Browsing by Author "Sajadian, S."

Now showing 1 - 6 of 6
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    Digging deeper into the dense Galactic globular cluster Terzan 5 with electron-multiplying CCDs Variable star detection and new discoveries
    (2024) Jaimes, R. Figuera; Catelan, M.; Horne, K.; Skottfelt, J.; Snodgrass, C.; Dominik, M.; Jorgensen, U. G.; Southworth, J.; Hundertmark, M.; Longa-Pena, P.; Sajadian, S.; Tregolan-Reed, J.; Hinse, T. C.; Andersen, M. I.; Bonavita, M.; Bozza, V.; Burgdorf, M. J.; Haikala, L.; Khalouei, E.; Korhonen, H.; Peixinho, N.; Rabus, M.; Rahvar, S.
    Context. High frame-rate imaging was employed to mitigate the effects of atmospheric turbulence (seeing) in observations of globular cluster Terzan 5.
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    Gaia21blx: Complete resolution of a binary microlensing event in the Galactic disk
    (2024) Rota, P.; Bozza, V.; Hundertmark, M.; Bachelet, E.; Street, R.; Tsapras, Y.; Cassan, A.; Dominik, M.; Jaimes, R. Figuera; Rybicki, K. A.; Wambsganss, J.; Wyrzykowski, L.; Zielinski, P.; Bonavita, M.; Hinse, T. C.; Jorgensen, U. G.; Khalouei, E.; Korhonen, H.; Longa-Pena, P.; Peixinho, N.; Rahvar, S.; Sajadian, S.; Skottfelt, J.; Snodgrass, C.; Tregolan-Reed, J.
    Context. Gravitational microlensing is a method that is used to discover planet-hosting systems at distances of several kiloparsec in the Galactic disk and bulge. We present the analysis of a microlensing event reported by the Gaia photometric alert team that might have a bright lens. Aims. In order to infer the mass and distance to the lensing system, the parallax measurement at the position of Gaia21blx was used. In this particular case, the source and the lens have comparable magnitudes and we cannot attribute the parallax measured by Gaia to the lens or source alone. Methods. Since the blending flux is important, we assumed that the Gaia parallax is the flux-weighted average of the parallaxes of the lens and source. Combining this assumption with the information from the microlensing models and the finite source effects we were able to resolve all degeneracies and thus obtained the mass, distance, luminosities and projected kinematics of the binary lens and the source. Results. According to the best model, the lens is a binary system at 2.18 +/- 0.07 kpc from Earth. It is composed of a G star with 0.95 +/- 0.17 M-circle dot and a K star with 0.53 +/- 0.07 M-circle dot. The source is likely to be an F subgiant star at 2.38 +/- 1.71 kpc with a mass of 1.10 +/- 0.18 M-circle dot. Both lenses and the source follow the kinematics of the thin-disk population. We also discuss alternative models, that are disfavored by the data or by prior expectations, however.
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    Precision measurement of a brown dwarf mass in a binary system in the microlensing event OGLE-2019-BLG-0033/MOA-2019-BLG-035
    (2022) Herald, A.; Udalski, A.; Bozza, V.; Rota, P.; Bond, I. A.; Yee, J. C.; Sajadian, S.; Mroz, P.; Poleski, R.; Skowron, J.; Szymanski, M. K.; Soszynski, I.; Pietrukowicz, P.; Kozlowski, S.; Ulaczyk, K.; Rybicki, K. A.; Iwanek, P.; Wrona, M.; Gromadzki, M.; Abe, F.; Barry, R.; Bennett, D. P.; Bhattacharya, A.; Fukui, A.; Fujii, H.; Hirao, Y.; Itow, Y.; Kirikawa, R.; Kondo, I.; Koshimoto, N.; Matsubara, Y.; Matsumoto, S.; Miyazaki, S.; Muraki, Y.; Olmschenk, G.; Ranc, C.; Okamura, A.; Rattenbury, N. J.; Satoh, Y.; Sumi, T.; Suzuki, D.; Silva, S. Ishitani; Toda, T.; Tristram, P. J.; Vandorou, A.; Yama, H.; Beichman, C. A.; Bryden, G.; Novati, S. Calchi; Carey, S.; Gaudi, B. S.; Gould, A.; Henderson, C. B.; Johnson, S.; Shvartzvald, Y.; Zhu, W.; Dominik, M.; Hundertmark, M.; Jorgensen, U. G.; Longa-Pena, P.; Skottfelt, J.; Tregloan-Reed, J.; Bach-Moller, N.; Burgdorf, M.; D'Ago, G.; Haikala, L.; Hitchcock, J.; Khalouei, E.; Peixinho, N.; Rahvar, S.; Snodgrass, C.; Southworth, J.; Spyratos, P.; Zang, W.; Yang, H.; Mao, S.; Bachelet, E.; Maoz, D.; Street, R. A.; Tsapras, Y.; Christie, G. W.; Cooper, T.; de Almeida, L.; do Nascimento, J. -D., Jr.; Green, J.; Han, C.; Hennerley, S.; Marmont, A.; McCormick, J.; Monard, L. A. G.; Natusch, T.; Pogge, R.
    Context. Brown dwarfs are transition objects between stars and planets that are still poorly understood, for which several competing mechanisms have been proposed to describe their formation. Mass measurements are generally difficult to carry out for isolated objects as well as for brown dwarfs orbiting low-mass stars, which are often too faint for a spectroscopic follow-up.
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    Star-spot activity, orbital obliquity, transmission spectrum, physical properties, and transit time variations of the HATS-2 planetary system
    (2024) Biagiotti, F.; Mancini, L.; Southworth, J.; Tregloan-Reed, J.; Naponiello, L.; Jorgensen, U. G.; Bach-Moller, N.; Basilicata, M.; Bonavita, M.; Bozza, V.; Burgdorf, M. J.; Dominik, M.; Jaimes, R. Figuera; Henning, Th.; Hinse, T. C.; Hundertmark, M.; Khalouei, E.; Longa-Pena, P.; Peixinho, N.; Rabus, M.; Rahvar, S.; Sajadian, S.; Skottfelt, J.; Snodgrass, C.; Jongen, Y.; Vignes, J. -p
    Aims. Our aim in this paper is to refine the orbital and physical parameters of the HATS-2 planetary system and study transit timing variations and atmospheric composition thanks to transit observations that span more than 10 yr and that were collected using different instruments and pass-band filters. We also investigate the orbital alignment of the system by studying the anomalies in the transit light curves induced by starspots on the photosphere of the parent star. Methods. We analysed new transit events from both ground-based telescopes and NASA's TESS mission. Anomalies were detected in most of the light curves and modelled as starspots occulted by the planet during transit events. We fitted the clean and symmetric light curves with the JKTEBOP code and those affected by anomalies with the PRISM+GEMC codes to simultaneously model the photometric parameters of the transits and the position, size, and contrast of each starspot. Results. We found consistency between the values we found for the physical and orbital parameters and those from the discovery paper and ATLAS9 stellar atmospherical models. We identified different sets of consecutive starspot-crossing events that temporally occurred in less than five days. Under the hypothesis that we are dealing with the same starspots, occulted twice by the planet during two consecutive transits, we estimated the rotational period of the parent star and, in turn the projected and the true orbital obliquity of the planet. We find that the system is well aligned. We identified the possible presence of transit timing variations in the system, which can be caused by tidal orbital decay, and we derived a low-resolution transmission spectrum.
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    Transit timing variations in the WASP-4 planetary system
    (2019) Southworth, J.; Dominik, M.; Jorgensen, U. G.; Andersen, M. I.; Bozza, V.; Burgdorf, M. J.; D'Ago, Giuseppe; Dib, S.; Jaimes, R. F.; Fujii, Y. I.; Gill, S.; Haikala, L. K.; Hinse, T. C.; Hundertmark, M.; Khalouei, E.; Korhonen, H.; Longa Pena, P.; Mancini, L.; Peixinho, N.; Rabus, Markus; Rahvar, S.; Sajadian, S.; Skottfelt, J.; Snodgrass, C.; Spyratos, P.; Tregloan Reed, J.; Unda Sanzana, E.; Von Essen, C.