RT info:eu-repo/semantics/bachelorThesis
T1 Selección de objetos para los estudios de arqueología galáctica con el instrumento WEAVE
A1 García Jiménez, Francisco Javier
AB After the success of the Gaia mission launched in 2013, which was intended to beoperational for 5 years, providing measurements of parallax, positions and propermovements of stars and photometry; It was proposed to extend the mission time foranother 5 years due to its excellent results. But this time the Gaia probe will not bealone in its mission, it is intended to use the data that Gaia provides so that the WEAVEinstrument (WHT Enhanced Area Velocity Explorer), which is a multi-objectspectrograph that is intended to be incorporated into the William Herschel telescope(WHT) from the Roque De Los Muchachos observatory located on the island of LaPalma, supplement the measurements and information collected by Gaia and combine itwith its own measurements.Four studies related to galactic archeology are planned with the WEAVE instrument,but the one related to this TFG is a low-resolution study of the high latitude of theMilky Way. In this mapping, the WEAVE instrument carries out a study of stars foundin a certain latitude in the sky that corresponds to a field of view in which it is intendedto have a view of the galactic halo and the thick disk, but eliminating the thin disk.On its own, Gaia is capable of measuring parallax to determine distances, propermovements to determine tangential velocities and low-resolution spectroscopy, it alsohas a radial velocity spectrometer that provides chemical information about stars andradial velocities as its name suggests. However, for magnitude intervals between16 <~ G <~ 21 mag, the radial velocity spectrometer is unable to provide suchinformation and this is where the WEAVE instrument comes into play, complementingGaia with measurements of basic chemical information and radial velocitymeasurements (aside from the various studies that WEAVE plans to conduct, but notrelated to this work). However, the problem is that the WEAVE instrument is notcapable of performing measurements for as many stars as Gaia so it is necessary toselect exhaustively the elements to study.The following are chosen as targets for the study of the high latitude of the galaxy: redgiants, candidates for extremely metal-poor stars, stars from the blue horizontal branch,and stars that have deviated from the main sequence. Within WEAVE, a selection hasalready been made for the giants using magnitude and color, as well as parallax andself-motion information provided by Gaia's astrometric instrument to reject local redmain sequence stars from the selection.Although this selection is already good enough, there is still a fraction of unwanted starsthat fall within the range of quite considerable selected parameters, so it is thought thatthis selection can be optimized. That is precisely the objective of this study, to optimizethe selection of stars based on the data collected from Gaia's low-resolutionspectrometer.In order to do this, we are going to start with a synthetic spectra that are used tosimulate the data set that in advance will be supplied by Gaia's low resolutionspectrograph (which are not yet available), and in this way to create a model that allows us, using these already known data (those from the synthetic spectrum), to obtain arelationship that works to a greater or lesser extent, to later be able to differentiate thetwo types of stars that are measured in the mission, which we call giants and dwarfs,requiring only flow measurements.To do this, in the first place, the data from the synthetic spectra library are transformedso that these are expressed in the same way that the Gaia spectrometer will provide itsmeasurements, making transmitivity corrections, change of units, etc.To do this, we started from a code provided by the researcher Sergey Koposov, in whichthose transformations were carried out and from which the rest of the research andsubsequent analysis could be developed, once the code was analyzed, the main task wasunderstanding what was carried out in each part and looking if there was some kind ofoptimization flaw in it.In this study, the different properties of the set of synthetic "stars" provided by thesynthetic spectra are analyzed, such as the metallicity and effective temperaturedistributions with respect to flow and logarithm of surface gravity, the distribution offluxes with respect to wavelengths by means of percentiles or the various properties thathighlight the differences in magnitude, among several others.The most promising method has seemed to be one based on comparisons of the differentmagnitude differences at different frequencies between the two groups of stars, reachingquite promising results with a selection of stars with a low percentage of contamination,however, the results they have turned out to be perhaps insufficient by themselves,although in collaboration with the WEAVE distinction method it could be quite usefulas a purge in certain cases.Apart from this, several paths have been followed which, if they have not all reachedthe desired method, have provided us with very interesting information on thecharacteristics of the star distributions and are worthy of study and comment.From here on, the introduction section provides a scientific context about the project, aswell as its motivation and some relevant data, the objectives section talks about thepurpose of the work itself and what it is intended to obtain ; In the methodology section,it is explained how, starting from a series of synthetic data, we are going to operate withthem to arrange them in a way that we can use them to investigate as if they were realmeasurements. In the different analyzes that are proposed, we will study the differentmethods followed and briefly discuss the results obtained with each of them, andfinally, in the conclusions section, the information obtained and the result itself of thework carried out are discussed above all, finally several reasons are discussed why itwould be interesting to continue investigating the method used.
YR 2020
FD 2020
LK http://riull.ull.es/xmlui/handle/915/21546
UL http://riull.ull.es/xmlui/handle/915/21546
LA es
DS Repositorio institucional de la Universidad de La Laguna
RD 26-nov-2024