2,163 research outputs found
Ultraviolet Radiation from Evolved Stellar Populations: II. The Ultraviolet Upturn Phenomenon in Elliptical Galaxies
We present an analysis of the far-ultraviolet upturn phenomenon (UVX)
observed in elliptical galaxies and spiral galaxy bulges. Our premise is that
the UV radiation from these systems emanates primarily from extreme horizontal
branch (EHB) stars and their progeny. We re-derive the broad-band UV colors
and for globular clusters and elliptical galaxies from the
available satellite data and investigate color-color and color-line strength
correlations. We also provide the ingredients necessary for constructing models
with arbitrary HB morphologies.Comment: uuencoded compressed postscript file, 60pp. (revisions on pp.
7,8,22,33,37 & 57
UV Properties of Galactic Globular Clusters with GALEX II. Integrated colors
We present ultraviolet (UV) integrated colors of 44 Galactic globular
clusters (GGCs) observed with the Galaxy Evolution Explorer (GALEX) in both FUV
and NUV bands. This data-base is the largest homogeneous catalog of UV colors
ever published for stellar systems in our Galaxy. The proximity of GGCs makes
it possible to resolve many individual stars even with the somewhat low spatial
resolution of GALEX. This allows us to determine how the integrated UV colors
are driven by hot stellar populations, primarily horizontal branch stars and
their progeny. The UV colors are found to be correlated with various parameters
commonly used to define the horizontal branch morphology. We also investigate
how the UV colors vary with parameters like metallicity, age, helium abundance
and concentration. We find for the first time that GCs associated with the
Sagittarius dwarf galaxy have (FUV-V) colors systematically redder than GGCs
with the same metallicity. Finally, we speculate about the presence of an
interesting trend, suggesting that the UV color of GCs may be correlated with
the mass of the host galaxy, in the sense that more massive galaxies possess
bluer clusters.Comment: Accepted for publication by The Astronomical Journal. 36 pages, 9
figures, 1 tabl
The Quantum Langevin Equation
The macroscopic description of a quantum particle with passive dissipation and moving in an arbitrary external potential is formulated in terms of the generalized Langevin equation. The coupling with the heat bath corresponds to two terms: a mean force characterized by a memory function μ(t) and an operator-valued random force. Explicit expressions are given for the correlation of the random force. The random force is never Markovian. It is shown that μ̃(z), the Fourier transform of the memory function, is a positive real function, analytic in the upper half plane and with Re{μ̃(ω + i0^+)} a positive distribution on the real axis. This form is then derived for the independent-oscillator (IO) model of a heat bath. It is shown that the most general quantum Langevin equation can be realized by this simple model. A critical comparison is made with a number of other models which have appeared in the literature
Hot Populations in M87 Globular Clusters
We have obtained HST/STIS far- and near-UV photometry of globular clusters in
four fields in the gE galaxy M87. To a limit of m(FUV) = 25 we detect a total
of 66 globular clusters (GCs) in common with the deep HST optical-band study of
Kundu et al. (1999). Despite strong overlap in V- and I-band properties, the
M87 GCs have UV/optical properties that are distinct from clusters in the Milky
Way and in M31. M87 clusters, especially metal-poor ones, produce larger hot HB
populations than do Milky Way analogues. Cluster mass is probably not a factor
in these distinctions. The most metal-rich M87 GCs in our sample are near Z_sun
and overlap the local E galaxy sample in estimated Mg_2 line indices.
Nonetheless, the clusters produce much more UV light at a given Mg_2, being up
to 1 mag bluer than any gE galaxy in (FUV-V) color. The M87 GCs do not appear
to represent a transition between Milky Way-type clusters and E galaxies. The
differences are in the correct sense if the clusters are significantly older
than the E galaxies. Comparisons with Galactic open clusters indicate that the
hot stars lie on the extreme horizontal branch, rather than being blue
stragglers, and that the EHB becomes well populated for ages > 5 Gyr. We find
that 43 of our UV detections have no optical-band counterparts. Most appear to
be UV-bright background galaxies, seen through M87. Eleven NUV variable sources
detected at only one epoch in the central field are probably classical novae.
[Abridged]Comment: 70 pages, 25 figures (including 4 jpgs), 7 tables. To appear in AJ.
Full resolution version available at
http://www.astro.virginia.edu/~rwo/m87/m87-hotpops.pd
Comment on the exact calculation of the partition function for a quantum oscillator interacting with the radiation field
In their recent paper [Phys. Rev. A 35, 4122 (1987)] Castrigiano and Kokiantonis claim to present an exact calculation of the partition function for a quantum oscillator interacting with the blackbody radiation field. In this Comment it is shown that their result is in fact wrong, due essentially to their neglect at the outset of the A^2 term in the Hamiltonian. It is further shown how their error can be repaired to give the correct result given by us in an earlier publication [Phys. Rev. Lett. 55, 2273, (1985)]
Formation of spatially periodic fronts of high-energy electrons in a radio-frequency driven surface microdischarge
The generation of spatially periodic fronts of high-energy electrons (>13.48 eV) has been investigated in a radio-frequency surface microdischarge in atmospheric-pressure argon. Optical emission spectroscopy is used to study the Ar I 2p1−1s2 transition surrounding a filamentary microdischarge, both spatially and with respect to the phase of the applied voltage. The formation of excitation fronts, which remain at a constant propagation distance throughout the RF cycle and for the duration of the pulse, may be explained by a localized increase in the electric field at the tip of surface-charge layers that are deposited during the extension phase
Nanosecond optical imaging spectroscopy of an electrothermal radiofrequency plasma thruster plume
Nanosecond optical imaging spectroscopy is employed to investigate the spatio-temporal dynamics of the plasma plume expanding from a 4.2 mm-diameter, 20 mm-long cylindrical capacitively coupled electrothermal radiofrequency (rf) driven thruster using 10 W of power at 12.50 MHz and an argon pressure of 1.5 Torr. On-axis, the plume exhibits four distinct peaks of optical emission intensity within the rf period. The plume has a spherical shape with a transient radial extension (during half of the rf cycle) at the thruster exit plane due to an rf current to ground when the grounded electrode acts as an anode
The Origin of Extreme Horizontal Branch Stars
Strong mass loss on the red giant branch (RGB) can result in the formation of
extreme horizontal branch (EHB) stars. The EHB stars spend most of their He
core and shell burning phase at high temperatures and produce copious
ultraviolet flux. They have very small hydrogen envelopes and occupy a small
range in mass. We have computed evolutionary RGB models with mass loss for
stars with a range of metallicities at initial masses < 1.1 Msun corresponding
to populations ages between 12.5 and 14.5 Gyr. We used the Reimers formula to
characterize mass loss, but investigated a larger range of the mass loss
efficiency parameter, eta, than is common. To understand how the number of EHB
stars varies with metallicity in a stellar population we considered how the
zero-age horizontal branch (ZAHB) is populated. The range in eta producing EHB
stars is comparable to that producing `mid-HB' stars. Somewhat surprisingly,
neither the range nor magnitude of eta producing EHB stars varies much
metallicity. In contrast, the range of eta producing mid-HB stars decreases
with increasing metallicity. Hence the HB of populations with solar metallicity
and higher, such as expected in elliptical galaxies and spiral bulges, will be
bimodal if the distribution covers a sufficiently large range in eta.Comment: AASLaTeX v.4, 29pp., postscript available at
http://shemesh.gsfc.nasa.gov/~dorman/Ben.htm
Aspects of slurry management on pig farms.
End of Project ReportThe objectives of manure or slurry management on intensive pig farms
are the provision of adequate slurry storage capacity and the efficient
recycling of the slurry nutrients for crop production. However, recent
surveys of pig slurry dry matter suggest there is excessive dilution of
raw pig slurry with water. This has two important implications for
management. The first is greater storage capacity will be required due
to the increased volume of slurry generated. Slurry storage is expensive.
For example, a 350 sow unit adding 10 weeks storage needs to
invest £50,000. Secondly, evidence from the literature indicates an
improved slurry nitrogen efficiency with the more dilute manure. The results of field trials showed that higher dry matter pig slurries
reduced the relative efficiency of pig slurry nitrogen for second cut
silage production. This is probably linked to reduced ammonia volatilisation
losses, consequent to the less viscous nature of dilute slurry
which permits a more rapid infiltration of the ammonium nitrogen into
the soil. The use of a band spreader or shallow injection rather than
the conventional splash plate were shown to increase the efficiency of
pig slurry nitrogen for grass silage production. Therefore, the potential
for the higher pig slurry dry matter, required for cost effective storage/
handling costs, to reduce the efficiency of its nitrogen for grass
silage production can be partially offset by using band spreaders or
shallow injection spreading systems. These have the added advantage
of reducing odour emissions from the land spreading operation.Teagasc Walsh Fellowship Programm
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