A comparison of the classification systems of luminous stars in the northern Milky Way II and IV, for stars assigned two-dimensional spectral types from objective-prism plates

1966 ◽  
Vol 24 ◽  
pp. 70-73
Author(s):  
C. B. Stephenson
Keyword(s):  
Milky Way ◽  
Classification Systems ◽  
Two Dimensional ◽  
Joint Project ◽  
Ob Stars ◽  
Luminosity Class ◽  
Objective Prism ◽  
The Mean ◽  
The Difference ◽  
Hydrogen Lines

For some years a survey for early-type luminous stars in the northern Milky Way has been underway at the Warner and Swasey Observatory and the Hamburg Observatory, as a joint project by the two institutions (1). With the aid of ultraviolet-transmitting objective prisms (Schott UBK7 glass), it has been possible at both institutions to recognize OB stars at a dispersion of about 600Å/mm. Moreover, the appearance of the Balmer discontinuity at low dispersion affords a valuable aid to two-dimensional classification of stars of late B to late F types (2, 3). These two-dimensional classifications, which are based essentially upon the appearance of the continuum (especially the Balmer discontinuity), the hydrogen lines, the K line, and the G band, are assigned in the MK classification nomenclature since they are well correlated with classifications made by means of the real MK classification criteria. The quality of the correlation depends upon location in the HR diagram, but the random probable error appears to be upward of one MK luminosity class and about a quarter of a full letter division in temperature class, except that luminosity class IV is nowhere well distinguished from class V, and class Iab is not really well distinguished from Ia and Ib.The present Cleveland system of assigning two-dimensional spectral types to stars from ultraviolet-included objective-prism plates tends to assign lower luminosities than those of the LS II (–LS I?) system. This fact alone accounts for certainly most of the difference between the numbers of stars assigned two-dimensional spectral types in LS II and in LS IV. The origin of this systematic difference of over a luminosity class is not well explained, but the difference is hardly alarming. The numbers of OB stars in the two catalogues are quite comparable and this is consistent with the fact that no classification system difference for OB stars is known to exist between these two catalogues.Slit spectrograms so far available support the belief that LS IV agrees better in the mean with the MK system than does LS II, though LS IV may also be slightly overluminous in the mean. There is one factor always tending to confuse the transformation from this objective-prism system to MK spectral types: stars having abnormally strong Balmer discontinuities will usually be included in our catalogues with some kind of MK classification, While those with abnormally weak Balmer discontinuities will more often be excluded or assigned to the OB group. This problem is by no means so serious as to detract significantly from the desirability of making objective-prism surveys that pay special heed to the Balmer discontinuity.

scholarly journals Searching for a kinematic signature of the moderately metal-poor stars in the Milky Way bulge using N-body simulations

2018 ◽  
Vol 615 ◽  
pp. A100 ◽  
Author(s):  
A. Gómez ◽  
P. Di Matteo ◽  
M. Schultheis ◽  
F. Fragkoudi ◽  
M. Haywood ◽  
...  
Keyword(s):  
Milky Way ◽  
Thin Disk ◽  
Secular Evolution ◽  
Thick Disc ◽  
Thin Disc ◽  
The Mean ◽  
The Difference ◽  
Different Origins ◽  
Argos Data ◽  
Internal Evolution

Although there is consensus that metal-rich stars in the Milky Way bulge are formed via secular evolution of the thin disc, the origin of their metal-poor counterparts is still under debate. Two different origins have been invoked for metal-poor stars: they might be classical bulge stars or stars formed via internal evolution of a massive thick disc. We use N-body simulations to calculate the kinematic signature given by the difference in the mean Galactocentric radial velocity (ΔVGC) between metal-rich stars ([Fe/H] ≥ 0) and moderately metal-poor stars (–1.0 ≤ [Fe/H] < 0) in two models, one containing a thin disc and a small classical bulge (B/D = 0.1), and the other containing a thin disc and a massive centrally concentrated thick disc. We reasonably assume that thin-disk stars in each model may be considered as a proxy of metal-rich stars. Similarly, bulge stars and thick-disc stars may be considered as a proxy of metal-poor stars. We calculate ΔVGC at different latitudes (b = 0°, − 2°, − 4°, − 6°, − 8° and − 10°) and longitudes (l = 0°, ± 5°, ± 10° and ± 15°) and show that the ΔVGC trends predicted by the two models are different. We compare the predicted results with ARGOS data and APOGEE DR13 data and show that moderately metal-poor stars are well reproduced with the co-spatial stellar discs model, which has a massive thick disc. Our results give more evidence against the scenario that most of the metal-poor stars are classical bulge stars. If classical bulge stars exists, most of them probably have metallicities [Fe/H] < –1 dex, and their contribution to the mass of the bulge should be a small percentage of the total bulge mass.

scholarly journals Progress report on the Cleveland-Chile survey for southern OB stars

1970 ◽  
Vol 38 ◽  
pp. 276-277
Author(s):  
C. B. Stephenson ◽  
N. Sanduleak
Keyword(s):  
Milky Way ◽  
Progress Report ◽  
The State ◽  
Published Data ◽  
Ob Stars ◽  
Systematic Survey ◽  
The North ◽  
Objective Prism

From some standpoints it should seem surprising that not all of the OB stars of our Galaxy that can be identified to a feasible limiting magnitude (say 12–13) by conventional objective prism techniques have yet been so identified, but this is in fact the state of our published data. Some people here will recall that such a systematic survey for the northern Milky Way was carried out several years ago jointly by the Hamburg and Warner and Swasey Observatories. Now at the Warner and Swasey Observatory we are extending this northern survey into the southern Milky Way that could not be reached from the north, and we are making this extension as homogeneous as possible with respect to the northern survey.

Water Sensation During Passive Propulsion for Expert and Nonexpert Swimmers

2017 ◽  
Vol 124 (3) ◽  
pp. 662-673 ◽  
Author(s):  
Kenta Kusanagi ◽  
Daisuke Sato ◽  
Yasuhiro Hashimoto ◽  
Norimasa Yamada
Keyword(s):  
Skin Resistance ◽  
National Level ◽  
Absolute Error ◽  
Transformation Method ◽  
Two Dimensional ◽  
Eyes Closed ◽  
Video Recordings ◽  
Linear Transformation Method ◽  
The Mean ◽  
The Difference

This study determined whether expert swimmers, compared with nonexperts, have superior movement perception and physical sensations of propulsion in water. Expert (national level competitors, n = 10) and nonexpert (able to swim 50 m in > 3 styles, n = 10) swimmers estimated distance traveled in water with their eyes closed. Both groups indicated their subjective physical sensations in the water. For each of two trials, two-dimensional coordinates were obtained from video recordings using the two-dimensional direct linear transformation method for calculating changes in speed. The mean absolute error of the difference between the actual and estimated distance traveled in the water was significantly lower for expert swimmers (0.90 ± 0.71 meters) compared with nonexpert swimmers (3.85 ± 0.84 m). Expert swimmers described the sensation of propulsion in water in cutaneous terms as the “sense of flow” and sensation of “skin resistance.” Therefore, expert swimmers appear to have a superior sense of distance during their movement in the water compared with that of nonexpert swimmers. In addition, expert swimmers may have a better perception of movement in water. We propose that expert swimmers integrate sensations and proprioceptive senses, enabling them to better perceive and estimate distance moved through water.

Implementation of a Mixing Length Turbulence Formulation Into the Dynamic Wake Meandering Model

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Rolf-Erik Keck ◽  
Dick Veldkamp ◽  
Helge Aagaard Madsen ◽  
Gunner Larsen
Keyword(s):  
Cross Section ◽  
Turbulent Mixing ◽  
Eddy Viscosity ◽  
High Fidelity ◽  
Mixing Length ◽  
Two Dimensional ◽  
Wake Region ◽  
Mean Velocity ◽  
The Mean ◽  
The Difference

The work presented in this paper focuses on improving the description of wake evolution due to turbulent mixing in the dynamic wake meandering (DWM) model. From wake investigations performed with high-fidelity actuator line simulations carried out in ELLIPSYS3D, it is seen that the current DWM description, where the eddy viscosity is assumed to be constant in each cross-section of the wake, is insufficient. Instead, a two-dimensional eddy viscosity formulation is proposed to model the shear layer generated turbulence in the wake, based on the classical mixing length model. The performance of the modified DWM model is verified by comparing the mean wake velocity distribution with a set of ELLIPSYS3D actuator line calculations. The standard error (defined as the standard deviation of the difference between the mean velocity field of the DWM and the actuator line model), in the wake region extending from 3 to 12 diameters behind the rotor, is reduced by 27% by using the new eddy viscosity formulation.

scholarly journals Wake Decay: Effect of Freestream Swirl

1997 ◽  
Author(s):  
J. M. Brookfield ◽  
I. A. Waitz ◽  
J. Sell
Keyword(s):  
Three Dimensional ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Mixing Rate ◽  
Rotating Blade ◽  
Blade Row ◽  
The Mean ◽  
The Difference ◽  
Fan Blade

A study of the effects of freestream swirl on the decay characteristics of wakes shed from a rotating blade row is presented. The freestream swirl behind the rotor causes the wakes to skew tangentially, stretching the wakes as they are convected from the rotor to the stator. The effect of stretching on wake decay is illustrated using a simplified two-dimensional model. The model is described and the results are compared to 1) measurements from a two-dimensional cascade facility where no stretching or skewing of the wakes occurs, 2) solutions obtained using a three-dimensional, Reynolds-averaged Navier-Stokes solver, and 3) experimental wake measurements taken behind a low hub-to-tip ratio fan. For typical fan geometries with hub-to-tip ratios of approximately 0.5 and rotor-stator spacings of one to two rotor chord lengths, the wake can be stretched by over 50 percent. The stretching increases the mixing rate which leads to a reduction in the mean wake velocity deficit of approximately thirty percent and a widening of the wake of about fifteen percent. These effects account for much of the difference seen between cascade wake measurements and those taken behind rotating fan blade rows. It is therefore important to include such effects when using cascade data for prediction of fluid mechanic, acoustic, or structural phenomena associated with fan wakes. Finally, the study also suggests a potential for small (< 3 dB) reductions in wake-stator interaction noise through tailoring the fan loading distribution to produce particular span wise wake decay characteristics.

scholarly journals Correcting for Gaussian Aerial Smoothing

1955 ◽  
Vol 8 (1) ◽  
pp. 54 ◽  
Author(s):  
RN Bracewell
Keyword(s):  
Two Dimensional ◽  
The Mean ◽  
Standard Deviations ◽  
The Difference

Let a. two-dimensional survey with a Gaussian aerial beam establish values at intervals of standard deviations. Then the correction for aerial smoothing is simply calculated as the difference between the value to be corrected and the mean of the neighbouring four values.

scholarly journals Observations of Stellar Rotation and Line Strengths for Ob Stars

1970 ◽  
Vol 4 ◽  
pp. 115-115
Author(s):  
William Buscombe
Keyword(s):  
National Science Foundation ◽  
Absorption Lines ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
B Stars ◽  
Ob Stars ◽  
Luminosity Class ◽  
National Science ◽  
Balmer Lines ◽  
Hydrogen Lines

For 121 southern stars of spectral types between 05 and A3, including 35 supergiants, equivalent widths and values of ve sini have been measured for absorption lines on direct-intensity tracings of coudé spectrograms from Mount Stromlo, with original dispersion 150 microns per angstrom. For stars of a particular temperature and luminosity class, the strength of the hydrogen lines is weaker and the triplet helium lines stronger in fast rotators than in sharp-lined objects which are rotating more slowly. Full details are in print (Monthly Notices Roy. Astron. Soc. 144 (1969), 1): subsequent papers in press present detailed profiles of the Balmer lines for 23 slowly rotating stars and details of emission features shown by several fast rotators.The investigation is being continued with spectrograms of northern B stars secured at the Dominion Astrophysical Observatory, supported in part by grant GP-13544 from the National Science Foundation.

scholarly journals An infrared survey of the Southern Milky Way

1964 ◽  
Vol 20 ◽  
pp. 160-167 ◽  
Author(s):  
B. E. Westerlund
Keyword(s):  
Spectral Region ◽  
Milky Way ◽  
Galactic Plane ◽  
Galactic Structure ◽  
The Sun ◽  
Ob Stars ◽  
Objective Prism ◽  
Blue Spectral Region ◽  
Infrared Survey

The determination by optical means of the galactic structure at great distances from the Sun is becoming more and more important. Most optical investigations, using ordinary techniques — objective-prism survey in the blue spectral region + UBV photometry — do not reach very far out owing to the heavy obscuration in most directions in the galactic plane. Only a few very luminous OB stars and some rare supergiants have been identified in some selected regions at distances exceeding 4 kpc.

scholarly journals A New Objective Prism Catalogue of OB and Supergiant B, A, F and G Stars in the Magellanic Clouds

1979 ◽  
Vol 47 ◽  
pp. 155-157
Author(s):  
A. G. Davis Philip ◽  
N. Sanduleak
Keyword(s):  
Magellanic Clouds ◽  
Schmidt Telescope ◽  
Ob Stars ◽  
Objective Prism ◽  
Hydrogen Lines

The Michigan Curtis Schmidt telescope at Cerro Tololo Inter-American Observatory has been used with the “thin” prism (Blanco 1974) to survey the Large and Small Magellanic Clouds. Four plates, covering approximately 90 square degrees, and three plates, covering approximately 70 square degrees, were taken of the Large and Small Magellanic Clouds respectively. One hour exposures on nitrogen baked, IIIa-J plates were obtained. The limiting magnitude of the plates is V = 16 mag. At the dispersion of 1360 Å/mm OB stars can be recognized by their long uv extension, in which no sign of a Balmer discontinuity can be seen. The supergiants can be recognized by the appearance of a Balmer discontinuity and classified into temperature types by the strength of the hydrogen lines.

Spectrophotometric measurements of objective-prism spectra

1966 ◽  
Vol 24 ◽  
pp. 118-119
Author(s):  
Th. Schmidt-Kaler
Keyword(s):  
Progress Report ◽  
Two Dimensional ◽  
Objective Prism ◽  
Made In

I should like to give you a very condensed progress report on some spectrophotometric measurements of objective-prism spectra made in collaboration with H. Leicher at Bonn. The procedure used is almost completely automatic. The measurements are made with the help of a semi-automatic fully digitized registering microphotometer constructed by Hög-Hamburg. The reductions are carried out with the aid of a number of interconnected programmes written for the computer IBM 7090, beginning with the output of the photometer in the form of punched cards and ending with the printing-out of the final two-dimensional classifications.

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