Studying the accretion geometry of EXO 2030+375 at luminosities close to the propeller regime

The Be X-ray binary EXO 2030+375 was in an extended low luminosity state during most of 2016. We observed this state with NuSTAR and Swift, supported by INTEGRAL observations as well as optical spectroscopy with the NOT. We present a comprehensive spectral and timing analysis of these data here to study the accretion geometry and investigate a possible onset of the propeller effect. The H-alpha data show that the circumstellar disk of the Be-star is still present. We measure equivalent widths similar to values found during more active phases in the past, indicating that the low-luminosity state is not simply triggered by a smaller Be disk. The NuSTAR data, taken at a 3-78 keV luminosity of ~6.8e35 erg/s (for a distance of 7.1 kpc), are well described by standard accreting pulsar models, such as an absorbed power-law with a high-energy cutoff. We find that pulsations are still clearly visible at these luminosities, indicating that accretion is continuing despite the very low mass transfer rate. In phase-resolved spectroscopy we find a peculiar variation of the photon index from ~1.5 to ~2.5 over only about 3% of the rotational period. This variation is similar to that observed with XMM-Newton at much higher luminosities. It may be connected to the accretion column passing through our line of sight. With Swift/XRT we observe luminosities as low as 1e34 erg/s during which the data quality did not allow us to search for pulsations, but the spectrum is much softer and well described by either a blackbody or soft power-law continuum. This softer spectrum might be due to the fact that accretion has been stopped by the propeller effect and we only observe the neutron star surface cooling.Comment: 11 pages, 6 figures, accepted for publication in A&A (v2 including language edits

The Use of Sunn Hemp as Forage in Florida

Sunn hemp (Crotalaria juncea L.) is a warm-season annual legume that has been widely used as cover crop; however, there is potential to use sunn hemp as forage in subtropical regions. The objective of this study was to evaluate management practices to improve the efficiency of using sunn hemp as a forage crop. The study was conducted in Ona, Florida, USA from 2016 to 2018 and tested the factorial arrangement of five sunn hemp genotypes (Crescent Sunn, Ubon, Blue Leaf, and AU Golden) and two harvest times (60 d after seeding or flowering) with four replicates. There was a cultivar × harvest period effect on HA, crude protein (CP), and in vitro digestible organic matter (IVDOM) concentrations. Herbage accumulation was greater at flowering than 60 d harvest for all cultivars; however, the magnitude of increase was greater for Blue Leaf and Crescent Sun than AU Golden and Ubon. AU Golden and Ubon flowered at 83 and 92 d after seeding, while Blue Leaf and Crescent Sun flowered or were harvested at 166 d after seeding. AU Golden and Crescent Sunn had the greatest CP at 60 d harvest, and Blue Leaf and Ubon had the least CP concentrations. AU Golden and Crescent Sun had the greatest IVDOM at 60-d harvest; however, AU Golden and Ubon had greater IVDOM than Blue Leaf and Crescent Sun at flowering. Sunn hemp may be a feasible warm-season annual legume to be used in forage systems in Florida and harvest 60 d after seeding would results in forage with greater nutritive value