11,207 research outputs found
Detailed Abundances of Two Very Metal-Poor Stars in Dwarf Galaxies
The most metal-poor stars in dwarf spheroidal galaxies (dSphs) can show the nucleosynthetic patterns of one or a few supernovae (SNe). These SNe could have zero metallicity, making metal-poor dSph stars the closest surviving links to Population III stars. Metal-poor dSph stars also help to reveal the formation mechanism of the Milky Way (MW) halo. We present the detailed abundances from Keck/HIRES spectroscopy for two very metal-poor stars in two MW dSphs. One star, in the Sculptor dSph, has [Fe I/H] = -2.40. The other star, in the Ursa Minor dSph, has [Fe I/H] = -3.16. Both stars fall in the previously discovered low-metallicity, high-[Îą/Fe] plateau. Most abundance ratios of very metal-poor stars in these two dSphs are largely consistent with very metal-poor halo stars. However, the abundances of Na and some r-process elements lie at the lower end of the envelope defined by inner halo stars of similar metallicity. We propose that the metallicity dependence of SN yields is the cause. The earliest SNe in low-mass dSphs have less gas to pollute than the earliest SNe in massive halo progenitors. As a result, dSph stars at â3 < [Fe/H] < â2 sample SNe with [Fe/H] Lt â3, whereas halo stars in the same metallicity range sample SNe with [Fe/H] ~ â3. Consequently, enhancements in [Na/Fe] and [r/Fe] were deferred to higher metallicity in dSphs than in the progenitors of the inner halo
The impact of advances in information technology on the cartographic interface in social planning
The Peculiar Chemical Inventory of NGC 2419: an Extreme Outer Halo "Globular Cluster"
NGC 2419 is a massive outer halo Galactic globular cluster (GC) whose stars have previously been shown to have
somewhat peculiar abundance patterns. We have observed seven luminous giants that are members of NGC 2419
with Keck/HIRES at reasonable signal-to-noise ratio. One of these giants is very peculiar, with an extremely low
[Mg/Fe] and high [K/Fe] but normal abundances of most other elements. The abundance pattern does not match
the nucleosynthetic yields of any supernova model. The other six stars show abundance ratios typical of inner halo
Galactic GCs, represented here by a sample of giants in the nearby GC M30. Although our measurements show
that NGC 2419 is unusual in some respects, its bulk properties do not provide compelling evidence for a difference between inner and outer halo GCs
Spectroscopic Confirmation of the Dwarf Galaxies Hydra II and Pisces II and the Globular Cluster Laevens 1
We present Keck/DEIMOS spectroscopy of stars in the recently discovered Milky
Way satellites Hydra II, Pisces II, and Laevens 1. We measured a velocity
dispersion of 5.4 (+3.6 -2.4) km/s for Pisces II, but we did not resolve the
velocity dispersions of Hydra II or Laevens 1. We marginally resolved the
metallicity dispersions of Hydra II and Pisces II but not Laevens 1.
Furthermore, Hydra II and Pisces II obey the luminosity-metallicity relation
for Milky Way dwarf galaxies ( = -2.02 +/- 0.08 and -2.45 +/- 0.07,
respectively), whereas Laevens 1 does not ( = -1.68 +/- 0.05). The
kinematic and chemical properties suggest that Hydra II and Pisces II are dwarf
galaxies, and Laevens 1 is a globular cluster. We determined that two of the
previously observed blue stars near the center of Laevens 1 are not members of
the cluster. A third blue star has ambiguous membership. Hydra II has a radial
velocity = 303.1 +/- 1.4 km/s, similar to the leading arm of the
Magellanic stream. The mass-to-light ratio for Pisces II is 370 (+310 -240)
M_sun/L_sun. It is not among the most dark matter-dominated dwarf galaxies, but
it is still worthy of inclusion in the search for gamma rays from dark matter
self-annihilation.Comment: Accepted to ApJ. v2 has been revised in response to the referee's
repor
Linguistic Reflection in Java
Reflective systems allow their own structures to be altered from within. Here
we are concerned with a style of reflection, called linguistic reflection,
which is the ability of a running program to generate new program fragments and
to integrate these into its own execution. In particular we describe how this
kind of reflection may be provided in the compiler-based, strongly typed
object-oriented programming language Java. The advantages of the programming
technique include attaining high levels of genericity and accommodating system
evolution. These advantages are illustrated by an example taken from persistent
programming which shows how linguistic reflection allows functionality (program
code) to be generated on demand (Just-In-Time) from a generic specification and
integrated into the evolving running program. The technique is evaluated
against alternative implementation approaches with respect to efficiency,
safety and ease of use.Comment: 25 pages. Source code for examples at
http://www-ppg.dcs.st-and.ac.uk/Java/ReflectionExample/ Dynamic compilation
package at http://www-ppg.dcs.st-and.ac.uk/Java/DynamicCompilation
The Dynamics and Metallicity Distribution of the Distant Dwarf Galaxy VV124
VV124 (UGC 4879) is an isolated, dwarf irregular/dwarf spheroidal (dIrr/dSph) transition-type
galaxy at a distance of 1.36 Mpc. Previous low-resolution spectroscopy yielded inconsistent radial
velocities for different components of the galaxy, and photometry hinted at the presence of a stellar
disk. In order to quantify the stellar dynamics, we observed individual red giants in VV124 with the Keck/DEIMOS spectrograph. We validated members based on their positions in the color-magnitude
diagram, radial velocities, and spectral features. Our sample contains 67 members. The average
radial velocity is = â29.1 Âą 1.3 km s^(â1), in agreement with the previous radio measurements
of H I gas. The velocity distribution is Gaussian, indicating that VV124 is supported primarily by
velocity dispersion inside a radius of 1.5 kpc. Outside that radius, our measurements provide only an
upper limit of 8.6 km s^(â1) on any rotation in the photometric disk-like feature. The velocity dispersion
is Ď_v = 9.4Âą 1.0 km s^(â1), from which we inferred a mass of M_(1/2) = (2.1 Âą 0.2)Ă 10^7 M_â and a mass-to-
light ratio of (M/L_V)_(1/2) = 5.2 Âą 1.1 M_â/L_â, both measured within the half-light radius. Thus,
VV124 contains dark matter. We also measured the metallicity distribution from neutral iron lines.
The average metallicity, = â1.14 Âą 0.06, is consistent with the mass-metallicity relation
defined by dwarf spheroidal galaxies. The dynamics and metallicity distribution of VV124 appear
similar to dSphs of similar stellar mass
A Method for Greatly Reduced Edge Effects and Crosstalk in CCT Magnets
Iron-free CCT magnet design offers many advantages, one being the excellent
field quality and the absence of multipole components. However, edge effects
are present, although they tend to integrate out over the length of the magnet.
Many modern accelerator applications, however, require that these magnets are
placed in an area of rapidly varying optics parameters, so magnets with greatly
reduced edge effects have an advantage. We have designed such a magnet (a
quadrupole) by adding multipole components of the opposite sign to the edge
distortions of the magnet. A possible application could be the final focus
magnets of the FCC-ee, where beam sizes at the entry and exit point of the
magnets vary by large factors. We have then used this technique to effectively
eliminate cross talk between adjacent final focus quadrupoles for the incoming
and outgoing beams.Comment: Poster presented at MT25,25th International Conference on Magnet
Technology, Amsterdam, August 27 - September 1, 201
Translatory shock absorber for attitude sensors
A translatory shock absorber is provided for mounting an attitude sensor thereon for isolating a sensor from translatory vibrations. The translatory shock absorber includes a hollow block structure formed as one piece to form a parallelogram. The absorber block structure includes a movable top plate for supporting the attitude sensor and a fixed base plate with opposed side plates interposed between. At the junctions of the side plates, and the base and top plates, there are provided grooves which act as flexible hinges for attenuating translatory vibrations. A damping material is supported on a pedestal which is carried on the base plate between the side plates thereof. The top of the damping material rests against the bottom surface of the top plate for eliminating the resonant peaks of vibration
Program Notes for A Graduate Piano Recital
The objective of this research paper is to provide extended program notes to the Graduate Recital of Jenny Kirby, presented on May 8, 2015. The following pieces were performed: Franz Schubertâs Sonata in A minor, D. 845 (1825), Alexander Scriabinâs Five Preludes, Op. 74 (1914), J.S Bachâs Prelude and Fugue in G major, BWV 884 (1724), and Igor Stravinskyâs Trois Mouvements de PĂŠtroushka (1921)
The effectiveness of an oculometer training tape on pilot and copilot trainees in a commercial flight training program
A study was designed to evaluate the effectiveness of a video tape detailing the various aspects of instrument scanning by experienced pilots on performance by pilots and copilots undergoing flight training in a Boeing 737 flight simulator. The performance ratings by instructor pilots (IP's) and self-reported instrument scan behavior by trainees were compared with those of a control group. The results indicated that the training tape had little or no effect on performance by trainees in the experimental group. Feedback from the IP's and trainees suggested that a feedback strategy providing each trainee's individual instrument scan behavior might be more beneficial in flight training than the general instructional strategy of the oculometer training tape. Flight training personnel and trainees' reports of performance decrements on or around the third day of flight simulator training were investigated. The IP's performance ratings of 27 pilot and copilot trainees failed to reveal a systematic performance decrement; however, feedback from the trainees revealed that their own attribution of performance decrements was associated with the order in which their training occurred within a session. Further research was suggested
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