413 research outputs found
Globular Clusters as Tracers of Stellar Bimodality in Elliptical Galaxies: The Case of NGC 1399
Globular cluster systems (GCS) frequently show a bi-modal distribution of the
cluster integrated colours. This work explores the arguments to support the
idea that the same feature is shared by the diffuse stellar population of the
galaxy they are associated with. In the particular case of NGC 1399 the results
show that the galaxy brightness profile and colour gradient as well as the
behaviour of the cumulative globular cluster specific frequency, are compatible
with the presence of two dominant stellar populations, associated with the so
called "blue" and "red" globular cluster families. These globular families are
characterized by different intrinsic specific frequencies (defined in terms of
each stellar population): Sn=3.3 +/- 0.3 in the case of the red globulars and
Sn=14.3 +/- 2.5 for the blue ones. We stress that this result is not
necessarily conflicting with recent works that point out a clear difference
between the metallicity distribution of (resolved) halo stars and globulars
when comparing their number statistics. The inferred specific frequencies imply
that, in terms of their associated stellar populations, the formation of the
blue globulars took place with an efficiency about 6 times higher than that
corresponding to their red counterparts. The similarity of the spatial
distribution of the blue globulars with that inferred for dark matter, as well
as with that of the X ray emiting hot gas associated with NGC 1399, is
emphasized. The impact of a relatively unconspicuous low metallicity
population, that shares the properties of the blue globulars, as a possible
source of chemical enrichment early in the formation history of the galaxy is
also briefly discussed.Comment: 15 pages; MNRAS (accepted; October 2004
Alexandru Davila – The Project as Work of Art. The Father Complex
Taking as a central focus the complex figure of the famous Romanian playwright Alexandru Davila, this paper follows the line of his life and career, from his aristocratic origins to his family relations and from his revolutionary activity as an intransigent theatre director to the plays and literature he wrote. A special accent is put on his best text, Vlaicu Vodă [Prince Vlaicu] a historical play, classical in its construction but very modern due to the psychological refinement manifested by the protagonist, as well as from his doubly meaningful physiognomy – he was a voivode in times of dark adversity, but also, from an archetypal perspective, a tragic hero of certain historic immutabilities. Forced to act prudently under the threat of a catastrophic failure, Vlaicu capitalized, in a refined manner, the experience of the Romanian people itself, which had become accustomed, due to the hardships of history, to keep silent and endure in expectation of an occasion appropriate for action
The complex star cluster system of NGC 1316 (Fornax A)
This paper presents Gemini- high quality photometry for cluster
candidates in the field of NGC 1316 (Fornax A) as part of a study that also
includes GMOS spectroscopy. A preliminary discussion of the photometric data
indicates the presence of four stellar cluster populations with distinctive
features in terms of age, chemical abundance and spatial distribution. Two of
them seem to be the usually old (metal poor and metal rich) populations
typically found in elliptical galaxies. In turn, an intermediate-age (5 Gyr)
globular cluster population is the dominant component of the sample (as
reported by previous papers). We also find a younger cluster population with a
tentative age of 1 Gyr
Mapping the galaxy NGC 4486 (M87) through its Globular Cluster System
As shown in previous works, globular clusters can be used to trace the
overall structure of the diffuse stellar populations in early type galaxies if
the number of clusters per unit stellar mass depends on metallicity. In this
paper we further test this assumption in the galaxy NGC 4486 (M 87), by
combining several data sources. The results show that globular clusters allow
the mapping of the galaxy in terms of the surface brightness profile,
integrated colour gradient, chemical abundance, and mass to luminosity ratios
up to 1000 arcsec (or 80.4 kpc) from its centre (i.e. some 10 effective radii).
The analysis indicates the presence of a dominant high metallicity bulge
associated with the red globulars, whose ellipticity increases outwards, and of
a more flattened low metallicity halo connected with the blue globulars. The
chemical abundance gradient of the composite stellar population is remarkably
similar to that inferred from X ray observations of hot gas. The
mass-metallicity spectrum of the stellar population can, in principle, be
understood in terms of inhomogeneous enrichment models. In turn, the
distribution of the bluest GCs, and lowest metallicity halo stars, has an
intriguing similarity with that of dark matter, a feature shared with NGC 1399.
Also, in these two galaxies, the number of blue GCs per dark mass unit is
identical within the errors, \approx 1.0(\pm0.3) \times 10^{-9} . The total
stellar mass derived for NGC 4486 is 6.8(\pm1.1) \times 10^{11} M\odot with a
baryonic mass fraction fb = 0.08(\pm 0.01).Comment: 18 pages, 23 figure
About the linearity of the color-magnitude relation of early-type galaxies in the Virgo cluster
We revisit the color-magnitude relation (CMR) of the Virgo cluster early-type
galaxies in order to explore its alleged non-linearity. To this aim, we
reanalyze the relation already published from data obtained within the ACS
Virgo Cluster Survey of the Hubble Space Telescope, and perform our own
photometry and analysis of the images of the 100 early-type galaxies observed
as part of this survey. In addition, we compare our results with those reported
in the literature from data of the Sloan Digital Sky Survey. We have found that
when the brightest galaxies and untypical systems are excluded from the sample,
a linear relation arises in agreement with what is observed in other groups and
clusters. The central regions of the brightest galaxies also follow this
relation. In addition, we notice that Virgo contains at least four compact
elliptical galaxies besides the well known object VCC 1297 (NGC 4486B). Their
locations in the -luminosity diagram define a different trend to that
followed by normal early-type dwarf galaxies, setting an upper limit in
effective surface brightness and a lower limit in effective radius for their
luminosities. Based on the distribution of different galaxy sub-samples in the
color-magnitude and -luminosity diagrams we draw some conclusions on
their formation and the history of their evolution.Comment: 21 pages, 4 figures, 2 tables. Accepted for publication in Ap
A SLUGGS and Gemini/GMOS combined study of the elliptical galaxy M60: wide-field photometry and kinematics of the globular cluster system
We present new wide-field photometry and spectroscopy of the globular clusters (GCs) around NGC 4649 (M60), the third brightest galaxy in the Virgo cluster. Imaging of NGC 4649 was assembled from a recently obtained Hubble Space Telescope/Advanced Camera for Surveys mosaic, and new Subaru/Suprime-Cam and archival Canada-France- Hawaii Telescope/MegaCam data. About 1200 sources were followed up spectroscopically using combined observations from three multi-object spectrographs: Keck/Deep Imaging Multi-Object Spectrograph, Gemini/Gemini Multi-Object Spectrograph and Multiple Mirror Telescope/Hectospec. We confirm 431 unique GCs belonging to NGC 4649, a factor of 3.5 larger than previous data sets and with a factor of 3 improvement in velocity precision. We confirm significant GC colour bimodality and find that the red GCs are more centrally concentrated, while the blue GCs are more spatially extended. We infer negative GC colour gradients in the innermost 20 kpc and flat gradients out to large radii. Rotation is detected along the galaxy major axis for all tracers: blue GCs, red GCs, galaxy stars and planetary nebulae. We compare the observed properties of NGC 4649 with galaxy formation models. We find that formation via amajor merger between two gas-poor galaxies, followed by satellite accretion, can consistently reproduce the observations of NGC 4649 at different radii. We find no strong evidence to support an interaction between NGC 4649 and the neighbouring spiral galaxy NGC 4647. We identify interesting GC kinematic features in our data, such as counter-rotating subgroups and bumpy kinematic profiles, which encode more clues about the formation history of NGC 4649.La lista completa de autores que integran el documento puede consultarse en el archivo.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat
IGBT thermal stress reduction using advance control strategy
Next-generation advances in stress control strategy will enable renewable energies, such as solar energy, to become more reliable and available. Critical components, such as power electronics, present uncertainties to the system control in malfunctioning process, which reduces the target of more clean energy development and CO2 emission reduction. Thus, developing and harnessing sustainable energy requires mitigating the impact of the variability of the source of energy and the impact of the adaptive stress control deployed for the proportional, integral, derivative (PID) controller to minimize the thermal stress in the power switch insulated gate bipolar transistor (IGBT). In response to this challenge, a fuzzy linear matrix inequality (FLMI) PID controller proposes initiatives for customizing parameters of PID controller corresponding to the uncertainty of IGBTs. In this paper, the uncertainty of the boost converter has been evaluated in the dynamic of the LMI model and Takagi-Sugino (TS) has applied in closed loop control to overcome the instability of the Boost converter parameters.
Paper originally presented at the 5th International Conference in Through-life Engineering Services Cranfield University, 1st and 2nd November 2016
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