1,101 research outputs found
A Binary Progenitor for the Type IIb Supernova 2011dh in M51
We perform binary stellar evolutionary calculations following the
simultaneous evolution of both stars in the system to study a potential
progenitor system for the Type IIb supernova 2011dh. Pre-explosion photometry
as well as light-curve modeling have provided constraints on the physical
properties of the progenitor system. Here we present a close binary system that
is compatible with such constraints. The system is formed by stars of solar
composition with 16 Msun + 10 Msun on a circular orbit with an initial period
of 125 days. The primary star ends its evolution as a yellow supergiant with a
mass of ~4 Msun, a final hydrogen content of ~3-5E-03 Msun and with an
effective temperature and luminosity in agreement with the HST pre-explosion
observations of SN 2011dh. These results are nearly insensitive to the adopted
accretion efficiency factor beta. At the time of explosion, the companion star
has an effective temperature of 22 to 40 thousand Kelvin, depending on the
value of beta, and lies near the zero age main sequence. Considering the
uncertainties in the HST pre-SN photometry the secondary star is only
marginally detectable in the bluest observed band. Close binary systems, as
opposed to single stars, provide a natural frame to explain the properties of
SN 2011dh.Comment: 12 pages, 15 figures, 3 tables. Accepted for publication in The
Astrophysical Journal on October June 27, 201
The Massive Progenitor of the Possible Type II-Linear Supernova 2009hd in Messier 66
We present observations of SN2009hd in the nearby galaxy M66. This SN is one
of the closest to us in recent years but heavily obscured by dust, rendering it
unusually faint in the optical, given its proximity. We find that the observed
properties of SN2009hd support its classification as a possible Type II-L SN, a
relatively rare subclass of CC-SNe. High-precision relative astrometry has been
employed to attempt to identify a SN progenitor candidate, based on a
pixel-by-pixel comparison between HST F555W and F814W images of the SN site
prior to explosion and at late times. A progenitor candidate is identified in
the F814W images only; this object is undetected in F555W. Significant
uncertainty exists in the astrometry, such that we cannot definitively identify
this object as the SN progenitor. Via insertion of artificial stars into the
pre-SN HST images, we are able to constrain the progenitor's properties to
those of a possible supergiant, with M(F555W)0>-7.6 mag and (V-I) 0>0.99 mag.
The magnitude and color limits are consistent with a luminous RSG; however,
they also allow for the possibility that the star could have been more yellow
than red. From a comparison with theoretical massive-star evolutionary tracks,
which include rotation and pulsationally enhanced mass loss, we can place a
conservative upper limit on the initial mass for the progenitor of <20 M_sun.
If the actual mass of the progenitor is near the upper range allowed by our
derived mass limit, then it would be consistent with that for the identified
progenitors of the SNII-L 2009kr and the high-luminosity SNII-P 2008cn. The
progenitors of these three SNe may possibly bridge the gap between lower-mass
RSG that explode as SNeII-P and LBV, or more extreme RSG, from which the more
exotic SNeII-n may arise. Very late-time imaging of the SN2009hd site may
provide us with more clues regarding the true nature of its progenitor.Comment: 19 pages, 9 figures, 3 tables, accepted for publication in Ap
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RNA Interference and Single Particle Tracking Analysis of Hepatitis C Virus Endocytosis
Hepatitis C virus (HCV) enters hepatocytes following a complex set of receptor interactions, culminating in internalization via clathrin-mediated endocytosis. However, aside from receptors, little is known about the cellular molecular requirements for infectious HCV entry. Therefore, we analyzed a siRNA library that targets 140 cellular membrane trafficking genes to identify host genes required for infectious HCV production and HCV pseudoparticle entry. This approach identified 16 host cofactors of HCV entry that function primarily in clathrin-mediated endocytosis, including components of the clathrin endocytosis machinery, actin polymerization, receptor internalization and sorting, and endosomal acidification. We next developed single particle tracking analysis of highly infectious fluorescent HCV particles to examine the co-trafficking of HCV virions with cellular cofactors of endocytosis. We observe multiple, sequential interactions of HCV virions with the actin cytoskeleton, including retraction along filopodia, actin nucleation during internalization, and migration of internalized particles along actin stress fibers. HCV co-localizes with clathrin and the ubiquitin ligase c-Cbl prior to internalization. Entering HCV particles are associated with the receptor molecules CD81 and the tight junction protein, claudin-1; however, HCV-claudin-1 interactions were not restricted to Huh-7.5 cell-cell junctions. Surprisingly, HCV internalization generally occurred outside of Huh-7.5 cell-cell junctions, which may reflect the poorly polarized nature of current HCV cell culture models. Following internalization, HCV particles transport with GFP-Rab5a positive endosomes, which is consistent with trafficking to the early endosome. This study presents technical advances for imaging HCV entry, in addition to identifying new host cofactors of HCV infection, some of which may be antiviral targets.</p
A Massive Progenitor of the Luminous Type IIn Supernova 2010jl
The bright, nearby, recently discovered supernova SN2010jl is a member of the
rare class of relatively luminous Type~IIn events. Here we report archival HST
observations of its host galaxy UGC5189A taken roughly 10yr prior to explosion,
as well as early-time optical spectra of the SN. The HST images reveal a
bright, blue point source at the position of the SN, with an absolute magnitude
of -12.0 in the F300W filter. If it is not just a chance alignment, the source
at the SN position could be (1) a massive young (less than 6 Myr) star cluster
in which the SN resided, (2) a quiescent, luminous blue star with an apparent
temperature around 14,000K, (3) a star caught during a bright outburst akin to
those of LBVs, or (4) a combination of option 1 and options 2 or 3. Although we
cannot confidently choose between these possibilities with the present data,
any of them imply that the progenitor of SN2010jl had an initial mass above
30Msun. This reinforces mounting evidence that many SNe IIn result from very
massive stars, that massive stars can produce visible SNe without collapsing
quietly to black holes, and that massive stars can retain their H envelopes
until shortly before explosion. Standard stellar evolution models fail to
account for these observed properties.Comment: 6 pages, 4 figures, submitted to Ap
The Yellow and Red Supergiants of M33
Yellow and red supergiants are evolved massive stars whose numbers and
locations on the HR diagram can provide a stringent test for models of massive
star evolution. Previous studies have found large discrepancies between the
relative number of yellow supergiants observed as a function of mass and those
predicted by evolutionary models, while a disagreement between the predicted
and observed locations of red supergiants on the HR diagram was only recently
resolved. Here we extend these studies by examining the yellow and red
supergiant populations of M33. Unfortunately, identifying these stars is
difficult as this portion of the color-magnitude diagram is heavily
contaminated by foreground dwarfs. We identify the red supergiants through a
combination of radial velocities and a two-color surface gravity discriminant
and, after re-characterizing the rotation curve of M33 with our newly selected
red supergiants, we identify the yellow supergiants through a combination of
radial velocities and the strength of the OI 7774 triplet. We examine
~1300 spectra in total and identify 121 yellow supergiants (a sample which is
unbiased in luminosity above log(L/L\odot) ~ 4.8) and 189 red supergiants.
After placing these objects on the HR diagram, we find that the latest
generation of Geneva evolutionary tracks show excellent agreement with the
observed locations of our red and yellow supergiants, the observed relative
number of yellow supergiants with mass and the observed red supergiant upper
mass limit. These models therefore represent a drastic improvement over
previous generations.Comment: Accepted for publication in the Astrophysical Journa
Circumstellar dust as a solution to the red supergiant supernova progenitor problem
We investigate the red supergiant problem: the apparent dearth of Type IIP
supernova progenitors with masses between 16 and 30 M_sun. Although red
supergiants with masses in this range have been observed, none have been
identified as progenitors in pre-explosion images. We show that by failing to
take into account the additional extinction resulting from the dust produced in
the red supergiant winds, we risk underestimating the luminosity of the most
massive red supergiants at the end of their lives. We estimate the initial
masses of all Type IIP progenitors for which observations exist and analyse the
resulting population. We find that the most likely maximum mass for a Type IIP
progenitor is 21^{+2}_{-1} M_sun. This is in closer agreement with the limit
predicted from single star evolution models.Comment: 10 pages, 6 figures and 4 tables. Accepted for publication in MNRA
Upper limits on bolometric luminosities of ten type Ia supernova progenitors from Chandra observations
We present an analysis of Chandra observations of the position of ten nearby
(< 25 Mpc) type Ia supernovae, taken before the explosions. No sources
corresponding to progenitors were found in any of the observations. We
calculated upper limits on the bolometric luminosities of the progenitors
assuming black-body X-ray spectra with temperatures of 30-150 eV. This is
inspired by the fact that luminous super-soft X-ray sources have been suggested
as the direct progenitors of type Ia supernovae. The upper limits of two
supernovae in our sample are comparable to the luminosities of the brightest
observed super-soft sources, ruling out such sources as the progenitors of
these supernovae. In contrast to Liu et al (2012) we find that for SN2011fe we
can rule out Eddington luminosity systems for black body temperatures as low as
40 eV. Our findings are consistent with statistical studies comparing the
observed type Ia supernova rate to the number of super-soft sources or the
integrated X-ray luminosity in external galaxies. This suggest that either the
progenitors of type Ia supernovae are not accreting, nuclear burning white
dwarfs, or that they do not look like the classical super-soft sources, e.g.
because they are obscured.Comment: Accepted, MNRAS. 10 pages, 11 figures, 3 table
Supernovae from Red Supergiants with Extensive Mass Loss
We calculate multicolor light curves (LCs) of supernovae (SNe) from red
supergiants (RSGs) exploded within dense circumstellar medium (CSM). Multicolor
LCs are calculated by using a multi-group radiation hydrodynamics code STELLA.
If CSM is dense enough, the shock breakout signal is delayed and smeared by CSM
and kinetic energy of SN ejecta is efficiently converted to thermal energy
which is eventually released as radiation. We find that explosions of RSGs are
affected by CSM in early epochs when mass-loss rate just before the explosions
is higher than 10^{-4} Msun/yr. Their characteristic features are that the LC
has a luminous round peak followed by a flat LC, that multicolor LCs are
simultaneously bright in ultraviolet and optical at the peak, and that
photospheric velocity is very low at these epochs. We calculate LCs for various
CSM conditions and explosion properties, i.e., mass-loss rates, radii of CSM,
density slopes of CSM, explosion energies of SN ejecta, and SN progenitors
inside, to see their influence on LCs. We compare our model LCs to those of
ultraviolet-bright Type IIP SN 2009kf and show that the mass-loss rate of the
progenitor of SN 2009kf just before the explosion is likely to be higher than
10^{-4} Msun/yr. Combined with the fact that SN 2009kf is likely to be an
energetic explosion and has large 56Ni production, which implies that the
progenitor of SN 2009kf is a massive RSG, our results indicate that there could
be some mechanism to induce extensive mass loss in massive RSGs just before
their explosions.Comment: 16 pages, 17 figures, 3 tables, accepted by Monthly Notices of the
Royal Astronomical Society, the unit of Lbol in Table 3 corrected in v
Generalized Phase Synchronization in unidirectionally coupled chaotic oscillators
We investigate phase synchronization between two identical or detuned
response oscillators coupled to a slightly different drive oscillator. Our
result is that phase synchronization can occur between response oscillators
when they are driven by correlated (but not identical) inputs from the drive
oscillator. We call this phenomenon Generalized Phase Synchronization (GPS) and
clarify its characteristics using Lyapunov exponents and phase difference
plots.Comment: 4 pages, 5 figure
SN 2008jb: A "Lost" Core-Collapse Supernova in a Star-Forming Dwarf Galaxy at ~10 Mpc
We present the discovery and follow-up observations of SN 2008jb, a
core-collapse supernova in the dwarf irregular galaxy ESO 302-14 at 9.6 Mpc.
This transient was missed by galaxy-targeted surveys and was only found in
archival optical images obtained by CRTS and ASAS. It was detected shortly
after explosion and reached a bright optical maximum, Vmax = 13.6 mag (M_Vmax ~
-16.5). The shape of the light curve shows a plateau of 100 days, followed by a
drop of 1.4 mag in V-band to a decline with the approximate Co 56 decay slope,
consistent with 0.04 Msun of Ni 56 synthesized in the explosion. A spectrum
obtained 2 years after explosion shows a broad, boxy Halpha emission line,
which is unusual for type IIP supernovae. We detect the supernova in archival
Spitzer and WISE images obtained 8-14 months after explosion, which show clear
signs of warm dust emission. The dwarf irregular host galaxy has a low
gas-phase oxygen abundance, 12 + log(O/H) = 8.2 (~1/5 Solar), similar to those
of the SMC and the hosts of long gamma-ray bursts and luminous core-collapse
supernovae. We study the host environment using GALEX FUV, R-band, and Halpha
images and find that the supernova occurred in a large star-formation complex.
The morphology of the Halpha emission appears as a large shell (R = 350 pc)
surrounding the FUV and optical emission. We estimate an age of ~9 Myr and a
total mass of ~2 x 10^5 Msun for the star-formation complex. These properties
are consistent with the expanding Halpha supershells observed in well-studied
nearby dwarf galaxies, which are tell-tale signs of feedback from the
cumulative effect of massive star winds and supernovae. The age estimated for
the star-forming region suggests a relatively high-mass progenitor star with
initial mass of ~20 Msun. We discuss the implications of these findings in the
study of core-collapse supernova progenitors. (Abridged)Comment: 41 pages, 10 figures, accepted in ApJ; small changes, conclusions
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