1,721,088 research outputs found
An M dwarf planet search programme using the photometric transit method: implementation of a new ground-based survey
Full text linkThis work describes the most relevant steps undertaken for the development and installation of the survey APACHE (A PAthway toward the Characterization of Habitable Earths), and some of the main results obtained after the first observing season are presented. APACHE is the first long-term observing campaign based in Europe which is devised expressly for detecting extrasolar planets orbiting well selected, nearby M dwarfs by using the photometric transit method. The project was conceived at the end of 2008 and he survey makes use of an array of five automated 40 cm telescopes which started routine observations between July 2012 and March 2013. In the Thesis introduction some key issues are discussed which in the last years have placed the cool stars at the centre of the planet hunters’ interests, producing an increase in the number of photometric and high resolution spectroscopic surveys targeted on red dwarfs. In Chapters 1 and 2 the milestones which led to the preparation and initial design of APACHE are presented (the feasibility and pilot study), while Chapter 3 is focused on the description of the most relevant characteristics of the survey structure, as the accurate definition of the catalogue of eligible targets (the APACHE Input Catalogue) and observing strategy, and the implementation of the software package used for obtaining and analyzing the light curves. In Chapter 4 the preliminary results obtained after the first observing season at regime are presented and discussed, with the analysis mainly focused on the study of the photometric variability of more than 130 M dwarfs. Three targets showed evidence of stellar flares, and rotation periods have been measured for five stars through the analysis of their light curve periodograms. A simple single-spot model has been applied to the time series of these stars to describe the observed sinusoidal-like modulation in terms of stellar spots/active regions, obtaining in particular an estimate of the spin-axis inclination angle relative to the line of sight. The Chapter ends with a presentation of more than 90 new variable stars discovered in the stellar fields observed by the APACHE telescopes during the first year. The Thesis concludes with Chapter 5, where the strategic synergy established between APACHE and the large National observing programme GAPS (Global Architecture of Planetary Systems) is described. GAPS observations are carried out with the high resolution spectrograph HARPS-N at the Telescopio Nazionale Galileo (TNG, @ La Palma island in the Canary archipelago) for an extensive study in the field of extrasolar planets. Among the goals of GAPS, of particular relevance is the detection of planets orbiting M dwarfs by analyzing the time variations of the stellar radial velocities, and in Chapter 5 preliminary results are presented for a sample of targets in common with the APACHE project. In particular, it is highlighted the importance of having photometric light curves as a support for a correct interpretation of periodical signals found in the radial velocity time series which could be due to the gravitational effects induced on the star by a planetary mass companion. The results discussed in this Thesis should demonstrate how effectively a large photometric database such that of APACHE is expected to contribute to both the exoplanet science and the physics of the cool starsIn questo lavoro sono descritti i passi più importanti che hanno portato allo sviluppo e alla messa in funzione della survey APACHE (A PAthway toward the Characterization of Habitable Earths), e vengono presentati alcuni dei principali risultati ottenuti dopo la prima stagione osservativa. APACHE è la prima campagna osservativa di lunga durata con base in Europa finalizzata alla ricerca di pianeti in orbita attorno a stelle nane rosse nelle vicinanze del Sole accuratamente selezionate, utilizzando il metodo fotometrico del transito. Il progetto è stato concepito alla fine del 2008 e la schiera di cinque telescopi automatici di 40 cm di diametro utilizzati per le ricerche sono entrati in funzione tra luglio 2012 e marzo 2013. L’introduzione presenta alcuni aspetti chiave che negli ultimi anni hanno portato le nane rosse al centro degli interessi dei cacciatori di mondi alieni, determinando la crescita del numero di campagne osservative dedicate al monitoraggio delle stelle pi`ù fredde, sia fotometricamente che tramite spettroscopia ad alta risoluzione. Vengono poi ripercorse le tappe fondamentali che sono servite per preparare e definire il design iniziale della survey APACHE (studio di fattibilità e studio pilota, discussi nei Capitoli 1 e 2), mentre il Capitolo 3 si concentra sulla descrizione delle caratteristiche più rilevanti dell’impianto della campagna osservativa, come la definizione del catalogo con i potenziali target osservativi (APACHE Input Catalogue) e della strategia osservativa, e la costruzione del software utilizzato per ottenere e analizzare le curve di luce. Nel Capitolo 4 sono presentati i risultati preliminari ottenuti dopo il primo anno di osservazioni a regime, e l’analisi si concentra soprattutto sullo studio della variabilità fotometrica di oltre 130 nane rosse. Tre target hanno mostrato evidenza di brillamenti stellari, e sono stati misurati periodi di rotazione attorno al proprio asse di cinque stelle attraverso l’analisi dei periodogrammi relativi alle loro curve di luce. Alle serie temporali fotometriche di queste stelle è stato applicato un semplice modello a singola macchia per descrivere la modulazione quasi-sinusoidale osservata in termini di macchie stellari/regioni attive, ottendo in particolare una stima dell’angolo di inclinazione dell’asse di rotazione rispetto alla linea di vista. Il Capitolo si conclude con la presentazione di più di 90 nuove stelle variabili scoperte da APACHE nel corso del primo anno. Il lavoro si chiude con il Capitolo 5, dove viene descritta la strategica sinergia instaurata tra il progetto APACHE e l’esteso programma osservativo nazionale GAPS (Global Architecture of Planetary Systems) che fa uso dello spettrografo ad alta risoluzione HARPS-N montato al Telescopio Nazionale Galileo (Isola di La Palma, arcipelago delle Canarie) per ricerche nell’ambito dei pianeti extrasolari. Tra gli obiettivi di GAPS c’è quello di scoprire pianeti in orbita attorno a nane rosse attraverso l’analisi delle variazioni temporali delle velocità radiali stellari, e il Capitolo 5 presenta i risultati preliminari ottenuti per i target in comune con il progetto APACHE. In particolare, viene sottolineata l’importanza delle serie temporali fotometriche come aiuto per una corretta interpretazione di segnali periodici trovati nelle serie temporali di velocità radiali che potrebbero essere dovuti agli effetti gravitazionali indotti sulla stella da un compagno di massa planetaria. I risultati discussi in questa Tesi dovrebbero dimostrare l’importante contributo che un ricco archivio di dati come quello prodotto dalla survey APACHE potrà assicurare sia alla scienza dei pianeti extrasolari che allo studio delle nane ross
TASTE: The Asiago Search for Transit timing variations of Exoplanets. I. Overview and improved parameters for HAT-P-3b and HAT-P-14b
No full textA promising method for detecting earth-sized exoplanets is the timing analysis of a known transit. The technique allows a search for variations in either the transit duration or the center induced by the perturbation of a third body, e.g. a second planet or an exomoon. By applying this method, the TASTE (The Asiago search for transit timing variations of Exoplanets) project will collect high-precision, short-cadence light curves for a selected sample of transits by using imaging di fferential photometry at the Asiago 1.82 m telescope. The first light curves show that our project can achieve a competitive timing accuracy, as well as a significant improvement of the orbital parameters.We derived refined ephemerides for HAT-P-3b and HAT-P-14b with a timing accuracy of 11 and 25 s, respectively. © ESO 2011
TASTE: The Asiago Search for Transit timing variations of Exoplanets II. A new observational study of transit time variations in HAT-P-13b.
No full textA promising method for detecting earth-sized exoplanets is the timing analysis of a known transit. The technique allows a search for variations in either the transit duration or the center induced by the perturbation of a third body, e.g. a second planet or an exomoon. By applying this method, the TASTE (The Asiago search for transit timing variations of Exoplanets) project will collect high-precision, short-cadence light curves for a selected sample of transits by using imaging differential photometry at the Asiago 1.82 m telescope. The first light curves show that our project can achieve a competitive timing accuracy, as well as a significant improvement of the orbital parameters. We derived refined ephemerides for HAT-P-3b and HAT-P-14b with a timing accuracy of 11 and 25 s, respectively.
Photometric data is only a vailable in electronic form at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/viz-bin/qcat?J/A+A/527/A8
VSX J071108.7+695227: a Newly Discovered Short-period Eclipsing Binary
No full textWe report the discovery of an EW variable, VSX J071108.7+695227, with a short orbital period of ~0.238 day. This period is very close to the lower limit of ~0.22 day that has been found for EW systems. Here we present and discuss photometric and spectroscopic data of the variable, collected at the Astronomical Observatory of the Autonomous Region of the Aosta Valley and at the Asiago Astrophysical Observatory. The light curves show some asymmetries and the spectra suggest a dK4 classification for the two components. It could be interesting to carry out further observations of this system at different epochs because such systems frequently show variations in period and in the features of the light curve
Searching for planetary signals in Doppler time series: a performance evaluation of tools for periodogram analysis
Full text linkWe carry out a comparative analysis of the performance of three algorithms widely used to identify significant periodicities in radial-velocity (RV) data sets: the generalized Lomb-Scargle (GLS) periodogram, its modified version based on Bayesian statistics (BGLS) and the multifrequency periodogram scheme called FREquency DEComposer (FREDEC). We apply the algorithms to a suite of numerical simulations of (single and multiple) low-amplitude Keplerian RV signals induced by low-mass companions around M-dwarf primaries. The global performance of the three period search approaches is quite similar in the limit of an idealized, best-case scenario (single planets, circular orbits, white noise). However, GLS, BGLS and FREDEC are not equivalent when it comes to the correct identification of more complex signals (including correlated noise of stellar origin, eccentric orbits, multiple planets), with variable degrees of efficiency loss as a function of system parameters and degradation in completeness and reliability levels. The largest discrepancy is recorded in the number of false detections: the standard approach of residual analyses adopted for GLS and BGLS translates in large fractions of false alarms (∼30 per cent) in the case of multiple systems, as opposed to ∼10 per cent for the FREDEC approach of simultaneous multifrequency search. Our results reinforce the need for the strengthening and further development of the most aggressive and effective ab initio strategies for the robust identification of low-amplitude planetary signals in RV data sets, particularly now that RV surveys are beginning to achieve sensitivity to potentially habitable Earth-mass planets around late-type stars
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Starting Up a Data Model for Exoplanetary Data
No full textThe effort for searching, studying and characterizing extrasolar planets and planetary systems is a growing and improving field of astrophysical research. Alongside the growing knowledge on the field, the data resources are also growing, both from observations and numerical simulations. To tackle interoperability of these data, an effort is starting (under the EU H2020 ASTERICS project) to delineate a data model to allow a common sharing of the datasets and collections of exoplanetary data. The data model will pick up model components from the IVOA specifications, either existing or under investigation, and attach new ones where needed. Here are presented the first results in drafting the exoplanetary systems dedicated data model. Relationships are reported with existing and proposed IVOA models; new key components not yet available in the interoperable scenario are shown. The results here reported cover a first set of requirements and considerations and take into account aspects like the observations of exoplanetary systems, the usage of existing exoplanets catalogues, the investigation of atmospheres of confirmed exoplanets and the simulation of exoplanet's atmospheres devoted to characterize exoplanets habitability. ..
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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