96 research outputs found
Angular dimensions of planetary nebulae
We have measured angular dimensions of 312 planetary nebulae from their
images obtained in Halpha (or Halpha + [NII]). We have applied three methods of
measurements: direct measurements at the 10% level of the peak surface
brightness, Gaussian deconvolution and second-moment deconvolution. The results
from the three methods are compared and analysed. We propose a simple
deconvolution of the 10% level measurements which significantly improves the
reliability of these measurements for compact and partially resolved nebulae.
Gaussian deconvolution gives consistent but somewhat underestimated diameters
compared to the 10% measurements. Second-moment deconvolution gives results in
poor agreement with those from the other two methods, especially for poorly
resolved nebulae. From the results of measurements and using the conclusions of
our analysis we derive the final nebular diameters which should be free from
systematic differences between small (partially resolved) and extended (well
resolved) objects in our sample.Comment: 10 figures, 2 table
Characteristics of low nickel ferritic-austenitic corrosion resistant cast steel
The article presents the results of microscopic examinations of corrosion resistant cast steel with reduced nickel content obtained in a test casting with varying wall thickness. Investigations were carried out in as-cast condition and after heat treatment. Regardless of the casting wall thickness, increasing the manganese and nitrogen content to about 5 % and 2 500 ppm, respectively, yields the material with a two-phase microstructure containing ferrite in an amount of 55,6 ÷ 57,2 % (magnetic method) and 52,3 ÷ 55,2 % (analytical method). Based on the results of metallographic examinations, total elimination of the secondary austenite from the microstructure was observed. Microhardness measurements showed average values of 352,3 μHV20 and 267 μHV20 for the chromium ferrite and austenite, respectively
V4332 Sagittarii revisited
The eruption of V4332 Sgr discovered in February 1994 shows striking
similarities to that of V838 Mon started in January 2002. The nature of these
eruptions is, however, enigmatic and unclear. We present new photometric and
spectroscopic data on V4332 Sgr obtained in April-May 2003 at the SAAO. The
obtained spectrum shows an unusual emission-line component superimposed on an
early M-type stellar spectrum. The emission-line spectrum is of very low
excitation and is dominated by lines from neutral elemets (NaI, FeI, CaI) and
molecular bands (TiO, ScO, AlO). We also analyse all the observational data,
mainly photometric measurements, available for V4332 Sgr. This allows us to
follow the evolution of the effective temperature, radius and luminosity of the
object since February 1994 till 2003. We show that the observed decline of
V4332 Sgr can be accounted for by a gravitational contraction of an inflated
stellar envelope. The combined optical and infrared photometry in 2003 shows
that apart from the M-type stellar component there is a strong infrared excess
in the KLM bands. This excess was absent in the 2MASS measurements done in 1998
but was probably starting to appear in K in 1999 when the object was observed
in the DENIS survey. We interpret the results in terms of a stellar merger
scenario proposed by Soker & Tylenda. The infrared excess is likely to be due
to a disc-like structure which is either of protostellar nature or has been
produced during the 1994 eruption and stores angular momentum from the merger
event.Comment: 11 pages, 5 figures, accepted in Astronomy & Astrophysic
Carbon chemistry in Galactic Bulge Planetary Nebulae
Galactic Bulge Planetary Nebulae show evidence of mixed chemistry with
emission from both silicate dust and PAHs. This mixed chemistry is unlikely to
be related to carbon dredge up, as third dredge-up is not expected to occur in
the low mass Bulge stars. We show that the phenomenon is widespread, and is
seen in 30 nebulae out of 40 of our sample, selected on the basis of their
infrared flux. HST images and UVES spectra show that the mixed chemistry is not
related to the presence of emission-line stars, as it is in the Galactic disk
population. We also rule out interaction with the ISM as origin of the PAHs.
Instead, a strong correlation is found with morphology, and the presence of a
dense torus. A chemical model is presented which shows that hydrocarbon chains
can form within oxygen-rich gas through gas-phase chemical reactions. The model
predicts two layers, one at where small hydrocarbons form from
reactions with C, and one at , where larger chains (and by
implication, PAHs) form from reactions with neutral, atomic carbon. These
reactions take place in a mini-PDR. We conclude that the mixed chemistry
phenomenon occurring in the Galactic Bulge Planetary Nebulae is best explained
through hydrocarbon chemistry in an UV-irradiated, dense torus.Comment: 13 pages, 10 figue
The physical structure of the point-symmetric and quadrupolar planetary nebula NGC 6309
We analyse the point-symmetric planetary nebula NGC 6309 in terms of its
three-dimensional structure and of internal variations of the physical
conditions to deduce the physical processes involved in its formation. We used
VLA-D 3.6-cm continuum, ground-based, and HST-archive imaging as well as long
slit high- and low-dispersion spectroscopy. The low-dispersion spectra indicate
a high excitation nebula, with low to medium variations of its internal
physical conditions. In the optical images, the point-symmetric knots show a
lack of [NII] emission as compared with similar features previously known in
other PNe. A rich internal structure of the central region is seen in the HST
images, resembling a deformed torus. Long slit high-dispersion spectra reveal a
complex kinematics in the central region. The spectral line profiles from the
external regions of NGC 6309 indicate expanding lobes (~40 km/s) as those
generally found in bipolar nebulae. Finally, we have found evidence for the
presence of a faint halo, possibly related to the envelope of the AGB-star
progenitor. Our data indicate that NGC 6309 is a quadrupolar nebula with two
pairs of bipolar lobes whose axes are oriented PA=40 and PA=76. Equatorial and
polar velocities for these two pairs of lobes are 29 and 86 km/s for the
bipolar system at PA=40 and 25 and 75 km/s for the bipolar system at PA=76.
There is also a central torus that is expanding at 25 km/s. Kinematical age for
all these structures is around 3700 to 4000 yr. We conclude that NGC 6309 was
formed by a set of well-collimated bipolar outflows (jets), which were ejected
in the initial stages of its formation as a planetary nebula. These jets carved
the bipolar lobes in the previous AGB wind and their remnants are now observed
as the point-symmetric knots tracing the edges of the lobes.Comment: To be published in Astronomy & Astrophysics; 11 pages, 8 figures, 4
table
Formation & evolution of the Galactic bulge: constraints from stellar abundances
We compute the chemical evolution of the Galactic bulge in the context of an
inside-out model for the formation of the Milky Way. The model contains updated
stellar yields from massive stars. The main purpose of the paper is to compare
the predictions of this model with new observations of chemical abundance
ratios and metallicity distributions in order to put constraints on the
formation and evolution of the bulge. We computed the evolution of several
alpha-elements and Fe and performed several tests by varying different
parameters such as star formation efficiency, slope of the initial mass
function and infall timescale. We also tested the effect of adopting a primary
nitrogen contribution from massive stars. The [alpha/Fe] abundance ratios in
the Bulge are predicted to be supersolar for a very large range in [Fe/H], each
element having a different slope. These predictions are in very good agreement
with most recent accurate abundance determinations. We also find a good fit of
the most recent Bulge stellar metallicity distributions. We conclude that the
Bulge formed on a very short timescale (even though timescales much shorter
than about 0.1 Gyr are excluded) with a quite high star formation efficiency of
about 20 Gyr and with an initial mass function more skewed toward high
masses (i.e. x <= 0.95) than the solar neighbourhood and rest of the disk. The
results obtained here are more robust than previous ones since they are based
on very accurate abundance measurements.Comment: 26 pages, 9 figures, accepted for publication in A&
Određivanje alergena Asp f 1 (Aspergillus fumigatus) u peradarniku enzimimunokemijskom metodom
Poultry farms contain high levels of allergenic fungi, and Aspergillus spp. is the most common genus of moulds. Aspergillus fumigatus antigens are responsible for the development of several respiratory diseases including asthma. The aim of this study was to measure the mass fraction of Asp f 1, a major allergen of Asperillus fumigatus in 37 indoor dust samples collected from four poultry farms in a rural area of the Zagreb County (Croatia) using the enzyme-linked immunosorbent assay. More than 62 % of dust samples had detectable Asp f 1 levels (limit of detection 3.6 ng g-1). The overall mean Asp f 1 level was 17.9 ng g-1 [range (3.8 to 72.4) ng g-1]. Satisfactory results were obtained for analytical within-run imprecision
(6.7 %), between-run imprecision (10.5 %), and accuracy (91 % to 115 %). Microclimate parameters (air temperature, relative humidity, and velocity) were within the recommended ranges in all poultry farms.
This study has shown that Asp f 1 settles on dust at poultry farms and that occupational exposure to this allergen deserves monitoring in livestock buildings.Peradarnici sadržavaju veliku koncentraciju alergenih plijesni, a rod Aspergillus najčešće je zastupljen.
Antigeni soja Aspergillus fumigatus odgovorni su za nastanak nekoliko respiratornih bolesti uključujući astmu. Cilj ovoga rada bio je odrediti masenu frakciju Asp f 1, glavnog alergena soja Asperillus fumigatus u 37 uzoraka prašine uzorkovanih u četiri peradarnika sa šireg područja Zagrebačke županije rabeći enzimimunokemijsku
metodu. Više od 62 % uzoraka prašine u tri peradarnika imalo je mjerljivu koncentraciju Asp f 1 (granica detekcije = 3.6 ng g-1). Ukupni srednji maseni udio Asp f 1 iznosio je 17.9 ng g-1 (raspon od
3.8 ng g-1 do 72.4 ng g-1). Dobiveni su zadovoljavajući rezultati za analitičku nepreciznost u seriji (6.7 %), nepreciznost iz dana u dan (10.5 %) i točnost (91 % do 115 %). Mikroklimatski parametri (temperatura zraka, relativna vlaga i protok zraka) u svim peradarnicima bili su u okviru preporučenih vrijednosti.
Rezultati ovoga rada pokazuju da Asp f 1 sedimentira na prašinu u peradarnicima te da profesionalnu izloženost tom alergenu treba pratiti u jedinicama za uzgoj stoke
Izloženost alergenima plijesni u unutarnjem okolišu
Humid indoor environments may be colonised by allergenic fi lamentous microfungi (moulds), Aspergillus spp., Penicillium spp., Cladosporium spp., and Alternaria spp. in particular. Mould-induced respiratory diseases are a worldwide problem. In the last two decades, mould allergens and glucans have been used as markers of indoor exposure to moulds. Recently, mould allergens Alt a 1 (Alternaria alternata) and Asp f 1 (Aspergillus fumigatus) have been analysed in various environments (residential and occupational) with enzyme-linked immunosorbent assays, which use monoclonal or polyclonal antibodies. Household Alt a 1 and Asp f 1 levels were usually under the limit of the method detection. By contrast, higher levels of mould allergens were found in environments with high levels of bioaerosols such as poultry farms and sawmills. Data on allergen Alt a 1 and Asp f 1 levels in agricultural settings may provide information on possible colonisation of respective moulds and point out to mould-related diseases in occupants.Vlažni, unutarnji prostori mogu biti kolonizirani alergogenim, filamentoznim mikrogljivicama (plijesni) uglavnom rodova Aspergillus, Penicillium, Cladosporium i Alternaria. Respiratorne bolesti uzrokovane plijesnima zdravstveni su problem diljem svijeta. U posljednja dva desetljeća, neki sastavni dijelovi plijesni kao alergeni i glukan rabe se kao pokazatelji izloženosti plijesni u unutarnjem okolišu. Nedavno su alergeni plijesni Alt a 1 (Alternaria alternata) i Asp f 1 (Aspergillus fumigatus) određivani u različitom okolišu (kućnom i profesionalnom) enzim-imunokemijskom metodom koja rabi monoklonska ili poliklonska antitijela. Razina Alt a 1 i Asp f 1 u kućnoj prašini ispod je granice detekcije. Nasuprot tomu, alergeni plijesni su određeni u okolišu s visokom razinom bioaerosola kao peradarnici i pilane. Razine alergena Alt a 1 i Asp f 1 u nekim poljoprivrednim objektima pružaju informaciju o mogućoj kolonizaciji plijesnima, što upućuje na moguće zdravstvene učinke kod zaposlenika
Effect of Titanium Addition and Cooling Rate on Primary α(Al) Grains and Tensile Properties of Al-Cu Alloy
Comprehensive modelling of the planetary nebula LMC-SMP 61 and its [WC]-type central star
We present a comprehensive study of the Magellanic Cloud planetary nebula SMP
61 and of its nucleus, a Wolf-Rayet type star classified [WC 5-6]. We have
performed a detailed spectral analysis of the central star, using the Potsdam
code for expanding atmospheres in non-LTE. The fluxes from the model stellar
atmosphere were used to compute photoionization models of the nebula. All the
available observations, within their error bars, were used to constrain these
models. We find that the ionizing fluxes predicted by the stellar model are
basically consistent with the fluxes needed by the photoionization model to
reproduce the nebular emission, within the error margins. However, there are
indications that the stellar model overestimates the number and hardness of
Lyman continuum photons. The photoionization models imply a clumped density
structure of the nebular material. The observed CIII] 1909/CII 4267 line ratio
implies the existence of carbon-rich clumps in the nebula. Such clumps are
likely produced by stellar wind ejecta, possibly mixed with the nebular
material. We discuss our results with regard to the stellar and nebular
post-AGB evolution.Comment: 16 pages, 10 figures, Astronomy and Astrophysics in pres
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