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Author Elorrieta, F.; Eyheramendy, S.; Palma, W. pdf  doi
openurl 
  Title Discrete-time autoregressive model for unequally spaced time-series observations Type Journal Article
  Year 2019 Publication Astronomy & Astrophysics Abbreviated Journal Astron. Astrophys.  
  Volume 627 Issue Pages 11 pp  
  Keywords methods: statistical; methods: data analysis; stars: general  
  Abstract Most time-series models assume that the data come from observations that are equally spaced in time. However, this assumption does not hold in many diverse scientific fields, such as astronomy, finance, and climatology, among others. There are some techniques that fit unequally spaced time series, such as the continuous-time autoregressive moving average (CARMA) processes. These models are defined as the solution of a stochastic differential equation. It is not uncommon in astronomical time series, that the time gaps between observations are large. Therefore, an alternative suitable approach to modeling astronomical time series with large gaps between observations should be based on the solution of a difference equation of a discrete process. In this work we propose a novel model to fit irregular time series called the complex irregular autoregressive (CIAR) model that is represented directly as a discrete-time process. We show that the model is weakly stationary and that it can be represented as a state-space system, allowing efficient maximum likelihood estimation based on the Kalman recursions. Furthermore, we show via Monte Carlo simulations that the finite sample performance of the parameter estimation is accurate. The proposed methodology is applied to light curves from periodic variable stars, illustrating how the model can be implemented to detect poor adjustment of the harmonic model. This can occur when the period has not been accurately estimated or when the variable stars are multiperiodic. Last, we show how the CIAR model, through its state space representation, allows unobserved measurements to be forecast.  
  Address [Elorrieta, Felipe] Univ Santiago Chile, Fac Ciencia, Dept Matemat, Av Libertador Bernardo OHiggins 3663, Santiago, Chile, Email: susana@mat.puc.cl  
  Corporate Author Thesis  
  Publisher Edp Sciences S A Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1432-0746 ISBN Medium  
  Area Expedition Conference  
  Notes WOS:000475288300001 Approved no  
  Call Number UAI @ eduardo.moreno @ Serial 1016  
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Author Mancini, L.; Sarkis, P.; Henning, T.; Bakos, G.A.; Bayliss, D.; Bento, J.; Bhatti, W.; Brahm, R.; Csubry, Z.; Espinoza, N.; Hartman, J.; Jordan, A.; Penev, K.; Rabus, M.; Suc, V.; de Val-Borro, M.; Zhou, G.; Chen, G.; Damasso, M.; Southworth, J.; Tan, T.G. doi  openurl
  Title The highly inflated giant planet WASP-174b Type Journal Article
  Year 2020 Publication Astronomy & Astrophysics Abbreviated Journal Astron. Astrophys.  
  Volume 633 Issue Pages 12 pp  
  Keywords planetary systems; stars: fundamental parameters; stars: individual: WASP-174; techniques: photometric; techniques: radial velocities; methods: data analysis  
  Abstract Context. The transiting exoplanetary system WASP-174 was reported to be composed by a main-sequence F star (V = 11.8 mag) and a giant planet, WASP-174b (orbital period P-orb = 4.23 days). However only an upper limit was placed on the planet mass (<1.3 M-Jup), and a highly uncertain planetary radius (0.7-1.7 R-Jup) was determined.Aims. We aim to better characterise both the star and the planet and precisely measure their orbital and physical parameters.Methods. In order to constrain the mass of the planet, we obtained new measurements of the radial velocity of the star and joined them with those from the discovery paper. Photometric data from the HATSouth survey and new multi-band, high-quality (precision reached up to 0.37 mmag) photometric follow-up observations of transit events were acquired and analysed for getting accurate photometric parameters. We fit the model to all the observations, including data from the TESS space telescope, in two different modes: incorporating the stellar isochrones into the fit, and using an empirical method to get the stellar parameters. The two modes resulted to be consistent with each other to within 2<sigma>.Results. We confirm the grazing nature of the WASP-174b transits with a confidence level greater than 5 sigma, which is also corroborated by simultaneously observing the transit through four optical bands and noting how the transit depth changes due to the limb-darkening effect. We estimate that approximate to 76% of the disk of the planet actually eclipses the parent star at mid-transit of its transit events. We find that WASP-174b is a highly-inflated hot giant planet with a mass of M-p = 0.330 +/- 0.091 M-Jup and a radius of R-p = 1.435 +/- 0.050 R-Jup, and is therefore a good target for transmission-spectroscopy observations. With a density of rho (p) = 0.135 +/- 0.042 g cm(-3), it is amongst the lowest-density planets ever discovered with precisely measured mass and radius.  
  Address [Mancini, L.] Univ Roma Tor Vergata, Dept Phys, Via Ric Sci 1, I-00133 Rome, Italy, Email: lmancini@roma2.infn.it  
  Corporate Author Thesis  
  Publisher Edp Sciences S A Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1432-0746 ISBN Medium  
  Area Expedition Conference  
  Notes WOS:000505741300005 Approved no  
  Call Number UAI @ eduardo.moreno @ Serial 1093  
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Author Sandford, E.; Espinoza, N.; Brahm, R.; Jordan, A. doi  openurl
  Title Estimation of singly transiting K2 planet periods with Gaia parallaxes Type Journal Article
  Year 2019 Publication Monthly Notices Of The Royal Astronomical Society Abbreviated Journal Mon. Not. Roy. Astron. Soc.  
  Volume 489 Issue 3 Pages 3149-3161  
  Keywords methods: data analysis; methods: statistical; planets and satellites: fundamental parameters; stars: planetary systems  
  Abstract When a planet is only observed to transit once, direct measurement of its period is impossible. It is possible, however, to constrain the periods of single transiters, and this is desirable as they are likely to represent the cold and far extremes of the planet population observed by any particular survey. Improving the accuracy with which the period of single transiters can be constrained is therefore critical to enhance the long-period planet yield of surveys. Here, we combine Gaia parallaxes with stellar models and broad-band photometry to estimate the stellar densities of K2 planet host stars, then use that stellar density information to model individual planet transits and infer the posterior period distribution. We show that the densities we infer are reliable by comparing with densities derived through asteroseismology, and apply our method to 27 validation planets of known (directly measured) period, treating each transit as if it were the only one, as well as to 12 true single transiters. When we treat eccentricity as a free parameter, we achieve a fractional period uncertainty over the true single transits of 94(-58)(+87) per cent, and when we fix e = 0, we achieve fractional period uncertainty 15(-6)(+30) per cent, a roughly threefold improvement over typical period uncertainties of previous studies.  
  Address [Sandford, Emily] Columbia Univ, Dept Astron, 550 W 120th St, New York, NY 10027 USA, Email: esandford@astro.columbia.edu  
  Corporate Author Thesis  
  Publisher Oxford Univ Press Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0035-8711 ISBN Medium  
  Area Expedition Conference  
  Notes WOS:000489288600015 Approved no  
  Call Number UAI @ eduardo.moreno @ Serial 1088  
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