X-ray Flares of EV Lac: Statistics, Spectra, Diagnostics

We study the spectral and temporal behavior of X-ray flares from the active M-dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare parameters by fitting an empirical function which characterizes the amplitude, shape, and scale. The flares range from very short (<1 ks) to long (10 ks) duration events with a range of shapes and amplitudes for all durations. We extract spectra for composite flares to study their mean evolution and to compare flares of different lengths. Evolution of spectral features in the density-temperature plane shows probable sustained heating. The short flares are significantly hotter than the longer flares. We determined an upper limit to the Fe K fluorescent flux, the best fit value being close to what is expected for compact loops.Comment: 9 pages; 9 figures; latex/emulateapj style; Submitted to The Astrophysical Journa

The Radio Spectrum of TVLM513-46546: Constraints on the Coronal Properties of a Late M Dwarf

We explore the radio emission from the M9 dwarf, TVLM513-46546, at multiple radio frequencies, determining the flux spectrum of persistent radio emission, as well as constraining the levels of circular polarization. Detections at both 3.6 and 6 cm provide spectral index measurement $\alpha$ (where S$_{\nu} \propto \nu^{\alpha}$) of $-0.4\pm0.1$. A detection at 20 cm suggests that the spectral peak is between 1.4 and 5 GHz. The most stringent upper limits on circular polarization are at 3.6 and 6 cm, with $V/I <$15%. These characteristics agree well with those of typical parameters for early to mid M dwarfs, confirming that magnetic activity is present at levels comparable with those extrapolated from earlier M dwarfs. We apply analytic models to investigate the coronal properties under simple assumptions of dipole magnetic field geometry and radially varying nonthermal electron density distributions. Requiring the spectrum to be optically thin at frequencies higher than 5 GHz and reproducing the observed 3.6 cm fluxes constrains the magnetic field at the base to be less than about 500 G. There is no statistically significant periodicity in the 3.6 cm light curve, but it is consistent with low-level variability.Comment: 11 pages, 2 figures Accepted for publication in the Astrophysical Journa

Butterfly pea - a legume success story in cropping lands of central Queensland

The central Queensland region is a major producer of wheat, sorghum and beef. Changes in relative values of cereals and beef, together with a market demand to finish steers at a younger age, has induced farmers to invest more resources into their beef enterprises. Soil fertility decline is seen as a major constraint to cereal production and one that can be overcome by use of pasture phases in crop rotations. Within this environment, butterfly pea (Clitoria ternatea) has emerged as a well-adapted summer-growing legume for the heavy textured cropping soils of the region. It is being sown into existing or new permanent pastures and in pasture phases within cropping rotations to improve animal production and soil nitrogen status. Butterfly pea is relatively inexpensive to establish and can provide liveweight gain of between 0.75 and 1.3 kg/head/day. The combination of farmer, extension and research inputs has resulted in widespread adoption with > 12,000 ha being successfully established over the past 3 years

The Search for Signatures Of Transient Mass Loss in Active Stars

The habitability of an exoplanet depends on many factors. One such factor is the impact of stellar eruptive events on nearby exoplanets. Currently this is poorly constrained due to heavy reliance on solar scaling relationships and a lack of experimental evidence. Potential impacts of Coronal Mass Ejections (CMEs), which are a large eruption of magnetic field and plasma from a star, are space weather and atmospheric stripping. A method for observing CMEs as they travel though the stellar atmosphere is the type II radio burst, and the new LOw Frequency ARray (LOFAR) provides a means for detection. We report on 15 hours of observation of YZ Canis Minoris (YZ CMi), a nearby M dwarf flare star, taken in LOFAR's beam-formed observation mode for the purposes of measuring transient frequency-dependent low frequency radio emission. The observations utilized Low-Band Antenna (10-90 MHz) or High-Band Antenna (110-190 MHz) for five three-hour observation periods. In this data set, there were no confirmed type II events in this frequency range. We explore the range of parameter space for type II bursts constrained by our observations Assuming the rate of shocks is a lower limit to the rate at which CMEs occur, no detections in a total of 15 hours of observation places a limit of $\nu_{type II} < 0.0667$ shocks/hr $\leq \nu_{CME}$ for YZ CMi due to the stochastic nature of the events and limits of observational sensitivity. We propose a methodology to interpret jointly observed flares and CMEs which will provide greater constraints to CMEs and test the applicability of solar scaling relations

Metal semiconductor metal photodiodes based on all-epitaxial Ge-on-insulator-on-Si(111), grown by molecular beam epitaxy

We report on the fabrication and characterisation of an all-epitaxial Germanium-on-Insulator (GOI) Metal-Semiconductor-Metal (MSM) photodetector. The MSM photodetector is fabricated on a (111)-oriented epitaxial Ge layer, grown on an epitaxial Gd 2 O 3 /Si(111) substrate, by molecular beam epitaxy (MBE). The first step is the growth of the 15-nm thick Gd 2 O 3 epitaxial layer over CMOS-grade silicon, atop which an epitaxial layer of Ge is grown. Near infrared (NIR) MSM photodetectors have been fabricated over the Ge epitaxial layer with an inter-digitated (IDT) contact structure, with an active area of 100 μm x 124 μm. For the particular IDT dimensions, the dark current has been measured to be 475 μA. A responsivity of ∼ 2 mA/W is observed at a-5V bias, when excited at 1550 nm. © 2019 SPIE

Radio Constraints on Activity in Young Brown Dwarfs

We report on searches for radio emission from three of the nearest known young brown dwarfs using the Very Large Array. We have obtained sensitive upper limits on 3.6cm emission from 2MASSW J1207334-393254, TWA~5B and SSSPM J1102-3431, all of which are likely members of the $\sim$8-Myr-old TW Hydrae association. We derive constraints on the magnetic field strength and the number density of accelerated electrons, under the assumption that young brown dwarf atmospheres are able to produce gyrosynchrotron emission, as seems to be indicated in older brown dwarfs. For the young brown dwarf TWA~5B, the ratio of its detected X-ray luminosity to the upper limit on radio luminosity places it within the expected range for young stars and older, active stars. Thus, its behavior is anomalous compared to older brown dwarfs, in which radio luminosity is substantially enhanced over the expected relationship. Our observations deepen the conundrum of magnetic activity in brown dwarfs, and suggest that a factor other than age is more important for determining radio emission in cool substellar objects.Comment: accepted, ApJL replaced earlier version: typo in astro-ph author fiel

A New Calculation of Ne IX Line Diagnostics

We describe the effect that new atomic calculations, including fully-relativistic R-matrix calculations of collisional excitation rates and level-specific dielectronic and radiative recombination rates, have on line ratios from the astrophysically significant ion Ne IX. The new excitation rates systematically change some predicted Ne IX line ratios by 25% at temperatures at or below the temperature of maximum emissivity (4x10^6 K), while the new recombination rates lead to systematic changes at higher temperatures. The new line ratios are shown to agree with observations of Capella and sigma^2 CrB significantly better than older line ratios, showing that 25-30% accuracy in atomic rates is inadequate for high-resolution X-ray observations from existing spectrometers.Comment: 5 pages, 6 figure