1,242 research outputs found
Supernovae in Early-Type Galaxies: Directly Connecting Age and Metallicity with Type Ia Luminosity
We have obtained optical spectra of 29 early-type (E/S0) galaxies that hosted
type Ia supernovae (SNe Ia). We have measured absorption-line strengths and
compared them to a grid of models to extract the relations between the
supernova properties and the luminosity-weighted age/composition of the host
galaxies. The same analysis was applied to a large number of early-type field
galaxies selected from the SDSS spectroscopic survey. We find no difference in
the age and abundance distributions between the field galaxies and the SN Ia
host galaxies. We do find a strong correlation suggesting that SNe Ia in
galaxies whose populations have a characteristic age greater than 5 Gyr are ~ 1
mag fainter at V(max) than those found in galaxies with younger populations.
However, the data cannot discriminate between a smooth relation connecting age
and supernova luminosity or two populations of SN Ia progenitors. We find that
SN Ia distance residuals in the Hubble diagram are correlated with host-galaxy
metal abundance, consistent with the predictions of Timmes, Brown & Truran
(2003). The data show that high iron abundance galaxies host less-luminous
supernovae. We thus conclude that the time since progenitor formation primarily
determines the radioactive Ni production while progenitor metal abundance has a
weaker influence on peak luminosity, but one not fully corrected by light-curve
shape and color fitters. Assuming no selection effects in discovering SNe Ia in
local early-type galaxies, we find a higher specific SN Ia rate in E/S0
galaxies with ages below 3 Gyr than in older hosts. The higher rate and
brighter luminosities seen in the youngest E/S0 hosts may be a result of recent
star formation and represents a tail of the "prompt" SN Ia progenitors.Comment: 44 pages, 11 figures, 4 tables; ApJ Accepted (Sept. 20, 2008 issue
The Evolution of Quasar CIV and SiIV Broad Absorption Lines Over Multi-Year Time Scales
We investigate the variability of CIV 1549A broad absorption line (BAL)
troughs over rest-frame time scales of up to ~7 yr in 14 quasars at redshifts
z>2.1. For 9 sources at sufficiently high redshift, we also compare CIV and
SiIV 1400A absorption variation. We compare shorter- and longer-term
variability using spectra from up to four different epochs per source and find
complex patterns of variation in the sample overall. The scatter in the change
of absorption equivalent width (EW), Delta EW, increases with the time between
observations. BALs do not, in general, strengthen or weaken monotonically, and
variation observed over shorter (<months) time scales is not predictive of
multi-year variation. We find no evidence for asymmetry in the distribution of
Delta EW that would indicate that BALs form and decay on different time scales,
and we constrain the typical BAL lifetime to be >~30 yr. The BAL absorption for
one source, LBQS 0022+0150, has weakened and may now be classified as a
mini-BAL. Another source, 1235+1453, shows evidence of variable, blue continuum
emission that is relatively unabsorbed by the BAL outflow. CIV and SiIV BAL
shape changes are related in at least some sources. Given their high
velocities, BAL outflows apparently traverse large spatial regions and may
interact with parsec-scale structures such as an obscuring torus. Assuming BAL
outflows are launched from a rotating accretion disk, notable azimuthal
symmetry is required in the outflow to explain the relatively small changes
observed in velocity structure over times up to 7 yr
Clustering of solutions in the random satisfiability problem
Using elementary rigorous methods we prove the existence of a clustered phase
in the random -SAT problem, for . In this phase the solutions are
grouped into clusters which are far away from each other. The results are in
agreement with previous predictions of the cavity method and give a rigorous
confirmation to one of its main building blocks. It can be generalized to other
systems of both physical and computational interest.Comment: 4 pages, 1 figur
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Precision cancer monitoring using a novel, fully integrated, microfluidic array partitioning digital PCR platform.
A novel digital PCR (dPCR) platform combining off-the-shelf reagents, a micro-molded plastic microfluidic consumable with a fully integrated single dPCR instrument was developed to address the needs for routine clinical diagnostics. This new platform offers a simplified workflow that enables: rapid time-to-answer; low potential for cross contamination; minimal sample waste; all within a single integrated instrument. Here we showcase the capability of this fully integrated platform to detect and quantify non-small cell lung carcinoma (NSCLC) rare genetic mutants (EGFR T790M) with precision cell-free DNA (cfDNA) standards. Next, we validated the platform with an established chronic myeloid leukemia (CML) fusion gene (BCR-ABL1) assay down to 0.01% mutant allele frequency to highlight the platform's utility for precision cancer monitoring. Thirdly, using a juvenile myelomonocytic leukemia (JMML) patient-specific assay we demonstrate the ability to precisely track an individual cancer patient's response to therapy and show the patient's achievement of complete molecular remission. These three applications highlight the flexibility and utility of this novel fully integrated dPCR platform that has the potential to transform personalized medicine for cancer recurrence monitoring
Optical and ultraviolet observations of nova Vul 1987
The outburst for a nova discovered in Nov. 1987 and followed since then is summarized. Although it was possible to observe it with the IUE at maximum, its ultraviolet energy faded rapidly, and after the first 2 weeks it was impossible to observe it at IUE wavelengths. It is observed to form a thick dust shell and is in the nebular stage
The Star Clusters in the Starburst Irregular Galaxy NGC 1569
We examine star clusters in the irregular, starburst galaxy NGC 1569 from HST
images. In addition to the two known super star clusters, we identify 45 other
clusters that are compact but resolved. Integrated UVI colors of the clusters
span a large range, and suggest that ages range from 3 Myrs to 1 Gyr. However,
most of the clusters were formed at the tail end of the recent starburst.
Numerous clusters in addition to the know super star clusters are similar in
luminosity to a small globular cluster. We examined the radial surface
brightness of four of the clusters. Their half-light radii and core radii are
in the range observed in present-day globular clusters. Therefore, conditions
that produced the recent starburst have also been those necessary for producing
compact, bright star clusters.
We examine resolved stars in the outer parts of the two super star clusters.
Cluster A is dominated by bright blue stars with a small population of red
supergiants. Sub-components A1 and A2 have similar colors and a two-dimensional
color map does not offer evidence that one component is dominated by red
supergiants and the other not. The contradiction of the presence of red super-
giants with Wolf-Rayet stars may instead not be a contradiction at all since
there coexistence in a coeval population is not inconsistent with the evolution
of massive stars. Cluster B is dominated by red supergiants, and this is
confirmed by the presence of the stellar CO absorption feature in an integrated
spectrum. The various age indicators are consistent with a picture in which
cluster B is of order 10--20 Myrs old, and cluster A is >4-5 Myrs old.Comment: To be published in AJ, November 200
Evidence of a vertical kinematic oscillation beyond the Radcliffe Wave
The Radcliffe Wave (RW) is a recently discovered sinusoidal vertical feature
of dense gas in the proximity of the Sun. In the disk plane, it is aligned with
the Local Arm. However, the origin of its vertical undulation is still unknown.
This study constrains the kinematics of the RW, using young stars and open
clusters as tracers, and explores the possibility of this oscillation being
part of a more extended vertical mode. We study the median vertical velocity
trends of the young stars and clusters along with the RW and extend it further
to the region beyond it. We discover a kinematic wave in the Galaxy, distinct
from the warp, with the amplitude of oscillation depending on the age of the
stellar population. We perform a similar analysis in the N-body simulation of a
satellite as massive as the Sagittarius dwarf galaxy impacting the galactic
disk. When projected in the plane, the spiral density wave induced by the
satellite impact is aligned with the RW, suggesting that both may be the
response of the disk to an external perturbation. However, the observed
kinematic wave is misaligned. It appears as a kinematic wave travelling
radially, winding up faster than the density wave matched by the RW,
questioning its origin. If a satellite galaxy is responsible for this kinematic
wave, we predict the existence of a vertical velocity dipole that should form
across the disk and this may be measurable with the upcoming Gaia DR3 and DR4.Comment: Accepted for publication in Astronomy & Astrophysics Letter
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