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We apply two methods to estimate the 21-cm bispectrum from data taken within the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA). Using data acquired with the Phase II compact array allows a direct bispectrum estimate to be undertaken on the multiple redundantly spaced triangles of antenna tiles, as well as an estimate based on data gridded to the uv-plane. The direct and gridded bispectrum estimators are applied to 21 h of high-band (167–197 MHz; z = 6.2–7.5) data from the 2016 and 2017 observing seasons. Analytic predictions for the bispectrum bias and variance for point-source foregrounds are derived. We compare the output of these approaches, the foreground contribution to the signal, and future prospects for measuring the bispectra with redundant and non-redundant arrays. We find that some triangle configurations yield bispectrum estimates that are consistent with the expected noise level after 10 h, while equilateral configurations are strongly foreground-dominated. Careful choice of triangle configurations may be made to reduce foreground bias that hinders power spectrum estimators, and the 21-cm bispectrum may be accessible in less time than the 21-cm power spectrum for some wave modes, with detections in hundreds of hours.
Antenna-pattern measurements obtained from a double-metal supra-terahertz-frequency (supra-THz) quantum cascade laser (QCL) are presented. The QCL is mounted within a mechanically micro-machined waveguide cavity containing dual diagonal feedhorns. Operating in continuous-wave mode at 3.5 THz, and at an ambient temperature of ~60 K, QCL emission has been directed via the feedhorns to a supra-THz detector mounted on a multi-axis linear scanner. Comparison of simulated and measured far-field antenna patterns shows an excellent degree of correlation between beamwidth (full-width-half-maximum) and sidelobe content and a very substantial improvement when compared with unmounted devices. Additionally, a single output has been used to successfully illuminate and demonstrate an optical breadboard arrangement associated with a future supra-THz Earth observation space-borne payload. Our novel device has therefore provided a valuable demonstration of the effectiveness of supra-THz diagonal feedhorns and QCL devices for future space-borne ultra-high-frequency Earth-observing heterodyne radiometers.
We describe the motivation and design details of the ‘Phase II’ upgrade of the Murchison Widefield Array radio telescope. The expansion doubles to 256 the number of antenna tiles deployed in the array. The new antenna tiles enhance the capabilities of the Murchison Widefield Array in several key science areas. Seventy-two of the new tiles are deployed in a regular configuration near the existing array core. These new tiles enhance the surface brightness sensitivity of the array and will improve the ability of the Murchison Widefield Array to estimate the slope of the Epoch of Reionisation power spectrum by a factor of ∼3.5. The remaining 56 tiles are deployed on long baselines, doubling the maximum baseline of the array and improving the array u, v coverage. The improved imaging capabilities will provide an order of magnitude improvement in the noise floor of Murchison Widefield Array continuum images. The upgrade retains all of the features that have underpinned the Murchison Widefield Array’s success (large field of view, snapshot image quality, and pointing agility) and boosts the scientific potential with enhanced imaging capabilities and by enabling new calibration strategies.
The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (~2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.
We are a group of researchers and clinicians with collective experience in child survival, nutrition, cognitive and social development, and treatment of common mental conditions. We join together to welcome an expanded definition of child development to guide global approaches to child health and overall social development. We call for resolve to integrate maternal and child mental health with child health, nutrition, and development services and policies, and see this as fundamental to the health and sustainable development of societies. We suggest specific steps toward achieving this objective, with associated global organizational and resource commitments. In particular, we call for a Global Planning Summit to establish a much needed Global Alliance for Child Development and Mental Health in all Policies.
High signal-to-noise Reticon spectra for 87 members of 8 open clusters and associations together with 37 stars having reliable parallaxes (early A-type stars with reliable trigonometric parallaxes, eclipsing binaries, and visual binaries) have been used to calibrate the W(Hγ)-Mv relation for spectral types 0 to early A of luminosity classes III-V. The new calibration has a mean probable dispersion of ±0.28 mag. The distance modulus of the Pleiades is 5.54 ± 0.06 mag, which is in excellent agreement with other, recent determinations, as are the distance moduli for all the calibrating clusters. The use of visual-binary parallaxes implies a Hyades distance modulus of about 3.0 which is significantly smaller than the Hanson (1980) value of 3.30 mag. Although no spectral-type corrections are necessary, stellar evolution probably affects the construction of the new calibration and special care should be taken when determining distance moduli from slightly evolved cluster sequences or for individual stars. Systematic departures from the calibration may be present for stars with Vsin i ≥ 220–250 km/sec. Significant residuals are found between our values of W(Hγ) and those of Petrie in the range 1–13 Å equivalent width, which are due in part to systematic errors in Petrie's W(Hγ) measures. Our distance modulus of 11.11 mag for NGC 2244 is in excellent agreement with the photometric distance. The new calibration is compared to other early type star calibrations for main sequence stars. It is 1.2 mag brighter than Petrie's (1965) Hγ calibration at spectral type 06 and 0.7 mag brighter at A3. For types B1 and earlier the new calibration averages 0.4 mag brighter than the Balona and Crampton (1974) Hγ calibration. There is generally good agreement with the Blaauw (1963) MK calibration although the latter is 0.4 mag brighter at spectral type BO. The Crawford (1978) Hβ calibration is up to 0.5 mag brighter for the earlier spectral types and 0.4 mag fainter for later types. More complete discussions of the Hγ-luminosity calibration are available in Millward and Walker (1984, 1985).
By imposing absorption lines of HF in stellar spectra we can measure changes in r.v. with a precision of ~10m/s from a single spectrum, provided stellar line profiles are not distorted by atmospheric motions. The precision of absolute radial velocities is currently limited to ~100m/s by knowledge of rest wavelengths. Representative results are presented from our three, active PRV programs: velocity variations of δ Scuti stars; a search for unseen companions to late-type stars; and routine observations of certain IAU velocity ‘standards’.
Trigonometric parallaxes have been measured by Dahn et al. (2002) for 28 cool dwarfs and brown dwarfs, including 17 L dwarfs and three T dwarfs. Broadband CCD and near-IR photometry (VRIz*JHK) have been obtained for these objects and for 24 additional late-type dwarfs. These data have been supplemented with astrometry and photometry from the literature, including parallaxes for the brighter companions of ten L and two T dwarfs. The absolute magnitudes and colors are reviewed here. The I - J color and the spectral type are both good predictors of absolute magnitude for late-M and L dwarfs. MJ becomes monotonically fainter with I - J color and with spectral type through late-L dwarfs, then brightens for early-T dwarfs. In contrast, the J - K color correlates poorly with absolute magnitude for L dwarfs. Using several other parameters from the literature (Li detection, Hα emission strength, projected rotation velocity, and tangential velocity), we fail to uncover any measurable parameter that correlates with the anomalous J - K color.
We have compiled a catalogue of H ii regions detected with the Murchison Widefield Array between 72 and 231 MHz. The multiple frequency bands provided by the Murchison Widefield Array allow us identify the characteristic spectrum generated by the thermal Bremsstrahlung process in H ii regions. We detect 306 H ii regions between 260° < l < 340° and report on the positions, sizes, peak, integrated flux density, and spectral indices of these H ii regions. By identifying the point at which H ii regions transition from the optically thin to thick regime, we derive the physical properties including the electron density, ionised gas mass, and ionising photon flux, towards 61 H ii regions. This catalogue of H ii regions represents the most extensive and uniform low frequency survey of H ii regions in the Galaxy to date.
The technology leading to very large aperture telescopes and their optics has progressed well in the period since 1984 and plans for many new large aperture telescopes have been made. Focal plane instrumentation continues to become more sophisticated or more efficient: multi-object capabilities, automatic instrument control and operation, and increasing use of CCDs are examples of areas to which this applies. The proportion of time devoted to observations using two-dimensional photoelectronic detectors has grown substantially at many observatories, particularly with telescopes of moderate aperture; and the use of high quantum efficiency array detectors is now being extended into the infrared spectral region. Important advances have also been made in instrumentation and techniques for ground-based high angular resolution interferometry.
The data contained in this report have been taken from two sources: (1) Information received from astronomers active in the field of Commission 37 in response to a circular letter mailed July 1969; (2) Surveys of special fields, prepared by W. Becker on “Open star clusters and spiral structure”, by G. Larsson-Leander on “Clusters and stellar evolution”, by M. Walker on “Young clusters’, and by P. -B. Bouvier on “Dynamical models and numerical computations’. It is a pleasure to thank them and all of those who have contributed to the preparation of this report.
G. Alter reports that after a long delay the second edition of the Catalogue of Star Clusters and Associations. (G. Alter, J. Ruprecht, V. Vanýsek), which was discussed at a meeting of our commission at the Congress in Hamburg (1964) (Trans, IAU, 12B, 1966, 336), will now be published by Publishing House of the Hungarian Academy of Sciences. It is considerably enlarged, since it includes the contents of the annual Supplements published in B.A.C. between 1959 and 1967.
We have found large amplitude intraday variability in the radio quasar PKS 0405–385 on timescales less than an hour. If intrinsic to the source, the inferred brightness temperature is TB ~ 1021 K, far exceeding the inverse Compton limit for a static synchrotron source. We argue that our data are in agreement with interstellar scintillations of a source component which is < 5μarcsec in size.
We present some preliminary results based on new observations of the variable stars belonging to the Carina Dwarf Galaxy (DG). Photometric data were collected with the two wide field imagers available at ESO (WFI@2.2.) and CTIO (4m prime focus).
Two large sinusoidal variations with periods of 3.337 hrs and 2.018 hrs and other smaller variations have been detected from the period analysis of Hel Λ 6678 spectra obtained by our multi-site campaign for ζ Oph in May, 1993. The resultant periodgram is considerably improved (aliasing free) from those in previous publications. The periodicity may be consistent with previous studies except ambiguities of aliasing. It is surprising that almost all detected periods have a common superperiodicity of about 10.05 hrs. We emphasise the importance of multi-site campaign for the study of line-profile variations (lpv) in early-type stars.
A passive interplanetary dust collection experiment, currently in orbit aboard LDEF (Long Duration Exposure Facility), is described. The collectors, germanium target plates covered by metallized Mylar foils, are designed for secondary ion mass spectrometry (SIMS) measurements of the elemental and isotopic compositions of residues resulting from micrometeoroid (> 10−10 grams) impacts. Impact simulation experiments have demonstrated the validity of the collection concept. Quantitative elemental analyses are complicated by the non-uniform distribution of projectile-derived elements.
MOST (Microvariability & Oscillations of STars / Microvariabilite et Oscillations STellaire) is a Canadian microsatellite mission intended to detect rapid photometric oscillations at the μmag level in stars brighter than V ∼ 6. This limit is set primarily by the 15-cm aperture of the MOST telescope. The small size and mass of the MOST bus (similar to a suitcase) sets a limit on the pointing accuracy of about ±10 arcsec. To achieve the required photometric precision under these conditions, the MOST focal plane features a set of Fabry microlenses which can spread the target starlight into a pupil image of the telescope onto a CCD. The large size (∼1600 pixels) and positional stability (±0.1 pixel) of these images makes MOST insensitive to CCD flat-fielding errors. MOST is currently on schedule to be launched in early 2002.