5,064 research outputs found
New detections of H2O masers in planetary nebulae and post-AGB stars using the Robledo-70m antenna
Aims: We investigated the possible relationship between the evolutionary
stage of post-AGB stars and planetary nebulae (PNe) and the presence of water
masers in their envelopes.
Methods: We have used NASA's 70-m antenna in Robledo de Chavela (Spain) to
search for the water maser transition at 22235.08 MHz, towards a sample of 105
sources with IRAS colour characteristic of post-AGB stars and PNe at
declination >-32 deg. 83% of the sources in the sample are post-AGB stars, 15%
PNe or PN candidates, while only 2% seem to be HII regions.
Results: We have detected five water masers, of which four are reported for
the first time: two in PNe (IRAS 17443-2949 and IRAS 18061-2505), a ``water
fountain'' in a post-AGB star (IRAS 16552-3050), and one in a source previously
catalogued as a PN, but whose classification is uncertain (IRAS 17580-3111).
Conclusions: The unexpected detections of water masers in two objects among
the small subset of PNe led us to suggest that the PNe harbouring water masers
are a special type of massive, rapidly evolving PNe.Comment: 15 pages, 7 figures. Accepted for publication in Astronomy and
Astrophysic
Renewal of Grammatical Forms in the History of English
[Abstract] In the development of English, new relative pronouns (whwords) were introduced, while the relative pronouns used in Old English (se/seþe) underwent various restrictions of morphological nature (case, gender and number marking), thus tending to become progressively less frequently used. This paper attempts to describe the distribution of pronominal relativizers in Old and Middle English and reconstruct the conditions for their renewal
Nuevos horizontes en marketing: Relaciones intensas entre consumidor y marca
En este trabajo se exponen primero los principales avances en la disciplina de marketing en relación a los retos de investigación señalados por el Marketing Science Institute. Posteriormente, se aborda el tema de relaciones afectivas entre consumidor y marca. Se exponen los principales conceptos desde un punto de vista crítico con la investigación académica actual, destacándose la necesidad de formar equipos multidisciplinares de investigación que ayuden a las empresas a tomar decisiones y a entender las nuevas necesidades de los consumidores en el nuevo entorno de relaciones generado por las redes sociale
Indirect test of M-S circuits using multiple specification band guarding
Testing analog and mixed-signal circuits is a costly task due to the required test time targets and high end technical resources. Indirect testing methods partially address these issues providing an efficient solution using easy to measure CUT information that correlates with circuit performances. In this work, a multiple specification band guarding technique is proposed as a method to achieve a test target of misclassified circuits. The acceptance/rejection test regions are encoded using octrees in the measurement space, where the band guarding factors precisely tune the test decision boundary according to the required test yield targets. The generated octree data structure serves to cluster the forthcoming circuits in the production testing phase by solely relying on indirect measurements. The combined use of octree based encoding and multiple specification band guarding makes the testing procedure fast, efficient and highly tunable. The proposed band guarding methodology has been applied to test a band-pass Butterworth filter under parametric variations. Promising simulation results are reported showing remarkable improvements when the multiple specification band guarding criterion is used.Peer ReviewedPostprint (author's final draft
A Double Classification of Common Pitfalls in Ontologies
The application of methodologies for building ontologies has improved the ontology quality. However, such a quality is not totally guaranteed because of the difficulties involved in ontology modelling. These difficulties are related to the inclusion of anomalies or worst practices in the modelling. In this context, our aim in this paper is twofold: (1) to provide a catalogue of common worst practices, which we call pitfalls, and (2) to present a double classification of such pitfalls. These two products will serve in the ontology development in two ways: (a) to avoid the appearance of pitfalls in the ontology modelling, and (b) to evaluate and correct ontologies to improve their quality
An updated catalog of OH-maser-emitting planetary nebulae
Aims. We studied the characteristics of planetary nebulae (PNe) that show
both OH maser and radio continuum emission (hereafter OHPNe). These have been
proposed to be very young PNe, and therefore, they could be key objects for
understanding the formation and evolution of PNe. Methods. We consulted the
literature searching for interferometric observations of radio continuum and OH
masers toward evolved stars, including the information from several surveys. We
also processed radio continuum and OH maser observations toward PNe in the Very
Large Array data archive. The high positional accuracy provided by
interferometric observations allow us to confirm or reject the association
between OH maser and radio continuum emission. Results. We found a total of six
PNe that present both OH maser and radio continuum emissions, as confirmed with
radio interferometric observations. These are bona fide OHPNe. The confirmed
OHPNe present a bipolar morphology in resolved images of their ionized emission
at different wavelengths, suggesting that the OH maser emission in PNe is
related to nonspherical mass-loss phenomena. The OH maser spectra in PNe
present a clear asymmetry, tending to show blueshifted emission with respect to
the systemic velocity. Their infrared colors suggest that most of these objects
are very young PNe. OHPNe do not form a homogeneous group, and seem to
represent a variety of different evolutionary stages. We suggest that OH masers
pumped in the AGB phase may disappear during the post-AGB phase, but reappear
once the source becomes a PN and its radio continuum emission is amplified by
the OH molecules. Therefore, OH maser emission could last significantly longer
than the previously assumed 1000 yr after the end of the AGB phase. This maser
lifetime may be longer in PNe with more massive central stars, which ionize a
larger amount of gas in the envelope.Comment: 16 pages, 5 figures, 4 tables. Accepted for publication by Astronomy
& Astrophysic
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