123 research outputs found
Self-Excited Pulsations and the Instability Strip of Long-Period Variables: the Transition from Small-Amplitude Red Giants to Semi-Regular Variables
No full textWe use one-dimensional hydrodynamic calculations combined with synthetic stellar population models of the Magellanic Clouds to study the onset of
self-excited pulsation in luminous red giants. By comparing the results with OGLE observations in the period-luminosity diagram we are able to link the transition from small-amplitude red giants to semi-regular variables with a shift from stochastic driving to self-excited pulsations. This is consistent with previous studies relating this transition with an increase in mass-loss rate, dust formation, and the appearance of long secondary periods. The luminosity and effective temperature at the onset of pulsation are found to depend on metallicity, hydrogen content, and the adopted mixing length parameter. This confirms the role of partial hydrogen ionization in driving the pulsation, supporting the idea of a heat mechanism similar to that of classical pulsators. We examine the impact of turbulent viscosity, and find clear evidence that it must be adjusted according to the stellar chemical and physical parameters to fully match observations. In order to improve the predictive power of pulsation models, the turbulent viscosity and the temperature scale of pulsating red giants must be jointly calibrated. This is critical for model-based studies of the period-luminosity relations of evolved stars and to exploit their potential as distance and age indicators, in particular given the sensitivity of the onset of pulsation to the envelope composition. The grid of models is made publicly available with a companion interpolation routine
Calibrating the thermally-pulsing asymptotic giant branch phase through resolved stellar populations in nearby galaxies
No full textMost of the physical processes driving the Thermally-Pulsing Asymptotic Giant Branch (TP-AGB) evolution are not yet fully understood and they need to be modelled with parametrised descriptions. The uncertainties of the models affect the interpretation of the spectrophotometric properties of galaxies up to high-redshift. In the framework of the ERC - STARKEY project, the aim of this Thesis is to constrain the uncertain parameters, i.e. third dredge-up and mass-loss, that still affect the TP-AGB models. To this purpose, I perform detailed simulations of AGB star populations in the Small Magellanic Cloud (SMC) based on robust measurements of the space-resolved star formation history as derived from the deep near-infrared photometry of the VISTA survey of the Magellanic Clouds. I compare the resulting synthetic catalogues with high-quality observations of resolved stellar populations in the infrared passbands of 2MASS and Spitzer. A large grid of TP-AGB evolutionary tracks is computed with several combinations of third dredge-up and mass-loss prescriptions. By requiring the models to reproduce the star counts and the luminosity functions of the observed Oxygen-, Carbon-rich and extreme-AGB stars, I put quantitative constraints on the efficiencies of the third dredge-up and mass-loss. The observed luminosity functions in all the available infrared photometric filters are successfully reproduced by two set of models, one with a relatively high mass-loss efficiency for Oxygen-rich stars and the second with a lower mass-loss efficiency and a lower efficiency of the third dredge-up for the more massive TP-AGB stars, i.e. initial masses larger than three solar masses. On the basis of the best-fitting model I present a complete characterisation of the AGB population in terms of stellar parameters, including the predicted mass-loss rates, initial masses, and Carbon-to-Oxygen ratio. I use the TP-AGB models calibrated in the SMC to model the population of Long Period Variables (LPVs) in the Large Magellanic Cloud as observed by Gaia. The remarkable agreement between models and observations allows us to guide the interpretation of a new observational diagram that is able to photometrically distinguish the evolutionary stages, the initial masses and the chemical type of these stars. In the context of the Large Synoptic Survey Telescope (LSST) science collaboration, I produce catalogues containing the synthetic photometry of the Magellanic Clouds in the Gaia and LSST filters. These catalogues, together with the all-sky simulations of the Milky Way will be made available to the community through the NOAO Data Lab to help defining the observing strategy of the LSST mini-surveys. In addition, I simulate samples of AGB stars in Local Group dwarf galaxies and find a general agreement with the data. However, to properly consider these objects in the TP-AGB models calibration, the simulations should be improved to take into account the crowding effects and the different areas used for the star formation histories derivation and the AGB stars identification. Finally, the products of this work, namely calibrated stellar isochrones and pulsation periods of LPVs, will be publicly available and ready to use for the interpretation of the data coming from present and future observing facilities. The calibrated TP-AGB models may be included in population synthesis models used to probe the integrated light of galaxies in the extragalactic Universe
Indigenous peoples and climate justice. A critical analysis of international human rights law and governance
No full textThis book provides a new interpretation of international law specifically dedicated to Indigenous peoples in the context of a climate justice approach. The book presents a critical analysis of past and current developments at the intersection of human rights and international environmental law and governance. The book suggests new ways forward and demonstrates the need for a paradigmatic shift that would enhance the meaningful participation of Indigenous peoples as fundamental actors in the conservation of biodiversity and in the fight against climate change. The book offers guidance on a number of critical intersecting and interdependent issues at the forefront of climate change law and policy – inside and outside of the UN climate change regime. The author suggests that the adoption of a critical perspective on international law is needed in order to highlight inherent structural and systemic issues of the international law regime which are all issues that ultimately impede the pursue of climate justice for Indigenous peoples.
Giada Giacomini is an experienced researcher in international human rights law, international environmental law, climate change law and policy, and with an interest in climate vulnerable communities. She holds a PhD in Public, Comparative and International Law. She specializes in climate justice, critical legal studies and non-anthropocentric law. Upon completion of her PhD studies, she completed an Internship at the Independent Redress Mechanism of the Green Climate Fund. She is currently involved in several research projects dealing with ecosocial work, environmental conservation and Indigenous peoples, and climate litigation
Non-radial modes in AGB stars
No full textThe success of asteroseismology in characterising G-K giants has motivated the extension of the same techniques to stars after the central He-burning and M-giants. The latter have been usually studied only as radial pulsators; the presence, however, of fine-structure in the period-luminosity diagram of red variables in the Magellanic Clouds could result from the presence of non-radial oscillations, offering the potential of observational indexes based on non-radial oscillations also for luminous red giants. We present here the results of a first approach aiming to identify the origin of the sub-ridges in the sequence A of the LMC red variables
Characterisation of long-period variables in the Magellanic Clouds
No full textVariability due to stellar pulsation on the Asymptotic Giant Branch (AGB) has a great potential for applications such as distance measurements, the study the evolution of stars and galaxies, and the estimate of global stellar parameters, as well as to constrain stellar evolutionary models. Given the importance of long-period variables (LPVs) in this sense, and given the lack of recent, updated sets of pulsation models, we computed an extended grid of pulsation models widely covering the space of AGB stellar parameters, including up-to-date opacities and accounting for the chemical evolution associated with third dredge-up events. We present the relevant properties of this grid and discuss the main results it allowed to obtain in terms of the interpretation of the observed properties of LPVs in the Large Magellanic Cloud (LMC)...
Long-Period Variables in the Large Magellanic Cloud
No full textWe present the first results from a new set of linear, radial, non-adiabatic pulsation models of long-period variables (LPVs), widely covering the space of stellar parameters corresponding to evolution along the Asymptotic Giant Branch (AGB). This coverage includes several values of metallicity and carbon-enhanced compositions consistent with the occurrence of repeated third dredge-up events. Updated atomic and molecular opacity data were included consistently with chemical composition in order to produce realistic pulsation properties of both O-rich and C-rich variables. We combined the pulsation models with a stellar population synthesis tool in order to study the population of LPVs in the Large Magellanic Cloud (LMC). We found the models to be reasonably good at reproducing the observed period-luminosity (PL) sequences, as well as the distribution of observed amplitudes. We provide a new interpretation of the PL sequences of LPVs that can bring into alignment previously discordant interpretations...
Modelling long-period variables - I. A new grid of O-rich and C-rich pulsation models
No full textWe present a new grid of non-adiabatic, linear pulsation models of long-period variables (LPVs), including periods and growth rates for radial modes from the fundamental to the fourth overtone. The models span a wide range in mass, luminosity, metallicity, C/O ratio, and helium abundance, effectively covering the whole thermally pulsing asymptotic giant branch (TP-AGB) evolution, and representing a significant update with respect to previous works. The main improvement is the inclusion of detailed atomic and molecular opacities, consistent with the models chemical mixture, that makes the present set of models the first to systematically account for variability in C-stars. We examine periods and growth rates in the models, and find that, while the fundamental mode is affected by the structure of the envelope, overtones are less sensitive to the interior and largely determined by the global properties. In the models, the frequency of the overtone with the largest degree of excitation is found to scale with the acoustic cut-off frequency at the stellar surface, a behaviour similar to that observed for the frequency of maximum oscillation power for solar-like oscillations in less evolved red giants. This allows us to provide a simple analytic prescription to predict the most-likely dominant mode as a function of stellar parameters. Best-fitting relations for periods are also provided. By applying results of pulsation models to evolutionary tracks, we present a general picture of the evolution of long-period variability during the TP-AGB, that we find consistent with observations. Models are made public through a dedicated web interface
Indigenous peoples and climate change. The Yanesha people’s case from a participatory justice perspective
No full textThis paper analyses the main results of the fieldwork conducted by the author for the purposes of determining the impacts of climate change in traditionally living Yanesha communities of the Palcazu, Peru. It gives an overview of the relationship between the Yanesha people and their sacred territory before delving into the data gathered during the fieldwork carried out in November 2018. It concludes by linking the Yanesha people’s case to the broader issue of climate justice, arguing that Indigenous peoples’ participatory rights should be at the centre of a fair and inclusive international and national climate governance regime that recognizes both their vulnerability and their role as agents of environmental conservation
A New Interpretation of the Period–Luminosity Sequences of Long-period Variables
No full textPeriod-luminosity (PL) sequences of long-period variables (LPVs) are commonly interpreted as different pulsation modes, but there is disagreement on the modal assignment. Here, we re-examine the observed PL sequences in the Large Magellanic Cloud, including the sequence of long secondary periods (LSPs), and their associated pulsation modes. First, we theoretically model the sequences using linear, radial, nonadiabatic pulsation models and a population synthesis model of the LMC red giants. Then, we use a semi-empirical approach to assign modes to the pulsation sequences by exploiting observed multi-mode pulsators. As a result of the combined approaches, we consistently find that sequences B and C′ both correspond to first overtone pulsation, although there are some fundamental mode pulsators at low luminosities on both sequences. The masses of these fundamental mode pulsators are larger at a given luminosity than the mass of the first overtone pulsators. These two sequences, B and C′, are separated by a small period interval in which large amplitude pulsation in a long secondary period (sequence D variability) occurs, meaning that the first overtone pulsation is not seen as the primary mode of pulsation. Observationally, this leads to the splitting of the first overtone pulsation sequence into the two observed sequences, B and C′. Our two independent examinations also show that sequences A′, A, and C correspond to third overtone, second overtone, and fundamental mode pulsation, respectively
Orientarsi tra le nuvole: cartografie, atlanti e pratiche mappanti nel racconto a fumetti
No full textA partire dalla recente nascita della ‘comic book geography’ (Dittmer 2014), il contributo intende proporre la ‘comic book cartography’ come un’ulteriore linea di ricerca volta ad esplorare le contaminazioni tra fumetto e cartografia.
L’approccio transdisciplinare proposto si fonda sull’intersezione tra geografia e analisi geocritica, tra ‘comics studies’ e teoria cartografica post-rappresentazionale. Attraverso una lettura ‘carto-centrata’ di alcuni casi di studio italiani e internazionali, il fumetto viene inteso come una mappa che coinvolge autore e lettore in una vera e propria pratica di orientamento.
[Abstract eng] Orientating among the balloons: maps, atlases and mapping practices in comic books
Starting from the recently emerged field of ‘comic book geography’ (Dittmer 2014), the article proposes ‘comic book cartography’ as a further research line to explore the intersections bewteen comics and cartography.
The proposed transdisciplinary approach is based on the encounter between geography and geocriticism, comics studies and post-representational theories in cartography. Through a ‘carto-centred’ reading of both Italian and international case studies, the comic book is interpreted as a map inolving author and reader in an orientation practice
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