ABSTRACT
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 H
α
emission in nearby M dwarfs. This includes 466 with photometric rotation periods. Stars with masses between 0.1 and 0.6
M
⊙
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 H
α
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
H
α
/
L
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
L
H
α
/
L
bol
. Our data also show a clear power-law decay in
L
H
α
/
L
bol
with Rossby number for slow rotators, with an index of −1.7 ± 0.1.
ABSTRACT The Kepler Space Telescope is currently searching for planets transiting stars along the ecliptic plane as part of its extended K2 mission. We processed the publicly released data from the ...first year of K2 observations (Campaigns 0, 1, 2, and 3) and searched for periodic eclipse signals consistent with planetary transits. Out of the 59,174 targets that we searched, we detect 234 planetary candidates around 208 stars. These candidates range in size from gas giants to smaller than the Earth, and range in orbital periods from hours to over a month. We conducted initial reconnaissance spectroscopy of 68 of the brighter candidate host stars, and present high-resolution optical spectra for these stars. We make all of our data products, including light curves, spectra, and vetting diagnostics available to users online.
Black hole binary systems with companion stars are typically found via their x-ray emission, generated by interaction and accretion. Noninteracting binaries are expected to be plentiful in the Galaxy ...but must be observed using other methods. We combine radial velocity and photometric variability data to show that the bright, rapidly rotating giant star 2MASS J05215658+4359220 is in a binary system with a massive unseen companion. The system has an orbital period of ~83 days and near-zero eccentricity. The photometric variability period of the giant is consistent with the orbital period, indicating star spots and tidal synchronization. Constraints on the giant's mass and radius imply that the unseen companion is Formula: see text solar masses, indicating that it is a noninteracting low-mass black hole or an unexpectedly massive neutron star.
Planets in young clusters are powerful probes of the evolution of planetary systems. Here we report the discovery of three planets transiting EPIC 247589423, a late-K dwarf in the Hyades ( 800 Myr) ...cluster, and robust detection limits for additional planets in the system. The planets were identified from their K2 light curves as part of our survey of young clusters and star-forming regions. The smallest planet has a radius comparable to Earth ( ), making it one of the few Earth-sized planets with a known, young age. The two larger planets are likely a mini-Neptune and a super-Earth, with radii of and , respectively. The predicted radial velocity signals from these planets are between 0.4 and 2 m s−1, achievable with modern precision RV spectrographs. Because the target star is bright (V = 11.2) and has relatively low-amplitude stellar variability for a young star (2-6 mmag), EPIC 247589423 hosts the best known planets in a young open cluster for precise radial velocity follow-up, enabling a robust test of earlier claims that young planets are less dense than their older counterparts.
Since 2014, NASA's K2 mission has observed large portions of the ecliptic plane in search of transiting planets and has detected hundreds of planet candidates. With observations planned until at ...least early 2018, K2 will continue to identify more planet candidates. We present here 275 planet candidates observed during Campaigns 0-10 of the K2 mission that are orbiting stars brighter than 13 mag (in Kepler band) and for which we have obtained high-resolution spectra (R = 44,000). These candidates are analyzed using the vespa package in order to calculate their false-positive probabilities (FPP). We find that 149 candidates are validated with an FPP lower than 0.1%, 39 of which were previously only candidates and 56 of which were previously undetected. The processes of data reduction, candidate identification, and statistical validation are described, and the demographics of the candidates and newly validated planets are explored. We show tentative evidence of a gap in the planet radius distribution of our candidate sample. Comparing our sample to the Kepler candidate sample investigated by Fulton et al., we conclude that more planets are required to quantitatively confirm the gap with K2 candidates or validated planets. This work, in addition to increasing the population of validated K2 planets by nearly 50% and providing new targets for follow-up observations, will also serve as a framework for validating candidates from upcoming K2 campaigns and the Transiting Exoplanet Survey Satellite, expected to launch in 2018.
IMPORTANCE: Neurophysiologic measures of early auditory information processing (EAP) are used as endophenotypes in genomic studies and biomarkers in clinical intervention studies. Research in ...schizophrenia has established correlations among measures of EAP, cognition, clinical symptoms, and functional outcome. Clarifying these associations by determining the pathways through which deficits in EAP affect functioning would suggest when and where to therapeutically intervene. OBJECTIVES: To characterize the pathways from EAP to outcome and to estimate the extent to which enhancement of basic information processing might improve cognition and psychosocial functioning in schizophrenia. DESIGN, SETTING, AND PARTICIPANTS: Cross-sectional data were analyzed using structural equation modeling to examine the associations among EAP, cognition, negative symptoms, and functional outcome. Participants were recruited from the community at 5 geographically distributed laboratories as part of the Consortium on the Genetics of Schizophrenia 2 from July 1, 2010, through January 31, 2014. This well-characterized cohort of 1415 patients with schizophrenia underwent EAP, cognitive, and thorough clinical and functional assessment. MAIN OUTCOME AND MEASURES: Mismatch negativity, P3a, and reorienting negativity were used to measure EAP. Cognition was measured by the Letter Number Span test and scales from the California Verbal Learning Test–Second Edition, the Wechsler Memory Scale–Third Edition, and the Penn Computerized Neurocognitive Battery. Negative symptoms were measured by the Scale for the Assessment of Negative Symptoms. Functional outcome was measured by the Role Functioning Scale. RESULTS: Participants included 1415 unrelated outpatients diagnosed with schizophrenia or schizoaffective disorder (mean SD age, 46 11 years; 979 males 69.2% and 619 white 43.7%). Early auditory information processing had a direct effect on cognition (β = 0.37, P < .001), cognition had a direct effect on negative symptoms (β = −0.16, P < .001), and both cognition (β = 0.26, P < .001) and experiential negative symptoms (β = −0.75, P < .001) had direct effects on functional outcome. The indirect effect of EAP on functional outcome was significant as well (β = 0.14, P < .001). Overall, EAP had a fully mediated effect on functional outcome, engaging general rather than modality-specific cognition, with separate pathways that involved or bypassed negative symptoms. CONCLUSIONS AND RELEVANCE: The data support a model in which EAP deficits lead to poor functional outcome via impaired cognition and increased negative symptoms. Results can be used to help guide mechanistically informed, personalized treatments and support the strategy of using EAP measures as surrogate end points in early-stage procognitive intervention studies.
Diseases of the brain involve early axon dysfunction that often precedes outright degeneration. Pruning of dendrites and their synapses represents a potential driver of axonopathy by reducing ...activity. Optic nerve degeneration in glaucoma, the world’s leading cause of irreversible blindness, involves early stress to retinal ganglion cell (RGC) axons from sensitivity to intraocular pressure (IOP). This sensitivity also influences survival of RGC dendrites and excitatory synapses in the retina. Here we tested in individual RGCs identified by type the relationship between dendritic organization and axon signaling to light following modest, short-term elevations in pressure. We found dendritic pruning occurred early, by 2 wk of elevation, and independent of whether the RGC responded to light onset (ON cells) or offset (OFF cells). Pruning was similarly independent of ON and OFF in the DBA/2J mouse, a chronic glaucoma model. Paradoxically, all RGCs, even those with significant pruning, demonstrated a transient increase in axon firing in response to the preferred light stimulus that occurred on a backdrop of generally enhanced excitability. The increased response was not through conventional presynaptic signaling, but rather depended on voltage-sensitive sodium channels that increased transiently in the axon. Pruning, axon dysfunction, and deficits in visual acuity did not progress between 2 and 4 wk of elevation. These results suggest neurodegeneration in glaucoma involves an early axogenic response that counters IOP-related stress to excitatory dendritic architecture to slow progression and maintain signaling to the brain. Thus, short-term exposure to elevated IOP may precondition the neural system to further insult.
In the central nervous system, glycogen-derived bioenergetic resources in astrocytes help promote tissue survival in response to focal neuronal stress. However, our understanding of the extent to ...which these resources are mobilized and utilized during neurodegeneration, especially in nearby regions that are not actively degenerating, remains incomplete. Here we modeled neurodegeneration in glaucoma, the world’s leading cause of irreversible blindness, and measured how metabolites mobilize through astrocyte gap junctions composed of connexin 43 (Cx43). We elevated intraocular pressure in one eye and determined how astrocyte-derived metabolites in the contralateral optic projection responded. Remarkably, astrocyte networks expand and redistribute metabolites along distances even 10 mm in length, donating resources from the unstressed to the stressed projection in response to intraocular pressure elevation. While resource donation improves axon function and visual acuity in the directly stressed region, it renders the donating tissue susceptible to bioenergetic, structural, and physiological degradation. Intriguingly, when both projections are stressed in a WT animal, axon function and visual acuity equilibrate between the two projections even when each projection is stressed for a different length of time. This equilibration does not occur when Cx43 is not present. Thus, Cx43-mediated astrocyte metabolic networks serve as an endogenous mechanism used to mitigate bioenergetic stress and distribute the impact of neurodegenerative disease processes. Redistribution ultimately renders the donating optic nerve vulnerable to further metabolic stress, which could explain why local neurodegeneration does not remain confined, but eventually impacts healthy regions of the brain more broadly.
Abstract
Irradiated Jovian atmospheres are complex and dynamic and can undergo temporal variations due to the close proximity of their parent stars. Of the Jovian planets that have been cataloged to ...date, KELT-9b is the hottest gas giant known, with an equilibrium temperature of 4050 K. We probe the temporal variability of transmission spectroscopic signatures from KELT-9b via a set of archival multiyear ground-based transit observations, performed with the TRES facility on the 1.5 m reflector at the Fred Lawrence Whipple Observatory. Our observations confirm past detections of Fe
i
, Fe
ii
, and Mg
i
over multiple epochs, in addition to excess absorption at H
α
, which is an indicator for ongoing mass loss. From our multiyear data set, the H
α
light curve consistently deviates from a standard transit and follows a “W” shape that is deeper near ingress and egress and shallower midtransit. To search for and quantify any seasonal variations that may be present, we parameterize a “cometary tail” model to fit for the H
α
transit. We find no detectable variations between the different observed epochs. Though a “cometary tail” describes the H
α
flux variations well, we note that such a scenario requires a high density of neutral hydrogen in the
n
= 2 excited state far beyond the planetary atmosphere. Other scenarios, such as center-to-limb variations larger than that expected from 1D atmosphere models, may also contribute to the observed H
α
transit shape. These multiepoch observations highlight the capabilities of small telescopes to provide temporal monitoring of the dynamics of exoplanet atmospheres.
Modern theories of galaxy formation predict that the Galactic stellar halo was hierarchically assembled from the accretion and disruption of smaller systems. This hierarchical assembly is expected to ...produce a high degree of structure in the combined phase and chemistry space; this structure should provide a relatively direct probe of the accretion history of our Galaxy. Revealing this structure requires precise 3D positions (including distances), 3D velocities, and chemistry for large samples of stars. The Gaia satellite is delivering proper motions and parallaxes for >1 billion stars to G 20. However, radial velocities and metallicities will only be available to G 15, which is insufficient to probe the outer stellar halo ( 10 kpc). Moreover, parallaxes will not be precise enough to deliver high-quality distances for stars beyond ∼10 kpc. Identifying accreted systems throughout the stellar halo therefore requires a large ground-based spectroscopic survey to complement Gaia. Here we provide an overview of the H3 Stellar Spectroscopic Survey, which will deliver precise stellar parameters and spectrophotometric distances for 200,000 stars to r = 18. Spectra are obtained with the Hectochelle instrument at the MMT, which is configured for the H3 Survey to deliver resolution R 23,000 spectra covering the wavelength range 5150-5300 . The survey is optimized for stellar halo science and therefore focuses on high Galactic latitude fields ( ), sparsely sampling 15,000 sq. degrees. Targets are selected on the basis of Gaia parallaxes, enabling very efficient selection of bona fide halo stars. The survey began in the fall of 2017 and has collected 88,000 spectra to-date. All of the data, including the derived stellar parameters, will eventually be made publicly available via the survey website: h3survey.rc.fas.harvard.edu.
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