High Dispersion Spectroscopy of the PN K 648 in the Globular Cluster M 15

The use CCD detectors has allowed a major progress in abundance derivations for globular cluster stars in the last years. Abundances deduced from high dispersion spectra now correlates well with other abundance indicators. I discuss some problems concerning the derivation of accurate metal abundances for globular clusters using high dispersion spectra from both the old photographic and the most recent CCD data. The discrepant low abundances found by Cohen (1980), from photographic material for M71 giants, are found to be due to the use of too high microturbulences.

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Recent Advances in High Dispersion Spectroscopy of Globular Cluster Stars

The Impact of Very High S/N Spectroscopy on Stellar Physics ◽

10.1007/978-94-009-2937-1_95 ◽

1988 ◽

pp. 525-530

Author(s):

Raffaele G. Gratton

Keyword(s):

Globular Cluster ◽

High Dispersion ◽

Recent Advances

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The Composition of Warm Giants in M 71 and M 5

Symposium - International Astronomical Union ◽

10.1017/s0074180900042790 ◽

1988 ◽

Vol 126 ◽

pp. 497-498

Author(s):

Catherine A. Pilachowski ◽

Christopher Sneden

Keyword(s):

High Resolution ◽

Globular Cluster ◽

Globular Clusters ◽

High Dispersion ◽

High Signal ◽

Signal To Noise

In 1979 a disturbing controversy arose in the field of globular cluster research when Cohen (1980) and Pilachowski, Canterna, and Wallerstein (1980) announced the results of the first high dispersion studies of the composition of giants in the globular clusters M 71 and 47 Tucanae. In contrast to earlier studies, which found metallicities of typically −0.3 and −0.5 dex, these investigators obtained values of −1.3 and −1.1. Since then, many have attempted to redetermine the abundances of M 71 and 47 Tuc to explain the discrepant results. These efforts have all suffered from the absence of high signal-to-noise, high resolution spectra of stars with temperatures above 4300 K.

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Chemical Properties of Individual Globular Clusters

Symposium - International Astronomical Union ◽

10.1017/s0074180900092214 ◽

1980 ◽

Vol 85 ◽

pp. 385-400 ◽

Cited By ~ 1

Author(s):

Judith G. Cohen

Keyword(s):

Spectroscopic Study ◽

Globular Cluster ◽

Globular Clusters ◽

Chemical Properties ◽

High Dispersion ◽

The Past ◽

The Many

Rapid improvements in instrumentation over the past few years have made the spectroscopic study of individual globular cluster giants feasable. Three years ago I began a program of high dispersion abundance analyses of such stars to provide a calibration for the many photometric systems used to rank globular clusters in metallicity. The results for four clusters (M92, M15, M13, and M3) of low and intermediate metallicity have already appeared (Cohen, 1978, 1979), and additional detailed analyses of stars in M5 and M13 (Pilachowski, Wallerstein and Leep, 1979) will soon be available. Ignoring the elements C, N, and O, to which we shall return later, these detailed abundance analyses yielded few great surprises; perhaps the metallicity scale that had previously been used was too high by about 0.2 dex, and also it became clear that M3 was a very metal poor cluster. However, the calibration of the metal rich globulars beyond the simple ranking level of Mould, Struthman, and McElroy (1979) had not been attempted.

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HST and Keck Observations of a Young Globular Cluster in the Spiral Galaxy NGC 6946

Symposium - International Astronomical Union ◽

10.1017/s0074180900224595 ◽

2002 ◽

Vol 207 ◽

pp. 700-702

Author(s):

Søren S. Larsen ◽

Jean P. Brodie ◽

Bruce G. Elmegreen ◽

Yuri N. Efremov ◽

Paul W. Hodge ◽

...

Keyword(s):

Globular Cluster ◽

Velocity Dispersion ◽

High Dispersion ◽

Population Synthesis ◽

Core Radius ◽

Peculiar Star ◽

Dynamical Mass ◽

Star Forming ◽

Ngc 6946 ◽

Mass Estimate

Using new (Cycle 9) HST / WFPC2 data, we have studied a peculiar star forming region in the nearby Sc-type spiral NGC 6946. The region has a bubble-like shape and a diameter of about 600 pc. Near the centre is an extremely luminous young globular cluster with MV = −13.2 mag. The cluster has a compact core with a core radius of about 1.3 pc but is surrounded by an extended halo with a power-law luminosity profile similar to that observed for young LMC clusters. From Keck / HIRES high-dispersion spectroscopy we measure a velocity dispersion of 10 km s−1, leading to a dynamical mass estimate of about 1.7 × 106 solar masses. The dynamical mass estimate is comparable to the expectation from population synthesis modelling under the assumption of a Salpeter IMF extending down to 0.1 M⊙.

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Galactic orbits of stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900105340 ◽

1966 ◽

Vol 25 ◽

pp. 93-97

Author(s):

Richard Woolley

Keyword(s):

Globular Cluster ◽

Potential Field ◽

High Velocity ◽

Velocity Vector ◽

Variable Stars ◽

The Sun ◽

Proper Motions ◽

Rr Lyrae ◽

The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

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Spectroscopic Observations of Visual Double Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100027536 ◽

1965 ◽

Vol 5 ◽

pp. 109-111

Author(s):

Frederick R. West

Keyword(s):

Radial Velocity ◽

High Dispersion ◽

Velocity Difference ◽

Spectrograph Slit ◽

Spectroscopic Observations ◽

Double Stars ◽

Visual Double Stars ◽

Relative Orbit ◽

Two Component ◽

Star Images

There are certain visual double stars which, when close to a node of their relative orbit, should have enough radial velocity difference (10-20 km/s) that the spectra of the two component stars will appear resolved on high-dispersion spectrograms (5 Å/mm or less) obtainable by use of modern coudé and solar spectrographs on bright stars. Both star images are then recorded simultaneously on the spectrograph slit, so that two stellar components will appear on each spectrogram.

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Tributary Mapping Multiplexing an Efficient Technique for High Speed Fiber Optic Communication

Pakistan Journal of Engineering Technology & Science ◽

10.22555/pjets.v6i2.1963 ◽

2018 ◽

Vol 6 (2) ◽

Author(s):

Usman Illahi ◽

Javed Iqbal ◽

Muhammad Ismail Sulaiman ◽

Muhammad Alam ◽

Mazliham Mohd Su'ud

Keyword(s):

Spectral Efficiency ◽

High Speed ◽

Fiber Optic ◽

Single Channel ◽

Efficient Technique ◽

High Dispersion ◽

Optical Filtering ◽

Fiber Optic Communication ◽

Optic Communication ◽

Dispersion Tolerance

<p>A novel technique of multiplexing called Tributary Mapping Multiplexing (TMM) is<br />applied to a single channel wavelength division multiplexing system and performance is monitored on the basis of simulation results. To elaborate the performance of TMM in this paper, a 4-User TMM system over single wavelength channel is demonstrated. TMM showed significant tolerance against narrow optical filtering as compared to that of conventional TDM at the rate of 40 Gbit/s. The above calculations are made by optical filter bandwidth and dispersion tolerance that was allowed at minimum. The spectral efficiency achieved by this TMM was 1 b/s/Hz and it was executed by using transmitters and receivers of 10 Gbit/s without polarized multiplexing. The high spectral efficiency, high dispersion tolerance and tolerance against strong optical filtering makes TMM an efficient technique for High<br />Speed Fiber Optic Communication.</p>

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