Màster Oficial - Astrofísica, Física de Partícules i Cosmologia

URI permanent per a aquesta col·leccióhttps://hdl.handle.net/2445/95852

Treballs finals del Màster Oficial d'Astrofísica, Física de Partícules i Cosmologia de la Facultat de Física de la Universitat de Barcelona.

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Searching for open clusters with density-based clustering algorithms in Gaia era
(2017-06) Morvan, Mario; Jordi i Nebot, Carme; Julbe, Francesc
The imminent publication of the second Gaia data release (GDR2) scheduled for April2018 will mark the beginning of Big Data in Astrometry. On the one hand, this will require an adaptation of IT infrastructures and software to cope with the huge volumeand diversity of data. On the other hand, by making available the positions, velocities, and photometric measurements for more than one billion stars with unprecedentedaccuracy, it paves the way for Machine Learning and Data Mining techniques to be used in various areas of Galactic Astronomy. In this context, the search for Galactic open clusters is probably one of the fieldsof research which will benefit most from this new data. Indeed, owing to their history, these groups of stars naturally share many properties, and are thus very well suitedfor the use of clustering algorithms. This work investigates the potential of densitybased algorithms (kNN, DBSCAN, OPTICS) in the search for open clusters withina 5D astrometric space. It proposes a method to carefully set hyperparameters andapplies it to the analysis of Tycho-Gaia Astrometric Solution (TGAS) data, yielding 60 new open cluster candidates. This algorithm will eventually be scalable to GDR2 and other forthcoming large astrometric datasets.
Understanding the CubeSat faint object population with 2-meter class telescope observations
(2024-07) Lichaj, Aleksandra; Carrasco, José Manuel (Carrasco Martínez); Vilardell Sallés, Francesc
Context: The exponential growth in the number of CubeSats and very faint objects (VFOs) in orbit presents significant challenges for space traffic management and astronomical observations. Aims: This research aims to evaluate the feasibility of using 2-meter class telescopes for Space Surveillance and Tracking (SST) of CubeSats and VFOs. Methods: Observations were conducted using the Calar Alto (CAHA) 2.2m telescope and the 2m Liverpool Telescope (LT). For planning and pointings, Senplanner was used. Data reduction and astrometric analysis were performed using Gendared, and orbit determination was conducted with Sstod COTS. Results: The results demonstrate the capability of 2-meter class telescopes to detect and track CubeSats and VFOs. For instance, the LT showed residuals in right ascension ranging from -0.8 to 0.6 millidegrees, indicating high accuracy. The CAHA demonstrated reliable detection with residuals in right ascension from -2.2 to 3.1 millidegrees, showcasing the potential for improving SST with these telescopes. Conclusions: The study underscores the importance of larger telescopes in space traffic management, highlighting the need for longterm monitoring and consistent calibration. Future strategies should focus on improving observation techniques and expanding the network of large telescopes for comprehensive space surveillance.
Aspects of the Running Vacuum Model in Quantum Field Theory
(2024-06) González Fuentes, Alex; Solà Peracaula, Joan
The measured non-zero value of a Cosmological Constant (CC), Λ, has been the source of many theoretical discussions at the core of the concordance ΛCDM. The identification of the value of Λ/(8πG) in the gravitational action with the vacuum energy density (VED) leads to a huge discrepancy between theory and observations, due to ∼ m4 contributions (for any quantum field with mass m) and forces an absurd fine-tuning of the parameters. Running Vacuum Models (RVM), characterized by a dependence of the VED with even powers of the Hubble rate, offer a possible solution to this fine-tuning problem. Phenomenologically, even though the ΛCDM model has been an observational triumph for some time, precision measurements of CMB, BAO, SNIa, LSS and other sources currently threaten its validity because of tensions around the observational values of H0 and σ8. In this context, the RVM proposal predicts an evolving behaviour that might help alleviate these tensions. The aim of this work is to expose how the method of adiabatic renormalization in curved spacetime applied to a quantized scalar field non-minimally coupled to gravity reproduces the dynamical VED of the RVM, ρvac(H). We find how in the recent universe this VED deviates from the CC through a mild component ∼ νH2, with |ν| ≪ 1, accompanied with a logarithmic running of the gravitational coupling G(lnH). We also study the impact of quantum effects in the equation of state of the vacuum, which is no longer wvac = −1. Finally, we verify how the higher order O(H4) contributions may be responsible for a genuinely new mechanism of inflation in the early universe, called RVM-inflation
The phase-space distribution of present-day lenticular galaxies in relaxed galaxy clusters
(2024-06) Gort, Mathias; Solanes, José M. (José María); Tous Mayol, Josep Lluís
Aims. In this work we investigate the distribution of lenticular galaxies (S0s) in the projected phase space (PPS) of local, relaxed galaxy clusters. The aim is to shed further light on the still debated formation and evolutionary processes that shape S0s, by probing the properties of different subpopulations of actively star-forming (SF) and passive systems in which the heterogeneous class of lenticular galaxies can be divided. Methods. Optical and X-ray cluster identifications, along with tests to estimate the degree of virialization and substructure of galaxy associations, are used to select a sample of cluster regions with maximally relaxed cores. A PPS diagram is then constructed for this ensemble of clusters. Subsequently, a series of statistical tests are applied to the S0 member galaxies to compare the phase-space distributions of various S0 subpopulations and their times since cluster infall. Finally, line-of-sight velocity dispersion and specific star-formation rate (SSFR) radial profiles are constructed for both active and passive S0s. Results. Local, relaxed galaxy clusters contain ∼80% of passive S0s and ∼20% of star-forming S0s. The PPS distributions of these two classes of S0s are significantly different, with the passive systems concentrated closer to the cluster centers, and the active S0s being more abundant in the outer cluster regions.We find evidence that active S0s have been accreted more recently than passive S0s, with a gap in mean cluster infall time of about 1 Gyr. Despite these differences, the LOS velocity dispersions of these two subpopulations of S0s exhibit surprisingly similar projected radial profiles, consistent with radial infall. However, the SSFR radial profiles differ markedly: passive S0s show a flat profile up to three virial radii, while active lenticulars experience a sharp decline in SSFR between ∼2.5 and 1.5Rvir, followed by a more gradual decrease extending to the cluster center.
Interactions of Pions with the QCD String and Light Quark Mass Dependencies
(2023-07) Tomàs Valls, Sandra; Soto Riera, Joan
This thesis is centered around computing interactions between string excitations (quarkonium) and pion states, with the aim of understanding how observables are influenced by the light quark masses. The pion mass serves as a parameter to express this dependence on the quark mass. By incorporating the pion mass into the analysis, we investigate how the light quark masses affect the long-distance behavior of the quarkonium hyperfine potential. To achieve this, we employ Chiral Theory and Effective String Theory methodologies, deriving mathematical functions for some observables that depend on the length of the string, the pion mass, and the momentum of the external pions involved. This analysis provides insights into the corrections to the static potential due to the presence of the pion mass and the interplay between potential and pion mass (light quark mass). We find a dependence of the light quark masses on the string tension and successfully compute the elastic collision between a pion and the string ground state. Additionally, we calculate transition amplitudes from string excited states to the string ground state by the emission of two pions, covering a range from N = 1 up to one state of N = 3. These results are particularly relevant for studying transitions with pion emission between states of large principal quantum number in quarkonium and between hybrids and quarkonium states.
Stochastic inflation in the Constant Roll regime
(2023-10) Tuells Miralles, Daniel; Germani, Cristiano
We investigate the inhomogeneities generated during the inflationary epoch from the point of view of the stochastic formalism, which attempts to transform a problem of quantum fluctuations into a statistical one. The formalism, that we derive in the text, is based on the use of the Arnowitt-Deser-Misner (ADM) equations, which are convenient to describe inhomogeneities in the context of inflation, as well as gradient expansion, which works at zeroth order in spatial gradients but at all orders in the amplitudes of the fluctuations, and is therefore intended to capture non-perturbative effects. Finally, the perturbations are split into long- and short-wavelength modes, where the latter act as a stochastic noise for the former when crossing a certain scale. We demonstrate that the use of certain approximations in the derivation of this formalism, which are intended to make the system of stochastic differential equations (SDEs) Markovian and described with white noises, causes the method to become restricted to the reproduction of Linear Perturbation Theory (LPT). This framework, nonetheless, is still useful since it can be used as a test for the validity of the linear approximation, signalling the coming into play of non-perturbative effects. Specifically, we solve the system of SDEs numerically for the Constant Roll (CR) inflationary scenario, and show that this regime is in accordance with LPT.
The star formation history of the Milky Way disc from Gaia DR3 and BGM FASt
(2023-10) Alcázar i Julià, Marc del; Figueras Siñol, Francesca
We use the Besan¸con Galaxy Model FASt Approximate Simulations (BGM FASt) framework together with the Approximate Bayesian Computation (ABC) algorithm to derive the posterior probability distribution function of the parameters defining the initial mass function (IMF) and the star formation history (SFH) in the Solar neighbourhood. We propose new strategies to unveil the influence of some BGM Std model ingredients from the Poissonian distance metric and the posterior distribution of the ratio between pseudo-simulation and data in the Hess diagrams. Gaia DR3 up to G=13 and a set of consolidated executions of the BGM FASt + ABC code on a Cloud Environment, using both different Mother Simulations and priors, allow us to confirm the existence of the star formation burst in the Galactic disc 2-4 Gyr ago proposed by [Mor et al. 2019]. Furthermore, for the composite IMF, we obtain the slopes of α2 and α3 constrained to the range [1.7, 2.8] and [1.8, 2.4], respectively, in agreement with recent values from the literature. The wide range of values obtained for the total stellar surface mass density of the thin disc at the Solar neighbourhood, between 30-50 M⊙pc−2, demonstrates that, before concluding on the set of best ingredients for the Galactic stellar population model, we shall loop the process to fit again both, the Galactic potential as described in Robin et al. [2022], and the BGM FASt IMF and SFH parameters.
Structure and Kinematics of the Milky Way through A stars
(2022-06) Ardèvol Guillamón, Judith; Monguió i Montells, Maria
In the context of the Gaia era, the analysis of the structure and the kinematics of the Milky Way is an ongoing active field of research. Despite A-type stars have a relatively high intrinsic brightness and are moderately numerous as well as kinetically cold, they have been scarcely used as tracers of Galactic properties. This work opens a new window by studying a sample of A-type stars selected using the IGAPS photometric survey. It covers the Galactic plane within 30 ° ≤ l ≤ 215 ° and |b| ≤ 5 ° up to magnitude r ≤ 19 mag with around 3.5 million sources. Gaia EDR3 astrometry and proper motions, together with Gaia DR3 line-of-sight velocities, are used to analyse large-scale features of the Galactic disc. This sample allows to unveil structure and kinematic properties of the Milky Way disc at inter-mediate stellar ages. This includes a study of the obtained density distributions completeness, and a comparison between the b < 0° and b > 0° regions. Furthermore, the sample shows clear evidences of the Galactic warp in its vertical kinematics. Possible biases caused by interstellar extinction or by the usage of some kinematic estimators are examined to verify the results. The last goal of this study is to demonstrate the high potential of A-type stars as Galactic-scale tracers. They can be used to fill the age gap between the youngest OB stars and the old red giants, allowing to expand our knowledge about the evolution of the Galaxy.
Exploring new Physics with neutrino oscillation experiments
(2023-01) King, Gavin; González García, Ma. Concepción; Maltoni, Michele
Neutrino oscillation experiments set out to measure the differences in mass between the three neutrino flavors of the Standard Model of particle physics, and probe the elements of the lepton mixing (PMNS) matrix encoding the relationship between neutrino mass and interaction eigenstates. In this work, we use the results of these experiments for a different purpose: to place constraints on parameters which, if found to be nonzero, would indicate the existence of new physics (NP) beyond the Standard Model. Neutrino flavor oscillations arise from differences in mass between the three neutrino mass eigenstates, which enter the Hamiltonian in a term inversely proportional to the energy of the propagating neutrino. In the high-energy limit, all three flavors are effectively massless, the mass splittings vanish, and the oscillation wavelength grows too large for oscillations to be detectable. The NP effects we consider here result from introducing new terms into the Hamiltonian with a different energy dependence, either: • independent of energy, for the case of “vector-like” interactions, or • directly proportional to energy, for the case of “tensor-like” interactions. Thus, the new physics would manifest as a deviation from the expected suppression of neutrino flavor oscillations at high energy. If such new physics exists, and is detectable in current experiments, we would expect to observe a contribution to the oscillation wavelength which remains constant or grows with energy. The effects which may be represented within this generic framework include nonstandard interactions between neutrinos and matter, couplings with spacetime torsion fields, violations of Lorentz invariance or of the equivalence principle, and violations of CPT symmetry. The 2004 work of Gonzalez Garcia & Maltoni inferred limits on parameters encoding NP effects on two-flavor neutrino oscillations, using atmospheric neutrino data from Super-Kamiokande, along with data from the long baseline KEK to Kamioka (K2K) experiment. Here, we continue to use data from atmospheric and accelerator neutrino experiments to compute upper bounds on NP parameters. We begin by reproducing the results of [1] using updated data on atmospheric neutrino oscillations, incorporating the latest data from Super-Kamiokande, together with new data from DeepCore. We then consider the NP parameters of a model with three neutrino flavors, and calculate constraints using data from particle accelerators: Tokai to Kamioka (T2K), MINOS, and NOvA.
The multiplicity fraction in 324 open clusters from Gaia
(2022-06) Donada Oliu, Judit; Anders, Friedrich; Jordi i Nebot, Carme
This Master’s thesis is devoted to the estimation of the multiplicity fraction of high-mass ratio main-sequence multiple systems in Galactic open clusters. The main study consists in estimating in an automated fashion the unresolved multiplicity fraction through the location of the unresolved multiple systems in colour-magnitude diagrams, using Gaia DR2 and EDR3 data. Regarding this study, this thesis is a continuation of the previous preliminary work of my bachelor thesis (Donada, 2021), which explored the possibility of applying a Gaussian mixture model algorithm. Now we revise and improve this method, and also develop an alternative implementation using a Markov chain Monte Carlo method. The unresolved multiplicity fractions obtained through both methods are compared and characterized using custom realistic Gaia-like open cluster simulations performed with the Gaia Object Generator (Luri et al., 2014). Using these simulations we estimate the effective limiting mass ratio above which the Markov chain Monte Carlo method is able to detect the presence of a secondary companion (i.e., the high mass ratio range which our estimated unresolved multiplicity fraction comprises). The simulations further enable us to correct for the presence of resolved multiple systems. So, as a second part of the study, we estimate the total high mass ratio multiplicity fraction of the open clusters’ main sequences. Finally, we compare our results to the ones estimated through ASteCA (Automated Stellar Cluster Analysis package). The main result of this work is the largest homogeneous catalogue of multiplicity fractions in open clusters to date, including the unresolved and total multiplicity fractions of main-sequence systems with mass ratio larger than 0.6+0.05 −0.15 for 324 open clusters, estimated through the Markov chain Monte Carlo method. All studied open clusters are closer than 1.5 kpc, and have ages between 3.9 Myr and 4.3 Gyr. Their total multiplicity fractions, between 0.05 and 0.71, are found to increase with the mass of the primary star, display an overall decreasing trend with the open cluster age up until ages about 100-320 Myr, above which the trend increases; and do not depend on the open cluster position in the Galaxy.
Study of the dynamics of the local group using N-body cosmological simulations
(2022-07) Santander Garrote, Adrián; Miralda Escudé, Jordi
The Gaia satellite has been a revolution for the photometry and astrometry fields, providing a large amount of data (positions, parallaxes, proper motions) for the Local Group objects with a high accuracy never seen before. The goal of this work is to study the dynamics history of the Local Group galaxies from now to near to the time at the Big Bang using N-body simulations and taking advantage of the new proper motions measurements recently provided by Gaia. In order to obtain the 3D motion back in time of each Local Group galaxy, we have programmed an original N-body code in Fortran 90 which implements the Leapfrog algorithm which allows to solve numerically the equations of motion in classical mechanics for self-gravitating systems. We have done an exhaustive search in the literature to find the largest number of Local Group galaxies with updated measured proper motions and radial velocities. We have found a sample of 67 Local Group galaxies including the prominent members: the Milky Way, M31 and M33; and its dwarf satellites. We have transformed the right ascension, declination, heliocentric distance, line of sight velocity and proper motions obtained from the literature for all our sample of 67 galaxies into 6D phase-space coordinates in a Galactocentric reference system. We have run several N-body simulations with our code and our galaxy sample, and we have obtained the orbits back in time for 24 galaxies selected of the sample of 67 galaxies following two criteria: galaxies more distant than 50 kpc and with an error of their transverse velocity smaller than 50 km/s. Moreover, we have performed N-body simulations using only the Milky Way, M31 and M33 and we have compared the resulting orbits back in time. In addition, we have reviewed and described different important methods used to study some features of the dynamics of the Local Group, like the “Least Action Principle” or the “Timing Argument” which allows to estimate the mass of the Local Group
Detection Limits and Planet Occurrence Rate in the CARMENES Sample
(2020) Muñoz Sánchez, Juan Carlos; Morales Peralta, Juan Carlos; Jordi i Nebot, Carme
The CARMENES survey is monitoring more than 300 M-dwarf stars looking for exoplanets. Besides planet discoveries, the data it produces can also be used to estimate the statistics of planets around late-type stars. In this work, we aim at estimating the detection limits of the CARMENES survey, and the occurrence rate of Jupiter- and Neptune-like planets around M-dwarf stars. For this purpose, we use a sample with 324 stars for which values for the radial velocity as a function of time have been measured. We remove the signals produced by planets or intrinsic stellar variability to analyse the instrumental noise. In this noise we look for the minimum planetary mass that could be discovered, obtaining a lower detection limit. With this result we estimate the occurrence rate of M-dwarf planets at different minimum mass and orbital period ranges. For Jupiter- and Neptune-like planets we obtained an occurrence rate of ~ 1%.
Event horizon in a compact binary coalescence
(2020) Marín Pina, Daniel; Emparan García de Salazar, Roberto A.
In this work we introduce a general method, mostly analytical with relatively simple numerics, for obtaining the event horizon in a compact binary coalescence in which one of the components is a supermassive black hole with a mass much greater than its companion's. We not only reproduce previous literature but also go beyond it by not restricting the smaller object to be a black hole. We apply this procedure to study the mergers of the large black hole with: (a) a Schwarzschild black hole, (b) a charged black hole, (c) a charged singularity and (d) several models of neutron stars. For the uncharged black hole, we recover the exact results in the literature using a slightly different method for solving (numerically) the equations. For the charged case, our results agree qualitatively with the results for the event horizon in the neutral case. For the charged singularity, we find that a \hole" (not a black hole) appears in the event horizon, due to the repulsive gravitational effect of the singularity, which we argue is physically pathological. For neutron stars, we discover that the structure of the merger depends on their compactness: above a certain threshold, the supermassive black hole induces the formation of a black hole inside the star, thus making the merger to happen \inside-out" in a phenomenon that we have named \precursory collapse". Our study of the mergers between neutron stars and black holes has given rise to an article that we have submitted for publication
Identification and study of white dwarfs in J-PLUS Data Release 1
(2019) Cubero Pérez, Alicia; Carrasco Martínez, José Manuel
Context. The Javalambre Photometric Local Universe Survey, with 12 wide and narrow photometric bands, enable the reconstruction of spectral information that can be key to characterize the astronomical sources observed in the survey. Aims. Making use of the data published in the first data release we build a method to identify white dwarfs using photometry and parallaxes, to obtain a catalogue of WDs candidates. Methods. The classification is made using the random forest classifier, a machine learning algorithm. The first step is to select available sources to build training and test datasets. For this we use the available white dwarfs catalogue using information from Gaia DR2 and select the rest of objects (non-WDs) using sources outside the white dwarfs locus in the color-magnitude diagram. Different attempts of the classification model are done and discussed, until finding the best option incorporating progressively the information from the 12 J-PLUS passbands, 3 Gaia passbands, parallaxes from Gaia DR2 and their errors. Results. Parallax is the most important information for the classification of WDs, as well as the extreme bands, the bluest (u, J0378, J0395) and the reddest (i, J0861, z). The resulting candidates are well placed in many diagrams. The final catalogue contains 24634 white dwarf candidates present in J-PLUS first data release, with information from 15 different filters (12 from J-PLUS and 3 from Gaia), parallax and a probability evaluating how reliable the classification is. Conclusions. The classification model developed is be a very promising tool for the identification of white dwarfs using J-PLUS data, which will be improved in future data releases using data for all the northern celestial hemisphere.
Quantum tunneling during large field inflation
(2018-06) Wagner, Fabian László Konstantin; Notari, Alessio
Vacuum decays through quantum tunneling constitute a substantial part of inflationary theory If occurring at sufficiently close to the end of inflation, the corresponding implications on observables are manifold. In this study a family of large field potentials that inherit the possibility of primordial tunnelling events is analysed for a scalar inflaton; namely, they contain a positive metastable false vacuum and a true vacuum at the origin. Furthermore, the scalar field is considered in two different cases: minimally and non-minimally coupled to gravity. Thus, the tensor-to-scalar ratio, the scalar spectral index and the amplitude of scalar perturbations corresponding to these models are calculated and compared to CMB measurements. Furthermore, the process of tunnelling out of said false vacuum is described analytically as well as numerically. Finally, the consequences of tunelling in the treated descriptions of inflation are carried out also taking into account a scenario with cosmic friction by decay into abelian gauge-bosons
Spacetime thermodynamics and entanglement entropy: the Einstein field equations
(2019-09) Berenguer Mimó, Martí; Emparan García de Salazar, Roberto A.
In this master thesis, the posibility of a connection between spacetime dynamics (driven by the Einstein equations) and thermodynamics is discussed. Some known results, like the Raychaudhuri equation or the Unruh effect are reviewed in order to make the presentation self-contained. The Einstein equations are derived in two different ways from thermodynamic arguments. Some questions regarding the implications of this thermodynamic interpretation of spacetime are discussed as a conclusion of the thesis.
Spectral features of SO Galaxies in low- and high-density environments
(2018-06) Tous Mayol, Josep Lluís; Solanes, José M. (José María)
We aim to investigate the possibility that the formation pathway of lenticular galaxies depends on the environment, using their spectra. To this end, we estimate extinction-corrected local densities for all the galaxies with z . 0:1 in the Sloan Digital Sky Survey Data Release 12 within the limits of the Legacy Survey. The local densities are cross-matched with two morphological catalogues, one in which galaxies are visually classified by Nair and Abraham (2010), and one in which morphologies are assigned by a neural network based classification by Domínguez Sánchez et al. (2018), in order to compile subsets of lenticular galaxies in low- and high-density environments. We also compute the mean spectra representative of each one of the datasets by stacking the normalized, rest-frame shifted individual spectra. The efffects of inclination biases and morphological misclassifications in these composite spectra are discussed. We find that lenticular galaxies in low-density regions are generally bluer with enhanced emission lines in comparison with their high-density counterparts. The comparative also reveals a possible excess of automatically classified S0 galaxies in low-density regions with a relevant reservoir of ionized gas and star formation activity, which may indicate contamination from Sa. In visually classified galaxies the misclassification errors involve both Sa and E and tend to be more important in galaxies with intermediate (30o < i < 60o) inclinations
Neutrino oscillations and CP violation: analysis of NOvA data
(2016-06) Esteban Muñoz, Iván; González García, Ma. Concepción
This work represents the initiation of the author into research in the phenomenology of neutrino oscillations in the present experimental context. As a start, the formalism and most important aspects of neutrino oscillation phenomenology are reviewed in Chapter 1. Additionally, a brief overview of the different experiments that have led to the current global picture is presented, giving particular attention to accelerator neutrino experiments.The original part of this work focuses on the analysis of the results from the NOvA experiment, the latest in the neutrino oscillation experimental programme, with the aim of quantifying their impact in the present understanding of neutrino oscillation parameters.
Interpreting the b s u+u- anomaly in a heavy fermion model with Minimal Flavor Violation
(2017-06) Hormigos Feliu, Clara; Espriu, D. (Domènec)
Discrepancies with the Standard Model (SM) have recently been observed in b s transitions, which hint at a possible description in terms of four-fermion operators. In this work, we seek to describe the anomaly by introducing new heavy fermions. Firstly we build four-fermion operators out of SM and new fermions and introduce the hypothesis of Minimal Flavor Violation. Next we integrate out the heavy degrees of freedom to form operators of four SM fields and obtain an effective coupling constant.
Can the Tremaine - Weinberg method be used to determine the pattern speed of the bar and the spiral arms of the Milky Way?
(2016-06) Reina Campos, Marta; Figueras Siñol, Francesca; Antoja Castelltort, M. Teresa; Romero Gómez, Mercè; Roca Fàbrega, Santi
The pattern speed of the non-axisymmetric structures of the galactic disc is a key parameter to understand the dynamics in the MilkyWay. For neither the Galactic bar nor the spiral arms it is well determined. All previous determinations have large uncertainties associated avoiding to shed some light on the nature of these structures.

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