Brett C. Addison^{1}, Duncan J. Wright^{1}, Belinda A. Nicholson^{2}, Belinda A. Nicholson^{1} +111 more

02 Mar 2021-Monthly Notices of the Royal Astronomical Society (Oxford University Press)-Vol. 502, Iss: 3, pp 3704-3722

Abstract: We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA’s Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to be of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the Minerva-Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of MP = 0.138 ± 0.023 $\rm {M_J}$ (43.9 ± 7.3 $\, M_{\rm \oplus}$), a radius of RP = 0.639 ± 0.013 $\rm {R_J}$ (7.16 ± 0.15 $\, \mathrm{ R}_{\rm \oplus}$), bulk density of $0.65^{+0.12}_{-0.11}$ (cgs), and period $18.38818^{+0.00085}_{-0.00084}$ $\rm {days}$. TOI-257b orbits a bright (V = 7.612 mag) somewhat evolved late F-type star with M* = 1.390 ± 0.046 $\rm {M_{sun}}$, R* = 1.888 ± 0.033 $\rm {R_{sun}}$, Teff = 6075 ± 90 $\rm {K}$, and vsin i = 11.3 ± 0.5 km s−1. Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a ∼71 day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (∼100) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known sample of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems.

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Topics: Type (model theory) (59%)

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26 results found

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01 Dec 2006-

Abstract: Recently NAFU SA and other role players expressed some criticism about government programmes. The criticism was not so much about the objectives and content of these programmes, but rather about their accessibility, or lack thereof, to emerging farmers.

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Topics: Criticism (59%), Government (53%)

570 Citations

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01 Jan 2011-

236 Citations

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Abstract: Doppler spectroscopy has uncovered or confirmed all the known planets orbiting nearby stars. Two main techniques are used to obtain precision Doppler measurements at optical wavelengths. The first approach is the gas cell method, which consists on the least-squares matching of the spectrum of Iodine imprinted on the spectrum of the star. The second method relies on the construction of a stabilized spectrograph externally calibrated in wavelength. The most precise stabilized spectrometer in operation is HARPS, operated by ESO in La Silla Observatory/Chile. The Doppler measurements obtained with HARPS are typically obtained using the Cross-Correlation Function technique (CCF). It consists of multiplying the stellar spectrum with a weighted binary mask and finding the minimum of such product as a function of the Doppler shift. It is known that CCF is suboptimal in exploiting the Doppler information in the stellar spectrum. Here, we describe an algorithm to obtain precision RV measurements using least-squares matching of each observed spectrum to a high signal-to-noise ratio template derived from the same observations. Such algorithm is implemented in our software called HARPS-TERRA (Template Enhanced Radial velocity Re-analysis Application). New radial velocity measurements on a representative sample of stars observed by HARPS is used to illustrate the benefits of the proposed method. We show that, compared to CCF, template matching provides a significant improvement in accuracy, specially when applied to M dwarfs.

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Topics: Doppler spectroscopy (61%), Radial velocity (54%), Doppler effect (53%) ... show more

163 Citations

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M. Lamm^{1}, Coryn A. L. Bailer-Jones^{1}, Reinhard Mundt^{1}, William Herbst^{2} +1 more•Institutions (2)

Abstract: We present the results of an extensive search for periodic and irregular variable pre-main sequence (PMS) stars in the young (2-4 Myr) open cluster NGC 2664, based on photometric monitoring using the Wide Field Imager (WFI) on the 2.2m telescope on La Silla (Chile). In total, about 10600 stars with I_c magnitudes between 9.8mag and 21mag have been monitored in our 34x33 arcmin field. Time series data were obtained in the I_c band in 44 nights between Dec. 2000 and March 2001; altogether we obtained 88 data points per star. Using two different time series analysis techniques (Scargle and CLEAN) we found 543 periodically variable stars with periods between 0.2 days and 15 days. Also, 484 irregular variable stars were identified using a chi-squared-test. In addition we have carried out nearly simultaneous observations in V, R_c and a narrow-band Halpha filter. The photometric data enable us to reject background and foreground stars from our sample of variable stars according to their location in the I_c vs. (R_c-I_c) colour-magnitude and (R_c-Halpha) vs. (R_c-I_c) colour-colour diagram. We could in the end identify 405 periodically variable and 184 irregular variable PMS stars as cluster members using these two different tests. In addition 35 PMS stars for which no significant variablilty were detected could be identified as members using an Halpha emission index criterion. This yields to a total of 624 PMS stars in NGC 2264, of which only 182 were known before. Most of the newly found PMS stars are fainter than I_c = 16 and of late spectral type (>M2). (abridged)

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Topics: Stars (56%), Variable star (56%), Open cluster (55%)

118 Citations

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Jonathan Horner^{1}, Stephen R. Kane^{2}, Jonathan P. Marshall^{3}, Paul A. Dalba^{2} +15 more•Institutions (11)

Abstract: Over the past three decades, we have witnessed one of the great revolutions in our understanding of the cosmos - the dawn of the Exoplanet Era. Where once we knew of just one planetary system (the Solar system), we now know of thousands, with new systems being announced on a weekly basis. Of the thousands of planetary systems we have found to date, however, there is only one that we can study up-close and personal - the Solar system.
In this review, we describe our current understanding of the Solar system for the exoplanetary science community - with a focus on the processes thought to have shaped the system we see today. In section one, we introduce the Solar system as a single well studied example of the many planetary systems now observed. In section two, we describe the Solar system's small body populations as we know them today - from the two hundred and five known planetary satellites to the various populations of small bodies that serve as a reminder of the system's formation and early evolution. In section three, we consider our current knowledge of the Solar system's planets, as physical bodies. In section four, we discuss the research that has been carried out into the Solar system's formation and evolution, with a focus on the information gleaned as a result of detailed studies of the system's small body populations. In section five, we discuss our current knowledge of planetary systems beyond our own - both in terms of the planets they host, and in terms of the debris that we observe orbiting their host stars.
As we learn ever more about the diversity and ubiquity of other planetary systems, our Solar system will remain the key touchstone that facilitates our understanding and modelling of those newly found systems, and we finish section five with a discussion of the future surveys that will further expand that knowledge.

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Topics: Exoplanet (53%), Solar System (53%), Planetary system (51%) ... show more

65 Citations

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187 results found

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Abstract: The history of the development of statistical hypothesis testing in time series analysis is reviewed briefly and it is pointed out that the hypothesis testing procedure is not adequately defined as the procedure for statistical model identification. The classical maximum likelihood estimation procedure is reviewed and a new estimate minimum information theoretical criterion (AIC) estimate (MAICE) which is designed for the purpose of statistical identification is introduced. When there are several competing models the MAICE is defined by the model and the maximum likelihood estimates of the parameters which give the minimum of AIC defined by AIC = (-2)log-(maximum likelihood) + 2(number of independently adjusted parameters within the model). MAICE provides a versatile procedure for statistical model identification which is free from the ambiguities inherent in the application of conventional hypothesis testing procedure. The practical utility of MAICE in time series analysis is demonstrated with some numerical examples.

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Topics: Likelihood function (61%), Akaike information criterion (61%), Statistical model (60%) ... show more

42,619 Citations

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Abstract: The problem of selecting one of a number of models of different dimensions is treated by finding its Bayes solution, and evaluating the leading terms of its asymptotic expansion. These terms are a valid large-sample criterion beyond the Bayesian context, since they do not depend on the a priori distribution.

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Topics: Bayesian information criterion (57%), g-prior (55%), Bayes' theorem (55%) ... show more

35,659 Citations

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01 Jan 2005-

Abstract: The problem of selecting one of a number of models of different dimensions is treated by finding its Bayes solution, and evaluating the leading terms of its asymptotic expansion. These terms are a valid large-sample criterion beyond the Bayesian context, since they do not depend on the a priori distribution.

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Topics: Bayes' theorem (56%), Context (language use) (54%), Asymptotic expansion (54%) ... show more

33,801 Citations

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Abstract: Matplotlib is a 2D graphics package used for Python for application development, interactive scripting,and publication-quality image generation across user interfaces and operating systems

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Topics: 2D computer graphics (56%), Computer graphics (55%), Python (programming language) (54%) ... show more

16,056 Citations

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Abstract: The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System. Furthermore, it is an essential refer ...

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Topics: Solar chemical (55%)

7,780 Citations