119 research outputs found
Constraining the Variability and Binary Fraction of Galactic Center Young Stars
We present constraints on the variability and binarity of young stars in the
central 10 arcseconds (~0.4 pc) of the Milky Way Galactic Center (GC) using
Keck Adaptive Optics data over a 12 year baseline. Given our experiment's
photometric uncertainties, at least 36% of our sample's known early-type stars
are variable. We identified eclipsing binary systems by searching for periodic
variability. In our sample of spectroscopically confirmed and likely early-type
stars, we detected the two previously discovered GC eclipsing binary systems.
We derived the likely binary fraction of main sequence, early-type stars at the
GC via Monte Carlo simulations of eclipsing binary systems, and find that it is
at least 32% with 90% confidence.Comment: Accepted for publication in Proceedings of IAU Symposium 322: The
Multi-Messenger Astrophysics of the Galactic Centre, 2 pages, 1 figur
High-Resolution, Mid-Infrared Color Temperature Mapping of the Central 10 Arcseconds of the Galaxy
The neighborhood of the Galactic black hole boasts a plethora of extended
interstellar gas and dust features as well as populations of compact
(unresolved, or marginally resolved) features such as the G objects. Most are
well manifested in the infrared. To disentangle and characterize the infrared
structure of extended features and identify compact sources, we used 3.8~m
(L' filter) data from the NIRC2 imager at the Keck Observatory and 8.6~m
(PAH1 filter) data from the VISIR imager at the Very Large Telescope (VLT) to
produce the highest-resolution mid-IR color-temperature map of the inner
half-parsec of the Galactic Center to date. From this map, we compile a catalog
of features that stand out from their background. In particular, we identify 33
compact sources that stand out against the local background temperature, 11 of
which are newly identified and are candidates for being members of the G
objects population. Additionally, we resolve and newly characterize the
morphology of several known extended features. These results prepare the way
for ongoing and future JWST studies that have access to a greater range of
mid-infrared wavelengths, and thus will allow for refined estimation of the
trends of dust temperatures.Comment: 22 pages, 14 figure
The Orbital Eccentricities of Directly Imaged Companions Using Observable-Based Priors: Implications for Population-level Distributions
The eccentricity of a sub-stellar companion is an important tracer of its
formation history. Directly imaged companions often present poorly constrained
eccentricities. A recently developed prior framework for orbit fitting called
''observable-based priors'' has the advantage of improving biases in derived
orbit parameters for objects with minimal phase coverage, which is the case for
the majority of directly imaged companions. We use observable-based priors to
fit the orbits of 21 exoplanets and brown dwarfs in an effort to obtain the
eccentricity distributions with minimized biases. We present the objects'
individual posteriors compared to their previously derived distributions,
showing in many cases a shift toward lower eccentricities. We analyze the
companions' eccentricity distribution at a population level, and compare this
to the distributions obtained with the traditional uniform priors. We fit a
Beta distribution to our posteriors using observable-based priors, obtaining
shape parameters and . This represents an approximately flat distribution of
eccentricities. The derived and parameters are consistent with
the values obtained using uniform priors, though uniform priors lead to a tail
at high eccentricities. We find that separating the population into high and
low mass companions yields different distributions depending on the
classification of intermediate mass objects. We also determine via simulation
that the minimal orbit coverage needed to give meaningful posteriors under the
assumptions made for directly imaged planets is 15% of the inferred
period of the orbit.Comment: Accepted for publication in AJ, 20 pages, 13 figure
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A Schrödinger Equation for Evolutionary Dynamics
We establish an analogy between the Fokker–Planck equation describing evolutionary landscape dynamics and the Schrödinger equation which characterizes quantum mechanical particles, showing that a population with multiple genetic traits evolves analogously to a wavefunction under a multi-dimensional energy potential in imaginary time. Furthermore, we discover within this analogy that the stationary population distribution on the landscape corresponds exactly to the ground-state wavefunction. This mathematical equivalence grants entry to a wide range of analytical tools developed by the quantum mechanics community, such as the Rayleigh–Ritz variational method and the Rayleigh–Schrödinger perturbation theory, allowing us not only the conduct of reasonable quantitative assessments but also exploration of fundamental biological inquiries. We demonstrate the effectiveness of these tools by estimating the population success on landscapes where precise answers are elusive, and unveiling the ecological consequences of stress-induced mutagenesis—a prevalent evolutionary mechanism in pathogenic and neoplastic systems. We show that, even in an unchanging environment, a sharp mutational burst resulting from stress can always be advantageous, while a gradual increase only enhances population size when the number of relevant evolving traits is limited. Our interdisciplinary approach offers novel insights, opening up new avenues for deeper understanding and predictive capability regarding the complex dynamics of evolving populations
A Schr\"odinger Equation for Evolutionary Dynamics
We establish an analogy between the Fokker-Planck equation describing
evolutionary landscape dynamics and the Schr\"{o}dinger equation which
characterizes quantum mechanical particles, showing how a population with
multiple genetic traits evolves analogously to a wavefunction under a
multi-dimensional energy potential in imaginary time. Furthermore, we discover
within this analogy that the stationary population distribution on the
landscape corresponds exactly to the ground-state wavefunction. This
mathematical equivalence grants entry to a wide range of analytical tools
developed by the quantum mechanics community, such as the Rayleigh-Ritz
variational method and the Rayleigh-Schr\"{o}dinger perturbation theory,
allowing us to not only make reasonable quantitative assessments but also
explore fundamental biological inquiries. We demonstrate the effectiveness of
these tools by estimating the population success on landscapes where precise
answers are elusive, and unveiling the ecological consequences of
stress-induced mutagenesis -- a prevalent evolutionary mechanism in pathogenic
and neoplastic systems. We show that, even in a unchanging environment, a sharp
mutational burst resulting from stress can always be advantageous, while a
gradual increase only enhances population size when the number of relevant
evolving traits is limited. Our interdisciplinary approach offers novel
insights, opening up new avenues for deeper understanding and predictive
capability regarding the complex dynamics of evolving populations
HIV-Associated TB in An Giang Province, Vietnam, 2001–2004: Epidemiology and TB Treatment Outcomes
BACKGROUND: Mortality is high in HIV-infected TB patients, but few studies from Southeast Asia have documented the benefits of interventions, such as co-trimoxazole (CTX), in reducing mortality during TB treatment. To help guide policy in Vietnam, we studied the epidemiology of HIV-associated TB in one province and examined factors associated with outcomes, including the impact of CTX use. METHODOLOGY/PRINCIPAL FINDINGS: We retrospectively abstracted data for all HIV-infected persons diagnosed with TB from 2001-2004 in An Giang, a province in southern Vietnam in which TB patients receive HIV counseling and testing. We used standard WHO definitions to classify TB treatment outcomes. We conducted multivariate analysis to identify risk factors for the composite outcome of death, default, or treatment failure during TB treatment. From 2001-2004, 637 HIV-infected TB patients were diagnosed in An Giang. Of these, 501 (79%) were male, 321 (50%) were aged 25-34 years, and the most common self-reported HIV risk factor was sex with a commercial sex worker in 221 (35%). TB was classified as smear-positive in 531 (83%). During TB treatment, 167 (26%) patients died, 9 (1%) defaulted, and 6 (1%) failed treatment. Of 454 patients who took CTX, 116 (26%) had an unsuccessful outcome compared with 33 (70%) of 47 patients who did not take CTX (relative risk, 0.4; 95% confidence interval [CI], 0.3-0.5). Adjusting for male sex, rural residence, TB smear status and disease location, and the occurrence of adverse events during TB treatment in multivariate analysis, the benefit of CTX persisted (adjusted odds ratio for unsuccessful outcome 0.1; CI, 0.1-0.3). CONCLUSIONS/SIGNIFICANCE: In An Giang, Vietnam, HIV-associated TB was associated with poor TB treatment outcomes. Outcomes were significantly better in those taking CTX. This finding suggests that Vietnam should consider applying WHO recommendations to prescribe CTX to all HIV-infected TB patients
Unprecedented Near-infrared Brightness and Variability of Sgr A*
The electromagnetic counterpart to the Galactic center supermassive black hole, Sgr A*, has been observed in the near-infrared for over 20 yr and is known to be highly variable. We report new Keck Telescope observations showing that Sgr A* reached much brighter flux levels in 2019 than ever measured at near-infrared wavelengths. In the K' band, Sgr A* reached flux levels of ~6 mJy, twice the level of the previously observed peak flux from >13,000 measurements over 130 nights with the Very Large Telescope and Keck Telescopes. We also observe a factor of 75 change in flux over a 2 hr time span with no obvious color changes between 1.6 and 2.1 μm. The distribution of flux variations observed this year is also significantly different than the historical distribution. Using the most comprehensive statistical model published, the probability of a single night exhibiting peak flux levels observed this year, given historical Keck observations, is less than 0.3%. The probability of observing flux levels that are similar to all four nights of data in 2019 is less than 0.05%. This increase in brightness and variability may indicate a period of heightened activity from Sgr A* or a change in its accretion state. It may also indicate that the current model is not sufficient to model Sgr A* at high flux levels and should be updated. Potential physical origins of Sgr A*'s unprecedented brightness may be from changes in the accretion flow as a result of the star S0-2's closest passage to the black hole in 2018, or from a delayed reaction to the approach of the dusty object G2 in 2014. Additional multi-wavelength observations will be necessary to both monitor Sgr A* for potential state changes and to constrain the physical processes responsible for its current variability
The Galactic Center with Roman
We advocate for a Galactic center (GC) field to be added to the Galactic
Bulge Time Domain Survey (GBTDS). The new field would yield high-cadence
photometric and astrometric measurements of an unprecedented 3.3
million stars toward the GC. This would enable a wide range of science cases,
such as finding star-compact object binaries that may ultimately merge as
LISA-detectable gravitational wave sources, constraining the mass function of
stars and compact objects in different environments, detecting populations of
microlensing and transiting exoplanets, studying stellar flares and variability
in young and old stars, and monitoring accretion onto the central supermassive
black hole. In addition, high-precision proper motions and parallaxes would
open a new window into the large-scale dynamics of stellar populations at the
GC, yielding insights into the formation and evolution of galactic nuclei and
their co-evolution with the growth of the supermassive black hole. We discuss
the possible trade-offs between the notional GBTDS and the addition of a GC
field with either an optimal or minimal cadence. Ultimately, the addition of a
GC field to the GBTDS would dramatically increase the science return of Roman
and provide a legacy dataset to study the mid-plane and innermost regions of
our Galaxy.Comment: 19 pages, 3 figures. Submitted to the NASA Roman Core Community
Surveys White Paper Cal
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