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Al-Edhari, Ali Jaber. "Complex organic molecules in solar-type star forming regions." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY048/document.
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Le but de la présente thèse est l'étude de la compléxité moléculaire dans les régions de formation stellaires. Cette thèse s'axe sur deux classes de molécule aux caractéristiques prébiotiques : les molécules organiques complexes et les cyanopolyynes.Dans ce contexte, j'ai analysé des données d'un seul échantillon de relevés spec- traux en exploitant des codes de transfert radiatif à l'équilibre thermodynamique local (LTE) et/ou non-LTE pour deux sources : une proto-étoile de type solaire dans un environnement calme (IRAS 16293-2422) et un proto-ama constitué de proto-étoile de type solaire (OMC2-FIR4).L'objectif est de trouver des similar- ités et des différences entre ces deux cas.J'ai utilisé des données issu de deux relevés spectraux : TIMASSS (The IRAS16293-2422 Millimeter And Submilimeter Spectral Survey) réalisés en 2011 (Caux et al. 2011), et ASAI(Astrochemical Surveys At IRAM) réalisés pen- dant la période 2013-2015 (eg Lopez-Sepulcre et al.2015). J'ai extrais les lignes (identification et intensité intégrée) en utilisant le paquet disponible publique- ment : CASSIS (Centre d'Analyse Scientifique de Spectres Infrarouges et Sub- millimetrique). Pour finir, j'ai utilisé le paquet GRAPES (GRenoble Analysis of Protostellar Envelope Spectral) afin de modéliser la distribution spectrale énergétique de ligne (SLED) des molécules détectées, mais aussi afin d'estimer leurs abondances à travers l'envelope de IRAS16293 et du coeur chaud OMC2- FIR4.Les principaux résultats de la thèse sont :1. Le premier recensement complet des molecules organiques complexes (COMs) dans IRAS162932. La première détéction de COMs dans l'enveloppe froide d'une proto-étoile de type solaire (IRAS16293-2422) supportant l'idée qu'un méchanisme de formation, relativement efficace pour les COMs détectées, doit exister en phase gazeuse froide.3. La découverte d'une fine corrélation entre le diméthyle-éther (DME) et le méthyle-formate (MF) suggère une relation mère fille entre ces deux espèces.4. La detection de formamide, espèce avec un très fort potentiel prébiotique, dans plusieurs protoétoiles incluant IRAS16293-2422 et OMC2-FIR4.5. Le recensement complet des cyanopolyynes dans IRAS16293 et OMC2- FIR4 avec la détection de HC3N, HC5N, DC3N et pour OMC2-FIR4: le C13 isotopologue du HC3N cyanopolyynes.Ces résultats sont le sujet principal de deux publications (Jaber et al.2014, ApJ; Lopez-Sepulcre, Jaber et al.2015,MNRAS), un article accepté (Jaber et al., A & A) et un article à soumettre (Jaber et al. A & A)<br>The present PhD thesis goal is the study of the molecular complexity in solar type star forming regions. It specifically focuses on two classes of molecules with a pre-biotic value, the complex organic molecules and the cyanopolyynes.At this scope, I analyzed data from single-dish spectral surveys by means of non-LTE or/and non-LTE radiative transfer codes in two sources, a solar type protostar in an isolated and quiet environment (IRAS16293-2422) and a proto-cluster of solar type protostars (OMC2-FIR4). The goal is to find similarities and differences between these two cases.I used data from two spectra surveys: TIMASSS (The IRAS16293-2422 Millimeter And Submillimeter Spectral Survey), which has been carried out in 2011 (Caux et al. 2011), and ASAI (Astrochemical Surveys At IRAM), which has been carried out in 2013-2015 (e.g. Lopez-Sepulcre et al. 2015).I extracted the lines (identification and integrated intensity) by means of the publicly available package CASSIS (Centre dAnalyse Scientifique de Spectres Infrarouges et Submillimtriques).Finally, I used the package GRAPES (GRenoble Analysis of Protostellar Envelope Spectra) to model the Spectral Line Energy Distribution (SLED) of the detected molecules, and to estimate their abundance across the envelope and hot corino of IRAS16293-2422 and OMC2-FIR4, respectively.The major results of the thesis are:1) The first full census of complex organic molecules (COMs) in IRAS16293-2422;2) The first detection of COMs in the cold envelope of a solar type protostar (IRAS16293-2422), supporting the idea that a relatively efficient formation mechanism for the detected COMs must exist in the cold gas phase;3) The discovery of a tight correlation between the dimethyl ether (DME) and methyl format (MF), suggesting a mother-daughter relationship;4) The detection of formamide, a species with a very high pre-biotic value, in several protostars, included IRAS16293-2422 and OMC2-FIR4;5) The full census of the cyanopolyynes in IRAS16293-2422 and OMC2-FIR4, with the detection of HC3N and HC5N, DC3N and, for OMC2-FIR4, the 13C isotopologue of HC3N cyanopolyynes.These results are the focus of two published articles (Jaber et al. 2014, ApJ; Lopez-Sepulcre, Jaber et al. 2015, MNRAS), one accepted article (Jaber et al., A&A) and a final article to be submitted (Jaber et al., A&A)
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Mengel, Matthew Wayne. "The active young solar-type star HR 1817 (=HD 35850)." University of Southern Queensland, Faculty of Sciences, 2005. http://eprints.usq.edu.au/archive/00001474/.
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The active F dwarf HR 1817 represents the upper temperature extreme of what are broadly termed solar-type stars - stars which have the same internal structure as the Sun, albeit in this case with a much smaller convective zone. To date, studies of the active surface features and magnetic fields of solar-type stars have been restricted to G and K dwarfs. This thesis investigates the surface and magnetic features of HR 1817 using the techniques of Doppler and Zeeman Doppler Imaging, resulting in tomographic maps of the stellar surface and magnetic field. Cooler stars than HR 1817 exhibit large polar spots, and while HR 1817 also exhibits a polar spot, it is not nearly as large as those usually seen. The lower-latitude surface features of HR 1817 are weak but well defined and cover a relatively small area of the stellar surface. Total spot coverage is relatively small (~ 1.7 - 2 per cent). Zeeman Doppler Imaging reveals that HR 1817 exhibits a richly-detailed, though weak magnetic topography. A ring of azimuthal field appears around the pole, while the radial field exhibits many well-defined and distinct bipolar mid-latitude magnetic features, perhaps indicating a more dominant interface dynamo as opposed to the posited distributed dynamo of cooler active dwarfs. Finally, a differential rotation measurement of the star indicates an extremely large rotational shear. Values for the equatorial rotation and rotational shear of 6.494 +/- 0.010 rad/d and 0.256 +/- 0.017 rad/d respectively are found. This equatorial rotation is equivalent to a rotational period for HR 1817 of ~ 0.98 days. The very high rotational shear of 0.256 rad/d is fast enough for the equator to lap the pole in approximately 23 days.
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Namekata, Kousuke. "Observational Studies of Extreme Stellar Magnetic Activities: Spots, Flares, and Mass Ejections." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263473.
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Fuentes, Pineda Rosinda. "Triphenylamine-based hole transport materials for perovskite solar cells." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31410.
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The rapid development in perovskite solar cells (PSC) has generated a tremendous interest in the photovoltaic community. The power conversion efficiency (PCE) of these devices has increased from 3.8% in 2009 to a recent certified efficiency of over 20% which is mainly the product of the remarkable properties of the perovskite absorber material. One of the most important advances occurred with the replacement of the liquid electrolyte with a solid state hole conductor which enhanced PCE values and improved the device stability. Spiro-OMeTAD (2,2',7,7'-tetrakis(N,N'-di-p-methoxyphenylamine)- 9,9'-spirobifluorene) is the most common hole transport material in perovskite solar cells. Nevertheless, the poor conductivity, low charge transport and expensive synthetic procedure and purification have limited its commercialisation. Triphenylamines (TPA) like Spiro-OMeTAD are commonly employed due to the easy oxidation of the nitrogen centre and good charge transport. Other triarylamines have similar properties to Spiro-OMeTAD but are easier to synthesise. The aim of this doctoral thesis is to investigate different types of hole transport materials in perovskite solar cells. Three different series of triphenylamine-based HTM were designed, synthesised, characterised and studied their function in perovskite solar cells. A series of five diacetylide-triphenylamine (DATPA) derivatives (Chapter 3) with different alkyl chain length in the para position was successfully synthesised through a five step synthesis procedure. A range of characterisation techniques was carried out on the molecules including; optical, electrochemical, thermal and computational methods. The results show that the new HTMs have desirable optical and electrochemical properties, with absorption in the UV, a reversible redox property and a suitable highest occupied molecular orbital (HOMO) energy level for hole transport. Perovskite solar cell device performances were studied and discussed in detail. This project studied the effect of varying the alkyl chain length on structurally similar triarylamine-based hole transport materials on their thermal, optical, electrochemical and charge transport properties as well as their molecular packing and solar cell parameters, thus providing insightful information on the design of hole transport materials in the future. The methoxy derivative showed the best semiconductive properties with the highest charge mobility, better interfacial charge transfer properties and highest PCE value (5.63%). The use of p-type semiconducting polymers are advantageous over small molecules because of their simple deposition, low cost and reproducibility. Styrenic triarylamines (Chapter 4) were prepared by the Hartwig-Buchwald coupling followed by their radical polymerization. All monomers and polymers were fully characterised through electrochemical, spectroscopic and computational techniques showing suitable HOMO energy levels and desirable optoelectrochemical properties. The properties and performance of these monomers and polymers as HTMs in perovskite solar cells were compared in terms of their structure. Despite the lower efficiencies, the polymers showed superior reproducibility on each of the device parameters in comparison with the monomers and spiro-OMeTAD. Finally, star-shaped structures combine the advantages of both small molecules, like well-defined structures and physical properties, and polymers such as good thermal stability. Two star-shaped triarylamine-based molecules (Chapter 5) were synthesised, fully characterised and their function as hole-transport materials in perovskite solar cells studied. These materials afford a PCE of 13.63% and high reproducibility and device stability. In total this work provided three series of triarylamine-based hole transport materials for perovskite solar cells application and enabled a comparison of the pros and cons of different design structures: small-molecule, polymeric and star-shaped.
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Benbakoura, Mansour. "Evolution des étoiles de faible masse en interaction : observations multi-techniques et modélisation des systèmes multiples." Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7027.
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Cette thèse est consacrée à l'étude des étoiles de faible masse ayant dans leur environnement proche d'autres étoiles ou des planètes. Nous nous sommes concentrés sur l'influence des interactions avec ces compagnons sur l'évolution stellaire ainsi que leurs conséquences observables.Dans la première partie, nous présentons le modèle d'évolution des systèmes étoile–planète que nous avons développé au cours de cette thèse, nommé ESPEM (Évolution des Systèmes Planétaires Et Magnétisme). Ce modèle prend en compte de façon ab-initio des effets du vent stellaire magnétisé et de la dissipation de marée sur la rotation stellaire et l'orbite planétaire, simultanément avec l'évolution structurelle de l'étoile. Premièrement, nous l'utilisons pour étudier l'évolution séculaire de la rotation des étoiles hôtes de systèmes planétaires et montrons notamment que cette évolution peut être significativement différente de celle des étoiles isolées. Ensuite, nous examinons les prédictions de ce modèle concernant l'architecture orbitale des systèmes étoile–planète. Nos résultats suggèrent une interprétation aux distributions de périodes orbitales et de de rotation stellaire observées.Dans la deuxième partie, nous montrons en quoi l'observation d'étoiles binaires évoluées permet de tester les théories astrophysiques, notamment l'astérosismologie et l'interaction de marée. Dans un premier temps, nous présentons les résultats d'un programme d'observations que nous avons mené pendant plus de deux ans et qui nous a permis de caractériser 16 systèmes binaires à éclipses. Ensuite, nous comparons ces résultats avec ceux que nous avons obtenus en analysant cet échantillon à l'aide d'outils astérosismiques dans le but de vérifier l'exactitude de ces derniers. Enfin, en élargissant l'échantillon étudié à 30 autres étoiles binaires évoluées, nous testons la théorie de l'évolution de marée. Ceci nous permet à la fois de valider la théorie et de comprendre l'évolution des systèmes observés dans ce travail.Ce travail met en avant deux aspects de la spécificité des systèmes multiples. Premièrement, il montre en quoi l'évolution des étoiles est impactée par la présence d'un compagnon stellaire ou planétaire. Deuxièmement, il met en avant l'intérêt des étoiles binaires pour tester les théories astrophysiques et renforce la compréhension actuelle de l'évolution stellaire<br>This thesis is devoted to the study of low-mass stars having other stars or planets in their immediate environment. We focused on the influence of interactions with these companions on stellar evolution and their observable consequences.In the first part, we present the model of evolution of star–planet systems that we developed during this thesis, called ESPEM (French acronym for Evolution of Planetary Systems and Magnetism). This model incorporates ab-initio prescriptions to quantify the effects of magnetized stellar wind and tidal dissipation on stellar rotation and planetary orbit, simultaneously with the star's structural evolution. First, we use it to study the secular evolution of the rotation of planet-host stars and show that this evolution can be significantly different from that of isolated stars. Next, we examine the predictions of this model regarding the orbital architecture of star–planet systems. Our results suggest an interpretation to the observed distributions of orbital and stellar rotation periods.In the second part of the manuscript, we show how the observation of advanced binary stars allows us to test astrophysical theories, in particular asteroseismology and tidal interaction. First, we present the results of an observation program that we conducted for more than two years and that allowed us to characterize 16 eclipsing binary systems. Then, we compare these results with those obtained by analyzing this sample using asteroseismic tools to verify the accuracy of the latter. Finally, by extending the studied sample to 30 other advanced binary stars including an evolved primary, we test the theory of tidal evolution. This allows us both to validate the theory and to understand the evolution of the systems observed in this work.This work highlights two aspects of the specificity of multiple systems. First, it shows how the evolution of stars is affected by the presence of a stellar or planetary companion. Second, it emphasizes the interest of binary stars in testing astrophysical theories and reinforces the current understanding of stellar evolution
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Hawkins, Keith A. "Searching for Solar-Type Hypervelocity Stars." Ohio University Honors Tutorial College / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1367583430.
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Notsu, Yuta. "Observational studies on solar-type superflare stars." Kyoto University, 2019. http://hdl.handle.net/2433/242613.
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Corporon, Patrice. "La binarité des étoiles Ae/Be de Herbig vue par l'optique adaptative et la spectroscopie : une étude du système triple TY CrA." Phd thesis, Université Joseph Fourier (Grenoble), 1998. http://tel.archives-ouvertes.fr/tel-00724469.
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Les étoiles multiples sont nombreuses, tant parmi les objets jeunes de faible masse, les étoiles T Tauri, que parmi les astres de la Séquence Principale (SP). En ce qui concerne les étoiles jeunes de masse intermédiaire, les étoiles Ae/Be de Herbig (HAeBe), le statut de la binarité est peu connu. Nous avons réalisé une recherche systématique de binaires HAeBe en utilisant deux techniques: l'imagerie à haute résolution angulaire avec la méthode de l'Optique Adaptative d'une part, et la spectroscopie visible à haute résolution d'autre part. Ces techniques complémentaires nous ont permis d'identifier plus d'une vingtaine de nouvelles étoiles binaires; la fréquence de binarité déduite est d'au moins 50 %, voir supérieure à cause des biais observationnels discutés dans la thèse. Pour la première fois, les types spectraux des compagnons ont pu être déterminés dans une vingtaine de systèmes visuels. Les implications de nos observations pour la présence de disques de poussières et la détection d'émission X dans les étoiles HAeBe sont présentées. Les contraintes apportées pour les théories de formation des binaires sont discutées. Une partie importante de la thèse est consacrée à une étude approfondie de l'étoile triple TY CrA, l'unique système spectroscopique hiérarchisé parmi les étoiles Ae/Be de Herbig. Après une description complète des paramètres orbitaux et stellaires, la modélisation de la dynamique de cet objet particulier a été réalisée. Nos calculs théoriques montrent que la cohésion du système est assurée par effet de marée à l'oeuvre dans la binaire à éclipse centrale. L'environnement circumstellaire de TY CrA a également été étudié à partir d'observations spectroscopiques infrarouges avec le télescope spatial ISO et à partir d'images en Optique Adaptative dans le proche infrarouge.
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Hamilton, Devon. "Observational signatures of convection in solar type stars." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58914.pdf.
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Mamajek, Eric E. "Identification and characterization of young, nearby, solar-type stars." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280625.
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Post-T Tauri stars (PTTSs) are low-mass, pre-MS stars which have ceased accreting, and are not necessarily near star-forming molecular clouds. Historically, they have been difficult to identify due to their benign spectroscopic signatures. With recent all-sky X-ray surveys and proper motion catalogs, it is now possible to find PTTSs in large numbers. The nearest PTTSs will be important targets for future imaging surveys characterizing dust disks and planetary systems around young solar analogs. The goal of this work is to systematically identify samples of PTTSs, investigate the evolution of circumstellar disks, to infer the fossil star-formation history of molecular clouds, and to estimate kinematic distances to young stars lacking trigonometric parallaxes. We present the results of a spectroscopic survey which identified 110 PTTS members of the nearest OB association (Sco-Cen). We find that 2/3rds of the low-mass star-formation in each OB subgroup occurred in <5 Myr, and that only ∼1% of solar-type stars with mean age ∼13 Myr shows signs of accretion from a circumstellar disk. In order to assess how long circumstellar material is detectable around PTTSs, we conducted a 10 μm imaging survey of post-T Tauri members of the ∼30-Myr-old Tuc-Hor association. The goal was to find evidence of either remnant accretion disks or dusty debris disks with orbital radii of ≲10 AU. Combined with data from other surveys, we conclude that mid-IR emission from warm dust grains in the terrestrial planet zones around young stars become undetectable compared to the stellar photosphere for nearly all stars by age ∼20 Myr. Lastly, we present a technique for calculating distances isolated young field stars that currently lack trigonometric parallax measurements. The technique is a generalization of the classical cluster parallax method, but can handle anisotropic velocity dispersions and non-zero Oort parameters. Distances and isochronal ages are estimated for a subsample of PTTSs included in the Formation and Evolution of Planetary Systems (FEPS) Spitzer Space Telescope (SST) Legacy Science program. The techniques developed in this thesis will allow one to efficiently conduct a systematic survey to identify the nearest, youngest stars to the Sun using existing databases.
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Sousa, Sérgio António Gonçalves de. "Spectroscopic, interferometric and seismic study of solar-type stars." Tese, Porto : [s.n.], 2009. http://catalogo.up.pt/F?func=find-b&local_base=FCB01&find_code=SYS&request=000103827.
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Sousa, Sérgio António Gonçalves de. "Spectroscopic, interferometric and seismic study of solar-type stars." Doctoral thesis, Porto : [s.n.], 2009. http://hdl.handle.net/10216/64296.
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Raghavan, Deepak. "A Survey of Stellar Families: Multiplicity of Solar-type Stars." unrestricted, 2009. http://etd.gsu.edu/theses/available/etd-04212009-165714/.
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Thesis (Ph. D.)--Georgia State University, 2009.<br>Title from file title page. Harold A. McAlister, committee chair; Russel J. White, Brian D. Mason, Douglas R. Gies, David W. Latham, A.G. Unil Perera, Todd J. Henry, committee members. Description based on contents viewed Aug. 24, 2009. Includes bibliographical references (p. 391-410).
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Önehag, Anna. "Solar Type Stars as Calibrators : A Photometric and Spectroscopic Study on the Atmospheric Properties of Late-type Stars." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-158709.
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Detailed knowledge of solar-type stars is essential in the understanding of the evolutionary past, presence and future of the Sun as well as the formation of its planetary system. Moreover, solar-type stars are of key significance for the study of the evolution of the Galaxy. The ages of solar-type stars map the full galactic evolution. Their surface layers are well mixed and just little affected by the interior nuclear processes. They may therefore be used as samples of the gas from which the stars were once formed. Models of stellar atmospheres are used to derive fundamental stellar quantities such as chemical composition, effective temperature, surface gravity, age and rotation. It is therefore also important to investigate the progress and shortcomings of the atmospheric models and the reliability of calibrations based upon these. In this thesis we explore the potential of synthetic uvbyHβ colours for deriving atmospheric parameters. The theoretical colours are derived using high-resolution synthetic spectra based on 1D atmosphere models of late-type stars. Furthermore, possible applications of the established synthetic colours on globular stellar clusters are tested. Observations of solar-type stars have demonstrated the existence of stars very similar to the Sun, so-called solar twins. A detailed chemical analysis of these stars, however, shows that most solar-twins are systematically richer, as compared with the Sun, in refractory elements such as Fe, Ni and Al, relative to volatile elements like C, N and O. This chemical abundance pattern has been suggested to be related to the formation of planets or the birth environment of the respective star. In this thesis we present a high-accuracy study on a solar-twin star in the old open cluster M67. We find that the star is very similar to the Sun when comparing their atmospheric parameters, effective temperature, surface gravity and metallicity. Remarkably enough, unlike most solar twins observed in the solar vicinity, the cluster twin shows the same refractory to volatile pattern as the Sun.The reason for this similarity is still unknown but further observations of the cluster will help to clarify the matter. M dwarfs constitute a large fraction of the detectable baryonic matter. In spite of this, detailed knowledge on the numerous neighbouring low-mass stars is still not available. The presence of strong molecular features in the spectra, and incomplete line lists for the corresponding molecules have made metallicity determinations of M dwarfs difficult. Furthermore, the faint M dwarfs require long exposure times for a signal-to-noise ratio sufficient for detailed spectroscopic abundance analysis. In this thesis we present a high resolution spectroscopic study of early-type M dwarfs in the infrared. The lack of prominent molecular bands in parts of the infrared J-band (1100--1400 nm) allows a precise continuum placement. Furthermore, we verify the adequacy of using the model atmospheres for abundance determination by observing a set of binary systems with a solar-type primary and an M dwarf companion. We present a reliable zero-point for the metallicity scale of early-type M dwarfs and verify the reliability of spectroscopic abundance analyses in the infrared.
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Hutcheon, Richard J. "Fundamental properties of solar-type eclipsing binary stars, and kinematic biases of exoplanet host stars." Thesis, Keele University, 2015. http://eprints.keele.ac.uk/1202/.
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This thesis is in three parts: 1) a kinematical study of exoplanet host stars, 2) a study of the detached eclipsing binary V1094 Tau and 3) and observations of other eclipsing binaries. Part I investigates kinematical biases between two methods of detecting exoplanets; the ground based transit and radial velocity methods. Distances of the host stars from each method lie in almost non-overlapping groups. Samples of host stars from each group are selected. They are compared by means of matching comparison samples of stars not known to have exoplanets. The detection methods are found to introduce a negligible bias into the metallicities of the host stars but the ground based transit method introduces a median age bias of about -2 Gyr. Part II describes a detailed analysis of V1094 Tau. Spectra were analysed by the cross-correlation software TODCOR to obtain radial velocities, and uvby photometric light curves were analysed by the JKTEBOP software. Part III describes an observing run at SAAO Sutherland, aimed to survey detached eclipsing binaries. Light curves and two spectra each from two binaries were analysed, to determine masses and radii to the 10 to 30% level. This is a proof in principle that runs on 2-metre class telescopes can identify targets for detailed follow-up observations.
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Currie, Thayne, Olivier Guyon, Motohide Tamura, et al. "Subaru/SCExAO First-light Direct Imaging of a Young Debris Disk around HD 36546." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624379.
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We present H-band scattered light imaging of a bright debris disk around the A0 star HD 36546 obtained from the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system with data recorded by the HiCIAO camera using the vector vortex coronagraph. SCExAO traces the disk from r similar to 0."3 to r similar to 1" (34-114 au). The disk is oriented in a near east-west direction (PA similar to 75 degrees), is inclined by i similar to 70 degrees-75 degrees, and is strongly forward-scattering (g > 0.5). It is an extended disk rather than a sharp ring; a second, diffuse dust population extends from the disk's eastern side. While HD 36546 intrinsic properties are consistent with a wide age range (t similar to 1-250 Myr), its kinematics and analysis of coeval stars suggest a young age (3-10 Myr) and a possible connection to Taurus-Auriga's star formation history. SCExAO's planet-to-star contrast ratios are comparable to the first-light Gemini Planet Imager contrasts; for an age of 10 Myr, we rule out planets with masses comparable to HR 8799 b beyond a projected separation of 23 au. A massive icy planetesimal disk or an unseen super-Jovian planet at r > 20 au may explain the disk's visibility. The HD 36546 debris disk may be the youngest debris disk yet imaged, is the first newly identified object from the now-operational SCExAO extreme AO system, is ideally suited for spectroscopic follow-up with SCExAO/CHARIS in 2017, and may be a key probe of icy planet formation and planet-disk interactions.
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Telleschi, Alessandra Silvia. "Coronal evolution of solar-like stars : X-ray spectroscopy of stars in star-forming regions and the solar neighborhood /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17018.
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Kirkpatrick, Joseph Davy. "Spectroscopic and photometric studies of main sequence M stars and a search for late-type dwarfs in the solar vicinity." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185978.
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As any introductory astronomy student knows, M dwarfs are the most common stars in the Galaxy and are the faintest of the core hydrogen burners. A comprehensive study of these faint objects is crucial to our understanding of the stellar composition of the Galaxy and necessary for a more complete knowledge of the transition between main sequence M stars and their slightly less massive counterparts, the brown dwarfs, which never achieve hydrogen burning in their cores. In this thesis, a spectroscopic catalog of 125 K and M dwarfs is first presented. This catalog covers the wavelength range from 6300 to 9000 Å, near where these objects emit most of their light. Eight of these spectra, covering classes M2 through M9, are combined with infrared spectra from 0.9 to 1.5 μm to create a second catalog. The two sets of spectra are used to search for temperature-sensitive atomic lines and molecular bands, which are then used in fitting the observed spectra to a sequence of theoretical models. As a result, a new temperature scale for M dwarfs is determined, and this scale is more accurate than previous determinations which have depended on blackbody energy distributions. The sequence of spectra is also used to compare the spectrum of the brown dwarf candidate GD 165 B to known M dwarfs. Furthermore, the spectral catalog is used in an attempt to separate the spectra of faint companions from their M dwarf primaries in systems where the two objects are too close for conventional spectroscopy to resolve the individual components. A survey for faint M dwarfs is also launched using the data acquired through the CCD/Transit Instrument (CTI) on Kitt Peak, Arizona. Follow-up spectroscopy is presented for 133 of these objects, and several more very late M dwarfs are identified. This spectroscopy combined with photometric data from the CTI are used to construct a luminosity function for M dwarfs which is in excellent agreement with determinations from previous surveys. Finally, possible avenues for future work are discussed. These include spectroscopic follow-up of the reddest of Luyten's proper motion objects--the first results from which have uncovered, in just twelve observations, two objects of type M7 and one of type M8, among the coolest objects yet recognized. Future searches, such as an all-sky survey for objects of extremely high proper motion, are also outlined.
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Sinukoff, Evan, Andrew W. Howard, Erik A. Petigura, et al. "ELEVEN MULTIPLANET SYSTEMS FROM K2 CAMPAIGNS 1 AND 2 AND THE MASSES OF TWO HOT SUPER-EARTHS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621388.
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We present a catalog of 11 multiplanet systems from Campaigns 1 and 2 of the K2 mission. We report the sizes and orbits of 26 planets split between seven two-planet systems and four three-planet systems. These planets stem from a systematic search of the K2 photometry for all dwarf stars observed by K2 in these fields. We precisely characterized the host stars with adaptive optics imaging and analysis of high-resolution optical spectra from Keck/HIRES and medium-resolution spectra from IRTF/SpeX. We confirm two planet candidates by mass detection and validate the remaining 24 candidates to >99% confidence. Thirteen planets were previously validated or confirmed by other studies, and 24 were previously identified as planet candidates. The planets are mostly smaller than Neptune (21/26 planets), as in the Kepler mission, and all have short periods (P < 50 days) due to the duration of the K2 photometry. The host stars are relatively bright (most have Kp < 12.5 mag) and are amenable to follow-up characterization. For K2-38, we measured precise radial velocities using Keck/HIRES and provide initial estimates of the planet masses. K2-38b is a short-period super-Earth with a radius of 1.55 +/- 0.16 R-circle plus, a mass of 12.0 +/- 2.9M(circle plus), and a high density consistent with an iron-rich composition. The outer planet K2-38c is a lower-density sub-Neptune-size planet with a radius of 2.42 +/- 0.29 R-circle plus and a mass of 9.9 +/- 4.6M(circle plus) that likely has a substantial envelope. This new planet sample demonstrates the capability of K2 to discover numerous planetary systems around bright stars.
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Farrington, Christopher Donald. "The Separated Fringe Packet Survey: Updating Multiplicity of Solar-Type Stars within 22 Parsecs." Digital Archive @ GSU, 2008. http://digitalarchive.gsu.edu/phy_astr_diss/26.
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Over the past half century, multiplicity studies have provided a foundation for the theories of stellar formation and evolution through understanding how likely it is that stars form alone or with companions. If spectroscopic orbits are combined with techniques that can determine visual orbits, we can access the most fundamental parameter of stellar evolution, stellar mass. This dissertation is composed of two main sections. The first involves the investigation of the seminal multiplicity study of Duquennoy & Mayor (1991b) which has been the ``gold standard" for solar-type stars for nearly 20 years. Improvements in technology in the intervening years have improved the measurement accuracy for radial velocities and distances on which the study was based. Using Georgia State University's CHARA Array to search the systems in Duquennoy & Mayor's multiplicity survey for overlooked companions along with a literature search covering regimes unreachable by the CHARA Array, we have found that more than 40% of the Duquennoy & Mayor's sample was further than originally believed and the uncorrected multiplicity percentages change from 57:38:4:1:0% (single:double:triple:quad:quint%) to 48:42.5:7.5:1:1% with the discoveries of multiple previously undiscovered companions. The second part of this project describes the application of separated fringe packets for resolving the astrometric position of secondaries with small angular separations on long-baseline optical interferometers. The longest baselines of the CHARA Array allow access to a previously inaccessible range of separations compared with other techniques (<40 milliarcseconds) and the ability to very accurately angularly resolve a large number of single- and double-lined spectroscopic binaries. Combining astrometric and spectroscopic orbits provides assumption-free stellar masses and using the CHARA Array allows access to many previously unreachable systems available for high-accuracy mass determinations. We report the first angular separation measurements of seven spectroscopic binary systems, five additional separated fringe packet detections, ten systems with probably overlapping fringe packets, four systems with new data on pre-existing orbits, one completely new visual orbit for a SB2 system previously unresolved, and the detection of two previously unknown companions.
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Sierchio, Jennifer Marie. "Debris Disks Around Solar-Type Stars: Observations of the Pleiades with Spitzer Space Telescope." Thesis, The University of Arizona, 2011. http://hdl.handle.net/10150/144962.
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Murdoch, Kaylene A. "A high-precision radial-velocity search for substellar companions to southern solar-type stars." Thesis, University of Canterbury. Astronomy, 1992. http://hdl.handle.net/10092/8073.
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A system has been developed at the Mt John University Observatory to enable relative radial velocities of solar-type stars to be obtained with a characteristic random error of 55 m/s. The high radial-velocity precision has been achieved by interfacing a single optical fibre feed between the telescope and spectrograph, which has enabled the spectrograph to be mounted in a thermally and mechanically stable configuration and has virtually eliminated guiding errors.
Using this system, a programme of observation of 29 solar-type stars and 10 giant International Astronomical Union radial-velocity standard stars was carried out over 2.5 years with a view to the detection of low-mass companions to the dwarf stars. One star, HR3220, turned out to have a previously-undiscovered stellar companion but no dwarfs showed obvious radial-velocity variability suggesting the presence of sub-stellar companions, although β Hyi showed a possible variation. This is despite the programme's sensitivity to the discovery of companions of mass 20 M₄ or greater in orbits of periods less than about 8 years (and larger masses in longer period orbits). In contrast, at least half the giant 'standard' stars were variable in radial velocity. Four and possibly five of the giant standards are probably intrinsic (pulsating) red or yellow (Walker et al. 1989) variables. Two further standards, β Aqr and δ Sgr, showed long-period variability suggestive of companions of indeterminable but low mass.
The lack of brown dwarfs observed in this programme is consistent with the results of other recent surveys. High-mass brown dwarfs appear to be rare as companions to stars and are probably rare in the field as well. They are unlikely to contribute significantly to the local mass density. Low-mass brown dwarfs (or high-mass planets) seem to be rare in orbits closer than 10 AU but could yet be found to abound in wider orbits or in the field.
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Baumann, Patrick. "The chemical composition of solar-type stars and its impact on the presence of planets." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-156280.
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Sperauskas, J., S. Bartašiūtė, R. P. Boyle, V. Deveikis, S. Raudeliūnas, and A. R. Upgren. "Radial velocities of K–M dwarfs and local stellar kinematics." EDP SCIENCES S A, 2016. http://hdl.handle.net/10150/622691.
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Aims. The goal of this paper is to present complete radial-velocity data for the spectroscopically selected McCormick sample of nearby K-M dwarfs and, based on these and supplementary data, to determine the space-velocity distributions of late-type stars in the solar neighborhood. Methods. We analyzed nearly 3300 measurements of radial velocities for 1049 K-M dwarfs, that we obtained during the past decade with a CORAVEL-type instrument, with a primary emphasis on detecting and eliminating from kinematic calculations the spectroscopic binaries and binary candidates. Combining radial-velocity data with HIPPARCOS/Tycho-2 astrometry we calculated the space-velocity components and parameters of the galactic orbits in a three-component model potential for the stars in the sample, that we use for kinematical analysis and for the identification of possible candidate members of nearby stellar kinematic groups. Results. We present the catalog of our observations of radial velocities for 959 stars which are not suspected of velocity variability, along with the catalog of U, V, W velocities and Galactic orbital parameters for a total of 1088 K-M stars which are used in the present kinematic analysis. Of these, 146 stars were identified as possible candidate members of the known nearby kinematic groups and suspected subgroups. The distributions of space-velocity components, orbital eccentricities, and maximum distances from the Galactic plane are consistent with the presence of young, intermediate-age and old populations of the thin disk and a small fraction (similar to 3%) of stars with the thick disk kinematics. The kinematic structure gives evidence that the bulk of K-M type stars in the immediate solar vicinity represents a dynamically relaxed stellar population. The star MCC 869 is found to be on a retrograde Galactic orbit (V = -262 km s(-1)) of low inclination (4 degrees) and can be a member of stellar stream of some dissolved structure. The Sun's velocity with respect to the Local Standard of Rest, derived from the distributions of space-velocity components, is (U-circle dot, V-circle dot, W-circle dot) = (9.0 +/- 1.4, 13.1 +/- 0.6, 7.2 +/- 0.8) km s(-1). The radial solar motion derived via the Stromberg's relation, V-circle dot = 14.2 +/- 0.8 km s(-1), agrees within the errors with the value obtained directly from the V distribution of stars on nearly circular orbits.
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Schneider, Glenn, Carol A. Grady, Christopher C. Stark, et al. "DEEP HST /STIS VISIBLE-LIGHT IMAGING OF DEBRIS SYSTEMS AROUND SOLAR ANALOG HOSTS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621501.
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We present new Hubble Space Telescope observations of three a priori known starlight-scattering circumstellar debris systems (CDSs) viewed at intermediate inclinations around nearby close-solar analog stars: HD 207129, HD 202628, and HD 202917. Each of these CDSs possesses ring-like components that are more massive analogs of our solar system's Edgeworth-Kuiper Belt. These systems were chosen for follow-up observations to provide imaging with higher fidelity and better sensitivity for the sparse sample of solar-analog CDSs that range over two decades in systemic ages, with HD 202628 and HD 207129 (both similar to 2.3 Gyr) currently the oldest CDSs imaged in visible or near-IR light. These deep (10-14 ks) observations, made with six-roll point-spread-function template visible-light coronagraphy. using the Space Telescope Imaging Spectrograph, were designed to better reveal their angularly large debris rings of diffuse/low surface brightness, and for all targets probe their exo-ring environments for starlight-scattering materials that present observational challenges for current ground-based facilities and instruments. Contemporaneously also observing with a narrower occulter position, these observations additionally probe the CDS endo-ring environments that are seen to be relatively devoid of scatterers. We discuss the morphological, geometrical, and photometric properties of these CDSs also in the context of other CDSs hosted by FGK stars that we have previously imaged as a homogeneously observed ensemble. From this combined sample we report a general decay in quiescent-disk F-disk/F-star optical brightness similar to t(-0.8), similar to what is seen at thermal IR wavelengths, and CDSs with a significant diversity in scattering phase asymmetries, and spatial distributions of their starlight-scattering grains.
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Baumann, Patrick [Verfasser], and Achim [Akademischer Betreuer] Weiss. "The chemical composition of solar-type stars and its impact on the presence of planets / Patrick Baumann. Betreuer: Achim Weiss." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2013. http://d-nb.info/1034813250/34.
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Heinze, Aren Nathaniel. "Planets Around Solar-Type Stars: Methods for Detection and Constraints on their Distribution from an L' and M Band Adaptive Optics Survey." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/196022.
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We have attempted adaptive optics (AO) imaging of planets around nearby stars in the L' and M bands, using the Clio instrument on the MMT. The MMT AO system, with its deformable secondary mirror, offers uniquely low background AO-corrected images in these bands. This allowed us to explore a wavelength regime that has not been well utilized in searches for extrasolar planets, but offers some advantages over the more commonly used shorter-wavelength H band regime. We have taken deep L' and M band images of the interesting debris disk stars Vega and ϵ Eri. Our observations of ϵ Eri attain better sensitivity to low mass planets within 3 arcseconds of the star than any other AO observations to date. At 1.7 arcsec, the maximum separation of the known planet ϵ Eri b, our M band sensitivity corresponds to objects only 9-16 times brighter than the predicted brightness of this planet. M is by far the most promising band for directly imaging this planet for the first time, though Clio would require a multi-night integration. We have carried out a survey of 50 nearby stars, using mostly the L' band. The survey objective was to determine whether power law fits to the statistics of planet mass m and orbital semimajor axis a from radial velocity (RV) surveys apply when extrapolated to orbital radii beyond the outer limits of RV sensitivity. Given dN/dm ~ m^{-1.44}, our survey null result rules out dN/da ~ a^{-0.2} extending beyond 155 AU, or dN/da constant extending beyond 70 AU, at the 95% confidence level. We have not placed as tight constraints on the planet distributions as the best H band surveys. However, we have probed older planet populations and by using a different wavelength regime have helped diversify results against model uncertainties. We have developed careful and well-tested observing, image processing, sensitivity analysis, and source detection methods, and helped advance L' and M band AO astronomy. These wavelengths will become increasingly important with the advent of new giant telescopes sensitive to interesting, low-temperature planets with red H-L' and H-M colors.
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Terquem, Caroline. "Déformation des disques circumstellaires par effet de marée : application aux objets stellaires jeunes." Phd thesis, Grenoble 1, 1993. http://tel.archives-ouvertes.fr/tel-00686407.
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Les observations des étoiles de type T Tauri ont mis en évidence le très grand nombre de systèmes binaires parmi cette classe d'objets stellaires jeunes. Cette constatation, associée à celle de l'influence de la déformation des disques circumstellaires sur les distributions spectrales d'énergie des T Tauri, nous a conduit à étudier les effets de marée dans les sytèmes binaires d'étoiles jeunes. Dans un premier temps, nous avons donc calculé la perturbation engendrée par des effets de marée dans un disque circumstellaire, auto-gravitant ou d'accrétion. De façon à obtenir un développement analytique, nous avons dans cette étude supposé la perturbation faible. Pour évaluer l'incidence de cette déformation sur la distribution spectrale d'énergie, nous avons ensuite calculé l'énergie émise dans une direction donnée par le système constitué du disque déformé et de l'étoile située en son centre. Cette étude a quant à elle été menée dans le cas d'une déformation d'amplitude quelconque, et rien n'a été négligé du point de vue géométrique, c'est-à-dire qu'ont été prises en considération l'ombre portée par le disque sur l'étoile et celle portée par l'étoile sur le disque. Puis nous avons appliqué ces deux études aux systèmes binaires d'étoiles jeunes de type T Tauri. Nous avons ainsi montré que dans le cas de faibles perturbations, c'est-àdire de systèmes binaires dans lesquels la séparation entre les deux composantes est supérieure ou de l'ordre de la centaine d'unités astronomiques, les effets de marée dans le disque circumstellaire ont une incidence tout à fait significative sur le domaine submillimétrique de la distribution spectrale d'énergie. Pour évaluer l'influence de ces effets dans les systèmes binaires plus serrés, nous avons ensuite décrit la déformation de manière paramétrique. Les distributions spectrales d'énergie obtenues alors nous conduisent à proposer une nouvelle interprétation des observations d'objets stellaires jeunes de classe I, et nous permettent également de reproduire des distributions spectrales d'énergie d'étoiles de type T Tauri ayant un fort excès dans l'infra-rouge. Enfin, nous abordons de façon préliminaire le problème de l'influence de la déformation sur le taux d'accrétion dans le disque.
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Tsantaki, Maria. "Precise spectroscopic analysis of solar-type Stars with moderate and fast rotation." Tese, 2015. https://repositorio-aberto.up.pt/handle/10216/78163.
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Tsantaki, Maria. "Precise spectroscopic analysis of solar-type Stars with moderate and fast rotation." Doctoral thesis, 2015. https://repositorio-aberto.up.pt/handle/10216/78163.
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Pereira, Luís Filipe Regala. "Development of automatic tools for measuring acoustic glitches in seismic data of solar-type stars." Dissertação, 2016. https://repositorio-aberto.up.pt/handle/10216/90991.
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Pereira, Luís Filipe Regala. "Development of automatic tools for measuring acoustic glitches in seismic data of solar-type stars." Master's thesis, 2016. https://repositorio-aberto.up.pt/handle/10216/90991.
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Marković, Dragoljub. "Black holes in the early universe, in compact binaries, and as energy sources inside solar-type stars." Thesis, 1994. https://thesis.library.caltech.edu/7688/2/markovic%201994.pdf.
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<p>This thesis consists of three separate studies of roles that black holes might
play in our universe. </p>
<p>In the first part we formulate a statistical method for inferring the cosmological
parameters of our universe from LIGO/VIRGO measurements of the gravitational
waves produced by coalescing black-hole/neutron-star binaries. This method is
based on the cosmological distance-redshift relation, with "luminosity distances"
determined directly, and redshifts indirectly, from the gravitational waveforms.
Using the current estimates of binary coalescence rates and projected "advanced"
LIGO noise spectra, we conclude that by our method the Hubble constant should
be measurable to within an error of a few percent. The errors for the mean density
of the universe and the cosmological constant will depend strongly on the size of
the universe, varying from about 10% for a "small" universe up to and beyond
100% for a "large" universe. We further study the effects of random gravitational
lensing and find that it may strongly impair the determination of the cosmological
constant. </p>
<p>In the second part of this thesis we disprove a conjecture that black holes cannot
form in an early, inflationary era of our universe, because of a quantum-field-theory induced
instability of the black-hole horizon. This instability was supposed to arise
from the difference in temperatures of any black-hole horizon and the inflationary
cosmological horizon; it was thought that this temperature difference would make
every quantum state that is regular at the cosmological horizon be singular at
the black-hole horizon. We disprove this conjecture by explicitly constructing a
quantum vacuum state that is everywhere regular for a massless scalar field. We
further show that this quantum state has all the nice thermal properties that one
has come to expect of "good" vacuum states, both at the black-hole horizon and
at the cosmological horizon. </p>
<p>In the third part of the thesis we study the evolution and implications of a hypothetical
primordial black hole that might have found its way into the center of the
Sun or any other solar-type star. As a foundation for our analysis, we generalize
the mixing-length theory of convection to an optically thick, spherically symmetric
accretion flow (and find in passing that the radial stretching of the inflowing fluid
elements leads to a modification of the standard Schwarzschild criterion for convection).
When the accretion is that of solar matter onto the primordial hole, the
rotation of the Sun causes centrifugal hangup of the inflow near the hole, resulting
in an "accretion torus" which produces an enhanced outflow of heat. We find, however, that the turbulent viscosity, which accompanies the convective transport
of this heat, extracts angular momentum from the inflowing gas, thereby buffering
the torus into a lower luminosity than one might have expected. As a result, the
solar surface will not be influenced noticeably by the torus's luminosity until at
most three days before the Sun is finally devoured by the black hole. As a simple
consequence, accretion onto a black hole inside the Sun cannot be an answer to
the solar neutrino puzzle. </p>
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Meibom, Søren Christian Dalgaard. "An observational exploration of the evolution of angular momentum in close detached binary and singular stars of solar type." 2005. http://catalog.hathitrust.org/api/volumes/oclc/70809820.html.
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Stahn, Thorsten. "Analysis of time series of solar-like oscillations - Applications to the Sun and HD52265." Doctoral thesis, 2010. http://hdl.handle.net/11858/00-1735-0000-0006-B52E-5.
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