6,659 research outputs found
Capacity limits and matching properties of lateral flux integrated capacitors
Theoretical limits for the capacitance density of lateral flux and quasi-fractal capacitors are calculated. These limits are used to investigate the efficiency of various capacitive structures such as lateral flux and quasi-fractal structures. This study leads to two new capacitor structures with high lateral field efficiency. Simulation and experimental results demonstrate higher capacity and superior matching properties compared to the standard horizontal parallel plate and previously reported lateral-field capacitors
Circular-geometry oscillators
5.3GHz 0.18ÎĽm CMOS circular-geometry oscillator exploits high Q of slab inductors. The oscillator draws 10mA from 1.4V with a phase noise of -147.3dBc/Hz at 10MHz offset. A second 5.4GHz circular-geometry VCO has a tuning range of 8% with phase noise of -142.2dBc/Hz at 10MHz offset while drawing 12mA from a 1.8V supply
The Stellar Content and the Star Formation History of the Local Group Dwarf Galaxy LGS 3
The star formation history (SFH) and the properties of the dwarf galaxy LGS3
are analyzed using color-magnitude (CM) diagrams plotted from VRI photometry of
736 stars. The distance to the galaxy is estimated through the position of the
tip or the red giant branch. Two acceptable results have been obtained:
0.77+/-0.07 Mpc and 0.96+/-0.07 Mpc, although the first value is favored by
complementary considerations on the stellar content of the galaxy. Both values
make LGS3 a possible satellite of M31 or of M33. The SFH is investigated for
each of the two adopted distances comparing the observed CM diagrams with model
CM diagrams computed for different star formation rates (psi(t)) and chemical
enrichment laws (Z(t)).
The results are compatible with LGS3 having been forming stars since an early
epoch, 15-12 Gyr ago, at an almost constant rate if distance is 0.77 Mpc or at
an exponentially decreasing rate if distance is 0.96 Mpc. According to our
models, the current metallicity would range from Z~0.0007 to Z~0.002. Other
results are the current psi(t): (0.55+/-0.04)x10^(-10) Mo yr^(-1) pc^(-2) or
(0.47+/-0.07)x10^(-10) Mo yr^(-1) pc^(-2), depending of the distance, and its
average for the entire life of the galaxy, =(1.4+/-0.1)x10^(-10) Mo
yr^(-1) pc^(-2). At the present psi(t), the probability of LGS3 having an HII
region is 0.2, which is compatible with the fact that no HII regions have been
found in the galaxy. Its fraction of gas relative to the mass intervening in
the chemical evolution is about 0.40 and its percentage of dark matter (that
which cannot be explained as stellar remnants or by extrapolation of the used
IMF to low masses) is 95%. The results for psi(t) and Z(t) for d=0.77 Mpc are
compatible with a moderate outflow of well mixed material (lambda=3), but largeComment: 23 pages, 3 tables, 14 figures. AJ in pres
Photometric catalog of nearby globular clusters (I)
We present the first part of the first large and homogeneous CCD
color-magnitude diagram (CMD) data base, comprising 52 nearby Galactic globular
clusters (GGC) imaged in the V and I bands using only two telescopes (one for
each hemisphere). The observed clusters represent 75% of the known Galactic
globulars with (m-M)v<=16.15 mag, cover most of the globular cluster
metallicity range (-2.2 <= [Fe/H] <= -0.4), and span Galactocentric distances
from ~1.2 to ~18.5 kpc.
In this paper, the CMDs for the 39 GGCs observed in the southern hemisphere
are presented. The remaining 13 northern hemisphere clusters of the catalog are
presented in a companion paper. For four clusters (NGC 4833, NGC 5986, NGC
6543, and NGC 6638) we present for the first time a CMD from CCD data. The
typical CMD spans from the 22nd V magnitude to the tip of the red giant branch.
Based on a large number of standard stars, the absolute photometric calibration
is reliable to the ~0.02 mag level in both filters.
This catalog, because of its homogeneity, is expected to represent a useful
data base for the measurement of the main absolute and relative parameters
characterizing the CMD of GGCs.Comment: 34 pages, 108 figures, Astronomy & Astrophysics Supplement Series, in
press. Full resolution figures can be obtained from the authors upon reques
Rotation of Hot Horizontal Branch Stars in Galactic Globular Clusters
We present high resolution UVES+VLT spectroscopic observations of 61 stars in
the extended blue horizontal branches of the Galactic globular clusters NGC
1904 (M79), NGC 2808, NGC 6093 (M80), and NGC 7078 M15). Our data reveal for
the first time the presence in NGC 1904 of a sizable population of fast (v
sin(i) >= 20 km/s) horizontal branch (HB) rotators, confined to the cool end of
the EHB, similar to that found in M13. We also confirm the fast rotators
already observed in NGC 7078. The cooler stars (T_eff < 11,500 K) in these
three clusters show a range of rotation rates, with a group of stars rotating
at ~ 15 km/s or less, and a fast rotating group at ~ 30 km/s. Apparently, the
fast rotators are relatively more abundant in NGC 1904 and M13, than in NGC
7078. No fast rotators have been identified in NGC 2808 and NGC 6093. All the
stars hotter than T_eff ~ 11,500 K have projected rotational velocities vsini<
12 km/s. The connection between photometric gaps in the HB and the change in
the projected rotational velocities is not confirmed by the new data. However,
our data are consistent with a relation between this discontinuity and the HB
jump.Comment: 2 pages, 1 figure, A.S.P. Conf. Ser., in press in Vol. 296, 200
The stellar content of the Local Group dwarf galaxy Phoenix
We present new deep ground-based photometry of the Local Group dwarf
galaxy Phoenix. Our results confirm that this galaxy is mainly dominated by red
stars, with some blue plume stars indicating recent (100 Myr old) star
formation in the central part of the galaxy. We have performed an analysis of
the structural parameters of Phoenix based on an ESO/SRC scanned plate, in
order to search for differentiated component. The results were then used to
obtain the color-magnitude diagrams for three different regions of Phoenix in
order to study the variation of the properties of its stellar population. The
young population located in the central component of Phoenix shows a clear
asymmetry in its distribution, that could indicate a propagation of star
formation across the central component. The HI cloud found at 6 arcmin
Southwest by Young & Lo (1997) could have been involved in this process.
We also find the presence of a substantial intermediate-age population in the
central region of Phoenix that would be less abundant or absent in its outer
regions. This result is also consistent with the gradient found in the number
of horizontal branch stars, whose frequency relative to red giant branch stars
increases towards the outer part of the galaxy. These results, together with
those of our morphological study, suggest the existence of an old, metal-poor
population with a spheroidal distribution surrounding the younger inner
component of Phoenix. This two-component structure may resemble the halo-disk
structure observed in spirals, although more data, in particular on kinematics,
are necessary to confirm this.Comment: 46 pages, 21 figures, 9 Tables, to be published in AJ, August 9
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