New multi-roll coronagraphic images of the HD181327 debris disk obtained using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope reveal the debris ring in its entirety at ...high signal-to-noise ratio and unprecedented spatial resolution. We present and apply a new multi-roll image processing routine to identify and further remove quasi-static point-spread function-subtraction residuals and quantify systematic uncertainties. We also use a new iterative image deprojection technique to constrain the true disk geometry and aggressively remove any surface brightness asymmetries that can be explained without invoking dust density enhancements/deficits. The measured empirical scattering phase function for the disk is more forward scattering than previously thought and is not well-fit by a Henyey-Greenstein function. The empirical scattering phase function varies with stellocentric distance, consistent with the expected radiation pressured-induced size segregation exterior to the belt. Within the belt, the empirical scattering phase function contradicts unperturbed debris ring models, suggesting the presence of an unseen planet. The radial profile of the flux density is degenerate with a radially varying scattering phase function; therefore estimates of the ring's true width and edge slope may be highly uncertain. We detect large scale asymmetries in the disk, consistent with either the recent catastrophic disruption of a body with mass >1% the mass of Pluto, or disk warping due to strong interactions with the interstellar medium.
We present new, near-infrared (1.1-2.4 m) high-contrast imaging of the debris disk around HD 15115 with the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system coupled with the Coronagraphic ...High Angular Resolution Imaging Spectrograph (CHARIS). The SCExAO/CHARIS resolves the disk down to ∼ 0 2 (rproj ∼ 10 au), a factor of ∼3-5 smaller than previous recent studies. We derive a disk position angle of PA ∼ 279 4-280 5 and an inclination of i ∼ 85 3-86.2 . While recent SPHERE/IRDIS imagery of the system could suggest a significantly misaligned two-ring disk geometry, CHARIS imagery does not reveal conclusive evidence for this hypothesis. Moreover, optimizing models of both one- and two-ring geometries using differential evolution, we find that a single ring having a Hong-like scattering phase function matches the data equally well within the CHARIS field of view ( 1″). The disk's asymmetry, well evidenced at larger separations, is also recovered; the west side of the disk appears, on average, around 0.4 mag brighter across the CHARIS bandpass between 0 25 and 1″. Comparing Space Telescope Imaging Spectrograph (STIS) 50CCD optical photometry (2000-10500 ) with CHARIS near-infrared photometry, we find a red (STIS/50CCD−CHARIS broadband) color for both sides of the disk throughout the 0 4-1″ region of overlap, in contrast to the blue color reported at similar wavelengths for regions exterior to ∼2″. Further, this color may suggest a smaller minimum grain size than previously estimated at larger separations. Finally, we provide constraints on planetary companions and discuss possible mechanisms for the observed inner disk flux asymmetry and color.
We observe a significant change in the TW Hya disk interior to 40 au via archival unpolarized multi-wavelength Hubble Space Telescope/STIS and NICMOS images with an inner working angle of 0".4 (22 ...au). Our images show the outer edge of a clearing at every wavelength with similar behavior, demonstrating that the feature is structural, rather than due to some property of polarized light in the disk. We compare our observations to those taken by Akiyama et al. and Rapson et al., and discuss the spectral evolution of the disk interior to 80 au. We construct a model with two gaps: one at 30 au and one at 80 au that fit the observed surface brightness profile but overpredicts the absolute brightness of the disk. Our models require an additional dimming to be consistent with observations, which we tentatively ascribe to shadowing. The gap structures seen in scattered light are spatially coincident with sub-millimeter detections of CO and N sub(2) H+, and are near expected condensation fronts of these molecular species, providing tentative evidence that the structures seen in scattered light may be correlated with chemical changes in the disk.
ABSTRACT We present the first images of four debris disks observed in scattered light around the young (4-250 Myr old) M dwarfs TWA 7 and TWA 25, the K6 star HD 35650, and the G2 star HD 377. We ...obtained these images by reprocessing archival Hubble Space Telescope NICMOS coronagraph data with modern post-processing techniques as part of the Archival Legacy Investigation of Circumstellar Environments program. All four disks appear faint and compact compared with other debris disks resolved in scattered light. The disks around TWA 25, HD 35650, and HD 377 appear very inclined, while TWA 7's disk is viewed nearly face-on. The surface brightness of HD 35650's disk is strongly asymmetric. These new detections raise the number of disks resolved in scattered light around M and late-K stars from one (the AU Mic system) to four. This new sample of resolved disks enables comparative studies of heretofore scarce debris disks around low-mass stars relative to solar-type stars.
Background
A multi-level county-wide campaign to reduce sugary drink consumption was associated with significant decreases in retail sales of soda and fruit drinks. The aim of the current study was ...to examine changes in adolescent beverage consumption during the campaign by race/ethnicity and neighborhood food environment.
Methods
Beverage consumption among adolescents was evaluated at four time points in a repeated cross-sectional survey of a racially and ethnically diverse sample of sixth graders (N = 13,129) from public middle schools in the county. Each school’s surrounding attendance zone (i.e., neighborhoods where students live) was characterized as providing high or low exposure to unhealthy food retail (e.g., convenience stores, fast-food restaurants). Logistic and multiple linear regression models were used to evaluate changes in beverage consumption over time by student race/ethnicity and high versus low unhealthy food exposure.
Results
Over the 5 years, there were significant declines in the overall share of students who reported daily sugary drink consumption (49.4 to 36.9%) and their reported daily calories from these products (220 to 158 calories). However, disparities were observed, with higher levels of consumption among Black and Hispanic youth and among youth living in neighborhoods with more unhealthy food retail. Notably, Black students living in healthier neighborhood food environments reported significant decreases in daily consumption and calories after 5 years, while Black students living in neighborhoods with more convenience stores and fast-food outlets did not.
Conclusion
These findings suggest that both race/ethnicity and neighborhood food environments are important considerations when designing interventions to reduce sugary drink consumption among adolescents.
We present Hubble Space Telescope Near-Infrared Camera and Multi-Object Spectrometer coronagraphic imaging polarimetry of the TW Hydrae protoplanetary disk. These observations simultaneously measure ...the total and polarized intensity, allowing direct measurement of the polarization fraction across the disk. In accord with the self-shadowing hypothesis recently proposed by Debes et al., we find that the total and polarized intensity of the disk exhibits strong azimuthal asymmetries at projected distances consistent with the previously reported bright and dark ring-shaped structures (∼45-99 au). The sinusoidal-like variations possess a maximum brightness at position angles near ∼268°-300° and are up to ∼28% stronger in total intensity. Furthermore, significant radial and azimuthal variations are also detected in the polarization fraction of the disk. In particular, we find that regions of lower polarization fraction are associated with annuli of increased surface brightness, suggesting that the relative proportion of multiple-to-single scattering is greater along the ring and gap structures. Moreover, we find strong (∼20%) azimuthal variation in the polarization fraction along the shadowed region of the disk. Further investigation reveals that the azimuthal variation is not the result of disk flaring effects, but is instead from a decrease in the relative contribution of multiple-to-single scattering within the shadowed region. Employing a two-layer scattering surface, we hypothesize that the diminished contribution in multiple scattering may result from shadowing by an inclined inner disk, which prevents direct stellar light from reaching the optically thick underlying surface component.
Large-scale spiral arms have been revealed in scattered light images of a few protoplanetary disks. Theoretical models suggest that such arms may be driven by and corotate with giant planets, which ...has called for remarkable observational efforts to look for them. By examining the rotation of the spiral arms for the MWC 758 system over a 10 year timescale, we are able to provide dynamical constraints on the locations of their perturbers. We present reprocessed Hubble Space Telescope (HST)/NICMOS F110W observations of the target in 2005, and the new Keck/NIRC2 L′-band observations in 2017. MWC 758's two well-known spiral arms are revealed in the NICMOS archive at the earliest observational epoch. With additional Very Large Telescope (VLT)/SPHERE data, our joint analysis leads to a pattern speed of at 3 for the two major spiral arms. If the two arms are induced by a perturber on a near-circular orbit, its best-fit orbit is at 89 au (0 59), with a 3 lower limit of 30 au (0 20). This finding is consistent with the simulation prediction of the location of an arm-driving planet for the two major arms in the system.
We present resolved images of the HR 4796A debris disk using the Magellan adaptive optics system paired with Clio-2 and VisAO. We detect the disk at 0.77 mum, 0.91 mum, 0.99 mum, 2.15 mum, 3.1 mum, ...3.3 mum, and 3.8 mum. We find that the deprojected center of the ring is offset from the star by 4.76 + or - 1.6 AU and that the deprojected eccentricity is 0.06 + or - 0.02, in general agreement with previous studies. We find that the average width of the ring is (ProQuest: Formulae and/or non-USASCII text omitted) ((ProQuest: Formulae and/or non-USASCII text omitted) AU), also comparable to previous measurements. Combining our new scattered light data with archival Hubble Space Telescope images at ~0.5-2 mum, along with previously unpublished Spitzer/MIPS thermal emission data and all other literature thermal data, we set out to constrain the chemical composition of the dust grains. After testing 19 individual root compositions and more than 8400 unique mixtures of these compositions, we find that good fits to the scattered light alone and thermal emission alone are discrepant, suggesting that caution should be exercised if fitting to only one or the other. When we fit to both data sets simultaneously, we find that silicates and organics are generally the most favored, while large abundances of water ice are usually not favored. These results suggest the HR 4796A dust grains are similar to interstellar dust and solar system comets, though improved modeling is necessary to place better constraints on the exact chemical composition of the dust.
We present new high-fidelity optical coronagraphic imagery of the inner ∼50 au of AU Mic's edge-on debris disk using the BAR5 occulter of the Hubble Space Telescope Imaging Spectrograph (HST/STIS) ...obtained on 2018 July 26-27. This new imagery reveals that "feature A," residing at a projected stellocentric separation of 14.2 au on the southeast side of the disk, exhibits an apparent "loop-like" morphology at the time of our observations. The loop has a projected width of 1.5 au and rises 2.3 au above the disk midplane. We also explored Transiting Exoplanet Survey Satellite photometric observations of AU Mic that are consistent with evidence of two starspot complexes in the system. The likely co-alignment of the stellar and disk rotational axes breaks degeneracies in detailed spot modeling, indicating that AU Mic's projected magnetic field axis is offset from its rotational axis. We speculate that small grains in AU Mic's disk could be sculpted by a time-dependent wind that is influenced by this offset magnetic field axis, analogous to co-rotating solar interaction regions that sculpt and influence the inner and outer regions of our own Heliosphere. Alternatively, if the observed spot modulation is indicative of a significant misalignment of the stellar and disk rotational axes, we suggest that the disk could still be sculpted by the differential equatorial versus polar wind that it sees with every stellar rotation.
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