74 research outputs found
Shock excitation of the knots of Hen 3-1475
We present new optical STIS HST spectroscopic observations of the jets of the
proto-planetary nebula Hen 3-1475. The excitation conditions of the knots of
Hen 3-1475 are derived from the observed optical spectra, confirming that the
knots are shock excited. The shocked spectra are qualitatively reproduced by
simple ``3/2''D bow shock models. We present a set of bow shock models devoted
to planetary nebulae, and discuss the effects of the pre-ionization conditions,
the bow shock velocity, the bow shock shape and the chemical abundances on the
predicted spectra.
To explore the reliability of the ``3/2''D bow shock models, we also compare
the observed spectra of other three proto-planetary nebulae (M 1-92, M 2-56 and
CRL 618) to the predicted spectra.Comment: 13 pages. A&A (in press
Unveiling the structure of the planetary nebula M 2-48: Kinematics and physical conditions
The kinematics and physical conditions of the bipolar planetary nebula M 2-48
are analysed from high and low dispersion long-slit spectra. Previous CCD
narrow-band optical observations have suggested that this nebula is mainly
formed by a pair of symmetric bow-shocks, an off-center semi-circular shell,
and an internal bipolar structure. The bipolar outflow has a complex structure,
characterised by a series of shocked regions located between the bright core
and the polar tips. There is an apparent kinematic discontinuity between the
bright bipolar core and the outer regions. The fragmented ring around the
bright bipolar region presents a low expansion velocity and could be associated
to ejection in the AGB-PN transition phase, although its nature remains
unclear. The chemical abundances of the central region are derived, showing
that M 2-48 is a Type I planetary nebula (PN)
Clouds and aerosols in Puerto Rico ─ a new evaluation
The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to better understand warm cloud formation in a tropical marine environment, a period of intensive measurements took place in December 2004 in Puerto Rico, using some of the latest developments in online instrumentation such as aerosol mass spectrometers, cloud condensation nuclei counters and a hygroscopicity tandem differential mobility analyser. Simultaneous online measurements of aerosol size distributions, composition, hygroscopicity and optical properties were made near the lighthouse of Cape San Juan in the north-eastern corner of the island and at the top of East Peak mountain (1040 m a.s.l.), the two sites separated by 17 km. Additional measurements of the cloud droplet residual and interstitial aerosol properties were made at the mountain site, accompanied by measurements of cloud droplet size distributions, liquid water content and the chemical composition of cloud and rain water samples. <br><br> Both aerosol composition and cloud properties were found to be sensitive to wind sector. Air from the east-northeast (ENE) was mostly free of anthropogenic influences, the submicron fraction being mainly composed of non-sea salt sulphate, while that from the east-southeast (ESE) was found to be moderately influenced by populated islands upwind, adding smaller (<100 nm), externally mixed, carbonaceous particles to the aerosol that increased the number concentrations by over a factor of 3. This change in composition was also accompanied with a reduction in the measured hygroscopicity and fractional cloud activation potential of the aerosol. At the mountain site, the average cloud droplet concentrations increased from 193 to 519 cm<sup>−3</sup>, median volume diameter decreased from 20 to 14 ÎĽm and the liquid water content increased from 0.24 to 0.31 g m<sup>−3</sup> when the winds shifted from the ENE to ESE. Larger numbers of interstitial particles were recorded, most notably at sizes greater than 100 nm, which were absent during clean conditions. The average size of the residual particles and concentrations of cloudwater nitrate, sulphate and insoluble material increased during polluted conditions. <br><br> Previous studies in Puerto Rico had reported the presence of a significant non-anthropogenic organic fraction in the aerosols measured and concluded that this was a factor controlling the in situ cloud properties. However, this was not observed in our case. In contrast to the 1.00±0.14 ÎĽg m<sup>−3</sup> of organic carbon measured in 1992 and 1995, the organic matter measured in the current study of 0.17±0.35 ÎĽg m<sup>−3</sup> is many times lower, most of which can be attributed to anthropogenic sources. During clean conditions, the submicron aerosol was observed to be almost entirely inorganic, an observation supported by the hygroscopicity measurements. This suggests that organic aerosols from marine sources may not be completely ubiquitous (either spatially or temporally) in this environment and requires further investigation to quantify their true extent and implications, with more extensive, longer-term sampling in conjunction with wind field analyses
Learning to live together: a challenge for schools located in contexts of social vulnerability
Currently, there are many educational centres that demonstrate the need to promote initiatives to improve coexistence at school at the international level, especially in those located in contexts of social vulnerability. A socio-educational programme has been developed, applied and evaluated at a Singular Education Action Centre (Centro de AcciĂłn Educativa Singular - C.A.E.S) in the city of Valencia (Spain). To ascertain the programme's impact and possible generalization to other contexts, a quasi-experimental pretest-posttest design with a control group was used. Information was collected from 297 students and 54 teachers based on questionnaires assessing coexistence at school. The results obtained demonstrate the satisfactory functioning of the programme. The faculty and students from the experimental group affirm the importance of continuing to work in this direction to invest in creating a democratic school that firmly believes in coexistence and participation. Areas for improvement include the need to incorporate actions to increase family participation and develop strategies to facilitate the implementation of a more comprehensive programme
Exploring the effects of high-velocity flows in abundance determinations in H II regions. Bidimensional spectroscopy of HH 204 in the Orion Nebula
We present results from integral field optical spectroscopy with the Potsdam
Multi-Aperture Spectrograph of the Herbig-Haro (HH) object HH 204, with a
spatial sampling of 1 x 1 arcsec^2. We have obtained maps of different emission
lines, physical conditions and ionic abundances from collisionally excited
lines. The ionization structure of the object indicates that the head of the
bow shock is optically thick and has developed a trapped ionization front. The
density at the head is at least five times larger than in the background
ionized gas. We discover a narrow arc of high T_e([N II]) values delineating
the southeast edge of the head. The temperature in this zone is about 1,000 K
higher than in the rest of the field and should correspond to a shock-heated
zone at the leading working surface of the gas flow. This is the first time
this kind of feature is observed in a photoionized HH object. We find that the
O^+ and O abundance maps show anomalous values at separate areas of the bow
shock probably due to: a) overestimation of the collisional de-excitation
effects of the [O II] lines in the compressed gas at the head of the bow shock,
and b) the use of a too high T_e([N II]) at the area of the leading working
surface of the flow.Comment: 12 pages, 7 Postscript figures, accepted for publication in MNRA
Kinematics of the H2O masers at the centre of the PN K3-35
We have studied the kinematics traced by the water masers located at the
centre of the planetary nebula (PN) K3-35, using data from previous Very Large
Array (VLA) observations. An analysis of the spatial distribution and
line-of-sight velocities of the maser spots allows us to identify typical
patterns of a rotating and expanding ring in the position-velocity diagrams,
according to our kinematical model. We find that the distribution of the masers
is compatible with tracing a circular ring with a ~0.021 arcsec (~100 AU)
radius, observed with an inclination angle with respect to the line of sight of
55 degrees. We derive expansion and rotation velocities of 1.4 and 3.1 km/s,
respectively. The orientation of the ring projected on the plane of the sky, at
PA 158 degrees, is almost orthogonal to the direction of the innermost region
of the jet observed in K3-35, suggesting the presence of a disc or torus that
may be related to the collimation of the outflow.Comment: 7 pages, 4 figures, 2 tables. Accepted by MNRA
A wide-angle outflow with the simultaneous presence of a high-velocity jet in the high-mass Cepheus A HW2 system
We present five epochs of VLBI water maser observations around the massive
protostar Cepheus A HW2 with 0.4 mas (0.3 AU) resolution. The main goal of
these observations was to follow the evolution of the remarkable water maser
linear/arcuate structures found in earlier VLBI observations. Comparing the
data of our new epochs of observation with those observed five years before, we
find that at "large" scales of > 1" (700 AU) the main regions of maser emission
persist, implying that both the surrounding medium and the exciting sources of
the masers have been relatively stable during that time span. However, at
smaller scales of < 0.1" (70 AU) we see large changes in the maser structures,
particularly in the expanding arcuate structures R4 and R5. R4 traces a nearly
elliptical patchy ring of ~ 70 mas size (50 AU) with expanding motions of ~ 5
mas/yr (15 km/s). This structure is probably driven by the wind of a still
unidentified YSO located at the centre of the ring (~ 0.18" south of HW2). On
the other hand, the R5 expanding bubble structure (driven by the wind of a
previously identified YSO located ~ 0.6" south of HW2) is currently dissipating
in the circumstellar medium and losing its previous degree of symmetry,
indicating a very short-lived event. In addition, our results reveal, at scales
of ~ 1" (700 AU), the simultaneous presence of a relatively slow (~ 10-70 km/s)
wide-angle outflow (opening angle of ~ 102 deg, traced by the masers, and the
fast (~ 500~km/s) highly collimated radio jet associated with HW2 (opening
angle of ~ 18 deg, previously observed with the VLA. This simultaneous presence
of a wide-angle outflow and a highly collimated jet associated with a massive
protostar is similar to what is found in some low-mass YSOs. The implications
of these results in the study of the formation of high-mass stars are
discussed.Comment: 28 pages, 7 figures. Animations will be included as supporting
material online (MNRAS web page
K 4-47: a planetary nebula excited by photons and shocks
K 4-47 is an unusual planetary nebula composed of a compact high-ionization
core and a pair of low-ionization knots. Long-slit medium-resolution spectra of
the knots and core are analyzed in this paper. Assuming photoionization from
the central star, we have derived physical parameters for all the nebular
components, and the (icf) chemical abundances of the core, which appear similar
to Type-I PNe for He and N/O but significantly deficient in oxygen. The nebula
has been further modelled using both photoionization (CLOUDY) and shock
(MAPPINGS) codes. From the photoionization modelling of the core, we find that
both the strong auroral [O III] 4363A and [N II] 5755A emission lines observed
and the optical size of the core cannot be accounted for if a homogeneus
density is adopted. We suggest that a strong density stratification, matching
the high-density core detected at radio wavelengths and the much lower density
of the optical core, might solve the problem. From the bow-shock modelling of
the knots, on the other hand, we find that knots' chemistry is also represented
by Type-I PN abundances, and that they would move with velocities of 250 - 300
km/s.Comment: 9 pages including 4 figures and 2 tables. MNRAS in pres
New young planetary nebulae in IPHAS
Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory. DOI: 10.1051/0004-6361/200811575Aims. We search for very small-diameter galactic planetary nebulae (PNe) representing the earliest phases of PN evolution. The IPHAS catalogue of H-emitting stars provides a useful basis for this study since all sources present in this catalogue must be of small angular diameter. Methods. The PN candidates are selected based on their location in two colour-colour diagrams: IPHAS (r' - H) vs. (r' - i'), and 2MASS (J - H) vs. (H - ). Spectroscopic follow-up was carried out on a sample of candidates to confirm their nature. Results. We present a total of 83 PN candidates. We were able to obtain spectra or find the classification from the literature for 35 candidates. Five of these objects are likely to be new PNe, including one large bipolar PN discovered serendipitously close to an emission-line star. PN distances deduced from extinction-distance relations based on IPHAS field-star photometry are presented for the first time. These yield distance estimates for our objects in the range 2 kpc and 6 kpc. From the data in hand, we conclude that four of the discovered objects are probably young PNe.Peer reviewe
Properties of the ionized gas in HH202. II: Results from echelle spectrophotometry with UVES
We present results of deep echelle spectrophotometry of the brightest knot of
the HH202 in the Orion Nebula --HH202-S-- using the ultraviolet Visual Echelle
Spectrograph (UVES). The high spectral resolution has permitted to separate the
component associated with the ambient gas from that associated with the gas
flow. We derive electron densities and temperatures for both components, as
well as the chemical abundances of several ions and elements from collisionally
excited lines, including the first determinations of Ca^{+} and Cr^{+}
abundances in the Orion Nebula. We also calculate the He^{+}, C^{2+}, O^{+} and
O^{2+} abundances from recombination lines. The difference between the O^{2+}
abundances determined from collisionally excited and recombination lines --the
so-called abundance discrepancy factor-- is 0.35 dex and 0.11 dex for the shock
and nebular components, respectively. Assuming that the abundance discrepancy
is produced by spatial variations in the electron temperature, we derive values
of the temperature fluctuation parameter, t^2, of 0.050 and 0.016, for the
shock and nebular components, respectively. Interestingly, we obtain almost
coincident t^2 values for both components from the analysis of the intensity
ratios of He I lines. We find significant departures from case B predictions in
the Balmer and Paschen flux ratios of lines of high principal quantum number n.
We analyze the ionization structure of HH202-S, finding enough evidence to
conclude that the flow of HH202-S has compressed the ambient gas inside the
nebula trapping the ionization front. We measure a strong increase of the total
abundances of nickel and iron in the shock component, the abundance pattern and
the results of photoionization models for both components are consistent with
the partial destruction of dust after the passage of the shock wave in HH202-S.Comment: 23 pages, 7 figures. Accepted for publication in MNRA
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