196 research outputs found
The most rapidly rotating He-strong emission line star: HR7355
Using archival spectroscopic and photometric data, we searched for massive
stars with Balmer-emission consistent with magnetically confined circumstellar
material. HR 7355 is a formerly unknown He-strong star showing Balmer emission.
At V=6.02 mag, it is one of the brightest objects simultaneously showing
anomalous helium absorption and hydrogen emission. Among similar objects, only
sigma Ori E has so far been subjected to any systematic analysis of the
circumstellar material responsible for the emission. We argue that the
double-wave photometric period of 0.52d corresponds to the rotation period. In
tandem with the high projected equatorial velocity, v sin i=320 km/s, this
short period suggests that HR 7355 is the most rapidly rotating He-strong star
known to date; a class that was hitherto expected to host stars with slow to
moderate rotation only.Comment: 4 pages with 2 figures. Accepted for publication as Research Note by
Astronomy and Astrophysic
Post-melting encapsulation of glass microwires for multipath light waveguiding within phosphate glasses
Glass waveguides remain the fundamental component of advanced photonic
circuits and with a significant role in other applications such as quantum
information processing, light generation, imaging, data storage, and sensing
platforms. Up to date, the fabrication of glass waveguides relies mainly on
demanding chemical processes or on the employment of expensive ultrafast laser
equipment. In this work, we demonstrate the feasibility of a simple,
low-temperature, post-melting encapsulation procedure for the development of
advanced glass waveguides. Namely, silver iodide phosphate glass microwires
(MWs) are drawn from typical splat-quenched samples. Following this, the MWs
are incorporated in a controlled manner within previously prepared transparent
silver phosphate glass rectangular prisms. The composition of the employed
glasses is chosen so that the host phosphate glass has a lower refractive index
than the embedded MWs. In such case, the waveguide mechanism relies on the
propagation of light inside the encapsulated higher refractive index MWs.
Moreover, the presence of silver nanoparticles within the MWs enhances the
light transmission due to scattering effects. Waveguide devices with either one
or two incorporated MWs were fabricated. Remarkably, in the latter case, the
transmission of light of different colors and in multipath direction is
possible, rendering the developed waveguides outstanding candidates for various
photonic circuits, optoelectronic, and smart sign glass applications
Neutron-induced background in the CONUS experiment
CONUS is a novel experiment aiming at detecting elastic neutrino nucleus
scattering in the fully coherent regime using high-purity Germanium (Ge)
detectors and a reactor as antineutrino () source. The detector setup
is installed at the commercial nuclear power plant in Brokdorf, Germany, at a
very small distance to the reactor core in order to guarantee a high flux of
more than 10/(scm). For the experiment, a good
understanding of neutron-induced background events is required, as the neutron
recoil signals can mimic the predicted neutrino interactions. Especially
neutron-induced events correlated with the thermal power generation are
troublesome for CONUS. On-site measurements revealed the presence of a thermal
power correlated, highly thermalized neutron field with a fluence rate of
(74530)cmd. These neutrons that are produced by nuclear
fission inside the reactor core, are reduced by a factor of 10 on
their way to the CONUS shield. With a high-purity Ge detector without shield
the -ray background was examined including highly thermal power
correlated N decay products as well as -lines from neutron
capture. Using the measured neutron spectrum as input, it was shown, with the
help of Monte Carlo simulations, that the thermal power correlated field is
successfully mitigated by the installed CONUS shield. The reactor-induced
background contribution in the region of interest is exceeded by the expected
signal by at least one order of magnitude assuming a realistic ionization
quenching factor of 0.2.Comment: 28 pages, 28 figure
X-ray Evidence of the Common Envelope Phase of V471 Tauri
Chandra Low Energy Transmission Grating Spectrograph observations of the
pre-cataclysmic binary V471 Tau have been used to estimate the C/N abundance
ratio of the K dwarf component for the first time. While the white dwarf
component dominates the spectrum longward of 50 AA, at shorter wavelengths the
observed X-ray emission is entirely due to coronal emission from the K dwarf.
The H-like resonance lines of C and N yield an estimate of their logarithmic
abundance ratio relative to the Sun of [C/N]=-0.38+/-0.15 - half of the
currently accepted solar value. We interpret this result as the first clear
observational evidence for the presumed common envelope phase of this system,
during which the surface of the K dwarf was contaminated by CN-cycle processed
material dredged up into the red giant envelope. We use the measured C/N ratio
to deduce that 0.015-0.04 Msun was accreted by the K dwarf while engulfed, and
show that this is consistent with a recent tentative detection of 13C in the K
dwarf photosphere, and with the measured Li abundance in the scenario where the
red giant companion was Li-rich during the common envelope phase.Comment: 6 pages, 2 figures, ApJL accepte
GJ 900: A new hierarchical system with low-mass components
Speckle interferometric observations made with the 6 m telescope of the
Special Astrophysical Observatory of the Russian Academy of Sciences in 2000
revealed the triple nature of the nearby ( mas)
low-mass young ( Myr) star GJ 900. The configuration of the triple
system allowed it to be dynamically unstable. Differential photometry performed
from 2000 through 2004 yielded - and -band absolute magnitudes and
spectral types for the components to be =6.660.08,
=9.150.11, =10.080.26, =4.840.08,
=6.760.20, =7.390.31, K5--K7,
M3--M4, M5--M6. The ``mass--luminosity''
relation is used to estimate the individual masses of the components:
,
,
. From the observations of the
components relative motion in the period 2000--2006, we conclude that GJ 900 is
a hierarchical triple star with the possible orbital periods
P80 yrs and P20 yrs. An analysis of the 2MASS
images of the region around GJ 900 leads us to suggest that the system can
include other very-low-mass components.Comment: 7 pages, 5 figure
Coronal X-Ray Emission from the Stellar Companions to Transiently Accreting Black Holes
Observations of soft X-ray transients (SXTs) in quiescence have found that
the binaries harboring black holes are fainter than those that contain a
neutron star. Narayan and collaborators postulated that the faint X-ray
emission from black hole binaries was powered by an advection dominated
accretion flow (ADAF). We explore an alternative explanation for the quiescent
X-ray emission from the black hole systems: coronal emission from the rapidly
rotating optical companion. This is commonly observed and well studied in other
tidally locked binaries, such as the RS CVns. We show that two of the three
X-ray detected black hole binaries (A0620-00 and GRO J1655-40) exhibit X-ray
fluxes entirely consistent with coronal emission. The X-ray spectra of these
objects should be best fit with thermal Raymond-Smith models rich in lines when
coronal emission predominates. One black hole system (V404 Cyg) is too X-ray
bright to be explained as coronal emission. The quiescent X-ray emission from
the neutron star binaries is far too bright for coronal emission. It might be
that all SXT's have variable accretion rates in quiescence and that the basal
quiescent X-ray flux is set by either coronal emission from the companion or --
when present -- by thermal emission from the neutron star. We also show that
the lithium abundances in the black hole systems are comparable to those in the
RS CVns, reducing the need for production mechanisms that involve the compact
object.Comment: ApJ, accepted (v541; Oct 1, 2000); Changes to figures and tables,
minor modifications to text. Uses emulateapj.sty. 14 pages, 3 figure
Limits on the release of Rb isotopes from a zeolite based 83mKr calibration source for the XENON project
The isomer 83mKr with its half-life of 1.83 h is an ideal calibration source
for a liquid noble gas dark matter experiment like the XENON project. However,
the risk of contamination of the detector with traces of the much longer lived
mother isotop 83Rb (86.2 d half-life) has to be ruled out. In this work the
release of 83Rb atoms from a 1.8 MBq 83Rb source embedded in zeolite beads has
been investigated. To do so, a cryogenic trap has been connected to the source
for about 10 days, after which it was removed and probed for the strongest 83Rb
gamma-rays with an ultra-sensitive Germanium detector. No signal has been
found. The corresponding upper limit on the released 83Rb activity means that
the investigated type of source can be used in the XENON project and similar
low-background experiments as 83mKr generator without a significant risk of
contaminating the detector. The measurements also allow to set upper limits on
the possible release of the isotopes 84Rb and 86Rb, traces of which were
created alongside the production of 83Rb at the Rez cyclotron.Comment: 11 pages, 7 figures, submitted to Journal of Instrumentatio
Noncovalent Functionalization of Graphene and Graphene Oxide for Energy Materials, Biosensing, Catalytic, and Biomedical Applications
This Review focuses on noncovalent functionalization of graphene and graphene oxide with various species involving biomolecules, polymers, drugs, metals and metal oxide-based nanoparticles, quantum dots, magnetic nanostructures, other carbon allotropes (fullerenes, nanodiamonds, and carbon nanotubes), and graphene analogues (MoS2, WS2). A brief description of pi-pi interactions, van der Waals forces, ionic interactions, and hydrogen bonding allowing noncovalent modification of graphene and graphene oxide is first given. The main part of this Review is devoted, to tailored functionalization for applications in drug delivery, energy materials, solar cells, water splitting, biosensing, bioimaging, environmental, catalytic, photocatalytic, and biomedical technologies. A significant part of this Review explores the possibilities of graphene/graphene oxide-based 3D superstructures and their use in lithium-ion batteries. This Review ends with a look at challenges and future prospects of noncovalently modified graphene and graphene oxideope
Coude-feed stellar spectral library - atmospheric parameters
Context: Empirical libraries of stellar spectra play an important role in
different fields. For example, they are used as reference for the automatic
determination of atmospheric parameters, or for building synthetic stellar
populations to study galaxies. The CFLIB (Coude-feed library, Indo-US) database
is at present one of the most complete libraries, in terms of its coverage of
the atmospheric parameters space (Teff, log g and [Fe/H]) and wavelength
coverage 3460 - 9464 A at a resolution of 1 A FWHM. Although the atmospheric
parameters of most of the stars were determined from detailed analyses of
high-resolution spectra, for nearly 300 of the 1273 stars of the library at
least one of the three parameters is missing. For the others, the measurements,
compiled from the literature, are inhomogeneous.
Aims: In this paper, we re-determine the atmospheric parameters, directly
using the CFLIB spectra, and compare them to the previous studies.
Methods: We use the ULySS program to derive the atmospheric parameters, using
the ELODIE library as a reference.
Results: Based on comparisons with several previous studies we conclude that
our determinations are unbiased. For the 958 F,G, and K type stars the
precision on Teff, log g, and [Fe/H] is respectively 43 K, 0.13 dex and 0.05
dex. For the 53 M stars they are 82 K, 0.22 dex and 0.28 dex. And, for the 260
OBA type stars the relative precision on Teff is 5.1%, and on log g, and [Fe/H]
the precision is respectively 0.19 dex and 0.16 dex. These parameters will be
used to re-calibrate the CFLIB fluxes and to produce synthetic spectra of
stellar populations.Comment: 51 pages, accepted for publication in Astronomy and Astrophysic
Commissioning of the vacuum system of the KATRIN Main Spectrometer
The KATRIN experiment will probe the neutrino mass by measuring the
beta-electron energy spectrum near the endpoint of tritium beta-decay. An
integral energy analysis will be performed by an electro-static spectrometer
(Main Spectrometer), an ultra-high vacuum vessel with a length of 23.2 m, a
volume of 1240 m^3, and a complex inner electrode system with about 120000
individual parts. The strong magnetic field that guides the beta-electrons is
provided by super-conducting solenoids at both ends of the spectrometer. Its
influence on turbo-molecular pumps and vacuum gauges had to be considered. A
system consisting of 6 turbo-molecular pumps and 3 km of non-evaporable getter
strips has been deployed and was tested during the commissioning of the
spectrometer. In this paper the configuration, the commissioning with bake-out
at 300{\deg}C, and the performance of this system are presented in detail. The
vacuum system has to maintain a pressure in the 10^{-11} mbar range. It is
demonstrated that the performance of the system is already close to these
stringent functional requirements for the KATRIN experiment, which will start
at the end of 2016.Comment: submitted for publication in JINST, 39 pages, 15 figure
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