132 research outputs found
STROOPWAFEL: Simulating rare outcomes from astrophysical populations, with application to gravitational-wave sources
Gravitational-wave observations of double compact object (DCO) mergers are
providing new insights into the physics of massive stars and the evolution of
binary systems. Making the most of expected near-future observations for
understanding stellar physics will rely on comparisons with binary population
synthesis models. However, the vast majority of simulated binaries never
produce DCOs, which makes calculating such populations computationally
inefficient. We present an importance sampling algorithm, STROOPWAFEL, that
improves the computational efficiency of population studies of rare events, by
focusing the simulation around regions of the initial parameter space found to
produce outputs of interest. We implement the algorithm in the binary
population synthesis code COMPAS, and compare the efficiency of our
implementation to the standard method of Monte Carlo sampling from the birth
probability distributions. STROOPWAFEL finds 25-200 times more DCO
mergers than the standard sampling method with the same simulation size, and so
speeds up simulations by up to two orders of magnitude. Finding more DCO
mergers automatically maps the parameter space with far higher resolution than
when using the traditional sampling. This increase in efficiency also leads to
a decrease of a factor 3-10 in statistical sampling uncertainty for the
predictions from the simulations. This is particularly notable for the
distribution functions of observable quantities such as the black hole and
neutron star chirp mass distribution, including in the tails of the
distribution functions where predictions using standard sampling can be
dominated by sampling noise.Comment: Accepted. Data and scripts to reproduce main results is publicly
available. The code for the STROOPWAFEL algorithm will be made publicly
available. Early inquiries can be addressed to the lead autho
THE Hα EMISSION OF NEARBY M DWARFS AND ITS RELATION TO STELLAR ROTATION
The high-energy emission from low-mass stars is mediated by the magnetic dynamo. Although the mechanisms by which fully convective stars generate large-scale magnetic fields are not well understood, it is clear that, as for solar-type stars, stellar rotation plays a pivotal role. We present 270 new optical spectra of low-mass stars in the Solar Neighborhood. Combining our observations with those from the literature, our sample comprises 2202 measurements or non-detections of Hα emission in nearby M dwarfs. This includes 466 with photometric rotation periods. Stars with masses between 0.1 and 0.6 M[subscript ⊙] are well-represented in our sample, with fast and slow rotators of all masses. We observe a threshold in the mass–period plane that separates active and inactive M dwarfs. The threshold coincides with the fast-period edge of the slowly rotating population, at approximately the rotation period at which an era of rapid rotational evolution appears to cease. The well-defined active/inactive boundary indicates that Hα activity is a useful diagnostic for stellar rotation period, e.g., for target selection for exoplanet surveys, and we present a mass-period relation for inactive M dwarfs. We also find a significant, moderate correlation between L[suscript Hα]/L[subscript bol] and variability amplitude: more active stars display higher levels of photometric variability. Consistent with previous work, our data show that rapid rotators maintain a saturated value of LHα/Lbol. Our data also show a clear power-law decay in L[subscript Hα]/L[subscript bol] with Rossby number for slow rotators, with an index of −1.7 ± 0.1.National Science Foundation (U.S.). Astronomy and Astrophysics Postdoctoral Fellowship (Award AST-1602597
Progress in research on Tourette syndrome
Tourette syndrome (TS) is a heritable neuropsychiatric disorder commonly complicated by obsessions and compulsions, but defined by frequent unwanted movements (motor tics) and vocalizations (phonic tics) that develop in childhood or adolescence. In recent years, research on TS has progressed rapidly on several fronts. Inspired by the Fifth International Scientific Symposium on Tourette Syndrome, the articles in this special issue review advances in the phenomenology, epidemiology, genetics, pathophysiology, and treatment of TS
Pilot Testing Behavior Therapy for Chronic Tic Disorders in Neurology and Developmental Pediatrics Clinics
Comprehensive Behavioral Intervention for Tics (CBIT) is an efficacious treatment with limited regional availability. As neurology and pediatric clinics are often the first point of therapeutic contact for individuals with tics, the present study assessed preliminary treatment response, acceptability, and feasibility of an abbreviated version, modified for child neurology and developmental pediatrics clinics. Fourteen youth (9-17) with Tourette disorder across 2 child neurology clinics and one developmental pediatrics clinic participated in a small case series. Clinician-rated tic severity (Yale Global Tic Severity Scale) decreased from pre- to posttreatment, z = –2.0, P \u3c .05, r = –.48, as did tic-related impairment, z = –2.4, P \u3c .05, r = –.57. Five of the 9 completers (56%) were classified as treatment responders. Satisfaction ratings were high, and therapeutic alliance ratings were moderately high. Results provide guidance for refinement of this modified CBIT protocol
Spatial reorganization of putaminal dopamine D2-like receptors in cranial and hand dystonia
The putamen has a somatotopic organization of neurons identified by correspondence of firing rates with selected body part movements, as well as by complex, but organized, differential cortical projections onto putamen. In isolated focal dystonia, whole putaminal binding of dopamine D(2)-like receptor radioligands is quantitatively decreased, but it has not been known whether selected parts of the putamen are differentially affected depending upon the body part affected by dystonia. The radioligand [(18)F]spiperone binds predominantly to D(2)-like receptors in striatum. We hypothesized that the spatial location of [(18)F]spiperone binding within the putamen would differ in patients with dystonia limited to the hand versus the face, and we tested that hypothesis using positron emission tomography and magnetic resonance imaging. To address statistical and methodological concerns, we chose a straightforward but robust image analysis method. An automated algorithm located the peak location of [(18)F]spiperone binding within the striatum, relative to a brain atlas, in each of 14 patients with cranial dystonia and 8 patients with hand dystonia. The mean (left and right) |x|, y, and z coordinates of peak striatal binding for each patient were compared between groups by t test. The location of peak [(18)F]spiperone binding within the putamen differed significantly between groups (cranial dystonia z<hand dystonia z, p = 0.016). We conclude that in isolated focal dystonia, dopamine D(2)-like receptors are distributed differently in the putamen depending on the body part manifesting dystonia
HST survey of the Orion Nebula Cluster in the HO 1.4 m absorption band: I. A census of substellar and planetary mass objects
In order to obtain a complete census of the stellar and sub-stellar
population, down to a few M in the Myr old Orion Nebula
Cluster, we used the infrared channel of the Wide Field Camera 3 of the Hubble
Space Telescope with the F139M and F130N filters. These bandpasses correspond
to the m HO absorption feature and an adjacent line-free continuum
region. Out of detected sources, (about ) appear fainter
than m (Vega mag) in the F130N filter, a brightness corresponding to
the hydrogen-burning limit mass (M) at Myr. Of
these, however, only sources have a negative F130M-139N color index,
indicative of the presence of HO vapor in absorption, and can therefore be
classified as bona-fide M and L dwarfs, with effective temperatures T K at an assumed Myr cluster age. On our color-magnitude diagram, this
population of sources with HO absorption appears clearly distinct from the
larger background population of highly reddened stars and galaxies with
positive F130M-F139N color index, and can be traced down to the sensitivity
limit of our survey, m, corresponding to a Myr old
M, planetary mass object under about 2 magnitudes of visual
extinction. Theoretical models of the BT-Settl family predicting substellar
isochrones of and Myr (down to M) fail to reproduce
the observed HO color index at MM. We perform a
Bayesian analysis to determine extinction, mass and effective temperature of
each sub-stellar member of our sample, together with its membership
probability.Comment: Accepted for publication in the Astrophysical Journal. The resolution
of several figures has been downgraded to comply with the size limit of arXiv
submission
Mid-to-Late M Dwarfs Lack Jupiter Analogs
Cold Jovian planets play an important role in sculpting the dynamical
environment in which inner terrestrial planets form. The core accretion model
predicts that giant planets cannot form around low-mass M dwarfs, although this
idea has been challenged by recent planet discoveries. Here, we investigate the
occurrence rate of giant planets around low-mass (0.1-0.3M) M dwarfs.
We monitor a volume-complete, inactive sample of 200 such stars located within
15 parsecs, collecting four high-resolution spectra of each M dwarf over six
years and performing intensive follow-up monitoring of two candidate
radial-velocity variables. We use TRES on the 1.5 m telescope at the Fred
Lawrence Whipple Observatory and CHIRON on the Cerro Tololo Inter-American
Observatory 1.5 m telescope for our primary campaign, and MAROON-X on Gemini
North for high-precision follow-up. We place a 95%-confidence upper limit of
1.5% (68%-confidence limit of 0.57%) on the occurrence of sin1M giant planets out to the water snow line and provide additional
constraints on the giant planet population as a function of sin
and period. Beyond the snow line ( K K), we place
95%-confidence upper limits of 1.5%, 1.7%, and 4.4% (68%-confidence limits of
0.58%, 0.66%, and 1.7%) for 3MsinM,
0.8MsinM, and 0.3MsinM giant planets; i.e., Jupiter analogs are rare around
low-mass M dwarfs. In contrast, surveys of Sun-like stars have found that their
giant planets are most common at these Jupiter-like instellations.Comment: Accepted for publication in AJ; 19 pages, 5 figures, 2 table
Treatment Use Among Children with Tourette Syndrome Living in The United States, 2014
Treatment of Tourette syndrome (TS) can be complicated by changes over time in tic expression, severity, and co-occurring disorders. Using the 2014 National Survey of the Diagnosis and Treatment of ADHD and Tourette Syndrome, this study provides descriptive estimates of the use of behavioral interventions and medication among children living with TS. Parent-reported data on 115 children aged 5–17 years ever diagnosed with TS were analyzed to provide descriptive, unweighted results. Overall, 77.4% of children had current or past use of any TS treatment; 59.1% ever used behavioral interventions and 56.1% had ever taken TS medication. Children with moderate” or “severe” versus “mild” TS, ≥1 co-occurring disorders, and tics that interfered with functioning were significantly more likely to have used one or more TS treatments. Side effects were reported for 84.4% of children who took TS medication. Most parents of children with current TS (87.2%) were satisfied with the management of their child\u27s TS. However, parents of children with “moderate” or “severe” current TS were significantly more dissatisfied compared to parents of children with “mild” TS. Findings from this study could be used to inform efforts to support children living with TS and their families
DASCH Discovery of A Possible Nova-like Outburst in A Peculiar Symbiotic Binary
We present photometric and spectroscopic observations of a peculiar variable
(designated DASCH J075731.1+201735 or J0757) discovered from our DASCH project
using the digitized Harvard College Observatory archival photographic plates.
It brightened by about 1.5 magnitudes in B within a year starting in 1942, and
then slowly faded back to its pre-outburst brightness from 1943 to the 1950s.
The mean brightness level was stable before and after the outburst, and
ellipsoidal variations with a period of days are seen,
suggesting that the star is tidally distorted. Radial-velocity measurements
indicate that the orbit is nearly circular () with a
spectroscopic period that is the same as the photometric period. The binary
consists of a M0III star, and a
companion, very likely a white dwarf (WD). Unlike other symbiotic binaries,
there is no sign of emission lines or a stellar wind in the spectra. With an
outburst timescale of ~10 years and estimated B band peak luminosity M_B~0.7,
J0757 is different from any other known classic or symbiotic novae. The most
probable explanation of the outburst is Hydrogen shell-burning on the WD,
although an accretion-powered flare cannot be ruled out.Comment: 12 pages, 6 figures, accepted for publication in Ap
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