604 research outputs found
Radio continuum properties of young planetary nebulae
We have selected a small sample of post-AGB stars in transition towards the
planetary nebula and present new Very Large Array multi-frequency high-angular
resolution radio observations of them. The multi-frequency data are used to
create and model the targets' radio continuum spectra, proving that these stars
started their evolution as very young planetary nebulae. In the optically thin
range, the slopes are compatible with the expected spectral index (-0.1). Two
targets (IRAS 18062+2410 and 17423-1755) seem to be optically thick even at
high frequency, as observed in a handful of other post-AGB stars in the
literature, while a third one (IRAS 20462+3416) shows a possible contribution
from cold dust. In IRAS 18062+2410, where we have three observations spanning a
period of four years, we detect an increase in its flux density, similar to
that observed in CRL 618.
High-angular resolution imaging shows bipolar structures that may be due to
circumstellar tori, although a different hypothesis (i.e., jets) could also
explain the observations. Further observations and monitoring of these sources
will enable us to test the current evolutionary models of planetary nebulae.Comment: 8 pages, 3 figures, accepted for publication in MNRA
VISIR/VLT and VLA joint imaging analysis of the circumstellar nebula around IRAS~18576+0341
High spatial and sensitivity images of the Luminous Blue Variable IRAS
18576+0341 were obtained using the mid infrared imager VISIR at the Very Large
Telescope and the Very Large Array interferometer. The resulting mid-infrared
continuum maps show a similar clumpy and approximately circular symmetric
nebula, which contrasts sharply with the asymmetry that characterizes the
ionized component of the envelope, as evidenced from the radio and [Ne II] line
images obtained with comparable spatial resolution. In particular, there is
excellent overall agreement between the 12.8 micron map and the radio images,
consistent with free-free emission from circumstellar ionized material
surrounding a central stellar wind. The color temperature and optical depth
maps obtained from mid-infrared images show only slight fluctuations,
suggesting quite uniform dust characteristics over the dust shell. We explore
various possibilities to understand the cause of the different morphology of
the dusty and gaseous component of the circumstellar envelope which are
compatible with the observations.Comment: 26 pages, 8 figures. Accepted for publication in The Astrophysical
Journa
Expanded Very Large Array Observations of the Nebula Around G79.29+0.46
We have observed the radio nebula surrounding the Galactic luminous blue variable candidate G79.29+0.46 with the Expanded Very Large Array (EVLA) at 6 cm. These new radio observations allow a morphological comparison between the radio emission, which traces the ionized gas component, and the mid-IR emission, a tracer of the dust component. The InfraRed Array Camera (8 μm) and the Multiband Imaging Photometer for Spitzer (24 μm and 70 μm) images have been reprocessed and compared with the EVLA map. We confirm the presence of a second shell at 24 μm and also provide evidence for its detection at 70 μm. The differences between the spatial morphology of the radio and mid-IR maps indicate the existence of two dust populations, the cooler one emitting mostly at longer wavelengths. Analysis of the two dusty, nested shells have provided us with an estimate of the characteristic timescales for shell ejection, providing important constraints for stellar evolutionary models. Finer details of the ionized gas distribution can be appreciated thanks to the improved quality of the new 6 cm image, most notably the highly structured texture of the nebula. Evidence of interaction between the nebula and the surrounding interstellar medium can be seen in the radio map, including brighter features that delineate regions where the shell structure is locally modified. In particular, the brighter filaments in the southwest region appear to frame the shocked southwestern clump reported from CO observations
SCORPIO-II: Spectral indices of weak Galactic radio sources
In the next few years the classification of radio sources observed by the
large surveys will be a challenging problem, and spectral index is a powerful
tool for addressing it. Here we present an algorithm to estimate the spectral
index of sources from multiwavelength radio images. We have applied our
algorithm to SCORPIO (Umana et al. 2015), a Galactic Plane survey centred
around 2.1 GHz carried out with ATCA, and found we can measure reliable
spectral indices only for sources stronger than 40 times the rms noise. Above a
threshold of 1 mJy, the source density in SCORPIO is 20 percent greater than in
a typical extra-galactic field, like ATLAS (Norris et al. 2006), because of the
presence of Galactic sources. Among this excess population, 16 sources per
square degree have a spectral index of about zero, suggesting optically thin
thermal emission such as Hii regions and planetary nebulae, while 12 per square
degree present a rising spectrum, suggesting optically thick thermal emission
such as stars and UCHii regions.Comment: 12 pages, 11 figures, accepted by MNRA
The Radio Corona of AR Lacertae
We present multifrequency VLA and VLBA observations at 8.4 GHz of the RS CVn
system AR Lac, that were performed in autumn 1997 simultaneously with X-ray
observations obtained from Rodono` et al. (1999). Our VLBA data indicate a
resolved source with dimension close to the system separation, while the study
of the flux density curve evidences a small amplitude outside of the eclipse
variability. The derived five-frequencies spectra, combined with the size
information from VLBA data, are compared with gyrosynchrotron emission from a
two component structured source. A comparison with the results of the X-ray
observations allow us to exclude the possibility that thermal gyrosynchrotron
is responsible for the radio emission, but it is compatible with the hypothesis
of co-spatial X-ray and radio emitting sources.Comment: 9 pages, 7 figures. Accepted for publication in A&
Humanised IgG1 antibody variants targeting membrane-bound carcinoembryonic antigen by antibody-dependent cellular cytotoxicity and phagocytosis
BACKGROUND: The effect of glycoengineering a membrane specific anti-carcinoembryonic antigen (CEA) (this paper uses the original term CEA for the formally designated CEACAM5) antibody (PR1A3) on its ability to enhance killing of colorectal cancer (CRC) cell lines by human immune effector cells was assessed. In vivo efficacy of the antibody was also tested. METHODS: The antibody was modified using EBNA cells cotransfected with beta-1,4-N-acetylglucosaminyltransferase III and the humanised hPR1A3 antibody genes. RESULTS: The resulting alteration of the Fc segment glycosylation pattern enhances the antibody's binding affinity to the FcgammaRIIIa receptor on human immune effector cells but does not alter the antibody's binding capacity. Antibody-dependent cellular cytotoxicity (ADCC) is inhibited in the presence of anti-FcgammaRIII blocking antibodies. This glycovariant of hPR1A3 enhances ADCC 10-fold relative to the parent unmodified antibody using either unfractionated peripheral blood mononuclear or natural killer (NK) cells and CEA-positive CRC cells as targets. NK cells are far more potent in eliciting ADCC than either freshly isolated monocytes or granulocytes. Flow cytometry and automated fluorescent microscopy have been used to show that both versions of hPR1A3 can induce antibody-dependent cellular phagocytosis (ADCP) by monocyte-derived macrophages. However, the glycovariant antibody did not mediate enhanced ADCP. This may be explained by the relatively low expression of FcgammaRIIIa on cultured macrophages. In vivo studies show the efficacy of glycoengineered humanised IgG1 PR1A3 in significantly improving survival in a CRC metastatic murine model. CONCLUSION: The greatly enhanced in vitro ADCC activity of the glycoengineered version of hPR1A3 is likely to be clinically beneficial
The Luminous Blue Variable RMC127 as seen with ALMA and ATCA
We present ALMA and ATCA observations of the luminous blue variable \rmc. The
radio maps show for the first time the core of the nebula and evidence that the
nebula is strongly asymmetric with a Z-pattern shape. Hints of this morphology
are also visible in the archival \emph{HST} image, which overall
resembles the radio emission. The emission mechanism in the outer nebula is
optically thin free-free in the radio. At high frequencies, a component of
point-source emission appears at the position of the star, up to the ALMA
frequencies. The rising flux density distribution () of this object suggests thermal emission from the ionized
stellar wind and indicates a departure from spherical symmetry with
. We examine different scenarios to explain this excess
of thermal emission from the wind and show that this can arise from a bipolar
outflow, supporting the suggestion by other authors that the stellar wind of
\rmc is aspherical. We fit the data with two collimated ionized wind models and
we find that the mass-loss rate can be a factor of two or more smaller than in
the spherical case. We also fit the photometry obtained by IR space telescopes
and deduce that the mid- to far-IR emission must arise from extended, cool
() dust within the outer ionized nebula. Finally we discuss two
possible scenarios for the nebular morphology: the canonical single star
expanding shell geometry, and a precessing jet model assuming presence of a
companion star.Comment: Accepted for publication in ApJ (minor revision included
The rich molecular environment of the luminous blue variable star AFGL 2298
We investigated the molecular environment of AFGL 2298, an obscured Galactic
Luminous blue variable (LBV) star which hosts a highly structured circumstellar
environment with hints of multiple mass-loss events in the last few a.
We present spectral line observations of AFGL 2298 at 1 and 3 mm performed with
the IRAM 30m radio telescope. Furthermore, we report the detection of several
carbon- and nitrogen- bearing species (CO, CO, CO, CO,
HCO, HCN, HNC, HCO, CN, NH, and CH) in the
surroundings of AFGL 2298. In addition, we identified three velocity components
that clearly stand out from the Galactic background. The morphology,
kinematics, masses and isotopic ratios, together with a comparative study of
the fractional abundances, lead us to suggest that two of these components (36
and 70 km/s) have a stellar origin. The other component (46 km/s) most likely
traces swept-up interstellar material, probably harbouring also a
photon-dominated region. The first inventory of the circumstellar molecular gas
around AFGL 2298 is provided. The results are compatible with the hypothesis of
former mass-loss events, produced before the one that created the infrared
nebula. There are chemical hints of the presence of ejected stellar material,
and also swept up gas. These findings will help to better understand the
mass-loss history of this class of evolved massive stars, which heavily
influence the overall chemical evolution of the Galaxy.Comment: Accepted to Astronomy and Astrophysics. 15 pages, 4 tables, 11
figure
The dusty Nebula surrounding HR Car: a Spitzer view
We present mid-IR observations of the Galactic Luminous Blue Variable (LBV)
HR Car and its associated nebula carried out with the Spitzer Space Telescope
using both IRAC and IRS, as part of a GTO program aimed to study stellar ejecta
from evolved stars. Our observations reveal a rich mid-IR spectrum of the inner
nebula showing both solid state and atomic gas signatures. Strong
low-excitation atomic fine structure lines such as m [\ion{Fe}{2}]
and m [\ion{Si}{2}], indicate, for the first time, the presence of a
PDR in this object class. While the physics and chemistry of the low-excitation
gas appears to be dominated by photodissociation, a possible contribution due
to shocks can be inferred from the evidence of gas phase Fe abundance
enhancement. The presence of amorphous silicates, inferred from the observed
characteristic broad feature at m located in the inner nebula, suggests
that dust has formed during the LBV outburst. This is in contrast with the
detection of crystalline dust in other probably more evolved Galactic LBVs,
which is similar to the crystalline dust observed in red supergiants. This has
been considered to be evidence of dust production during evolutionary phases
prior to the outburst.Comment: 27 pages, 6 figures. accepted by Ap
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