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Search Results: 1 - 10 of 223876 matches for " R. Launhardt "
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Fragmentation of a Protostellar Core: The Case of CB230
R. Launhardt
Physics , 2000,
Abstract: The Bok globule CB230 (L1177) contains an active, low-mass star-forming core which is associated with a double NIR reflection nebula, a collimated bipolar molecular outflow, and strong mm continuum emission. The morphology of the NIR nebula suggests the presence of a deeply embedded, wide binary protostellar system. High-angular resolution observations now reveal the presence of two sub-cores, two distinct outflow centers, and an embedded accretion disk associated with the western bipolar NIR nebula. In terms of separation and specific angular momentum, the CB230 double protostar system probably results from core fragmentation and can be placed at the upper end of the pre-main sequence binary distribution.
A young protoplanetary disk in the Bok globule CB26?
R. Launhardt,A. I. Sargent
Physics , 2001, DOI: 10.1086/338193
Abstract: We present sub-arcsecond resolution millimeter-wave images of a circumstellar disk in the Bok globule CB26. The presence of an edge-on disk is confirmed by the dust continuum morphology and the velocity field of 13CO emission, which displays a Keplerian rotation pattern about an axis perpendicular to the long axis of the dust emission. We deduce a mass ~0.3 Msun for the obscured central star. The disk is optically thick at mm wavelengths inside 120 AU, has a symmetric 20 degree warp beyond 120 AU, an outer radius of ~200 AU, and a mass of at least 0.1 Msun. We suggest that the CB26 system is in an intermediate stage between deeply embedded protostellar accretion disks and the more evolved, perhaps protoplanetary, disks around T Tauri stars.
The Nuclear Bulge of the Galaxy. III. Large-Scale Physical Characteristics of Stars and Interstellar Matter
R. Launhardt,R. Zylka,P. G. Mezger
Physics , 2002, DOI: 10.1051/0004-6361:20020017
Abstract: We analyse IRAS and COBE DIRBE data at wavelengths between 2.2 and 240 mu of the central 500pc of the Galaxy and derive the large-scale distribution of stars and interstellar matter in the Nuclear Bulge. Models of the Galactic Disk and Bulge are developed in order to correctly decompose the total surface brightness maps and to apply proper extinction corrections. The Nuclear Bulge appears as a distinct, massive disk-like complex of stars and molecular clouds which is, on a large scale, symmetric with respect to the Galactic Centre. It is distinguished from the Galactic Bulge by its flat disk-like morphology, very high density of stars and molecular gas, and ongoing star formation. The Nuclear Bulge consists of an R^-2 Nuclear Stellar Cluster at the centre, a large Nuclear Stellar Disk with radius 230+-20 pc and scale height 45+-5 pc, and a Nuclear Molecular Disk of same size. Its total stellar mass and luminosity are 1.4+-0.6 10^9 M_sun and 2.5+-1 10^9 L_sun, respectively. The total mass of interstellar hydrogen in the Nuclear Bulge is 2+-0.3 10^7 M_sun. Interstellar matter in the Nuclear Bulge is very clumpy with ~90% of the mass contained in dense and massive molecular clouds with a volume filling factor of only a few per cent. This extreme clumpiness enables the strong interstellar radiation field to penetrate the entire Nuclear Bulge and explains the relatively low average extinction towards the Galactic Centre. In addition, we find 4 10^7 M_sun of cold and dense material located outside the Nuclear Bulge, which gives rise to the observed asymmetry in the distribution of interstellar matter in the Central Molecular Zone.
Search for Binary Protostars
R. Launhardt,A. I. Sargent,H. Zinnecker
Physics , 2000,
Abstract: In an effort to shed more light on the formation process of binary stars, we have started a program to study multiplicity among nearby low- and intermediate-mass protostars using the OVRO Millimeter Array. Here, we describe the project and present the first results on the protostellar core in the Bok globule CB230 (L1177). At 10 arcsec resolution, the molecular core is resolved into two components separated by 5000 AU. The morphology and kinematics of the double core suggest that it formed from a single cloud core due to rotational fragmentation.
A close view on the protoplanetary disk in the Bok globule CB26
R. Launhardt,B. Stecklum,A. I. Sargent
Physics , 2001, DOI: 10.1007/10856518_41
Abstract: We present new sub-arcsecond-resolution near-infrared polarimetric imaging and millimetre interferometry data on the circumstellar disk system in the Bok globule CB26. The data imply the presence of a M > 0.01 M_sun edge-on disk of >400 AU in diameter, being in Keplerian rotation around a young ~0.35 M_sun star. The mm dust emission from the inner 200 AU is highly optically thick, but the outer parts are optically thin and made of small dust grains. Planetesimal growth in the inner disk could neither be comfirmed nor excluded. The outer optically thin part of the disk is strongly warped. We argue that the CB 26 disk is a very young protoplanetary disk and show that it is comparable to the early solar system.
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.
Structure of CB 26 Protoplanetary Disk Derived from Millimeter Dust Continuum Maps
V. Akimkin,Ya. Pavlyuchenkov,R. Launhardt,T. Bourke
Physics , 2013, DOI: 10.1134/S1063772912120013
Abstract: Observations of the circumstellar disk in the Bok globule CB 26 at 110, 230, and 270 GHz are presented together with the results of the simulations and estimates of the disk parameters. These observations were obtained using the SMA, IRAM Plateau de Bure, and OVRO interferometers. The maps have relatively high angular resolutions (0.4-1"), making it possible to study the spatial structure of the gas-dust disk. The disk parameters are reconstructed via a quantitative comparison of observational and theoretical intensity maps. The disk model used to construct the theoretical maps is based on the assumption of hydrostatic and radiative equilibrium in the vertical direction, while the radial surface density profile is described phenomenologically. The system of equations for the transfer of the infrared and ultraviolet radiation is solved in the vertical direction, in order to compute the thermal structure of the disk. The disk best-fit parameters are derived for each map and all the maps simultaneously, using a conjugate gradient method. The degrees of degeneracy of the parameters describing the thermal structure and density distribution of the disk are analyzed in detail. All three maps indicate the presence of an inner dust-free region with a radius of approximately 35 AU, in agreement with the conclusions of other studies. The inclination of the disk is 78 deg, which is smaller than the value adopted in our earlier study of rotating molecular outflows from CB 26. The model does not provide any evidence for the growth of dust particles above a_max=0.02 cm.
Exoplanet search with astrometry
Ralf Launhardt
Physics , 2009, DOI: 10.1016/j.newar.2010.07.006
Abstract: Searching for extrasolar planets by direct detection is extremely challenging for current instrumentation. Indirect methods, that measure the effect of a planet on its host star, are much more promising and have indeed led to the discovery of nearly all extrasolar systems known today. While the most successful method thus far is the radial velocity technique, new interferometric instruments like PRIMA at the VLTI will enable us to carry out astrometric measurements accurate enough to detect extrasolar planets and to determine all orbital parameters, including their orbit inclination and true mass. In this article I describe the narrow-angle astrometry technique, how it will be realized with PRIMA, what kind of planets we can find, and what kind of preparatory observations are required.
HD 144432: a young triple system
A. Mueller,A. Carmona,M. E. van den Ancker,R. van Boekel,Th. Henning,R. Launhardt
Physics , 2011, DOI: 10.1051/0004-6361/201117971
Abstract: We present new imaging and spectroscopic data of the young Herbig star HD 144432 A, which was known to be a binary star with a separation of 1.47 arcsec. High-resolution NIR imaging data obtained with NACO at the VLT reveal that HD 144432 B itself is a close binary pair with a separation of 0.1 arcsec. High-resolution optical spectra, acquired with FEROS at the 2.2m MPG/ESO telescope in La Silla, of the primary star and its co-moving companions were used to determine their main stellar parameters such as effective temperature, surface gravity, radial velocity, and projected rotational velocity by fitting synthetic spectra to the observed stellar spectra. The two companions, HD 144432 B and HD 144432 C, are identified as low-mass T Tauri stars of spectral type K7V and M1V, respectively. From the position in the HRD the triple system appears to be co-eval with a system age of 6+/-3 Myr.
Simulated ALMA observations of collapsing low-mass dense cores
F. Levrier,B. Commer?on,A. J. Maury,Th. Henning,R. Launhardt,C. Dullemond
Physics , 2013,
Abstract: We present a possible identification strategy for first hydrostatic core (FHSC) candidates and make predictions of ALMA dust continuum emission maps from these objects. We analyze the results given by the different bands and array configurations and identify which combinations of the two represent our best chance of solving the fragmentation issue in these objects. If the magnetic field is playing a role, the emission pattern will show evidence of a pseudo-disk and even of a magnetically driven outflow, which pure hydrodynamical calculations cannot reproduce.
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