442 research outputs found
Southern Durchmusterung (Schoenfeld 1886): Documentation for the machine-readable version
The machine-readable version of the catalog, as it is currently being distributed from the Astronomical Data Center, is described. The Southern Durchmusterung (SD) was computerized at the Centre de Donnees Astronomiques de Strasbourg and at the Astronomical Data Center at the National Space Science Data Center, NASA/Goddard Space Flight Center. Corrigenda listed in the original SD volume and published by Kuenster and Sticker were incorporated into the machine file. In addition, one star indicated to be missing in a published list, and later verified, is flagged so that it can be omitted from computer plotted charts if desired. Stars deleted in the various errata lists were similarly flagged, while those with revised data are flagged and listed in a separate table. This catalog covers the zones -02 to -23 degrees; zones +89 to -01 degrees (the Bonner Durchmusterung) are included in a separate catalog available in machine-readable form
Huge Transverse Magnetization in the Field-Induced Phase of the Antiferromagnetic Molecular Wheel CsFe8
The 1H-NMR spectrum and nuclear relaxation rate 1/T_1 in the
antiferromagnetic wheel CsFe8 were measured to characterize the previously
observed magnetic field-induced low-temperature phase around the level crossing
at 8 T. The data show that the phase is characterized by a huge staggered
transverse polarization of the electronic Fe spins, and the opening of a gap,
providing microscopic evidence for the interpretation of the phase as a
field-induced magneto-elastic instability.Comment: 5 pages, 4 figures, REVTEX4, to appear in PR
Exchange Interactions and High-Energy Spin States in Mn_12-acetate
We perform inelastic neutron scattering measurements on the molecular
nanomagnet Mn_12-acetate to measure the excitation spectrum up to 45meV (500K).
We isolate magnetic excitations in two groups at 5-6.5meV (60-75K) and
8-10.5meV (95-120K), with higher levels appearing only at 27meV (310K) and
31meV (360K). From a detailed characterization of the transition peaks we show
that all of the low-energy modes appear to be separate S = 9 excitations above
the S = 10 ground state, with the peak at 27meV (310K) corresponding to the
first S = 11 excitation. We consider a general model for the four exchange
interaction parameters of the molecule. The static susceptibility is computed
by high-temperature series expansion and the energy spectrum, matrix elements
and ground-state spin configuration by exact diagonalization. The theoretical
results are matched with experimental observation by inclusion of cluster
anisotropy parameters, revealing strong constraints on possible parameter sets.
We conclude that only a model with dominant exchange couplings J_1 ~ J_2 ~
5.5meV (65K) and small couplings J_3 ~ J_4 ~ 0.6meV (7K) is consistent with the
experimental data.Comment: 17 pages, 12 figure
X-ray Detections of Two Young Bona-Fide Brown Dwarfs
I report here the detection of two bona-fide brown dwarfs by XMM-Newton:
[GY92] 141 in the rho-Ophiuchus star forming region and DENIS-P J155601-233809
in the Upper Scorpius OB association. The two objects have been detected with
luminosities of Lx=8.35\pm2.86*10^28 erg/s and Lx=6.54\pm1.35*10^28 erg/s
respectively, corresponding to luminosity ratios of log(Lx/Lbol)= -2.07 and
log(Lx/Lbol)= -2.69. The two sources were close to the limit of detection of
the instruments at only 2~3-sigma above the background level, and no
significant flare or variation could be detected during the 48.3ks and 33.9ks
observations. [GY92] 141 had already been observed 10 months earlier with
Chandra (see 2001 ApJ, 563, 361) with a luminosity ~14 times fainter than the
one I report here, meaning that the X-ray emission of this object is strongly
variable.Comment: 9 pages, 3 figures, accepted for A&
II.5 Where to find the CoRoT data?
This book is dedicated to all the people interested in the CoRoT mission and the beautiful data that were delivered during its six year duration. Either amateurs, professional, young or senior researchers, they will find treasures not only at the time of this publication but also in the future twenty or thirty years. It presents the data in their final version, explains how they have been obtained, how to handle them, describes the tools necessary to understand them, and where to find them. It also highlights the most striking first results obtained up to now. CoRoT has opened several unexpected directions of research and certainly new ones still to be discovered
Multi-Conjugate Adaptive Optics images of the Trapezium Cluster
Multi-Conjugate Adaptive Optics (MCAO) combines the advantages of standard
adaptive optics, which provides high contrast and high spatial resolution, and
of wide field ~1' imaging. Up to recently, MCAO for astronomy was limited to
laboratory experiments. In this paper, we present the first scientific results
obtained with the first MCAO instrument put on the sky. We present a new study
of the Trapezium cluster using deep MCAO images with a field of view of 1'x1'
obtained at the VLT. We have used deep J, H and Ks images recently obtained
with the prototype MCAO facility MAD at the VLT in order to search for new
members and new multiple systems in the Trapezium cluster. On bright targets
(Ks~9mag), these images allow us to reach DeltaKs~6mag as close as 0.4" We
report the detection of 128 sources, including 10 new faint objects in the
magnitude range between 16.1<Ks<17.9mag. In addition to all previously known
multiple systems with separations greater than 0.1", we confirm the
multiplicity of TCC-055. We also report the detection in J, H and Ks of a very
red extended embedded protostellar object, HC419, previously detected in the
thermal infrared only. The analysis of the first MCAO images obtained on the
sky demonstrates not only the technical feasibility of MCAO but also its great
potential and versatility in terms of scientific outputs.Comment: High resolution version available on
http://arrakeen.free.fr/pub/madorion.pdf Accepted 25 Sep. 2007 for
publication in A&A, 14 pages, 11 figure
Near and mid-IR sub-arcsecond structure of the dusty symbiotic star R Aqr
The results of a high-resolution interferometric campaign targeting the
symbiotic long-period variable (LPV) R~Aqr are reported. With both
near-infrared measurements on baselines out to 10m and mid-infrared data
extending to 32m, we have been able to measure the characteristic sizes of
regions from the photosphere of the LPV and its extended molecular atmosphere,
out to the cooler circumstellar dust shell. The near-infrared data were taken
using aperture masking interferometry on the Keck-I telescope and show R~Aqr to
be partially resolved for wavelengths out to 2.2 microns but with a marked
enlargement, possibly due to molecular opacity, at 3.1 microns. Mid-infrared
interferometric measurements were obtained with the U.C. Berkeley Infrared
Spatial Interferometer (ISI) operating at 11.15 microns from 1992 to 1999.
Although this dataset is somewhat heterogeneous with incomplete coverage of the
Fourier plane and sampling of the pulsation cycle, clear changes in the
mid-infrared brightness distribution were observed, both as a function of
position angle on the sky and as a function of pulsation phase. Spherically
symmetric radiative transfer calculations of uniform-outflow dust shell models
produce brightness distributions and spectra which partially explain the data,
however limitations to this approximation are noted. Evidence for significant
deviation from circular symmetry was found in the mid-infrared and more
tentatively at 3.08 microns in the near-infrared, however no clear detection of
binarity or of non-LPV elements in the symbiotic system is reported.Comment: Accepted to Astrophysical Journal. To appear in volume 534. 14 pages;
3 postscript figure
The core fundamental plane of B2 radio galaxies
The photometric, structural and kinematical properties of the centers of
elliptical galaxies, harbor important information of the formation history of
the galaxies. In the case of non active elliptical galaxies these properties
are linked in a way that surface brightness, break radius and velocity
dispersion of the core lie on a fundamental plane similar to that found for
their global properties. We construct the Core Fundamental Plane (CFP) for a
sizeable sample of low redshift radio galaxies and compare it with that of non
radio ellipticals. To pursue this aim we combine data obtained from high
resolution HST images with medium resolution optical spectroscopy to derive the
photometric and kinematic properties of ~40 low redshift radio galaxies. We
find that the CFPs of radio galaxies is indistinguishable from that defined by
non radio elliptical galaxies of similar luminosity. The characteristics of the
CFP of radio galaxies are also consistent (same slope) with those of the
Fundamental Plane (FP) derived from the global properties of radio (and non
radio) elliptical galaxies. The similarity of CFP and FP for radio and non
radio ellipticals suggests that the active phase of these galaxies has minimal
effects for the structure of the galaxies.Comment: 8 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Proper motions of cool and ultracool candidate members in the Upper Scorpius OB association
Proper motion measurements of the cool and ultracool populations in the Upper
Scorpius OB association are crucial to confirm membership and to identify
possible run-away objects.
We cross-match samples of photometrically selected and spectroscopically
confirmed cool and ultracool (K5<SpT<M8.5) candidate members in the Upper
Scorpius OB association using the literature and the USNO-B and the UCAC2
catalogues. 251 of these objects have a USNO-B and/or UCAC2 counterpart with
proper motion measurements.
A significant fraction (19 objects, 7.6+-1.8%) of spectroscopically confirmed
young objects show discrepant proper motion. They must either belong to
unidentified coincident foreground associations, or originate from neighboring
star forming regions or have recently experienced dynamical interactions within
the association. The observed accretor and disc frequencies are lower among
outliers, but with only 19 objects it is unreliable to draw firm statistical
conclusions. Finally, we note that transverse velocities of very low mass
members are indistinguishable from those of low mass members within 4km/sComment: accepted for publication in A&
A mid-infrared study of very low mass stars and brown dwarfs in Upper Scorpius
We report the results of mid-IR observations with VISIR at the VLT of 10
ultracool dwarfs members of the nearby Upper Scorpius OB association in four
filters ranging between 8.59 (PAH1) to 12.8 m (Ne II), and one brown dwarf
with Spitzer between 3.6 and 24 m. Seven of our targets are detected in at
least one of the bands, and we derive upper limits on the fluxes of the
remaining 4. These results combined with previous studies from the literature
lead to an improved disk frequency of 5012%. This frequency is
significantly higher than that of accretors (16.3%6.2%). Only one object
showing mid-IR excess also has H emission at a level indicating that it
must be accreting. Four of the detected targets are multiple system candidates.
The observed disk frequency for sub-stellar objects in the Upper Scorpius
association is similar to that of stars, consistent with a common formation
scenario. It is also similar to the disk fractions observed in younger
clusters, suggesting that the disk lifetimes might be longer for ultracool
dwarfs than for higher-mass stars.Comment: 10 pages, 4 figures, accepted for A&
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