238 research outputs found
Chemical compositions and plasma parameters of planetary nebulae with Wolf-Rayet and wels type central stars
Aims: Chemical compositions and other properties of planetary nebulae around
central stars of spectral types [WC], [WO], and wels are compared with those of
`normal' central stars, in order to clarify the evolutionary status of each
type and their interrelation. Methods: We use plasma diagnostics to derive from
optical spectra the plasma parameters and chemical compositions of 48 planetary
nebulae. We also reanalyze the published spectra of a sample of 167 non-WR PN.
The results as well as the observational data are compared in detail with those
from other studies of the objects in common. Results: The central star's
spectral type is clearly correlated with electron density, temperature and
excitation class of the nebula, [WC] nebulae tend to be smaller than the other
types. All this corroborates the view of an evolutionary sequence from cool [WC
11] central stars inside dense, low excitation nebulae towards hot [WO 1] stars
with low density, high excitation nebulae. The wels PN, however, appear to be a
separate class of objects, not linked to WRPN by evolution, --abridged--Comment: 17 pages, 28 figures, Accepted in A&A. Accepted in A&
The evolving spectrum of the planetary nebula Hen 2-260
We analysed the planetary nebula Hen 2-260 using optical spectroscopy and
photometry. We compared our observations with the data from literature to
search for evolutionary changes. The nebular line fluxes were modelled with the
Cloudy photoionization code to derive the stellar and nebular parameters. The
planetary nebula shows a complex structure and possibly a bipolar outflow. The
nebula is relatively dense and young. The central star is just starting ionization (). Comparison of our
observations with literature data indicates a 50% increase of the [OIII] 5007
\AA\ line flux between 2001 and 2012. We interpret it as the result of the
progression of the ionization of . The central star evolves to
higher temperatures at a rate of . The heating rate
is consistent with a final mass of
or for two different sets of
post-AGB evolutionary tracks from literature. The photometric monitoring of Hen
2-260 revealed variations on a timescale of hours or days. The variability may
be caused by pulsations of the star. The temperature evolution of the central
star can be traced using spectroscopic observations of the surrounding
planetary nebula spanning a timescale of roughly a decade. This allows us to
precisely determine the stellar mass, since the pace of the temperature
evolution depends critically on the core mass. The kinematical age of the
nebula is consistent with the age obtained from the evolutionary track. The
final mass of the central star is close to the mass distribution peak for
central stars of planetary nebulae found in other studies. The object belongs
to a group of young central stars of planetary nebulae showing photometric
variability.Comment: accepted for publication in A&
New groups of planetary nebulae with peculiar dust chemistry towards the Galactic bulge
We investigate Galactic bulge planetary nebulae without emission-line central
stars for which peculiar infrared spectra have been obtained with the Spitzer
Space Telescope, including the simultaneous signs of oxygen and carbon based
dust. Three separate sub-groups can be defined characterized by the different
chemical composition of the dust and the presence of crystalline and amorphous
silicates.
We find that the classification based on the dust properties is reflected in
the more general properties of these planetary nebulae. However, some observed
properties are difficult to relate to the common view of planetary nebulae. In
particular, it is challenging to interpret the peculiar gas chemical
composition of many analyzed objects in the standard picture of the evolution
of planetary nebulae progenitors.
We confirm that the dual-dust chemistry phenomenon is not limited to
planetary nebulae with emission-line central stars.Comment: 17 pages, 13 figure
The populations of planetary nebulae in the direction of the Galactic bulge
We have observed 44 planetary nebulae (PNe) in the direction of the Galactic
bulge, and merged our data with published ones. We have distinguished, in the
merged sample of 164 PNe, those PNe most likely to prtain physically to the
Galactic bulge and those most likely to belong to the Galactic disk. We have
determined the chemical composition of all the 164 objects in a coherent way.
We looked for stellar emission features and discovered 14 new [WR] stars and 15
new weak emission line central stars.
The analyzed data led us to the following conclusions: (1) The spectral type
distribution of [WR] stars is very different in the bulge and in the disk of
the Galaxy. However, the observed distributions are strongly dependent on
selection effects. (2) The proportion of [WR] PNe is significantly larger in
the bulge than in the disk. (3) The oxygen abundances in [WR] stars do no
appear to be significantly affected by nucleosynthesis and mixing in the
progenitors. (4) The O/H gradient of the Galactic disk PNe population flattens
in the most internal parts of the Galaxy. (5) The median oxygen abundance in
the bulge PN population is larger by 0.2 dex than in the disk population seen
in the direction of the bulge. (6) Bulge PNe with smaller O/H tend to have
smaller radial velocities. (7) The oxygen abundance distribution of bulge PNe
is similar in shape to that of the metallicity distribution of bulge giants,
but significantly narrower. (8) The location of SB 32 (PN G 349.7-09.1) in the
(V_lsr, l_II) diagram and its low oxygen abundance argues that it probably
belongs to the halo population.Comment: 14 pages, 16 figures. Accepted for publication in A&
Planetary nebulae with emission-line central stars
The kinematic structure of a sample of planetary nebulae, consisting of 23
[WR] central stars, 21 weak emission line stars (wels) and 57 non-emission line
central stars, is studied. The [WR] stars are shown to be surrounded by
turbulent nebulae, a characteristic shared by some wels but almost completely
absent from the non-emission line stars. The fraction of objects showing
turbulence for non-emission-line stars, wels and [WR] stars is 7%, 24% and 91%,
respectively. The [WR] stars show a distinct IRAS 12-micron excess, indicative
of small dust grains, which is not found for wels. The [WR]-star nebulae are on
average more centrally condensed than those of other stars. On the
age-temperature diagram, the wels are located on tracks of both high and low
stellar mass, while [WR] stars trace a narrow range of intermediate masses.
Emission-line stars are not found on the cooling track. One group of wels may
form a sequence wels--[WO] stars with increasing temperature. For the other
groups both the wels and the [WR] stars appear to represent several,
independent evolutionary tracks. We find a discontinuity in the [WR] stellar
temperature distribution and suggest different evolutionary sequences above and
below the temperature gap. One group of cool [WR] stars has no counterpart
among any other group of PNe and may represent binary evolution. A prime factor
distinguishing wels and [WR] stars appears to be stellar luminosity. We find no
evidence for an increase of nebular expansion velocity with time.Comment: 14 pages, 9 figures, accepted to A&
Kinematics, turbulence and evolution of planetary nebulae
This paper discusses the location of a sample of planetary nebulae on the HR diagram. We determine the internal velocity fields of 14 planetary nebulae from high-resolution echelle spectroscopy, with the help of photoionization models. The mass averaged velocity is shown to be a robust, simple parameter describing the outflow. The expansion velocity and radius are used to define the dynamical age; together with the stellar temperature, this gives a measurement of the luminosity and core mass of the central star. The same technique is applied to other planetary nebulae with previously measured expansion velocities, giving a total sample of 73 objects. The objects cluster closely around the Schoenberner track of 0.61 M_sun, with a very narrow distribution of core masses. The masses are higher than found for local white dwarfs. The luminosities determined in this way tend to be higher by a factor of a few than those derived from the nebular luminosities. The discrepancy is highest for the hottest (most evolved) stars. We suggest photon leakage as the likely cause. The innermost regions of the non-[WC] nebulae tend to show strong acceleration. Together with the acceleration at the ionization front, the velocity field becomes 'U'-shaped. The presence of strong turbulent motions in [WC] nebulae is confirmed. Except for this, we find that the [WC] stars evolve on the same tracks as non-[WC] stars
Emission of polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene and xylene (BTEX) from the furan moulding sands with addition of the reclaim
In this paper, the results of decomposition of a moulding sand with furfuryl resin also on a quartz matrix and with additions of a reclaimed material, under industrial conditions, are presented. Investigations of the gases emission in the test foundry plant were performed according to the original method developed in the Faculty of Foundry Engineering, AGH UST. The dependence of the emitted PAHs and BTEX group substances and ignition losses on the reclaim fraction in a moulding sand are of a linear character of a very high correlation coefficient R2. On the bases of the derived equations, it is possible to determine the amount of the emitted hazardous substances from the moulding sand containing the known fraction of the reclaim
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
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