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Aslan Z.,TUBI TAK National Observatory | Gumerov R.,Kazan Federal University | Jin W.,Shanghai Astronomical Observatory | Khamitov I.,TUBI TAK National Observatory | And 4 more authors.
Astronomy and Astrophysics | Year: 2010

We discuss the results of an investigation of astrometric positions of extragalactic radio sources from a list for the International Celestial Reference Frame. About 300 fields around extragalactic radio sources were observed during the years 2000-2003. The observations were performed mainly using two telescopes equipped with CCD cameras at TUG, Turkey (Russian-Turkish Telescope - RTT150) and at YAO (1 m telescope), (Kunming, China). The mean accuracies of the measured positions are 38 mas in right ascension and 35 mas in declination. A comparison between the measured optical positions determined using the UCAC2 catalog and the radio positions from the current ICRF shows that the overall optical-minus- radio offsets are -4 and +15 mas for right ascension and declination, respectively. The formal internal errors of these mean offsets are 4 mas. The results of optical positions with respect to the reference catalogue 2MASS are also given. A search for a relation between optical and radio reference frames indicates that the orientation angles are near zero within their accuracy of about 5 mas. The link accuracy becomes 3 mas when our observations are combined with other studies. © ESO, 2010.

Thuillot W.,Lille University of Science and Technology | Bancelin D.,Lille University of Science and Technology | Bancelin D.,University of Vienna | Ivantsov A.,Lille University of Science and Technology | And 75 more authors.
Astronomy and Astrophysics | Year: 2015

Aims. Astrometric observations performed by the Gaia Follow-Up Network for Solar System Objects (Gaia-FUN-SSO) play a key role in ensuring that moving objects first detected by ESA's Gaia mission remain recoverable after their discovery. An observation campaign on the potentially hazardous asteroid (99 942) Apophis was conducted during the asteroid's latest period of visibility, from 12/21/2012 to 5/2/2013, to test the coordination and evaluate the overall performance of the Gaia-FUN-SSO. Methods. The 2732 high quality astrometric observations acquired during the Gaia-FUN-SSO campaign were reduced with the Platform for Reduction of Astronomical Images Automatically (PRAIA), using the USNO CCD Astrograph Catalogue 4 (UCAC4) as a reference. The astrometric reduction process and the precision of the newly obtained measurements are discussed. We compare the residuals of astrometric observations that we obtained using this reduction process to data sets that were individually reduced by observers and accepted by the Minor Planet Center. Results. We obtained 2103 previously unpublished astrometric positions and provide these to the scientific community. Using these data we show that our reduction of this astrometric campaign with a reliable stellar catalog substantially improves the quality of the astrometric results. We present evidence that the new data will help to reduce the orbit uncertainty of Apophis during its close approach in 2029. We show that uncertainties due to geolocations of observing stations, as well as rounding of astrometric data can introduce an unnecessary degradation in the quality of the resulting astrometric positions. Finally, we discuss the impact of our campaign reduction on the recovery process of newly discovered asteroids. © 2015 ESO.

Usenko I.A.,Odessa I I Mechnikov National University | Usenko I.A.,Nikolaev Astronomical Observatory | Klochkova V.G.,Russian Academy of Sciences | Tavolzhanskaya N.S.,Russian Academy of Sciences
Astronomy Letters | Year: 2013

A new set of 16 high-resolution spectra for the small-amplitude Cepheid SU Cas obtained in 2007-2009 has allowed us to determine its atmospheric parameters (Teff= 6345 ± 30 K, log g= 2.40, Vt= 3.25 km s-1) and to measure its radial velocities. The latter were added to the general list of radial velocities (375 estimates) obtained in the last 90 years. Using a frequency analysis, we have refined the pulsation and orbital periods of the Cepheid. Apart from the well-known fundamental pulsation period [Figure not available: see fulltext.], we have detected a possible secondary period of [Figure not available: see fulltext.]. Their ratio of 0.96 suggests the existence of nonradial pulsations in the Cepheid's atmosphere. Based on photoelectric photometry in the last 60 years, we have shown that the effective temperature undergoes cyclic secular changes of ±200 K with an unknown period. The mean effective temperature Teff= 6395 ± 52 K estimated from photometric data agrees well with our estimate from spectroscopic data. The variations of the mean color index, effective temperature, and γ-velocity (in 90 years of observations) point to a possible orbital motion of the well-known hot companion with the most probable periods of [Figure not available: see fulltext.], [Figure not available: see fulltext.], and [Figure not available: see fulltext.]. The elemental abundances in the atmosphere of SU Cas confirm the conclusion that this Cepheid is a typical yellow supergiant after the first dredge-up. Our Teff estimate gives a radius of 32R⊙ and a distance of 455 pc for it, which is inconsistent with its membership in the open cluster Alessi 95. The question about the pulsation mode of SU Cas still remains open. © 2013 Pleiades Publishing, Ltd.

Nechaeva M.,Ventspils International Radio Astronomy Center | Antipenko A.,Radiophysical Research Institute RRI | Bezrukovs V.,Ventspils International Radio Astronomy Center | Bezrukov D.,Ventspils International Radio Astronomy Center | And 17 more authors.
Baltic Astronomy | Year: 2013

An experiment on radar location of space debris objects using of the method of VLBI was carried out in April, 2012. The radar VLBI experiment consisted in irradiation of some space debris objects (4 rocket stages and 5 inactive satellites) with a signal of the transmitter with RT-70 in Evpatoria, Ukraine. Reflected signals were received by a complex of radio telescopes in the VLBI mode. The following VLBI stations took part in the observations: Ventspils (RT-32), Urumqi (RT-25), Medicina (RT-32) and Simeiz (R.T-22). The experiment included measurements of the Doppler frequency shift and the delay for orbit refining, and measurements of the rotation period and sizes of objects by the amplitudes of output interferometer signals. The cross-correlation of VLBI-data is performed at a correlator NIRFI-4 of Radiophysical Research Institute (Nizhny Novgorod). Preliminary data processing resulted in the series of Doppler frequency shifts, which comprised the information on radial velocities of the objects. Some results of the experiment are presented.

Usenko I.A.,Odessa I I Mechnikov National University | Usenko I.A.,Nikolaev Astronomical Observatory | Kniazev A.Y.,South African Astronomical Observatory | Kniazev A.Y.,Southern African Large Telescope Foundation | And 4 more authors.
Astronomy Letters | Year: 2014

This paper is devoted to spectroscopic studies of three bright Cepheids (BG Cru, R Cru, and T Cru) and continues the series of our works aimed at determining the atmospheric parameters and chemical composition of southern-hemisphere Cepheids. We have studied 12 high-resolution spectra taken with the 1.9-m telescope of the South African Astronomical Observatory and the 8-m VLT telescope of the European Southern Observatory in Chile. The atmospheric parameters and chemical composition have been determined for these stars. The averaged atmospheric parameters are: T eff = 6253 ± 30 K, log g = 2.15, V t = 4.30 km s-1 for BG Cru; T eff = 5812 ± 22 K, log g = 1.65, V t = 3.80 km s-1 for R Cru; and T eff = 5588 ± 21 K, log g = 1.70, V t = 4.30 km s-1 for T Cru. All these Cepheids exhibit a nearly solar metallicity ([Fe/H] = +0.04 dex for BG Cru, +0.06 dex for R Cru, and +0.08 dex for T Cru); the carbon, oxygen, sodium, magnesium, and aluminum abundances suggest that the objects have already passed the first dredge-up. The abundances of other elements are nearly solar. An anomalous behavior of the absorption lines of metals (neutral atoms and ions) in the atmosphere of the small-amplitude Cepheid BG Cru is pointed out. The main components in these lines split up into additional blue and red analogs that are smaller in depth and equivalent width and vary with pulsation phase. Such splitting of the absorption lines of metals (with the hydrogen lines being invariable) is known for the classical Cepheid X Sgr. The calculated nonlinear pulsation model of BG Cru with the parameters L = 2000 L ⊙, T eff = 6180 K, and M = 4.3M ⊙ shows that this small-amplitude Cepheid pulsates in the first overtone and is close to the blue boundary of the Cepheid instability strip. According to the model, the extent of the Cepheid's atmosphere is relatively small. Therefore, no spectroscopic manifestations of shock waves through variability are possible in this Cepheid and the observed blue and red components in metal absorption lines can be explained solely by the presence of an extended circumstellar envelope around BG Cru. © 2014 Pleiades Publishing, Inc.

Andruk V.M.,Ukrainian Academy of Sciences | Golovnia V.V.,Ukrainian Academy of Sciences | Ivanov G.A.,Ukrainian Academy of Sciences | Yizhakevich E.M.,Ukrainian Academy of Sciences | And 3 more authors.
Kinematics and Physics of Celestial Bodies | Year: 2016

The catalog of equatorial coordinates α and δ and B-magnitudes of stars has been created at the Main Astronomical Observatory, National Academy of Sciences of Ukraine (MAO NASU), for the circumpolar region (from 58° to 90°) of the Northern Sky Survey (FON) project within the work on the rational use of resources accumulated in the JDA (Joint Digital Archive) of the Ukrainian Virtual Observatory (UkrVO). The total number of processed plates is 477. The plates were digitized with the using Microtek ScanMaker 9800XL TMA and Epson Expression 10000XL scanners (scanning mode was 1200 dpi, the linear size of plates was 30 × 30 cm or 13000 × 13000 px). The catalog includes 1 975 967 stars and galaxies with B of up to 16.5m as of the epoch of 1985.28. The coordinates of stars and galaxies were obtained in the Tycho-2 reference system and B-magnitudes were obtained in the system of photoelectric standards. The internal errors of the catalog for all the objects are σαδ = 0.23′′ and σB = 0.12m, and those for stars of the B range from 8m–14m, 0.11′′ and 0.06m, respectively. The convergence between the calculated and reference positions is σαδ = 0.06′′ (for 171124 stars from Tycho-2), and that between the photoelectric stellar B-magnitudes is σB = 0.15m (for 5130 stars). The external error from the comparison with UCAC-4 are σαδ = 0.33′′ (1928367 stars and galaxies have been cross identified). © 2016, Allerton Press, Inc.

Martynov M.V.,Nikolaev Astronomical Observatory | Maigurova N.V.,Nikolaev Astronomical Observatory | Pinigin G.I.,Nikolaev Astronomical Observatory
Kinematics and Physics of Celestial Bodies | Year: 2013

As a result of observations in 2008-2011 with the axial meridian circle of the Nikolaev Astronomical Observatory, we compiled two catalogs with a total of 284557 objects. We conducted a search for probable candidates for binary and multiple systems using the method checking differences between quasi-instantaneous and long-term proper motions for statistical significance. The resulting list of probable candidates for double and multiple systems with invisible companions contains 9379 objects. © 2013 Allerton Press, Inc.

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