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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of The Korean Astronomical Society
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The Korean Astronomical Society
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Volume & Issues
Volume 46, Issue 6 - Dec 2013
Volume 46, Issue 5 - Oct 2013
Volume 46, Issue 4 - Aug 2013
Volume 46, Issue 3 - Jun 2013
Volume 46, Issue 2 - Apr 2013
Volume 46, Issue 1 - Feb 2013
Selecting the target year
THEOREMS ON NULL-PATHS AND REDSHIFT
Wanas, M.I. ; Morcos, A.B. ;
Journal of The Korean Astronomical Society, volume 46, issue 3, 2013, Pages 97~102
DOI : 10.5303/JKAS.2013.46.3.97
In the present work, we prove the validity of two theorems on null-paths in a version of absolute parallelismgeometry. A version of these theorems has been originally established and proved by Kermak, McCrea and Whittaker (KMW) in the context of Riemannian geometry. The importance of such theorems lies in their applications to derive a general formula for the redshift of spectral lines coming from distant objects. The formula derived in the present work can be applied to both cosmological and astrophysical redshifts. It takes into account the shifts resulting from gravitation, different motions of the source of photons, spin of the moving particle (photons) and the direction of the line of sight. It is shown that this formula cannot be derived in the context of Riemannian geometry, but it can be reduced to a formula given by KMW under certain conditions.
SEJONG OPEN CLUSTER SURVEY (SOS). 0. TARGET SELECTION AND DATA ANALYSIS
Sung, Hwankyung ; Lim, Beomdu ; Bessell, Michael S. ; Kim, Jinyoung S. ; Hur, Hyeonoh ; Chun, Moo-Young ; Park, Byeong-Gon ;
Journal of The Korean Astronomical Society, volume 46, issue 3, 2013, Pages 103~123
DOI : 10.5303/JKAS.2013.46.3.103
Star clusters are superb astrophysical laboratories containing cospatial and coeval samples of stars with similar chemical composition. We initiate the Sejong Open cluster Survey (SOS) - a project dedicated to providing homogeneous photometry of a large number of open clusters in the SAAO Johnson-Cousins` UBV I system. To achieve our main goal, we pay much attention to the observation of standard stars in order to reproduce the SAAO standard system. Many of our targets are relatively small sparse clusters that escaped previous observations. As clusters are considered building blocks of the Galactic disk, their physical properties such as the initial mass function, the pattern of mass segregation, etc. give valuable information on the formation and evolution of the Galactic disk. The spatial distribution of young open clusters will be used to revise the local spiral arm structure of the Galaxy. In addition, the homogeneous data can also be used to test stellar evolutionary theory, especially concerning rare massive stars. In this paper we present the target selection criteria, the observational strategy for accurate photometry, and the adopted calibrations for data analysis such as color-color relations, zero-age main sequence relations, Sp - MV relations, Sp -
relations, Sp - color relations, and
- BC relations. Finally we provide some data analysis such as the determination of the reddening law, the membership selection criteria, and distance determination.
BETTI NUMBERS OF GAUSSIAN FIELDS
Park, Changbom ; Pranav, Pratyush ; Chingangbam, Pravabati ; Van De Weygaert, Rien ; Jones, Bernard ; Vegter, Gert ; Kim, Inkang ; Hidding, Johan ; Hellwing, Wojciech A. ;
Journal of The Korean Astronomical Society, volume 46, issue 3, 2013, Pages 125~131
DOI : 10.5303/JKAS.2013.46.3.125
We present the relation between the genus in cosmology and the Betti numbers for excursion sets of three- and two-dimensional smooth Gaussian random fields, and numerically investigate the Betti numbers as a function of threshold level. Betti numbers are topological invariants of figures that can be used to distinguish topological spaces. In the case of the excursion sets of a three-dimensional field there are three possibly non-zero Betti numbers;
is the number of connected regions,
is the number of circular holes (i.e., complement of solid tori), and
is the number of three-dimensional voids (i.e., complement of three-dimensional excursion regions). Their sum with alternating signs is the genus of the surface of excursion regions. It is found that each Betti number has a dominant contribution to the genus in a specific threshold range.
dominates the high-threshold part of the genus curve measuring the abundance of high density regions (clusters).
dominates the genus near the median thresholds which measures the topology of negatively curved iso-density surfaces, and
corresponds to the low-threshold part measuring the void abundance. We average the Betti number curves (the Betti numbers as a function of the threshold level) over many realizations of Gaussian fields and find that both the amplitude and shape of the Betti number curves depend on the slope of the power spectrum n in such a way that their shape becomes broader and their amplitude drops less steeply than the genus as n decreases. This behaviour contrasts with the fact that the shape of the genus curve is fixed for all Gaussian fields regardless of the power spectrum. Even though the Gaussian Betti number curves should be calculated for each given power spectrum, we propose to use the Betti numbers for better specification of the topology of large scale structures in the universe.
CAN MASSIVE GRAVITY EXPLAIN THE MASS DISCREPANCY-ACCELERATION RELATION OF DISK GALAXIES?
Trippe, Sascha ;
Journal of The Korean Astronomical Society, volume 46, issue 3, 2013, Pages 133~140
DOI : 10.5303/JKAS.2013.46.3.133
The empirical mass discrepancy-acceleration (MDA) relation of disk galaxies provides a key test for models of galactic dynamics. In terms of modified laws of gravity and/or inertia, the MDA relation quantifies the transition from Newtonian to modified dynamics at low centripetal accelerations
. As yet, neither dynamical models based on dark matter nor proposed modifications of the laws of gravity/inertia have predicted the functional form of the MDA relation. In this work, I revisit the MDA data and compare them to four different theoretical scaling laws. Three of these scaling laws are entirely empirical; the fourth one - the "simple
" function of Modified Newtonian Dynamics - derives from a toy model of gravity based on massive gravitons (the "graviton picture"). All theoretical MDA relations comprise one free parameter of the dimension of an acceleration, Milgrom`s constant aM. I find that the "simple
" function provides a good fit to the data free of notable systematic residuals and provides the best fit among the four scaling laws tested. The best-fit value of Milgrom`s constant is $a_M
SPIRAL ARM MORPHOLOGY OF NEARBY GALAXIES
Ann, Hong Bae ; Lee, Hyun-Rok ;
Journal of The Korean Astronomical Society, volume 46, issue 3, 2013, Pages 141~149
DOI : 10.5303/JKAS.2013.46.3.141
We analyze the spiral structure of 1725 nearby spiral galaxies with redshift less than 0.02. We use the color images provided by the Sloan Digital Sky Survey. We determine the arm classes (grand design, multiple-arm, flocculent) and the broad Hubble types (early, intermediate, late) as well as the bar types (SA, SAB, SB) by visual inspection. We find that flocculent galaxies are mostly of late Hubble type while multiple-arm galaxies are likely to be of early Hubble type. The fractional distribution of grand design galaxies is nearly constant along the Hubble type. The dependence of arm class on bar type is not as strong as that of the Hubble type. However, there is about a three times larger fraction of grand design spirals in SB galaxies than in SA galaxies, with nearly constant fractions of multiple-arm galaxies. However, if we consider the Hubble type and bar type together, grand design spirals are more frequent in early types than in late types for SA and SAB galaxies, while they are almost constant along the Hubble type for SB galaxies. There are clear correlations between spiral structures and the local background density: strongly barred, early-type, grand design spirals favor high-density regions, while non-barred, late-type, flocculent galaxies are likely to be found in low-density regions.