Search Publications
The puzzling high velocity G5 supergiant star HD 179821: new insight from Gaia DR2 data
Jasniewicz, G.; Parthasarathy, M.; Thěvenin, F.
HD 179821 is classified as G5 Ia star. From the IRAS colors and spectral energy distributions it was classified as a post-AGB star. But some studies classify it as a massive (30 to
Seasonal change of CH4/H2 ratio in the atmosphere of Uranus
Tu, Cui; Wang, Cong; Hu, Xiong
Uranus is mainly composed of elements heavier than hydrogen and helium, such as C, S, even though very little information about these elements has been detected. Methane is one of the most important component of the atmosphere of Uranus. Analysis of the full-disk spectra of Uranus, as observed by the Xinglong 2.16m telescope with BFOSC (Beijing-Fa…
Search for variable stars in the northern sky: analysis of photometric time series for 3598 stars
Tautvaišienė, G.; Drazdauskas, A.; Mikolaitis, Š. +6 more
As extensive ground-based observations and characterisation of different variable stars are of the utmost importance in preparing optimal input catalogues for space missions, our aim was to search for new variable stars in selected fields of the northern sky. We obtained 24 470 CCD images and analysed photometric time series of stars using the DAO…
The intermediate age population of the Galactic halo
Mould, Jeremy
We have learned recently that the inner halo of the Milky Way contains a kinematically coherent component (Gaia-Enceladus) from a significant merger 10 Gyrs ago. By contrast the inner (defined to exclude the Magellanic Stream) halo contains no similar intruder stellar population of billion year age. The tracer we use to set the corresponding upper…
The Pleiades apex and its kinematical structure
Yadav, R. K. S.; Vereshchagin, S. V.; Chupina, N. V. +4 more
A study of cluster characteristics and internal kinematical structure of the middle-aged Pleiades open star cluster is presented. The individual star apexes and various cluster kinematical parameters including the velocity ellipsoid parameters are determined using both Hipparcos and Gaia data. Modern astrometric parameters were taken from the Gaia…
A simultaneous spectroscopic and photometric study of two eclipsing binaries: V566 Oph and V972 Her
Yılmaz, M.; Selam, S. O.; Esmer, E. M. +4 more
In this study, we have performed simultaneous solutions of light and radial velocity curves of two eclipsing binary systems, V566 Oph and V972 Her. We observed both systems spectroscopically with a very recently installed spectrograph on the 40 cm telescope, T40, located in Ankara University Kreiken Observatory (AUKR), for the first time. We made …
A study of pulsation & rotation in a sample of A-K type stars in the Kepler field
Paul, K. T.; Engelbrecht, Chris A.; Joshi, Santosh +3 more
We present the results of time-series photometric analysis of 15106 A-K type stars observed by the Kepler space mission. We identified 513 new rotational variables and measured their starspot rotation periods as a function of spectral type and discuss the distribution of their amplitudes. We examined the well-established period-color relationship …
Memberships, distance and proper-motion of the open cluster NGC 188 based on a machine learning method
Gao, Xin-Hua
In this paper, we present an investigation of the memberships, distance and proper motion for the old open cluster NGC 188 using a machine-learning-based method. This method combines two widely used algorithms: spectral clustering (SC) and random forest (RF). The former one is used to construct a reliable training set, the membership probabilities…
Protostellar classification using supervised machine learning algorithms
Miettinen, O.
Classification of young stellar objects (YSOs) into different evolutionary stages helps us to understand the formation process of new stars and planetary systems. Such classification has traditionally been based on spectral energy distribution (SED) analysis. An alternative approach is provided by supervised machine learning algorithms, which can …
The global modulation of Galactic and Jovian electrons in the heliosphere
Potgieter, Marius S.; Nndanganeni, Rendani R.
A full three-dimensional, numerical model is used to study the modulation of Jovian and Galactic electrons from 1 MeV to 50 GeV, and from the Earth into the heliosheath. For this purpose the very local interstellar spectrum and the Jovian electron source spectrum are revisited. It is possible to compute the former with confidence at kinetic energi…