$ kpc.

astro-ph↗

arXiv2005

Classical Cepheids as Age Indicators

Theoretical Period-Age and Period-Age-Color relations for different chemical compositions have been recently derived using an updated homogeneous set of evolutionary and pulsational models. We apply these relations to Cepheids in the Magellanic Clouds to constrain the recent star formation history of these dwarf galaxies. Finally, we also compare the radial distribution of classical Cepheids with young clusters and star forming regions.

astro-ph↗

arXiv2005

Recent results on Pre-main sequence delta Scuti stars

Intermediate mass Pre-main sequence stars (1.5 $M_{\odot}< M < 5M_{\odot}$) cross the instability strip on their way to the main sequence. They are therefore expected to be pulsating in a similar way as the $δ$ Scuti stars. In this contribution we present the status of the observational studies of pulsations in these stars with special emphasis on recent results from our group. The prospects for future investigations of these objects from the ground and from space are discussed.

astro-ph↗

arXiv2005

B, V, I photometry of the complete sample of 23 Cepheids in the field of NGC 1866

We present the result of BVI photometry, obtained by using FORS@VLT, of the Cepheids present in the field of the Large Magellanic Cloud cluster NGC 1866. We found the 22 known variables plus an additional new Cepheid located about 10' from the cluster center. The accuracy of the photometry allowed us to derive B, V and I mean magnitudes with an uncertainty lower than 0.02 mag for 22 out of the 23 objects, with the exception of only one Cepheid (WS9) which presents a noisy light curve due to the probable occurrence of image blending. As a result, we provide accurate observational data for a substantial sample of variables all lying at the same distance and with a common original composition. The resulting period-luminosity relations are presented and briefly discussed.

astro-ph↗

arXiv2005

Variable stars in the globular cluster NGC 2419

We have used DOLORES at the TNG to obtain B,V time series photometry of NGC 2419, one of the most distant and bright clusters in the Galactic halo. These data will be used to study its variable star population in order to check whether the cluster could be the relic of an extragalactic system accreted by the Milky Way. Using the Image Subtraction technique (Alard 2000) we have identified about 300 candidate variables, many of which are in the cluster central regions. Several of the variables appear to be RR Lyrae stars, but we detected variability also around the tip of the red giant branch, and in other regions of the colour-magnitude diagram. To improve the light curve sampling and to resolve variables in the cluster inner regions, the TNG data were combined with HST archive data. Preliminary results are presented on the light curves from the combined data set.

astro-ph↗

arXiv2005

Cepheid pulsation models at varying metallicity and DY/DZ

In this paper we present an extended set of nonlinear convective pulsation models at varying the metallicity and DY/DZ ratio. The predicted instability strip and bolometric light curves are discussed by comparing the new models with our previous ones. In particular, the dependence on both metal and helium abundances is investigated. By transforming the bolometric light curves into the observational bands we are able to derive both Period-Color-Luminosity and Wesenheit relations for each selected chemical composition. Synthetic Period-Luminosity relations are obtained by populating the instability strip according to specific assumptions on the number of pulsators and the mass distribution. These theoretical results are compared with recent accurate data by Sandage et al. and Kervella et al., in order to test the predictive capabilities of the models. We confirm our previous results that the theoretical metallicity correction to the Key Project Cepheid distance scale depends both on the period range and DY/DZ ratio, becoming important for periods longer than 20 days and DY/DZ > 1.5.

astro-ph↗

arXiv2005

Pulsation and evolutionary masses of classical Cepheids. I. Milky Way variables

We investigate a selected sample of Galactic classical Cepheids with available distance and reddening estimates in the framework of the theoretical scenario provided by pulsation models, computed with metal abundance Z=0.02, helium content in the range of Y=0.25 to 0.31, and various choices of the stellar mass and luminosity. After transforming the bolometric light curve of the fundamental models into BVRIJK magnitudes, we derived analytical relations connecting the pulsation period with the stellar mass, the mean (intensity-averaged) absolute magnitude, and the color of the pulsators. These relations are used together with the Cepheid observed absolute magnitudes in order to determine the "pulsation" mass -M_p- of each individual variable. The comparison with the "evolutionary" masses -M_(e,can)- given by canonical (no convective core overshooting, no mass-loss) models of central He-burning stellar structures reveals that the M_p/M_(e,can) ratio is correlated with the Cepheid period, ranging from about 0.8 at logP=0.5 to about 1 at logP=1.5. We discuss the effects of different input physics and/or assumptions on the evolutionary computations, as well as of uncertainties in the adopted Cepheid metal content, distance, and reddening. Eventually, we find that the pulsational results can be interpreted in terms of mass-loss during or before the Cepheid phase, whose amount increases as the Cepheid original mass decreases. It vanishes around 13M_(sun) and increases up to about 20% at 4M_(sun).

astro-ph↗

arXiv2005

Predicted and empirical radii of RR Lyrae stars

We present new theoretical Period-Radius-Metallicity (PRZ) relations for RR Lyrae stars. Current predictions are based on a large set of nonlinear, convective models that cover a broad range of chemical abundances and input parameters. We also provide new and homogeneous estimates of angular diameters for a sample of field RR Lyrae stars using a recent calibration of the Barnes-Evans surface brightness relation. Predicted and empirical radii are, within the errors, in reasonable agreement, but in the short-period range the latter present a larger scatter. As a working hypothesis we suggest that this discrepancy might be due to the occurrence either of nonlinear features such as bumps or a steep rising branch. New distance determination for RR Lyr itself is in very good agreement with HST trigonometric parallax and with pulsation parallax.

astro-ph↗

arXiv2005

Near-Infrared Observations of RR Lyrae variables in Galactic Globular Clusters: I. The case of M92

We present near-infrared J,H, and K-band time series observations of the Galactic Globular Cluster (GGC) M92. On the basis of these data, we derived well-sampled light curves for eleven out of the seventeen cluster RR Lyrae variables, and in turn, accurate mean near-infrared (NIR) magnitudes. The comparison between predicted and empirical slopes of NIR Period-Luminosity (PL) relations indicates a very good agreement. Cluster distance determinations based on independent theoretical NIR $PL$ relations present uncertainties smaller than 5% and agree quite well with recent distance estimates based on different distance indicators. We also obtained accurate and deep NIR color-magnitude diagrams (CMDs) ranging from the tip of the Red Giant Branch (RGB) down to the Main Sequence Turn-Off. We detected the RGB bump and the NIR luminosities of this evolutionary feature are, within theoretical and empirical uncertainties, in good agreement with each other.

astro-ph↗