171 research outputs found
New perspectives on the supernova remnant Puppis A based on a radio polarization study
We present a polarization study towards the supernova remnant (SNR) Puppis A based on original observations performed with the Australia Telescope Compact Array. Based on the analysis of a feature detected outside the SNR shell (called 'the tail' throughout the paper), it was possible to disentangle the emission with origin in Puppis A itself from that coming from the foreground Vela SNR. We found a very low polarization fraction, of about 3 per cent on average. The upper limit of the magnetic field component parallel to the line of sight is estimated to be B ~ 20 μG. The statistical behaviour of the magnetic vectors shows two preferential directions, almost perpendicular to each other, which are approximately aligned with the flat edges of Puppis A. A third, narrow peak oriented perpendicular to the Galactic plane suggests the existence of an interstellar magnetic field locally aligned in this direction. There is evidence that the magnetic vectors along the shell are aligned with the shock front direction. The low polarization fraction and the statistical behaviour of the magnetic vectors are compatible with a scenario where the SNR evolves inside a stellar wind bubble with a box-like morphology, produced by the interaction of the different stellar winds, one of them magnetized, launched by the SN progenitor. This scenario can furthermore explain the morphology of Puppis A, rendering little support to the previously accepted picture which involved strong density gradients to explain the flat, eastern edge of the shell.Fil: Reynoso, Estela Marta. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Velázquez, P. F.. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; MéxicoFil: Cichowolski, Silvina. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
The orthocerid Dawsonoceras? (Nautiloidea) from the Lipeón Formation (Silurian, Northwestern Argentina)
Turic et al. (1982) erected the name "Rectogloma" zaplensis for a problematic fossil found at Las Capillas River, 20 km northeast of San Salvador de Jujuy city (figure 1). The fossil was collected from beds belonging to the Lipeón Formation (Turner,1960), on the western flank of the Zapla range (Subandean Ranges). Based on the work of Antelo (1978), the Lipeón Formation was assigned to the Llandovery-Wenlock interval. The fossil was assigned to the problematic genus Rectogloma, described by Tuyl and Berckhemer (1914) for R. problematica but based on a more complete ornamentation and the presence of sinuous striations, which denotes its better preservation state, they defined a new species: "Rectogloma" zaplensis (Turic et al., 1982). A restudy of the specimen indicates that the fossil is a nautiloid cephalopod that can be assigned with reservation to the genus Dawsonoceras Hyatt, 1884.Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin
A review of the endocerid cephalopod Protocyptendoceras from the Floian (Lower Ordovician) of the Eastern Cordillera, Argentina
Ordovician cephalopods from Western Gondwana are still poorly known and published data is in need of systematic and stratigraphical revision. In this work, the endocerid proterocameroceratid Protocyptendoceras from the Floian of the Eastern Cordillera of Argentina is revised using new material from La Ciénaga, 5 km upstream from Purmamarca. The species P. corvalani and P. teicherti are considered to be junior synonyms of P. fuenzalidae, which is redescribed in detail and reillustrated. Specimens preserve adapical parts of isolated siphuncles, related here to the presence of endocones in a posterior portion. Evidently P. fuenzalidae had a nektobenthic mode of life in a shallow water environment, oriented horizontally. Its palaeobiogeographical affinities are mainly with Floian proterocameroceratids from Eastern Gondwana, such as Anthoceras decorum and the related genera Lobendoceras, Ventroloboceras, and Notocycloceras.Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin
Lamellorthoceratid cephalopods in the cold waters of Southwestern Gondwana: Evidences from the Lower Devonian of Argentina
Based on three specimens assigned to Arthrophyllum sp., the family Lamellorthoceratidae is reported from the Lower Devonian Talacasto Formation in the Precordillera Basin, central western Argentina. These Devonian cephalopods have been known only from low to mid palaeolatitudes and its presence in the cold water settings of southwestern Gondwana is notable. A nektonic mode of life, not strictly demersal but eventually pelagic, with a horizontal orientation of the conch is proposed for adults lamellorthoceratids, whereas a planktonic habit is suggested for juvenile individuals. These features would had allow their arrival to this southern basin, explaining their unusual presence in the Malvinokaffric Realm, and reinforcing the need of re-evaluate the distribution pattern of several groups of cephalopods.Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Rustán, Juan José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina. Universidad Nacional de La Rioja; Argentin
An Effelsberg HI study of the ISM around WR 126, WR 154 and WR 155
The neutral hydrogen distribution has been studied in the direction of three Galactic Wolf-Rayet (WR) stars using the 100 m Effelsberg radio telescope. Cavities in the HI distribution, regions of low HI emissivity, are observed over a 8-9 km s-1 velocity range for WR 126 (≡ST 2), WR 154 (≡HD 213049) and WR 155 (≡HD 214419). These minima are interpreted as the observable 21-cm HI line counterpart of interstellar bubbles created by the winds of the WR stars and their progenitors. The HI cavities are elongated structures depicting an axial ratio ranging from 1.3 (WR 155) to 3 (WR 126). The WR stars are always eccentric with respect to either the geometric centre of the HI cavity or the absolute minimum inside it. This offset ranges from 50% to 80% of the HI hole's minor axis. The major axis of these structures range from 13 (WR 155) to 27 pc (WR 126), while the missing HI mass amounts to 45-50 M⊙ (WR 126), 60 M⊙ (WR 155) and 85 M⊙ (WR 154).Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí
GS100-02-41: a new large HI shell in the outer part of the Galaxy
Massive stars have a profound effect on the surrounding interstellar medium.
They ionize and heat the neutral gas, and due to their strong winds, they swept
the gas up forming large HI shells. In this way, they generate a dense shell
where the physical conditions for the formation of new stars are given. The aim
of this study is to analyze the origin and evolution of the large HI shell
GS100-02-41 and its role in triggering star forming processes.To characterize
the shell and its environs, we carry out a multi-wavelength study. We analyze
he HI 21 cm line, the radio continuum, and infrared emission distributions. The
analysis of the HI data shows an expanding shell structure centred at (l, b) =
(100.6 deg, -2.04 deg) in the velocity range from -29 to -51.7 km/s.
We infer for GS100-02-41, a kinematical distance of 2.8 +/- 0.6 kpc. Several
massive stars belonging to Cep OB1 are located in projection within the large
HI, shell boundaries. The analysis of the radio continuum and infrared data
reveal that there is no continuum counterpart of the HI shell. On the other
hand, three slightly extended radio continuum sources are observed in
projection onto the dense HI shell. From their flux density determinations we
infer that they are thermal in nature. An analysis of the HI emission
distribution in the environs of these sources shows, for each of them, a region
of low emissivity having a good morphological correlation with the ionized gas
in a velocity range similar to the one where GS100-02-41 is detected. The
origin of GS100-02-41 could have been mainly due to the action of the Cep OB1
massive stars located inside the HI shell. The obtained age difference between
the HI shell and the HII regions, together with their relative location, led us
to conclude that the ionizing stars could have been created as a consequence of
the shell evolution.Comment: Accepted for publication in A&
The infrared and molecular environment surrounding the Wolf-Rayet star WR130
We present a study of the molecular CO gas and mid/far infrared radiation
arising from the environment surrounding the Wolf-Rayet (W-R) star 130. We use
the multi-wavelength data to analyze the properties of the dense gas and dust,
and its possible spatial correlation with that of Young Stellar Objects (YSOs).
We use CO J=1-0 data from the FCRAO survey as tracer of the molecular gas, and
mid/far infrared data from the recent WISE and Herschel space surveys to study
the dust continuum radiation and to identify a population of associated
candidate YSOs. The spatial distribution of the molecular gas shows a ring-like
structure very similar to that observed in the HI gas, and over the same
velocity interval. The relative spatial distribution of the HI and CO
components is consistent with a photo-dissociation region. We have identified
and characterized four main and distinct molecular clouds that create this
structure. Cold dust is coincident with the dense gas shown in the CO
measurements. We have found several cYSOs that lie along the regions with the
highest gas column density, and suggest that they are spatially correlated with
the shell. These are indicative of regions of star formation induced by the
strong wind and ionization of the WR star.Comment: 15 pages, 12 figures, 6 Tables. Accepted for publication in MNRA
Triggered star formation in a molecular shell created by a SNR?
We present a study of a new molecular shell, G126.1-0.8-14, using available
multiwavelegth Galactic plane surveys and optical Gemini observations. A well
defined shell-like structure is observed in the CO(1--0) line emission at (l,b)
= (126.1, -0.8), in the velocity range --10.5 to --15.5 km/s. The HI, emission
shows a region of low emissivity inside G126.1-0.8-14, while radio continuum
observations reveal faint non-thermal emission possibly related to this shell.
Optical spectra obtained with Gemini South show the existence of B-type stars
likely to be associated with G126.1-0.8-14. An estimate of the stellar wind
energy injected by these stars show that they alone can not be able to create
such a structure. On the other hand, one supernova explosion would provide
enough energy to generate the shell. Using the MSX, IRAS, and WISE Point Source
Catalogues we have found about 30 young stellar objects candidates, whose birth
could have been triggered by the expansion of G126.1-0.8-14. In this context,
Sh2-187 could be a consequence of the action on its surroundings of the most
massive (and thus most evolve) of the stars formed by the expanding molecular
shell.Comment: 13 pages, 10 figures, accepted in MNRA
GSH 91.5+2-114: A large HI shell in the outer part of the Galaxy
GSH91.5+2-114 is a large HI shell located in the outer Galaxy at a kinematic
distance of about 15 kpc. It was first identified in the Canadian Galactic
Plane Survey (CGPS) by Pineault et al. (2002) as being possibly associated with
objects possessing infrared colors which indicates strong stellar winds. The HI
shell has no obvious continuum counterpart in the CGPS radio images at 408 and
1420 MHz or in the IRAS images. We found no evidence for early-type massive
stars, most likely as a result of the large extinction that is expected for
this large distance. An analysis of the energetics and of the main physical
parameters of the HI shell shows that this shell is likely the result of the
combined action of the stellar winds and supernova explosions of many stars. We
investigate whether a number of slightly extended regions characterized by a
thermal radio continuum and located near the periphery of the HI shell could be
the result of star formation triggered by the expanding shell.Comment: Accepted for publication in A&A, October 2010. Some figures were
degraded to reduce file siz
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