DOCSLIB.ORG

Exploration in Automatic Thesaurus Discovery

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Exploration in Automatic Thesaurus Discovery See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/266452571 Exploration in Automatic Thesaurus Discovery Article · January 1994 DOI: 10.1007/978-1-4615-2710-7 CITATIONS READS 496 36 1 author: Gregory Grefenstette Florida Institute for Human and Machine Cognition 152 PUBLICATIONS 3,893 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Ontology Development from NLP View project All content following this page was uploaded by Gregory Grefenstette on 16 September 2016. The user has requested enhancement of the downloaded file. EXPLORATIONS IN AUTOMATIC THESAURUS DISCOVERY EXPLORATIONS IN AUTOMATIC THESAURUS DISCOVERY Gregory GREFENSTETTE University of Pittsburgh Pittsburgh, Pennsylvania, USA Rank Xerox Research Centre Grenoble, France KLUWER ACADEMIC PUBLISHERS BostonLondonDo rdrecht CONTENTS PREFACE v 1 INTRODUCTION 1 2 SEMANTIC EXTRACTION 7 2.1 Historical Overview 7 2.2 Cognitive Science Approaches 8 2.3 Recycling Approaches 17 2.4 Knowledge-PoorApproaches 23 3 SEXTANT 33 3.1 Philosophy 33 3.2 Methodology 34 3.3 Other examples 54 3.4 Discussion 57 4 EVALUATION 69 4.1 DeeseAntonymsDiscovery 70 4.2 Artificial Synonyms 75 4.3 GoldStandardsEvaluations 81 4.4 Webster's 7th 89 4.5 Syntactic vs. Document Co-occurrence 91 4.6 Summary 100 5 APPLICATIONS 101 5.1 Query Expansion 101 5.2 Thesaurus enrichment 114 i Automatic Thesaurus Discovery ii Explorations in 5.3 WordMeaningClustering 126 5.4 AutomaticThesaurusConstruction 131 5.5 DiscussionandSummary 133 6 CONCLUSION 137 6.1 Summary 137 6.2 Criticisms 139 6.3 Future Directions 141 6.4 Vision 147 1 PREPROCESSORS 149 2 WEBSTER STOPWORD LIST 151 3 SIMILARITY LIST 153 4 SEMANTIC CLUSTERING 163 5 AUTOMATIC THESAURUS GENERATION 171 6 CORPORA TREATED 181 6.1 ADI 181 6.2 AI 187 6.3 AIDS 192 6.4 ANIMALS 197 6.5 BASEBALL 202 6.6 BROWN 207 6.7 CACM 212 6.8 CISI 219 6.9 CRAN 228 6.10 HARVARD 235 6.11 JFK 240 6.12 MED 247 6.13 MERGERS 252 6.14 MOBYDICK 257 6.15 NEJM 261 6.16 NPL 266 Contents iii 6.17 SPORTS 273 6.18 TIME 278 6.19 XRAY 285 6.20 THESIS 290 INDEX 303 Automatic Thesaurus Discovery iv Explorations in PREFACE by David A. Evans Associate Professor of Linguistics and Computer Science Carnegie Mellon University There are several `quests' in contemporary computational linguistics; at least one version of the `Holy Grail' is represented by a procedure to discovery semantic relations in free text, automatically. No one has found such a procedure, but everyone could use one. Semantic relations are important, of course, because the essential content of texts is not revealed by `words' alone. To identify the propositions, the attributes and their values, even the phrases that count as `names' or other lexicalatomsintexts,onemustappealtosemanticrelations. Indeed, all natural- language understanding (NLU) efforts require resources for representing semantic relations and some mechanism to interpret them. Of course, not all systems that process natural language aspire to natural- language understanding. Historically, for example, information retrieval systems have not attempted to use natural-language processing (NLP) of any sort, let alone processing requiring semantic relations, in analyzing (indexing) free text. Increasingly, however, in the face of degrading performance in large- scale applications, the designers of such systems are attempting to overcome the problem of language variation (e.g., the many ways to express the `same' idea) and the polysemy of `words' by using linguistic and semantic resources. Unfortunately, the modest success of computational linguists who have used knowledge bases and declarative representations of lexical-semantic relations to support NLP systems for relatively constrained domains have not been repeated in the context of large-scale information retrieval systems. The reasons are no mystery: no general, comprehensive linguisticknowledge bases exist; no one knows how to build them; even with adequate understanding, no one could afford to build them; the number of `senses' of words and the v Automatic Thesaurus Discovery vi Explorations in number of relation types is virtually unlimited- each new corpus requires new knowledge. The interests and needs of information scientists, computational linguists, and NL-applications-oriented computer scientists have been converging. But robust and reliable techniques to support larger-scale linguistic processing have been hard to find. In such a context, the work presented in this volume is remarkable. Dr. Grefenstette has not only developed novel techniques to solve practical problems of large-scale text processing but he has demonstrated effective methods for discovering classes of related lexical items (or `concepts') and he has proposed a variety of independent techniques for evaluating the results of semantic-relation discovery. While the results of Dr. Grefenstette's processing are not `semantic' networks or interpretations of texts, they are arguably sets of related concepts - going beyond a simple notion of synonymy to include pragmatically associated terms. Such association sets reveal implicit sense restrictions and manifest the attributes of more complex semantic frames that would be required for a complete, declarative representation of the target concepts. The key function facilitated by Dr. Grefenstette's process is the discovery of such sets of related terms `on the fly', as they are expressed in the actual texts in a database or domain. There is no need for `external' knowledge (such as thesauri) to suggest the structure of information in a database; the process effectively finds empirically-based and pragmatically appropriate term-relation sets for idiosyncratic corpora. Dr. Grefenstette's approach is distinctive, in part, because it combines both linguistic and information-scientific perspectives. He begins with the obser- vations (that others have made as well) that (1) ``you can begin to know the meaning of a word (or term) by the company it keeps'' and (2) ``words or terms that occur in `the same contexts' are `equivalent' ''. He has followed the logical implication: if you find a sensible definition for ``context'' and you keep track of all the co-occurring elements in that context, you will find a `co-substitution set,' arguably a semantic property revealed through syntactic analysis. For Dr. Grefenstette, a practical definition of ``context'' is given by a handful of syntactic features. In particular, he takes both syntactic structural relations (such as ``subject of the verb v'' or ``modifier of the noun n'') as well as general relations (such as ``in the clause c'' or ``in the sentence s'') to be potential contexts. He identifies all the elements (= words or terms) that occur or co-occur in a context and finds statistically prominent patterns of Preface vii co-occurrence. Each element, then, can be identified with a vector (or list) of other elements, which are the context markers or attributes of the head element. By calculating `similarity' scores for each vector, he can find lists of elements that are `close' to each other, as determined by their shared attributes. These sets are, operationally, the equivalence classes of the words or terms relative to the documents that were analyzed. Dr. Grefenstette's work is noteworthy in several respects. First, he uses sophisticated (but practical and robust) NLP to derive context sets from free text. This sets his work apart from most other research in information science that has addressed similar concerns. While some scientists are beginning to discover the utility of combining NLP with information-management technology, Dr. Grefenstette has already begun using varieties of NLP tools in routine processing. It should be emphasized that Dr. Grefenstette's work has involved serious NLP: his parser is an excellent example of a `robust' NLP tool practically tuned to its task. Second, Dr. Grefenstette asks (and answers) empirical questions over large quantities of data. This distinguishes his work both from theoretical linguists, who generally have neither the means nor the inclination to work with large volumes of performance data, and also from many computational linguists (and artificial-intelligence researchers), whose tools are less robust than Dr. Grefenstette's. In fact, in exploring the thesis presented in this volume, Dr. Grefenstette processed more than a dozen separate databases, representing more than thirty megabytes of text. While multi-megabyte collections are not unusual in information-science applications, they are still rare in AI and linguistic research targeted on semantic features of language. Finally, Dr. Grefenstette focuses his efforts as much on the scientific evaluation of his techniques as on their implementation and raw performance. This is an especially challenging and important concern because there are no well- established techniques for evaluating the results of processes that operate over large volumes of free text. If we are to make scientific progress, however, we must establish new techniques for measuring success or failure. Dr. Grefenstette has embraced this challenge. For example, he evaluates his results from the point of view of intuitive validity by appealing to psychological data. He considers the question of the stability of his techniques by testing whether the results found in increasingly large subcollections of a corpus converge. He assesses the results of (pseudo-)synonym discovery by comparing
Load more

Recommended publications
  • Lurking in the Shadows: Wide-Separation Gas Giants As Tracers of Planet Formation
    Lurking in the Shadows: Wide-Separation Gas Giants as Tracers of Planet Formation Thesis by Marta Levesque Bryan In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 2018 Defended May 1, 2018 ii © 2018 Marta Levesque Bryan ORCID: [0000-0002-6076-5967] All rights reserved iii ACKNOWLEDGEMENTS First and foremost I would like to thank Heather Knutson, who I had the great privilege of working with as my thesis advisor. Her encouragement, guidance, and perspective helped me navigate many a challenging problem, and my conversations with her were a consistent source of positivity and learning throughout my time at Caltech. I leave graduate school a better scientist and person for having her as a role model. Heather fostered a wonderfully positive and supportive environment for her students, giving us the space to explore and grow - I could not have asked for a better advisor or research experience. I would also like to thank Konstantin Batygin for enthusiastic and illuminating discussions that always left me more excited to explore the result at hand. Thank you as well to Dimitri Mawet for providing both expertise and contagious optimism for some of my latest direct imaging endeavors. Thank you to the rest of my thesis committee, namely Geoff Blake, Evan Kirby, and Chuck Steidel for their support, helpful conversations, and insightful questions. I am grateful to have had the opportunity to collaborate with Brendan Bowler. His talk at Caltech my second year of graduate school introduced me to an unexpected population of massive wide-separation planetary-mass companions, and lead to a long-running collaboration from which several of my thesis projects were born.
    [Show full text]
  • Li Abundances in F Stars: Planets, Rotation, and Galactic Evolution,
    A&A 576, A69 (2015) Astronomy DOI: 10.1051/0004-6361/201425433 & c ESO 2015 Astrophysics Li abundances in F stars: planets, rotation, and Galactic evolution, E. Delgado Mena1,2, S. Bertrán de Lis3,4, V. Zh. Adibekyan1,2,S.G.Sousa1,2,P.Figueira1,2, A. Mortier6, J. I. González Hernández3,4,M.Tsantaki1,2,3, G. Israelian3,4, and N. C. Santos1,2,5 1 Centro de Astrofisica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal e-mail: [email protected] 2 Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal 3 Instituto de Astrofísica de Canarias, C/via Lactea, s/n, 38200 La Laguna, Tenerife, Spain 4 Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain 5 Departamento de Física e Astronomía, Faculdade de Ciências, Universidade do Porto, Portugal 6 SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, UK Received 28 November 2014 / Accepted 14 December 2014 ABSTRACT Aims. We aim, on the one hand, to study the possible differences of Li abundances between planet hosts and stars without detected planets at effective temperatures hotter than the Sun, and on the other hand, to explore the Li dip and the evolution of Li at high metallicities. Methods. We present lithium abundances for 353 main sequence stars with and without planets in the Teff range 5900–7200 K. We observed 265 stars of our sample with HARPS spectrograph during different planets search programs. We observed the remaining targets with a variety of high-resolution spectrographs.
    [Show full text]
  • SILICON and OXYGEN ABUNDANCES in PLANET-HOST STARS Erik Brugamyer, Sarah E
    The Astrophysical Journal, 738:97 (11pp), 2011 September 1 doi:10.1088/0004-637X/738/1/97 C 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A. SILICON AND OXYGEN ABUNDANCES IN PLANET-HOST STARS Erik Brugamyer, Sarah E. Dodson-Robinson, William D. Cochran, and Christopher Sneden Department of Astronomy and McDonald Observatory, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712, USA; [email protected] Received 2011 February 4; accepted 2011 June 22; published 2011 August 16 ABSTRACT The positive correlation between planet detection rate and host star iron abundance lends strong support to the core accretion theory of planet formation. However, iron is not the most significant mass contributor to the cores of giant planets. Since giant planet cores are thought to grow from silicate grains with icy mantles, the likelihood of gas giant formation should depend heavily on the oxygen and silicon abundance of the planet formation environment. Here we compare the silicon and oxygen abundances of a set of 76 planet hosts and a control sample of 80 metal-rich stars without any known giant planets. Our new, independent analysis was conducted using high resolution, high signal-to-noise data obtained at McDonald Observatory. Because we do not wish to simply reproduce the known planet–metallicity correlation, we have devised a statistical method for matching the underlying [Fe/H] distributions of our two sets of stars. We find a 99% probability that planet detection rate depends on the silicon abundance of the host star, over and above the observed planet–metallicity correlation.
    [Show full text]
  • HISTORY and ANALYSIS of the CREATION RESEARCH SOCIETY by William E
    AN ABSTRACT OF THE THESIS OF William E. Elliott for the degree ofMaster of Science in General Science presented on March 1, 1990. Title: History and Analysis of theCreation ltee Society Redacted for Privacy Abstractapproved: The resurgence of creationismthe past few years has been led by advocates of recent-creationism. These individuals, a minority among creationists in general, argue that the entire universe was created approximately 10,000 years ago in one six- day period of time.Recent-creationists support their position by appealing to the Genesis account of creation and scientific data. Their interpretation of Genesis is based on the doctrines of conservative, evangelical Christianity. Their interpretation of scientific data is informed by their theological presuppositions. The scientific side of recent-creationism is supported by several organizations, most of which had their origin in one group, the Creation Research Society. The CRS is a major factor in the rise of the modern creationist movement. Founded in 1963, this small (c. 2000 mem- bers) group claims to be a bona-fide scientific society engaged in valid scientific re- search conducted from a recent-creationist perspective. These claims are analyzed and evaluated. The Society's history is discussed, including antecedent creationist groups. Most of the group's founders were members of the American Scientific Affiliation, and their rejection of changes within the ASA was a significant motivating factor in founding the CRS. The organization, functioning, and finances of the Society are de- tailed with special emphasis on the group's struggles for independence and credibility. founding the CRS. The organization, functioning, and finances of the Society are de- tailed with special emphasis on the group's struggles for independence and credibility.
    [Show full text]
  • Mètodes De Detecció I Anàlisi D'exoplanetes
    MÈTODES DE DETECCIÓ I ANÀLISI D’EXOPLANETES Rubén Soussé Villa 2n de Batxillerat Tutora: Dolors Romero IES XXV Olimpíada 13/1/2011 Mètodes de detecció i anàlisi d’exoplanetes . Índex - Introducció ............................................................................................. 5 [ Marc Teòric ] 1. L’Univers ............................................................................................... 6 1.1 Les estrelles .................................................................................. 6 1.1.1 Vida de les estrelles .............................................................. 7 1.1.2 Classes espectrals .................................................................9 1.1.3 Magnitud ........................................................................... 9 1.2 Sistemes planetaris: El Sistema Solar .............................................. 10 1.2.1 Formació ......................................................................... 11 1.2.2 Planetes .......................................................................... 13 2. Planetes extrasolars ............................................................................ 19 2.1 Denominació .............................................................................. 19 2.2 Història dels exoplanetes .............................................................. 20 2.3 Mètodes per detectar-los i saber-ne les característiques ..................... 26 2.3.1 Oscil·lació Doppler ........................................................... 27 2.3.2 Trànsits
    [Show full text]
  • A Substellar Companion in a 1.3 Yr Nearly-Circular Orbit of HD 16760
    A Substellar Companion in a 1.3 yr Nearly-circular Orbit of HD 167601,2 Bun’ei Sato3, Debra A. Fischer4, Shigeru Ida5, Hiroki Harakawa5, Masashi Omiya6, John A. Johnson7, Geoffrey W. Marcy8, Eri Toyota9, Yasunori Hori5, Howard Isaacson4, Andrew W. Howard8, and Kathryn M.G. Peek8 [email protected] ABSTRACT We report the detection of a substellar companion orbiting the G5 dwarf HD 16760 from the N2K sample. Precise Doppler measurements of the star from Sub- aru and Keck revealed a Keplerian velocity variation with a period of 466.47±0.35 d, a semiamplitude of 407.71±0.84 m s−1, and an eccentricity of 0.084±0.003. Adopting a stellar mass of 0.78±0.05 M⊙, we obtain a minimum mass for the com- panion of 13.13±0.56 MJUP, which is close to the planet/brown-dwarf transition, and the semimajor axis of 1.084±0.023 AU. The nearly circular orbit despite the large mass and intermediate orbital period makes this companion unique among known substellar companions. Subject headings: planetary systems – stars: individual (HD 16760) 1Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. 2Based on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology. Keck time has been granted by NOAO and NASA. arXiv:0907.5080v1 [astro-ph.EP] 29 Jul 2009 3Global Edge Institute, Tokyo Institute of Technology, 2-12-1-S6-6 Ookayama, Meguro-ku, Tokyo 152- 8550 4Department of Physics & Astronomy, San Francisco State University, San Francisco, CA 94132 5Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro- ku, Tokyo 152-8551 6Department of Physics, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292 7Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 8Department of Astronomy, University of California, Berkeley, CA 9Kobe Science Museum, 7-7-6 Minatoshima-Nakamachi, Chuo-ku, Kobe, Hyogo 650-0046 –2– 1.
    [Show full text]
  • Archival VLT/Naco Multiplicity Investigation of Exoplanet Host Stars
    A&A 620, A102 (2018) Astronomy https://doi.org/10.1051/0004-6361/201731341 & c ESO 2018 Astrophysics Archival VLT/NaCo multiplicity investigation of exoplanet host stars J. Dietrich1,2 and C. Ginski1,3 1 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands e-mail: [email protected] 2 Harvard University, Cambridge, MA 02138, USA 3 Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands Received 9 June 2017 / Accepted 27 June 2018 ABSTRACT Context. The influence of stellar multiplicity on planet formation is not yet well determined. Most planets are found using indirect detection methods via the small radial velocity or photometric variations of the primary star. These indirect detection methods are not sensitive to wide stellar companions. High-resolution imaging is thus needed to identify potential (sub)stellar companions to these stars. Aims. In this study we aim to determine the (sub)stellar multiplicity status of exoplanet host stars, that were not previously investigated for stellar multiplicity in the literature. For systems with non-detections we provide detailed detection limits to make them accessible for further statistical analysis. Methods. For this purpose we have employed previously unpublished high-resolution imaging data taken with VLT/NACO in a wide variety of different scientific programs and publicly accessible in the ESO archive. We used astrometric and theoretical population synthesis to determine whether detected companion candidates are likely to be bound or are merely chance-projected background objects. Results. We provide detailed detection limits for 39 systems and investigate 29 previously unknown companion candidates around five systems.
    [Show full text]
  • Abstracts for Poster Session 2
    EPS-12: General Conference Trends in Physics (26-30 August 2002 Budapest) Poster Session 2 Poster Session 2 1 EPS-12: General Conference Trends in Physics (26-30 August 2002 Budapest) 2 Poster Session 2 EPS-12: General Conference Trends in Physics (26-30 August 2002 Budapest) P2 – 1 THERMAL EFFECT OF RADIATION ON DUST PARTICLES L.G. Astafyeva* B.I.Stepanov Institute of Physics, National Academy of Sciences of Belarus Cosmic dust grains are an important component of the interstellar medium. They play a central role in the star-formation process, the energy balance of gas clouds and so on. For the calculation of the thermal effect of various kinds of radiation on dust particles the absorption and heating of particles have to be known over a wide interval of particle composition and sizes. As dust grains may be both uniform and composite collections of particles of distinct materials, including voids agglomerated together, such particles can be simulated by homogeneous spheres and by a series of concentric spherical layers, each of which has the optical properties of one material or vacuum. The one-layer grains of amorphous silicate and carbonaceous material are considered. Then composite grains with two materials: amorphous carbon and vacuum or amorphous silicate particles coated with a carbonaceous “mantle” will be examined. Some computer codes for calculations of internal intensity distributions in multilayer particles and heating of them were developed. This work was partially supported by INTAS Grant No: 99-652. * Corresponding author: e-mail: [email protected] Poster Session 2 3 EPS-12: General Conference Trends in Physics (26-30 August 2002 Budapest) P2 – 2 CALCULATION OF OPTICAL FIELDS INSIDE SPHEROIDAL PARTICLES OF COSMIC DUST: COMPARISON OF DIFFERENT METHODS: GMT, T - MATRIX, SVM V.A.
    [Show full text]
  • The N2K Consortium VI: Doppler Shifts Without Templates and Three
    The N2K Consortium VI: Doppler Shifts Without Templates and Three New Short–Period Planets 1 John Asher Johnson2, Geoffrey W. Marcy2, Debra A. Fischer3, Gregory Laughlin4, R. Paul Butler5, Gregory W. Henry6, Jeff A. Valenti7, Eric B. Ford2, Steven S. Vogt4, Jason T. Wright2 [email protected] ABSTRACT We present a modification to the iodine cell Doppler technique that eliminates the need for an observed stellar template spectrum. For a given target star, we iterate toward a synthetic template spectrum beginning with an existing spec- trum of a similar star. We then perturb the shape of this first–guess template to match the program observation of the target star taken through an iodine cell. The elimination of a separate template observation saves valuable telescope time, a feature that is ideally suited for the quick–look strategy employed by the “Next 2000 Stars” (N2K) planet search program. Tests using Keck/HIRES spec- tra indicate that synthetic templates yield a short–term precision of3ms−1 and a long–term, run–to–run precision of 5 m s−1. We used this new Doppler tech- nique to discover three new planets: a 1.50 MJup planet in a 2.1375 d orbit around HD 86081; a 0.71 MJup planet in circular, 26.73 d orbit around HD 224693; and a Saturn–mass planet in an 18.179 d orbit around HD 33283. The remarkably short period of HD 86081b bridges the gap between the extremely short–period planets detected in the OGLE survey and the 16 Doppler–detected hot jupiters arXiv:astro-ph/0604348v2 22 May 2006 1Based on observations obtained at the W.
    [Show full text]
  • Determining the True Mass of Radial-Velocity Exoplanets with Gaia 9 Planet Candidates in the Brown-Dwarf/Stellar Regime and 27 Confirmed Planets
    Astronomy & Astrophysics manuscript no. exoplanet_mass_gaia c ESO 2020 September 30, 2020 Determining the true mass of radial-velocity exoplanets with Gaia 9 planet candidates in the brown-dwarf/stellar regime and 27 confirmed planets F. Kiefer1; 2, G. Hébrard1; 3, A. Lecavelier des Etangs1, E. Martioli1; 4, S. Dalal1, and A. Vidal-Madjar1 1 Institut d’Astrophysique de Paris, Sorbonne Université, CNRS, UMR 7095, 98 bis bd Arago, 75014 Paris, France 2 LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France? 3 Observatoire de Haute-Provence, CNRS, Universiteé d’Aix-Marseille, 04870 Saint-Michel-l’Observatoire, France 4 Laboratório Nacional de Astrofísica, Rua Estados Unidos 154, 37504-364, Itajubá - MG, Brazil Submitted on 2020/08/20 ; Accepted for publication on 2020/09/24 ABSTRACT Mass is one of the most important parameters for determining the true nature of an astronomical object. Yet, many published exoplan- ets lack a measurement of their true mass, in particular those detected thanks to radial velocity (RV) variations of their host star. For those, only the minimum mass, or m sin i, is known, owing to the insensitivity of RVs to the inclination of the detected orbit compared to the plane-of-the-sky. The mass that is given in database is generally that of an assumed edge-on system (∼90◦), but many other inclinations are possible, even extreme values closer to 0◦ (face-on). In such case, the mass of the published object could be strongly underestimated by up to two orders of magnitude.
    [Show full text]
  • Evidence for Enhanced Chromospheric Ca II H and K Emission in Stars with Close-In Extrasolar Planets
    A&A 540, A82 (2012) Astronomy DOI: 10.1051/0004-6361/201118247 & c ESO 2012 Astrophysics Evidence for enhanced chromospheric Ca II H and K emission in stars with close-in extrasolar planets T. Krejcovᡠ1 and J. Budaj2 1 Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlárskᡠ2, 61137 Brno, Czech Republic e-mail: [email protected] 2 Astronomical Institute, Slovak Academy of Sciences, 05960 Tatranská Lomnica, Slovak Republic e-mail: [email protected] Received 11 October 2011 / Accepted 13 February 2012 ABSTRACT Context. The planet-star interaction is manifested in many ways. It has been found that a close-in exoplanet causes small but mea- surable variability in the cores of a few lines in the spectra of several stars, which corresponds to the orbital period of the exoplanet. Stars with and without exoplanets may have different properties. Aims. The main goal of our study is to search for the influence that exoplanets might have on atmospheres of their host stars. Unlike the previous studies, we do not study changes in the spectrum of a host star or differences between stars with and without exoplanets. We aim to study a large number of stars with exoplanets and the current level of their chromospheric activity and to look for a possible correlation with the exoplanetary properties. Methods. To analyse the chromospheric activity of stars, we exploited our own and publicly available archival spectra, measured the equivalent widths of the cores of Ca II H and K lines, and used them to trace their activity. Subsequently, we searched for their dependence on the orbital parameters and the mass of the exoplanet.
    [Show full text]
  • Radial Velocities from the N2K Project: 6 New Cold Gas Giant Planets Orbiting HD 55696, HD 98736, HD 148164, HD 203473, and HD 211810 Kristo Ment,1, 2 Debra A
    Draft version September 6, 2018 Typeset using LATEX preprint style in AASTeX62 Radial velocities from the N2K Project: 6 new cold gas giant planets orbiting HD 55696, HD 98736, HD 148164, HD 203473, and HD 211810 Kristo Ment,1, 2 Debra A. Fischer,1 Gaspar Bakos,3 Andrew W. Howard,4 and Howard Isaacson5 1Department of Astronomy, Yale University, 52 Hillhouse Avenue, New Haven, CT 06511, USA 2Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 3Department of Astrophysical Sciences, Princeton University, NJ 08544, USA 4Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA 5Department of Astronomy, University of California, Berkeley, CA 94720, USA (Received February 15, 2018; Revised August 23, 2018; Accepted August 29, 2018) Submitted to AJ ABSTRACT The N2K planet search program was designed to exploit the planet-metallicity cor- relation by searching for gas giant planets orbiting metal-rich stars. Here, we present the radial velocity measurements for 378 N2K target stars that were observed with the HIRES spectrograph at Keck Observatory between 2004 and 2017. With this data set, we announce the discovery of six new gas giant exoplanets: a double-planet system or- biting HD 148164 (M sin i of 1.23 and 5.16 MJUP) and single planet detections around HD 55696 (M sin i = 3.87 MJUP), HD 98736 (M sin i= 2.33 MJUP), HD 203473 (M sin i = 7.8 MJUP), and HD 211810 (M sin i = 0.67 MJUP). These gas giant companions have orbital semi-major axes between 1.0 and 6.2 AU and eccentricities ranging from 0.13 to 0.71.
    [Show full text]