1,737 research outputs found
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
Estimation of interdomain flexibility of N-terminus of factor H using residual dipolar couplings
Characterization of segmental flexibility is needed to understand the biological mechanisms of the very large category of functionally diverse proteins, exemplified by the regulators of complement activation, that consist of numerous compact modules or domains linked by short, potentially flexible, sequences of amino acid residues. The use of NMR-derived residual dipolar couplings (RDCs), in magnetically aligned media, to evaluate interdomain motion is established but only for two-domain proteins. We focused on the three N-terminal domains (called CCPs or SCRs) of the important complement regulator, human factor H (i.e. FH1-3). These domains cooperate to facilitate cleavage of the key complement activation-specific protein fragment, C3b, forming iC3b that no longer participates in the complement cascade. We refined a three-dimensional solution structure of recombinant FH1-3 based on nuclear Overhauser effects and RDCs. We then employed a rudimentary series of RDC datasets, collected in media containing magnetically aligned bicelles (disk-like particles formed from phospholipids) under three different conditions, to estimate interdomain motions. This circumvents a requirement of previous approaches for technically difficult collection of five independent RDC datasets. More than 80% of conformers of this predominantly extended three-domain molecule exhibit flexions of < 40 °. Such segmental flexibility (together with the local dynamics of the hypervariable loop within domain 3), could facilitate recognition of C3b via initial anchoring and eventual reorganization of modules to the conformation captured in the previously solved crystal structure of a C3b:FH1-4 complex
Sex, love and security: accounts of distance and commitment in LAT relationships
Drawing on a 2011 national survey and 50 semi-structured interviews, we explore the differing ways in which those in living apart together (LAT) relationships discuss and experience notions of commitment . We found that sexual exclusivity in LAT is expected by the large majority, regardless of their reasons for living apart. The majority of the interviewees also expressed a high degree of commitment to their partner in terms of love, care and intimacy, as well an appreciation of the increased freedom and autonomy that living apart has to offer. Respondents were divided into four groups according to their perceived commitment: 1. Autonomous commitment, 2. Contingent commitment, 3. Ambivalent commitment, and 4. Limited commitment. Despite differing degrees of commitment, however, the overall finding was that the importance of relating and making relational decisions was central, even in the lives of those living in such unconventional relationship styles
The origin of dust in galaxies revisited: the mechanism determining dust content
The origin of cosmic dust is a fundamental issue in planetary science. This
paper revisits the origin of dust in galaxies, in particular, in the Milky Way,
by using a chemical evolution model of a galaxy composed of stars, interstellar
medium, metals (elements heavier than helium), and dust. We start from a review
of time-evolutionary equations of the four components, and then, we present
simple recipes for the stellar remnant mass and yields of metal and dust based
on models of stellar nucleosynthesis and dust formation. After calibrating some
model parameters with the data from the solar neighborhood, we have confirmed a
shortage of the stellar dust production rate relative to the dust destruction
rate by supernovae if the destruction efficiency suggested by theoretical works
is correct. If the dust mass growth by material accretion in molecular clouds
is active, the observed dust amount in the solar neighborhood is reproduced. We
present a clear analytic explanation of the mechanism for determining dust
content in galaxies after the activation of accretion growth: a balance between
accretion growth and supernova destruction. Thus, the dust content is
independent of the uncertainty of the stellar dust yield after the growth
activation. The timing of the activation is determined by a critical metal mass
fraction which depends on the growth and destruction efficiencies. The solar
system formation seems to have occurred well after the activation and plenty of
dust would have existed in the proto-solar nebula.Comment: 12 pages, 11 figure
A Spitzer Space Telescope far-infrared spectral atlas of compact sources in the Magellanic Clouds. I. The Large Magellanic Cloud
[abridged] We present 52-93 micron spectra obtained with Spitzer in the
MIPS-SED mode, of a representative sample of luminous compact far-IR sources in
the LMC. These include carbon stars, OH/IR AGB stars, post-AGB objects and PNe,
RCrB-type star HV2671, OH/IR red supergiants WOHG064 and IRAS05280-6910, B[e]
stars IRAS04530-6916, R66 and R126, Wolf-Rayet star Brey3a, Luminous Blue
Variable R71, supernova remnant N49, a large number of young stellar objects,
compact HII regions and molecular cores, and a background galaxy (z~0.175). We
use the spectra to constrain the presence and temperature of cold dust and the
excitation conditions and shocks within the neutral and ionized gas, in the
circumstellar environments and interfaces with the surrounding ISM. Evolved
stars, including LBV R71, lack cold dust except in some cases where we argue
that this is swept-up ISM. This leads to an estimate of the duration of the
prolific dust-producing phase ("superwind") of several thousand years for both
RSGs and massive AGB stars, with a similar fractional mass loss experienced
despite the different masses. We tentatively detect line emission from neutral
oxygen in the extreme RSG WOHG064, with implications for the wind driving. In
N49, the shock between the supernova ejecta and ISM is revealed by its strong
[OI] 63-micron emission and possibly water vapour; we estimate that 0.2 Msun of
ISM dust was swept up. Some of the compact HII regions display pronounced
[OIII] 88-micron emission. The efficiency of photo-electric heating in the
interfaces of ionized gas and molecular clouds is estimated at 0.1-0.3%. We
confirm earlier indications of a low nitrogen content in the LMC. Evidence for
solid state emission features is found in both young and evolved object; some
of the YSOs are found to contain crystalline water ice.Comment: Accepted for publication in The Astronomical Journal. This paper
accompanies the Summer 2009 SAGE-Spec release of 48 MIPS-SED spectra, but
uses improved spectrum extraction. (Fig. 2 reduced resolution because of
arXiv limit.
Dust formation in the ejecta of the Type II-P supernova 2004dj
Core-collapse supernovae (CC SNe), especially Type II-Plateau ones, are
thought to be important contributors to cosmic dust production. SN 2004dj, one
of the closest and brightest SN since 1987A, offered a good opportunity to
examine dust formation processes. To find signs of newly formed dust, we
analyze all available mid-infrared (MIR) archival data from the Spitzer Space
Telescope. We re-reduce and analyze data from IRAC, MIPS and IRS instruments
obtained between +98 and +1381 days after explosion, generating light curves
and spectra for each epoch. Observed spectral energy distributions are fitted
with both analytic and numerical models, using the radiative-transfer code
MOCASSIN for the latter ones. We also use imaging polarimetric data obtained at
+425 days by the Hubble Space Telescope. We present convincing evidence of dust
formation in the ejecta of SN 2004dj from MIR light curves and spectra.
Significant MIR excess flux is detected in all bands between 3.6 and 24 um. In
the optical, a ~0.8% polarization is also detected at a 2-sigma level, which
exceeds the interstellar polarization in that direction. Our analysis shows
that the freshly-formed dust around SN 2004dj can be modeled assuming a nearly
spherical shell containing amorphous carbon grains, cooling from ~700 K to ~400
K between +267 and +1246 days. Persistent excess flux has been found above 10
um, which is explained by a cold (~115 K) dust component. If this cold dust is
of circumstellar origin, it is likely to be condensed in a cool, dense shell
between the forward and reverse shocks. Pre-existing circumstellar dust is less
likely, but cannot be ruled out. An upper limit of ~8x10^{-4} M_sun was derived
for the dust mass, which is similar to previously published values for other
dust-producing SNe.Comment: 15 pages, 11 figures, 8 tables; accepted for publication in A&A; new
version after minor corrections and language editio
The global gas and dust budget of the Large Magellanic Cloud: AGB stars and supernovae and the impact on the ISM evolution
‘The definitive version is available at: www3.interscience.wiley.com '. Copyright Blackwell / Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.14743.xWe report on an analysis of the gas and dust budget in the interstellar medium (ISM) of the Large Magellanic Cloud (LMC). Recent observations from the Spitzer Space Telescope enable us to study the mid-infrared dust excess of asymptotic giant branch (AGB) stars in the LMC. This is the first time we can quantitatively assess the gas and dust input from AGB stars over a complete galaxy, fully based on observations. The integrated mass-loss rate over all intermediate and high mass-loss rate carbon-rich AGB candidates in the LMC is 8.5 × 10−3 M⊙ yr−1 , up to 2.1 × 10−2 M⊙ yr−1 . This number could be increased up to 2.7 × 10−2 M⊙ yr−1 if oxygen-rich stars are included. This is overall consistent with theoretical expectations, considering the star formation rate (SFR) when these low- and intermediate-mass stars where formed, and the initial mass functions. AGB stars are one of the most important gas sources in the LMC, with supernovae (SNe), which produces about 2–4 × 10−2 M⊙ yr−1 . At the moment, the SFR exceeds the gas feedback from AGB stars and SNe in the LMC, and the current star formation depends on gas already present in the ISM. This suggests that as the gas in the ISM is exhausted, the SFR will eventually decline in the LMC, unless gas is supplied externally. Our estimates suggest 'a missing dust-mass problem' in the LMC, which is similarly found in high-z galaxies: the accumulated dust mass from AGB stars and possibly SNe over the dust lifetime (400–800 Myr) is significant less than the dust mass in the ISM. Another dust source is required, possibly related to star-forming regions.Peer reviewe
Study of e+e- --> pi+ pi- pi0 process using initial state radiation with BABAR
The process e+e- --> pi+ pi- pi0 gamma has been studied at a center-of-mass
energy near the Y(4S) resonance using a 89.3 fb-1 data sample collected with
the BaBar detector at the PEP-II collider. From the measured 3pi mass spectrum
we have obtained the products of branching fractions for the omega and phi
mesons, B(omega --> e+e-)B(omega --> 3pi)=(6.70 +/- 0.06 +/- 0.27)10-5 and
B(phi --> e+e-)B(phi --> 3pi)=(4.30 +/- 0.08 +/- 0.21)10-5, and evaluated the
e+e- --> pi+ pi- pi0 cross section for the e+e- center-of-mass energy range
1.05 to 3.00 GeV. About 900 e+e- --> J/psi gamma --> pi+ pi- pi0 gamma events
have been selected and the branching fraction B(J/psi --> pi+ pi- pi0)=(2.18
+/- 0.19)% has been measured.Comment: 21 pages, 37 postscript figues, submitted to Phys. Rev.
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