2MASS J06164006-6407194: The First Outer Halo L Subdwarf

We present the serendipitous discovery of an L subdwarf, 2MASS J06164006-6407194, in a search of the Two Micron All Sky Survey for T dwarfs. Its spectrum exhibits features indicative of both a cool and metal poor atmosphere including a heavily pressured-broadened K I resonant doublet, Cs I and Rb I lines, molecular bands of CaH, TiO, CrH, FeH, and H2O, and enhanced collision induced absorption of H2. We assign 2MASS 0616-6407 a spectral type of sdL5 based on a comparison of its red optical spectrum to that of near solar-metallicity L dwarfs. Its high proper motion (mu =1.405+-0.008 arcsec yr-1), large radial velocity (Vrad = 454+-15 km s-1), estimated uvw velocities (94, -573, 125) km s-1 and Galactic orbit with an apogalacticon at ~29 kpc are indicative of membership in the outer halo making 2MASS 0616-6407 the first ultracool member of this population.Comment: Accepted for publication in Ap

New measurements of total ionizing dose in the lunar environment

[1] We report new measurements of solar minimum ionizing radiation dose at the Moon onboard the Lunar Reconnaissance Orbiter (LRO) from June 2009 through May 2010. The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument on LRO houses a compact and highly precise microdosimeter whose design allows measurements of dose rates below 1 micro-Rad per second in silicon achieved with minimal resources (20 g, ∼250 milliwatts, and ∼3 bits/second). We envision the use of such a small yet accurate dosimeter in many future spaceflight applications where volume, mass, and power are highly constrained. As this was the first operation of the microdosimeter in a space environment, the goal of this study is to verify its response by using simultaneous measurements of the galactic cosmic ray ionizing environment at LRO, at L1, and with other concurrent dosimeter measurements and model predictions. The microdosimeter measured the same short timescale modulations in the galactic cosmic rays as the other independent measurements, thus verifying its response to a known source of minimum-ionizing particles. The total dose for the LRO mission over the first 333 days was only 12.2 Rads behind ∼130 mils of aluminum because of the delayed rise of solar activity in solar cycle 24 and the corresponding lack of intense solar energetic particle events. The dose rate in a 50 km lunar orbit was about 30 percent lower than the interplanetary rate, as one would expect from lunar obstruction of the visible sky

Recovery of Yearling Calves from Fescue Toxicosis

Tall fescue (Lolium arundinaceum (Schreb.) S.J. Darbyshire) is widely utilized for grazing in the transition zone between the temperate and subtropical regions of the eastern U.S.A. Cattle grazing tall fescue frequently exhibit fescue toxicosis, a malady caused by consumption of toxins produced by the endophyte, Neotyphodium coenophialum. Symptoms of fescue toxicosis include retention of rough hair coat, increased body temperature and laboured respiration. Heat stress may be severe at onset of high ambient temperature and humidity. Transporting cattle exhibiting toxicosis can therefore be difficult because combined stresses of the toxicosis and transporting often result in high mortality. An experiment was conducted to measure trends in rectal temperatures for yearling steers following removal from tall fescue and placement on a fescue-free diet

Radiation risks from large solar energetic particle events

Solar energetic particles (SEPs) constitute a radiation hazard to both humans and hardware in space. Over the past few years there have been significant advances in our knowledge of the composition and energy spectra of SEP events, leading to new insights into the conditions that contribute to the largest events. This paper summarizes the energy spectra and frequency of large SEP events, and discusses the interplanetary conditions that affect the intensity of the largest events

Solar Energetic Particle Spectral Breaks

The five large solar particle events during October–November 2003 presented an opportunity to test shock acceleration models with in-situ observations. We use solar particle spectra of H to Fe ions, measured by instruments on ACE, SAMPEX, and GOES-11, to investigate the Q/M-dependence of spectral breaks in the 28 October 2003 event. We find that the break energies scale as (Q/M)^b with b ≈ 1.56 to 1.75, somewhat less than predicted. We also conclude that SEP spectra >100 MeV/nucleon are best fit by a double power-law shape. ©2005 American Institute of Physic

How efficient are coronal mass ejections at accelerating solar energetic particles?

The largest solar energetic particle (SEP) events are thought to be due to particle acceleration at a shock driven by a fast coronal mass ejection (CME). We investigate the efficiency of this process by comparing the total energy content of energetic particles with the kinetic energy of the associated CMEs. The energy content of 23 large SEP events from 1998 through 2003 is estimated based on data from ACE, GOES, and SAMPEX, and interpreted using the results of particle transport simulations and inferred longitude distributions. CME data for these events are obtained from SOHO. When compared to the estimated kinetic energy of the associated coronal mass ejections (CMEs), it is found that large SEP events can extract ~10% or more of the CME kinetic energy. The largest SEP events appear to require massive, very energetic CMEs

Hubble Space Telescope Observations of Field Ultracool Dwarfs at High Galactic Latitude

We present a sample of 17 newly discovered ultracool dwarf candidates later than ~M8, drawn from 231.90 arcmin2 of {\it Hubble Space Telescope} Wide Field Camera 3 infrared imaging. By comparing the observed number counts for 17.5<J_125<25.5 AB mag to an exponential disk model, we estimate a vertical scale height of z_scl=290 +- 25 (random) +- 30 (systematic) pc for a binarity fraction of f_b=0. While our estimate is roughly consistent with published results, we suggest that the differences can be attributed to sample properties, with the present sample containing far more substellar objects than previous work. We predict the object counts should peak at J_{125}~24 AB mag due to the exponentially-declining number density at the edge of the disc. We conclude by arguing that trend in scale height with spectral type may breakdown for brown dwarfs since they do not settle onto the main sequence.Comment: 9 pages, 6 figures, 3 tables, accepted to ApJ (v2 is consistent with Referee changes

Anomalous cosmic ray argon and other rare elements at 1-4 MeV/nucleon trapped within the Earth's magnetosphere

We summarize over 6 years of observations of ∼1–4 MeV/nucleon heavy ions trapped in the Earth's magnetosphere on L shells of 1.7–3. We obtained these new results in low Earth orbit with the SAMPEX spacecraft; they extend the observations of trapped heavy ions in this L range to much lower energies than had previously been examined in detail. At 1–4 MeV/nucleon we observed a trapped population with a peak intensity near L∼2.3 that includes the anomalous cosmic ray species O, Ne, and Ar also observed in interplanetary space at 1 AU. We also found elements with low first ionization potential (C, Mg-S, and Fe) trapped with the same spatial distribution. The low-energy trapped population increased in intensity between 1996 and 1997, roughly during solar minimum and minimum geomagnetic activity. It is possible that the 1–4 MeV/nucleon trapped population originates from a number of sources, including high-energy trapped anomalous cosmic rays that have lost energy in the residual atmosphere in the case of O and Ne, and directly incident, singly charged anomalous cosmic rays that have become stripped and subsequently trapped in the case of Ar. The group of trapped elements with low first ionization potential (C, Mg-S, and Fe) have roughly solar wind abundances relative to one another, suggesting a possible link between this trapped component and recently discovered solar wind pickup ions released from dust grains within the inner heliosphere

Dioxin Exposure Blocks Lactation Through a Direct Effect on Mammary Epithelial Cells Mediated by the Aryl Hydrocarbon Receptor Repressor

In mammals, lactation is a rich source of nutrients and antibodies for newborn animals. However, millions of mothers each year experience an inability to breastfeed. Exposure to several environmental toxicants, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), has been strongly implicated in impaired mammary differentiation and lactation. TCDD and related polyhalogenated aromatic hydrocarbons are widespread industrial pollutants that activate the aryl hydrocarbon receptor (AHR). Despite many epidemiological and animal studies, the molecular mechanism through which AHR signaling blocks lactation remains unclear. We employed in vitro models of mammary differentiation to recapitulate lactogenesis in the presence of toxicants. We demonstrate AHR agonists directly block milk production in isolated mammary epithelial cells. Moreover, we define a novel role for the aryl hydrocarbon receptor repressor (AHRR) in mediating this response. Our mechanistic studies suggest AHRR is sufficient to block transcription of the milk gene β-casein. Since TCDD is a prevalent environmental pollutant that affects women worldwide, our results have important public health implications for newborn nutrition