Aims. The work is aimed at studying the circumstellar disk of the bright classical binary Be star π Aqr. Methods. We analysed variations of a double-peaked profile of the H α emission line in the spectrum of π Aqr that was observed in many phases during ∼40 orbital cycles in 2004−2013. We applied the discrete Fourier transform (DFT) method to search for periodicity in the peak intensity ratio (V/R). Doppler tomography was used to study the structure of the disk around the primary. Results. The dominant frequency in the power spectrum of the H α V/R ratio is 0.011873 day −1 , which corresponds to a period of 84.2(2) days and agrees with the earlier determined orbital period of the system, P orb = 84.1 days. The V/R shows a sinusoidal variation that is phase-locked with the orbital period. Doppler maps of all our spectra show a non-uniform structure of the disk around the primary: a ring with the inner and outer radii at V in ≈ 450 km s −1 and V out ≈ 200 km s −1 , respectively, along with an extended stable region (spot) at V x ≈ 225 km s −1 and V y ≈ 100 km s −1 . The disk radius of ≈65 R = 0.33 AU was estimated by assuming Keplerian motion of a particle on a circular orbit at the disk's outer edge.

We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the New Horizons extended mission. Three of the four efforts led to positive detections of the body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by SOFIA with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape consistent with a contact binary with rough dimensions of 20 by 30 km for the overall outline. A visible albedo of 10% was derived from these data. Twenty-two systems were deployed for the fourth event on 2018 Aug 4 and resulted in two chords. The combination of the occultation data and the flyby results provides a significant refinement of the rotation period, now estimated to be 15.9380 ± 0.0005 hours. The occultation data also provided high-precision astrometric constraints on the position of the object that were crucial for supporting the navigation for the New Horizons flyby. This work demonstrates an effective method for obtaining detailed size and shape information and probing for rings and dust on distant Kuiper Belt objects as well as being an important source of positional data that can aid in spacecraft navigation that is particularly useful for small and distant bodies.

The objectives of this paper are to characterize an "ideal" environmental impact assessment (e.i.a.); to review the contemporary status of e.i.a. for several major activities and areas of development; and to identify successes, failures, and future needs in e.i.a.The institutional procedures to be followed for e.i.a. have been formalized in a number of countries, but the scientific basis and methods are still developing. We propose that the following elements comprise an ideal e.i.a.: (1) definition of scientific objectives, (2) background preparation, (3) identification of main impacts, (4) prediction of effects, (5) formulation of usable recommendations, (6) monitoring and assessment, (7) sufficient lead time, (8) public participation, (9) adequate funding, and (10) evidence that recommendations were used.The "best available" predictive, preoperational e.i.a.'s involving aquatic resources (power plants, fossil fuels, recreation, reservoirs, wastewater treatment, forestry, and dredging and water diversion in estuaries) were reviewed and scored on a 0–5 scale for each of the elements identified above. Mean scores for the criteria which could be assessed (nos. 1–8) indicated that the quality of the best available e.i.a.'s does not exceed our defined average but improves when legally required documents are excluded from the calculations. The lowest means, for criteria within the scientist's control (nos. 1–5), were obtained for "Prediction of effects" and ' "Formulation of usable recommendations." Overall mean scores for each development area (criteria 1–5) indicated three broad groups which included studies of above average quality (wastewater treatment, recreation); studies of approximately average quality (estuarine impacts, power plants, reservoirs, and fossil fuels); and studies of below average quality (forestry practices).Environmental impact assessment has had the following successes: increased environmental awareness due to public involvement in e.i.a., some environmental protection, and elucidation of intriguing research problems. The list of failures of e.i.a. is, however, longer: "tokenism," unrealistic time constraints, uncertainty of program or development schedules, difficult access to e.i.a. literature, questionable ethics, lack of coordination among studies, and poor research design.Future organizational/administrative needs of e.i.a. include improved access to e.i.a. literature, increased accountability for e.i.a.'s and their authors, improved public input into project decisions and designs, and improved organization and presentation of e.i.a. reports. Future scientific/research needs include development of methods to define and quantify relationships between biological, esthetic, and economic impacts; support for independent biological inventory programs; adequate time frames; improved design of research; inclusion of monitoring and assessment in every e.i.a.; study of cumulative impacts on a regional or national scale; and improved communication between scientists and planners.Key words: environmental impact assessment, aquatic ecology, power plants, fossil fuels, recreation, reservoirs, wastewater treatment, forestry, dredging and water diversion (estuaries)

We report the results of two multi-chord stellar occultations by the dwarf planet (1) Ceres that were observed from Brazil on 2010 August 17, and from the USA on 2013 October 25. Four positive detections were obtained for the 2010 occultation, and nine for the 2013 occultation. Elliptical models were adjusted to the observed chords to obtain Ceres' size and shape. Two limb fitting solutions were studied for each event. The first one is a nominal solution with an indeterminate polar aspect angle. The second one was constrained by the pole coordinates as given by Drummond et al. Assuming a Maclaurin spheroid, we determine an equatorial diameter of 972 ± 6 km and an apparent oblateness of 0.08 ± 0.03 as our best solution. These results are compared to all available size and shape determinations for Ceres made so far, and shall be confirmed by the NASA's Dawn space mission.

We present observations of five stellar occultations for (11351) Leucus and reports from two efforts on (21900) Orus. Both objects are prime mission candidate targets for the Lucy Discovery mission. Combined results for Leucus indicate a very dark surface with p V = 0.037 ± 0.001, which is derived from the average of the multichord occultations. Our estimate of the triaxial ellipsoidal shape is for axial diameters of 63.8 × 36.6 × 29.6 km assuming that the spin pole is normal to the line of sight. The actual shape of the object is only roughly elliptical in profile at each epoch. Significant topography is seen with horizontal scales up to 30 km and vertical scales up to 5 km. The most significant feature is a large depression on the southern end of the object as seen from a terrestrial viewpoint. For this work we developed a method to correct for differential refraction, accounting for the difference in color between the target object and the reference stars for astrometry derived from ground-based images.