An Optical-Infrared Study of the Young Multipolar Planetary Nebula NGC 6644

High-resolution HST imaging of the compact planetary nebula NGC 6644 has revealed two pairs of bipolar lobes and a central ring lying close to the plane of the sky. From mid-infrared imaging obtained with the Gemini Telescope, we have found a dust torus which is oriented nearly perpendicular to one pair of the lobes. We suggest that NGC 6644 is a multipolar nebula and have constructed a 3-D model which allows the visualization of the object from different lines of sight. These results suggest that NGC 6644 may have similar intrinsic structures as other multipolar nebulae and the phenomenon of multipolar nebulosity may be more common than previously believed.Comment: 31 pages, 13 figures, accepted for publication in Ap

Automatic classification of spectra from the Infrared Astronomical Satellite (IRAS)

A new classification of Infrared spectra collected by the Infrared Astronomical Satellite (IRAS) is presented. The spectral classes were discovered automatically by a program called Auto Class 2. This program is a method for discovering (inducing) classes from a data base, utilizing a Bayesian probability approach. These classes can be used to give insight into the patterns that occur in the particular domain, in this case, infrared astronomical spectroscopy. The classified spectra are the entire Low Resolution Spectra (LRS) Atlas of 5,425 sources. There are seventy-seven classes in this classification and these in turn were meta-classified to produce nine meta-classes. The classification is presented as spectral plots, IRAS color-color plots, galactic distribution plots and class commentaries. Cross-reference tables, listing the sources by IRAS name and by Auto Class class, are also given. These classes show some of the well known classes, such as the black-body class, and silicate emission classes, but many other classes were unsuspected, while others show important subtle differences within the well known classes

Characterization of the visit-to-visit Stability of the GR700XD Wavelength Calibration for NIRISS/SOSS Observations

When utilizing the NIRISS/SOSS mode on JWST, the pupil wheel (tasked with orienting the GR700XD grism into the optical path) does not consistently settle into its commanded position resulting in a minor misalignment with deviations of a few fractions of a degree. These small offsets subsequently introduce noticeable changes in the trace positions of the NIRISS SOSS spectral orders between visits. This inconsistency, in turn, can lead to variations of the wavelength solution. In this report, we present the visit-to-visit characterization of the NIRISS GR700XD Wavelength Calibration for spectral orders 1 and 2. Employing data from Calibration Program 1512 (PI: Espinoza), which intentionally and randomly sampled assorted pupil wheel positions during observations of the A-star BD+60-1753, as well as data from preceding commissioning and calibration activities to model this effect, we demonstrate that the wavelength solution can fluctuate in a predictable fashion between visits by up to a few pixels. We show that via two independent polynomial regression models for spectral orders 1 and 2, respectively, using the measured x-pixel positions of known Hydrogen absorption features in the A-star spectra and pupil wheel positions as regressors, we can accurately predict the wavelength solution for a particular visit with an RMS error within a few tenths of a pixel. We incorporate these models in PASTASOSS, a Python package for predicting the GR700XD spectral traces, which now allows to accurately predict spectral trace positions and their associated wavelengths for any NIRISS/SOSS observation.Comment: 12 pages, package to predict wavelength solution for NIRISS/SOSS: https://github.com/spacetelescope/pastasos

Characterization of the visit-to-visit Stability of the GR700XD Spectral Traces for NIRISS/SOSS Observations

In this report, we present the results of our analysis of trace position changes during NIRISS/SOSS observations. We examine the visit-to-visit impact of the GR700XD pupil wheel (PW) position alignment on trace positions for spectral orders 1 and 2 using the data obtained to date. Our goal is to improve the wavelength solution by correlating the trace positions on the detector with the PW position angle. We find that there is a one-to-one correspondence between PW position and spectral trace rotation for both orders. This allowed us in turn to find an analytic model that is able to predict a trace position/shape as a function of PW position with sub-pixel accuracy of about ~0.1 pixels. Such a function can be used to predict the trace position in low signal-to-noise ratio cases, and/or as a template to track trace position changes as function of time in Time Series Observations (TSOs).Comment: 9 pages, package to predict spectral traces for NIRISS/SOSS: https://github.com/spacetelescope/pastasos

Unidentified infrared bands and the formation of PAHs around carbon stars

Although unidentified infrared bands (UIBs) have been observed in many astrophysical environments, there is one notable exception: carbon (C) stars. Only a handful of C stars have been shown to emit UIBs and most have hot companions. This makes C stars with hot companions an ideal location to investigate the emitters of the UIBs. PAHs are excited by absorption of single photons whose energy is then distributed over the whole molecule. These molecules then emit the energy at the characteristic wavelengths, but the precise wavelengths and strength ratios depend on the size, composition and charge state of the individual PAHs. Furthermore, the wavelength of photons needed to excite PAHs depends on their size and charge state. While small PAHs undoubtedly need higher energy (UV) photons, it has been suggested that large or ionized PAHS (\u3e100 C atoms) can be excited by visible or even near-IR photons. The lack of PAH emission from single carbon stars suggests that either PAHs do not form around C stars or that only small neutral grains form, which cannot be excited by a C star\u27s radiation field. There are two competing formation mechanisms for PAHs around C stars: (1) bottom-up where acetylene molecules react to form aromatic rings, building up to PAHs; or (2) top-down, where small carbon grains react with H atoms and desorb PAHs Using spatially resolved spectroscopic observations from Gemini/Michelle, of five carbon stars with hot companions, we investigate the circumstance under which PAH emission occurs and try to discriminate between formation mechanisms. © 2008 International Astronomical Union

An Infrared Imaging Study of the Bipolar Proto-Planetary Nebula IRAS 16594-4656

High-resolution mid-infrared images have been obtained in N-band and Q-band for the proto-planetary nebula IRAS 16594-4656. A bright equatorial torus and a pair of bipolar lobes can clearly be seen in the infrared images. The torus appears thinner at the center than at the edges, suggesting that it is viewed nearly edge-on. The infrared lobes correspond to the brightest lobes of the reflection nebula seen in the Hubble Space Telescope (HST) optical image, but with no sign of the point-symmetric structure seen in the visible image. The lobe structure shows a close correspondence with a molecular hydrogen map obtained with HST, suggesting that the dust emission in the lobes traces the distribution of the shocked gas. The shape of the bipolar lobes shows clearly that the fast outflow is still confined by the remnant circumstellar envelope of the progenitor asymptotic giant branch (AGB) star. However, the non-detection of the dust outside of the lobes suggests that the temperature of the dust in the AGB envelope is too low for it to be detected at 20 microns.Comment: Accepted by the Astrophysical Journa

State Regulation of Coverage Options Outside of the Affordable Care Act: Limiting the Risk to the Individual Market

ABSTRACTIssue: Certain forms of individual health coverage are not required to comply with the consumer protections of the Affordable Care Act (ACA). These "alternative coverage arrangements" — including transitional policies, short-term plans, health care sharing ministries, and association health plans — tend to have lower upfront costs and offer far fewer benefits than ACA-compliant insurance. While appealing to some healthy individuals, they are often unattractive, or unavailable, to people in less-than-perfect health. By leveraging their regulatory advantages to enroll healthy individuals, these alternatives to marketplace coverage may contribute to a smaller, sicker, and less stable ACA-compliant market. The Trump administration recently has acted to reduce federal barriers to these arrangements.Goal: To understand how states regulate coverage arrangements that do not comply with the ACA's individual health insurance market reforms.Methods: Analysis of the applicable laws, regulations, and guidance of the 50 states and the District of Columbia.Findings and Conclusions: No state's regulatory framework fully protects the individual market from adverse selection by the alternative coverage arrangements studied. However, states have the authority to ensure a level playing field among coverage options to promote market stability

Integration of Neural Architecture within a Finite Element Framework for Improved Neuromusculoskeletal Modeling

Neuromusculoskeletal (NMS) models can aid in studying the impacts of the nervous and musculoskeletal systems on one another. These computational models facilitate studies investigating mechanisms and treatment of musculoskeletal and neurodegenerative conditions. In this study, we present a predictive NMS model that uses an embedded neural architecture within a finite element (FE) framework to simulate muscle activation. A previously developed neuromuscular model of a motor neuron was embedded into a simple FE musculoskeletal model. Input stimulation profiles from literature were simulated in the FE NMS model to verify effective integration of the software platforms. Motor unit recruitment and rate coding capabilities of the model were evaluated. The integrated model reproduced previously published output muscle forces with an average error of 0.0435 N. The integrated model effectively demonstrated motor unit recruitment and rate coding in the physiological range based upon motor unit discharge rates and muscle force output. The combined capability of a predictive NMS model within a FE framework can aid in improving our understanding of how the nervous and musculoskeletal systems work together. While this study focused on a simple FE application, the framework presented here easily accommodates increased complexity in the neuromuscular model, the FE simulation, or both