806 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
Late-time Light Curves of Type II Supernovae: Physical Properties of SNe and Their Environment
We present BVRIJHK band photometry of 6 core-collapse supernovae, SNe 1999bw,
2002hh, 2003gd, 2004et, 2005cs, and 2006bc measured at late epochs (>2 yrs)
based on Hubble Space Telescope (HST), Gemini north, and WIYN telescopes. We
also show the JHK lightcurves of a supernova impostor SN 2008S up to day 575.
Of our 43 HST observations in total, 36 observations are successful in
detecting the light from the SNe alone and measuring magnitudes of all the
targets. HST observations show a resolved scattered light echo around SN 2003gd
at day 1520 and around SN 2002hh at day 1717. Our Gemini and WIYN observations
detected SNe 2002hh and 2004et, as well. Combining our data with previously
published data, we show VRIJHK-band lightcurves and estimate decline magnitude
rates at each band in 4 different phases. Our prior work on these lightcurves
and other data indicate that dust is forming in our targets from day ~300-400,
supporting SN dust formation theory. In this paper we focus on other physical
properties derived from the late time light curves. We estimate 56Ni masses for
our targets (0.5-14 x 10^{-2} Msun) from the bolometric lightcurve of each for
days ~150-300 using SN 1987A as a standard (7.5 x 10^{-2} Msun). The flattening
or sometimes increasing fluxes in the late time light curves of SNe 2002hh,
2003gd, 2004et and 2006bc indicate the presence of light echos. We estimate the
circumstellar hydrogen density of the material causing the light echo and find
that SN 2002hh is surrounded by relatively dense materials (n(H) >400 cm^{-3})
and SNe 2003gd and 2004et have densities more typical of the interstellar
medium (~1 cm^{-3}). The 56Ni mass appears well correlated with progenitor mass
with a slope of 0.31 x 10^{-2}, supporting the previous work by Maeda et al.
(2010), who focus on more massive Type II SNe. The dust mass does not appear to
be correlated with progenitor mass.Comment: We corrected the 56Ni mass of SN2005cs and Figures 8 (a) and 8 (c
Novel withanolides target medullary thyroid cancer through inhibition of both RET phosphorylation and the mammalian target of rapamycin pathway
Background
Despite development of current targeted therapies for medullary thyroid cancer (MTC), long-term survival remains unchanged. Recently isolated novel withanolide compounds from Solanaceae physalis are highly potent against MTCs. We hypothesize that these withanolides uniquely inhibit RET phosphorylation and the mammalian target of rapamycin (mTOR) pathway in MTC cells as a mechanism of antiproliferation and apoptosis.
Methods
MTC cells were treated with novel withanolides and MTC-targeted drugs. In vitro studies assessed cell viability and proliferation (MTS; trypan blue assays), apoptosis (flow cytometry with Annexin V/PI staining; confirmed by Western blot analysis), long-term cytotoxic effects (clonogenic assay), and suppression of key regulatory proteins such as RET, Akt, and mTOR (by Western blot analysis).
Results
The novel withanolides potently reduced MTC cell viability (half maximal inhibitory concentration [IC50], 270–2,850 nmol/L; 250–1,380 nmol/L for vandetanib; 360–1,640 nmol/L for cabozantinib) with induction of apoptosis at <1,000 nmol/L of drug. Unique from other targeted therapies, withanolides suppressed RET and Akt phosphorylation and protein expression (in a concentration- and time-dependent manner) as well as mTOR activity and translational activity of 4E-BP1 and protein synthesis mediated by p70S6kinase activation at IC50 concentrations.
Conclusion
Novel withanolides from Physalis selectively and potently inhibit MTC cells in vitro. Unlike other MTC-targeted therapies, these compounds uniquely inhibit both RET kinase activity and the Akt/mTOR prosurvival pathway. Further translational studies are warranted to evaluate their clinical potential
Optical and Infrared Analysis of Type II SN 2006BC
We present nebular phase optical imaging and spectroscopy and near/mid-IR
imaging of the Type II SN 2006bc. Observations reveal the central wavelength of
the symmetric H line profile to be red-shifted with respect to the host
galaxy H emission by day 325. Such an phenomenon has been argued to
result from an asymmetric explosion in the iron-peak elements resulting in a
larger mass of Ni and higher excitation of hydrogen on the far side of
the SN explosion. We also observe a gradual blue-shifting of this H
peak which is indicative of dust formation in the ejecta. Although showing a
normal peak brightness, V -17.2, for a core-collapse SN, 2006bc fades by
6 mag during the first 400 days suggesting either a relatively low
Ni yield, an increase in extinction due to new dust, or both. A short
duration flattening of the light curve is observed from day 416 to day 541
suggesting an optical light echo. Based on the narrow time window of this echo,
we discuss implications on the location and geometry of the reflecting ISM.
With our radiative transfer models, we find an upper limit of 2 x 10
M of dust around SN 2006bc. In the event that all of this dust were
formed during the SN explosion, this quantity of dust is still several orders
of magnitude lower than that needed to explain the large quantities of dust
observed in the early universe.Comment: 6 pages, 10 figures, accepted for publication in Ap
What Powers the 3000-Day Light Curve of SN 2006gy?
SN 2006gy was the most luminous supernova (SN) ever observed at the time of its discovery and the first of the newly defined class of superluminous supernovae (SLSNe). The extraordinary energetics of SN 2006gy and all SLSNe (>10^(51) erg) require either atypically large explosion energies (e.g. pair-instability explosion) or the efficient conversion of kinetic into radiative energy (e.g. shock interaction). The mass-loss characteristics can therefore offer important clues regarding the progenitor system. For the case of SN 2006gy, both a scattered and thermal light echo from circumstellar material (CSM) have been reported at later epochs (day ∼800), ruling out the likelihood of a pair-instability event and leading to constraints on the characteristics of the CSM. Owing to the proximity of the SN to the bright host-galaxy nucleus, continued monitoring of the light echo has not been trivial, requiring the high resolution offered by the Hubble Space Telescope (HST) or ground-based adaptive optics (AO). Here, we report detections of SN 2006gy using HST and Keck AO at ∼3000 d post-explosion and consider the emission mechanism for the very late-time light curve. While the optical light curve and optical spectral energy distribution are consistent with a continued scattered-light echo, a thermal echo is insufficient to power the K′-band emission by day 3000. Instead, we present evidence for late-time infrared emission from dust that is radiatively heated by CSM interaction within an extremely dense dust shell, and we consider the implications on the CSM characteristics and progenitor system
JWST mirror and actuator performance at cryo-vacuum
The James Webb Space Telescope (JWST) telescope’s Secondary Mirror Assembly (SMA) and eighteen Primary Mirror Segment Assemblies (PMSAs) are each actively controlled in rigid body position via six hexapod actuators. Each of the PMSAs additionally has a radius of curvature actuator. The mirrors are stowed to the mirror support structure to survive the launch environment and then must be deployed 12.5 mm to reach the nominally deployed position before the Wavefront Sensing & Control (WFSC) alignment and phasing process begins. JWST requires testing of the full optical system in a Cryogenic Vacuum (CV) environment before launch. The cryo vacuum test campaign was executed in Chamber A at the Johnson Space Center (JSC) in Houston Texas. The test campaign consisted of an ambient vacuum test, a cooldown test, a cryo stable test at 65 Kelvin, a warmup test, and finally a second ambient vacuum test. Part of that test campaign was the functional and performance testing of the hexapod actuators on the flight mirrors. This paper will describe the testing that was performed on all 132 hexapod and radius of curvature actuators. The test campaign first tests actuators individually then tested how the actuators perform in the hexapod system. Telemetry from flight sensors on the actuators and measurements from external metrology devices such as interferometers, photogrammetry systems and image analysis was used to demonstrate the performance of the JWST actuators. The mirror move commanding process was exercised extensively during the JSC CV test and many examples of accurately commanded moves occurred. The PMSA and SMA actuators performed extremely well during the JSC CV test, and we have demonstrated that the actuators are fully functional both at ambient and cryo temperatures and that the mirrors will go to their commanded positions with the accuracy needed to phase and align the telescope
The destruction and survival of dust in the shell around SN 2008S
SN 2008S erupted in early 2008 in the grand design spiral galaxy NGC 6946.
The progenitor was detected by Prieto et al. in Spitzer Space Telescope images
taken over the four years prior to the explosion, but was not detected in deep
optical images, from which they inferred a self-obscured object with a mass of
about 10 Msun. We obtained Spitzer observations of SN 2008S five days after its
discovery, as well as coordinated Gemini and Spitzer optical and infrared
observations six months after its outburst.
We have constructed radiative transfer dust models for the object before and
after the outburst, using the same r^-2 density distribution of pre-existing
amorphous carbon grains for all epochs and taking light-travel time effects
into account for the early post-outburst epoch. We rule out silicate grains as
a significant component of the dust around SN 2008S. The inner radius of the
dust shell moved outwards from its pre-outburst value of 85 AU to a
post-outburst value of 1250 AU, attributable to grain vaporisation by the light
flash from SN 2008S. Although this caused the circumstellar extinction to
decrease from Av = 15 before the outburst to 0.8 after the outburst, we
estimate that less than 2% of the overall circumstellar dust mass was
destroyed.
The total mass-loss rate from the progenitor star is estimated to have been
(0.5-1.0)x10^-4 Msun yr^-1. The derived dust mass-loss rate of 5x10^-7 Msun
yr^-1 implies a total dust injection into the ISM of up to 0.01 Msun over the
suggested duration of the self-obscured phase. We consider the potential
contribution of objects like SN 2008S to the dust enrichment of galaxies.Comment: 9 pages, 7 figures, 3 tables. rv2. To appear in MNRA
Supernovae and radio transients in M 82
We present optical and near-infrared (IR) photometry and near-IR spectroscopy
of SN 2004am, the only optically detected supernova (SN) in M 82. These
demonstrate that SN 2004am was a highly reddened type II-P SN similar to the
low luminosity type II-P events such as SNe 1997D and 2005cs. We show that SN
2004am was located coincident with the obscured super star cluster M 82-L, and
from the cluster age infer a progenitor mass of 12 +7/-3 Msun. In addition to
this, we present a high spatial resolution Gemini-N K-band adaptive optics
image of the site of SN 2008iz and a second transient of uncertain nature, both
detected so far only at radio wavelengths. Using image subtraction techniques
together with archival data from the Hubble Space Telescope, we are able to
recover a near-IR transient source co-incident with both objects. We find the
likely extinction towards SN 2008iz to be not more than Av ~ 10. The nature of
the second transient remains elusive and we regard an extremely bright
microquasar in M 82 as the most plausible scenario.Comment: 14 pages, 8 figures, accepted for publication in MNRA
The effects of dust on the optical and infrared evolution of SN 2004et
We present an analysis of multi-epoch observations of the Type II-P supernova
SN 2004et. New and archival optical spectra of SN 2004et are used to study the
evolution of the Halpha and [O I] 6300A line profiles between days 259 and 646.
Mid-infrared imaging was carried out between 2004 to 2010. We include Spitzer
`warm' mission photometry at 3.6 and 4.5um obtained on days 1779, 1931 and
2151, along with ground-based and HST optical and near-infrared observations
obtained between days 79 and 1803. Multi-wavelength light curves are presented,
as well as optical-infrared spectral energy distributions (SEDs) for multiple
epochs. Starting from about day 300, the optical light curves provide evidence
for an increasing amount of circumstellar extinction attributable to newly
formed dust, with the additional extinction reaching 0.8-1.5 magnitudes in the
V-band by day 690. The overall SEDs were fitted with multiple blackbody
components, in order to investigate the luminosity evolution of the supernova,
and then with Monte Carlo radiative transfer models using smooth or clumpy dust
distributions, in order to estimate how much new dust condensed in the ejecta.
The luminosity evolution was consistent with the decay of 56Co in the ejecta up
until about day 690, after which an additional emission source is required, in
agreement with the findings of Kotak et al. (2009). Clumped dust density
distributions consisting of 20% amorphous carbons and 80% silicates by mass
were able to match the observed optical and infrared SEDs, with dust masses
that increased from 8x10^{-5} Msun on day 300 to 1.5x10^{-3} Msun on day 690,
still significantly lower than the values needed for core collapse supernovae
to make a significant contribution to the dust enrichment of galaxies.Comment: 24 pages, 12 figures, 9 tables, published in MNRA
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