179 research outputs found
Statistical Confirmation of a Stellar Upper Mass Limit
We derive the expectation value for the maximum stellar mass (m_max) in an
ensemble of N stars, as a function of the IMF upper-mass cutoff (m_up) and N.
We statistically demonstrate that the upper IMF of the local massive star
census observed thus far in the Milky Way and Magellanic Clouds clearly
exhibits a universal upper mass cutoff around 120 - 200 M_sun for a Salpeter
IMF, although the result is more ambiguous for a steeper IMF.Comment: PDF, 5 pages, 4 figures. Accepted to the Astrophysical Journal
Letter
VLT/NACO near-infrared imaging and spectroscopy of N88A in the SMC
We present near-infrared imaging and spectroscopic high spatial resolution
observations of the SMC region N88 containing the bright, excited, extincted
and compact H II region N88A of size ~ 1 pc. To investigate its stellar content
and reddening, N88 was observed using spectroscopy and imagery in the JHKs- and
L'-band at a spatial resolution of ~ 0.1-0.3", using the VLT UT4 equipped with
the NAOS adaptive optics system. In order to attempt to establish if the origin
of the infra-red (IR) excess is due to bright nebulosity, circumstellar
material and/or local dust, we used Ks vs J-K colour-magnitude (CM) and JHK
colour-colour (CC) diagrams, as well as L' imagery.Our IR-data reveal in the
N88 area an IR-excess fraction of geq 30 per cent of the detected stars,as well
as an unprecedently detailed morphology of N88A. It consists of an embedded
cluster of ~3.5" (~ 1 pc) in diameter, of at least thirteen resolved stars
superposed with an unusual bright continuum centered on a very bright star. The
four brightest stars in this cluster lie red-ward of H-K geq 0.45 mag, and
could be classified as young stellar object (YSO) candidates. Four other
probable YSO candidates are also detected in N88 along a south-north bow-shaped
thin H2 filament at ~ 7" east of the young central bright star. At 0.2" east of
this star, a heavily embedded core is detected that could be a massive class I
protostar candidate. The 2.12 mu H2 image of N88A resembles a shell of diameter
~ 3" ~ 0.9 pc) centered on the bright star. The line ratios of H2 2-1 S(1) and
1-0 S(0) relative to 1-0 S(1), as well as the presence of high v lines, are
indicative of photodissociation regions, rather than shocks.Comment: 15 pages, 14 figures, accepted by Astronomy and Astrophysics, uses
pdflatex, aa.cl
Deconvolution with correct sampling
A new method for improving the resolution of astronomical images is
presented. It is based on the principle that sampled data cannot be fully
deconvolved without violating the sampling theorem. Thus, the sampled image
should not be deconvolved by the total Point Spread Function, but by a narrower
function chosen so that the resolution of the deconvolved image is compatible
with the adopted sampling. Our deconvolution method gives results which are, in
at least some cases, superior to those of other commonly used techniques: in
particular, it does not produce ringing around point sources superimposed on a
smooth background. Moreover, it allows to perform accurate astrometry and
photometry of crowded fields. These improvements are a consequence of both the
correct treatment of sampling and the recognition that the most probable
astronomical image is not a flat one. The method is also well adapted to the
optimal combination of different images of the same object, as can be obtained,
e.g., from infrared observations or via adaptive optics techniques.Comment: 22 pages, LaTex file + 10 color jpg and postscript figures. To be
published in ApJ, Vol 484 (1997 Feb.
Active star formation in N11B Nebula in the Large Magellanic Cloud: a sequential star formation scenario confirmed
The second largest HII region in the Large Magellanic Cloud, N11B has been
surveyed in the near IR.We present JHKs images of the N11B nebula.These images
are combined with CO(1-0) emission line data and with archival NTT and
HST/WFPC2 optical images to address the star formation activity of the
region.IR photometry of all the IR sources detected is given.We confirm that a
second generation of stars is currently forming in the N11B region. Our IR
images show the presence of several bright IR sources which appear located
towards the molecular cloud as seen from the CO emission in the area.Several of
these sources show IR colours with YSO characteristics and they are prime
candidates to be intermediate-mass Herbig Ae/Be stars.For the first time an
extragalactic methanol maser is directly associated with IR sources embedded in
a molecular core.Two IR sources are found at 2"(0.5 pc) of the methanol maser
reported position.Additionally, we present the association of the N11A compact
HII region to the molecular gas where we find that the young massive O stars
have eroded a cavity in the parental molecular cloud, typical of a champagne
flow. The N11 region turns out to be a very good laboratory for studying the
interaction of winds, UV radiation and molecular gas.Several photodissociation
regions are found.Comment: 11 figures, accepted in Astronomical Journal (April 2003), needs
AASTEX packag
Osteosarcoma growth on trabecular bone mimicking structures manufactured via laser direct write
This paper describes the direct laser write of a photocurable acrylate-based PolyHIPE (High Internal Phase Emulsion) to produce scaffolds with both macro- and microporosity, and the use of these scaffolds in osteosarco-ma-based 3D cell culture. The macroporosity was introduced via the application of stereolithography to produce a clas-sical woodpile structure with struts having an approximate diameter of 200 ?m and pores were typically around 500 ?m in diameter. The PolyHIPE retained its microporosity after stereolithographic manufacture, with a range of pore sizes typically between 10 and 60 ?m (with most pores between 20 and 30 ?m). The resulting scaffolds were suitable substrates for further modification using acrylic acid plasma polymerisation. This scaffold was used as a structural mimic of the trabecular bone and in vitro determination of biocompatibility using cultured bone cells (MG63) demon-strated that cells were able to colonise all materials tested, with evidence that acrylic acid plasma polymerisation im-proved biocompatibility in the long term. The osteosarcoma cell culture on the 3D printed scaffold exhibits different growth behaviour than observed on tissue culture plastic or a flat disk of the porous material; tumour spheroids are ob-served on parts of the scaffolds. The growth of these spheroids indicates that the osteosarcoma behave more akin to in vivo in this 3D mimic of trabecular bone. It was concluded that PolyHIPEs represent versatile biomaterial systems with considerable potential for the manufacture of complex devices or scaffolds for regenerative medicine. In particular, the possibility to readily mimic the hierarchical structure of native tissue enables opportunities to build in vitro models closely resembling tumour tissue
The ages of suspicion, diagnosis, amplification, and intervention in deaf children
Objectives: The present study sought to determine the average ages of suspicion, diagnosis, and amplification of profound hearing loss and intervention in deaf children and to compare at-risk and not-at-risk children based on the studied ages. Methods: This study was conducted on 86 children under 6 years of age with profound bilateral hearing loss in Newsha Aural Rehabilitation Center in Tehran from July to December 2005. Data were gathered through the completion of a questionnaire by the children's parents, and the children's medical and rehabilitative records were utilized in order to determine the kind and degree of hearing loss. Results: The mean ages of suspicion, diagnosis, amplification, and intervention were 12.6 ± 8.9, 15.2 ± 9.3, 20.5 ± 11.1, and 22.3 ± 11.6 months, respectively; there being statistically significant differences between them. 47.7 of the children were in the high-risk group, and statistically there were no significant differences between the at-risk and not-at-risk children in the studied ages. Of all the neonatal diseases investigated, hyperbilirubinemia was the most frequent (40.7), and there were also four cases of meningitis and six cases of measles. In terms of consanguinity, mating of first cousins was 41.9 and mating of second cousins and farther familial relationships was 14. After suspecting hearing loss in their children, the parents had visited physicians (57), audiologists (37.2), speech therapists (2.3), or other specialists (3.5) for the first time. The economic circumstances of the families had a significant bearing on the average ages of suspicion, diagnosis, amplification, and intervention. Conclusions: Despite the remarkable improvement in the average ages of suspicion, diagnosis, amplification, and intervention in comparison with those reported in a previous study carried out in Iran (2002), there is still noticeable difference between these ages and those suggested by the Joint Committee on Infant Hearing. © 2006 Elsevier Ireland Ltd. All rights reserved
Results of the ESO-SEST Key Programme on CO in the Magellanic Clouds. IX. The giant LMC HII region complex N11
We present maps and a catalogue containing the J=1-0 12CO parameters of 29
individual molecular clouds in the second-brightest LMC star formation complex,
N11. In the southwestern part of N11, molecular clouds occur in a ring or shell
surrounding the major OB star association LH9. In the northeastern part, a
chain of molecular clouds delineates the rim of one of the so-called supergiant
shells in the LMC. The well-defined clouds have dimensions close to those of
the survey beam (diameters of 25 pc or less). Some of the clouds were also
observed in J=2-1 12CO, and in the lower two transitions of 13CO. Clouds mapped
with a twice higher angular resolution in J=2-1 12CO show substructure with
dimensions once again comparable to those of the mapping beam. The few clouds
for which we could model physical parameters have fairly warm (T(kin) = 60 -
150 K) and moderately dense (n(H2) = 3000 cm-3) gas. The northeastern chain of
CO clouds, although lacking in diffuse intercloud emission, is characteristic
of the more quiescent regions of the LMC and appears to have been subject to
relatively little photo-processing. The clouds forming part of the southwestern
shell or ring, however, are almost devoid of diffuse intercloud emission and
also exhibit other characteristics of an extreme photon-dominated region (PDR).Comment: 14 pages; accepted for publication in A&
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