scholarly journals Evidence of Expansion in the Central Region of NGC 2346

1989 ◽  
Vol 131 ◽  
pp. 187-187
Author(s):  
D.P.K. Banerjee ◽  
B. G. Anandarao ◽  
J. N. Desai ◽  
S. K. Jain ◽  
D.C.V. Mallik
Keyword(s):  
High Resolution ◽  
Spectral Range ◽  
Central Region ◽  
Planetary Nebula ◽  
Signal To Noise Ratio ◽  
Emission Lines ◽  
Expansion Velocity ◽  
Signal To Noise ◽  
Central Spot ◽  
Fabry Perot

We present observations of the bipolar planetary nebula NGC 2346 carried out with the 1-m telescope at the Vainu Bappu Observatory in Kavalur, India using (1) a high resolution piezo-electric scanned Fabry-Pérot Spectrometer (with a velocity resolution of 10 km s−1) for line studies in the 6000 A - 7000 A spectral range and (2) a pressure scanned Fabry-Pérot spectrometer (with a velocity-resolution of 5 km s−1) in the green region. The nebula was observed in the H I 6563 A and [N II] 6583 A emission lines using a 15″ aperture and in the [O III] 5007 A line using an 8″ aperture centered on the bright central spot. A number of scans in each of these lines were co-added to improve the signal-to-noise ratio. The [O III] profile shows a well defined split between the blue and the red component, typical of an expanding shell. The [N II] profile does not show a well resolved split, although a pronounced suggestion of a split was observed in all the scans. The Hα profile was broad and asymmetric. The composite [O III] and [N II] profiles were decomposed into two individual Gaussians for obtaining the expansion velocity.

scholarly journals The Central Region of the Planetary Nebula A58

1993 ◽  
Vol 155 ◽  
pp. 387-387
Author(s):  
D.L. Pollacco ◽  
P.W. Hill ◽  
R.E.S. Clegg
Keyword(s):  
High Resolution ◽  
Central Region ◽  
Planetary Nebula ◽  
Emission Lines

We present images and high–resolution spectra of the hydrogen deficient knot at the centre of the old planetary nebula A58. The spectra confirm that this region contains essentially no hydrogen, as previously suspected. Emission lines from the knot are broad (FWHM ∼ 180 and 270 km/s for [NII] and [OIII] lines respectively) and are blue–shifted by ∼100 km/s relative to the systematic velocity.

scholarly journals On cross-correlations, averages and noise in electron microscopy

2019 ◽  
Vol 75 (1) ◽  
pp. 12-18 ◽  
Author(s):  
Michael Radermacher ◽  
Teresa Ruiz
Keyword(s):  
High Resolution ◽  
Cross Correlation ◽  
Signal To Noise Ratio ◽  
3D Structure ◽  
Signal To Noise ◽  
High Resolution Structure ◽  
Multiple Copies ◽  
High Level ◽  
2D Images ◽  
Resolution Structure

Biological samples are radiation-sensitive and require imaging under low-dose conditions to minimize damage. As a result, images contain a high level of noise and exhibit signal-to-noise ratios that are typically significantly smaller than 1. Averaging techniques, either implicit or explicit, are used to overcome the limitations imposed by the high level of noise. Averaging of 2D images showing the same molecule in the same orientation results in highly significant projections. A high-resolution structure can be obtained by combining the information from many single-particle images to determine a 3D structure. Similarly, averaging of multiple copies of macromolecular assembly subvolumes extracted from tomographic reconstructions can lead to a virtually noise-free high-resolution structure. Cross-correlation methods are often used in the alignment and classification steps of averaging processes for both 2D images and 3D volumes. However, the high noise level can bias alignment and certain classification results. While other approaches may be implicitly affected, sensitivity to noise is most apparent in multireference alignments, 3D reference-based projection alignments and projection-based volume alignments. Here, the influence of the image signal-to-noise ratio on the value of the cross-correlation coefficient is analyzed and a method for compensating for this effect is provided.

scholarly journals Kinematic Structure and Chemical Composition of the Double Shell PN NGC 3242

1989 ◽  
Vol 131 ◽  
pp. 200-200
Author(s):  
K. C. Sahu ◽  
S. R. Pottasch ◽  
B. G. Anandarao ◽  
J. N. Desai
Keyword(s):  
Chemical Composition ◽  
High Resolution ◽  
Outer Shell ◽  
Expansion Velocity ◽  
Kinematic Structure ◽  
Line Profiles ◽  
Kinematic Study ◽  
Fabry Perot

Kinematic study of the multiple shell PN NGC 3242 was carried out by obtaining Hα and [O III] line profiles at 9 positions of the nebula using a high-resolution (R ≅ 50,000) Fabry-Pérot spectrometer. The positions cover both the bright inner shell and the faint outer shell. It is shown here that the two apparently continuous shells are kinematically separate: the faint outer shell was ejected ∼ 5000 years earlier and has less expansion velocity than the bright inner shell.

scholarly journals The Structure and Velocity Field of A78

1989 ◽  
Vol 131 ◽  
pp. 185-185
Author(s):  
P. Pismis ◽  
M. A. Moreno
Keyword(s):  
Velocity Field ◽  
Planetary Nebula ◽  
Image Intensifier ◽  
Radial Velocities ◽  
Central Hole ◽  
Expansion Velocity ◽  
San Pedro ◽  
Systemic Velocity ◽  
Fabry Perot ◽  
The Face

We present a velocity field of the planetary nebula A78 based on three Fabry Pérot Hα (10A) interferograms taken with a focal reducer attached to the 2.1 m reflector of the Observatorio Astronómico Nacional at San Pedro Mártir, Mexico. We have used a single-stage Varo image intensifier and two different étalons with interorder separations of 283 km s−1 (2 interf.) and 100 km s−1 (1 interf.). The scale of the original photographs is 49 arcsec mm−1. Our data have yielded radial velocities in the Hα line at 110 points on the face of A78; the velocity field is far from being smooth. The rings are wide around the central hole, and a few show definite splittings; from these splittings we have estimated an overall expansion velocity of 27 km s−1. The average systemic velocity is found to be around −3 km s−1.

Development of a Philips cryo-TEM provided with a liquid helium cooled tilt stage and a vacuum transfer system

1998 ◽  
Vol 4 (S2) ◽  
pp. 400-401
Author(s):  
R. Wagner ◽  
A.F. de Jong ◽  
A.G. Koster ◽  
R. Morrison ◽  
F. Tothill ◽  
...  
Keyword(s):  
High Resolution ◽  
Liquid Helium ◽  
Signal To Noise Ratio ◽  
Transfer System ◽  
Helium Temperature ◽  
Single Particles ◽  
Signal To Noise ◽  
Specimen Holder ◽  
2D Crystals ◽  
Beam Damage

In order to reduce beam damage, biological TEM specimens are often observed at temperatures close to the boiling point of liquid nitrogen (77 K). Recently, encouraging results on single particles as well as on 2D crystals have appeared, derived from images taken near liquid helium temperature (4 K), in dedicated TEMs. At these temperatures the high resolution frequencies are much better preserved, increasing the allowable dose and thus the signal to noise ratio.4 Here we present the design of a new dedicated Philips He-TEM which combines the full functionality of a CM300 TWIN with a vacuum transfer system and a liquid helium cooled specimen holder.A schematic overview of the Cryo-TEM is shown in figure 1. The key differences compared to a standard CM microscope are: 1) The tip of the specimen rod is cooled below 10 K and the rod itself cannot be taken out of the goniometer (CompuStage). 2) The specimen enters the column on the opposite side.

scholarly journals 53 Piscium, an SPB Star with Activity

2002 ◽  
Vol 185 ◽  
pp. 236-237
Author(s):  
J.-M. Le Contel ◽  
P. Mathias ◽  
E. Chapellier ◽  
J.-C. Valtier
Keyword(s):  
High Resolution ◽  
False Alarm ◽  
High Frequency ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Correlation Technique ◽  
Signal To Noise ◽  
Spectroscopic Observations ◽  
Auto Correlation ◽  
Frequency Variations

The star 53 Psc (HD 3379, B2.5IV) has been observed as variable by several authors (Sareyan et al., 1979) with frequencies around 10 c d–1 and has been classified as a β Cephei star. Conversely, other authors (e.g. Percy, 1971) found it to be constant.New high resolution, high signal-to-noise ratio, Spectroscopic observations have been performed at the Observatoire de Haute-Provence in 1996 over 11 nights. The spectral domain covers around 200 Å and is centered on Hδ. Radial velocities were deduced from an auto-correlation technique with a scatter around 0.4kms−1.No high frequency variations are observed. Three frequencies have been detected with a false alarm detection above the 1 % level. A fourth one may be present but its amplitude is below this 1 % level. Results are displayed in Table 1.

scholarly journals High-resolution coherency functionals for velocity analysis: An application for subbasalt seismic exploration

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. U53-U63 ◽  
Author(s):  
Andrea Tognarelli ◽  
Eusebio Stucchi ◽  
Alessia Ravasio ◽  
Alfredo Mazzotti
Keyword(s):  
High Resolution ◽  
Seismic Data ◽  
Field Data ◽  
Signal To Noise Ratio ◽  
Synthetic Seismograms ◽  
Seismic Exploration ◽  
Velocity Analysis ◽  
Signal To Noise ◽  
Geologic Setting ◽  
Analytic Signals

We tested the properties of three different coherency functionals for the velocity analysis of seismic data relative to subbasalt exploration. We evaluated the performance of the standard semblance algorithm and two high-resolution coherency functionals based on the use of analytic signals and of the covariance estimation along hyperbolic traveltime trajectories. Approximate knowledge of the wavelet was exploited to design appropriate filters that matched the primary reflections, thereby further improving the ability of the functionals to highlight the events of interest. The tests were carried out on two synthetic seismograms computed on models reproducing the geologic setting of basaltic intrusions and on common midpoint gathers from a 3D survey. Synthetic and field data had a very low signal-to-noise ratio, strong multiple contamination, and weak primary subbasalt signals. The results revealed that high-resolution coherency functionals were more suitable than semblance algorithms to detect primary signals and to distinguish them from multiples and other interfering events. This early discrimination between primaries and multiples could help to target specific signal enhancement and demultiple operations.

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