226 research outputs found
The UKIDSS Galactic Plane Survey
'The definitive version is available at www.blackwell-synergy.com .' Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.13924.xThe UKIDSS Galactic Plane Survey (GPS) is one of the five near-infrared Public Legacy Surveys that are being undertaken by the UKIDSS consortium, using the Wide Field Camera on the United Kingdom Infrared TelescopePeer reviewe
A multi-color and Fourier study of RR Lyrae variables in the globular cluster NGC 5272 (M3)
We have performed a detailed study of the pulsational and evolutionary
characteristics of 133 RR Lyrae stars in the globular cluster NGC5272 (M3)
using highly accurate BVI data taken on 5 separate epochs. M3 seems to contain
no less than ~32% of Blazhko stars, and the occurrence and characteristics of
the Blazhko effect have been analyzed in detail. We have identified a good
number (~ 14%) of overluminous RR Lyrae stars that are likely in a more
advanced evolutionary stage off the Zero Age Horizontal Branch (ZAHB). Physical
parameters (i.e. temperature, luminosity, mass) have been derived from (B--V)
colors and accurate color-temperature calibration, and compared with Horizontal
Branch evolutionary models and with the requirements of stellar pulsation
theory. Additional analysis by means of Fourier decomposition of the V light
curves confirms, as expected, that no metallicity spread is present in M3.
Evolution off the ZAHB does not affect [Fe/H] determinations, whereas Blazhko
stars at low amplitude phase do affect [Fe/H] distributions as they appear more
metal-rich. Absolute magnitudes derived from Fourier coefficients might provide
useful average estimates for groups of stars, if applicable, but do not give
reliable {\em individual} values. Intrinsic colors derived from Fourier
coefficients show significant discrepancies with the observed ones, hence the
resulting temperatures and temperature-related parameters are unreliable.Comment: 86 pages, 19 figures, 13 tables, in press A
HST Snaphot Study of Variable Stars in Globular Clusters: Inner Region of NGC 6441
[Abridged] We present the results of a Hubble Space Telescope snapshot
program to survey the inner region of the globular cluster NGC 6441 for its
variable stars. A total of 57 variable stars was found including 38 RR Lyrae
stars, 6 Population II Cepheids, and 12 long period variables. Of the RR Lyrae
stars observed in this survey, 26 are pulsating in the fundamental mode with a
mean period of 0.753d and 12 are first-overtone mode pulsators with a mean
period of 0.365d. These values match up very well with those found in
ground-based surveys. Combining all the available data for NGC 6441, we find
mean periods of 0.759d and 0.375d for the RRab and RRc stars, respectively. We
also find that the RR Lyrae in this survey are located in the same regions of a
period-amplitude diagram as those found in ground-based surveys. Although NGC
6441 is a metal-rich globular cluster, its RR Lyrae more closely resemble those
in Oosterhoff type II globular clusters. However, even compared to typical
Oosterhoff type II systems, the mean period of its RRab stars is unusually
long. We also derived I-band period-luminosity relations for the RR Lyrae
stars. Of the six Population II Cepheids, five are of W Virginis type and one
is a BL Herculis variable stars. This makes NGC 6441, along with NGC 6388, the
most metal-rich globular cluster known to contain these types of variable
stars. Another variable, V118, may also be a Population II Cepheid given its
long period and its separation in magnitude from the RR Lyrae stars. We argue
that there does not appear to be a change in the period-luminosity relation
slope between the BL Herculis and W Virginis stars, but that a change of slope
does occur when the RV Tauri stars are added to the period-luminosity relation.Comment: 28 pages, including 9 figures and 8 tables, emulateapj5/apjfonts
style. Accepted by the Astronomical Journal. Approximate publication date
September 2003. We recommend the interested reader to download the preprint
with full-resolution figures, which can be found at
http://www.astro.puc.cl/~mcatelan/Pritzl.zi
Investigating the Therapeutic Potential of a Probiotic in a Rat Model for Infection Following Fracture Fixation
Background: Staphylococcus aureus (S. aureus) is the most common pathogen responsible for osteomyelitis.
Objectives: Our objective was to investigate the potential of a probiotic as a treatment for S. aureus-induced infection following fracture fixation in a rat model.
Methods: Fifty male Sprague-Dawley rats were assigned to five groups (Control, S. aureus, S. aureus +ceftriaxone, S. aureus + once weekly probiotic, and S. aureus + twice weekly probiotic). Lactobacillus casei subsp. casei (ATCC: 39392) was selected from eight strains of probiotic bacteria with anti-staphylococcal activity. Infection was induced by inoculation with106 colony-forming units (CFU) of S. aureus in a closed femur fracture model stabilized with an intramedullary pin. Three weeks after the surgery, the development of infection and response to the therapy was documented using radiographs, microbiological and histopathological analysis.
Results: No bacteria were recovered from rats in the Control group. The analysis of variance revealed a significant difference in the CFU/femur (P < 0.001) and CFU/pin (P = 0.001) across all five treatment groups. When the results were compared, the CFU/femur was significantly lower in the S. aureus + Probiotic twice weekly in comparison with S. aureus (P = 0.008) and the S. aureus + ceftriaxone (P = 0.012) groups. Repeated measure ANOVA to test the radiographic scores during the follow-up time between the intervention groups revealed no significant differences (P = 0.179).
Conclusions: Parenteral administration of viable L. casei inhibits S. aureus-induced infection as shown by the bacteriologic analysis, but makes no difference to the radiological union rates. This could be the first step towards developing an effective, biologic adjunctive therapy for the management of osteomyelitis following fracture fixation
Reminiscence bump in memory for public events
People tend to recall more personal events from adolescence and early adulthood than from other lifetime periods. Most evidence suggests that differential encoding causes this reminiscence bump. However, the question why personal events are encoded better in those periods is still unanswered. To shed more light on this discussion, we examined memory for public events. Since it is often impossible to ascertain that queried events are equally difficult, we circumvented the issue of equivalence by calculating deviation scores for each trial. We found that participants more frequently answered questions correctly about events that occurred in the period in which they were between 10 and 25 years old. Furthermore, we found that the reminiscence bump was more pronounced for cued recall than for recognition. We argue that these results support the biological account that events are stored better, because the memory system is working more efficiently during adolescence and early adulthood. These results do not falsify the other accounts for differential encoding, because they are not mutually exclusive. People speak of autobiographical memory when they are referring to the memories they have of their own life experiences (Robinson, 1986). Autobiographical memory does not only consist of personal memories that are remembered vividly, but also of autobiographical facts (Brewer, 1986). Some researchers have examined the contents of autobiographical memories (e.g., Fitzgerald, 1988; Niedźwieńska, 2003; Robinson, 1976), whereas other researchers have focused on the temporal distribution of memories of personal events across the lifespan (e.g., Janssen, Chessa, &
The Metallicity-Luminosity Relation, Effective Yields, and Metal Loss in Spiral and Irregular Galaxies
I present results on the correlation between galaxy mass, luminosity, and
metallicity for a sample of spiral and irregular galaxies having well-measured
abundance profiles, distances, and rotation speeds. Additional data for low
surface brightness galaxies from the literature are also included for
comparison. These data are combined to study the metallicity-luminosity and
metallicity-rotation speed correlations for spiral and irregular galaxies. The
metallicity luminosity correlation shows its familiar form for these galaxies,
a roughly uniform change in the average present-day O/H abundance of about a
factor 100 over 11 magnitudes in B luminosity. However, the O/H - V(rot)
relation shows a change in slope at a rotation speed of about 125 km/sec. At
faster V(rot), there appears to be no relation between average metallicity and
rotation speed. At lower V(rot), the metallicity correlates with rotation
speed. This change in behavior could be the result of increasing loss of metals
from the smaller galaxies in supernova-driven winds. This idea is tested by
looking at the variation in effective yield, derived from observed abundances
and gas fractions assuming closed box chemical evolution. The effective yields
derived for spiral and irregular galaxies increase by a factor of 10-20 from
V(rot) approximately 5 km/sec to V(rot) approximately 300 km/sec, asympotically
increasing to approximately constant y(eff) for V(rot) > 150 km/sec. The trend
suggests that galaxies with V(rot) < 100-150 km/sec may lose a large fraction
of their SN ejecta, while galaxies above this value tend to retain metals.Comment: 40 pages total, including 7 encapsulated postscript figures. Accepted
for publication in 20 Dec 2002 Ap
VISTA Milky Way public survey
We propose a public IR variability survey, named \Vista Variables in the Vía Láctea" (V V V ), of the Milky Way bulge and an adjacent section of the mid-plane where star formation activity is high. This would take 1920 hours, covering ~ 109 point sources within an area of 520 sq deg, including 33 known globular clusters and ~ 350 open clusters. The final products will be a deep IR atlas in 5 passbands and a catalogue of ~ 106 variable point sources. These will produce a 3-D map of the surveyed region (unlike single-epoch surveys that only give 2-D maps) using well-understood primary distance indicators such as RR Lyrae stars. It will yield important information on the ages of the populations. The observations will be combined with data from MACHO, OGLE, EROS, VST, SPITZER, HST, CHANDRA, INTEGRAL, and ALMA for a complete understanding of the variable sources in the inner Milky Way. Several important implications for the history of the Milky Way, for globular cluster evolution, for the population census of the bulge and center, and for pulsation theory would follow from this survey
MALT90 Kinematic Distances to Dense Molecular Clumps
Using molecular-line data from the Millimetre Astronomy Legacy Team 90 GHz Survey (MALT90), we have estimated kinematic distances to 1905 molecular clumps identified in the ATLASGAL 870 μm continuum survey over the longitude range 295° < l < 350°. The clump velocities were determined using a flux-weighted average of the velocities obtained from Gaussian fits to the HCO+, HNC, and N2H+ (1–0) transitions. The near/far kinematic distance ambiguity was addressed by searching for the presence or absence of absorption or self-absorption features in 21 cm atomic hydrogen spectra from the Southern Galactic Plane Survey. Our algorithm provides an estimation of the reliability of the ambiguity resolution. The Galactic distribution of the clumps indicates positions where the clumps are bunched together, and these locations probably trace the locations of spiral arms. Several clumps fall at the predicted location of the far side of the Scutum–Centaurus arm. Moreover, a number of clumps with positive radial velocities are unambiguously located on the far side of the Milky Way at galactocentric radii beyond the solar circle. The measurement of these kinematic distances, in combination with continuum or molecular-line data, now enables the determination of fundamental parameters such as mass, size, and luminosity for each clump
Faint High Latitude Carbon Stars Discovered by the Sloan Digital Sky Survey: Methods and Initial Results
We report the discovery of 39 Faint High Latitude Carbon Stars (FHLCs) from
Sloan Digital Sky Survey commissioning data. The objects, each selected
photometrically and verified spectroscopically, range over 16.6 < r* < 20.0,
and show a diversity of temperatures as judged by both colors and NaD line
strengths. At the completion of the Sloan Survey, there will be many hundred
homogeneously selected and observed FHLCs in this sample. We present proper
motion measures for each object, indicating that the sample is a mixture of
extremely distant (>100 kpc) halo giant stars, useful for constraining halo
dynamics, plus members of the recently-recognized exotic class of very nearby
dwarf carbon (dC) stars. Motions, and thus dC classification, are inferred for
40-50 percent of the sample, depending on the level of statistical significance
invoked. The new list of dC stars presented here, although selected from only a
small fraction of the final SDSS, doubles the number of such objects found by
all previous methods. (Abstract abridged).Comment: Accepted for publication in The Astronomical Journal, Vol. 124, Sep.
2002, 40 pages, 7 figures, AASTeX v5.
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