160 research outputs found
A Method of Hospital Infection Surveillance Incorporating the Use of the Computer
The records of all patients in the hospital on a particular date were studied for hospital-acquired infections. Results were compared with a continuing surveillance based on discharge reporting. Collection of data was programmed for analysis by using the hospital computer. Thirteen per cent of the patients manifested an infection after admission, but before or on the survey day. Results elsewhere are similar. Areas of the hospital with a relatively higher incidence of infection did not have clusters of particular pathogens
High Mass Triple Systems: The Classical Cepheid Y Car
We have obtained an HST STIS ultraviolet high dispersion Echelle mode
spectrum the binary companion of the double mode classical Cepheid Y Car. The
velocity measured for the hot companion from this spectrum is very different
from reasonable predictions for binary motion, implying that the companion is
itself a short period binary. The measured velocity changed by 7 km/ s during
the 4 days between two segments of the observation confirming this
interpretation. We summarize "binary" Cepheids which are in fact members of
triple system and find at least 44% are triples. The summary of information on
Cepheids with orbits makes it likely that the fraction is under-estimated.Comment: accepted by A
The MACHO Project LMC Variable Star Inventory. VI. The Second-overtone Mode of Cepheid Pulsation From First/Second Overtone (FO/SO) Beat Cepheids
MACHO Project photometry of 45 LMC FO/SO beat Cepheids which pulsate in the
first and second overtone (FO and SOo, respectively) has been analysed to
determine the lightcurve characteristics for the SO mode of Cepheid pulsation.
We predict that singly-periodic SO Cepheids will have nearly sinusoidal
lightcurves; that we will only be able to discern SO Cepheids from fundamental
(F) and (FO) Cepheids for P <= 1.4 days; and that the SO distribution will
overlap the short-period edge of the LMC FO Cepheid period-luminosity relation
(when both are plotted as a function of photometric period).
We also report the discovery of one SO Cepheid candidate,
MACHO*05:03:39.670:04:32, with a photometric period of 0.775961 +/- 0.000019
days and an instrumental amplitude of 0.047 +/- 0.009 mag in V.Comment: 23 pages, 7 Encapsulated PostScript figures. Accepted for publication
in the Astrophysical Journa
New homogeneous iron abundances of double-mode Cepheids from high-resolution echelle spectroscopy
Aims: We define the relationship between the double-mode pulsation of
Cepheids and metallicity in a more accurate way, determine the empirical
metallicities of double-mode Cepheids from homogeneous, high-resolution
spectroscopic data, and study of the period-ratio -- metallicity dependence.
Methods: The high S/N echelle spectra obtained with the FEROS spectrograph were
analyzed using a self-developed IRAF script, and the iron abundances were
determined by comparing with synthetic spectra assuming LTE. Results: Accurate
[Fe/H] values of 17 galactic beat Cepheids were determined. All these stars
have solar or slightly subsolar metallicity. Their period ratio P1/P0 shows
strong correlation with their derived [Fe/H] values. The corresponding period
ratio -- metallicity relation has been evaluated.Comment: 10 pages, 7 figures, accepted in A&
The Chemical Compositions of the Type II Cepheids -- The BL Her and W Vir Variables
Abundance analyses from high-resolution optical spectra are presented for 19
Type II Cepheids in the Galactic field. The sample includes both short-period
(BL Her) and long-period (W Vir) stars. This is the first extensive abundance
analysis of these variables. The C, N, and O abundances with similar spreads
for the BL Her and W Vir show evidence for an atmosphere contaminated with
-process and CN-cycling products. A notable anomaly of the BL Her
stars is an overabundance of Na by a factor of about five relative to their
presumed initial abundances. This overabundance is not seen in the W Vir stars.
The abundance anomalies running from mild to extreme in W Vir stars but not
seen in the BL Her stars are attributed to dust-gas separation that provides an
atmosphere deficient in elements of high condensation temperature, notably Al,
Ca, Sc, Ti, and -process elements. Such anomalies have previously been seen
among RV Tau stars which represent a long-period extension of the variability
enjoyed by the Type II Cepheids. Comments are offered on how the contrasting
abundance anomalies of BL Her and W Vir stars may be explained in terms of the
stars' evolution from the blue horizontal branch.Comment: 41 pages including 11 figures and 4 tables; Accepted for publication
in Ap
The pulsating DA white dwarf star EC 14012-1446: results from four epochs of time-resolved photometry
The pulsating DA white dwarfs are the coolest degenerate stars that undergo
self-driven oscillations. Understanding their interior structure will help to
understand the previous evolution of the star. To this end, we report the
analysis of more than 200 h of time-resolved CCD photometry of the pulsating DA
white dwarf star EC 14012-1446 acquired during four observing epochs in three
different years, including a coordinated three-site campaign. A total of 19
independent frequencies in the star's light variations together with 148
combination signals up to fifth order could be detected. We are unable to
obtain the period spacing of the normal modes and therefore a mass estimate of
the star, but we infer a fairly short rotation period of 0.61 +/- 0.03 d,
assuming the rotationally split modes are l=1. The pulsation modes of the star
undergo amplitude and frequency variations, in the sense that modes with higher
radial overtone show more pronounced variability and that amplitude changes are
always accompanied by frequency variations. Most of the second-order
combination frequencies detected have amplitudes that are a function of their
parent mode amplitudes, but we found a few cases of possible resonantly excited
modes. We point out the complications in the analysis and interpretation of
data sets of pulsating white dwarfs that are affected by combination
frequencies of the form f_A+f_B-f_C intruding into the frequency range of the
independent modes.Comment: 14 pages, 6 figures, 6 tables. MNRAS, in pres
Classical Cepheid Pulsation Models. III. The Predictable Scenario
Within the current uncertainties in the treatment of the coupling between
pulsation and convection, limiting amplitude, nonlinear, convective models
appear the only viable approach for providing theoretical predictions about the
intrinsic properties of radial pulsators. In this paper we present the results
of a comprehensive set of Cepheid models computed within such theoretical
framework for selected assumptions on their original chemical composition.Comment: 24 pages, 1 latex file containing 6 tables, 10 postscript figures,
accepted for publication on Ap
Formation and Evolution of Planetary Systems: Cold Outer Disks Associated with Sun-like stars
We present the discovery of debris systems around three solar mass stars
based upon observations performed with the Spitzer Space Telescope as part of a
Legacy Science Program, ``the Formation and Evolution of Planetary Systems''
(FEPS). We also confirm the presence of debris around two other stars. All the
stars exhibit infrared emission in excess of the expected photospheres in the
70 micron band, but are consistent with photospheric emission at <= 33 micron.
This restricts the maximum temperature of debris in equilibrium with the
stellar radiation to T < 70 K. We find that these sources are relatively old in
the FEPS sample, in the age range 0.7 - 3 Gyr. Based on models of the spectral
energy distributions, we suggest that these debris systems represent materials
generated by collisions of planetesimal belts. We speculate on the nature of
these systems through comparisons to our own Kuiper Belt, and on the likely
planet(s) responsible for stirring the system and ultimately releasing dust
through collisions. We further report observations of a nearby star HD 13974 (d
=11 pc) that is indistinguishable from a bare photosphere at both 24 micron and
70 micron. The observations place strong upper limits on the presence of any
cold dust in this nearby system (L_IR/L_* < 10^{-5.2}).Comment: 31 pages, 9 figures, accepted for publication in Ap
The stellar content of the Hamburg/ESO survey. I. Automated selection of DA white dwarfs
We describe automatic procedures for the selection of DA white dwarfs in the
Hamburg/ESO objective-prism survey (HES). For this purpose, and the selection
of other stellar objects (e.g., metal-poor stars and carbon stars), a flexible,
robust algorithm for detection of stellar absorption and emission lines in the
digital spectra of the HES was developed. Broad band (U-B, B-V) and narrow band
(Str\"omgren c_1) colours can be derived directly from HES spectra, with
precisions of sigma(U-B)=0.092mag; sigma(B-V)=0.095mag; sigma(c_1)=0.15mag.
We describe simulation techniques that allow to convert model or slit spectra
to HES spectra. These simulated objective-prism spectra are used to determine
quantitative selection criteria, and for the study of selection functions. We
present an atlas of simulated HES spectra of DA and DB white dwarfs.
Our current selection algorithm is tuned to yield maximum efficiency of the
candidate sample (minimum contamination with non-DAs). DA candidates are
selected in the B-V versus U-B and c_1 versus W_\lambda(Hbeta+Hgamma+Hdelta)
parameter spaces. The contamination of the resulting sample with hot subdwarfs
is expected to be as low as ~8%, while there is essentially no contamination
with main sequence or horizontal branch stars. We estimate that with the
present set of criteria, ~80% of DAs present in the HES database are recovered.
A yet higher degree of internal completeness could be reached at the expense of
higher contamination. However, the external completeness is limited by
additional losses caused by proper motion effects and the epoch differences
between direct and spectral plates used in the HES.Comment: A&A in press. 15 pages, 15 figures. Includes table with coordinates
and magnitudes for 46 spectroscopically confirmed DA white dwarfs and hot
subdwarf
Meeting the Cool Neighbors X: Ultracool dwarfs from the 2MASS All-Sky Data Release
Using data from the 2MASS All-Sky Point Source Catalogue, we have extended
our census of nearby ultracool dwarfs to cover the full celestial sphere above
Galactic latitute 15 degrees. Starting with an initial catalogue of 2,139,484
sources, we have winnowed the sample to 467 candidate late-type M or L dwarfs
within 20 parsecs of the Sun. Fifty-four of those sources already have
spectroscopic observations confirming them as late-type dwarfs. We present
optical spectroscopy of 376 of the remaining 413 sources, and identify 44 as
ultracool dwarfs with spectroscopic distances less than 20 parsecs. Twenty-five
of the 37 sources that lack optical data have near-infrared spectroscopy.
Combining the present sample with our previous results and data from the
literature, we catalogue 94 L dwarf systems within 20 parsecs. We discuss the
distribution of activity, as measured by H-alpha emission, in this
volume-limited sample. We have coupled the present ultracool catalogue with
data for stars in the northern 8-parsec sample and recent (incomplete)
statistics for T dwarfs to provide a snapshot of the current 20-parsec census
as a function of spectral type.Comment: Accepted for publication by the Astronomical Journa
- …