19 research outputs found
On the Completeness of Reflex Astrometry on Extrasolar Planets near the Sensitivity Limit
We provide a preliminary estimate of the performance of reflex astrometry on
Earth-like planets in the habitable zones of nearby stars. In Monte Carlo
experiments, we analyze large samples of astrometric data sets with low to
moderate signal-to-noise ratios. We treat the idealized case of a single planet
orbiting a single star, and assume there are no non-Keplerian complications or
uncertainties. The real case can only be more difficult. We use periodograms
for discovery and least-squares fits for estimating the Keplerian parameters.
We find a completeness for detection compatible with estimates in the
literature. We find mass estimation by least squares to be biased, as has been
found for noisy radial-velocity data sets; this bias degrades the completeness
of accurate mass estimation. When we compare the true planetary position with
the position predicted from the fitted orbital parameters, at future times, we
find low completeness for an accuracy goal of 0.3 times the semimajor axis of
the planet, even with no delay following the end of astrometric observations.
Our findings suggest that the recommendation of the ExoPlanet Task Force
(Lunine et al. 2008) for "the capability to measure convincingly wobble
semi-amplitudes down to 0.2 as integrated over the mission lifetime," may
not be satisfied by an instrument characterized by the noise floor of the Space
Interferometry Mission, as. An important,
unsolved, strategic challenge for the exoplanetary science program is figuring
out how to predict the future position of an Earth-like planet with accuracy
sufficient to ensure the efficiency and success of the science operations for
follow-on spectroscopy, which would search for biologically significant
molecules in the atmosphere.Comment: v2: 16 pages, 4 figures; ApJ accepte
Stellar Astrophysics with a Dispersed Fourier Transform Spectrograph. II. Orbits of Double-lined Spectroscopic Binaries
We present orbital parameters for six double-lined spectroscopic binaries
(iota Pegasi, omega Draconis, 12 Bootis, V1143 Cygni, beta Aurigae, and Mizar
A) and two double-lined triple star systems (kappa Pegasi and eta Virginis).
The orbital fits are based upon high-precision radial velocity observations
made with a dispersed Fourier Transform Spectrograph, or dFTS, a new instrument
which combines interferometric and dispersive elements. For some of the
double-lined binaries with known inclination angles, the quality of our RV data
permits us to determine the masses M_1 and M_2 of the stellar components with
relative errors as small as 0.2%.Comment: 41 pages, 8 figures, accepted by A
Interferometric Observations of Explosive Variables: V838 Mon, Nova Aql 2005, and RS Oph
During the last two years we have used the Palomar Testbed Interferometer to
observe several explosive variable stars, including V838 Monocerotis, V1663
Aquilae and recently RS Ophiuchi. We observed V838 Monocerotis approximately 34
months after its eruption, and were able to resolve the ejecta. Observations of
V1663 Aql were obtained starting 9 days after peak brightness and continued for
10 days. We were able to resolve the milliarcsecond-scale emission and follow
the expansion of the nova photosphere. When combined with radial-velocity
information, these observations can be used to infer the distance to the nova.
Finally we have resolved the recurrent nova RS Oph and can draw some
preliminary conclusions regarding the emission morphology.Comment: 8 Pages, SPIE Astronomical Telescopes and Instrumentation 2006,
Advances in Stellar Interferometery, 6268-16
Prenatal Buprenorphine/Naloxone or Methadone Use on Neonatal Outcomes in Michigan
Background: Maternal opioid exposure during pregnancy has various effects on neonatal health. Buprenorphine/naloxone and methadone are examples of medications for opioid use disorder (MOUD) used for the treatment of opioid use disorder (OUD). Research comparing the impacts of these MOUD modalities on neonatal outcomes when used to treat pregnant people with OUD remains limited. We evaluated the differences in outcomes between neonates with in-utero exposure to buprenorphine/naloxone versus methadone.
Methodology: We performed a retrospective cohort chart review between October 15, 2008, and October 15, 2019, evaluating mother/neonate dyads at two medical centers in Michigan. The charts of female patients, aged 18+, with OUD and buprenorphine/naloxone or methadone treatment, were examined. The charts of the corresponding neonates were also examined. Multiple regression analysis was performed.
Results: In total, 343 mother/infant dyads were included: 99 patients were treated with buprenorphine/naloxone and 232 patients were treated with methadone. The buprenorphine/naloxone group had significant differences in maternal age, hepatitis status, asthma, gestational age in weeks, neonatal intensive care unit (NICU) length of stay (LOS), neonatal opioid withdrawal syndrome (NOWS) peak score, birth head circumference, and birth weight compared to the methadone group at baseline. Adjusted multivariable regression analysis demonstrated neonates with exposure to buprenorphine/naloxone had a NOWS peak score 3.079 points less (95% confidence interval (CI): -4.525, 1.633; p = 0.001) and NICU LOS 8.955 days less (95% CI: -14.399, -3.511; p = 0.001) than neonates exposed to methadone.
Conclusions: Neonates with in-utero exposure to buprenorphine/naloxone had significantly lower NOWS scores and shorter NICU LOS compared to neonates with in-utero exposure to methadone. These findings demonstrate that buprenorphine/naloxone is potentially a more favorable treatment for the reduction in metrics representing adverse neonatal outcomes in pregnant people with OUD than methadone
Detecting the Companions and Ellipsoidal Variations of RS CVn Primaries: II. omicron Draconis, a Candidate for Recent Low-Mass Companion Ingestion
To measure the stellar and orbital properties of the metal-poor RS CVn binary
o Draconis (o Dra), we directly detect the companion using interferometric
observations obtained with the Michigan InfraRed Combiner at Georgia State
University's Center for High Angular Resolution Astronomy (CHARA) Array. The
H-band flux ratio between the primary and secondary stars is the highest
confirmed flux ratio (370 +/- 40) observed with long-baseline optical
interferometry. These detections are combined with radial velocity data of both
the primary and secondary stars, including new data obtained with the
Tillinghast Reflector Echelle Spectrograph on the Tillinghast Reflector at the
Fred Lawrence Whipple Observatory and the 2-m Tennessee State University
Automated Spectroscopic Telescope at Fairborn Observatory. We determine an
orbit from which we find model-independent masses and ages of the components
(M_A = 1.35 +\- 0.05 M_Sun, M_B = 0.99 +\- 0.02 M_Sun, system age = 3.0 -\+ 0.5
Gyr). An average of a 23-year light curve of o Dra from the Tennessee State
University Automated Photometric Telescope folded over the orbital period newly
reveals eclipses and the quasi-sinusoidal signature of ellipsoidal variations.
The modeled light curve for our system's stellar and orbital parameters confirm
these ellipsoidal variations due to the primary star partially filling its
Roche lobe potential, suggesting most of the photometric variations are not due
to stellar activity (starspots). Measuring gravity darkening from the average
light curve gives a best-fit of beta = 0.07 +\- 0.03, a value consistent with
conventional theory for convective envelope stars. The primary star also
exhibits an anomalously short rotation period, which, when taken with other
system parameters, suggests the star likely engulfed a low-mass companion that
had recently spun-up the star.Comment: 14 pages, 13 figures, Accepted to Ap
Stellar Astrophysics with a Dispersed Fourier Transform Spectrograph. I. Instrument Description and Orbits of Single-lined Spectroscopic Binaries
We have designed and constructed a second-generation version of the Dispersed
Fourier Transform Spectrograph, or dFTS. This instrument combines a spectral
interferometer with a dispersive spectrograph to provide high-accuracy,
high-resolution optical spectra of stellar targets. The new version, dFTS2, is
based upon the design of our prototype, with several modifications to improve
the system throughput and performance. We deployed dFTS2 to the Steward
Observatory 2.3-meter Bok Telescope from June 2007 to June 2008, and undertook
an observing program on spectroscopic binary stars, with the goal of
constraining the velocity amplitude K of the binary orbits with 0.1% accuracy,
a significant improvement over most of the orbits reported in the literature.
We present results for radial velocity reference stars and orbit solutions for
single-lined spectroscopic binaries.Comment: accepted by Ap
Isolating pure compounds from seeds of Bocconia frutescens to test for anti-fungal activity
Bocconia frutescens is a Costa Rican pioneer plant whose seeds persist for tens to hundreds of years in the buried “soil seed bank.” Previous work in our lab has shown that the longevity of these seeds is a result of chemical defense against pathogens and predators. For example, Veldman et al. (2007) identified four alkaloids from the crude seed extract, three of which were highly toxic to arthropods. My work extended this testing to fungi, and showed that the alkaloid 6-methoxydihydrochelirythrine is largely responsible for toxicity to Pythium irregulare, a known plant pathogen. Interestingly, this was the one alkaloid isolated from B. frutescens by Veldman et al. (2007) that was not sigificantly toxic to arthropods. Ongoing work in our lab will test these alkaloids for toxicity to other common seed pathogens as well, and will estimate the proportion of total toxicity that is attributable to each of the alkaloids present