Browsing by Author "Ivarsen, K. M."

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    Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue - IV. A 0.61+0.45 M⊙ binary in a multiple system
    (2012) Helminiak, K. G.; Konacki, M.; Rozyczka, M.; Kaluzny, J.; Ratajczak, M.; Borkowski, J.; Sybilski, P.; Muterspaugh, M. W.; Reichart, D. E.; Ivarsen, K. M.; Haislip, J. B.; Crain, J. A.; Foster, A. C.; Nysewander, M. C.; LaCluyze, A. P.
    We present the orbital and physical parameters of a newly discovered low-mass detached eclipsing binary from the All-Sky Automated Survey (ASAS) data base: ASAS J0113283821.1 A, which is a member of a visual binary system with the secondary component separated by about 1.4 arcsec. The radial velocities have been calculated from the high-resolution spectra obtained with the 1.9-m Radcliffe telescope/Grating Instrument for Radiation Analysis with a Fibre-Fed Echelle (GIRAFFE) spectrograph, the 3.9-m Anglo-Australian Telescope (AAT)/University College London Echelle Spectrograph (UCLES) and the 3.0-m Shane telescope/Hamilton Spectrograph (HamSpec) on the basis of the todcor technique and the positions of the Ha emission lines. For the analysis, we have used V- and I-band photometry obtained with the 1.0-m Elizabeth telescope and the 0.41-m Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT), supplemented with the publicly available ASAS light curve of the system. We have found that ASAS J0113283821.1 A is composed of two late-type dwarfs, which have masses of M1 = 0.612 +/- 0.030 M? and M2 = 0.445 +/- 0.019 M? and radii of R1 = 0.596 +/- 0.020 R? and R2 = 0.445 +/- 0.024 R?. Both show a substantial level of activity, which manifests in strong Ha and H beta emission and the presence of cool spots. The influence of the third light on the eclipsing pair properties has also been evaluated and the photometric properties of component B have been derived. A comparison with several popular stellar evolution models shows that the system is on its main-sequence evolution stage and that it is probably more metal-rich than the Sun. We have also found several clues to suggest that component B itself is a binary composed of two nearly identical similar to 0.5-M? stars.
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    PLUTO's ATMOSPHERE FROM STELLAR OCCULTATIONS IN 2012 AND 2013
    (2015) Dias-Oliveira, A.; Sicardy, B.; Lellouch, E.; Vieira-Martins, R.; Assafin, M.; Camargo, J. I. B.; Braga-Ribas, F.; Gomes-Junior, A. R.; Benedetti-Rossi, G.; Colas, F.; Decock, A.; Doressoundiram, A.; Dumas, C.; Emilio, M.; Fabrega Polleri, J.; Gil-Hutton, R.; Gillon, M.; Girard, J. H.; Hau, G. K. T.; Ivanov, V. D.; Jehin, E.; Lecacheux, J.; Leiva, R.; Lopez-Sisterna, C.; Mancini, L.; Manfroid, J.; Maury, A.; Meza, E.; Morales, N.; Nagy, L.; Opitom, C.; Ortiz, J. L.; Pollock, J.; Roques, F.; Snodgrass, C.; Soulier, J. F.; Thirouin, A.; Vanzi, L.; Widemann, T.; Reichart, D. E.; LaCluyze, A. P.; Haislip, J. B.; Ivarsen, K. M.; Dominik, M.; Jorgensen, U.; Skottfelt, J.
    We analyze two multi-chord stellar occultations by Pluto that were observed on 2012 July 18th and 2013 May 4th, and respectively monitored from five and six sites. They provide a total of fifteen light curves, 12 of which were used for a simultaneous fit that uses a unique temperature profile, assuming a clear (no haze) and pure N-2 atmosphere, but allowing for a possible pressure variation between the two dates. We find a solution that satisfactorily fits (i.e., within the noise level) all of the 12 light curves, providing atmospheric constraints between similar to 1190 km (pressure similar to 11 mu bar) and similar to 1450 km (pressure similar to 0.1 mu bar) from Pluto's center. Our main results are: (1) the best-fitting temperature profile shows a stratosphere with a strong positive gradient between 1190 km (at 36 K, 11 mu bar) and r = 1215 km (6.0 mu bar), where a temperature maximum of 110 K is reached; above it is a mesosphere with a negative thermal gradient of -0.2 K km(-1) up to similar to 1390 km (0.25 mu bar), where the mesosphere connects itself to a more isothermal upper branch around 81 K; (2) the pressure shows a small (6%) but significant increase (6 sigma level) between the two dates; (3) without a troposphere, Pluto's radius is found to be R-P = 1190 +/- 5 km. Allowing for a troposphere, R-P is constrained to lie between 1168 and 1195 km; and (4) the currently measured CO abundance is too small to explain the mesospheric negative thermal gradient. Cooling by HCN is possible, but only if this species is largely saturated. Alternative explanations like zonal winds or vertical compositional variations of the atmosphere are unable to explain the observed mesospheric negative thermal gradient.