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Search Results: 1 - 10 of 461786 matches for " Quirrenbach A. "
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A. Quirrenbach,S. Albrecht
Revista mexicana de astronomía y astrofísica , 2010,
Abstract: MWC349A es probablemente una estrella masiva joven rodeada por un disco y un fuerte viento ionizado desde la super cie del disco. Las caracter sticas m s espectaculares del disco de MWC349A son l neas m ser y l ser de recombinaci n del hidr geno en longitudes de onda milim trica, sub-milim trica y de IR-medio. Hemos conducido observaciones de MWC349A con el instrumento MIDI del VLTI a 10 um. Las visibilidades en el continuo muestran la rma caracter stica esperada en un disco de polvo. Adem s, las rmas de por lo menos una docena de l neas de emisi n han sido identi cadas en los datos interferom tricos.
Planets around Giant Stars
A. Quirrenbach,S. Reffert,C. Bergmann
Physics , 2011, DOI: 10.1063/1.3556189
Abstract: We present results from a radial-velocity survey of 373 giant stars at Lick Observatory, which started in 1999. The previously announced planets iota Dra b and Pollux b are confirmed by continued monitoring. The frequency of detected planetary companions appears to increase with metallicity. The star nu Oph is orbited by two brown dwarf companions with masses of 22.3 M_Jup and 24.5 M_Jup in orbits with a period ratio close to 6:1. It is likely that the two companions to nu Oph formed in a disk around the star.
ESPRI: Astrometric planet search with PRIMA at the VLTI
Quirrenbach A.,Geisler R.,Henning T.,Launhardt R.
EPJ Web of Conferences , 2011, DOI: 10.1051/epjconf/20111607005
Abstract: The ESPRI consortium will conduct an astrometric survey for extrasolar planets, using the PRIMA facility at the Very Large Telescope Interferometer. Our scientific goals include determining orbital inclinations and masses for planets already known from radial-velocity surveys, searches for planets around nearby stars of all masses, and around young stars. The consortium has built the PRIMA differential delay lines, developed an astrometric operation and calibration plan, and will deliver astrometric data reduction software.
A new concept for the combination of optical interferometers and high-resolution spectrographs
S. Albrecht,A. Quirrenbach,R. N. Tubbs,R. Vink
Physics , 2009, DOI: 10.1007/s10686-009-9181-6
Abstract: The combination of high spatial and spectral resolution in optical astronomy enables new observational approaches to many open problems in stellar and circumstellar astrophysics. However, constructing a high-resolution spectrograph for an interferometer is a costly and time-intensive undertaking. Our aim is to show that, by coupling existing high-resolution spectrographs to existing interferometers, one could observe in the domain of high spectral and spatial resolution, and avoid the construction of a new complex and expensive instrument. We investigate in this article the different challenges which arise from combining an interferometer with a high-resolution spectrograph. The requirements for the different sub-systems are determined, with special attention given to the problems of fringe tracking and dispersion. A concept study for the combination of the VLTI (Very Large Telescope Interferometer) with UVES (UV-Visual Echelle Spectrograph) is carried out, and several other specific instrument pairings are discussed. We show that the proposed combination of an interferometer with a high-resolution spectrograph is indeed feasible with current technology, for a fraction of the cost of building a whole new spectrograph. The impact on the existing instruments and their ongoing programs would be minimal.
AO Observations of Three Powerful Radio Galaxies
W. de Vries,W. van Breugel,A. Quirrenbach
Physics , 2002, DOI: 10.1117/12.457006
Abstract: The host galaxies of powerful radio sources are ideal laboratories to study active galactic nuclei (AGN). The galaxies themselves are among the most massive systems in the universe, and are believed to harbor supermassive black holes (SMBH). If large galaxies are formed in a hierarchical way by multiple merger events, radio galaxies at low redshift represent the end-products of this process. However, it is not clear why some of these massive ellipticals have associated radio emission, while others do not. Both are thought to contain SMBHs, with masses proportional to the total luminous mass in the bulge. It either implies every SMBH has recurrent radio-loud phases, and the radio-quiet galaxies happen to be in the "low" state, or that the radio galaxy nuclei are physically different from radio-quiet ones, i.e. by having a more massive SMBH for a given bulge mass. Here we present the first results from our adaptive optics imaging and spectroscopy pilot program on three nearby powerful radio galaxies. Initiating a larger, more systematic AO survey of radio galaxies (preferentially with Laser Guide Star equipped AO systems) has the potential of furthering our understanding of the physical properties of radio sources, their triggering, and their subsequent evolution.
Image Slicing with Infrared Fibers
J. E. Larkin,A. Quirrenbach,J. R. Graham
Physics , 1999,
Abstract: We are proposing to build a new integral field instrument (OSIRIS) for use with the Keck Adaptive Optics System. It will utilize a large (1024 element) fiber optic bundle to slice the field and feed a standard infrared spectrograph with a spectral resolution of 5000. To improve the fill factor of the fiber bundle, we plan on coupling it to a matched lenslet array. The spectrograph will have three plate scales of 0.05'', 0.10'' and 0.20'' per pixel, and full broad band spectra will fit on a single 2048x2048 infrared array. Other innovations include using some of the fibers for pseudo-slits and sky measurements and non-uniform spacing for the "linear" feed to the spectrograph.
Kinematics and mass modelling of NGC 1068
W. Dehnen,J. Bland-Hawthorn,A. Quirrenbach,G. Cecil
Physics , 1997, DOI: 10.1023/A:1000524016349
Abstract: We present the kinematics of the ionized gas over the inner 140 arcsec (10 kpc) of NGC 1068 from observations with the HIFI Fabry-Perot interferometer. There is clear evidence for density wave streaming and bar-driven streaming across the field, with bi-symmetric arms that penetrate to within 200 pc of the nucleus. CO maps show linear structures along (although slightly offset from) the bar consistent with a strong shock. Along the spiral arms which encircle the bar, the HII regions lie downstream of the CO gas in the rest frame of the bar, as do the dust lanes, only if the gas outruns the stellar bar. As a first step towards understanding the details of the gas kinematics, and attempting to determine the mass inflow rate towards the nucleus, we build a mass model for the central disk constrained by near-infrared images. We plan to use this model as gravitational background potential for hydro-dynamical simulations of the gas response to the bar. Comparing these with the data presented should enable us to constrain various quantities such as pattern speed, stellar mass-to-light ratio, central mass concentration, and gas fueling rate.
Dust and molecular shells in asymptotic giant branch stars - Mid-infrared interferometric observations of R Aql, R Aqr, R Hya, W Hya and V Hya
R. Zhao-Geisler,A. Quirrenbach,R. Koehler,B. Lopez
Physics , 2012, DOI: 10.1051/0004-6361/201118150
Abstract: Mid-IR (8 - 13 micron) interferometric data of four oxygen-rich AGB stars (R Aql, R Aqr, R Hya, and W Hya) and one carbon-rich AGB star (V Hya) were obtained with MIDI/VLTI between April 2007 and September 2009. The spectrally dispersed visibility data are analyzed by fitting a circular fully limb-darkened disk (FDD). Results. The FDD diameter as function of wavelength is similar for all oxygen-rich stars. The apparent size is almost constant between 8 and 10 micron and gradually increases at wavelengths longer than 10 micron. The apparent FDD diameter in the carbon-rich star V Hya essentially decreases from 8 to 12 micron. The FDD diameters are about 2.2 times larger than the photospheric diameters estimated from K-band observations found in the literature. The silicate dust shells of R Aql, R Hya and W Hya are located fairly far away from the star, while the silicate dust shell of R Aqr and the amorphous carbon (AMC) and SiC dust shell of V Hya are found to be closer to the star at around 8 photospheric radii. Phase-to-phase variations of the diameters of the oxygen-rich stars could be measured and are on the order of 15% but with large uncertainties. From a comparison of the diameter trend with the trends in RR Sco and S Ori it can be concluded that in oxygen-rich stars the overall larger diameter originates from a warm molecular layer of H2O, and the gradual increase longward of 10 micron can be most likely attributed to the contribution of a close Al2O3 dust shell. The chromatic trend of the Gaussian FWHM in V Hya can be explained with the presence of AMC and SiC dust. The observations suggest that the formation of amorphous Al2O3 in oxygen- rich stars occurs mainly around or after visual minimum. However, no firm conclusions can be drawn concerning the mass-loss mechanism.
CARMENES: Blue planets orbiting red dwarfs
Quirrenbach A.,Amado P.J.,Caballero J.A.,Mandel H.
EPJ Web of Conferences , 2013, DOI: 10.1051/epjconf/20134705006
Abstract: The CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) consortium, consisting of eleven Spanish and German institutions, has been established to conduct a radial-velocity survey of M dwarfs with the 3.5 m telescope at the Calar Alto Observatory. This survey will target ~300 M stars, with emphasis on spectral types M4V and later. The CARMENES instrument is currently under construction; it consists of two independent échelle spectrographs covering the wavelength ranges 0.55 …1.05 μm and 0.95 …1.7 μm, respectively, at a spectral resolution of R = 82,000. The spectrographs are fed by fibers from the Cassegrain focus of the telescope; calibration is performed simultaneously with emission-line lamps. The optical benches of the spectrographs are housed in vacuum tanks and climatic chambers, which provide the temperature-stabilized environments necessary to enable a 1 m/s radial velocity precision.
Precise radial velocities of giant stars V. A brown dwarf and a planet orbiting the K giant stars tau Gem and 91 Aqr
D. S. Mitchell,S. Reffert,T. Trifonov,A. Quirrenbach,D. A. Fischer
Physics , 2013, DOI: 10.1051/0004-6361/201321714
Abstract: We aim to detect and characterize substellar companions to K giant stars, to further our knowledge of planet formation and stellar evolution of intermediate-mass stars. For more than a decade we have used Doppler spectroscopy to acquire high precision radial velocity measurements of K giant stars. All data for this survey have been taken at Lick Observatory. Our survey includes 373 G and K giants. Radial velocity data showing periodic variations are fitted with Keplerian orbits using a chi^2 minimization technique. We report the presence of two substellar companions to the K giant stars tau Gem and 91 Aqr. The brown dwarf orbiting tau Gem has an orbital period of 305.5 +/- 0.1 days, a minimum mass of 20.6 M_Jup, and an eccentricity of 0.031 +/- 0.009. The planet orbiting 91 Aqr has an orbital period of 181.4 +/- 0.1 days, a minimum mass of 3.2 M_Jup, and an eccentricity of 0.027 +/- 0.026. Both companions have exceptionally circular orbits for their orbital distance, as compared to all previously discovered planetary companions.
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