7,441 research outputs found
A search for water maser emission toward obscured post-AGB star and planetary nebula candidates
Water maser emission at 22 GHz is a useful probe to study the transition
between the nearly spherical mass-loss in the AGB to a collimated one in the
post-AGB phase. In their turn, collimated jets in the post-AGB phase could
determine the shape of planetary nebulae (PNe) once photoionization starts. We
intend to find new cases of post-AGB stars and PNe with water maser emission,
including water fountains or water-maser-emitting PNe. We observed water maser
emission in a sample of 133 objects, with a significant fraction being post-AGB
and young PN candidate sources with strong obscuration. We detected this
emission in 15 of them, of which seven are reported here for the first time. We
identified three water fountain candidates: IRAS 17291-2147, with a total
velocity spread of ~96 km/s in its water maser components and two sources (IRAS
17021-3109 and IRAS 17348-2906) that show water maser emission outside the
velocity range covered by OH masers. We have also identified IRAS 17393-2727 as
a possible new water-maser-emitting PN. The detection rate is higher in
obscured objects (14%) than in those with optical counterparts (7%), consistent
with previous results. Water maser emission seems to be common in objects that
are bipolar in the near-IR (43% detection rate). The water maser spectra of
water fountain candidates like IRAS 17291-2147 show significantly less maser
components than others (e.g., IRAS 18113-2503). We speculate that most
post-AGBs may show water maser emission with wide enough velocity spread (> 100
km/s) when observed with enough sensitivity and/or for long enough periods of
time. Therefore, it may be necessary to single out a special group of "water
fountains", probably defined by their high maser luminosities. We also suggest
that the presence of both water and OH masers in a PN is a better tracer of its
youth, rather than the presence of just one of these species.Comment: To be published in Astronomy & Astrophysics. 16 pages, 1 figure
(spanning 5 pages). This version includes some minor language corrections and
fixes some errors in Table
Asignación de horarios de clase basado en los ritmos de aprendizaje de los estudiantes usando un algoritmo genético
The objective of this proposal is to implement a school day agenda focused on the learning rhythms of students of elementary and secondary schools using a genetic algorithm. The methodology of this proposal takes into account legal requirements and constraints on the assignment of teachers and classrooms in public educational institutions in Colombia. In addition, this proposal provides a set of constraints focused on cognitive rhythms and subjects are scheduled at the most convenient times according to the area of knowledge. The genetic algorithm evolves through a process of mutation and selection and builds a total solution based on the best solutions for each group. Sixteen groups in a school are tested and the results of class schedule assignments are presented. The quality of the solution obtained through the established approach is validated by comparing the results to the solutions obtained using another algorithm.El objetivo de esta propuesta es implementar una agenda de día escolar enfocada en los ritmos de aprendizaje de los estudiantes de escuelas primarias y secundarias utilizando un algoritmo genético. La metodología de esta propuesta tiene en cuenta los requisitos legales y las limitaciones en la asignación de maestros y aulas en instituciones educativas públicas en Colombia. Además, esta propuesta proporciona un conjunto de restricciones centradas en los ritmos cognitivos y los temas se programan en los momentos más convenientes según el área de conocimiento. El algoritmo genético evoluciona a través de un proceso de mutación y selección y construye una solución total basada en las mejores soluciones para cada grupo. Dieciséis grupos en una escuela se evalúan y se presentan los resultados de las tareas del horario de clases. La calidad de la solución obtenida a través del enfoque establecido se valida comparando los resultados con las soluciones obtenidas utilizando otro algoritmo
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Complete and Prolonged Response to Immune Checkpoint Blockade in POLE-Mutated Colorectal Cancer
Enid Robertson Logan Faculty Fellowship Fund6 month embargo; published online: 21 June 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
A system of three transiting super-Earths in a cool dwarf star
We present the detection of three super-Earths transiting the cool star
LP415-17, monitored by K2 mission in its 13th campaign. High resolution spectra
obtained with HARPS-N/TNG showed that the star is a mid-late K dwarf. Using
spectral synthesis models we infer its effective temperature, surface gravity
and metallicity and subse- quently determined from evolutionary models a
stellar radius of 0.58 R Sun. The planets have radii of 1.8, 2.6 and 1.9 R
Earth and orbital periods of 6.34, 13.85 and 40.72 days. High resolution images
discard any significant contamination by an intervening star in the line of
sight. The orbit of the furthest planet has radius of 0.18 AU, close to the
inner edge of the habitable zone. The system is suitable to improve our
understanding of formation and dynamical evolution of super-Earth systems in
the rocky - gaseous threshold, their atmospheres, internal structure,
composition and interactions with host stars.Comment: Accepted for publication in MNRAS Letter
Point Source Detection with Fully-Convolutional Networks: Performance in Realistic Simulations
Point sources (PS) are one of the main contaminants to the recovery of the
cosmic microwave background (CMB) signal at small scales, and their detection
is important for the next generation of CMB experiments. We develop a method
(PoSeIDoN) based on fully convolutional networks to detect PS in realistic
simulations, and we compare its performance against one of the most used PS
detection method, the Mexican hat wavelet 2 (MHW2). We produce realistic
simulations of PS taking into account contaminating signals as the CMB, the
cosmic infrared background, the Galactic thermal emission, the thermal
Sunyaev-Zel'dovich effect, and the instrumental and PS shot noises. We first
produce a set of training simulations at 217 GHz to train the network. Then we
apply both PoSeIDoN and the MHW2 to recover the PS in the validating
simulations at all 143, 217, and 353 GHz, comparing the results by estimating
the reliability, completeness, and flux density accuracy and by computing the
receiver operating characteristic curves. In the extra-galactic region with a
30{\deg} galactic cut, the network successfully recovers PS at 90% completeness
corresponding to 253, 126, and 250 mJy for 143, 217, and 353 GHz respectively.
The MHW2 with a 3 flux density detection limit recovers PS up to 181,
102, and 153 mJy at 90% completeness. In all cases PoSeIDoN produces a much
lower number of spurious sources with respect to MHW2. The results on spurious
sources for both techniques worsen when reducing the galactic cut to 10{\deg}.
Our results suggest that using neural networks is a very promising approach for
detecting PS, providing overall better results in dealing with spurious sources
with respect to usual filtering approaches. Moreover, PoSeIDoN gives
competitive results even at nearby frequencies where the network was not
trained.Comment: 12 pages, 6 figures, accepted Astronomy & Astrophysic
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