The Australian Square Kilometre Array Pathfinder: System Architecture and Specifications of the Boolardy Engineering Test Array

This paper describes the system architecture of a newly constructed radio telescope – the Boolardy engineering test array, which is a prototype of the Australian square kilometre array pathfinder telescope. Phased array feed technology is used to form multiple simultaneous beams per antenna, providing astronomers with unprecedented survey speed. The test array described here is a six-antenna interferometer, fitted with prototype signal processing hardware capable of forming at least nine dual-polarisation beams simultaneously, allowing several square degrees to be imaged in a single pointed observation. The main purpose of the test array is to develop beamforming and wide-field calibration methods for use with the full telescope, but it will also be capable of limited early science demonstrations.

X-ray Emission from G359.1-0.5

We report on the detection of X-ray emission from the supernova remnant (SNR) G359.1-0.5 in a deep ROSAT PSPC pointed observation. The diffuse emission is well confined within the radio shell of the SNR. Its spectrum can be represented by a thermal plasma model at T ~ 1 keV and Fx ~ 2×10−11 erg cm−2 s−1 (0.1–2.0 keV) modified by the column absorption of NH ~ 3 × 1022 cm−2. This result supports the view that the source is at a large distance consistent with that from radio observation, and helps to resolve a puzzle about the SNR in previous observations.

ROSAT Observations of Einstein EMSS AGNs

Active Galactic Nuclei (AGN) can be studied in the ROSAT energy band also when serendipitously observed during long pointed observation of unrelated targets. From the available ROSAT database three Extended Medium Sensitivity Survey (EMSS) AGNs, detected with more than 500 counts, have been studied. One AGN (MS 1803.6+6738 = Kaz 102) was observed twice and in one field the target is the BL Lac 0716+714.– Spectral studies reveal that all three AGNs are well described by a single power law. Values of relevance are summarized in the table where they are compared to previous values from Einstein and the ROSAT survey (Walter R. & Fink H.H., 1993, A&A, 274, 105). All four sources have a NH value well below the estimated value given by Stark et al. (1992, ApJS, 79, 77) and Elvis et al. (1989, ApJ, 97, 777). This probably is an indication that a soft excess is present.– Variability studies show flux variations for the BL Lac on time scales of days, while the photon index appears rather constant. The high count rate for this object allows to attribute a probability of variability greater than 99% (running a K-S test against constancy). In the case of Kaz 102, the comparison of previous measurements with the present one does not show evidence of long term (years) variability.

Rosat Observations of Stellar Flares

X-ray observations of stellar flares obtained during the ROSAT all-sky survey as well as in the ROSAT pointing program are discussed. The ROSAT all-sky survey allowed—for the first time—an unbiased search for stellar flares among all types of stars. A fundamentally new result obtained is that flares can occur on all types of late-type stars, thus supporting the view that the X-ray emission from these stars is controlled by magnetic processes. Long-duration flares can be studied with the all-sky survey data particularly well, and an especially well-observed long-duration flare event on the flare star EV Lacertae is presented and discussed in detail. Finally, the issue of time variability on the shortest detectable timescales and the question of microflaring is discussed using ROSAT data from a pointed observation of UV Ceti.Subject headings: stars: coronae — stars: flare — stars: late-type — X-rays: stars

Extended X-Ray Emission from Planetary Nebulae

We present first results from the ROSAT All Sky Survey on X-ray emission of planetary nebulae (PNe). For the first time extended X-ray emission from PNe was detected. This is the case for NGC 6543, NGC 6853, A 12, NGC 4361 (and LoTr 5). X-ray emission compatible with a point source was detected from BD+30°3639, however, the spectral distribution of the X-ray photons is leading to temperatures beyond 2 106 K. Thus in all cases, with the possible exception of LoTr 5, the central star of the PNe can be excluded as the main source of the observed X-ray emission. X-ray images and ROSAT spectra for all detected PNe are presented. The best observed PN in X-ray emission is NGC 6543. Due to the close vicinity to the north ecliptic pole, this object was regularly observed, every 90 minutes during the whole half year of the ROSAT All Sky Survey, resulting in 41 ksec of integration time. In addition NGC 6543 was observed in a 50 ksec pointed observation to the north ecliptic pole, taken in June 1990 during the calibration phase (Kreysing et al. 1992). A comparison of the semi-ring-like distribution of the X-ray emission of NGC 6543 with optical CCD-images shows, that most of the X-ray emission seems to originate from the boundary region between the nebula and the halo. Neither the central star nor the hot wind from the central star wind is the main source of the X-ray emission, as proposed by the interacting stellar wind model (Kwok 1982). An alternative model employing a possible coronal heating mechanism has been discussed by Kreysing (1992); accoustic waves, travelling outward from the nebula, encounter a sudden density decline at the boundary to the halo. As a consequence the waves degenerate into shock waves, dissipating their energy in a thin region of only some 1015 cm into the ambient medium.

Lexical Phonology: lexical and postlexical derivations

Paul Kiparsky's paper (1982) ‘From Cyclic to Lexical Phonology’ is the most interesting recent development in the line of research originated by Kiparsky (1973) and Mascaró (1976). The major task in this research is the investigation of the ways in which rules apply to phonological structures. Kiparsky (1973) makes the very pointed observation that some phonological rules apply exclusively in derived environments. An environment is derived if either (i) or (ii) is true:(i) the structure which is relevant to the application of the rule arises at morpheme boundaries: the environment is thus derived morphologically;(ii) the structure which is relevant to the application of the rule arises in the course of phonological derivation due to the application of an earlier phonological rule: the environment is thus derived phonologically.