1,591 research outputs found
Promoting Public Health In The Context Of The “Obesity Epidemic”: False Starts And Promising New Directions
In the battle to combat obesity rates in the United States, several misconceptions have dominated policy initiatives. We address those misconceptions, including the notion that restrictive diets lead to long-term weight loss, that stigmatizing obesity is an effective strategy for promoting weight reduction, and that weight and physical health should be considered synonymous with one another. In offering correctives to each of these points, we draw on psychological science to suggest new policies that could be enacted at both the local and national levels. Instead of policies that rely solely on individual willpower, which is susceptible to failure, we recommend those that make use of environmental changes to reduce the amount of willpower necessary to achieve healthy behavior. Ultimately, the most effective policies will promote health rather than any arbitrary level of weight
Radial Trends in IMF-Sensitive Absorption Features in Two Early-Type Galaxies: Evidence for Abundance-Driven Gradients
Samples of early-type galaxies show a correlation between stellar velocity
dispersion and the stellar initial mass function (IMF) as inferred from
gravity-sensitive absorption lines in the galaxies' central regions. To search
for spatial variations in the IMF, we have observed two early-type galaxies
with Keck/LRIS and measured radial gradients in the strengths of absorption
features from 4000-5500 \AA and 8000-10,000 \AA. We present spatially
resolved measurements of the dwarf-sensitive spectral indices NaI (8190 \AA)
and Wing-Ford FeH (9915 \AA), as well as indices for species of H, C, CN,
Mg, Ca, TiO, and Fe. Our measurements show a metallicity gradient in both
objects, and Mg/Fe consistent with a shallow gradient in \alpha-enhancement,
matching widely observed trends for massive early-type galaxies. The NaI index
and the CN index at 4160 \AA exhibit significantly steeper gradients,
with a break at ( pc). Inside this radius
NaI strength increases sharply toward the galaxy center, consistent with a
rapid central rise in [Na/Fe]. In contrast, the ratio of FeH to Fe index
strength decreases toward the galaxy center. This behavior cannot be reproduced
by a steepening IMF inside if the IMF is a single power law.
While gradients in the mass function above may occur,
exceptional care is required to disentangle these IMF variations from the
extreme variations in individual element abundances near the galaxies' centers.Comment: Accepted for publication in ApJ. Updates from v1 include an expanded
comparison of measured index strengths to SPS models. 20 page body + 7 page
appendix + references. Includes 25 figure
Testing the Metal of Late-Type Kepler Planet Hosts with Iron-Clad Methods
It has been shown that F, G, and early K dwarf hosts of Neptune-sized planets
are not preferentially metal-rich. However, it is less clear whether the same
holds for late K and M dwarf planet hosts. We report metallicities of Kepler
targets and candidate transiting planet hosts with effective temperatures below
4500 K. We use new metallicity calibrations to determine [Fe/H] from visible
and near-infrared spectra. We find that the metallicity distribution of late K
and M dwarfs monitored by Kepler is consistent with that of the solar
neighborhood. Further, we show that hosts of Earth- to Neptune-sized planets
have metallicities consistent with those lacking detected planets and rule out
a previously claimed 0.2 dex offset between the two distributions at 6sigma
confidence. We also demonstrate that the metallicities of late K and M dwarfs
hosting multiple detected planets are consistent with those lacking detected
planets. Our results indicate that multiple terrestrial and Neptune-sized
planets can form around late K and M dwarfs with metallicities as low as 0.25
of the solar value. The presence of Neptune-sized planets orbiting such
low-metallicity M dwarfs suggests that accreting planets collect most or all of
the solids from the disk and that the potential cores of giant planets can
readily form around M dwarfs. The paucity of giant planets around M dwarfs
compared to solar-type stars must be due to relatively rapid disk evaporation
or a slower rate of core accretion, rather than insufficient solids to form a
core.Comment: 9 pages, 5 figures. Accepted to Ap
Virus isolation studies suggest short-term variations in abundance in natural cyanophage populations of the Indian Ocean
Cyanophage abundance has been shown to fluctuate over long timescales and with depth, but little is known about how it varies over short timescales. Previous short-term studies have relied on counting total virus numbers and therefore the phages which infect cyanobacteria cannot be distinguished from the total count.
In this study, an isolation-based approach was used to determine cyanophage abundance from water samples collected over a depth profile for a 24 h period from the Indian Ocean. Samples were used to infect Synechococcus sp. WH7803 and the number of plaque forming units (pfu) at each time point and depth were counted. At 10 m phage numbers were similar for most time-points, but there was a distinct peak in abundance at 0100 hours. Phage numbers were lower at 25 m and 50 m and did not show such strong temporal variation. No phages were found below this depth. Therefore, we conclude that only the abundance of phages in surface waters showed a clear temporal pattern over a short timescale. Fifty phages from a range of depths and time points were isolated and purified. The molecular diversity of these phages was estimated using a section of the phage-encoded psbD gene and the results from a phylogenetic analysis do not suggest that phages from the deeper waters form a distinct subgroup
Orbital Parameter Determination for Wide Stellar Binary Systems in the Age of Gaia
The orbits of binary stars and planets, particularly eccentricities and
inclinations, encode the angular momentum within these systems. Within stellar
multiple systems, the magnitude and (mis)alignment of angular momentum vectors
among stars, disks, and planets probes the complex dynamical processes guiding
their formation and evolution. The accuracy of the \textit{Gaia} catalog can be
exploited to enable comparison of binary orbits with known planet or disk
inclinations without costly long-term astrometric campaigns. We show that
\textit{Gaia} astrometry can place meaningful limits on orbital elements in
cases with reliable astrometry, and discuss metrics for assessing the
reliability of \textit{Gaia} DR2 solutions for orbit fitting. We demonstrate
our method by determining orbital elements for three systems (DS Tuc AB, GK/GI
Tau, and Kepler-25/KOI-1803) using \textit{Gaia} astrometry alone. We show that
DS Tuc AB's orbit is nearly aligned with the orbit of DS Tuc Ab, GK/GI Tau's
orbit might be misaligned with their respective protoplanetary disks, and the
Kepler-25/KOI-1803 orbit is not aligned with either component's transiting
planetary system. We also demonstrate cases where \textit{Gaia} astrometry
alone fails to provide useful constraints on orbital elements. To enable
broader application of this technique, we introduce the python tool
\texttt{lofti\_gaiaDR2} to allow users to easily determine orbital element
posteriors.Comment: 18 pages, 10 figures, accepted for publication in Ap
Magnetic inflation and stellar mass. V. Intensification and saturation of M-dwarf absorption lines with Rossby number
In young Sun-like stars and field M-dwarf stars, chromospheric and coronal magnetic activity indicators such as Hα, X-ray, and radio emission are known to saturate with low Rossby number (Ro lesssim 0.1), defined as the ratio of rotation period to convective turnover time. The mechanism for the saturation is unclear. In this paper, we use photospheric Ti i and Ca i absorption lines in the Y band to investigate magnetic field strength in M dwarfs for Rossby numbers between 0.01 and 1.0. The equivalent widths of the lines are magnetically enhanced by photospheric spots, a global field, or a combination of the two. The equivalent widths behave qualitatively similar to the chromospheric and coronal indicators: we see increasing equivalent widths (increasing absorption) with decreasing Ro and saturation of the equivalent widths for Ro lesssim 0.1. The majority of M dwarfs in this study are fully convective. The results add to mounting evidence that the magnetic saturation mechanism occurs at or beneath the stellar photosphere.Published versio
A physically motivated and empirically calibrated method to measure effective temperature, metallicity, and Ti abundance of M dwarfs
The ability to perform detailed chemical analysis of Sun-like F-, G-, and
K-type stars is a powerful tool with many applications including studying the
chemical evolution of the Galaxy and constraining planet formation theories.
Unfortunately, complications in modeling cooler stellar atmospheres hinders
similar analysis of M-dwarf stars. Empirically-calibrated methods to measure M
dwarf metallicity from moderate-resolution spectra are currently limited to
measuring overall metallicity and rely on astrophysical abundance correlations
in stellar populations. We present a new, empirical calibration of synthetic M
dwarf spectra that can be used to infer effective temperature, Fe abundance,
and Ti abundance. We obtained high-resolution (R~25,000), Y-band (~1 micron)
spectra of 29 M dwarfs with NIRSPEC on Keck II. Using the PHOENIX stellar
atmosphere modeling code (version 15.5), we generated a grid of synthetic
spectra covering a range of temperatures, metallicities, and
alpha-enhancements. From our observed and synthetic spectra, we measured the
equivalent widths of multiple Fe I and Ti I lines and a temperature-sensitive
index based on the FeH bandhead. We used abundances measured from
widely-separated solar-type companions to empirically calibrate transformations
to the observed indices and equivalent widths that force agreement with the
models. Our calibration achieves precisions in Teff, [Fe/H], and [Ti/Fe] of 60
K, 0.1 dex, and 0.05 dex, respectively and is calibrated for 3200 K < Teff <
4100 K, -0.7 < [Fe/H] < +0.3, and -0.05 < [Ti/Fe] < +0.3. This work is a step
toward detailed chemical analysis of M dwarfs at a similar precision achieved
for FGK stars.Comment: accepted for publication in ApJ, all synthetic spectra available at
http://people.bu.edu/mveyette/phoenix
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