170 research outputs found
And the Stars in the Field of Blue
https://digitalcommons.library.umaine.edu/mmb-vp/5252/thumbnail.jp
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
Asymptotic Giant Branch Variables in the Galaxy and the Local Group
AGB variables, particularly the large amplitude Mira type, are a vital step
on the distance scale ladder. They will prove particularly important in the era
of space telescopes and extremely large ground-based telescopes with adaptive
optics, which will be optimized for infrared observing. Our current
understanding of the distances to these stars is reviewed with particular
emphasis on improvements that came from Hipparcos as well as on recent work on
Local Group galaxies. In addition to providing the essential calibration for
extragalactic distances Gaia may also provide unprecedented insight into the
poorly understood mass-loss process itself.Comment: Accepted for publication in Astrophysics and Space Science. From a
presentation at the conference "The Fundamental Cosmic Distance Scale: State
of the Art and Gaia Perspective, Naples May 2011. 8 Pages, 9 Figure
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
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&
The Dust Budget of the SMC: Are AGB Stars the Primary Dust Source at Low Metallicity?
We estimate the total dust input from the cool evolved stars in the Small
Magellanic Cloud (SMC), using the 8 micron excess emission as a proxy for the
dust-production rate. We find that Asymptotic Giant Branch (AGB) and red
supergiant (RSG) stars produce (8.6-9.5) x 10^7 solar masses per year of dust,
depending on the fraction of far-infrared sources that belong to the evolved
star population (with 10%-50% uncertainty in individual dust-production rates).
RSGs contribute the least (<4%), while carbon-rich AGB stars (especially the
so-called "extreme" AGB stars) account for 87%-89% of the total dust input from
cool evolved stars. We also estimate the dust input from hot stars and
supernovae (SNe), and find that if SNe produce 10^-3 solar masses of dust each,
then the total SN dust input and AGB input are roughly equivalent. We consider
several scenarios of SNe dust production and destruction and find that the
interstellar medium (ISM) dust can be accounted for solely by stellar sources
if all SNe produce dust in the quantities seen around the dustiest examples and
if most SNe explode in dense regions where much of the ISM dust is shielded
from the shocks. We find that AGB stars contribute only 2.1% of the ISM dust.
Without a net positive contribution from SNe to the dust budget, this suggests
that dust must grow in the ISM or be formed by another unknown mechanism.Comment: 10 pages, 5 figures. Accepted for publication in Ap
Sexual Dimorphism of the Zebra Finch Syrinx Indicates Adaptation for High Fundamental Frequencies in Males
In many songbirds the larger vocal repertoire of males is associated with sexual dimorphism of the vocal control centers and muscles of the vocal organ, the syrinx. However, it is largely unknown how these differences are translated into different acoustic behavior.Here we show that the sound generating structures of the syrinx, the labia and the associated cartilaginous framework, also display sexual dimorphism. One of the bronchial half rings that position and tense the labia is larger in males, and the size and shape of the labia differ between males and females. The functional consequences of these differences were explored by denervating syringeal muscles. After denervation, both sexes produced equally low fundamental frequencies, but the driving pressure generally increased and was higher in males. Denervation strongly affected the relationship between driving pressure and fundamental frequency.The syringeal modifications in the male syrinx, in concert with dimorphisms in neural control and muscle mass, are most likely the foundation for the potential to generate an enhanced frequency range. Sexually dimorphic vocal behavior therefore arises from finely tuned modifications at every level of the motor cascade. This sexual dimorphism in frequency control illustrates a significant evolutionary step towards increased vocal complexity in birds
Performance of Al-Mn Transition-Edge Sensor Bolometers in SPT-3G
SPT-3G is a polarization-sensitive receiver, installed on the South Pole
Telescope, that measures the anisotropy of the cosmic microwave background
(CMB) from degree to arcminute scales. The receiver consists of ten
150~mm-diameter detector wafers, containing a total of 16,000 transition-edge
sensor (TES) bolometers observing at 95, 150, and 220 GHz. During the 2018-2019
austral summer, one of these detector wafers was replaced by a new wafer
fabricated with Al-Mn TESs instead of the Ti/Au design originally deployed for
SPT-3G. We present the results of in-lab characterization and on-sky
performance of this Al-Mn wafer, including electrical and thermal properties,
optical efficiency measurements, and noise-equivalent temperature. In addition,
we discuss and account for several calibration-related systematic errors that
affect measurements made using frequency-domain multiplexing readout
electronics.Comment: 9 pages, 5 figures, submitted to the Journal of Low Temperature
Physics: LTD18 Special Editio
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