646 research outputs found
Astrophysics in 2006
The fastest pulsar and the slowest nova; the oldest galaxies and the youngest
stars; the weirdest life forms and the commonest dwarfs; the highest energy
particles and the lowest energy photons. These were some of the extremes of
Astrophysics 2006. We attempt also to bring you updates on things of which
there is currently only one (habitable planets, the Sun, and the universe) and
others of which there are always many, like meteors and molecules, black holes
and binaries.Comment: 244 pages, no figure
SN 1998bw at late phases
We present observations of the peculiar supernova SN 1998bw, which was
probably associated with GRB 980425. The photometric and spectroscopic
evolution is monitored up to 500 days past explosion. We also present modeling
based on spherically symmetric, massive progenitor models and very energetic
explosions. The models allow line identification and clearly show the
importance of mixing. From the late light curves we estimate that about 0.3-0.9
solar masses of ejected Nickel-56 is required to power the supernova.Comment: With 3 figures Accepted for ApJ Letter
Late Light Curves of Normal Type Ia Supernovae
We present late-epoch optical photometry (BVRI) of seven
normal/super-luminous Type Ia supernovae: SN 2000E, SN 2000ce, SN 2000cx, SN
2001C, SN 2001V, SN 2001bg, SN 2001dp. The photometry of these objects was
obtained using a template subtraction method to eliminate galaxy light
contamination during aperture photometry. We show the optical light curves of
these supernovae out to epochs of up to ~640 days after the explosion of the
supernova. We show a linear decline in these data during the epoch of 200-500
days after explosion with the decline rate in the B,V,& R bands equal to about
1.4 mag/100 days, but the decline rate of the I-band is much shallower at 0.94
mag/100 days.Comment: 33 pages, 11 figures, Accepted for publication in The Astronomical
Journa
Optical and near infrared observations of SN 1998bu
Infrared and optical spectra of SN 1998bu at an age of one year after
explosion are presented. The data show evidence for the radioactive decay of
56Co to 56Fe, long assumed to be the powering source for the supernova light
curve past maximum light. The spectra provide direct evidence for at least 0.4
solar masses of iron being present in the ejecta of the supernova. The fits to
the data also show that the widths of the emission lines increase with time.
Photometric measurements in the H-band show that the supernova is not fading
during the observation period. This is consistent with theoretical
expectations.Comment: accepted A&A, 7 pages, 9 figure
SN~1991T: Reflections of Past Glory
We have obtained photometry and spectra of SN~1991T which extend more than
1000 days past maximum light, by far the longest a SN~Ia has been followed.
Although SN~1991T exhibited nearly normal photometric behavior in the first 400
days following maximum, by 600 days its decline had slowed, and by 950~days the
supernova brightness was consistent with a constant apparent magnitude of
. Spectra near maximum showed minor variations on the SN~Ia theme
which grew less conspicuous during the exponential decline. At 270 days the
nebular spectrum was composed of Fe and Co lines common to SNe~Ia. However, by
750 days past maximum light, these lines had shifted in wavelength, and were
superimposed on a strong blue continuum. The luminosity of SN~1991T at 950 days
is more than ~ergs~s with a rate of
decline of less than mags/100~days. We show that this emission is likely
to be light that was emitted by SN~1991T near maximum light which has reflected
from foreground dust, much like the light echos observed around SN~1987A.Comment: 15 pages (includes figures and tables) uuencoded compressed
postscript, CfA Preprint - To Appear in ApJ
Photometric Identification of Type Ia Supernovae at Moderate Redshift
Large photometric surveys with the aim of identifying many Type Ia supernovae
(SNe) at moderate redshift are challenged in separating these SNe from other SN
types. We are motivated to identify Type Ia SNe based only on broadband
photometric information, since spectroscopic determination of the SN type, the
traditional method, requires significant amounts of time on large telescopes.
We consider the possible observables provided by a large synoptic photometry
survey. We examine the optical colors and magnitudes of many SN types from
z=0.1 to z=1.0, using space-based ultraviolet spectra and ground-based optical
spectra to simulate the photometry. We also discuss the evolution of colors
over the SN outburst and the use of host galaxy characteristics to aid in the
identification of Type Ia SNe. We consider magnitudes in both the SDSS
photometric system and in a proposed filter system with logarithmically spaced
bandpasses. We find that photometric information in four bands covering the
entire optical spectrum appears capable of providing identification of Type Ia
SNe based on their colors at a single observed epoch soon after maximum light,
even without independent estimates of the SN redshift. Very blue filters are
extremely helpful, as at moderate redshift they sample the restframe
ultraviolet spectrum where the SN types are very different. We emphasize the
need for further observations of SNe in the restframe ultraviolet to fully
characterize, refine, and improve this method of SN type identification.Comment: AASTeX, 37 pages with 12 figures, being resubmitted to A.J. Figures
3, 4 and 9 updated, minor typos correcte
Host response to fungal infections - how immunology and host genetics could help to identify and treat patients at risk.
In spite of the ever-increasing incidence and poor outcome of invasive fungal infections in immune compromised patients, there is currently no reliable method to accurately predict the risk, to monitor the outcome and to treat these infections. Protective immunity against Candida and Aspergillus depends on a highly coordinated interaction between the innate and adaptive immune systems. Genetic and immunological defects in components of these networks result in increased risk of invasive fungal infections among patients undergoing chemotherapy or transplant recipients. We review the most important genetic and immunological factors that influence human susceptibility to Candida and Aspergillus infections and discuss the potential role of basic research to promote precision medicine for infectious diseases. We discuss how immunogenetic studies can help to provide tools for improved identification of high-risk patients and the development of tailored antifungal therapies
Late Light Curves of Normally-Luminous Type Ia Supernovae
The use of Type Ia supernovae as cosmological tools has reinforced the need
to better understand these objects and their light curves. The light curves of
Type Ia supernovae are powered by the nuclear decay of . The late time light curves can provide insight into the behavior of
the decay products and their effect of the shape of the curves. We present the
optical light curves of six "normal" Type Ia supernovae, obtained at late times
with template image subtraction, and the fits of these light curves to
supernova energy deposition models.Comment: Proceedings of Astronomy with Radioactivities V Conferenc
Time Dilation from Spectral Feature Age Measurements of Type Ia Supernovae
We have developed a quantitative, empirical method for estimating the age of
Type Ia supernovae (SNe Ia) from a single spectral epoch. The technique
examines the goodness of fit of spectral features as a function of the temporal
evolution of a large database of SNe Ia spectral features. When a SN Ia
spectrum with good signal-to-noise ratio over the rest frame range 3800 to 6800
A is available, the precision of a spectral feature age (SFA) is (1-sigma) ~
1.4 days. SFA estimates are made for two spectral epochs of SN 1996bj (z=0.574)
to measure the rate of aging at high redshift. In the 10.05 days which elapsed
between spectral observations, SN 1996bj aged 3.35 3.2 days, consistent
with the 6.38 days of aging expected in an expanding Universe and inconsistent
with no time dilation at the 96.4 % confidence level. The precision to which
individual features constrain the supernova age has implications for the source
of inhomogeneities among SNe Ia.Comment: 14 pages (LaTex), 7 postscript figures to Appear in the Astronomical
Journa
Near-infrared evolution of the equatorial ring of SN 1987A
We use adaptive-optics imaging and integral field spectroscopy from the Very
Large Telescope, together with images from the \emph{Hubble Space Telescope},
to study the near-infrared (NIR) evolution of the equatorial ring (ER) of
SN~1987A. We study the NIR line and continuum flux and morphology over time in
order to lay the groundwork for \emph{James Webb Space Telescope} observations
of the system. We also study the differences in the interacting ring structure
and flux between optical, NIR and other wavelengths, and between line and
continuum emission, to constrain the underlying physical processes. Mostly the
evolution is similar in the NIR and optical. The morphology of the ER has been
skewed toward the west side (with roughly 2/3 of the NIR emission originating
there) since around 2010. A steady decline in the ER flux, broadly similar to
the MIR and the optical, is ongoing since roughly this time as well. The
expansion velocity of the ER hotspots in the NIR is fully consistent with the
optical. However, continuum emission forms roughly 70 per cent of the NIR
luminosity, and is relatively stronger outside the hotspot-defined extent of
the ER than the optical emission or NIR line emission since 2012--2013,
suggesting a faster-expanding continuum component. We find that this outer NIR
emission can have a significant synchrotron contribution. Even if emission from
hot (2000~K) dust is dominant within the ER, the mass of this dust must
be vanishingly small (a few ~M) compared to the total
dust mass in the ER (~M) to account for the observed
flux. The NIR continuum emission, however, expands slower than the more
diffuse 180-K dust emission that dominates in the MIR, indicating a different
source, and the same hot dust component cannot account for the -band
emission.Comment: 17 pages, 17 figures. Accepted for publication in Astronomy &
Astrophysic
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