5,807 research outputs found
Laser Guide Star Adaptive Optics Integral Field Spectroscopy of a Tightly Collimated Bipolar Jet from the Herbig Ae star LkHa 233
We have used the integral field spectrograph OSIRIS and laser guide star
adaptive optics at Keck Observatory to obtain high angular resolution (0.06"),
moderate spectral resolution (R ~ 3800) images of the bipolar jet from the
Herbig Ae star LkHa 233, seen in near-IR [Fe II] emission at 1.600 & 1.644
microns. This jet is narrow and tightly collimated, with an opening angle of
only 9 degrees, and has an average radial velocity of ~ 100 km/s. The jet and
counterjet are asymmetric, with the red-shifted jet much clumpier than its
counterpart at the angular resolution of our observations. The observed
properties are in general similar to jets seen around T Tauri stars, though it
has a relatively large mass flux of (1.2e-7 +- 0.3e-7) M_sun/year, near the
high end of the observed mass flux range around T Tauri stars. We also
spatially resolve an inclined circumstellar disk around LkHa 233, which
obscures the star from direct view. By comparison with numerical radiative
transfer disk models, we estimate the disk midplane to be inclined i = 65 +- 5
degrees relative to the plane of the sky. Since the star is seen only in
scattered light at near-infrared wavelengths, we detect only a small fraction
of its intrinsic flux. Because previous estimates of its stellar properties did
not account for this, either LkHa 233 must be located closer than the
previously believed, or its true luminosity must be greater than previously
supposed, consistent with its being a ~4 M_sun star near the stellar birthline.Comment: Accepted for publication in the Ap
Spiralling out of control: 3D hydrodynamical modelling of the colliding winds in Carinae
Three dimensional (3D) adaptive-mesh refinement (AMR) hydrodynamical
simulations of the wind-wind collision between the enigmatic super-massive star
\etacar and its mysterious companion star are presented which include radiative
driving of the stellar winds, gravity, optically-thin radiative cooling, and
orbital motion. Simulations with static stars with a periastron passage
separation reveal that the preshock companion star's wind speed is sufficiently
reduced that radiative cooling in the postshock gas becomes important,
permitting the runaway growth of non-linear thin shell (NTSI) instabilities
which massively distort the WCR. However, large-scale simulations which include
the orbital motion of the stars, show that orbital motion reduces the impact of
radiative inhibition, and thus increases the acquired preshock velocities. As
such, the postshock gas temperature and cooling time see a commensurate
increase, and sufficient gas pressure is preserved to stabilize the WCR against
catastrophic instability growth. We then compute synthetic X-ray spectra and
lightcurves and find that, compared to previous models, the X-ray spectra agree
much better with {\it XMM-Newton} observations just prior to periastron. The
narrow width of the 2009 X-ray minimum can also be reproduced. However, the
models fail to reproduce the extended X-ray mimimum from previous cycles. We
conclude that the key to explaining the extended X-ray minimum is the rate of
cooling of the companion star's postshock wind. If cooling is rapid then
powerful NTSIs will heavily disrupt the WCR. Radiative inhibition of the
companion star's preshock wind, albeit with a stronger radiation-wind coupling
than explored in this work, could be an effective trigger.Comment: 25 pages, 20 figures, accepted for publication in Ap
Detection of the compressed primary stellar wind in eta Carinae
A series of three HST/STIS spectroscopic mappings, spaced approximately one
year apart, reveal three partial arcs in [Fe II] and [Ni II] emissions moving
outward from eta Carinae. We identify these arcs with the shell-like
structures, seen in the 3D hydrodynamical simulations, formed by compression of
the primary wind by the secondary wind during periastron passages.Comment: Accepted for publication in the Astrophysical Journal Letter
Seroprevalence of rubella antibodies among antenatal patients in the Western Cape
Objectives. To determine the seroprevalence of rubella virus infection among antenatal patients aged between 15 and 45 years in the Western Cape province of South Africa, in order to provide data to determine the need for vaccination to protect women of childbearing age.Design. A cross-sectional study.Setting. Virology laboratory, Groote Schuur Hospital, National Health Laboratory Service (NHLS), South Africa.Subjects and methods. One thousand two hundred provincial serum specimens from participants in the 2003 Department of Health antenatal HIV /syphilis serosurvey were selected from the 4 districts of the Western Cape. The specimens were agestratified and screened qualitatively for rubellaimmunoglobulin G (IgG) antibodies by means of a commercial immunoassay during October 2004.Results. Within the Western Cape a total o£95.3% of women in the 15- 24-year age group, 97.5% in the 25 - 34-year group and 98% in the 35 - 45-year age group were immune to rubella. There was no statistically significant difference in the rate of rubella susceptibility between the 4 districts tested.Conclusions. The study is an important step in addressing the seroprevalence of rubella infection in women of childbearing age in South Africa. Further information is needed on rubella seroprevalence from the other provinces in South Africa as well as formal implementation of rubella and congenital rubella syndrome surveillance to determine the feasibility of routine rubella immunisation
Investigation of laser frequency stabilization
Frequency stabilization of far infrared lase
Adolescents Growing Up in Stressful Environments, Dual Diagnosis, and Sources of Success
This article considers the social and psychological challenges to youth in contemporary society. The authors examine the variety of social impediments that face youths in most of our social institutions, from schools and the juvenile justice system to the family. They underscore the need for prevention, health promotion, and comprehensive assessment. Further, they assert that ‘‘dual diagnosis’’ needs to be considered not as a ‘‘special population’’ but as the typical or common experience of at-risk youths once they are diagnosed at mental health centers or juvenile justice reception and diagnostic centers. They conclude that evidence-based assessment, intervention, prevention, and health promotion will start to unravel the matter of misdirected diagnosis and treatment. The articles in this special issue amply illustrate what can be done
On the changes in the physical properties of the ionized region around the Weigelt structures in Eta Carinae over the 5.54-yr spectroscopic cycle
We present HST/STIS observations and analysis of two prominent nebular
structures around the central source of Eta Carinae, the knots C and D. The
former is brighter than the latter for emission lines from intermediate or high
ionization potential ions. The brightness of lines from intermediate and high
ionization potential ions significantly decreases at phases around periastron.
We do not see conspicuous changes in the brightness of lines from low
ionization potential (<13.6 eV) that the total extinction towards the Weigelt
structures is that the total extinction towards the Weigelt structures is AsubV
=2/0. that the total extinction towards the Weigelt structures is AV = 2.0.
Weigelt C and D are characterized by an electron density of that the total
extinction towards the Weigelt structures is AV = 2.0. Weigelt C and D are
characterized by an electron density of 10exp6.9 cm-3 that does not
significantly change throughout the orbital cycle. The electron temperature
varies from 5500 K (around periastron) to 7200 K (around apastron). The
relative changes in the brightness of He I lines are well reproduced by the
variations in the electron temperature alone. We found that, at phases around
periastron, the electron temperature seems to be higher for Weigelt C than that
of D. The Weigelt structures are located close to the Homunculus equatorial
plane, at a distance of about 1240 AU from the central source. From the
analysis of proper motion and age, the Weigelt complex can be associated with
the equatorial structure called the Butterfly Nebula surrounding the central
binary system.Comment: 19 pages, 18 figure
X-rays and Protostars in the Trifid Nebula
The Trifid Nebula is a young HII region recently rediscovered as a
"pre-Orion" star forming region, containing protostars undergoing violent mass
ejections visible in optical jets as seen in images from the Infrared Space
Observatory and the Hubble Space Telescope. We report the first X-ray
observations of the Trifid nebula using ROSAT and ASCA. The ROSAT image shows a
dozen X-ray sources, with the brightest X-ray source being the O7 star, HD
164492, which provides most of the ionization in the nebula. We also identify
85 T Tauri star and young, massive star candidates from near-infrared colors
using the JHKs color-color diagram from the Two Micron All Sky Survey (2MASS).
Ten X-ray sources have counterpart near-infrared sources. The 2MASS stars and
X-ray sources suggest there are potentially numerous protostars in the young
HII region of the Trifid. ASCA moderate resolution spectroscopy of the
brightest source shows hard emission up to 10 keV with a clearly detected Fe K
line. The best model fit is a two-temperature (T = 1.2x10^6 K and 39x10^6 K)
thermal model with additional warm absorbing media. The hotter component has an
unusually high temperature for either an O star or an HII region; a typical
Galactic HII region could not be the primary source for such hot temperature
plasma and the Fe XXV line emission. We suggest that the hotter component
originates in either the interaction of the wind with another object (a
companion star or a dense region of the nebula) or from flares from deeply
embedded young stars.Comment: Accepted in ApJ (Oct, 20 issue, 2001
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