1,268 research outputs found
Life Products of Stars
We attempt to document complete energetic transactions of stars in their
life. We calculate photon and neutrino energies that are produced from stars in
their each phase of evolution from 1 to 8 M_sun, using the state-of-the-art
stellar evolution code, tracing the evolution continuously from pre-main
sequence gravitational contraction to white dwarfs. We also catalogue
gravitational and thermal energies and helium, and heavier elements that are
stored in stars and those ejected into interstellar space in each evolutionary
phase.Comment: 26 pages, including 8 figures and 3 tables. Submitted to ApJ
The Ocular Albinism type 1 (OA1) G-Protein Coupled Receptor functions with MART-1 at early stages of melanogenesis to control melanosome identity and composition
OA1 (GPR143; GPCR, G-protein-coupled receptor), the protein product of the ocular albinism type 1 gene, encodes a pigment-cell-specific GPCR that localizes intracellularly to melanosomes. OA1 mutations result in ocular albinism due to alterations in melanosome formation, suggesting that OA1 is a key player in the biogenesis of melanosomes. To address the function of OA1 in melanosome biogenesis, we have used siRNA inactivation and combined morphological and biochemical methods to investigate melanosome ultrastructure, melanosomal protein localization and expression in human pigmented melanocytic cells. OA1 loss of function leads to decreased pigmentation and causes formation of enlarged aberrant premelanosomes harboring disorganized fibrillar structures and displaying proteins of mature melanosomes and lysosomes at their membrane. Moreover, we show that OA1 interacts biochemically with the premelanosomal protein MART-1. Inactivation of MART-1 by siRNA leads to a decreased stability of OA1 and is accompanied by similar defects in premelanosome biogenesis and composition. These data show for the first time that melanosome composition and identity are regulated at early stages by OA1 and that MART-1 likely acts as an escort protein for this GPCR
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
A Dramatic Decrease in Carbon Star Formation in M31
We analyze resolved stellar near-infrared photometry of 21 HST fields in M31
to constrain the impact of metallicity on the formation of carbon stars.
Observations of nearby galaxies show that the carbon stars are increasingly
rare at higher metallicity. Models indicate that carbon star formation
efficiency drops due to the decrease in dredge-up efficiency in metal-rich
thermally-pulsing Asymptotic Giant Branch (TP-AGB) stars, coupled to a higher
initial abundance of oxygen. However, while models predict a metallicity
ceiling above which carbon stars cannot form, previous observations have not
yet pinpointed this limit. Our new observations reliably separate carbon stars
from M-type TP-AGB stars across 2.6-13.7 kpc of M31's metal-rich disk using HST
WFC3/IR medium-band filters. We find that the ratio of C to M stars (C/M)
decreases more rapidly than extrapolations of observations in more metal-poor
galaxies, resulting in a C/M that is too low by more than a factor of 10 in the
innermost fields and indicating a dramatic decline in C star formation
efficiency at metallicities higher than [M/H] -0.1 dex. The
metallicity ceiling remains undetected, but must occur at metallicities higher
than what is measured in M31's inner disk ([M/H] +0.06 dex).Comment: 16 pages, 13 Figures; text clarifications in response to the referee.
Results are unchanged; accepted for publication in Ap
Probing AGB nucleosynthesis via accurate Planetary Nebula abundances
The elemental abundances of ten planetary nebulae, derived with high accuracy
including ISO and IUE spectra, are analysed with the aid of synthetic
evolutionary models for the TP-AGB phase. Model prescriptions are varied until
we achieve the simultaneous reproduction of all elemental features, which
allows placing important constraints on the characteristic masses and
nucleosynthetic processes experienced by the stellar progenitors. First of all,
it is possible to separate the sample into two groups of PNe, one indicating
the occurrence of only the third dredge-up during the TP-AGB phase, and the
other showing also the chemical signature of hot-bottom burning. The former
group is reproduced by stellar models with variable molecular opacities (see
Marigo 2002), adopting initial solar metallicity, and typical efficiency of the
third dredge-up 0.3-0.4. The latter group of PNe, with extremely high He
content 0.15<=He/H<=0.20 and marked oxygen deficiency, is consistent with
original sub-solar metallicity (i.e. LMC composition). Moreover, we are able to
explain quantitatively both the N/H-He/H correlation and the N/H-C/H
anti-correlation, thus solving the discrepancy pointed out long ago by Becker &
Iben (1980). This is obtained only under the hypothesis that intermediate-mass
TP-AGB progenitors (M > 4.5-5.0 Mo) with LMC composition have suffered a number
of very efficient, carbon-poor, dredge-up events. Finally, the neon abundances
of the He-rich PNe can be recovered by invoking a significant production of
22Ne during thermal pulses, which would imply a reduced role of the
22Ne(alpha,n)25Mg reaction as neutron source to the s-process nucleosynthesis
in these stars.Comment: 22 pages, accepted for publication in Astronomy & Astrophysic
Joint Analysis of near-infrared properties and surface brightness fluctuations of LMC star clusters
Surface brightness fluctuations have been proved to be a very powerful
technique to determine the distance and characterize the stellar content in
extragalactic systems. Nevertheless, before facing the problem of stellar
content in distant galaxies, we need to calibrate the method onto nearby
well-known systems. In this paper we analyze the properties at and
bands of a sample of 19 star clusters in the Large Magellanic Cloud (LMC), for
which accurate near-infrared (NIR) resolved star photometry, and integrated
photometry are available. For the same sample, we derive the SBF measurements
in and -bands. We use the multi-purpose stellar population code
\emph{SPoT (Stellar POpulations Tools)} to simulate the color-magnitude
diagram, stellar counts, integrated magnitudes, colors, and surface brightness
fluctuations of each cluster. The present procedure allows us to estimate the
age and metallicity of the clusters in a consistent way, and provides a new
calibration of the empirical -parameter. We take advantage of the high
sensitivity of NIR surface brightness fluctuations to thermally pulsing
asymptotic (TP-AGB) stars to test different mass-loss rates affecting the
evolution of such stars. We argue that NIR-SBFs can contribute to the
disentangling of the observable properties of TP-AGB stars, especially in
galaxies, where a large number of these stars are present.Comment: 25 pages, 12 figures, 4 tables, Accepted for publication in Ap
The AGB population of NGC 6822: distribution and the C/M ratio from JHK photometry
NGC 6822 is an irregular dwarf galaxy and part of the Local Group. Its close
proximity and apparent isolation provide a unique opportunity to study galactic
evolution without any obvious strong external influences. This paper aims to
study the spatial distribution of the asymptotic giant branch (AGB) population
and metallicity in NGC 6822. Using deep, high quality JHK photometry, taken
with WFCAM on UKIRT, carbon- and oxygen-rich AGB stars have been isolated. The
ratio between their number, the C/M ratio, has then been used to derive the
[Fe/H] abundance across the galaxy. The tip of the red giant branch is located
at K0 = 17.41 \pm 0.11 mag and the colour separation between carbon- and
oxygen-rich AGB stars is at (J - K)0 = 1.20 \pm 0.03 mag (i.e. (J - K)2MAS S
{\guillemotright} 1.28 mag). A C/M ratio of 0.62 \pm 0.03 has been derived in
the inner 4 kpc of the galaxy, which translates into an iron abundance of
[Fe/H] = -1.29\pm0.07 dex. Variations of these parameters were investigated as
a function of distance from the galaxy centre and azimuthal angle. The AGB
population of NGC 6822 has been detected out to a radius of 4 kpc giving a
diameter of 56 arcmin. It is metal-poor, but there is no obvious gradient in
metallicity with either radial distance from the centre or azimuthal angle. The
detected spread in the TRGB magnitude is consistent with that of a galaxy
surrounded by a halo of old stars. The C/M ratio has the potential to be a very
useful tool for the determination of metallicity in resolved galaxies but a
better calibration of the C/M vs. [Fe/H] relation and a better understanding of
the sensitivities of the C/M ratio to stellar selection criteria is first
required
Avaliação do efeito do Baculovirus anticarsia sobre Podisus nigrispinus (DALLAS, 1851), predador da lagarta da soja Anticarsia gemmatalis (HUBNER, 1818).
Este trabalho tem como objetivo conhecer os efeitos da ingestão de lagartas da soja infectadas com B. anticarsia pelo predador Podisus nigrispinus, avaliando-se os parâmetros biológicos de cada inseto.bitstream/CNPMA/5854/1/baculovirus_anticarsia.pd
Stellar populations in the surrounding field of the LMC clusters NGC 2154 and NGC 1898
In this paper we present a study and comparison of the star formation rates
(SFR) in the fields around NGC 1898 and NGC 2154, two intermediate-age star
clusters located in very different regions of the Large Magellanic Cloud. We
also present a photometric study of NGC 1898, and of seven minor clusters which
happen to fall in the field of NGC 1898, for which basic parameters were so far
unknown. We do not focus on NGC 2154, because this cluster was already
investigated in Baume et al. 2007, using the same theoretical tools. The ages
of the clusters were derived by means of the isochrone fitting method on their
color-magnitude diagrams. Two distinct populations of clusters were
found: one cluster (NGC 2154) has a mean age of 1.7 Gyr, with indication of
extended star formation over roughly a 1 Gyr period, while all the others have
ages between 100 and 200 Myr. The SFRs of the adjacent fields were inferred
using the downhill-simplex algorithm. Both SFRs show enhancements at 200, 400,
800 Myr, and at 1, 6, and 8 Gyr. These bursts in the SFR are probably the
result of dynamical interactions between the Magellanic Clouds (MCs), and of
the MCs with the Milky Way.Comment: 10 pages, 11 eps figures, in press in MNRAS. For a version including
references contact the author
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