arXiv subjects

Fabio Ragosta

Publications and source records attributed to Fabio Ragosta.

22 records · Page 2Linked to original sources

arXiv2020

Variability and transient search in the SUDARE-VOICE field: a new method to extract the light curves

The VST Optical Imaging of the CDFS and ES1 Fields (VOICE) Survey, in synergy with the SUDARE survey, is a deep optical $ugri$ imaging of the CDFS and ES1 fields using the VLT Survey Telescope (VST). The observations for the CDFS field comprise about 4.38 deg$^2$ down to $r\sim26$ mag. The total on-sky time spans over four years in this field, distributed over four adjacent sub-fields. In this paper, we use the multi-epoch $r$-band imaging data to measure the variability of the detected objects and search for transients. We perform careful astrometric and photometric calibrations and point spread function (PSF) modeling. A new method, referring to as differential running-average photometry, is proposed to measure the light curves of the detected objects. With the method, the difference of PSFs between different epochs can be reduced, and the background fluctuations are also suppressed. Detailed uncertainty analysis and detrending corrections on the light curves are performed. We visually inspect the light curves to select variable objects, and present some objects with interesting light curves. Further investigation of these objects in combination with multi-band data will be presented in our forthcoming paper.

astro-ph.IM↗

arXiv2019

Supernovae and photon frequency shift induced by the Standard-Model Extension

We revisit for 714 SNeIa the discrepancy between the red-shift associated to the distance modulus $μ$ and the spectroscopic red-shift. Previous work has shown that the total red-shift $z$ might be a combination of the expansion red-shift $z_{\rm C}$ and of a static, blue or red shift $z_{\rm LSV}(r)$, $r$ being the comoving distance. The latter is due to the energy non-conservation of the photon propagating through Electro-Magnetic (EM) background fields (host galaxy, intergalactic and Milky Way), under Lorentz(-Poincaré) Symmetry Violation (LSV), associated to the Standard-Model Extension (SME). The non-conservation stems from the vacuum expectation value of the vector and tensor LSV fields. For zero radiation $Ω_{\rm rad}$ and curvature $Ω_{\rm k}$ densities, and matter density $Ω_m = 0.28$, the SN1a positions in the ($μ$, z) plan are recovered according to the different strengths, orientations, alignments and space-time dependencies of the EM fields and LSV components. The LSV vacuum energy may be thus tantamount to $Ω_Λ\simeq 0.7$, but unrelated to an accelerated expansion. We present models with red or blue-shifts $z_{\rm LSV}$, below $10\%$ of $z$. The $ν$ frequency variation is below $10^{-19} Δν/ν$ per m.

astro-ph.CO↗

arXiv2019

The VMC Survey -- XXXV. Model fitting of LMC Cepheid light curves

We present the results of the light curve model fitting technique applied to optical and near-infrared photometric data for a sample of 18 Classical Cepheids (11 fundamentals and 7 first overtones) in the Large Magellanic Cloud (LMC). We use optical photometry from the OGLE III database and near--infrared photometry obtained by the European Southern bservatory public survey "VISTA near--infrared survey of the Magellanic Clouds system". Iso--periodic nonlinear convective model sequences have been computed for each selected Cepheid in order to reproduce the multi--filter light curve amplitudes and shape details. The inferred individual distances provide an intrinsic weighted mean value for the LMC distance modulus of $μ_0=18.56$ mag with a standard deviation of 0.13 mag. We derive also the Period--Radius, the Period--Luminosity and the Period--Wesenheit relations that are consistent with similar relations in the literature. The intrinsic masses and luminosities of the best--fitting models show that all the investigated pulsators are brighter than the redictions of the canonical evolutionary mass--luminosity relation, suggesting a significant efficiency of non--canonical phenomena, such as overshooting, mass loss and/or rotation.

astro-ph.SR↗

arXiv2016

The VMC survey - XXIII. Model fitting of light and radial velocity curves of Small Magellanic Cloud classical Cepheids

We present the results of the chi2 minimization model fitting technique applied to optical and near-infrared photometric and radial velocity data for a sample of 9 fundamental and 3 first overtone classical Cepheids in the Small Magellanic Cloud (SMC). The near- infrared photometry (JK filters) was obtained by the European Southern Observatory (ESO) public survey "VISTA near-infrared Y; J;Ks survey of the Magellanic Clouds system"(VMC). For each pulsator isoperiodic model sequences have been computed by adopting a nonlinear convective hydrodynamical code in order to reproduce the multi- filter light and (when available) radial velocity curve amplitudes and morphological details. The inferred individual distances provide an intrinsic mean value for the SMC distance modulus of 19.01 mag and a standard deviation of 0.08 mag, in agreement with the literature. Moreover the instrinsic masses and luminosities of the best fitting model show that all these pulsators are brighter than the canonical evolutionary Mass- Luminosity relation (MLR), suggesting a significant efficiency of core overshooting and/or mass loss. Assuming that the inferred deviation from the canonical MLR is only due to mass loss, we derive the expected distribution of percentage mass loss as a function of both the pulsation period and of the canonical stellar mass. Finally, a good agreement is found between the predicted mean radii and current Period-Radius (PR) relations in the SMC available in the literature. The results of this investigation support the predictive capabilities of the adopted theoretical scenario and pave the way to the application to other extensive databases at various chemical compositions, including the VMC Large Magellanic Cloud pulsators and Galactic Cepheids with Gaia parallaxes.

astro-ph.SR↗