Arcsec Diameter Research Articles

Preliminary results of the alignment and Hartmann tests of the AZT-22 telescope

The AZT-22 telescope installed in Turkey (Antalia) was aligned and tested on stars by the Hartmann method. The rms normal deviation of an equivalent optical system is 0.040±0.016 µm. The circle of confusion is 0.40±0.04 arcsec in diameter at a 50% energy level.

Axisymmetry in protoplanetary nebulae: using imaging polarimetry to investigate envelope structure

We use ground-based imaging polarimetry to detect and image the dusty circumstellar envelopes of a sample of proto-planetary nebulae (PPNe) at near-infrared wavelengths. This technique allows the scattered light from the faint envelope to be separated from the glare of the bright central star and is particularly well suited to this class of object. We detect extended (up to 9 arcsec diameter) circumstellar envelopes around 15 out of 16 sources with a range of morphologies including bipolars and shells. The distribution of scattered light in combination with its polarization (up to 40 per cent) provides unambiguous evidence for axisymmetry in 14 objects showing this to be a common trait of PPNe. We suggest that the range of observed envelope morphologies results from the development of an axisymmetric dust distribution during the superwind phase at the end of the AGB. We identify shells seen in polarized light with scattering from these superwind dust distributions which allows us to provide constraints on the duration of the superwind phase. In one object (IRAS 19475+3119) the circumstellar envelope has a two-armed spiral structure which we suggest results from the interaction of the mass losing star with a binary companion.

The Manchester occulting mask imager (MOMI): first results on the environment of P Cygni

The design and first use of the Manchester occulting mask imager (MOMI) is described. This device, when combined with the Cassegrain or Ritchey-Chretien foci of large telescopes, is dedicated to the imagery of faint line emission regions around bright central sources. Initial observations, with MOMI on the Nordic Optical telescope (NOT), of the V=4.8 mag P~Cygni environment, have revealed a $\geq$~5~arcmin long [NII] 6584A emitting filament projecting from the outer nebular shell of this luminous blue variable (LBV) star. The presence of a mono-polar lobe older than both the inner (22 arcsec diameter) and outer (1.6 arcmin diameter) shells is suggested.

An IR-Selected Galaxy Cluster at z=1.27

We report the discovery of a galaxy cluster at z=1.27. ClG J0848+4453 was found in a near-IR field survey as a high density region of objects with very red J-K colors. Optical spectroscopy of a limited number of 24 < R < 25 objects in the area shows that 6 galaxies within a 90 arcsec (0.49/h Mpc, q_O = 0.1) diameter region lie at z=1.273 +/- 0.002. Most of these 6 member galaxies have broad-band colors consistent with the expected spectral energy distribution of a passively-evolving elliptical galaxy formed at high redshift. An additional 2 galaxies located ~2 arcmin from the cluster center are also at z=1.27. Using all 8 of these spectroscopic members, we estimate the velocity dispersion is 700 +/- 180 km/s, similar to that of Abell R=1 clusters in the present epoch. A deep Rosat PSPC observation detects X-ray emission at the 5 sigma level coincident with the nominal cluster center. Assuming that the X-ray flux is emitted by hot gas trapped in the potential well of a collapsed system (no AGN is known to exist in the area), the resulting X-ray luminosity in the rest frame 0.1-2.4 keV band of L_x = 1.5 x 10^44 ergs/s suggests the presence of a moderately large mass. ClG J0848+4453 is the highest redshift cluster found without targetting a central active galaxy.

POLAR PLUME ANATOMY: RESULTS OF A COORDINATED OBSERVATION

On 7 and 8 March 1996, the SOHO spacecraft and several other space- and ground-based observatories cooperated in the most comprehensive observation to date of solar polar plumes. Based on simultaneous data from five instruments, we describe the morphology of the plumes observed over the south pole of the Sun during the SOHO observing campaign. Individual plumes have been characterized from the photosphere to approximately 15 R⊙ yielding a coherent portrait of the features for more quantitative future studies. The observed plumes arise from small (∼ 2-5 arc sec diameter) quiescent, unipolar magnetic flux concentrations, on chromospheric network cell boundaries. They are denser and cooler than the surrounding coronal hole through which they extend, and are seen clearly in both Feix and Fexii emission lines, indicating an ionization temperature between 1.0–1.5 x 106 K. The plumes initially expand rapidly with altitude, to a diameter of 20–30 Mm about 30 Mm off the surface. Above 1.2 R⊙ plumes are observed in white light (as ‘coronal rays’) and extend to above 12 R⊙. They grow superradially throughout their observed height, increasing their subtended solid angle (relative to disk center) by a factor of ∼10 between 1.05 R⊙ and 4–5 R⊙ and by a total factor of 20–40 between 1.05 R⊙ and 12 R⊙. On spatial scales larger than 10 arc sec, plume structure in the lower corona (R < 1.3 R⊙) is observed to be steady-state for periods of at least 24 hours; however, on spatial scales smaller than 10 arc sec, plume XUV intensities vary by 10–20% (after background subtraction) on a time scale of a few minutes.

The SN1987A Environment

The environment of the SN1987A is quite complex but also very regularly structured. Detailed analyses of direct images taken under good seeing conditions (0.3—0.8 arcsec) from the European Southern Observatory (ESO)'s New Technology Telescope (NTT) show that there are two nebular loops within the 3 arcsec environment of the SN. The inner loop is elliptical in shape. The kinematics of this loop as revealed by spectroscopic data with a spectral resolving power λ/Δλ « 30 000 provide further clues for the three dimensional structure of these two loops. The data show that the overall structure of the nebulosity can be understood by an hourglass-shaped shell with significant mass enhancement on its equatorial plane. A diffuse nebulosity called Napoleon's Hat is observed at a distance of about 5 arcsec to the north of the SN. It showed little size evolution since the first observation on Aug. 1989, until it disappeared on Jan, 1992. The Napoleon's Hat nebula appears to be a bow-shock coming from an interaction between the supernova progenitor's stellar wind and the interstellar medium, as the supernova progenitor moved through the interstellar medium with a velocity of around 5 kms-1. On an even larger scale, there is a huge dark bay of size around 100 arcsec in diameter, we suggested that this bay was also formed by interactions between the supernova progenitor and the interstellar medium.The narrow emission lines indicate that the electron density and temperature of the emission gas in the loops are steadily decreasing. However, the temperatures inferred from the [OIII] nebular lines remained persistently higher than 2 × 104K. They were around 104cm−3 and 2 × 104K on Aug. 30, 1990. In addition, a global difference in the electron density of the two major axis of the inner loop is observed in the images and spectra taken five years after the supernova explosion. We have also studied the two neighboring stars surrounding the supernova. We find that star 2 is a B star with Hα and Hβ emission lines.The supernova circumstellar nebulosity is remarkably similar to certain types of planetary nebula, e.g. NGC2392. Asymmetric wind interaction models for the formation of planetary nebula are applied to produce a model in the form of an hourglass shaped shell. This model invokes both a slow wind while the star was in its red supergiant phase and a fast wind during the later blue supergiant stage before explosion. Although such wind interaction models fit the observed nebular structures satisfactorily, they are so idealized that they tell us little about the origin of the seed asymmetry or the amount of seed asymmetry needed to produce the observed real nebula.

Hubble Space Telescope results in planetary science

The Hubble Space Telescope (HST) was placed into orbit by the Discovery shuttlecraft on April 25, 1990, and first light images were obtained on May 20, 1990 (Feinberg, 1990a; Palga, 1990). On June 26, NASA announced that the telescope suffered from spherical aberration and that , instead of focusing 70 percent of a star's light in an area 0.2 arcsec in diameter, the light was spread over an area with a diameter of 1.4 arcsec. The resulting point‐spread function (PSF) contained a 0.2 arc sec central spike that contained 15% of the light and, because the problem concerned two excellent yet mismatched mirrors, the resulting apron of the PSF could be represented by a predictable diffraction pattern, indicating that part of the resolution of the two cameras could be recovered by image deconvolution. As a part of the effort to assess the magnitude of the problem, the Wide Field/Planetary Camera (WFPC‐1) team obtained broad band blue, green and red images of Saturn on August 26, 1990 (Westphal et al, 1991). Using PSFs derived from a star for the 547 nm filter and theoretical PSFs for the 439 nm and 718 nm filters, the WFPC‐1 team used Lucy's algorithm (1974) to deconvolve the data and produced a composite three color image. This effort showed that a narrow gap, the Encke Division, in the outer ring could be resolved and produced an effective resolution of the deconvolved images that was better than the best groundbased results. Even with the focusing problems, this effective resolution ‐ combined with the fact that HST suffers less from scattered light, has UV sensitivity and yields the same resolution from observation to observation ‐ recommended it for planetary studies involving spatial and temporal variability. These initial observations revealed that Saturn's north polar hexagon, seen by Voyager (Allison et al, 1990), was visible, implying that it is not a transient feature. The latitudinal locations of belt‐zone interfaces differed from those recorded in 1981 Voyager images, indicating that seasonal or undetected sporadic convective activity had altered the reflective properties of the atmosphere.

A ring-like structure in the nuclear region of the post starburst galaxy NGC 4736

We observed the ring galaxy NGC 4736 in the V and I bands from March 31 to April 2, 1992, using the 1.0-m telescope of Yunnan Observatory. Processing with the Richardson-Lucy restoration and adaptive filter we found a ring-like structure of about 10 arcsec diameter in the V image.

Photometry of comet P/Brorsen-Metcalf (1989X) at the Skalnaté Pleso Observatory

The analysis of the pre-perihelion photoelectric measurements of P/Brorsen-Metcalf (1989X) made at the Skalnaté Pleso Observatory is presented. The photoelectric measurements of P/Brorsen-Metcalf in August 1989 were carried out with IHW/IAU filters CN, C 2, C 3, CO +, Cont. 365.0 and Cont. 484.5. Two focal diaphragms, 49.0 and 220.5 arc sec in diameter, were used. The magnitudes, fluxes and total numbers of molecules are presented. The results with the values of P/Halley (1986 III) at equal heliocentric distance, obtained with the same method and instrument, are compared. P/Brorsen-Metcalf emitted considerably fewer molecules than P/Halley in the same column of the coma. The ratios in the CN-emission and C 3-emission are 1:91 and 1:23, respectively. The results are in agreement with the conclusion that dusty comets tend to have more CN. The photoelectric C 2 magnitudes in the larger diaphragm agree with the mean values of the total visual estimates.

Measurements of Horizontal Flows in 1.6 μm Granulation

We report on a first analysis of the horizontal motions in a 45 minute (32 × 22 arcsec2 field of view) granulation time series (movie presented at the present IAU Symposium) obtained at 1.6 μm with the Vacuum Tower Telescope (VTT) of the National Solar Observatory at Sacramento Peak (NSO/SP). High signal/noise flow maps are obtained by use of the local cross correlation technique (November 1986) which incorporates efficient attenuation of seeing and 5-min oscillations. The flow pattern, showing a (≈ 30 arcsec diameter) supergranule with (≈ 8-15 arcsec) mesogranules superposed, is long lived compared to the 45 min of observations. The computed flows (velocity, divergence, vorticity) resemble the ones obtained at visible wavelengths (e.g., by Brandt et al. 1991, November 1989, November and Simon 1988, Simon et al. 1988). The high quality of the the flow maps (due to a large number of selected images (1500), and (supposedly) smaller 5-min oscillations and better seeing conditions at 1.6 μm) allows us to study time evolution (resolution ≈ 15 min) of the details of the flow (spatial resolution ≈ 3 arcsec). An interesting new finding is the short lifetime (&lt; 45 min) of vorticity as opposed to the long lived (≫ 45 min) divergence of the flow. Our study demonstrates the possibility of using the 1.6 μm window to the opacity minimum region to study the horizontal flows at these deep layers of the photosphere.

The kinematics of the Honeycomb nebula in the vicinity of SN 1987A

Spatially resolved observations of Hα line profiles have been made with the Manchester echelle spectrometer, combined with the Anglo-Australian Telescope, over the complex of 20 interlocking shells located in the vicinity of SN 1987A and known as the Honeycomb nebula. Complex motions are revealed. Individual ≃ 7 arcsec diameter shells are shown to be expanding towards the observer at 100-200 km s −1 with respect to the systemic radial velocity in this region of the Large Magellanic Cloud. Velocity'spikes'coincident with the filamentary edges of individual «shells» and with a similar range of radial velocities are also revealed in the position-velocity arrays of the Ha profiles

Extended infrared emission around IRAS 21282 + 5050

view Abstract Citations (9) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Extended Infrared Emission around IRAS 21282+5050 Bregman, Jesse D. ; Booth, John ; Gilmore, D. K. ; Kay, Laura ; Rank, David Abstract Multiaperture 3-4-micron spectra along with K- and L-band images of the compact planetary nebula IRAS 21282 + 5050 show a 5 arcsec - 20 arcsec diameter nebula with structure similar to many other planetary nebulae. The spectral observations and the L-band image show evidence for extended PAH emission out to a radius of 20 arcsec, while the K-band image shows a 5 arcsec diameter nebula. An observed linear increase of integrated brightness with aperture size at L band implies a 1/r exp 2 volume emissivity for a spherically symmetric model. The spectral similarity of the emission in the small and large apertures suggests fluorescent emission by the PAHs. If the observed emission is from PAHs which formed during the planetary nebulae stage of IRAs 21282 + 5050, then PAHs have been forming for not less than 3000 yr. If the PAH emission is from material produced during the earlier red giant phase, then the formation time frame was much longer. The morphological and spectral similarity of IRAS 21282 + 5050 to many other planetary nebulae suggests that this phenomenon may be widespread, and that planetary nebulae may be a significant source of interstellar PAHs. Publication: The Astrophysical Journal Pub Date: September 1992 DOI: 10.1086/171702 Bibcode: 1992ApJ...396..120B Keywords: Infrared Astronomy Satellite; Infrared Spectra; Planetary Nebulae; Red Giant Stars; Star Formation; Emission Spectra; Interstellar Matter; Line Spectra; Visible Spectrum; Astrophysics full text sources ADS | data products SIMBAD (2)

Solar imaging with a segmented adaptive mirror

A 19-segment adaptive-mirror system is currently being used on the Sacramento Peak 76-cm Tower Telescope to remove wave-front distortions resulting from atmospheric turbulence. The system has proven to be capable of substantially improving the quality of an image, at times achieving 0.33-arcsec resolution in visible wavelengths under 1-3-arcsec seeing conditions. An improvement in resolution seems to occur across a large field of view that is, at times, 30 arcsec in diameter.

High-resolution imaging of Brackett-gamma and H2 1-0 S(1) emission in the Seyfert galaxy NGC 1068

This paper reports 1-arcsec resolution imaging of 2-micron H I Br-gamma and H2 1-0 S(1) line emission toward the nucleus of the Seyfert 2 galaxy NGC 1068. The data, taken with a new imaging Fabry-Perot, show that the emission in both infrared lines originates from within 2 arcsec (170 pc) of the peak of radio, near-infrared, and visible continuum radiation. The vibrational H2 emission has a double-lobed shape, with a minimum toward the nucleus and two peaks about 1.3 arcsec on either side of the nucleus along position angle 70 deg east of north. In contrast, the Br-gamma emission is peaked on the nucleus, similar to the central radio continuum structure and the narrow-line region (NLR) in the visible. The Br-gamma emission has an about 1 arcsec (FWHM) diameter and is more compact than the distributions of visible NLR tracers. The H2 emission is probably produced in hot gas with mass a few 1000 solar masses. However, the total H2 mass in the circumnuclear region hydrogen may approach 10 to the 8th solar masses. The H2 emission is not produced in a 1-pc size obscuring torus but probably comes from a system of molecular clouds in the vicinity of themore » NLR. The molecular clouds probably contribute significantly to the extinction of the nuclear source. It is proposed that the circumnuclear Br-gamma and H2 emission lines are excited in gas heated by UV or X-ray photons emitted by a central nonstellar source. 35 refs.« less

Active Optics

This paper is the fourth, and last, in the series on active optics as realized in the ESO New Technology Telescope (NTT). It gives a detailed description of the set-up and optimization of the optical system, based on the three levels (i.e. time frequencies) of active correction. The first results in direct imagery with the telescope optimized only near zenith (‘Astronomical First Light’) yielded immediately the best star images ever recorded in ground-based astronomy with a full-width-half-maximum of 0·33 arcsec on a CCD detector with pixels of 0·123 arcsec diameter.

First Australia Telescope observations of SNR 0540-693

Observations of the LMC SNR 0540-693 using the Australia Telescope Compact Array at a wavelength of 6cm show that the remnant consists of a central core coincident with the associated pulsar and a partial ring of about 65 arcsec diameter.

A remarkable feature in the giant extragalactic H II region NGC 5471

The discovery of a very high velocity, low-intensity gas feature in the giant extragalactic H II region NGC 5471 is reported. A broad component in the emission lines of H-alpha + forbidden N II 6548, 6584 A is located within an area less than 1 arcsec in diameter at the position known as knot C. The broad component is characterized by its low intensity, a contribution of roughly 25 percent to the total flux of the lines, and an extension of roughly 3300 km/s at full width at zero intensity (FWZI). Supernovae explosions and stellar winds are considered as possible sources of the gas motions, and the observational evidence for their presence is discussed. 27 refs.

A subarcsecond H2O maser shell surrounding a variable star

Radio continuum and H{sub 2}O maser emission have been detected from the semiregular variable W Hya. The continuum emission at radio frequencies probably comes from the outer photosphere of the red giant star. A partial resolution of the stellar disk shows it to be approximately 0.09 arcsec in diameter. The H{sub 2}O maser emission arises from a ring of diameter 0.3 arcsec that is well centered on the star. These results for the first time yield a clear detection of a stellar photosphere at radio frequencies (except for the sun) and a radio measurement of the size of a stellar disk. Also, these are the first observations that precisely locate circumstellar maser emission with respect to the exciting star, allowing a detailed modeling of the maser amplification. The H{sub 2}O masers are unsaturated, amplify spontaneous emission, and are highly beamed. 13 refs.

Emission Line Profiles in the Planetary Nebulae IC 4593 and NGC 6153

The Planetary Nebulae IC 4593 and NGC 6153 are two rather compact objects not well studied. The nebula IC 4593 is about 12 arcsec in diameter and has a central star of Type 07 f; while the southern nebula NGC 6153 is about 22 arcsec in diameter and its central star is faint and of unknown spectral type. Using a high-resolution scanning Fabry-Pérot spectrometer we have made profile measurements of emission lines Hα λ6563 A, [O III] λ5007 A, and [N II] λ6584 A in the central regions of these two nebulae. We have found expansion velocities for IC 4593 of 40 km s−1 in [N II] and 16 km s−1 in [O III]. In the case of NGC 6153, we have obtained expansion velocities of 15 km s−1 in [N II] and 13 km s−1 in [O III] line. The profiles in Hα in both the nebulae dis not show a double peaked feature due to the larger thermal broadening. In the case of IC 4593, both [O III] and [N II] profiles showed complex structures. These results and their interpretation will be discussed.

Spatially Resolved Observations of the Unidentified Dust Features in BD +30°3639

High resolution spatial scans through the planetary nebula BD +30°3639 have been made with the UCL cooled grating spectrometer at the IRTF. A spectral resolution of λ/Δλ = 50 was sufficient to resolve the unidentified dust features at 8.6 and 11.3 μm and separate them from the continuum emission. The scans were made in .7 arcsec steps across the nebula with a 1.8 arcsec diameter beam.