540 research outputs found
A preliminary model of the coma of 2060 Chiron
We have included gravity in our fluid dynamic model with chemical kinetics of dusty comet comae and applied it with two dust sizes to 2060 Chiron. A progress report on the model and preliminary results concerning gas/dust dynamics and chemistry is given
OLFACTORY RESPONSES OF DEER MICE TO DOUGLAS-FIR SEED VOLATILES
An attempt was made to identify the olfactory cues produced by Douglas-fir seeds which attract deer mice (Peromyscus maniculatus) to the seeds. The olfactometers used are described, and the merits of different statistical analyses of the data are discussed. The odors produced by whole Douglas-fir seed and by the endosperm were preferred among the fractions tested to date. Deer mice were repelled by Douglas-fir turpentine, cedar oil, and, to a lesser degree, one extract
OLFACTORY RESPONSES OF DEER MICE TO DOUGLAS-FIR SEED VOLATILES
An attempt was made to identify the olfactory cues produced by Douglas-fir seeds which attract deer mice (Peromyscus maniculatus) to the seeds. The olfactometers used are described, and the merits of different statistical analyses of the data are discussed. The odors produced by whole Douglas-fir seed and by the endosperm were preferred among the fractions tested to date. Deer mice were repelled by Douglas-fir turpentine, cedar oil, and, to a lesser degree, one extract
A Push-Button Molecular Switch
The preparation, characterization, and switching mechanism of a unique single-station mechanically switchable hetero[2]catenane are reported. The facile synthesis utilizing a “threading-followed-by-clipping” protocol features Cu^(2+)-catalyzed Eglinton coupling as a mild and efficient route to the tetrathiafulvalene-based catenane in high yield. The resulting mechanically interlocked molecule operates as a perfect molecular switch, most readily described as a “push-button” switch, whereby two discrete and fully occupied translational states are toggled electrochemically at incredibly high rates. This mechanical switching was probed using a wide variety of experimental techniques as well as quantum-mechanical investigations. The fundamental distinctions between this single-station [2]catenane and other more traditional bi- and multistation molecular switches are significant
Imaging the molecular gas in a submm galaxy at z = 4.05: cold mode accretion or a major merger?
We present a high resolution (down to 0.18"), multi-transition imaging study
of the molecular gas in the z = 4.05 submillimeter galaxy GN20. GN20 is one of
the most luminous starburst galaxy known at z > 4, and is a member of a rich
proto-cluster of galaxies at z = 4.05 in GOODS-North. We have observed the CO
1-0 and 2-1 emission with the VLA, the CO 6-5 emission with the PdBI
Interferometer, and the 5-4 emission with CARMA. The H_2 mass derived from the
CO 1-0 emission is 1.3 \times 10^{11} (\alpha/0.8) Mo. High resolution imaging
of CO 2-1 shows emission distributed over a large area, appearing as partial
ring, or disk, of ~ 10kpc diameter. The integrated CO excitation is higher than
found in the inner disk of the Milky Way, but lower than that seen in high
redshift quasar host galaxies and low redshift starburst nuclei. The VLA CO 2-1
image at 0.2" resolution shows resolved, clumpy structure, with a few brighter
clumps with intrinsic sizes ~ 2 kpc. The velocity field determined from the CO
6-5 emission is consistent with a rotating disk with a rotation velocity of ~
570 km s^{-1} (using an inclination angle of 45^o), from which we derive a
dynamical mass of 3 \times 10^{11} \msun within about 4 kpc radius. The star
formation distribution, as derived from imaging of the radio synchrotron and
dust continuum, is on a similar scale as the molecular gas distribution. The
molecular gas and star formation are offset by ~ 1" from the HST I-band
emission, implying that the regions of most intense star formation are highly
dust-obscured on a scale of ~ 10 kpc. The large spatial extent and ordered
rotation of this object suggests that this is not a major merger, but rather a
clumpy disk accreting gas rapidly in minor mergers or smoothly from the
proto-intracluster medium. ABSTRACT TRUNCATEDComment: 33 pages, 8 figures, submitted to the ApJ, aas latex forma
Testing Comptonizing coronae on a long BeppoSAX observation of the Seyfert 1 galaxy NGC 5548
We test accurate models of Comptonization spectra over the high quality data
of the BeppoSAX long look at NGC 5548, allowing for different geometries of the
scattering region, different temperatures of the input soft photon field and
different viewing angles. We find that the BeppoSAX data are well represented
by a plane parallel or hemispherical corona viewed at an inclination angle of
30. For both geometries the best fit temperature of the soft photons
is close to 15 eV. The corresponding best fit values of the hot
plasma temperature and optical depth are 250--260 keV and
0.16--0.37 for the slab and hemisphere respectively. These values
are substantially different from those derived fitting the data with a
power-law + cut off approximation to the Comptonization component (kT_{\rm
e}\lta 60 keV, 2.4). This is due to the fact that accurate
Comptonization spectra in anisotropic geometries show "intrinsic" curvature
which reduces the necessity of a high energy cut-off. The Comptonization
parameter derived for the slab model {is} larger than predicted for a two phase
plane parallel corona in energy balance, suggesting that a more
``photon-starved'' geometry is necessary. The spectral softening detected
during a flare which occurred in the central part of the observation
corresponds to a decrease of the Comptonization parameter, probably associated
with an increase of the soft photon luminosity, the {hard} photon luminosity
remaining constant.Comment: 36 pages, 9 figures, accepted by Ap
The Growth of Black Holes and Their Host Spheroids in (Sub)mm-loud QSOs at High Redshift
We study the growth of black holes and stellar population in spheroids at
high redshift using several (sub)mm-loud QSO samples. Applying the same
criteria established in an earlier work, we find that, similar to IR QSOs at
low redshift, the far-infrared emission of these (sub)mm-loud QSOs mainly
originates from dust heated by starbursts. By combining low-z IR QSOs and
high-z (sub)mm-loud QSOs, we find a trend that the star formation rate
(\Mstardot) increases with the accretion rate (\Mdot). We compare the
values of \Mstardot/\Mdot for submm emitting galaxies (SMGs), far-infrared
ultraluminous/hyperluminous QSOs and typical QSOs, and construct a likely
evolution scenario for these objects. The (sub)mm-loud QSO transition phase has
both high \Mdot and \Mstardot and hence is important for establishing the
correlation between the masses of black holes and spheroids.Comment: 19 pages,3 figures,submitted to Chin. J. Astron. Astrophys. This
paper was first prepared for publication on August 10th, 200
Chandra X-rays from the redshift 7.54 quasar ULAS J1342+0928
We present a 45 ks Chandra observation of the quasar ULAS J1342+0928 at
z=7.54. We detect 14.0^{+4.8}_{-3.7} counts from the quasar in the
observed-frame energy range 0.5-7.0 keV (6-sigma detection), representing the
most distant non-transient astronomical source identified in X-rays to date.
The present data are sufficient only to infer rough constraints on the spectral
parameters. We find an X-ray hardness ratio of HR = -0.51^{+0.26}_{-0.28}
between the 0.5-2.0 keV and 2.0-7.0 keV ranges and derive a power-law photon
index of Gamma = 1.95^{+0.55}_{-0.53}. Assuming a typical value for
high-redshift quasars of Gamma = 1.9, ULAS J1342+0928 has a 2-10 keV rest-frame
X-ray luminosity of L_{2-10} = 11.6^{+4.3}_{-3.5} x 10^{44} erg/s. Its
X-ray-to-optical power-law slope is alpha_{OX}=-1.67^{+0.16}_{-0.10},
consistent with the general trend indicating that the X-ray emission in the
most bolometrically powerful quasars is weaker relative to their optical
emission.Comment: Accepted for publication in the Astrophysical Journal Letter
Massive skyrmions in quantum Hall ferromagnets
We apply the theory of elasticity to study the effects of skyrmion mass on
lattice dynamics in quantum Hall systems. We find that massive Skyrme lattices
behave like a Wigner crystal in the presence of a uniform perpendicular
magnetic field. We make a comparison with the microscopic Hartree-Fock results
to characterize the mass of quantum Hall skyrmions at and investigate
how the low temperature phase of Skyrme lattices may be affected by the
skyrmion mass.Comment: 6 pages and 2 figure
An 800-million-solar-mass black hole in a significantly neutral Universe at redshift 7.5
Quasars are the most luminous non-transient objects known and as a result
they enable studies of the Universe at the earliest cosmic epochs. Despite
extensive efforts, however, the quasar ULAS J1120+0641 at z=7.09 has remained
the only one known at z>7 for more than half a decade. Here we report
observations of the quasar ULAS J134208.10+092838.61 (hereafter J1342+0928) at
redshift z=7.54. This quasar has a bolometric luminosity of 4e13 times the
luminosity of the Sun and a black hole mass of 8e8 solar masses. The existence
of this supermassive black hole when the Universe was only 690 million years
old---just five percent of its current age---reinforces models of early
black-hole growth that allow black holes with initial masses of more than about
1e4 solar masses or episodic hyper-Eddington accretion. We see strong evidence
of absorption of the spectrum of the quasar redwards of the Lyman alpha
emission line (the Gunn-Peterson damping wing), as would be expected if a
significant amount (more than 10 per cent) of the hydrogen in the intergalactic
medium surrounding J1342+0928 is neutral. We derive a significant fraction of
neutral hydrogen, although the exact fraction depends on the modelling.
However, even in our most conservative analysis we find a fraction of more than
0.33 (0.11) at 68 per cent (95 per cent) probability, indicating that we are
probing well within the reionization epoch of the Universe.Comment: Updated to match the final journal versio
- …