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There are many astronomical, interferometric and space situational awareness applications for single and multiple 2-meter aperture optical and infrared mobile telescopes that are low cost, can be easily transported and quickly deployed at a variety of sites. A design concept is presented for a trailermounted 2-meter telescope with a novel micro-enclosure that allows the telescope to be moved and deployed quickly for observations. The telescope is protected from adverse weather using a weatherproof telescope tube instead of a conventional dome or enclosure. It has Cassegrain, Nasmyth and coude foci suitable for astronomical, interferometric, space situational awareness, and laser communications applications, and is designed for replication at low cost. An initial implementation is being developed to explore the performance of such a telescope using re-purposed primary and secondary mirrors and other components from the MAGNUM telescope.

The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve the 1.3 mm emission from this source on angular scales comparable to that of the general relativistic shadow. Previous EHT observations have used visibility amplitudes to infer the morphology of the millimeter-wavelength emission. Potentially much richer source information is contained in the phases. We report on 1.3 mm phase information on Sgr A* obtained with the EHT on a total of 13 observing nights over 4 years. Closure phases, the sum of visibility phases along a closed triangle of interferometer baselines, are used because they are robust against phase corruptions introduced by instrumentation and the rapidly variable atmosphere. The median closure phase on a triangle including telescopes in California, Hawaii, and Arizona is nonzero. This result conclusively demonstrates that the millimeter emission is asymmetric on scales of a few Schwarzschild radii and can be used to break 180-degree rotational ambiguities inherent from amplitude data alone. The stability of the sign of the closure phase over most observing nights indicates persistent asymmetry in the image of Sgr A* that is not obscured by refraction due to interstellar electrons along the line of sight., Comment: 11 pages, accepted to ApJ

We report results from very long baseline interferometric (VLBI) observations of the supermassive black hole in the Galactic center, Sgr A*, at 1.3 mm (230 GHz). The observations were performed in 2013 March using six VLBI stations in Hawaii, California, Arizona, and Chile. Compared to earlier observations, the addition of the APEX telescope in Chile almost doubles the longest baseline length in the array, provides additional {\it uv} coverage in the N-S direction, and leads to a spatial resolution of $\sim$30 $\mu$as ($\sim$3 Schwarzschild radii) for Sgr A*. The source is detected even at the longest baselines with visibility amplitudes of $\sim$4-13% of the total flux density. We argue that such flux densities cannot result from interstellar refractive scattering alone, but indicate the presence of compact intrinsic source structure on scales of $\sim$3 Schwarzschild radii. The measured nonzero closure phases rule out point-symmetric emission. We discuss our results in the context of simple geometric models that capture the basic characteristics and brightness distributions of disk- and jet-dominated models and show that both can reproduce the observed data. Common to these models are the brightness asymmetry, the orientation, and characteristic sizes, which are comparable to the expected size of the black hole shadow. Future 1.3 mm VLBI observations with an expanded array and better sensitivity will allow a more detailed imaging of the horizon-scale structure and bear the potential for a deep insight into the physical processes at the black hole boundary., Comment: 11 pages, 5 figures, accepted to ApJ

REhnu has now built up a year of experience operating two M-8 CPV generators with dish-receiver architecture described in Stalcup et al. 2017 [1]. The M-8 generators use 8 primary collector mirrors made of back-silvered low-iron glass, 1.65 m square with a 1.5 m focal length. Small sealed receivers at each dish focus house 36 Solar Junction 3J cells operating at 950× concentration. Over the year of operation, a good measure of output power vs DNI and atmospheric conditions has been obtained. The efficiency varies through the day depending on air mass. The system is currently best matched to the solar spectrum at air mass 2. The daily peak CSTC efficiency averages 31%, with seasonal variation of ±1% through the year, peaking at 32% in August. Several improvements were made over the year to ensure reliability and to improve optical throughput. A dry air purging system has mitigated damage to the cells from moisture. Material upgrades to secondary reflectors in the receiver have resolved a runaway failure mode that went previously undetected due to inadequate testing time.REhnu has now built up a year of experience operating two M-8 CPV generators with dish-receiver architecture described in Stalcup et al. 2017 [1]. The M-8 generators use 8 primary collector mirrors made of back-silvered low-iron glass, 1.65 m square with a 1.5 m focal length. Small sealed receivers at each dish focus house 36 Solar Junction 3J cells operating at 950× concentration. Over the year of operation, a good measure of output power vs DNI and atmospheric conditions has been obtained. The efficiency varies through the day depending on air mass. The system is currently best matched to the solar spectrum at air mass 2. The daily peak CSTC efficiency averages 31%, with seasonal variation of ±1% through the year, peaking at 32% in August. Several improvements were made over the year to ensure reliability and to improve optical throughput. A dry air purging system has mitigated damage to the cells from moisture. Material upgrades to secondary reflectors in the receiver have resolved a runaway failure mo...

REhnu has built and tested two 6 kW CPV-T trackers using dish-receiver architecture. In these trackers, only the light collection elements are large, namely mirrors on dual axis trackers. The inherently small parts, the multijunction cells, are packaged in a small, inexpensive receiver at each mirror focus. Optics in the receiver apportion the intensely focused sunlight equally to many cells, for high optical efficiency and simplified manufacture. Heat is removed by recirculated liquid. The tracker carries eight 2.7 m2 mirrors and receivers. The CSTC DC efficiency of the individual mirror receiver units is measured at 32.5%. When used for electrical generation alone, the tracker system delivers an AC electrical output of 6.27 kW to the grid, referenced to a solar flux of 1 kW/m2 DNI and 20°C ambient temperature, corresponding to a total CSOC system efficiency of 29.1%, matching the best grid-connected system efficiency reported for any CPV system4. When used to generate also a thermal output of 9 kW at 64...

The Richard F. Caris Mirror Lab at the University of Arizona is responsible for production of the eight 8.4 m segments for the primary mirror of the Giant Magellan Telescope, including one spare off-axis segment. We report on the successful casting of Segment 4, the center segment. Prior to generating the optical surface of Segment 2, we carried out a major upgrade of our 8.4 m Large Optical Generator. The upgrade includes new hardware and software to improve accuracy, safety, reliability and ease of use. We are currently carrying out an upgrade of our 8.4 m polishing machine that includes improved orbital polishing capabilities. We added and modified several components of the optical tests during the manufacture of Segment 1, and we have continued to improve the systems in preparation for Segments 2-8. We completed two projects that were prior commitments before GMT Segment 2: casting and polishing the combined primary and tertiary mirrors for the LSST, and casting and generating a 6.5 m mirror for the Tokyo Atacama Observatory.

The LSST M1/M3 combines an 8.4 m primary mirror and a 5.1 m tertiary mirror on one glass substrate. The combined mirror was completed at the Richard F. Caris Mirror Lab at the University of Arizona in October 2014. Interferometric measurements show that both mirrors have surface accuracy better than 20 nm rms over their clear apertures, in nearsimultaneous tests, and that both mirrors meet their stringent structure function specifications. Acceptance tests showed that the radii of curvature, conic constants, and alignment of the 2 optical axes are within the specified tolerances. The mirror figures are obtained by combining the lab measurements with a model of the telescope’s active optics system that uses the 156 support actuators to bend the glass substrate. This correction affects both mirror surfaces simultaneously. We showed that both mirrors have excellent figures and meet their specifications with a single bending of the substrate and correction forces that are well within the allowed magnitude. The interferometers do not resolve some small surface features with high slope errors. We used a new instrument based on deflectometry to measure many of these features with sub-millimeter spatial resolution, and nanometer accuracy for small features, over 12.5 cm apertures. Mirror Lab and LSST staff created synthetic models of both mirrors by combining the interferometric maps and the small highresolution maps, and used these to show the impact of the small features on images is acceptably small.

We report calculations of the evolution, under Reynolds viscosity, of the massive gaseous accretion discs thought to form in the centres of galaxies as a result of major galactic mergers at early epochs. Starting with the formation of such a disc and the postulated existence of a low-mass 'seed' black hole, we focus on the mass accretion rate, , and hence luminosity, L(GC), of a putative supermassive black hole (SMBH) in the galactic centre. Our computations cover a range of initial disc mass, M(d, 0), and outer radius, s(max, 0), and have been carried out under the assumption that cannot exceed the Eddington limit and that any excess mass supplied from the disc is lost from the system. Our purpose is to understand the extent to which such a model can account for the evolution with redshift of the observed properties of active galactic nuclei (AGNs). We show that within this framework: the initial mass supply rate from the disc increases with M(d, 0) and compactness, adjusts rapidly (on a viscous time-scale) to its peak value and decreases steadily thereafter; peak SMBH mass accretion rate and hence luminosity occurs when the (decreasing) disc flow rate equals the (increasing) black hole (BH) Eddington rate and is proportional to the BH mass, MEdd(BH), at that juncture; the fractional disc mass lost during the Eddington-limited phase increases with M(d, 0) and compactness so strongly that, for given (large) M(d, 0), the peak BH luminosity and corresponding mass occurs for some intermediate value of s(max, 0) so that MEdd(BH) declines for more compact initial discs; SMBHs with mass M(BH) >= 109 M(circle dot) and luminosity L(GC) >= 3 x 1013 L(circle dot) can form in a time t < 109 yr as required by the most luminous high-redshift quasi-stellar objects but the Eddington-induced mass-loss renders unlikely the creation of BHs of comparable or greater mass or luminosity in significantly shorter times; the most luminous quasars form and die at the earliest epochs while those of lower luminosity occur over successively longer periods ranging up to the present time; in general, AGNs that are at an early evolutionary phase accrete at or close to their Eddington rate but evolve into the sub-Eddington regime later on. The proposed scenario appears capable of accounting for many of the features of the observed quasar and AGN luminosity distribution with redshift and seems to be a natural consequence of the formation of massive central discs following major galaxy mergers.

A REhnu CPV module uses a 2.6 m2, back-silvered glass reflector to focus sunlight into a 150 mm diameter receiver housing 36 multijunction cells. Current modules use commercially available 8.8 mm cells operated at 950x concentration with a cell efficiency of 41% for an AM1.5 solar spectrum. Optics in the receiver format the sunlight to illuminate the cells which are mounted slightly apart on four flat circuit boards. Active cooling is provided by liquid circulated to a radiator which can easily be configured to also provide thermal energy in the form of hot fluid at an adjustable temperature up to 80 °C.Modules mounted in pairs on a dual axis tracker have been tested in the field. Module conversion efficiency, corrected to 25 °C cell temperature (CSTC), is found to peak at 31.2% for air mass 2.75. The I-V curve shows that the concentrated sunlight is distributed between the cells with a uniformity of ±7%. Steps are now being taken to improve uniformity, to reduce infrared losses caused by iron absorption ...

We report about a 230 GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO). We installed VLBI equipment and measured the APEX station position to 1 cm accuracy (1 sigma). We then observed 3C 279 on 2012 May 7 in a 5 hour 230 GHz VLBI track with baseline lengths of 2800 M$\lambda$ to 7200 M$\lambda$ and a finest fringe spacing of 28.6 micro-arcseconds. Fringes were detected on all baselines with SNRs of 12 to 55 in 420 s. The correlated flux density on the longest baseline was ~0.3 Jy/beam, out of a total flux density of 19.8 Jy. Visibility data suggest an emission region, Comment: accepted for publication in A&A

It is still an open question whether the super-massive black holes thought to be present in quasars are of primordial nature, or whether there is a viable way of forming them in the very short time scale (less than a billion years) permitted by the observational data. In this contribution, we present a way in which a galaxy-galaxy merger can provide not only the “fuel” for quasar activity, but can also build a super-massive black hole, i.e., “the engine”, in the first place.

Segment production for the Giant Magellan Telescope is well underway, with the off-axis Segment 1 completed, off-axis Segments 2 and 3 already cast, and mold construction in progress for the casting of Segment 4, the center segment. All equipment and techniques required for segment fabrication and testing have been demonstrated in the manufacture of Segment 1. The equipment includes a 28 m test tower that incorporates four independent measurements of the segment's figure and geometry. The interferometric test uses a large asymmetric null corrector with three elements including a 3.75 m spherical mirror and a computer-generated hologram. For independent verification of the large-scale segment shape, we use a scanning pentaprism test that exploits the natural geometry of the telescope to focus collimated light to a point. The Software Configurable Optical Test System, loosely based on the Hartmann test, measures slope errors to submicroradian accuracy at high resolution over the full aperture. An enhanced laser tracker system guides the figuring through grinding and initial polishing. All measurements agree within the expected uncertainties, including three independent measurements of radius of curvature that agree within 0.3 mm. Segment 1 was polished using a 1.2 m stressed lap for smoothing and large-scale figuring, and a set of smaller passive rigid-conformal laps on an orbital polisher for deterministic small-scale figuring. For the remaining segments, the Mirror Lab is building a smaller, orbital stressed lap to combine the smoothing capability with deterministic figuring.

The Steward Observatory Mirror Lab is nearing completion of the combined primary and tertiary mirrors of the Large Synoptic Survey Telescope. Fabrication of the combined mirror requires simulation of an active-optics correction that affects both mirror surfaces in a coordinated way. As is common for large mirrors, the specification allows correction of large-scale figure errors by a simulated bending of the substrate with the 156 mirror support actuators. Any bending affects both mirrors, so this active-optics correction is constrained by the requirement of bending the substrate so both mirrors meet their figure specifications simultaneously. The starting point of the simulated correction must be measurements of both mirrors with the substrate in the same shape, i. e. the same state of mechanical and thermal stress. Polishing was carried out using a 1.2 m stressed lap for smoothing and large-scale figuring, and a set of smaller passive rigid-conformal laps on an orbital polisher for deterministic small-scale figuring. The primary mirror is accurate to about 25 nm rms surface after the active-optics correction, while work continues toward completion of the tertiary.

Approximately 10% of active galactic nuclei exhibit relativistic jets, which are powered by accretion of matter onto super massive black holes. While the measured width profiles of such jets on large scales agree with theories of magnetic collimation, predicted structure on accretion disk scales at the jet launch point has not been detected. We report radio interferometry observations at 1.3mm wavelength of the elliptical galaxy M87 that spatially resolve the base of the jet in this source. The derived size of 5.5 +/- 0.4 Schwarzschild radii is significantly smaller than the innermost edge of a retrograde accretion disk, suggesting that the M87 jet is powered by an accretion disk in a prograde orbit around a spinning black hole., Comment: 12 pages, 3 figures, accepted version

Sagittarius A*, the ~4 x 10^6 solar mass black hole candidate at the Galactic Center, can be studied on Schwarzschild radius scales with (sub)millimeter wavelength Very Long Baseline Interferometry (VLBI). We report on 1.3 mm wavelength observations of Sgr A* using a VLBI array consisting of the JCMT on Mauna Kea, the ARO/SMT on Mt. Graham in Arizona, and two telescopes of the CARMA array at Cedar Flat in California. Both Sgr A* and the quasar calibrator 1924-292 were observed over three consecutive nights, and both sources were clearly detected on all baselines. For the first time, we are able to extract 1.3 mm VLBI interferometer phase information on Sgr A* through measurement of closure phase on the triangle of baselines. On the third night of observing, the correlated flux density of Sgr A* on all VLBI baselines increased relative to the first two nights, providing strong evidence for time-variable change on scales of a few Schwarzschild radii. These results suggest that future VLBI observations with greater sensitivity and additional baselines will play a valuable role in determining the structure of emission near the event horizon of Sgr A*., 8 pages, submitted to ApJL

The cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation (ref 1). Sagittarius A*, the compact source of radio, infrared and X-ray emission at the centre of the Milky Way, is the closest example of this phenomenon, with an estimated black hole mass that is 4 million times that of the Sun (refs. 2,3). A long-standing astronomical goal is to resolve structures in the innermost accretion flow surrounding Sgr A* where strong gravitational fields will distort the appearance of radiation emitted near the black hole. Radio observations at wavelengths of 3.5 mm and 7 mm have detected intrinsic structure in Sgr A*, but the spatial resolution of observations at these wavelengths is limited by interstellar scattering (refs. 4-7). Here we report observations at a wavelength of 1.3 mm that set a size of 37 (+16, -10; 3-sigma) microarcseconds on the intrinsic diameter of Sgr A*. This is less than the expected apparent size of the event horizon of the presumed black hole, suggesting that the bulk of SgrA* emission may not be not centred on the black hole, but arises in the surrounding accretion flow., 12 pages including 2 figures

We summarize our recent results on the evolution of super-massive black holes in the cores of galaxies. Our models are based on the viscous, Eddington-limited evolution of self-gravitating accretion disks. We find that, within this framework, one can explain the growth time scales and the luminosities of individual objects as well as the variation of these quantities for AGN with different black hole masses.

We report on new developments in VLBI, with emphasis on experiments performed at the highest frequencies possible to date (so called mm-VLBI). We have observed the nucleus of M 87 (Virgo A) with global VLBI at 3 mm. We show a new image of the inner-most jet region with an angular resolution of approx. 300 x 60 micro-arcseconds. In terms of Schwarzschild radii, this leads to an upper limit of the jet base of approx. 100 x 20 Schwarzschild radii. We also report on two VLBI pilot-experiments, which demonstrate the technical feasibility of global VLBI at 150 and 230 GHz (2 mm and 1.3 mm). The experiments lead to upper limits to the size of the unresolved AGN-cores in the 25 - 30 micro-arcsecond range. The participation of new and near-future mm-telescopes (like APEX, CARMA, SMA, LMT, ALMA, etc.) in global mm-VLBI will provide the necessary sensitivity for the imaging of black holes and their immediate environment.

We show that the rapid formation of super-massive black holes in quasars can indeed be understood in terms of major galaxy mergers followed by disk accretion. The necessary short disk evolution time can be achieved provided the disk viscosity is sufficiently large, which, for instance, is the case for hydrodynamic turbulence, unlimited by shock dissipation. We present numerical calculations for a representative case. This general picture can account for (a) the presence of highly luminous quasars at redshifts z > 6; (b) for the peak in quasar activity at z ~ 2; and (c) for a subsequent rapid disappearance of quasars at later epochs., 9 pages, 1 figure, to appear in the proceedings of the Xth Marcel Grossman Meeting, Rio de Janeiro, 2003

We present a plan for making the optics of a 21 m telescope that builds on advances in mirror design and fabrication developed for the Large Binocular Telescope (LBT) and other large telescopes. The 21 m telescope, with a fast f/0.7 primary mirror made of only seven large honeycomb-sandwich segments and an adaptive secondary with matching segments, is much stiffer than other designs and offers simpler and more accurate wavefront control. It can be a powerful stand-alone telescope, or one of a pair that move on a circular track to achieve coherent imaging with baselines up to 120 m (the 20/20 telescope). Each segment of the 21 m primary mirror is similar to an 8.4 m LBT primary, and each segment of the 2.1 m adaptive secondary mirror is similar to an LBT secondary. The off-axis segments of both mirrors can be made with the same methods and equipment currently used at the Steward Observatory Mirror Lab, and can be polished with the same stressed-lap polishing system used for the LBT mirrors. A change in algorithm to accommodate the asymmetric surface is required, but no new hardware development is needed because the lap bending is similar to that for the LBT mirrors. Each segment can be measured interferometrically, with a combination reflective and diffractive null corrector producing an accurate aspheric template wavefront and alignment references for the segments.

The primary mirror for the Multiple Mirror Telescope Conversion is the first 6.5 m honeycomb sandwich mirror cast and polished by the Steward Observatory Mirror Lab. We describe the optical fabrication and testing of the f/1.25 paraboloid, and present the final measurements of figure accuracy and inferred image quality. Figuring was performed with a 1.2 m stressed lap--which bends under active control to match the local curvature of the optical surface--and a variety of small passive tools. The mirror was pressurized to compensate for polishing loads and thereby eliminate print-through of the honeycomb structure. The net result is a smoother surface on scales of 5 - 20 cm than has been achieved on previous honeycomb sandwich mirrors. The figure was measured with IR and visible interferometers, using refractive null correctors to compensate 810 microns of aspheric departure. The final measurements were used to calculate synthetic stellar images in a variety of seeing conditions.

The Large Binocular Telescope (LBT) has been designed for optical/infrared interferometry that combines high sensitivity and resolution. Key scientific projects will be deep, wide field infrared images of the Hubble Deep Field, with nearly ten times the resolution of the Hubble telescope, and the study of planets and dust in extra-solar systems, from their formation onward. A basic requirement for interferometry of faint objects is that the aberrations across the two 8.4 m telescopes be corrected for atmospheric phase errors. This will be done at the telescopes' secondary mirrors, so as to preserve the very low emissivity of the direct beam combination optics. Sodium lasers projected co-axially from above each secondary will allow wavefront sensing for correction of even the faintest objects. The two telescopes are rigidly mounted close together on a single alt-azimuth mount, to cover a large fraction of the u-v plane in a single exposure, with baselines continuous from 0 to 23 m. Field rotation during the night completes the cover, to allow recovery of images with the full resolution of a diffraction limited 23 m telescope. The beam combining optics will be cryogenically cooled to maintain the very low thermal background from only 3 warm reflections in total (primary, adaptive secondary, tertiary). For wide field imaging, the beams will be combined and stabilized so that in a long exposure every source across a t 1 arcminute field is crossed by nterference fringes. From a set of such exposures the resultant deep image will have a resolution 0.02 arcsec in the 2.2.μm K band. For high contrast studies of exo-planetary systems, a Bracewell nulling system will be used with superposition by division of amplitude, for 99.99% suppression of the stellar radiation.

We summarize our recent results on the evolution of super-massive black holes in the cores of galaxies. Our models are based on the viscous, Eddington-limited evolution of self-gravitating accretion disks. We find that, within this framework, one can explain the growth time scales and the luminosities of individual objects as well as the variation of these quantities for AGN with different black hole masses.

The design for the Columbus binocular telescope has been completed and the project is now proceeding to the construction phase. The two 8-m f/1.2 borosilicate honeycomb mirrors will give an effective collecting area of 11.3 m and a baseline of 22 m for interferometry. The optics are supported on an exceedingly compact and rigid 'C-ring' mount with a lowest eigenfrequency of around 10 Hz. The system will be housed in a corotating enclosure and will be located on Mt. Graham in southeastern Arizona. Instrumentation priorities have been established for the telescope and conceptual designs are now under development.

The planned international observatory at Mount Graham, Arizona, provides a model of how environmental concerns should be met in a project of this size. But it remains vulnerable to Irresponsible "activists".

Analytical expressions are derived for the semimajor and semiminor axes and orientation angle of the ellipse projected by a triaxial asteroid, and the results are applied speckle-interferometry observations of the 433 Eros asteroid. The expressions were calculated as functions of the dimensions and pole of the body and of the asterocentric position of the earth and the sun. On the basis of the analytical expressions, the dimensions of 433 Eros are obtained. The light curve from December 18, 1981 is compared to the dimensions to obtain a geometric albedo of 0.156 (+ or - 0.010). A series of two-dimensional power spectra and autocorrelation functions for 433 Eros show that it is spinning in space.

We report speckle interferometric observations of Pluto and its moon (1978 P1) Charon obtained on 5 June 1980 with a single 1.8-m mirror of the Multiple Mirror Telescope. Our observations yield a separation of 0″.31 (±0″.05) between Pluto and Charon at position angle 285° (±7°) for JD 2444395.75. This result and other direct observations indicate an adjustment of +4.0 hr to the orbital epoch of R. S. Harrington and J. W. Christy [ Astron.J. 86 , 442–443 (1981)]. Our observation, which represents the first resolution of the system near minimum separation, also suggests that the inclination of the orbit to the plane of the sky should be increased by 3°; this will delay the onset of the predicted eclipsee season by one apparition to 1984 or 1985. Our data are consistent with Pluto diameter 0″.14 (±0″.02) = 3000 (±400) km and Charon diameter 0″..05 (±0″.03) = 1100 (±600) km.

This paper summarizes recent advances on the Columbus Project telescope and in the University of Arizona Mirror Lab. The Columbus telescope structure has been re-optimized to allow rapid changes between foci, while still maintaining high rigidity. Room has been made to translate secondary and tertiary spiders out of the light path to the center. A bill allowing construction of the telescope on Mt. Graham, Arizona, has been passed by Congress and signed into law. Two alternative enclosure designs, one with a co-rotating building and a second which opens like a flower, are being explored.

The evidence in favor of the hypothesis that Be stars owe their emission properties to material rotationally ejected from the equator is reviewed. The evolutionary state of Be Stars is then discussed with reference to evolutionary sequences of stellar models. It is concluded that (i) Be stars are not confined to the secondary contraction phase as previously proposed (ii) evolution probably proceeds with uniform rotation at least outside the initial convective core. Mechanisms for transporting angular momentum are briefly discussed.

The discrepancy between the masses of Cepheid variables deduced from evolution theory and pulsation theory is examined. The effect of input physics on evolutionary tracks is first discussed; in particular, changes in the opacity are considered. The sensitivity of pulsation masses to opacity changes and to the ascribed values of luminosity and effective temperature are then analyzed. The Cepheid mass discrepancy is discussed in the light of the results already obtained. Other astronomical evidence, including the mass-luminosity relation for main sequence stars, the solar neutrino flux, and cluster ages are also considered in an attempt to determine the most likely source of error in the event that substantial mass loss has not occurred.

Observations of a new type of rapidly varying radio source have recently been reported1. The principal characteristics of the four sources so far discovered may be summarized as follows—sharp pulses of radiation are received, separated by comparatively long intervals which themselves are remarkably constant (with variations of ≲ 1 part in 2 × 107 during the past 3 or 4 months). The pulse duration is no more than ~ 0·016 s, while the period is 1#x00B7;3372795 ±0#x00B7;0000020 s (ref. 1). We understand that the other objects show similar sharp pulses at intervals of the order of 1 s, which, although not identical, strongly suggest that a new type of physical system has been discovered. Hewish et al. propose that the objects may be pulsating white dwarfs or neutron stars. Although this may prove to be correct, there are certain difficulties associated with the constancy of the observed period. We suggest an alternative explanation for the observed phenomena.

We summarize the experiments which have used the Multiple Mirror Telescope (MMT) subapertures as a phased array in the optical, infrared, and submillimeter spectrum regions. Those experiments exploit the unique, very high angular resolution of the MMT being equivalent to that of a conventional telescope 686 cm in diameter. The operation of the MMT as a phased array is not only important for obtaining high angular resolution but also for obtaining the higher detection sensitivity which results from the better discrimination against the sky emission background for infrared diffraction limited images. We describe future plans to make the MMT into a phased telescope.

We describe a system for localization of photoelectron events utilizing an intensified Plumbicon camera and a Grinnell video digitizer. The Grinnell digitizer, arithmetic unit and memory are used to produce a real-time video difference between current pixel value and previous pixel value thereby suppressing multiple detection of the same event. A master clock provides synchronization with the camera in operation at 60 Hz in 240 lines/field, repeat field mode. Our event-localization scheme provides double-buffered line-address and event-amplitude for up to 32 events along a 512 pixel video line. A software algorithm allows localization of multiple detections of the same event, and provides a unique address interpolated with 1/2 line resolution by the host minicomputer in a 480 x 512 format.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Large gains in spatial resolution have been achieved at 0.5 and 5.0 µm by operating the MMT as a two-element interferometer with a maximum baseline of 6.9 m. Measurements of the resulting Michelson fringes at 5.0 µm have determined pathlength errors within the MMT and characterized pathlength stability versus elevation angle, temperature, and perturbations of the optical elements. At 0.5 μm, a "coherent beam-combiner" has successfully reconstructed a phased entrance pupil achieving a field >5 arcsec in diameter with 15 milli-arcsec resolution. Scientific measurements have fully resolved the 0.024 arcsec diameter disk α Tau (Aldebaran); resolved the 0.1 arcsec binary, β Tau; and provided new measurements of the spectroscopic binary, α Aur (Capella). Instrument designs employing only two additional reflections in each beam have been developed to phase the entire MMT for simultaneous applications at optical and infrared wavelengths. When configured as a phased array of four or six elements, the MMT responds to the full range of spatial frequencies present in a filled 6.9 m aperture with only a small degree of redundancy. A fully phased MMT possesses significant advantages for low background infrared photometry.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A four-stage electrostatic image intensifier transfer lens coupled to a plumbicon television camera is used both as a photoelectron event-detecting system and as an analogue detector for the Steward speckle camera. The system is capable of continuous logging of photoelectron event data allowing 100 percent utilization of telescope aperture time by use of a Grinnell GMR-27 video digitizer and graphic television display with a special modification for lag-free event detection. Data can be processed on-line at the site or recorded for off-line processing using a standard analogue video recorder. A seeing-corrected reconstruction of the diffraction limited image derived from the speckle interferometric image autocorrelation computed from 200 television frames of the magnified image of a seventh magnitude close visual binary star observed with the Steward 2.3 meter telescope is reported. The system has been applied to speckle interferometry of objects as faint as visual magnitude 16.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We discuss the various features of the optical and spectral developments of Nova Cygni 1975 (V1500 Cygni). The range of more than 19 magnitudes, the rounded maximum and steep decline and the absence of post-maximum absorption systems establish this as a unique object. We are able to explain these features if we assume that a thermonuclear runaway has taken place in the carbon-enhanced, hydrogen-rich, envelope of a single white dwarf where the hydrogen has been accreted by passage of the white dwarf through an interstellar cloud. This would be possible for Nova Cyg since it lies directly in the plane of the galaxy. The carbon enhancement, necessary for ejection, has occurred through the action of a surface convection zone which has mixed a fraction of the accreted hydrogen into the edge of the carbon core. We shall also discuss the observed oscillations and present alternative models for the object.

Speckle Interferometry has now been shown capable of yielding diffraction limited information on objects as faint as visual magnitude 16. Research in progress at Steward Observatiry is aimed at improving (a) the resolution, (by using the Multiple Mirror Telescope with its 6.9 meter baseline), (b) the accuracy of the derived results (by implementing better recording devices and reduction algorithms), and (c) the efficiency and speed with which the information can be provided (by means of high-speed digital signal-processing hardware). The instrumentation proposed here will improve patial resolution at visible wave-lengths to approximately 15 milliarc-seconds (75 x 10 ' radians, the best possible for any existing telescope), reduce detector induced image distortion to less than 1% and increase the throughput to essentially real-time complex Fourier transform amplitude and phase integrations at the telescope.

By adjustment of the optical pathlengths of the MMT telescopes, it is possible to make the MMT into a phased array with a 680 cm baseline. We will describe experiments in speckle interferometry and spectroscopy which have been done this way using 2 and 3 of the MMT telescopes. We will describe planned adjustments of the optical configuration of the MMT to achieve coherent operation over a large field of view with all six telescopes phased simultaneously.

Publisher Summary Image intensifiers are currently the primary detectors for ground-based optical astronomy. They are used with photographic emulsions and various electronic readout systems. They offer the advantages of reasonably high quantum efficiency, essentially noise-free amplification to very high gain values, and suitability for rapid readout. Progress in the development of a proximity intensifier for astronomy is very encouraging. A few samples have been produced that exhibit good blue response, resolution, gain, dark emission (when cooled), and freedom from field emission. However, the manufacturing yield of such samples is still low. An important step is to discover and eliminate the cause of lost-counting efficiency, observed in several diode intensifiers.

The evidence in favor of the hypothesis that Be stars owe their emission properties to material rotationally ejected from the equator is reviewed. The evolutionary state of Be Stars is then discussed with reference to evolutionary sequences of stellar models. It is concluded that (i) Be stars are not confined to the secondary contraction phase as previously proposed (ii) evolution probably proceeds with uniform rotation at least outside the initial convective core. Mechanisms for transporting angular momentum are briefly discussed.

We have equipped the APEX telescope for 1 mm VLBI and obtained first fringes on 3C 279 at 229 GHz in May 2012 with SMA (Hawaii) and SMTO (Arizona). The fringe spacing achieved was 29 microarcseconds, adequate to directly observe strong-field general-relativistic effects around the black hole in the Galactic center by resolving the expected diameter of the shadow of the event horizon in Sgr A* of ∼ 40 microarseconds. I present on behalf of the collaboration the unusual aspects of this high-altitude VLBI installation, and the prospects for upcoming observations with a global array at the highest resolution.

Global VLBI imaging at millimeter and sub-millimeter wavelength overcomes the opacity barrier of synchrotron self-absorption in AGN and opens the direct view into sub-pc scale regions not accessible before. Since AGN variability is more pronounced at short millimeter wavelength, mm-VLBI can reveal structural changes in very early stages after outbursts. When combined with observations at longer wavelength, global 3mm and 1mm VLBI adds very detailed information. This helps to determine fundamental physical properties at the jet base, and in the vicinity of super-massive black holes at the center of AGN. Here we present new results from multi-frequency mm-VLBI imaging of OJ287 during a major outburst. We also report on a successful 1.3mm VLBI experiment with the APEX telescope in Chile. This observation sets a new record in angular resolution. It also opens the path towards future mm-VLBI with ALMA, which aims at the mapping of the black hole event horizon in nearby galaxies, and the study of the roots of jets in AGN., Comment: 6 pages, to appear in 11th European VLBI Network Symposium, ed. P. Charlot et al., Bordeaux (France), October 9-12, 2012

The origin of the sharp near infrared cutoff in the continuous energy distribution of many compact non-thermal sources (active nuclei or knots in jets) is considered under the assumption that particle acceleration takes place in shockwaves. Energy losses due to synchrotron emission and Compton interactions set upper limits to both electron and proton energies. In this case the upstream disturbance of the flow is dominated by the most energetic protons which are postulated, by analogy with the solar wind, to excite a turbulent wave spectrum of Kolmogorov type in this region. We predict for near relativistic flows a spectral cutoff near 3 1014 Hz independent of magnetic field. The observation of a sharp spectral cutoff near 3 1014 Hz is thus independent evidence for near–relativistic flows in jets.

Correlation between position and red shift of quasars indicating anisotropic universe or galactic origin of quasars

The bursts of radio waves at decametric wavelengths emitted by Jupiter suggest a model for producing the signals from the pulsating radio sources. This mechanism includes polarization of the signals and structure within the pulses.

THE source 0048-097 was reported in the Parkes catalogue1 and later identified by Bolton and Ekers2 with an 18 mag blue galaxy in a small cluster. A number of accounts have been published of its rapid radio variability at high frequency3-6. Stull3 has pointed out that the radio spectrum (which shows no low frequency component) is similar to that of BL Lac. Kellermann and Pauliny-Toth7 have measured the radio spectrum up to 100 GHz and found a peak (at 1970.0) near 10 GHz. It is not, however, possible to determine the nature of the object from the radio spectrum alone.

THE purpose of this letter is to draw attention to the very high redshift, z = 3.40, of the QSO OH471.