arXiv subjects

Ester Marini

Publications and source records attributed to Ester Marini.

8 recordsLinked to original sources

arXiv2026

Unmasking (44) Nysa: Evidence for a trilobate structure

Context. (44) Nysa is one of the largest known E-type asteroids. Light curve inversion models have indicated that it may have an elongated shape commonly found in large binary systems. Aims. We aimed to identify the morphology and presence of possible satellites orbiting Nysa. Methods. We observed Nysa with the visible-wavelengths adaptive-optics instruments SHARK-VIS and SPHERE/ZIMPOL in order to image the object with the highest possible spatial resolution, and visually identified surface features on the object. A shape model was constructed from these images and photometric light curves using the ADAM code. Results. Imaging revealed a highly unusual morphology with multiple distinct surface features, including two distinct valleys most easily interpreted as colli. A faint satellite was identified in the deconvolution residuals in multiple datasets. Conclusions. We determine that (44) Nysa is a binary system most likely consisting of a contact-trinary or highly-irregular, coherent primary object and a small satellite.

astro-ph.EP↗

arXiv2026

LBT-MODS spectroscopy of young stellar objects in the distant metal-poor star forming region Sh2-284: Stellar and accretion properties

We present a spectroscopic survey of young stellar objects (YSOs) in Sh2-284, a distant (~4.5 kpc), low-metallicity (Z~1/3 Zsun) star-forming region (SFR) toward the Galactic anticenter. Candidate YSOs were selected using mid-infrared Spitzer/IRAC data with optical and near-infrared photometry. Follow-up spectroscopy was conducted with MODS at the Large Binocular Telescope. We characterize the stellar and accretion properties of the disk-bearing population in a metal-poor environment, probing stellar masses from ~2.95 Msun to ~0.35 Msun. This work constitutes the first wide-field (~45'x45') spectroscopic investigation of YSOs in Sh2-284, providing a comprehensive view of star formation in this Galactic environment. We provide tentative first estimates of iron abundance for three low-mass targets and lithium abundance for a limited number of objects, offering an initial characterization of the chemical properties of these stars. We adopt a multi-diagnostic approach based on nine tracers, exploiting the spectral coverage of the instrument, using H_alpha, H_beta, H_gamma, CaII infrared triplet, Pa_eta, Pa_zeta, and Pa_epsilon emission lines. We derive key accretion properties and compare them with those measured in nearby, solar-metallicity SFRs to explore potential metallicity-driven differences in accretion behavior and disk evolution. We tentatively find indications of a flattening in the flux-flux relations of the metal-poor YSOs compared to solar-metallicity samples, a behavior that is recovered across diagnostics. Our observations indicate that the selected disk-bearing YSOs in this metal-poor environment exhibit resilient accretion activity, spanning from ~2.3x10^(-10) Msun/yr and ~1.0x10^(-6) Msun/yr, and a median rate of ~2.2x10^(-8) Msun/yr. Overall, this demonstrates that gas accretion can be efficiently sustained in sub-solar metallicity environments.

astro-ph.GA↗

arXiv2026

Spectroscopic follow-up of Gaia alerted Young Stellar Object variables: the Large Binocular Telescope view

We analyzed optical/near-IR Large Binocular Telescope spectra of 16 sources alerted by Gaia between 2021 and 2024 due to significant photometric variability. Half of the spectra were taken during quiescence and the rest during a burst or at intermediate brightness. Our analysis of their ten-year light curves and photometric/spectroscopic features provide evidence that all 16 sources are accreting Young Stellar Objects (YSOs). One object, Gaia23bab, is a known EXor source. Other light curves either have peaks over a stable baseline, or significant variability throughout the entire observation period, suggesting multiple contributing processes. All spectra exhibit emission lines from accretion columns, and over half of them show atomic forbidden lines as signatures of outflowing gas. We determined stellar parameters, accretion luminosity (Lacc) and mass accretion rate (Macc) at different brightness phases. Only two sources showed variability primarily due to extinction. During quiescence, our sources exhibit Lacc and Macc values typical of T Tauri and Herbig Ae/Be (HAEBE) sources, supporting the hypothesis that any YSO may undergo episodic accretion. In bursts, the Lacc and Macc of sources with photometric variations exceeding 2 mag follow a shallower relation with stellar luminosity and mass, typical of known EXor sources. This group includes one Class I, one flat-spectrum, and two Class II sources. Notably, the other Class I source, Gaia24beh, shows an Lacc value about ten times higher than typical EXor bursts of the same mass. In the other cases, Lacc and Macc align with variability seen in T Tauri and HAEBE sources.

astro-ph.SR↗

arXiv2025

LBT Italia: Current Achievements and Future Directions

The Large Binocular Telescope (LBT) is a world-leading astronomical observatory, where the italian partnership has played an important role in increasing the telescope's productivity, both through an optimized observing strategy and through peer-reviewed publications that are well recognized by the international astronomical community. This manuscript provides an updated overview of the active and past instruments at LBT, together with the key usage statistics. In particular, we analyze the operational performance recorded in the LBT Italia night logs during INAF's observing time and assess the scientific impact of each instrument. Between 2014 and 2025 LBT Italia produced an average of 14 referred publication per year, based on an annual average of 311 hours of on-sky time. This corresponds to approximately 2.2 nights of telescope time per publication. The results of this analysis are placed in an international context to evaluate the competitiveness of LBT, and we outline future perspective for scientific exploitation.

astro-ph.IM↗

arXiv2025

A study of Andromeda to improve our knowledge on the evolution and dust production by AGB stars

We study the AGB population of the galaxy M31, based on available HST and Spitzer data, to characterize the individual sources in terms of mass, metallicity and formation epoch of the progenitors. Particular attention is dedicated to the derivation of the dust production rate of the stars, in the attempt of determining the global current dust production rate of the galaxy, divided between the silicates and the carbonaceous dust contributions. We use results from stellar evolution modelling complemented by the description of the dust formation process in the wind, to be used in a population synthesis approach, based on the star formation history and age-metallicity relationship obtained in previous investigations. The comparison between the results from synthetic modelling and the data available are used for the characterization of AGB stars in M31. We find that the bulk of the AGB population of M31 is composed by low-mass stars of different metallicity formed between 6 Gyr and 14 Gyr ago, with an additional, significant contribution from the progeny of 1.7-2.5Msun stars formed during the secondary peak in the star formation, which occurred between 1 and 2 Gyr ago. The dust production rate of the galaxy is mostly provided by carbon stars, whose contribution is of the order of 4x10^{-4} Msun/yr, completed by silicates production from massive AGB stars, occurring at a rate of 6x10^{-5} Msun/yr. The implications of the present results on the reliability of AGB modelling are also commented.

astro-ph.GA↗

arXiv2023

A study of carbon-rich post-AGB stars in the Milky Way to understand the production of carbonaceous dust from evolved stars

The goal of this study is to reconstruct the evolution and the dust formation processes during the final AGB phases of a sample of carbon-rich, post-AGB Galactic stars, with particular attention to the determination of the past mass-loss history. We study the IR excess of sources classified as single stars by means of dust formation modelling where dust grains form and grow in a static wind and expand from the surface of the star. The method is applied to various evolutionary stages of the final AGB phase of stars with different masses and metallicities. The detailed analysis of the SED of the sources investigated, which included the derivation of the luminosities and the dust properties, is used to infer information on mass loss, efficiency of dust formation, and wind dynamics. We confirm previous results that most of the investigated sources descend from low-mass(M<1.5Msun) progenitors that reached the C-star stage. Metal-poor carbon stars are characterised by higher IR excesses with respect to their more metal-rich counterparts of similar luminosity due to a higher surface carbon-to-oxygen excess. This work confirms previous conclusions that more luminous stars descending from higher-mass progenitors are generally more opaque due to shorter evolutionary timescales that place the dust shell closer to the central object. We also find that the mass-loss rate at the tip of the AGB phase of metal-rich low-mass carbon stars is approximately 1-1.5x10^-5Msun/yr, whereas in the metal-poor domain M~4-5x10^-5Msun/yr is required. These results indicate the need for an upwards revision of the theoretical mass-loss rates of low-mass carbon stars in the available literature, which in turn require a revised determination of carbon dust yields by AGB stars.

astro-ph.SR↗

arXiv2023

The spectra of IceCube Neutrino (SIN) candidate sources -- III. Optical spectroscopy and source characterization of the full sample

A correlation between astrophysical high-energy neutrinos and blazars has been suggested by various authors. In particular, a likely association between IceCube events and intermediate and high-energy peaked BL Lac objects has led to a sample of 47 objects having a high probability of being neutrino sources. In the first paper of this series we reported optical spectroscopy of 17 objects, which together with data taken from the literature covered 80 per cent of the sample. Here we present spectroscopy obtained at large aperture telescopes of a further 17 objects (plus four additional targets), which completes the sample coverage. For twelve objects we are able to determine the redshift (0.07 < z <1.6), while for the others we set a lower limit on it, based on either the robust detection of intervening absorption systems or on an estimation derived from the absence of spectral signatures of the host galaxy. With these new data we expand and reinforce the main results of our previous papers, namely the fact that in terms of their broad-band properties our sources appear to be indistinguishable from the rest of the blazar population and the relatively large (>34 per cent and possibly as high as 80 per cent) fraction of masquerading BL Lac objects, for which the low equivalent width of the emission lines is due to the brightness of the boosted continuum, rather than being an intrinsic property, in our sample.

astro-ph.HE↗

arXiv2022

Understanding dust production and mass loss on the AGB phase using post-AGB stars in the Magellanic Clouds

Aims: We aim to understand the variation of the surface chemistry that occurs during the AGB phase by analysing results from observations of single post-AGB stars in the Magellanic Clouds. We also aim at reconstruct dust formation processes, that are active in the circumstellar envelope of AGB stars. Methods: We study likely single post-AGB sources in the Magellanic Clouds that exhibit a double-peaked (shell-type) spectral energy distribution (SED). We interpret their SED by comparing with results from radiative transfer calculations, to derive the luminosity and the dust content of the individual sources. Additionally, we compare the observationally derived stellar parameters and the photospheric chemical abundances of the target sample with results from stellar evolution modelling of AGB and post-AGB stars. This allows for the characterization of the individual sources in terms of initial mass and formation epoch of the progenitors. Results: We find that amongst our target sample of 13 likely single post-AGB stars with shell-type SED, 8 objects are carbon stars descending from ~1-2.5 Msun progenitors. 5 of the 13 objects are of lower mass, descending from M<1 Msun stars. Based on the dust mineralogy, we find that these 5 stars are surrounded by silicate dust, and thus failed to become carbon stars. The dust optical depth and the luminosity of the stars are correlated, owing to the faster evolutionary time-scale brighter stars, which makes the dusty layer to be closer to the central object. From our detailed analysis of the SEDs, we deduce that the dust currently observed around post-AGB stars was released after the onset of the central star contraction and an increase in the effective temperature to ~3500-4000 K.

astro-ph.SR↗