Classical Cepheids: an updated theoretical scenario in the Gaia Era

Classical Cepheids are the most important primary distance indicators, and excellent tracers of relatively young and intermediate-age (from a few tens to a few hundreds of Myr) stellar populations. Indeed, they are well known to obey period-luminosity and period-luminosity-color relations which are traditionally used to calibrate secondary distance indicators and, hence, to estimate the Hubble constant. Stellar evolution predicts that the evolutionary phase of Classical Cepheids corresponds to the central helium-burning phase of massive and intermediate-mass stars. Stars in this evolutionary phase obey a mass-luminosity relation which is dependent on the chemical composition as well efficiency of some non canonical physical processes such as rotation, core convective overshooting, and mass loss efficiency during (mainly) the red giant branch stage. The mass-luminosity relation, adopted in the pulsational model computation, affects the shape of light curves and radial velocity curves, the coefficients of PLC and period-Wesenheit relations and, in turn, the Cepheid-based distance scale. The main focus of this PhD project is the modelling of radially pulsating stars, specifically, Classical Cepheids, through non linear hydrodynamical models. The primary goal is to constrain the extragalactic distance scale, and test the impact of the various ingredients entering the model computation, on the theoretical calibration of the Classical Cepheid distance scale. This PhD research was conducted, in the context of one of the most debated issues in current astrophysical literature: the Hubble Constant tension which is the discrepancy (at the level of 4.4 $\sigma$) between the value of the Hubble constant derived by Riess et al (2016, 2018) on the basis of Classical Cepheids and the Cosmic Microwave Background results. Indeed, the first part of this research is devoted to the evaluation of possible residual systematic errors on the cosmic Cepheid-based distance scale calibration and Hubble constant evaluation, in the context of one of the most debated issues in current astrophysical literature: the Hubble constant tension. The computation of updated and reliable pulsating stellar models for Classical Cepheids is the basis for the derivation of theoretical tools to constrain not only the distance but also intrinsic stellar properties such as the age and the mass of observed pulsators. Moreover, their comparison with valuable observational datasets, including that provided by the Gaia mission, allows us to test the predictive capability of current pulsation theory, and to trace the properties of Galactic and extra-galactic young and intermediate-age stellar populations. The pulsational framework developed in this PhD thesis is appropriate not only for typical Galactic Classical Cepheids, but also to chemical patterns characteristic of extra-galactic stellar systems such as the Magellanic Clouds. The pulsational scenario presented in this work is also important in order to constrain the physical and numerical assumptions adopted in current generation of stellar evolution models for massive and intermediate-mass stars. In this context, the final part of the PhD thesis is devoted to the use of Classical Cepheids as age indicators. By combining updated stellar evolution models with our updated pulsational scenario, new accurate Classical Cepheid period-age and the period-age-color relations in the Gaia filters are provided. The inferred period–age and period–age–color relations are applied to a selected sample of both fundamental and first overtone mode Cepheids observed with the Gaia spacecraft, and individual ages for the various adopted theoretical scenarios are derived. The thesis will end with a discussion on the first results of the chemical composition effect on the updated and homogeneous theoretical scenario for Classical Cepheids. Accurate metal-dependent relations which represent powerful tools for constraining stellar parameters of Classical Cepheid distances with simultaneous photometric and spectroscopic information in the Local Group of galaxies, are derived. The development of useful tools for constraining the individual distances and intrinsic stellar parameters in a variety of Galactic and extragalactic environments, involves a direct comparison between observed and predicted light curves. Therefore, in the era of Gaia astrometric measurements and in view of the next generation of the most advanced observational facilities, the work presented in the PhD thesis paves the way for future applications and comparisons between theory and observations

VITOM®-3D in lumbar disc herniation: Preliminary experience

Objectives: In neurosurgery, optimal illumination and surgeon view's magnification are essential to perform delicate and dangerous operations, such as aneurysms clipping and tumors removal. In this paper, the authors report their initial experience using a 3D-exoscope in spinal surgical procedures. Patients and methods: From January to July 2018 we performed 9 lumbar discectomies using a VITOM®-3D exoscope. We decided to examine these cases, with particular attention to the surgical timing and to the postoperative results in terms of pain control (VAS). Patient positioning, surgical instruments and approach technique were essentially the same used routinely in standard spinal disc herniation surgery.A "control" group composed of 9 cases was selected from patients who underwent a standard discectomy during the same period with the same neurosurgeons in order to obtain two homogeneous and comparable populations. Results: The length of operative time was measured and appeared to be longer in exoscope-assisted discectomies than in the traditional procedures (average 160 min vs 133 min); moreover the one-month postoperative VAS of the two groups were collected and compared but, after a statistical analysis, these differences resulted to be not statistically significant. No technical difficulties or surgical complications were noted. Conclusions: Despite the limited group of patients, the VITOM®-3D exoscope can be considered an interesting instrument in spinal procedures. It cannot permanently substitute the operating microscope but it shows interesting characteristics that make it a useful tool for surgeon's comfort and a versatile and relatively economic instrument in the neurosurgical armamentarium, as a part of a 3D working station composed by endoscope and exoscope. Keywords: Exoscope, Lumbar disc herniation, VITOM®-3D, Discectom

Updated theoretical Period-Age and Period-Age-Color relations for Galactic Classical Cepheids: an application to the Gaia DR2 sample

Updated evolutionary and pulsational model predictions are combined in order to interpret the properties of Galactic Classical Cepheids in the Gaia Data Release 2. In particular, the location of the instability strip boundaries and the analytical relations connecting pulsation periods to the intrinsic stellar parameters are combined with evolutionary tracks to derive reliable and accurate period-age, and the first theoretical period-age-color relations in the Gaia bands for a solar chemical abundance pattern ($Z$=$0.02$, $Y$=$0.28$). The adopted theoretical framework takes into account possible variations in the mass-luminosity relation for the core helium-burning stage as due to changes in the core convective overshooting and/or mass loss efficiency, as well as the impact on the instability strip boundaries due to different assumptions for superadiabatic convection efficiency. The inferred period-age and period-age-color relations are applied to a selected sample of both fundamental and first overtone Gaia Cepheids, and individual ages for the various adopted theoretical scenarios are derived. The retrieved age distributions confirm that a variation in the efficiency of superadiabatic convection in the pulsational model computations has a negligible effect, whereas a brighter Mass-Luminosity relation, as produced by mild overshooting, rotation or mass loss, implies significantly older age predictions. Moreover, older Cepheids are found at larger Galactocentric distances, while first overtone Cepheids are found to be systematically older than the fundamental ones. The comparison with independent age distribution analysis in literature supports the predictive capability of current theoretical framework.Comment: 14 pages, 11 figures, 8 tables, accepted for publication in MNRA

New insights into the use of Ultra Long Period Cepheids as cosmological standard candles

Ultra Long Period Cepheids (ULPs) are pulsating variable stars with a period longer than 80d and have been hypothesized to be the extension of the Classical Cepheids (CCs) at higher masses and luminosities. If confirmed as standard candles, their intrinsic luminosities, 1 to 3 mag brighter than typical CCs, would allow to reach the Hubble flow and, in turn, to determine the Hubble constant, H_0, in one step, avoiding the uncertainties associated with the calibration of primary and secondary indicators. To investigate the accuracy of ULPs as cosmological standard candles, we first collect all the ULPs known in the literature. The resulting sample includes 63 objects with a very large metallicity spread with 12 + log([O/H]) ranging from 7.2 to 9.2 dex. The analysis of their properties in the VI period-Wesenheit plane and in the color-magnitude diagram (CMD) supports the hypothesis that the ULPs are the extension of CCs at longer periods, higher masses and luminosities, even if, additional accurate and homogeneous data and a devoted theoretical scenario are needed to get firm conclusions. Finally, the three M31 ULPs, 8-0326, 8-1498 and H42, are investigated in more detail. For 8-1498 and H42, we cannot confirm their nature as ULPs, due to the inconsistency between their position in the CMD and the measured periods. For 8-0326, the light curve model fitting technique applied to the available time-series data allows us to constrain its intrinsic stellar parameters, distance and reddening.Comment: MNRAS - Accepted 2020 November 19. Received 2020 November 19; in original form 2020 July 15 - 9 pages and 8 figure

Gaia parallaxes versus updated model predictions

The Hubble constant tension between the value derived by Riess et al. (2016,2018) on the basis of Classical Cepheids distances and the Cosmic Microwave Background results is one of the most debated issues in current astrophysical literature. On the basis of an updated and extended set of nonlinear convective pulsation models, we are theoretically investigating the systematic effects on the Cepheid based extragalactic distance scale and the resulting Hubble constant. The predicted light curves and pulsation relations for both Galactic and Magellanic Cepheids, based on these new model sets, are tested on Gaia Data Release 2 (DR2) results. We find evidence of a Gaia DR2 parallax offset, consistent with independent results in the literature, but a general good agreement with the distances predicted by our theoretical pulsation scenario. We discuss the implications of our results and future perspectives, while waiting for Gaia Data Release 3

Trimethylamine-N-oxide (TMAO) as novel potential biomarker of early predictors of metabolic syndrome

There is a mechanistic link between the gut-derived metabolite trimethylamine-N-oxide (TMAO) and obesity-related diseases, suggesting that the TMAO pathway may also be linked to the pathogenesis of obesity. The Visceral Adiposity Index (VAI), a gender-specific indicator of adipose dysfunction, and the Fatty Liver Index (FLI), a predictor of non-alcoholic fatty liver disease (NAFLD), are early predictors of metabolic syndrome (MetS). In this cross-sectional observational study, we investigated TMAO levels in adults stratified according to Body Mass Index (BMI) and the association of TMAO with VAI and FLI. One hundred and thirty-seven adult subjects (59 males; 21⁻56 years) were enrolled. TMAO levels were detected using HPLC/MS analysis. Homeostatic Model Assessment of Insulin Resistance (HoMA-IR), VAI and FLI were included as cardio-metabolic indices. TMAO levels increased along with BMI and were positively associated with VAI and FLI, independently, on common potential covariates. The most sensitive and specific cut-offs for circulating levels of TMAO to predict the presence of NAFLD-FLI and MetS were ≥8.02 µM and ≥8.74 µM, respectively. These findings allow us to hypothesize a role of TMAO as an early biomarker of adipose dysfunction and NAFLD-FLI in all borderline conditions in which overt MetS is not present, and suggest that a specific cut-off of TMAO might help in identifying subjects at high risk of NAFLD

Predicted Masses of Galactic Cepheids in the Gaia Data Release 2

On the basis of recently computed nonlinear convective pulsation models of Galactic Cepheids, spanning wide ranges of input stellar parameters, we derive theoretical mass-dependent Period-Wesenheit relations in the Gaia bands, namely, G, G BP, and G BR, that are found to be almost independent of the assumed efficiency of superadiabatic convection. The application to a selected subsample of the Gaia Data Release 2 Galactic Cepheids database allows us to derive mass-dependent estimates of their individual distances. By imposing their match with the astrometric values inferred from Gaia, we are able to evaluate the individual mass of each pulsator. The inferred mass distribution is peaked around 5.6M o˙ and 5.4M o˙ for the F and FO pulsators, respectively. If the estimated Gaia parallax offset «Δϖ» mas is applied to Gaia parallaxes before imposing their coincidence with the theoretical ones, the inferred mass distribution is found to shift toward lower masses, namely, ∼5.2M o˙ and 5.1M o˙ for the F and FO pulsators, respectively. The comparison with independent evaluations of the stellar masses, for a subset of binary Cepheids in our sample, seems to support the predictive capability of the current theoretical scenario. By forcing the coincidence of our mass determinations with these literature values we derive an independent estimate of the mean offset to be applied to Gaia DR2 parallaxes, «Δϖ» = 0.053 ± 0.029 mas, slightly higher but in agreement within the errors with the Riess et al. value

Period-Age-Metallicity and Period-Age-Color-Metallicity relations for Classical Cepheids: an application to the Gaia EDR3 sample

Based on updated pulsation models for Classical Cepheids, computed for various assumptions about the metallicity and helium abundance, roughly representative of pulsators in the Small Magellanic Cloud ($Z$=$0.004$ and $Y$=$0.25$), Large Magellanic Cloud ($Z$=$0.008$ and $Y$=$0.25$), and M31 ($Z$=$0.03$ and $Y$=$0.28$), and self-consistent updated evolutionary predictions, we derived Period-Age and multi-band Period-Age-Color relations that also take into account variations in the Mass-Luminosity relation. These results, combined with those previously derived for Galactic Cepheids, were used to investigate the metallicity effect when using these variables as age indicators. In particular, we found that a variation in the metal abundance affects both the slope and the zero point of the above-mentioned relations. The new relations were applied to a sample of Gaia Early Data Release 3 Classical Cepheids. The retrieved distribution of the individual ages confirms that a brighter Mass-Luminosity relation produces older ages and that First Overtone pulsators are found to be concentrated towards older ages with respect to the Fundamental ones at a fixed Mass-Luminosity relation. Moreover, the inclusion of a metallicity term in the Period-Age and Period-Age-Color relations slightly modifies the predicted ages. In particular, the age distribution of the selected sample of Galactic Cepheids is found to be shifted towards slightly older values, when the F-mode canonical relations are considered, with respect to the case at a fixed solar chemical composition. A marginally opposite dependence can be found in the noncanonical F-mode and canonical FO-mode cases

The feasibility of three port endonasal, transorbital, and sublabial approach to the petroclival region: neurosurgical audit and multiportal anatomic quantitative investigation

Purpose: The petroclival region represents the "Achille's heel" for the neurosurgeons. Many ventral endoscopic routes to this region, mainly performed as isolated, have been described. The aim of the present study is to verify the feasibility of a modular, combined, multiportal approach to the petroclival region to overcome the limits of a single approach, in terms of exposure and working areas, brain retraction and manipulation of neurovascular structures. Methods: Four cadaver heads (8 sides) underwent endoscopic endonasal transclival, transorbital superior eyelid and contralateral sublabial transmaxillary-Caldwell-Luc approaches, to the petroclival region. CT scans were obtained before and after each approach to rigorously separate the contribution of each osteotomy and subsequentially to build a comprehensive 3D model of the progressively enlarged working area after each step. Results: The addition of the contralateral transmaxillary and transorbital corridors to the extended endoscopic endonasal transclival in a combined multiportal approach provides complementary paramedian trajectories to overcome the natural barrier represented by the parasellar and paraclival segments of the internal carotid artery, resulting in significantly greater area of exposure than a pure endonasal midline route (8,77 cm2 and 11,14 cm2 vs 4,68 cm2 and 5,83cm2, extradural and intradural, respectively). Conclusion: The use of different endoscopic "head-on" trajectories can be combined in a wider multiportal extended approach to improve the ventral route to the most inaccessible petroclival regions. Finally, by combining these approaches and reiterating the importance of multiportal strategy, we quantitatively demonstrate the possibility to reach "far away" paramedian petroclival targets while preserving the neurovascular structures

Impairment of the autophagic flux in astrocytes intoxicated by trimethyltin

Autophagy is generally considered a degradation pathway involved in many neurodegenerative processes. It is induced by different stress conditions such as starvation improving cell survival. Conversely, an excess activation of autophagy can drive cells to death by a sort of self-cannibalism. Toxic compounds such as arsenic and lead have been described to affect autophagy in a different way by blocking the correct execution of this pathway. Our previous results show that in hippocampal neuronal cultures the toxic compound trimethyltin (TMT) determines the formation of autophagic vacuoles and that autophagy inducers (lithum, rapamycin) improves neuronal survival (Fabrizi et al., 2012). The present data show that in astrocytes TMT similarly activates the autophagic pathway. Differently from neurons, in astrocytes autophagy inducers are ineffective in modifying cell survival. Moreover, the analysis of the LC3B conversion show in TMT-treated astrocytes a precocious block of the late stages of autophagy which ultimately leads to p62 accumulation, nrf-2 nuclear translocation and induction of ARE-responsive genes