2,201 research outputs found
Chandra X-ray observation of the HII region Gum 31 in the Carina Nebula complex
(abridged) We used the Chandra observatory to perform a deep (70 ksec) X-ray
observation of the Gum 31 region and detected 679 X-ray point sources. This
extends and complements the X-ray survey of the central Carina nebula regions
performed in the Chandra Carina Complex Project. Using deep near-infrared
images from our recent VISTA survey of the Carina nebula complex, our Spitzer
point-source catalog, and optical archive data, we identify counterparts for
75% of these X-ray sources. Their spatial distribution shows two major
concentrations, the central cluster NGC 3324 and a partly embedded cluster in
the southern rim of the HII region, but majority of X-ray sources constitute a
rather homogeneously distributed population of young stars. Our color-magnitude
diagram analysis suggests ages of ~1-2 Myr for the two clusters, whereas the
distributed population shows a wider age range up to ~10 Myr. We also identify
previously unknown companions to two of the three O-type members of NGC 3324
and detect diffuse X-ray emission in the region. Our results suggests that the
observed region contains about 4000 young stars in total. The distributed
population is probably part of the widely distributed population of ~ 1-10 Myr
old stars, that was identified in the CCCP area. This implies that the global
stellar configuration of the Carina nebula complex is a very extended stellar
association, in which the (optically prominent) clusters contain only a
minority of the stellar population.Comment: Accepted for publication in Astronomy & Astrophysics. A high quality
preprint is available at
http://www.usm.uni-muenchen.de/people/preibisch/publications.htm
Methods for Estimating Fluxes and Absorptions of Faint X-ray Sources
X-ray sources with very few counts can be identified with low-noise X-ray
detectors such as ACIS onboard the Chandra X-ray Observatory. These sources are
often too faint for parametric spectral modeling using well-established methods
such as fitting with XSPEC. We discuss the estimation of apparent and intrinsic
broad-band X-ray fluxes and soft X-ray absorption from gas along the line of
sight to these sources, using nonparametric methods. Apparent flux is estimated
from the ratio of the source count rate to the instrumental effective area
averaged over the chosen band. Absorption, intrinsic flux, and errors on these
quantities are estimated from comparison of source photometric quantities with
those of high S/N spectra that were simulated using spectral models
characteristic of the class of astrophysical sources under study. The concept
of this method is similar to the long-standing use of color-magnitude diagrams
in optical and infrared astronomy, with X-ray median energy replacing color
index and X-ray source counts replacing magnitude. Our nonparametric method is
tested against the apparent spectra of 2000 faint sources in the Chandra
observation of the rich young stellar cluster in the M17 HII region. We show
that the intrinsic X-ray properties can be determined with little bias and
reasonable accuracy using these observable photometric quantities without
employing often uncertain and time-consuming methods of non-linear parametric
spectral modeling. Our method is calibrated for thermal spectra characteristic
of stars in young stellar clusters, but recalibration should be possible for
some other classes of faint X-ray sources such as extragalactic AGN.Comment: Accepted for publication in The Astrophysical Journal. 39 pages, 15
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Chandra X-ray observation of the young stellar cluster NGC 3293 in the Carina Nebula Complex
We characterize the stellar population of the poorly explored young stellar
cluster NGC 3293 at the northwestern periphery of the Carina Nebula Complex, in
order to evaluate the cluster age and the mass function, and to test claims of
an abnormal IMF and a deficit of M <= 2.5 M_sun stars. We performed a deep (70
ksec) X-ray observation of NGC 3293 with Chandra and detected 1026 individual
X-ray point sources. We identify counterparts for 74% of the X-ray sources in
deep near-infrared images. Our data clearly show that NGC 3293 hosts a large
population of solar-mass stars, refuting claims of a lack of M <= 2.5 M_sun
stars. The analysis of the color magnitude diagram suggests an age of ~8-10 Myr
for the low-mass population of the cluster. There are at least 511 X-ray
detected stars with color magnitude positions that are consistent with young
stellar members within 7 arcmin of the cluster center. The number ratio of
X-ray detected stars in the 1-2 M_sun range versus the M >= 5 M_sun stars
(known from optical spectroscopy) is consistent with the expectation from a
normal field initial mass function. Most of the early B-type stars and 20% of
the later B-type stars are detected as X-ray sources. Our data shows that NGC
3293 is one of the most populous stellar clusters in the entire Carina Nebula
Complex. The cluster probably harbored several O-type stars, whose supernova
explosions may have had an important impact on the early evolution of the
Carina Nebula Complex.Comment: accepted for Astronomy & Astrophysic
European organization of telecom regulators and the impact on the pace of telecom innovations, Is EU modesty hampering innovation in telecom? Think global, act local…
In a recent political discussion about the optimal division of power and competence between national and European regulatory bodies for telecommunication markets, the European Commission, the Parliament and the Council fundamentally disagreed about the necessity and most suitable arrangement (if any) for a newly established regulatory body. In the end, a body of European Regulators for Electronic Communications (BEREC) resulted as a compromise. This paper initially describes the decision making process from which BEREC resulted and subsequently critically assesses the expected contribution of BEREC to the innovativeness of the internal telecommunication markets by confronting BEREC with innovation theory and general principles for effective market authority. One result of this analysis is that a more centralized model of market authority (as initially considered by the Commission) might contribute more to the innovative potential of the internal telecommunication markets than BEREC is expected to
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