6,788 research outputs found
The Determination of Stellar Parameters of Giants in the Galactic Disks and Bulge
Here, we present our on-going work on the determination of stellar parameters
of giants in the Galactic Disks and Bulge observed with UVES on the VLT. We
present some preliminarily results.Comment: 2 pages, IAU241 conference proceeding
The identification of physical close galaxy pairs
A classification scheme for close pairs of galaxies is proposed. The scheme
is motivated by the fact that the majority of apparent close pairs are in fact
wide pairs in three-dimensional space. This is demonstrated by means of
numerical simulations of random samples of binary galaxies and the scrutiny of
the resulting projected and spatial separation distributions.
Observational strategies for classifying close pairs according to the scheme
are suggested. As a result, physical (i.e., bound and spatially) close pairs
are identified.Comment: 16 pages, 5 figures, accepted for publication in The Astronomical
Journal, added text corrections on proof
Response to Invasion by Antigen and Effects of Threshold in an Immune Network Dynamical System Model with a Small Number of Degrees of Freedom
We study a dynamical system model of an idiotypic immune network with a small
number of degrees of freedom, mainly focusing on the effect of a threshold
above which antibodies can recognise antibodies. The response of the system to
invasions by antigens is investigated in the both models with and without the
threshold and it turns out that the system changes in a desirable direction for
moderate magnitude of perturbation. direction for moderate magnitude of
perturbation. Also, the propagation of disturbance by an antigen is
investigated in the system of one-dimensionally connected basic units taking
the closed 3-clone system as a unit, and it is clarified that the threshold of
the system has effects to enhance the stability of the network and to localise
the immune response.Comment: 6 pages, 6 figures. Submitted to Prog. Theor. Phy
Completeness of case ascertainment and survival time error in English cancer registries: impact on 1-year survival estimates.
BACKGROUND: It has been suggested that cancer registries in England are too dependent on processing of information from death certificates, and consequently that cancer survival statistics reported for England are systematically biased and too low. METHODS: We have linked routine cancer registration records for colorectal, lung, and breast cancer patients with information from the Hospital Episode Statistics (HES) database for the period 2001-2007. Based on record linkage with the HES database, records missing in the cancer register were identified, and dates of diagnosis were revised. The effects of those revisions on the estimated survival time and proportion of patients surviving for 1 year or more were studied. Cases that were absent in the cancer register and present in the HES data with a relevant diagnosis code and a relevant surgery code were used to estimate (a) the completeness of the cancer register. Differences in survival times calculated from the two data sources were used to estimate (b) the possible extent of error in the recorded survival time in the cancer register. Finally, we combined (a) and (b) to estimate (c) the resulting differences in 1-year cumulative survival estimates. RESULTS: Completeness of case ascertainment in English cancer registries is high, around 98-99%. Using HES data added 1.9%, 0.4% and 2.0% to the number of colorectal, lung, and breast cancer registrations, respectively. Around 5-6% of rapidly fatal cancer registrations had survival time extended by more than a month, and almost 3% of rapidly fatal breast cancer records were extended by more than a year. The resulting impact on estimates of 1-year survival was small, amounting to 1.0, 0.8, and 0.4 percentage points for colorectal, lung, and breast cancer, respectively. INTERPRETATION: English cancer registration data cannot be dismissed as unfit for the purpose of cancer survival analysis. However, investigators should retain a critical attitude to data quality and sources of error in international cancer survival studies
Seeing Galaxies Through Thick & Thin. III. HST Imaging of the Dust in Backlit Spiral Galaxies
We present analysis of WFPC2 imaging of two spiral galaxies partially backlit
by E/S0 systems in the pairs AM1316-241 and AM0500-620, and the spiral
foreground system in NGC 1275. Images in B and I are used to determine the
reddening curve of in these systems. The spiral component of AM1316-241 shows
dust strongly concentrated in discrete arms, with a reddening law very close to
the Milky Way mean. The dust distribution is scale-free between about 100 pc
and the arm scale. The spiral in AM0500-620 shows dust concentrated in arms and
interarm spurs, with measurable interarm extinction as well. Although its dust
properties are less well-determined, we find evidence for a steeper extinction
law here. The shape of the reddening law suggests that, at least in AM1316-241,
we have resolved most of the dust structure. In AM0500-620, the slope of the
fractal perimeter-scale relation steepens systematically from low to high
extinction. In AM1316-241, we cannot determine a unique fractal dimension from
the defining area-perimeter relation, so the projected dust distribution is
best defined as fractal-like. In neither galaxy do we see regions even on
single-pixel scales in spiral arms with AB > 2.5. The measurements in NGC 1275
are compromised by our lack of independent knowledge of the foreground system's
light distribution, but masked sampling of the absorption suggests an effective
reddening curve much flatter than the Milky Way mean (perhaps indicating that
the foreground system has been affected by immersion in the hot intracluster
gas).Comment: Astronomical Journal, in press. 13 figures. Full-size PostScript
figures available at http://www.astr.ua.edu/preprints/kee
The Hamburg/ESO R-process Enhanced Star survey (HERES) II. Spectroscopic analysis of the survey sample
We present the results of analysis of ``snapshot'' spectra of 253 metal-poor
halo stars -3.8 < [Fe/H] < -1.5 obtained in the HERES survey. The spectra are
analysed using an automated line profile analysis method based on the
Spectroscopy Made Easy codes of Valenti & Piskunov. Elemental abundances of
moderate precision have been obtained for 22 elements, C, Mg, Al, Ca, Sc, Ti,
V, Cr, Mn, Fe, Co, Ni, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, and Eu, where
detectable. Among the sample of 253 stars, we find 8 r-II stars and 35 r-I
stars. We also find three stars with strong enhancements of Eu which are
s-process rich. A significant number of new very metal-poor stars are
confirmed: 49 stars with [Fe/H] < -3 and 181 stars with -3 < [Fe/H] < -2. We
find one star with [Fe/H] < -3.5. We find the scatter in the abundance ratios
of Mg, Ca, Sc, Ti, Cr, Fe, Co, and Ni, with respect to Fe and Mg, to be similar
to the estimated relative errors and thus the cosmic scatter to be small,
perhaps even non-existent. The elements C, Sr, Y, Ba and Eu, and perhaps Zr,
show scatter at [Fe/H] < -2.5 significantly larger than can be explained from
the errors in the analysis, implying scatter which is cosmic in origin.
Significant scatter is observed in abundance ratios between light and heavy
neutron-capture elements at low metallicity and low levels of r-process
enrichment. (*** abridged ***)Comment: Accepted for A&A; 31 pages, 2 electronic tables presently available
at http://www.astro.uu.se/~barklem/papers/heres_tables.tar.gz ; Minor
corrections adde
Substructure around M31 : Evolution and Effects
We investigate the evolution of a population of 100 dark matter satellites
orbiting in the gravitational potential of a realistic model of M31. We find
that after 10 Gyr, seven subhalos are completely disrupted by the tidal field
of the host galaxy. The remaining satellites suffer heavy mass loss and
overall, 75% of the mass initially in the subhalo system is tidally stripped.
Not surprisingly, satellites with pericentric radius less than 30 kpc suffer
the greatest stripping and leave a complex structure of tails and streams of
debris around the host galaxy. Assuming that the most bound particles in each
subhalo are kinematic tracers of stars, we find that the halo stellar
population resulting from the tidal debris follows an r^{-3.5} density profile
at large radii. We construct B-band photometric maps of stars coming from
disrupted satellites and find conspicuous features similar both in morphology
and brightness to the observed Giant Stream around Andromeda. An assumed star
formation efficiency of 5-10% in the simulated satellite galaxies results in
good agreement with the number of M31 satellites, the V-band surface brightness
distribution, and the brightness of the Giant Stream. During the first 5 Gyr,
the bombardment of the satellites heats and thickens the disk by a small
amount. At about 5 Gyr, satellite interations induce the formation of a strong
bar which, in turn, leads to a significant increase in the velocity dispersion
of the disk.Comment: 45 pages, 18 figures. To be submitted to the Astrophysical Journal,
version 2.0 : scale height value corrected, references added, and some
figures have been modifie
The Structure of the Outer Halo of the Galaxy and its Relationship to Nearby Large-Scale Structure
We present evidence to support an earlier indication that the Galaxy is
embedded in an extended, highly inclined, triaxial halo outlined by the spatial
distribution of companion galaxies to the Milky Way. Signatures of this spatial
distribution are seen in 1) the angular variation of the radial-velocity
dispersion of the companion galaxies, 2) the spatial distribution of the M~31
sub-group of galaxies, 3) the spatial distribution of the isolated, mainly
dwarf irregular, galaxies of the Local Group, 4) the velocity anisotropy
quadrupole of a sub-group of high-velocity clouds, and 5) the spatial
distribution of galaxies in the Coma-Sculptor cloud. Tidal effects of M~31 and
surrounding galaxies on the Galaxy are not strong enough to have affected the
observed structure. We conclude that this distribution is a reflection of
initial conditions. A simple galaxy formation scenario is proposed which ties
together the results found here with those of Holmberg (1969) and Zaritsky et
al. (1997) on the peculiar distribution of satellites around a large sample of
spiral galaxies.Comment: Accepted for publication in the Astron J., March 2000, 12 pages with
1 figur
HST/STIS Imaging of the Host Galaxy of GRB980425/SN1998bw
We present HST/STIS observations of ESO 184-G82, the host galaxy of the
gamma-ray burst GRB 980425 associated with the peculiar Type Ic supernova
SN1998bw. ESO 184-G82 is found to be an actively star forming SBc sub-luminous
galaxy. We detect an object consistent with being a point source within the
astrometric uncertainty of 0.018 arcseconds of the position of the supernova.
The object is located inside a star-forming region and is at least one
magnitude brighter than expected for the supernova based on a simple
radioactive decay model. This implies either a significant flattening of the
light curve or a contribution from an underlying star cluster.Comment: 12 pages, 2 figures, AASTeX v5.02 accepted for publication in ApJ
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