scholarly journals 25. Commission de Photométrie Stellaire

1939 ◽  
Vol 6 ◽  
pp. 215-228
Author(s):  
M. F. H. Seares ◽  
MM. Baade ◽  
J. Baillaud ◽  
Beljawski ◽  
A. Bemporad ◽  
...  
Keyword(s):  
Zero Point ◽  
Colour Index ◽  
Visual Magnitude ◽  
International Polar ◽  
The Mean

The committee of the Carte du Ciel in 1910 adopted the following convention : That for Ao stars between magnitudes 5·5 and 6·5 the mean photographic magnitude should equal the mean Harvard visual magnitude. As a corollary, the colour index of Ao stars would then be zero.The zero point of the photographic magnitudes of the International Polar Sequence was fixed as nearly as possible in accordance with this definition; but it was by no means certain that the magnitudes thus adopted for the few stars of the Sequence represented the zero point defined by all the Ao stars specified.

scholarly journals Effect of the New Equinox Definition on the Zero-Point of Longitude of the Indian Calendar

1990 ◽  
Vol 141 ◽  
pp. 186-186
Author(s):  
A. K. Bhatnagar
Keyword(s):  
Initial Point ◽  
Zero Point ◽  
The Mean ◽  
Image Position ◽  
Calendar Reform

Indian calendars follow a sidereal system of astronomy taking a fixed initial point on the ecliptic as the origin from which the longitudes are measured. Its position for the official Indian Calendar has been defined by the Calendar Reform Committee (1955) as the point on the ecliptic whose true tropical longitude was 23°15′00″ as on 21 March 1956, 0h UT. Its position was determined upto the year 1984 in accordance with Newcomb's value for general precession using the relation where T is in centuries of 36525 ephemeris days from 1900 January 0.5 ET. Recent changes in the location and the motion of the equinox with reference to the epoch J2000.0 have necessitated corresponding changes to be included in the determination of the mean and true positions of the above initial point. The new algorithm worked out is where T is in Julian centuries of 36525 days from J2000.0.

scholarly journals Jet-disk connection in OJ287

2010 ◽  
Vol 6 (S275) ◽  
pp. 275-279
Author(s):  
Mauri J. Valtonen ◽  
Tuomas Savolainen ◽  
Kaj Wiik
Keyword(s):  
Black Hole ◽  
Time Lag ◽  
Zero Point ◽  
Position Angle ◽  
Viewing Angle ◽  
The Past ◽  
Basic Model ◽  
Optical Light Curve ◽  
The Mean ◽  
Free Parameters

AbstractA model for OJ 287 consisting of two orbiting black holes has been constructed using optical light curve data. The model has successfully predicted the occurrence of sharp optical outbursts of OJ 287 for the past 15 years. Here we test if also the variations in the radio jet position angle can be explained within the framework of this same model, which has most of its parameters fixed by the timing of the optical flares. The model applied here has only three free parameters left, the (trivial) zero point of the jet position angle, the time lag between changes in the disk and jet orientations, and the zero point of the viewing angle. Despite its simplicity and the small number of free parameters, the model appears to be able to reproduce the main properties of the observed position angle variations during the past 30 years. The best fits are obtained when the time lag is either ~4 or ~14 years. However, the jet orientation seems to be unrelated to the direction of the spin of the primary black hole. This implies, assuming that the basic model is correct, that the mean orientation of the jet is determined by the orientation of the inner accretion disk, not by the spin axis of the black hole.

scholarly journals New Metallicity Calibration Down to [Fe/H] = −2.75 dex

2003 ◽  
Vol 20 (2) ◽  
pp. 165-172 ◽  
Author(s):  
S. Karaali ◽  
S. Bilir ◽  
Y. Karataş ◽  
S. G. Ak
Keyword(s):  
Least Squares Method ◽  
Constant Term ◽  
Colour Index ◽  
High Resolution Spectroscopy ◽  
Mean Deviation ◽  
Galactic Latitude ◽  
The Sun ◽  
Degree Polynomial ◽  
The Mean ◽  
Different Sources

AbstractWe have taken 88 dwarfs, covering the colour-index interval 0.37 ≤ (B–V)0 ≤ 1.07 mag, with metallicities –2.70 ≤ [Fe/H] ≤ +0.26 dex, from three different sources for new metallicity calibration. The catalogue of Cayrel de Stroble et al. (2001), which includes 65% of the stars in our sample, supplies detailed information on abundances for stars with determination based on high-resolution spectroscopy. In constructing the new calibration we have used as ‘corner stones’ 77 stars which supply at least one of the following conditions: (i) the parallax is larger than 10 mas (distance relative to the Sun less than 100 pc) and the galactic latitude is absolutely higher than 30°; (ii) the parallax is rather large, if the galactic latitude is absolutely low and vice versa. Contrary to previous investigations, a third-degree polynomial is fitted for the new calibration: [Fe/H] = 0.10 – 2.76δ – 24.04δ2 + 30.00δ3. The coefficients were evaluated by the least-squares method, without regard to the metallicity of Hyades. However, the constant term is in the range of metallicity determined for this cluster, i.e. 0.08 ≤ [Fe/H] ≤ 0.11 dex. The mean deviation and the mean error in our work are equal to those of Carney (1979), for [Fe/H] ≥ –1.75 dex where Carney's calibration is valid.

scholarly journals On the environmental zero-point problem in microevolutionary climate response predictions

2022 ◽  
Author(s):  
Rolf Ergon
Keyword(s):  
Phenotypic Plasticity ◽  
Zero Point ◽  
Mean Value ◽  
Environmental Data ◽  
Global Maximum ◽  
Point Problem ◽  
Microevolutionary Change ◽  
Mean Fitness ◽  
The Mean ◽  
Parameter Values

It is well documented that populations adapt to climate change by means of phenotypic plasticity, but few reports on adaptation by means of genetically based microevolution caused by selection. Disentanglement of these separate effects requires that the environmental zero-point is defined, and this should not be done arbitrarily. Together with parameter values, the zero-point can be estimated from environmental, phenotypic and fitness data. A prediction error method for this purpose is described, with the feasibility shown by simulations. An estimated environmental zero-point may have large errors, especially for small populations, but may still be a better choice than use of an initial environmental value in a recorded time series, or the mean value, which is often used. Another alternative may be to use the mean value of a past and stationary stochastic environment, which the population is judged to have been fully adapted to, in the sense that the mean fitness was at a global maximum. An exception is here cases with constant phenotypic plasticity, where the microevolutionary change per generation follows directly from phenotypic and environmental data, independent of the chosen environmental zero-point.

The Calculation of Zero-Point Energies of Molecules by Perturbation Methods

1963 ◽  
Vol 18 (2) ◽  
pp. 216-224 ◽  
Author(s):  
Max Wolfsberg
Keyword(s):  
Perturbation Methods ◽  
Secular Equation ◽  
Isotope Effects ◽  
Normal Modes ◽  
Zero Point ◽  
Perturbation Series ◽  
Quantum Mechanical ◽  
Perturbation Scheme ◽  
Point Energy ◽  
The Mean

Two methods are proposed for calculating zero-point energies of molecules. The first makes use of the fact that one can easily write down the quantum mechanical HAMILTONian for a vibrating system. The zero-point energy can then be obtained by a perturbation scheme without solving the secular equation. The second method requires a knowledge of the normal modes and frequencies of a reference molecule, but then enables one to calculate isotope effects by a perturbation scheme. The methods are applied to some examples and the convergence of the perturbation series is investigated. The approximate validity of the law of the mean for the isotope effect on zero-point energies is explored within the framework of the methods.

THE EMISSION OF HEAVY CLUSTERS DESCRIBED IN THE MEAN-FIELD HFB THEORY: THE CASE OF 242Cm

2008 ◽  
Vol 17 (10) ◽  
pp. 2275-2282 ◽  
Author(s):  
L. M. ROBLEDO ◽  
M. WARDA
Keyword(s):  
Mean Field ◽  
Zero Point ◽  
Point Energy ◽  
Cluster Emission ◽  
Field Techniques ◽  
Hartree Fock ◽  
Moment Operator ◽  
Collective Coordinate ◽  
The Mean ◽  
Asymmetric Fission

The emission of a nucleus of 34 Si by the parent [Formula: see text] is a process in the diffuse borderline between cluster emission and standard mass asymmetric fission. In this paper we analyze in a microscopic framework such process using the standard mean field techniques used to describe cluster emission. They include Hartree-Fock-Bogoliubov constrained calculations with the Gogny D1S interaction and the octupole moment operator as the collective coordinate to describe the process. Collective masses and all kind of zero point energy corrections are considered which allows for a parameter free estimation of the process' half-life. The agreement with experiment is quite satisfactory.

scholarly journals On the Zero Point Constant of the Bolometric Correction Scale

2021 ◽  
Author(s):  
Z Eker ◽  
V Bakış ◽  
F Soydugan ◽  
S Bilir
Keyword(s):  
Similar Case ◽  
Zero Point ◽  
Magnitude Scale ◽  
General Assembly ◽  
Basic Definition ◽  
V Band ◽  
Visual Magnitude ◽  
General Assembly Resolution ◽  
Bolometric Correction

Abstract Arbitrariness attributed to the zero point constant of the V band bolometric corrections (BCV) and its relation to “bolometric magnitude of a star ought to be brighter than its visual magnitude” and “bolometric corrections must always be negative” was investigated. The falsehood of the second assertion became noticeable to us after IAU 2015 General Assembly Resolution B2, where the zero point constant of bolometric magnitude scale was decided to have a definite value CBol(W) = 71.197 425 ... . Since the zero point constant of the BCV scale could be written as C2 = CBol − CV, where CV is the zero point constant of the visual magnitudes in the basic definition BCV = MBol − MV = mbol − mV, and CBol > CV, the zero point constant (C2) of the BCV scale cannot be arbitrary anymore; rather, it must be a definite positive number obtained from the two definite positive numbers. The two conditions C2 > 0 and 0 < BCV < C2 are also sufficient for LV < L, a similar case to negative BCV numbers, which means that “bolometric corrections are not always negative”. In sum it becomes apparent that the first assertion is misleading causing one to understand bolometric corrections must always be negative, which is not necessarily true.

scholarly journals A New Procedure for the Photometric Parallax Estimation

2003 ◽  
Vol 20 (3) ◽  
pp. 270-278 ◽  
Author(s):  
S. Karaali ◽  
Y. Karataş ◽  
S. Bilir ◽  
S. G. Ak ◽  
E. Hamzaoğlu
Keyword(s):  
Main Sequence ◽  
Large Range ◽  
Absolute Magnitude ◽  
Colour Index ◽  
Ultraviolet Excess ◽  
Magnitude Diagram ◽  
Single Colour ◽  
The Mean ◽  
The Absolute ◽  
Absolute Magnitudes

AbstractWe present a new procedure for photometric parallax estimation. The data for 1236 stars provide calibrations between the absolute magnitude offset from the Hyades main-sequence and the ultraviolet-excess for eight different (B–V)0 colour-index intervals, (0.3 0.4), (0.4 0.5), (0.5 0.6), (0.6 0.7), (0.7 0.8), (0.8 0.9), (0.9 1.0) and (1.0 1.1). The mean difference between the original and estimated absolute magnitudes and the corresponding standard deviation are rather small, +0.0002 and ±0.0613 mag. The procedure has been adapted to the Sloan photometry by means of colour equations and applied to a set of artificial stars with different metallicities. The comparison of the absolute magnitudes estimated by the new procedure and the canonical one indicates that a single colour–magnitude diagram does not supply reliable absolute magnitudes for stars with large range of metallicity.

A new method of determining brightness and size of cometary nuclei

2020 ◽  
Vol 492 (3) ◽  
pp. 4175-4188 ◽  
Author(s):  
Mieczyslaw Leszek Paradowski
Keyword(s):  
Bulk Density ◽  
Exponential Decay ◽  
Linear Dependence ◽  
New Method ◽  
Nuclear Density ◽  
Decay Function ◽  
Cometary Nuclei ◽  
Exponential Decay Function ◽  
Visual Magnitude ◽  
The Mean

ABSTRACT This paper presents a new method of determining the brightness and size of cometary nuclei that has been applied to the following 32 observed comets: 2P/Encke, 29P/Schwassmann-Wachmann 1, 102P/Shoemaker 1, 103P/Hartley 2, 168P/Hergenrother, 189P/NEAT, 260P/McNaught, 315P/LONEOS, P/2012 NJ (La Sagra), P/2013 J2 (McNaught), C/2006 S3 (LONEOS), C/2009 P1 (Garradd), C/2010 S1 (LINEAR), C/2010 X1 (Elenin), C/2011 J2 (LINEAR), C/2011 L4 (PANSTARRS), C/2011 W3 (Lovejoy), C/2012 F6 (Lemmon), C/2012 J1 (Catalina), C/2012 K1 (PANSTARRS), C/2012 S1 (ISON), C/2013 R1 (Lovejoy), C/2013 US10 (Catalina), C/2014 B1 (Schwartz), C/2014 E2 (Jacques), C/2014 Q2 (Lovejoy), C/2015 F4 (Jacques), C/2015 V2 (Johnson), C/2015 ER61 (PANSTARRS), C/2015 VL62 (Lemmon-Yeung-PANSTARRS), C/2016 A8 (LINEAR), and C/2017 O1 (ASASSN). The method consists in fitting the exponential decay function to the measured coma brightness in the aperture radius range from 0.5 to 2 pixels, and extrapolating this function to 0 pixels to obtain nuclear brightness. The R-band absolute nuclear magnitude RN(1, 1, 0), and the logarithm of the nucleus diameter DN expressed in kilometres, follow a linear dependence with the absolute total visual magnitude H. This dependence is of the form RN(1, 1, 0) = 12.5943 + 0.648H, and log DN[km] = 1.2415 − 0.13H. Comet 2P/Encke does not fit this dependence due to its high nuclear density of 800 kg m−3 (Sosa & Fernández 2009). The mean bulk density of the observed comets (except 2P/Encke) is 453 ± 29 kg m−3. The accuracy of the method in determining the brightness of comet nuclei at a level of 1σ is 8 per cent.

scholarly journals Spectral Evolution of Nova Vulpeculae 1976

1977 ◽  
Vol 42 ◽  
pp. 182-184
Author(s):  
P. Rafanelli ◽  
A. Vittone
Keyword(s):  
Light Curve ◽  
Color Index ◽  
Mean Value ◽  
Spectral Evolution ◽  
Slow Recovery ◽  
Gradual Decline ◽  
Visual Magnitude ◽  
The Mean ◽  
Visual Light

Nova Vulpeculae 1976 was discovered by G.E.D. Alcock (1976) on October 21, 1976 as a star of visual magnitude 6.5 in position (1950): The visual light curve, plotted together with the color index B-V in fig.1, was obtained using the observations published in the I.A.U. Circulars. It shows a slow fall from maximum, about 2.5 magnitudes in 60 days, with characteristic fluctuations, an abrupt drop of about 3.5 magnitudes in 24 days, a slow recovery of one magnitude in 30 days, and a very gradual decline to minimum. The color index B-V remained almost constant near the mean value +1.1 during the slow early decline.

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