385 research outputs found
Abundances in the Galactic bulge: results from planetary nebulae and giant stars
Our understanding of the chemical evolution of the Galactic bulge requires
the determination of abundances in large samples of giant stars and planetary
nebulae (PNe). We discuss PNe abundances in the Galactic bulge and compare
these results with those presented in the literature for giant stars. We
present the largest, high-quality data-set available for PNe in the direction
of the Galactic bulge (inner-disk/bulge). For comparison purposes, we also
consider a sample of PNe in the Large Magellanic Cloud (LMC). We derive the
element abundances in a consistent way for all the PNe studied. By comparing
the abundances for the bulge, inner-disk, and LMC, we identify elements that
have not been modified during the evolution of the PN progenitor and can be
used to trace the bulge chemical enrichment history. We then compare the PN
abundances with abundances of bulge field giant. At the metallicity of the
bulge, we find that the abundances of O and Ne are close to the values for the
interstellar medium at the time of the PN progenitor formation, and hence these
elements can be used as tracers of the bulge chemical evolution, in the same
way as S and Ar, which are not expected to be affected by nucleosynthetic
processes during the evolution of the PN progenitors. The PN oxygen abundance
distribution is shifted to lower values by 0.3 dex with respect to the
distribution given by giants. A similar shift appears to occur for Ne and S. We
discuss possible reasons for this PNe-giant discrepancy and conclude that this
is probably due to systematic errors in the abundance derivations in either
giants or PNe (or both). We issue an important warning concerning the use of
absolute abundances in chemical evolution studies.Comment: 23 pages, 15 figures, 16 pages of online material, A&A in pres
The Multitude of Molecular Hydrogen Knots in the Helix Nebula
We present HST/NICMOS imaging of the H_2 2.12 \mu m emission in 5 fields in
the Helix Nebula ranging in radial distance from 250-450" from the central
star. The images reveal arcuate structures with their apexes pointing towards
the central star. Comparison of these images with comparable resolution ground
based images reveals that the molecular gas is more highly clumped than the
ionized gas line tracers. From our images, we determine an average number
density of knots in the molecular gas ranging from 162 knots/arcmin^2 in the
denser regions to 18 knots/arcmin^2 in the lower density outer regions. Using
this new number density, we estimate that the total number of knots in the
Helix to be ~23,000 which is a factor of 6.5 larger than previous estimates.
The total neutral gas mass in the Helix is 0.35 M_\odot assuming a mass of
\~1.5x10^{-5} M_\odot for the individual knots. The H_2 intensity, 5-9x10^{-5}
erg s^{-1} cm^{-2} sr^{-1}, remains relatively constant with projected distance
from the central star suggesting a heating mechanism for the molecular gas that
is distributed almost uniformly in the knots throughout the nebula. The
temperature and H_2 2.12 \mu m intensity of the knots can be approximately
explained by photodissociation regions (PDRs) in the individual knots; however,
theoretical PDR models of PN under-predict the intensities of some knots by a
factor of 10.Comment: 26 pages, 3 tables, 10 figures; AJ accepte
Longitudinal Study of Primary HIV-1 Isolates in Drug-Naïve Individuals Reveals the Emergence of Variants Sensitive to Anti-HIV-1 Monoclonal Antibodies
To study how virus evolution affects neutralization sensitivity and to determine changes that occur in and around epitopes, we tested the ability of 13 anti-HIV-1 gp120 (anti-V2, anti-V3, anti-CD4bd and anti-carbohydrate) human monoclonal antibodies (mAbs) to neutralize sequential viruses obtained from five HIV-1 chronically infected drug naïve individuals. Overall, primary viruses collected from patients at first visit were resistant to neutralization by all anti-HIV-1 mAbs with the exception of one virus sensitive to IgG1b12. Four of the five patients' viruses evolved increased sensitivity to neutralization by anti-V3 mAbs. Virus collected from a patient obtained 31 months later, evolved increased sensitivity to anti-V2, anti-V3, and anti-CD4bd mAbs. Furthermore, the anti-V2 and anti-CD4bd mAbs also exhibited increased neutralization capacities against virus collected from a patient 29 months later. Of the seven anti-V3 mAbs, five showed increased potency to neutralize the evolved virus from a patient collected after 11 months, and three exhibited increased potency against viruses from two patients collected 29 and 36 months later. Anti-V3 mAbs exhibited the most breadth and potency in neutralizing the evolving viruses. Sequence analysis of the envelope regions revealed amino acid conservation within the V3 loop, while most of the changes identified occurred outside the core epitopes and in particular within the C3 region; these may account for increased neutralization sensitivity. These studies demonstrate that in vivo, HIV-1 can evolve increased neutralization sensitivity to mAbs and that the spectrum of neutralization capacities by mAbs can be broader when studied in longitudinal analysis
A New Look At Carbon Abundances In Planetary Nebulae. IV. Implications For Stellar Nucleosynthesis
This paper is the fourth and final report on a project designed to study
carbon abundances in a sample of planetary nebulae representing a broad range
in progenitor mass and metallicity. We present newly acquired optical
spectrophotometric data for three Galactic planetary nebulae IC 418, NGC 2392,
and NGC 3242 and combine them with UV data from the IUE Final Archive for
identical positions in each nebula to determine accurate abundances of He, C,
N, O, and Ne at one or more locations in each object. We then collect
abundances of these elements for the entire sample and compare them with
theoretical predictions of planetary nebula abundances from a grid of
intermediate mass star models. We find some consistency between observations
and theory, lending modest support to our current understanding of
nucleosynthesis in stars below 8 M_o in birth mass. Overall, we believe that
observed abundances agree with theoretical predictions to well within an order
of magnitude but probably not better than within a factor of 2 or 3. But even
this level of consistency between observation and theory enhances the validity
of published intermediate-mass stellar yields of carbon and nitrogen in the
study of the abundance evolution of these elements.Comment: 41 pages, 11 figures. Accepted for publication in the Astrophysical
Journa
Morphology and Composition of the Helix Nebula
We present new narrow-band filter imagery in H-alpha and [N II] 6584 along
with UV and optical spectrophotometry measurements from 1200 to 9600 Angstroms
of NGC 7293, the Helix Nebula, a nearby, photogenic planetary nebula of large
diameter and low surface brightness. Detailed models of the observable ionized
nebula support the recent claim that the Helix is actually a flattened disk
whose thickness is roughly one-third its diameter with an inner region
containing hot, highly ionized gas which is generally invisible in narrow-band
images. The outer visible ring structure is of lower ionization and temperature
and is brighter because of a thickening in the disk. We also confirm a central
star effective temperature and luminosity of 120,000K and 100L_sun, and we
estimate a lower limit to the nebular mass to be 0.30M_sun. Abundance
measurements indicate the following values: He/H=0.12 (+/-0.017),
O/H=4.60x10^-4 (+/-0.18), C/O=0.87 (+/-0.12), N/O=0.54 (+/-0.14), Ne/O=0.33
(+/-0.04), S/O=3.22x10^-3 (+/-0.26), and Ar/O=6.74x10^-3 (+/-0.76). Our carbon
abundance measurements represent the first of their kind for the Helix Nebula.
The S/O ratio which we derive is anomalously low; such values are found in only
a few other planetary nebulae. The central star properties, the super-solar
values of He/H and N/O, and a solar level of C/O are consistent with a 6.5M_sun
progenitor which underwent three phases of dredge-up and hot bottom burning
before forming the planetary nebula.Comment: 50-page manuscript plus 11 postscript figures. This revised version
corrects a typo in earlier submission. Nothing else has changed. Accepted for
publication in the Astrophysical Journa
High-velocity collimated outflows in planetary nebulae: NGC 6337, He 2-186, and K 4-47
We have obtained narrow-band images and high-resolution spectra of the
planetary nebulae NGC 6337, He 2-186, and K 4-47, with the aim of investigating
the relation between their main morphological components and several
low-ionization features present in these nebulae. The data suggest that NGC
6337 is a bipolar PN seen almost pole on, with polar velocities higher than 200
km/s. The bright inner ring of the nebula is interpreted to be the "equatorial"
density enhancement. It contains a number of low-ionization knots and outward
tails that we ascribe to dynamical instabilities leading to fragmentation of
the ring or transient density enhancements due to the interaction of the
ionization front with previous density fluctuations in the ISM. The lobes show
a pronounced point-symmetric morphology and two peculiar low-ionization
filaments whose nature remains unclear. The most notable characteristic of He
2-186 is the presence of two high-velocity (higher than 135 km/s) knots from
which an S-shaped lane of emission departs toward the central star. K 4-47 is
composed of a compact core and two high-velocity, low-ionization blobs. We
interpret the substantial broadening of line emission from the blobs as a
signature of bow shocks, and using the modeling of Hartigan, Raymond, & Hartman
(1987), we derive a shock velocity of 150 km/s and a mild inclination of the
outflow on the plane of the sky. We discuss possible scenarios for the
formation of these nebulae and their low-ionization features. In particular,
the morphology of K 4-47 hardly fits into any of the usually adopted mass-loss
geometries for single AGB stars. Finally, we discuss the possibility that
point-symmetric morphologies in the lobes of NGC 6337 and the knots of He 2-186
are the result of precessing outflows from the central stars.Comment: 16 pages plus 7 figures, ApJ accepted. Also available at
http://www.iac.es/publicaciones/preprints.htm
Pre-Clinical Evaluation of a 213Bi-Labeled 2556 Antibody to HIV-1 gp41 Glycoprotein in HIV-1 Mouse Models as a Reagent for HIV Eradication
Any strategy for curing HIV infection must include a method to eliminate viral-infected cells. Based on our earlier proof-of-principle results targeting HIV-1 infected cells with radiolabeled antibody (mAb) to gp41 viral antigen, we embarked on identifying a suitable candidate mAb for preclinical development.Among the several human mAbs to gp41 tested, mAb 2556 was found to have high affinity, reactivity with multimeric forms of gp41 present on both the surface of virus particles and cells expressing HIV-1 Env, and recognition of a highly conserved epitope of gp41 shared by all HIV-1 subtypes. Also, mAb 2556 was the best in competition with HIV-1+ serum antibodies, which is an extremely important consideration for efficacy in the treatment of HIV patients. When radiolabeled with alpha-emitting radionuclide 213-Bismuth ((213)Bi) - (213)Bi-2556 efficiently and specifically killed ACH-2 human lymphocytes chronically infected with HIV-1, and HIV-1 infected human peripheral blood mononuclear cells (hPBMCs). The number of binding sites for (213)Bi-2556 on the surface of the infected cells was >10(6). The in vivo experiments were performed in two HIV-1 mouse models--splenic and intraperitoneal. In both models, the decrease in HIV-1 infected hPBMCs from the spleens and peritoneum, respectively, was dose-dependent with the most pronounced killing of hPBMCs observed in the 100 µCi (213)Bi-2556 group (P = 0.01). Measurement of the blood platelet counts and gross pathology of the treated mice demonstrated the lack of toxicity for (213)Bi-2556.We describe the preclinical development of a novel radiolabeled mAb reagent that could potentially be part of an HIV eradication strategy that is ready for translation into the clinic as the next step in its development. As viral antigens are very different from "self" human antigens - this approach promises high selectivity, increased efficacy and low toxicity, especially in comparison to immunotoxins
Theory of vortex excitation imaging via an NMR relaxation measurement
The temperature dependence of the site-dependent nuclear spin relaxation time
T_1 around vortices is studied in s-wave and d-wave superconductors.Reflecting
low energy electronic excitations associated with the vortex core, temperature
dependences deviate from those of the zero-field case, and T_1 becomes faster
with approaching the vortex core. In the core region, T_1^{-1} has a new peak
below T_c. The NMR study by the resonance field dependence may be a new method
to prove the spatial resolved vortex core structure in various superconductors.Comment: 5 pages, 3 figure
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