237 research outputs found
Time-Series Photometry of Stars in and around the Lagoon Nebula. I. Rotation Periods of 290 Low-Mass Pre-Main-Sequence Stars in NGC 6530
We have conducted a long-term, wide-field, high-cadence photometric
monitoring survey of ~50,000 stars in the Lagoon Nebula \ion{H}{2} region. This
first paper presents rotation periods for 290 low-mass stars in NGC 6530, the
young cluster illuminating the nebula, and for which we assemble a catalog of
infrared and spectroscopic disk indicators, estimated masses and ages, and
X-ray luminosities. The distribution of rotation periods we measure is broadly
uniform for 0.5 < P < 10 d; the short-period cutoff corresponds to breakup. We
observe no obvious bimodality in the period distribution, but we do find that
stars with disk signatures rotate more slowly on average. The stars' X-ray
luminosities are roughly flat with rotation period, at the saturation level
(). However, we find a significant
positive correlation between and co-rotation radius,
suggesting that the observed X-ray luminosities are regulated by centrifugal
stripping of the stellar coronae. The period-mass relationship in NGC 6530 is
broadly similar to that of the Orion Nebula Cluster (ONC), but the slope of the
relationship among the slowest rotators differs from that in the ONC and other
young clusters. We show that the slope of the period-mass relationship for the
slowest rotators can be used as a proxy for the age of a young cluster, and we
argue that NGC 6530 may be slightly younger than the ONC, making it a
particularly important touchstone for models of angular momentum evolution in
young, low-mass stars.Comment: 28 pages, 18 figures, Accepted for publication in ApJ. For a brief
video explaining the key results of this paper, see
http://www.youtube.com/user/OSUAstronomy#p/u/1/WarGh6GiWu
Gravitational vacuum polarization III: Energy conditions in the (1+1) Schwarzschild spacetime
Building on a pair of earlier papers, I investigate the various point-wise
and averaged energy conditions for the quantum stress-energy tensor
corresponding to a conformally-coupled massless scalar field in the in the
(1+1)-dimensional Schwarzschild spacetime. Because the stress-energy tensors
are analytically known, I can get exact results for the Hartle--Hawking,
Boulware, and Unruh vacua. This exactly solvable model serves as a useful
sanity check on my (3+1)-dimensional investigations wherein I had to resort to
a mixture of analytic approximations and numerical techniques. Key results in
(1+1) dimensions are: (1) NEC is satisfied outside the event horizon for the
Hartle--Hawking vacuum, and violated for the Boulware and Unruh vacua. (2) DEC
is violated everywhere in the spacetime (for any quantum state, not just the
standard vacuum states).Comment: 7 pages, ReV_Te
Gravitational vacuum polarization IV: Energy conditions in the Unruh vacuum
Building on a series of earlier papers [gr-qc/9604007, gr-qc/9604008,
gr-qc/9604009], I investigate the various point-wise and averaged energy
conditions in the Unruh vacuum. I consider the quantum stress-energy tensor
corresponding to a conformally coupled massless scalar field, work in the
test-field limit, restrict attention to the Schwarzschild geometry, and invoke
a mixture of analytical and numerical techniques. I construct a semi-analytic
model for the stress-energy tensor that globally reproduces all known numerical
results to within 0.8%, and satisfies all known analytic features of the
stress-energy tensor. I show that in the Unruh vacuum (1) all standard
point-wise energy conditions are violated throughout the exterior region--all
the way from spatial infinity down to the event horizon, and (2) the averaged
null energy condition is violated on all outgoing radial null geodesics. In a
pair of appendices I indicate general strategy for constructing semi-analytic
models for the stress-energy tensor in the Hartle-Hawking and Boulware states,
and show that the Page approximation is in a certain sense the minimal ansatz
compatible with general properties of the stress-energy in the Hartle-Hawking
state.Comment: 40 pages; plain LaTeX; uses epsf.sty (ten encapsulated postscript
figures); two tables (table and tabular environments). Should successfully
compile under both LaTeX 209 and the 209 compatibility mode of LaTeX2
A Giant Planet Undergoing Extreme-Ultraviolet Irradiation By Its Hot Massive-Star Host
The amount of ultraviolet irradiation and ablation experienced by a planet depends strongly on the temperature of its host star. Of the thousands of extrasolar planets now known, only six have been found that transit hot, A-type stars (with temperatures of 7,300–10,000 kelvin), and no planets are known to transit the even hotter B-type stars. For example, WASP-33 is an A-type star with a temperature of about 7,430 kelvin, which hosts the hottest known transiting planet, WASP-33b (ref. 1); the planet is itself as hot as a red dwarf star of type M (ref. 2). WASP-33b displays a large heat differential between its dayside and nightside2, and is highly inflated–traits that have been linked to high insolation3,4. However, even at the temperature of its dayside, its atmosphere probably resembles the molecule-dominated atmospheres of other planets and, given the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be substantially ablated over the lifetime of its star. Here we report observations of the bright star HD 195689 (also known as KELT-9), which reveal a close-in (orbital period of about 1.48 days) transiting giant planet, KELT-9b. At approximately 10,170 kelvin, the host star is at the dividing line between stars of type A and B, and we measure the dayside temperature of KELT-9b to be about 4,600 kelvin. This is as hot as stars of stellar type K4 (ref. 5). The molecules in K stars are entirely dissociated, and so the primary sources of opacity in the dayside atmosphere of KELT-9b are probably atomic metals. Furthermore, KELT-9b receives 700 times more extreme-ultraviolet radiation (that is, with wavelengths shorter than 91.2 nanometres) than WASP-33b, leading to a predicted range of mass-loss rates that could leave the planet largely stripped of its envelope during the main-sequence lifetime of the host star (ref. 6)
Dirty black holes: Quasinormal modes
In this paper, we investigate the asymptotic nature of the quasinormal modes
for "dirty" black holes -- generic static and spherically symmetric spacetimes
for which a central black hole is surrounded by arbitrary "matter" fields. We
demonstrate that, to the leading asymptotic order, the [imaginary] spacing
between modes is precisely equal to the surface gravity, independent of the
specifics of the black hole system.
Our analytical method is based on locating the complex poles in the first
Born approximation for the scattering amplitude. We first verify that our
formalism agrees, asymptotically, with previous studies on the Schwarzschild
black hole. The analysis is then generalized to more exotic black hole
geometries. We also extend considerations to spacetimes with two horizons and
briefly discuss the degenerate-horizon scenario.Comment: 15 pages; uses iopart.cls setstack.sty; V2: one additional reference
added, no physics changes; V3: two extra references, minor changes in
response to referee comment
Multi-modality machine learning predicting Parkinson's disease
Personalized medicine promises individualized disease prediction and treatment. The convergence of machine learning (ML) and available multimodal data is key moving forward. We build upon previous work to deliver multimodal predictions of Parkinson's disease (PD) risk and systematically develop a model using GenoML, an automated ML package, to make improved multi-omic predictions of PD, validated in an external cohort. We investigated top features, constructed hypothesis-free disease-relevant networks, and investigated drug-gene interactions. We performed automated ML on multimodal data from the Parkinson's progression marker initiative (PPMI). After selecting the best performing algorithm, all PPMI data was used to tune the selected model. The model was validated in the Parkinson's Disease Biomarker Program (PDBP) dataset. Our initial model showed an area under the curve (AUC) of 89.72% for the diagnosis of PD. The tuned model was then tested for validation on external data (PDBP, AUC 85.03%). Optimizing thresholds for classification increased the diagnosis prediction accuracy and other metrics. Finally, networks were built to identify gene communities specific to PD. Combining data modalities outperforms the single biomarker paradigm. UPSIT and PRS contributed most to the predictive power of the model, but the accuracy of these are supplemented by many smaller effect transcripts and risk SNPs. Our model is best suited to identifying large groups of individuals to monitor within a health registry or biobank to prioritize for further testing. This approach allows complex predictive models to be reproducible and accessible to the community, with the package, code, and results publicly available
Kaluza-Klein Induced Gravity Inflation
A D-dimensional induced gravity theory is studied carefully in a
dimensional Friedmann-Robertson-Walker space-time. We try to extract
information of the symmetry breaking potential in search of an inflationary
solution with non-expanding internal-space. We find that the induced gravity
model imposes strong constraints on the form of symmetry breaking potential in
order to generate an acceptable inflationary universe. These constraints are
analyzed carefully in this paper.Comment: 10 pages, title changed, corrected some typos, two additional
comments adde
KELT-16b: A Highly Irradiated, Ultra-short Period Hot Jupiter Nearing Tidal Disruption
We announce the discovery of KELT-16b, a highly irradiated, ultra-short period hot Jupiter transiting the relatively bright (V = 11.7) star TYC 2688-1839-1/KELT-16. A global analysis of the system shows KELT-16 to be an F7V star with K, , , , and . The planet is a relatively high-mass inflated gas giant with , , density g cm−3, surface gravity , and K. The best-fitting linear ephemeris is and day. KELT-16b joins WASP-18b, −19b, −43b, −103b, and HATS-18b as the only giant transiting planets with P \u3c 1 day. Its ultra-short period and high irradiation make it a benchmark target for atmospheric studies by the Hubble Space Telescope, Spitzer, and eventually the James Webb Space Telescope. For example, as a hotter, higher-mass analog of WASP-43b, KELT-16b may feature an atmospheric temperature–pressure inversion and day-to-night temperature swing extreme enough for TiO to rain out at the terminator. KELT-16b could also join WASP-43b in extending tests of the observed mass–metallicity relation of the solar system gas giants to higher masses. KELT-16b currently orbits at a mere ~1.7 Roche radii from its host star, and could be tidally disrupted in as little as a few ×105 years (for a stellar tidal quality factor of ). Finally, the likely existence of a widely separated bound stellar companion in the KELT-16 system makes it possible that Kozai–Lidov (KL) oscillations played a role in driving KELT-16b inward to its current precarious orbit
KELT-16b: A Highly Irradiated, Ultra-short Period Hot Jupiter Nearing Tidal Disruption
We announce the discovery of KELT-16b, a highly irradiated, ultra-short period hot Jupiter transiting the relatively bright (V = 11.7) star TYC 2688-1839-1/KELT-16. A global analysis of the system shows KELT-16 to be an F7V star with K and . The planet is a relatively high-mass inflated gas giant with density g cm-3, surface gravity , and K. The best-fitting linear ephemeris is and day. KELT-16b joins WASP-18b, -19b, -43b, -103b, and HATS-18b as the only giant transiting planets with P \u3c 1 day. Its ultra-short period and high irradiation make it a benchmark target for atmospheric studies by the Hubble Space Telescope, Spitzer, and eventually the James Webb Space Telescope. For example, as a hotter, higher-mass analog of WASP-43b, KELT-16b may feature an atmospheric temperature-pressure inversion and day-to-night temperature swing extreme enough for TiO to rain out at the terminator. KELT-16b could also join WASP-43b in extending tests of the observed mass-metallicity relation of the solar system gas giants to higher masses. KELT-16b currently orbits at a mere ∼1.7 Roche radii from its host star, and could be tidally disrupted in as little as a few ×105 years (for a stellar tidal quality factor of ). Finally, the likely existence of a widely separated bound stellar companion in the KELT-16 system makes it possible that Kozai-Lidov (KL) oscillations played a role in driving KELT-16b inward to its current precarious orbit
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