3,110 research outputs found
J08069+1527: A newly discovered high amplitude, hybrid subdwarf B pulsator
We present our discovery of a new hybrid pulsating subdwarf B star,
J08069+1527. The effective temperature and surface gravity of 28,500400\,K
and 5.370.04\,dex, respectively, place this object inside the instability
strip and also among other pulsating hot subdwarfs of a hybrid nature, right
next to another fascinating star: Balloon\,090100001. From this proximity, we
anticipated this star could pulsate in both high and low frequency modes.
Indeed, our analysis of photometric data confirmed our prediction. We detected
two peaks in the high frequency region and two other peaks at low frequencies.
In addition, the amplitude of the dominant mode is very high and comparable to
the dominant peaks in other hybrid subdwarf B stars. Since this star is bright,
we performed time-series low resolution spectroscopy. Despite a low
signal-to-noise (S/N) ratio, we were able to detect the main peak from these
data. All our results strongly indicate that J08069+1527 is a high amplitude
pulsating hot subdwarf B star of hybrid nature. By analogy to the other
pulsating sdB star, we judge that the dominant mode we detected here has radial
nature. Future stellar modeling should provide us with quite good constrains as
p- and g-modes presented in this star are driven in different parts of its
interior.Comment: 7 pages, 10 figures, accepted for publication in MNRA
Electronic structure and transport properties of CeNi9In2
We investigated CeNi9In2 compound, which has been considered as a mixed
valence (MV) system. Electrical resistivity vs. temperature variation was
analysed in terms of the model proposed by Freimuth for systems with unstable
4f shell. At low temperature the resistivity dependence is consistent with a
Fermi liquid state with a contribution characteristic of electron-phonon
interaction. Ultraviolet photoemission spectroscopy (UPS) studies of the
valence band did not reveal a Kondo peak down to 14 K. A difference of the
spectra obtained with photon energies of low and high photoionization cross
sections for Ce 4f electrons indicated that 4f states are located mainly close
to the Fermi energy. The peaks related to f_{5/2}^1 and f_{7/2}^1 final states
cannot be resolved but form a plateau between -0.3 eV and the Fermi energy.
X-ray photoemission spectroscopy (XPS) studies were realized for the cerium 3d
level. The analysis of XPS spectra within the Gunnarsson-Sh\"onhammer theory
yielded a hybridization parameter of 104 meV and non-integer f level
occupation, being close to 3. Calculations of partial densities of states were
realized by a full potential local orbital (FPLO) method. They confirm that the
valence band is dominated by Ni 3d states and are in general agreement with the
experiment except for the behavior of f-electrons.Comment: 10 pages, 5 figure
Logging Impacts on Aquatic Ecosystem Quality in Michaux State Forest, Pennsylvania
Logging can affect freshwater streams around logging sites, even years after the logging has occurred. In this study, we looked into how sustainable logging in Michaux State Forest (in Adams County, Pennsylvania) has affected two streams within the state park: Mountain Creek and Birch Run. Six sites were selected along each stream, with three upstream and three downstream from the logging area. We hypothesized that the water quality would be lower at the stream sites downstream from the logged areas as compared to the upstream sites. At each site, water samples were collected, including pH, water temperature, and turbidity, as were freshwater macroinvertebrates. Turbidity was low, indicating good stream quality at all sites, but pH was also low, indicating poor stream quality. Coarse woody debris (CWD) was examined at each site, as it can impact stream quality by creating extra particulate matter, but counts of CWD were low. Diversity of freshwater macroinvertebrates was relatively high, with most of the collected taxa showing good water quality, though a few indicated poor water quality. The Hilsenhoff Index and the EPT Index, both based on the presence or absence of specific macroinvertebrate taxa, indicated good water quality for all locations. This study determined that future research should be conducted on logging impacts on stream quality in Michaux State forest, as there were several indicators that the stream waters could be low quality, even if the majority of the indicators showed good water quality
KIC7668647: a 14 day beaming sdB+WD binary with a pulsating subdwarf
The recently discovered subdwarf B (sdB) pulsator KIC7668647 is one of the 18
pulsating sdB stars detected in the Kepler field. It features a rich g-mode
frequency spectrum, with a few low-amplitude p-modes at short periods.
We use new ground-based low-resolution spectroscopy, and the near-continuous
2.88 year Kepler lightcurve, to reveal that KIC7668647 consists of a subdwarf B
star with an unseen white-dwarf companion with an orbital period of 14.2d. An
orbit with a radial-velocity amplitude of 39km/s is consistently determined
from the spectra, from the orbital Doppler beaming seen by Kepler at 163ppm,
and from measuring the orbital light-travel delay of 27 by timing of the many
pulsations seen in the Kepler lightcurve. The white dwarf has a minimum mass of
0.40 M_sun.
We use our high signal-to-noise average spectra to study the atmospheric
parameters of the sdB star, and find that nitrogen and iron have abundances
close to solar values, while helium, carbon, oxygen and silicon are
underabundant relative to the solar mixture.
We use the full Kepler Q06--Q17 lightcurve to extract 132 significant
pulsation frequencies. Period-spacing relations and multiplet splittings allow
us to identify the modal degree L for the majority of the modes. Using the
g-mode multiplet splittings we constrain the internal rotation period at the
base of the envelope to 46-48d as a first seismic result for this star. The few
p-mode splittings may point at a slightly longer rotation period further out in
the envelope of the star.
From mode-visibility considerations we derive that the inclination of the
rotation axis of the sdB in KIC7668647 must be around ~60 degrees.
Furthermore, we find strong evidence for a few multiplets indicative of
degree 3 <= L <= 8, which is another novelty in sdB-star observations made
possible by Kepler.Comment: arXiv admin note: text overlap with arXiv:1206.387
Granular circulation in a cylindrical pan: simulations of reversing radial and tangential flows
Granular flows due to simultaneous vertical and horizontal excitations of a
flat-bottomed cylindrical pan are investigated using event-driven molecular
dynamics simulations. In agreement with recent experimental results, we observe
a transition from a solid-like state, to a fluidized state in which circulatory
flow occurs simultaneously in the radial and tangential directions. By going
beyond the range of conditions explored experimentally, we find that each of
these circulations reverse their direction as a function of the control
parameters of the motion. We numerically evaluate the dynamical phase diagram
for this system and show, using a simple model, that the solid-fluid transition
can be understood in terms of a critical value of the radial acceleration of
the pan bottom; and that the circulation reversals are controlled by the phase
shift relating the horizontal and vertical components of the vibrations. We
also discuss the crucial role played by the geometry of the boundary
conditions, and point out a relationship of the circulation observed here and
the flows generated in vibratory conveyors.Comment: 10 pages, 8 figure
On the Invariant Theory of Weingarten Surfaces in Euclidean Space
We prove that any strongly regular Weingarten surface in Euclidean space
carries locally geometric principal parameters. The basic theorem states that
any strongly regular Weingarten surface is determined up to a motion by its
structural functions and the normal curvature function satisfying a geometric
differential equation. We apply these results to the special Weingarten
surfaces: minimal surfaces, surfaces of constant mean curvature and surfaces of
constant Gauss curvature.Comment: 16 page
Kepler detection of a new extreme planetary system orbiting the subdwarf-B pulsator KIC10001893
KIC10001893 is one out of 19 subdwarf-B (sdB) pulsators observed by the
Kepler spacecraft in its primary mission. In addition to tens of pulsation
frequencies in the g-mode domain, its Fourier spectrum shows three weak peaks
at very low frequencies, which is too low to be explained in terms of g modes.
The most convincing explanation is that we are seeing the orbital modulation of
three Earth-size planets (or planetary remnants) in very tight orbits, which
are illuminated by the strong stellar radiation. The orbital periods are
P1=5.273, P2=7.807, and P3=19.48 hours, and the period ratios P2/P1=1.481 and
P3/P2=2.495 are very close to the 3:2 and 5:2 resonances, respectively. One of
the main pulsation modes of the star at 210.68 {\mu}Hz corresponds to the third
harmonic of the orbital frequency of the inner planet, suggesting that we see,
for the first time in an sdB star, g-mode pulsations tidally excited by a
planetary companion. The extreme planetary system that emerges from the Kepler
data is very similar to the recent discovery of two Earth-size planets orbiting
the sdB pulsator KIC05807616 (Charpinet et al. 2011a).Comment: 6 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
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