130 research outputs found
A method of open cluster membership determination
A new method for the determination of open cluster membership based on a
cumulative effect is proposed. In the field of a plate the relative x and y
coordinate positions of each star with respect to all the other stars are
added. The procedure is carried out for two epochs t_1 and t_2 separately, then
one sum is subtracted from another. For a field star the differences in its
relative coordinate positions of two epochs will be accumulated. For a cluster
star, on the contrary, the changes in relative positions of cluster members at
t_1 and t_2 will be very small. On the histogram of sums the cluster stars will
gather to the left of the diagram, while the field stars will form a tail to
the right. The procedure allows us to efficiently discriminate one group from
another. The greater the distance between t_1 and t_2 and the more cluster
stars present, the greater is the effect. The accumulation method does not
require reference stars, determination of centroids and modelling the
distribution of field stars, necessary in traditional methods. By the proposed
method 240 open clusters have been processed, including stars up to m<13. The
membership probabilities have been calculated and compared to those obtained by
the most commonly used Vasilevskis-Sanders method. The similarity of the
results acquired the two different approaches is satisfactory for the majority
of clusters.Comment: 10 pages, 5 figure
Analysis of Moon impact flashes detected during the 2012 and 2013 Perseids
We present the results of our Moon impact flashes detection campaigns
performed around the maximum activity period of the Perseid meteor shower in
2012 and 2013. Just one flash produced by a Perseid meteoroid was detected in
2012 because of very unfavourable geometric conditions, but 12 of these were
confirmed in 2013. The visual magnitude of the flashes ranged between 6.6 and
9.3. A luminous efficiency of 1.8 10 has been estimated for
meteoroids from this stream. According to this value, impactor masses would
range between 1.9 and 190 g. In addition, we propose a criterion to establish,
from a statistical point of view, the likely origin of impact flashes recorded
on the lunar surface.Comment: Accepted for publication in Astronomy and Astrophysics on March 11,
201
CCD Strömgren photometry of young reddened clusters
The capabilities of CCD uvby photometry for the study of reddened young clusters are investigated. Observations of four fields in the direction of the clusters Basel 1, Berkeley 86, NGC 6704, and NGC 6756, with a total of 1665 stars measured in at least the y and b bands, produce new estimates for the clusters parameters. The results are compared to those from previously published studies in different photometric systems showing good agreement in the values of color excess and distance modulus, with the exception of NGC 6756, for which an essentially larger distance is found. Furthermore, the ages estimated for this cluster, Basel 1, and NGC 6704 are found to be higher than previously assumed, in particular for the last one. The presence of red giants as cluster members is suggested in Basel 1, NGC 6704, and NGC 6756.Consejería de Educacion y Ciencia Junta de Andalucí
The 2011 October Draconids Outburst. II. Meteoroid Chemical Abundances from Fireball Spectroscopy
On October 8, 2011 the Earth crossed dust trails ejected from comet
21P/Giacobini-Zinner in the late 19th and early 20th Century. This gave rise to
an outburst in the activity of the October Draconid meteor shower, and an
international team was organized to analyze this event. The SPanish Meteor
Network (SPMN) joined this initiative and recorded the October Draconids by
means of low light level CCD cameras. In addition, spectroscopic observations
were carried out. Tens of multi-station meteor trails were recorded, including
an extraordinarily bright October Draconid fireball (absolute mag. -10.5) that
was simultaneously imaged from three SPMN meteor ob-serving stations located in
Andalusia. Its spectrum was obtained, showing a clear evolution in the relative
intensity of emission lines as the fireball penetrated deeper into the
atmosphere. Here we focus on the analysis of this remarkable spectrum, but also
discuss the atmospheric trajectory, atmospheric penetration, and orbital data
computed for this bolide which was probably released during
21P/Giacobini-Zinner return to perihelion in 1907. The spectrum is discussed
together with the tensile strength for the October Draconid meteoroids. The
chemical profile evolution of the main rocky elements for this extremely bright
bolide is compared with the elemental abundances obtained for 5 October
Draconid fireballs also recorded during our spectroscopic campaign but observed
only at a single station. Significant chemical heterogeneity between the small
meteoroids is found as we should expect for cometary aggregates being formed by
diverse dust components.Comment: Manuscript in press in Monthly Notices of the Royal Astronomical
Society. Accepted for publication in MNRAS on April 28th, 2013 Manuscript
Pages: 28 Tables: 5 Figures: 12. Manuscript associated: "The 2011 October
Draconids outburst. I. Orbital elements, meteoroid fluxes and
21P/Giacobini-Zinner delivered mass to Earth" by Trigo-Rodriguez et al. is
also in press in the same journa
OB Stars in the Solar Neighborhood I: Analysis of their Spatial Distribution
We present a newly-developed, three-dimensional spatial classification
method, designed to analyze the spatial distribution of early type stars within
the 1 kpc sphere around the Sun. We propose a distribution model formed by two
intersecting disks -the Gould Belt (GB) and the Local Galactic Disk (LGD)-
defined by their fundamental geometric parameters. Then, using a sample of
about 550 stars of spectral types earlier than B6 and luminosity classes
between III and V, with precise photometric distances of less than 1 kpc, we
estimate for some spectral groups the parameters of our model, as well as
single membership probabilities of GB and LGD stars, thus drawing a picture of
the spatial distribution of young stars in the vicinity of the Sun.Comment: 28 pages including 9 Postscript figures, one of them in color.
Accepted for publication in The Astronomical Journal, 30 January 200
The Northern χ -Orionid meteoroid stream and possible association with the potentially hazardous asteroid 2008XM1
We present new orbital data and dynamic results pointing towards the origin of the Northern χ -Orionid meteoroid stream, which is a part of the Taurid meteoroid complex. A new software package was developed to establish the potential parent bodies of meteoroid streams based on the similarity of their orbits. The analysis of a Northern χ -Orionid fireball observed on 2011 December 6 identified two potential parent bodies: the near-Earth object (NEO) 2002XM35 (previously proposed as the parent of this meteoroid stream) and the more recently discovered potentially hazardous asteroid 2008XM1. The calculation of the evolution of the orbital elements performed by using the Mercury 6 symplectic integrator supports the idea
that 2008XM1 is a better parent body. Our data sample was expanded by including also in the calculations the mean orbit of the χ -Orionid stream. The results are consistent with the fragmentation of a larger body in the past that could give rise to both NEOs and the Northern χ -Orionid stream. To confirm this, further observations to improve the orbital elements of these asteroids should be attempted before the objects are lost. The analysis of the emission spectrum recorded for this fireball supports a primitive nature for these meteoroids.Ministerio de Ciencia e Innovación AYA2009-13227, AYA2009-14000-C03- 01, AYA2011-26522CSIC 201050I043Junta de Andalucía P09-FQM-455
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