236 research outputs found
Evidence for Pre-Existing Dust in the Bright Type IIn SN 2010jl
SN 2010jl was an extremely bright, Type IIn SNe which showed a significant IR
excess no later than 90 days after explosion. We have obtained Spitzer 3.6 and
4.5 \mum and JHK observations of SN 2010jl \sim90 days post explosion. Little
to no reddening in the host galaxy indicated that the circumstellar material
lost from the progenitor must lie in a torus inclined out of the plane of the
sky. The likely cause of the high mid-IR flux is the reprocessing of the
initial flash of the SN by pre-existing circumstellar dust. Using a 3D Monte
Carlo Radiative Transfer code, we have estimated that between 0.03-0.35 Msun of
dust exists in a circumstellar torus around the SN located 6 \times 10 ^17 cm
away from the SN and inclined between 60-80\cdot to the plane of the sky. On
day 90, we are only seeing the illumination of approximately 5% of this torus,
and expect to see an elevated IR flux from this material up until day \sim 450.
It is likely this dust was created in an LBV-like mass loss event of more than
3 Msun, which is large but consistent with other LBV progenitors such as {\eta}
Carinae.Comment: Accepted in A
Expanding the set of rhodococcal Baeyer–Villiger monooxygenases by high-throughput cloning, expression and substrate screening
To expand the available set of Baeyer–Villiger monooxygenases (BVMOs), we have created expression constructs for producing 22 Type I BVMOs that are present in the genome of Rhodococcus jostii RHA1. Each BVMO has been probed with a large panel of potential substrates. Except for testing their substrate acceptance, also the enantioselectivity of some selected BVMOs was studied. The results provide insight into the biocatalytic potential of this collection of BVMOs and expand the biocatalytic repertoire known for BVMOs. This study also sheds light on the catalytic capacity of this large set of BVMOs that is present in this specific actinomycete. Furthermore, a comparative sequence analysis revealed a new BVMO-typifying sequence motif. This motif represents a useful tool for effective future genome mining efforts.
Cold Dust in Three Massive Evolved Stars in the LMC
Massive evolved stars can produce large amounts of dust, and far-infrared
(IR) data are essential for determining the contribution of cold dust to the
total dust mass. Using Herschel, we search for cold dust in three very dusty
massive evolved stars in the Large Magellanic Cloud: R71 is a Luminous Blue
Variable, HD36402 is a Wolf-Rayet triple system, and IRAS05280-6910 is a red
supergiant. We model the spectral energy distributions using radiative transfer
codes and find that these three stars have mass-loss rates up to 10^-3 solar
masses/year, suggesting that high-mass stars are important contributors to the
life-cycle of dust. We found far-IR excesses in two objects, but these excesses
appear to be associated with ISM and star-forming regions. Cold dust (T < 100
K) may thus not be an important contributor to the dust masses of evolved
stars.Comment: accepted to A&A as part of the Herschel first results special issu
The ALMA detection of CO rotational line emission in AGB stars in the Large Magellanic Cloud
Context. Low- and intermediate-mass stars lose most of their stellar mass at the end of their lives on the asymptotic giant branch (AGB). Determining gas and dust mass-loss rates (MLRs) is important in quantifying the contribution of evolved stars to the enrichment of the interstellar medium.
Aims: This study attempts to spectrally resolve CO thermal line emission in a small sample of AGB stars in the Large Magellanic Cloud (LMC).
Methods: The Atacama Large Millimeter Array was used to observe two OH/IR stars and four carbon stars in the LMC in the CO J = 2-1 line.
Results: We present the first measurement of expansion velocities in extragalactic carbon stars. All four C stars are detected and wind expansion velocities and stellar velocities are directly measured. Mass-loss rates are derived from modelling the spectral energy distribution and Spitzer/IRS spectrum with the DUSTY code. The derived gas-to-dust ratios allow the predicted velocities to agree with the observed gas-to-dust ratios. The expansion velocities and MLRs are compared to a Galactic sample of well-studied relatively low MLRs stars supplemented with extreme C stars with properties that are more similar to the LMC targets. Gas MLRs derived from a simple formula are significantly smaller than those derived from dust modelling, indicating an order of magnitude underestimate of the estimated CO abundance, time-variable mass loss, or that the CO intensities in LMC stars are lower than predicted by the formula derived for Galactic objects. This could be related to a stronger interstellar radiation field in the LMC.
Conclusions: Although the LMC sample is small and the comparison to Galactic stars is non-trivial because of uncertainties in their distances (hence luminosities), it appears that for C stars the wind expansion velocities in the LMC are lower than in the solar neighbourhood, while the MLRs appear to be similar. This is in agreement with dynamical dust-driven wind models
The evolutionary state of Miras with changing pulsation periods
Context: Miras are long-period variables thought to be in the asymptotic
giant branch (AGB) phase of evolution. In about one percent of known Miras, the
pulsation period is changing. It has been speculated that this changing period
is the consequence of a recent thermal pulse in these stars. Aims: We aim to
clarify the evolutionary state of these stars, and to determine in particular
whether or not they are in the thermally-pulsing (TP-)AGB phase. Methods: One
important piece of information that has been neglected so far when determining
the evolutionary state is the presence of the radio-active s-process element
technetium (Tc). We obtained high-resolution, high signal-to-noise-ratio
optical spectra of a dozen prominent Mira variables with changing pulsation
period to search for this indicator of TPs and dredge-up. We also use the
spectra to measure lithium (Li) abundances. Furthermore, we establish the
evolutionary states of our sample stars by means of their present-day periods
and luminosities. Results: Among the twelve sample stars observed in this
programme, five were found to show absorption lines of Tc. BH Cru is found to
be a carbon-star, its period increase in the past decades possibly having
stopped by now. We report a possible switch in the pulsation mode of T UMi from
Mira-like to semi-regular variability in the past two years. R Nor, on the
other hand, is probably a fairly massive AGB star, which could be true for all
meandering Miras. Finally, we assign RU Vul to the metal-poor thick disk with
properties very similar to the short-period, metal-poor Miras. Conclusions: We
conclude that there is no clear correlation between period change class and Tc
presence. The stars that are most likely to have experienced a recent TP are BH
Cru and R Hya, although their rates of period change are quite different.Comment: 11 pages, 7 figures, 2 tables; accepted for publication in A&
Satori 2023
The Satori is a student literary publication that expresses the artistic spirit of the students of Winona State University. Student poetry, prose, and graphic art are published in the Satori every spring since 1970.
The Satori 2023 editors are Gabriel Hathaway, Van Herman, Madeline Schonitzer, Brianna Strohbehn, Page Sutton, Willow Swinbank, and Emily Venné. The Satori 2023 faculty advisor is Dr. Jim Armstrong, Professor of English.https://openriver.winona.edu/satori/1010/thumbnail.jp
Long Period Variables in the Large Magellanic Cloud from the EROS-2 survey
Context. The EROS-2 survey has produced a database of millions of time series
from stars monitored for more than six years, allowing to classify some of
their sources into different variable star types. Among these, Long Period
Variables (LPVs), known to follow sequences in the period-luminosity diagram,
include long secondary period variables whose variability origin is still a
matter of debate.
Aims.We use the 856 864 variable stars available from the Large Magellanic
Cloud (LMC) in the EROS-2 database to detect, classify and characterize LPVs.
Methods. Our method to extract LPVs is based on the statistical Abbe test. It
investigates the regularity of the light curve with respect to the survey
duration in order to extract candidates with long-term variability. The period
search is done by Deeming, Lomb-Scargle and generalized Lomb-Scargle methods,
combined with Fourier series fit. Color-magnitude, period-magnitude and
period-amplitude diagrams are used to characterize our candidates.
Results. We present a catalog of 43 551 LPV candidates for the Large
Magellanic Cloud. For each of them, we provide up to five periods, mean
magnitude in EROS-2, 2MASS and Spitzer bands, BE-RE color, RE amplitude and
spectral type.We use infrared data to make the distinction between RGB, O-rich,
C-rich and extreme AGB stars. Properties of our LPV candidates are investigated
by analyzing period-luminosity and period-amplitude diagrams.Comment: Accepted for publication in A&
Comparing call-based versus subunit-based methods for categorizing Norwegian killer whale, Orcinus orca, vocalizations
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Animal Behaviour 81 (2011): 377-386, doi:10.1016/j.anbehav.2010.09.020.Students of animal communication face significant challenges when deciding how to
categorise calls into subunits, calls, and call series. Here, we use algorithms designed to parse
human speech to test different approaches for categorising calls of killer whales. Killer whale
vocalisations have traditionally been categorised by humans into discrete call types. These calls
often contain internal spectral shifts, periods of silence, and synchronously produced low and
high frequency components, suggesting that they may be composed of subunits. We describe
and compare three different approaches for modelling Norwegian killer whale calls. The first
method considered the whole call as the basic unit of analysis. Inspired by human speech
processing techniques, the second and third methods represented the calls in terms of subunits.
Subunits may provide a more parsimonious approach to modelling the vocal stream since (1)
there were fewer subunits than call types; (2) nearly 75% of all call types shared at least one
subunit. We show that contour traces from stereotyped Norwegian killer whale calls yielded
similar automatic classification performance using either whole calls or subunits. We also
demonstrate that subunits derived from Norwegian stereotyped calls were detected in some
Norwegian variable (non-stereotyped) calls as well as the stereotyped calls of other killer whale
populations. Further work is required to test whether killer whales use subunits to generate and
categorize their vocal repertoire.The undergraduate students were
supported by the Massachusetts Institute of Technology Undergraduate Research Opportunities
Program office and the Ocean Life Institute (OLI) at the Woods Hole Oceanographic Institution
(WHOI). Field work was financed by the OLI, National Geographic Society and WWF Sweden.
A. D. Shapiro was funded by a National Defense Science and Engineering Graduate Fellowship
and the WHOI Academic Programs Office
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