Yazar "Rhodes, Michael D." seçeneğine göre listele

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    Exoplanet system Kepler-2 with comparisons to Kepler-1 and 13
    (Springer, 2020) Rhodes, Michael D.; Puskullu, Caglar; Budding, Edwin; Banks, Timothy S.
    We have carried out an intensive study of photometric (Kepler Mission) and spectroscopic data on the system Kepler-2 (HAT-P-7A) using the dedicated software WinFitter 6.4. The mean individual data-point error of the normalized flux values for this system is 0.00015, leading to the model's specification for the mean reference flux to an accuracy of similar to 0.5 ppm. This testifies to the remarkably high accuracy of the binned data-set, derived from over 1.8 million individual observations. Spectroscopic data are reported with the similarly high-accuracy radial velocity amplitude measure of similar to 2 m s(-1). The analysis includes discussion of the fitting quality and model adequacy. Our derived absolute parameters for Kepler-2 are as follows: Mp (Jupiter) 1.80 +/- 0.13; R1.46 +/- 0.08x106 km; Rp km. These values imply somewhat larger and less condensed bodies than previously catalogued, but within reasonable error estimates of such literature parameters. We find also tidal, reflection and Doppler effect parameters, showing that the optimal model specification differs slightly from a 'cleaned' model that reduces the standard deviation of the similar to 3600 binned light curve points to less than 0.9 ppm. We consider these slight differences, making comparisons with the hot-Jupiter systems Kepler-1 (TrES-2) and 13. We confirm that the star's rotation axis must be shifted towards the line of sight, though how closely depends on what rotation velocity is adopted for the star. From joint analysis of the spectroscopic and photometric data we find an equatorial rotation speed of 11 +/- 3 km s(-1). A slightly brighter region of the photosphere that distorts the transit shape can be interpreted as an indication of the gravity effect at the rotation pole; however we note that the geometry for this does not match the spectroscopic result. We discuss this difference, rejecting the possibility that a real shift in the position of the rotation axis in the few years between the spectroscopic and photometric data-collection times.Alternative explanations are considered, but we conclude that renewed detailed observations are required to help settle these questions.
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    Optimization applied to selected exoplanets
    (Springer, 2021) Ng, Shi Yuan; Jiadi, Zhou; Püsküllü, Çağlar; Banks, Timothy; Budding, Edwin; Rhodes, Michael D.
    Transit and radial velocity models were applied to archival data in order to examine exoplanet properties, in particular for the recently discovered super-Earth GJ357b. There is however considerable variation in estimated model parameters across the literature, and especially their uncertainty estimates. This applies even for relatively uncomplicated systems and basic parameters. Some published accuracy values thus appear highly overoptimistic. We present our reanalyses with these variations in mind and specify parameters with appropriate confidence intervals for the exoplanets Kepler-1b, -2b, -8b, -12b, -13b, -14b, -15b, -40b and -77b and 51 Peg. More sophisticated models in WINFITTER (WF), EXOFAST and DACE were applied, leading to mean planet densities for Kepler-12b, -14b, -15b and -40b as: 0:11 0:01, 4:04 0:58, 0:43 0:05 and 1:19þ0:31 0:36 g per cc respectively. We confirm a rocky mean density for the Earth-like GJ357b, although we urge caution about the modelling given the low S/N data. We cannot confidently specify parameters for the other two proposed planets in this system.
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    V410 Puppis: A useful laboratory for early stellar evolution
    (Oxford Univ Press, 2022) Erdem, Ahmet; Surgit, Derya; Ozkardes, Burcu; Hadrava, Petr; Rhodes, Michael D.; Love, Tom; Blackford, Mark G.
    New spectrometric (HERCULES) and ground-based multicolour photometric data on the multiple star V410 Puppis are combined with satellite photometry (HIPPARCOS and TESS), as well as historic astrometric observations. Absolute parameters for V410 Pup Aab are derived: M-Aa = 3.15 +/- 0.10, M-Ab = 1.83 +/- 0.08 (M-circle dot); R-Aa = 2.12 +/- 0.10, R-Ab = 1.52 +/- 0.08 (R-circle dot); a = 6.57 +/- 0.04 R-circle dot; T-Aa = 12500 +/- 1000, T-Ab = 9070 +/- 800(K), and photometric distance 350 +/- 10 (pc). We report the discovery of a low-amplitude SPB variation in the light curve and also indications of an accretion structure around V410 Pup B as well as emission cores in V410 Pup C. We argue that V410 Pup is probably a young formation connected with the Vela 2 OB Association. The combined evidence allows an age in the range 7-25 Myr from comparisons with standard stellar evolution modelling.