96 research outputs found
First proper motions of thin dust filaments at the Galactic Center
Context: L'-band (3.8 micron) images of the Galactic Center show a large
number of thin filaments in the mini-spiral, located west of the mini-cavity
and along the inner edge of the Northern Arm. One possible mechanism that could
produce such structures is the interaction of a central wind with the
mini-spiral. Additionally, we identify similar features that appear to be
associated with stars. Aims: We present the first proper motion measurements of
the thin dust filaments observed in the central parsec around SgrA* and
investigate possible mechanisms that could be responsible for the observed
motions. Methods: The observations have been carried out using the NACO
adaptive optics system at the ESO VLT. The images have been transformed to a
common coordinate system and features of interest were extracted. Then a
cross-correlation technique could be performed in order to determine the
offsets between the features with respect to their position in the reference
epoch. Results: We derive the proper motions of a number of filaments and 2
cometary shaped dusty sources close (in projection) to SgrA*. We show that the
shape and the motion of the filaments does not agree with a purely Keplerian
motion of the gas in the potential of the supermassive black hole at the
position of SgrA*. Therefore, additional mechanisms must be responsible for
their formation and motion. We argue that the properties of the filaments are
probably related to an outflow from the disk of young mass-losing stars around
SgrA*. In part, the outflow may originate from the black hole itself. We also
present some evidence and theoretical considerations that the outflow may be
collimated.Comment: accepted for publication by A&
Compact mid-IR sources east of galactic center source IRS5
There are four less prominent compact sources east of IRS5, the natures of
which were unclear until now. We present near-infrared K-band long slit
spectroscopy of the four sources east of IRS5 obtained with the ISAAC
spectrograph at the ESO VLT in July 2005. We interpret the data in combination
with high angular resolution NIR and MIR images obtained with ISAAC and NACO at
the ESO VLT.Comment: 9 pages, 8 figures. accepted by A&
Near-infrared proper motions and spectroscopy of infrared excess sources at the Galactic Center
There are a number of faint compact infrared excess sources in the central
stellar cluster of the Milky Way. Their nature and origin is unclear. In
addition to several isolated objects of this kind we find a small but dense
cluster of co-moving sources (IRS13N) about 3" west of SgrA* just 0.5" north of
the bright IRS13E cluster of WR and O-type stars. Based on their color and
brightness, there are two main possibilities: (1) they may be dust embedded
stars older than few Myr, or (2) extremely young, dusty stars with ages less
than 1Myr. We present fist H- and Ks-band identifications or proper motions of
the IRS13N members, the high velocity dusty S-cluster object (DSO), and other
infrared excess sources in the central field. We also present results of NIR H-
and Ks-band ESO-SINFONI integral field spectroscopy of ISR13N. We show that
within the uncertainties, the proper motions of the IRS13N sources in Ks- and
L'-band are identical. This indicates that the bright L'-band IRS13N sources
are indeed dust enshrouded stars rather than core-less dust clouds. The proper
motions show that the IRS13N sources are not strongly gravitationally bound to
each other implying that they have been formed recently. We also present a
first H- and Ks-band identification as well as proper motions and HKsL'-colors
of a fast moving DSO which was recently found in the cluster of high speed
S-stars that surround the super-massive black hole Sagittarius A* (SgrA*). Most
of the compact L'-band excess emission sources have a compact H- or Ks-band
counterpart and therefore are likely stars with dust shells or disks. Our new
results and orbital analysis from our previous work favor the hypothesis that
the infrared excess IRS13N members and other dusty sources close to SgrA* are
very young dusty stars and that star formation at the GC is a continuously
ongoing process.Comment: 20 pages, 18 figures, 4 tables plus appendix with 16 figures and 3
tables accepted by A&
The mean infrared emission of SagittariusA*
(abridged) The massive black hole at the center of the Milky Way,
SagittariusA* is, in relative terms, the weakest accreting black hole
accessible to observations. At the moment, the mean SED of SgrA* is only known
reliably in the radio to mm regimes. The goal of this paper is to provide
constraints on the mean emission from SgrA* in the near-to-mid infrared.
Excellent imaging quality was reached in the MIR by using speckle imaging
combined with holographic image reconstruction, a novel technique for this kind
of data. No counterpart of SgrA* is detected at 8.6 microns. At this
wavelength, SgrA* is located atop a dust ridge, which considerably complicates
the search for a potential point source. An observed 3 sigma upper limit of ~10
mJy is estimated for the emission of SgrA* at 8.6 microns, a tighter limit at
this wavelength than in previous work. The de-reddened 3 sigma upper limit,
including the uncertainty of the extinction correction, is ~84 mJy . Based on
the available data, it is argued that, with currently available instruments,
SgrA* cannot be detected in the MIR, not even during flares. At 4.8 and 3.8
microns, on the other hand, SgrA* is detected at all times, at least when
considering timescales of a few up to 13 min. We derive well-defined
time-averaged, de-reddened flux densities of 3.8+-1.3 mJy at 4.8 microns and
5.0+-0.6 mJy at 3.8 microns. Observations with NIRC2/Keck and NaCo/VLT from the
literature provide good evidence that SgrA* also has a fairly well-defined
de-reddened mean flux of 0.5-2.5 mJy at wavelengths of 2.1-2.2 microns. We
present well-constrained anchor points for the SED of SgrA* on the
high-frequency side of the Terahertz peak. The new data are in general
agreement with published theoretical SEDs of the mean emission from SgrA*, but
we expect them to have an appreciable impact on the model parameters in future
theoretical work.Comment: accepted for publication by Astronomy & Astrophysics on 20 June 201
New Galactic Wolf-Rayet stars, and candidates. An annex to The VIIth Catalogue of Galactic Wolf-Rayet Stars
This paper gathers, from the literature and private communication, 72 new
Galactic Population I Wolf-Rayet stars and 17 candidate WCLd stars, recognized
and/or discovered after the publication of The VIIth Catalogue of Galactic
Wolf-Rayet Stars. This brings the total number of known Galactic Wolf-Rayet
stars to 298, of which 24 (8%) are in open cluster Westerlund 1, and 60 (20%)
are in open clusters near the Galactic Center.Comment: 10 pages. A&A Research Note, accepte
Interstellar gas within pc of Sgr A
We seek to obtain a coherent and realistic three-dimensional picture of the
interstellar gas out to about 10 pc of the dynamical center of our Galaxy,
which is supposed to be at Sgr A. We review the existing observational
studies on the different gaseous components that have been identified near Sgr
A, and retain all the information relating to their spatial configuration
and/or physical state. Based on the collected information, we propose a
three-dimensional representation of the interstellar gas, which describes each
component in terms of both its precise location and morphology and its
thermodynamic properties. The interstellar gas near Sgr A can represented
by five basic components, which are, by order of increasing size: (1) a central
cavity with roughly equal amounts of warm ionized and atomic gases, (2) a ring
of mainly molecular gas, (3) a supernova remnant filled with hot ionized gas,
(4) a radio halo of warm ionized gas and relativistic particles, and (5) a belt
of massive molecular clouds. While the halo gas fills of the
studied volume, the molecular components enclose of the
interstellar mass.Comment: 21 pages, 7 figure
Polymorphisms of methylenetetrahydrofolate reductase (MTHFR) and susceptibility to pediatric acute lymphoblastic leukemia in a German study population
BACKGROUND: Methylenetetrahydrofolate reductase (MTHFR) has a major impact on the regulation of the folic acid pathway due to conversion of 5,10-methylenetetrahydrofolate (methylene-THF) to 5-methyl-THF. Two common polymorphisms (677C>T and 1298A>C) in the gene coding for MTHFR have been shown to reduce MTHFR enzyme activity and were associated with the susceptibility to different disorders, including vascular disease, neural tube defects and lymphoid malignancies. Studies on the role of these polymorphisms in the susceptibility to acute lymphoblastic leukemia (ALL) led to discrepant results. METHODS: We retrospectively evaluated the association of the MTHFR 677C>T and 1298A>C polymorphisms with pediatric ALL by genotyping a study sample of 443 ALL patients consecutively enrolled onto the German multicenter trial ALL-BFM 2000 and 379 healthy controls. We calculated odds ratios of MTHFR genotypes based on the MTHFR 677C>T and 1298A>C polymorphisms to examine if one or both of these polymorphisms are associated with pediatric ALL. RESULTS: No significant associations between specific MTHFR variants or combinations of variants and risk of ALL were observed neither in the total patient group nor in analyses stratified by gender, age at diagnosis, DNA index, immunophenotype, or TEL/AML1 rearrangement. CONCLUSION: Our findings suggest that the MTHFR 677C>T and 1298A>C gene variants do not have a major influence on the susceptibility to pediatric ALL in the German population
Photoelectron circular dichroism of O 1-photoelectrons of uniaxially oriented trifluoromethyloxirane: Energy dependence and sensitivity to molecular configuration
The photoelectron circular dichroism (PECD) of the O 1s-photoelectrons of
trifluoromethyloxirane(TFMOx) is studied experimentally and theoretically for
different photoelectron kinetic energies. The experiments were performed
employing circularly polarized synchrotron radiation and coincidentelectron and
fragment ion detection using Cold Target Recoil Ion Momentum Spectroscopy. The
corresponding calculations were performed by means of the Single Center method
within the relaxed-core Hartree-Fock approximation. We concentrate on the
energy dependence of the differential PECD of uniaxially oriented TFMOx
molecules, which is accessible through the employed coincident detection. We
also compare results for differential PECD of TFMOx to those obtained for the
equivalent fragmentation channel and similar photoelectron kinetic energy of
methyloxirane (MOx), studied in our previous work. Thereby, we investigate the
influence of the substitution of the methyl-group by the trifluoromethyl-group
at the chiral center on the molecular chiral response. Finally, the presently
obtained angular distribution parameters are compared to those available in
literature.Comment: 6 fig
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