Comparing Three Spaceborne Optical Sensors via Fine Scale Pixel-based Urban Land Cover Classification Products

Accessibility to higher resolution earth observation satellites suggests an improvement in the potential for fine scale image classification. In this comparative study, imagery from three optical satellites (WorldView-2, Pleiades and RapidEye) were used to extract primary land cover classesfrom a pixel-based classification principle in a suburban area. Following a systematic working procedure, manual segmentation and vegetation indices were applied to generate smaller subsets to in turn develop sets of ISODATA unsupervised classification maps. With the focus on the land cover classification differences detected between the sensors at spectral level, the validation of accuracies and their relevance for fine scale classification in the built-up environment domain were examined. If an overview of an urban area is required, RapidEye will provide an above average (0.69 k) result with the built-up class sufficiently extracted. The higher resolution sensors such as WorldView-2 and Pleiades in comparison delivered finer scale accuracy at pixel and parcel level with high correlation and accuracy levels (0.65-0.71k) achieved from these two independent classifications

Fast quasi-periodic oscillations in the eclipsing polar VV Puppis from VLT and XMM-Newton observations

International audienceWe present high time resolution optical photometric data of the polar VV Puppis obtained simultaneously in three filters (u′, HeII λ4686, r′) with the ULTRACAM camera mounted at the ESO-VLT telescope. An analysis of a long 50 ks XMM-Newton observation of the source, retrieved from the database, is also provided. Quasi-periodic oscillations (QPOs) are clearly detected in the optical during the source bright phase intervals when the accreting pole is visible, confirming the association of the QPOs with the basis of the accretion column. QPOs are detected in the three filters at a mean frequency of ∼0.7 Hz with a similar amplitude ∼1%. Mean orbitally-averaged power spectra during the bright phase show a rather broad excess with a quality factor Q = ν/Δν = 5−7 but smaller data segments commonly show a much higher coherency with Q up to 30. The X-ray Multi-mirror Mission XMM (0.5–10 keV) observation provides the first accurate estimation of the hard X-ray component with a high kT ∼ 40 keV temperature and confirms the high extreme ultraviolet (EUV)-soft/hard ratio in the range of 4−15 for VV Pup. The detailed X-ray orbital light curve displays a short Δϕ ≃ 0.05 ingress into self-eclipse of the active pole, indicative of an accretion shock height of ∼75 km. No significant X-ray QPOs are detected with an amplitude upper limit of ∼30% in the range 0.1–5 Hz. Detailed hydrodynamical numerical simulations of the post-shock accretion region with parameters consistent with VV Pup demonstrate that the expected frequencies from radiative instability are identical for X-rays and optical regime at values ν ∼ 40–70 Hz, more than one order magnitude higher than observed. This confirms previous statements suggesting that present instability models are unable to explain the full QPO characteristics within the parameters commonly known for polars

1-Bromo-2-(10β-dihydro­artemisin­oxy)ethane

The title compound, C17H27BrO5, DEB, is a derivative of artemisinin which is used in malara therapy. The OR-group at C12 is cis to the CH3-group at C11 and axially oriented on ring D which has a chair conformation. The crystal packing is stabilized by several weak inter­molecular C—H⋯O inter­actions, which combine to form a C—H—O bonded network parallel to (001)

The structure of Chariklo's rings from stellar occultations

Two narrow and dense rings (called C1R and C2R) were discovered around the Centaur object (10199) Chariklo during a stellar occultation observed on 2013 June 3. Following this discovery, we planned observations of several occultations by Chariklo's system in order to better characterize the physical properties of the ring and main body. Here, we use 12 successful occulations by Chariklo observed between 2014 and 2016. They provide ring profiles (physical width, opacity, edge structure) and constraints on the radii and pole position. Our new observations are currently consistent with the circular ring solution and pole position, to within the $\pm 3.3$ km formal uncertainty for the ring radii derived by Braga-Ribas et al. The six resolved C1R profiles reveal significant width variations from $\sim 5$ to 7.5 km. The width of the fainter ring C2R is less constrained, and may vary between 0.1 and 1 km. The inner and outer edges of C1R are consistent with infinitely sharp boundaries, with typical upper limits of one kilometer for the transition zone between the ring and empty space. No constraint on the sharpness of C2R's edges is available. A 1$\sigma$ upper limit of $\sim 20$ m is derived for the equivalent width of narrow (physical width <4 km) rings up to distances of 12,000 km, counted in the ring plane

Stakeholder Relations and Ownership of a Community Wireless Network: The Case of iNethi

The primary objective for this study is to investigate multi-stakeholder understanding of ownership of a community wireless network (CWN) located in Ocean View, Cape Town. This is important because ownership and stakeholder relations are components that contribute to the success of a CWN. Using the convenience and snowball sampling method, we completed 11 semi-structured interviews with stakeholders from the University of Cape Town and the Ocean View community. We consider different ways ownership is conceived between stakeholders. We found that the involvement of the community at initiation of a CWN project is imperative in establishing ownership of a CWN. We characterize some of the ways in which discordant conceptions of ownership have resulted in miscommunication within this project and offer considerations for researchers to take into account as they collaborate with communities on joint initiatives

NGTS-21b: An Inflated Super-Jupiter Orbiting a Metal-poor K dwarf

We report the discovery of NGTS-21b, a massive hot Jupiter orbiting a low-mass star as part of the Next Generation Transit Survey (NGTS). The planet has a mass and radius of $2.36 \pm 0.21$ M$_{\rm J}$, and $1.33 \pm 0.03$ R$_{\rm J}$, and an orbital period of 1.543 days. The host is a K3V ($T_{\rm eff}=4660 \pm 41$, K) metal-poor (${\rm [Fe/H]}=-0.26 \pm 0.07$, dex) dwarf star with a mass and radius of $0.72 \pm 0.04$, M$_{\odot}$,and $0.86 \pm 0.04$, R$_{\odot}$. Its age and rotation period of $10.02^{+3.29}_{-7.30}$, Gyr and $17.88 \pm 0.08$, d respectively, are in accordance with the observed moderately low stellar activity level. When comparing NGTS-21b with currently known transiting hot Jupiters with similar equilibrium temperatures, it is found to have one of the largest measured radii despite its large mass. Inflation-free planetary structure models suggest the planet's atmosphere is inflated by $\sim21\%$, while inflationary models predict a radius consistent with observations, thus pointing to stellar irradiation as the probable origin of NGTS-21b's radius inflation. Additionally, NGTS-21b's bulk density ($1.25 \pm 0.15$, g/cm$^3$) is also amongst the largest within the population of metal-poor giant hosts ([Fe/H] < 0.0), helping to reveal a falling upper boundary in metallicity-planet density parameter space that is in concordance with core accretion formation models. The discovery of rare planetary systems such as NGTS-21 greatly contributes towards better constraints being placed on the formation and evolution mechanisms of massive planets orbiting low-mass stars.Comment: 12 pages, 13 figures, accepted for publication in MNRA

Size and Shape of Chariklo from Multi-epoch Stellar Occultation

We use data from five stellar occultations observed between 2013 and 2016 to constrain Chariklo’s size and shape, and the ring reflectivity. We consider four possible models for Chariklo (sphere, Maclaurin spheroid, triaxial ellipsoid, and Jacobi ellipsoid), and we use a Bayesian approach to estimate the corresponding parameters. The spherical model has a radius R = 129 ± 3 km. The Maclaurin model has equatorial and polar radii a=b={143}-6+3 {km} and c={96}-4+14 {km}, respectively, with density {970}-180+300 {kg} {{{m}}}-3. The ellipsoidal model has semiaxes a={148}-4+6 {km}, b={132}-5+6 {km}, and c={102}-8+10 {km}. Finally, the Jacobi model has semiaxes a = 157 ± 4 km, b = 139 ± 4 km, and c = 86 ± 1 km, and density {796}-4+2 {kg} {{{m}}}-3. Depending on the model, we obtain topographic features of 6–11 km, typical of Saturn icy satellites with similar size and density. We constrain Chariklo’s geometric albedo between 3.1% (sphere) and 4.9% (ellipsoid), while the ring I/F reflectivity is less constrained between 0.6% (Jacobi) and 8.9% (sphere). The ellipsoid model explains both the optical light curve and the long-term photometry variation of the system, giving a plausible value for the geometric albedo of the ring particles of 10%–15%. The derived mass of Chariklo of 6–8 × 1018 kg places the rings close to 3:1 resonance between the ring mean motion and Chariklo’s rotation period

The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package

The Astropy project supports and fosters the development of open-source and openly-developed Python packages that provide commonly-needed functionality to the astronomical community. A key element of the Astropy project is the core package Astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of inter-operable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy project