1,770 research outputs found
The Many Possible Interpretations of Microlensing Event OGLE-2002-BLG-055
Microlensing event OGLE-2002-BLG-055 is characterized by a smooth, slightly
asymmetric single-lens curve with an isolated, secure data point that is ~0.6
magnitudes brighter than neighboring points separated by a few days. It was
previously suggested that the single deviant data point and global asymmetry
were best explained by a planetary companion to the primary lens with mass
ratio log(q)=-3 to -2, and parallax effects induced by the motion of the Earth.
We revisit the interpretation of OGLE-2002-BLG-055, and show that the data can
be explained by wide variety of models. We find that the deviant data point can
be fit by a large number of qualitatively different binary-lens models whose
mass ratios range, at the ~3-sigma level, from log(q) ~ -4 to -1. This range is
consistent with a planet, brown dwarf, or M-dwarf companion for reasonable
primary masses of M> 0.8 M_sun. A subset of these binary-lens fits consist of a
family of continuously degenerate models whose mass ratios differ by an
order-of-magnitude, but whose light curves differ by <2% for the majority of
the perturbation. The deviant data point can also explained by a binary
companion to the source with secondary/primary flux ratio of ~1%. This model
has the added appeal that the global asymmetry is naturally explained by the
acceleration of the primary induced by the secondary. The binary-source model
yields a measurement of the Einstein ring radius projected on source plane of
\hat r_E=1.87 +/- 0.40 AU. OGLE-2002-BLG-055 is an extreme example that
illustrates the difficulties and degeneracies inherent in the interpretation of
weakly perturbed and/or poorly sampled microlensing light curves.Comment: 8 pages, 3 figures, 1 table. Minor changes. Accepted to ApJ, to
appear in the August 10, 2004 issue (v611
The Near-Infrared Photometric Properties of Bright Giants in the Central Regions of the Galactic Bulge
Images recorded through broad (J, H, K), and narrow (CO, and 2.2micron
continuum) band filters are used to investigate the photometric properties of
bright (K < 13.5) stars in a 6 x 6 arcmin field centered on the SgrA complex.
The giant branch ridgelines in the (K, J-K) and (K, H-K) color-magnitude
diagrams are well matched by the Baade's Window (BW) M giant sequence if the
mean extinction is A_K ~ 2.8 mag. Extinction measurements for individual stars
are estimated using the M_K versus infrared color relations defined by M giants
in BW, and the majority of stars have A_K between 2.0 and 3.5 mag. The
extinction is locally high in the SgrA complex, where A_K ~ 3.1 mag.
Reddening-corrected CO indices, CO_o, are derived for over 1300 stars with J,
H, and K brightnesses, and over 5300 stars with H and K brightnesses. The
distribution of CO_o values for stars with K_o between 11.25 and 7.25 can be
reproduced using the M_K versus CO_o relation defined by M giants in BW. The
data thus suggest that the most metal-rich giants in the central regions of the
bulge and in BW have similar photometric properties and 2.3micron CO strengths.
Hence, it appears that the central region of the bulge does not contain a
population of stars that are significantly more metal-rich than what is seen in
BW.Comment: 29 pages, including 14 figure
The Stellar Populations of NGC 3109: Another Dwarf Irregular Galaxy with a Population II Stellar Halo
We have obtained V and I-band photometry for about 17500 stars in the field
of the dwarf irregular galaxy NGC3109, located in the outskirts of the Local
Group. The photometry allows us to study the stellar populations present inside
and outside the disk of this galaxy. From the VI color-magnitude diagram we
infer metallicities and ages for the stellar populations in the main body and
in the halo of NGC3109. The stars in the disk of this galaxy have a wide
variety of ages, including very young stars with approximately 10^7 yr. Our
main result is to establish the presence of a halo consisting of population II
stars, extending out to about 4.5 arcmin (or 1.8 kpc) above and below the plane
of this galaxy. For these old stars we derive an age of > 10 Gyr and a
metallicity of [Fe/H] = -1.8 +/- 0.2. We construct a deep luminosity function,
obtaining an accurate distance modulus (m-M)_0 = 25.62 +/- 0.1 for this galaxy
based on the I-magnitude of the red giant branch (RGB) tip and adopting E(V-I)
= 0.05.Comment: Accepted for publication in the Astronomical Journal 23 pages, latex,
12 Figures (Fig 1 not available in electronic format
The visual orbits of the spectroscopic binaries HD 6118 and HD 27483 from the Palomar Testbed Interferometer
We present optical interferometric observations of two double-lined
spectroscopic binaries, HD 6118 and HD 27483, taken with the Palomar Testbed
Interferometer (PTI) in the K band. HD 6118 is one of the most eccentric
spectroscopic binaries and HD 27483 a spectroscopic binary in the Hyades open
cluster. The data collected with PTI in 2001-2002 allow us to determine
astrometric orbits and when combined with the radial velocity measurements
derive all physical parameters of the systems. The masses of the components are
2.65 +/- 0.27 M_Sun and 2.36 +/- 0.24 M_Sun for HD 6118 and 1.38 +/- 0.13 M_Sun
and 1.39 +/- 0.13 M_Sun for HD 27483. The apparent semi-major axis of HD 27483
is only 1.2 mas making it the closest binary successfully observed with an
optical interferometer.Comment: submitted to Ap
Ethical prescribing of psychotropic medications for people with neurodevelopmental disorders
Objectives People with neurodevelopmental disorders (NDDs) such as intellectual and developmental disabilities (IDD) and autism are subjected to restrictive practices like physical restraint and the overuse of psychotropic medications for challenging behaviour in the absence of a psychiatric disorder. This practice may lead to human rights violations. Rational and evidence-based shared decision-making for person-centred planning will help reduce this practice. Methods We have discussed in this paper the issue of the overmedication of people with NDD, explaining how this practice may violate the United Nations (UN) Convention on the Rights of Persons with Disabilities (CRPD). Results We have discussed how the following UN CRPD Articles may be affected by overmedication, including Article 15 (degrading treatment or punishment), 16 (abuse), 17 (the integrity of the person), and 25 (health). The other Articles that may be indirectly affected by this practice are 5 (equality and non-discrimination), 9 (accessibility), 19 (independent living and community inclusion), 21 (access to information), 24 (education), 26 (rehabilitation), 27 (work and employment), 28 (adequate living standard), and 30 (participation in recreation and leisure). Conclusions Overmedication of people with NDD, particularly the off-licence use of psychotropics for challenging behaviour, the side effects of these medications impacting the personâs quality of life are likely to violet several UN Articles on Rights of Persons with Disabilities. Following the right guidelines may help reduce these human rights violations
Near-Infrared Adaptive Optics Imaging of the Central Regions of Nearby Sc Galaxies: I. M33
Near-infrared images obtained with the Canada-France-Hawaii Telescope (CFHT)
Adaptive Optics Bonnette (AOB) are used to investigate the stellar content
within 18 arcsec of the center of the Local Group spiral galaxy M33. AGB stars
with near-infrared spectral-energy distributions similar to those of giants in
the solar neighborhood and Baade's Window are detected over most of the field.
The bolometric luminosity function (LF) of these stars has a discontinuity near
M_{bol} = -5.25, and comparisons with evolutionary tracks suggest that most of
the AGB stars formed in a burst of star formation 1 - 3 Gyr in the past. The
images are also used to investigate the integrated near-infrared photometric
properties of the nucleus and the central light concentration. The nucleus is
bluer than the central light concentration, in agreement with previous studies
at visible wavelengths. The CO index of the central light concentration 0.5
arcsec from the galaxy center is 0.05, which corresponds to [Fe/H] = -1.2 for
simple stellar systems. Hence, the central light concentration could not have
formed from the chemically-enriched material that dominates the present-day
inner disk of M33.Comment: 23 pages of text + 11 figures; to appear in A
Integral method coefficients for the ring-core technique to evaluate non-uniform residual stresses
The ring-core technique allows for the determination of non-uniform residual stresses from the surface up to relatively higher depths as compared to the hole-drilling technique. The integral method, which is usually applied to hole-drilling, can also be used for elaborating the results of the ring-core test since these two experimental techniques share the axisymmetric geometry and the 0°â45°â90° layout of the strain gage rosette. The aim of this article is to provide accurate coefficients which can be used for evaluating the residual stress distribution by the ring-core integral method. The coefficients have been obtained by elaborating the results of a very refined plane harmonic axisymmetric finite element model and verified with an independent three-dimensional model. The coefficients for small depth steps were initially provided, and then the values for multiple integer step depths were also derived by manipulating the high-resolution coefficient matrices, thus showing how the present results can be practically used for obtaining the residual stresses according to different depth sequences, even non-uniform. This analysis also allowed the evaluation of the eccentricity effect which turned out to be negligible due to the symmetry of the problem. An applicative example was reported in which the input of the experimentally measured relaxed strains was elaborated with different depth resolutions, and the obtained residual stress distributions were compared
Remnants of Sagittarius Dwarf Spheroidal Galaxy around the young globular cluster Palomar 12
Photometry of a large field around the young globular cluster Palomar 12 has
revealed the main-sequence of a low surface-brightness stellar system. This
main-sequence is indicative of a stellar population that varies significantly
in metallicity and/or age, but in the mean is more metal poor than Pal 12.
Under different assumptions for the properties of this population, we find
distances from the Sun in the range 17-24 kpc, which encompasses the distance
to Pal 12, kpc. The stellar system is also detected in a field
2\arcdeg North of Pal 12, which indicates it has a minimum diameter of
kpc. The orbit of Pal 12 (Dinescu et al. 2000), the color-magnitude
diagram of the stellar system, their positions on the sky, and their distances
suggest that they are debris from the tidal disruption of the Sgr dSph galaxy.
We discuss briefly the implications for the evolution of Sgr and the Galactic
halo.Comment: 16 pages, 2 figures, accepted for ApJ Letters. Some importante
changes after revision, including a new figur
Tracing out the Northern Tidal Stream of the Sagittarius Dwarf Spheoridal Galaxy
The main aim of this paper is to report two new detections of tidal debris in
the northern stream of the Sagittarius dwarf galaxy located at 45 arcdeg and 55
arcdeg from the center of galaxy. Our observational approach is based on deep
color-magnitude diagrams, that provides accurate distances, surface brightness
and the properties of stellar population of the studied region of this tidal
stream. The derived distances for these tidal debris wraps are 45 kpc and 54
kpc respectively.We also confirm these detections with numerical simulations of
the Sagittarius dwarf plus the Milky Way. The model reproduces the present
position and velocity of the Sagittarius main body and presents a long tidal
stream formed by tidal interaction with the Milky Way potential. This model is
also in good agreement with the available observations of the Sagittarius tidal
stream. We also present a method for estimating the shape of the Milky Way halo
potential using numerical simulations. From our simulations we obtain an
oblateness of the Milky Way dark halo potential of 0.85, using the current
database of distances and radial velocities of the Sagittarius tidal stream.
The color-magnitude diagram of the apocenter of Sagittarius shows that this
region of the stream shares the complex star formation history observed in the
main body of the galaxy. We present the first evidence for a gradient in the
stellar population along the stream, possibly correlated with its different
pericenter passages. (abridged)Comment: 43 pages (including 15 figures; for high resolution color figures,
please contact [email protected]). Submitted to Ap
The Evolved Red Stellar Contents of the Sculptor Group Galaxies NGC55, NGC300, and NGC7793
Deep J, H, and K images are used to probe the evolved stellar contents in the
central regions of the Sculptor group galaxies NGC55, NGC300, and NGC7793. The
brightest stars are massive red supergiants (RSGs) with K ~ 15 - 15.5. The peak
RSG brightness is constant to within ~0.5 mag in K, suggesting that NGC55,
NGC300, and NGC7793 are at comparable distances. Comparisons with bright RSGs
in the Magellanic Clouds indicate that the difference in distance modulus with
respect to the LMC is = 7.5. A rich population of asymptotic giant branch (AGB)
stars, which isochrones indicate have ages between 0.1 and 10 Gyr, dominates
the (K, J-K) color-magnitude diagram (CMD) of each galaxy. The detection of
significant numbers of AGB stars with ages near 10 Gyr indicates that the disks
of these galaxies contain an underlying old population. The CMDs and luminosity
functions reveal significant galaxy-to-galaxy variations in stellar content.
Star-forming activity in the central arcmin of NGC300 has been suppressed for
the past Gyr with respect to disk fields at larger radii. Nevertheless,
comparisons between fields within each galaxy indicate that star-forming
activity during intermediate epochs was coherent on spatial scales of a kpc or
more. A large cluster of stars, which isochrones suggest has an age near 100
Myr, is seen in one of the NGC55 fields. The luminosity function of the
brightest stars in this cluster is flat, as expected if a linear
luminosity-core mass relation is present.Comment: 30 pages, including 13 figure
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