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Cassini-Huygens results on Titan's surface

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Chinese Journal of Astronomy and Astrophysics 2009年第3期9卷 249-268页

作者： Athena Coustenis Mathieu Hirtzig LESIA Observatoire de Meudon

Our understanding of Titan, Saturn＇s largest satellite, has recently been considerably enhanced, thanks to the Cassini-Huygens mission. Since the Saturn Orbit Injection in July 2004, the probe has been harvesting new insights of the Kronian system. In particular, this mission orchestrated a climax on January 14, 2005 with the descent of the Huygens probe into Titan＇s thick atmosphere. The orbiter and the lander have provided us with picturesque views of extraterrestrial landscapes, new in composition but reassuringly Earth-like in shape. Thus, Saturn＇s largest satellite displays chains of mountains, fields of dark and damp dunes, lakes and possibly geologic activity. As on Earth, landscapes on Titan are eroded and modeled by some alien hydrology： dendritic systems, hydrocarbon lakes, and methane clouds imply periods of heavy rainfalls, even though rain was never observed directly. Titan＇s surface also proved to be geologically active - today or in the recent past - given the small number of impact craters listed to date, as well as a few possible cryovolcanic features. We attempt hereafter a synthesis of the most significant results of the Cassini-Huygens endeavor, with emphasis on the surface.

关键词： planets and satellites Titan - space vehicles

Micro-arcsecond Celestial Reference Frames:definition and realization——Impact of the recent IAU Resolutions

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Research in Astronomy and Astrophysics 2012年第8期12卷 1162-1184页

作者： Nicole Capitaine SYRTE Observatoire de ParisCNRSUPMC61 avenue de l’Observatoire75014ParisFrance

The adoption of the International Celestial Reference System （ICRS）, based on Very Long Baseline Interferometry （VLBI） observations of extragalactic radiosources by the International Astronomical Union （IAU） since 1998 January 1, opened a new era for astronomy. The ICRS and the corresponding frame, the International Celestial Reference Frame （ICRF）, replaced the Fundamental Catalog （FK5） based on positions and proper motions of bright stars, with the Hipparcos cat- alog being adopted as the primary realization of the ICRS in optical wavelengths. According to its definition, the ICRS is such that the barycentric directions of distant extragalactic objects show no global rotation with respect to these objects; this pro- vides a quasi-inertial reference for measuring the positions and angular motions of the celestial objects. Other resolutions on reference systems were passed by the IAU in 2000 and 2006 and endorsed by the International Union of Geodesy and Geophysics （IUGG） in 2003 and 2007, respectively. These especially concern the definition and re- alization of the astronomical reference systems in the framework of general relativity and transformations between them. First, the IAU 2000 resolutions refined the con- cepts and definition of the astronomical reference systems and parameters for Earth＇s rotation, and adopted the IAU 2000 precession-nutation. Then, the IAU 2006 resolutions adopted a new precession model that is consistent with dynamical theories; they also addressed definition, terminology or orientation issues relative to reference systems and time scales that needed to be specified after the adoption of the IAU 2000 resolutions. An additional IUGG 2007 resolution defined the International Terrestrial Reference System （ITRS） so that it strictly complies with the IAU recommendations. Finally, the IAU 2009 resolutions adopted a new system of astronomical constants and an improved realization of the ICRF. These fundamental changes have led to significant

关键词： astrometry and celestial mechanics: astrometry -- reference systems --Earth -- techniques: interferometric

BSN: The First Photometric Analysis of Contact Binary Systems V1961 Cyg and V0890 Lyr

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Research in Astronomy and Astrophysics 2024年第12期24卷 127-139页

作者： Sabrina Baudart Atila Poro Double Stars Committee SociétéAstronomique de France LUX Observatoire de ParisCNRSPSL

We presented the first photometric analysis of the V1961 Cyg and V0890 Lyr binary *** observed and analyzed these systems at an observatory in France as part of the Binary Systems of South and North （BSN）*** extracted and collected the times of minima from the observations and literature and presented a new ephemeris for each *** to the few observations about these systems over the years,both O–C diagrams were fitted *** PHysics Of Eclipsing BinariEs （PHOEBE） Python code and the Markov Chain Monte Carlo （MCMC） method were used for light curve *** light curve solution required a cold starspot on the hotter component in the V1961 Cyg binary *** compared and have close agreements between our mass ratios’results from the light curve analysis processes and a new method based on the light curve *** estimated the absolute parameters using an empirical relationship between the semimajor axis and orbital period for contact binary *** results show V1961 Cyg and V0890 Lyr are W-type contact binary *** displayed stars and systems’positions in the M–L,M–R,and logMtot-log *** also presented a new relationship between mass ratio and luminosity ratio.

关键词： (stars:) binaries: eclipsing methods: observational stars: individual (V1961 Cyg, V0890 Lyr)

Optical gravitational wave detectors on the ground and in space:theory and technology

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Research in Astronomy and Astrophysics 2010年第10期10卷 956-1004页

作者： Jean-Yves Vinet ARTEMIS observatoire de la Cte d'Azur Université de Nice-Sophia Antipolis 06304 NICE France

Major predictions of General Relativity, unforeseen at the beginning of the preceding century, are now under investigation. The existence of black holes of any mass from tens to billions of solar masses is now established, and the physics around these objects begins to be studied through direct observations in a wide electromagnetic spectrum from visible light to X-rays. General relativity, however, provides an extra medium which carries more information on the regions of intense gravitational field, namely gravitational waves （GWs）. Due to their extremely weak coupling to matter, GWs are precisely generated in those regions of spacetime undergoing strong curvature, which is very exciting for modern astrophysics. On the other hand, this weak coupling makes it difficult for GWs to cause appreciable effects in human made instruments. This is why technology of GW detectors took such a long time to reach a sensitivity level consistent with GW amplitudes predicted by theoretical models of sources. In the present status, apart from resonant solid detectors, two large interferometric antennas （LIGO in the USA and the French-Italian Virgo） are beginning to produce data, and a joint ESA-NASA space mission, resulting from a wide effort of European and American groups, is reaching a crucial approval phase. The aim of the present review is to give the theoretical bases of GW detectors using light.

关键词： gravitation -- gravitational waves -- interferometry

HⅠ emission from the red giant Y CVn with the VLA and FAST

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Research in Astronomy and Astrophysics 2017年第7期17卷 39-46页

作者： Do T.Hoai Pham T.Nhung Lynn D.Matthews Eric Grard Thibaut Le Bertre department of Astrophysics Vietnam National Satellite CenterVAST LERMA CNRSObservatoire de Paris/PSLSorbonne Universite's department of Astrophysics Vietnam National Satellite Center MIT Haystack Observatory GEPI CNRSObservatoire de Paris/PSL

Imaging studies with the Very Large Array（VLA） have revealed H I emission associated with the extended circumstellar shells of red giants. We analyze the spectral map obtained on Y CVn, a J-type carbon star on the Asymptotic Giant Branch. The H I line profiles can be interpreted with a model of a detached shell resulting from the interaction of a stellar outflow with the local interstellar *** reproduce the spectral map by introducing a distortion along a direction corresponding to the star＇s motion in space. We then use this fitting to simulate observations expected from the Five-hundred-meter Aperture Spherical radio Telescope（FAST）, and discuss its potential for improving our description of the outer regions of circumstellar shells.

关键词： stars AGB and post-AGB-- stars carbon - stars individual Y CVn - radio lines stars

Light variations of two new DA-type pulsating white dwarfs

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Chinese Science Bulletin 1997年第18期42卷 1554-1557页

作者： Fu, JN Vauclair, G Dolez, N Fremy, J Beijing Astronomical Observatory Chinese Academy of Sciences Beijing China observatoire Midi-Pyrénées Toulouse France observatoire de Paris-Meudon Meudon France

ASTEROSEISMOLOGY of pulsating white dwarfs is an effective tool for us to infer their internal structures and the activities of stars on the final stages of stellar evolution. DA-type pulsating white dwarfs, with hydrogen-rich shells and low temperatures, constitute an instability strip in the H-R diagram, which have only 24 members. In order to push forward the research work in this field, many astronomers have devoted themselves to the search of new possible members for a long time. During two nights on February of 1996, the authors observed five candidates selected from the Kiso survey (Noguchi et al., 1980; Kondo et al., 1984), with the 1.93-m telescope at observatoire de haute-provence, France. In the present note, we report the discovery of two new variables from this observation run: KUV 08368+4026 and KUV 11370+4222.

关键词： white dwarf photoelectric photometry pulsation.

On the central symmetry of the circumstellar envelope of RS Cnc

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Research in Astronomy and Astrophysics 2015年第5期15卷 713-724页

作者： Pham Tuyet Nhung Do Thi Hoai Jan Martin Winters Pierre Darriulat Eric Grard Thibaut Le Bertre VATLY INST 179 Hoang Quoc Viet Cau Giay Hanoi Vietnam LERMA UMR 8112 CNRS & Observatoire de Paris 61 av. de l’Observatoire F-75014 ParisFrance IRAM 300 rue de la Piscine Domaine Universitaire F-38406 St. Martin d’Heres France GEPI UMR 8111 CNRS & Observatoire de Paris 5 Place J. Janssen F-92195 Meudon CedexFrance

We present a phenomenological study of CO（1-0） and CO（2-1） emission from the circumstellar envelope （CSE） of the Asymptotic Giant Branch （AGB） star RS Cnc. It reveals departures from central symmetry that turn out to be efficient tools for the exploration of some of the properties of the CSE. We use a wind model including a bipolar flow with a typical wind velocity of ～8 km s^-1 that decreases to ～2 km s^-1 near the equator. This wind model is used to describe Doppler velocity spectral maps obtained by merging data collected at the IRAM Plateau de Bure Interferometer and Pico Veleta single dish radio telescope. Parameters describing the wind morphology and kinematics are obtained, together with the radial dependence of the gas temperature in the domain of the CSE probed by the CO observations. Significant north-south central asymmetries are revealed by the analysis, which we quantify using a simple phenomenological description. The origin of such asymmetries is unclear.

关键词： stars AGB and post-AGB -- stars individual (RS Cnc) -- stars mass loss -- radio lines general

The local contribution to the microwave background radiation

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Research in Astronomy and Astrophysics 2015年第4期15卷 461-474页

作者： Jean-Claude Pecker Jayant V.Narlikar Francois Ochsenbein Chandra Wickramasinghe College de France Inter-University Centre for Astronomy and Astrophysics Centre de Donnees astronomiques de Strasbourg (CDS) Observatoire de Strasbourg11rue de l’Universite 67000 StrasbourgFrance Buckingham Centre for Astrobiology University of Buckingham

The observed microwave background radiation （MBR） is commonly in- terpreted as the relic of an early hot universe, and its observed features （spectrum and anisotropy） are explained in terms of properties of the early universe. Here we describe a complementary, even possibly alternative, interpretation of MBR, first proposed in the early 20th century, and adapt it to modern observations. For example, the stellar Hipparcos data show that the energy density of starlight from the Milky Way, if suit- ably thermalized, yields a temperature of ~2.81 K. This and other arguments given here strongly suggest that the origin of MBR may lie, at least in a very large part, in re-radiation of thermalized galactic starlight. The strengths and weaknesses of this alternative radical explanation are discussed.

关键词： Galaxy: stellar content -- (cosmology:) cosmic microwave background-- cosmology: observations

Relative flux calibration for the Guoshoujing Telescope (LAMOST)

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Research in Astronomy and Astrophysics 2012年第4期12卷 453-464页

作者： Yi-Han Song A-Li Luo Georges Comte Zhong-Rui Bai Jian-Nan Zhang Wei Du Hao-Tong Zhang Jian-Jun Chen Fang Zuo Yong-Heng Zhao National Astronomical Observatories Chinese Academy of SciencesBeijing 100012China Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012China Graduate University of Chinese Academy of Sciences Beijing 100049China observatoire Astronomique Marseille-provence and Laboratoire d'Astrophysique de Marseille F-13388 Marseille CedexFrance

This paper presents a relative flux calibration method for the Guoshoujing Telescope （LAMOST）, which may be applied to connect a blue spectrum to a red spectrum to build the whole spectrum across the total wavelength range （3700 ～ 9000 A）. In each spectrograph, we estimate the effective temperatures of selected stars using a grid of spectral line indices in the blue spectral range and a comparison with stellar atmosphere models. For each spectrograph, stars of types A and F are selected as pseudo-standard stars, and the theoretical spectra are used to calibrate both the blue （3700 ～ 5900 A） and red spectrograph arms （5700 ～ 9000 A）. Then the spectral response function for these pseudo-standard stars could be used to correct the raw spectra provided by the other fibers of the spectrograph, after a fiber efficiency function has been derived from twilight flat-field exposures. A key problem in this method is the fitting of a pseudo stellar continuum, so we also give a detailed description of this step. The method is tested by comparing a small sample of LAMOST spectra calibrated in this way on stars also observed by the Sloan Digital Sky Survey. The result shows that the T eff estimation and relative flux calibration method are adequate.

关键词： techniques: spectroscopic — calibration: methods:data analysis