scholarly journals Photon-weighted barycentric correction and its importance for precise radial velocities

2019 ◽  
Vol 489 (2) ◽  
pp. 2395-2402 ◽  
Author(s):  
René Tronsgaard ◽  
Lars A Buchhave ◽  
Jason T Wright ◽  
Jason D Eastman ◽  
Ryan T Blackman
Keyword(s):  
Velocity Measurement ◽  
Correction Term ◽  
Systematic Errors ◽  
Order Effect ◽  
Second Order ◽  
Radial Velocities ◽  
Similar Measure ◽  
Radial Velocity Measurement ◽  
Existing Data ◽  
Flux Curve

ABSTRACT When applying the barycentric correction to a precise radial velocity measurement, it is common practice to calculate its value only at the photon-weighted mid-point time of the observation instead of integrating over the entire exposure. However, since the barycentric correction does not change linearly with time, this leads to systematic errors in the derived radial velocities. The typical magnitude of this second-order effect is of order 10 cm s−1, but it depends on several parameters, e.g. the latitude of the observatory, the position of the target on the sky, and the exposure time. We show that there are realistic observing scenarios, where the errors can amount to more than 1 m s−1. We therefore recommend that instruments operating in this regime always record and store the exposure meter flux curve (or a similar measure) to be used as photon-weights for the barycentric correction. In existing data, if the flux curve is no longer available, we argue that second-order errors in the barycentric correction can be mitigated by adding a correction term assuming constant flux.

scholarly journals Radial Velocity Observations of Binary Stars

1983 ◽  
Vol 62 ◽  
pp. 93-103
Author(s):  
C. D. Scarfe
Keyword(s):  
Radial Velocity ◽  
Binary Stars ◽  
Velocity Measurement ◽  
Cross Correlation ◽  
Radial Velocities ◽  
Measuring Instruments ◽  
Great Stability ◽  
Visual Binary Stars ◽  
Radial Velocity Measurement

AbstractThis review considers three main areas, leaving several others to be discussed in more detail in the contributed papers of this session.1.The need for spectrographs and measuring instruments of great stability for long-term projects such as radial velocity observations of visual binary stars.2.The use of cross-correlation devices, both analog (radial velocity scanners) and digital, for radial velocity measurement.3.The use of comparison spectra impressed directly onto the starlight and of polarisation instruments as means to very precise radial velocities.

Electromagnetism as a second order effect

1961 ◽  
Vol 3 (1) ◽  
pp. 28-44 ◽  
Author(s):  
W. G. V. Rosser
Keyword(s):  
Order Effect ◽  
Second Order

Simplified Analysis of Second-Order Effect on Staggered Truss Structure

2012 ◽  
Vol 446-449 ◽  
pp. 857-862
Author(s):  
Qi Shi Zhou ◽  
Xu Hong Zhou ◽  
Li Ming Yang
Keyword(s):  
Order Effect ◽  
Second Order ◽  
Truss Structure ◽  
Simplified Analysis

scholarly journals Proper Motions of OB Stars in Both Hemispheres

1974 ◽  
Vol 61 ◽  
pp. 227-227
Author(s):  
Haruo Yasuda
Keyword(s):  
Southern Hemisphere ◽  
Fundamental System ◽  
Systematic Errors ◽  
Radial Velocities ◽  
Distance Scale ◽  
Proper Motions ◽  
Stellar Kinematics ◽  
Ob Stars

From a comparison between the rotational velocities derived from radial velocities and space motions of OB stars, large systematic errors of FK4 proper motions in the southern hemisphere are evaluated; these may be expected, from the known accuracy of the FK4. The error of adopted distance scale is also examined. It is suggested that meridian observations of OB stars should be extended to the southern hemisphere to further researches, not only on stellar kinematics, but also on the fundamental system.

scholarly journals Steps Towards Absolute Accuracy In Radial Velocities

1999 ◽  
Vol 170 ◽  
pp. 58-62
Author(s):  
Dag Gullberg
Keyword(s):  
Systematic Errors ◽  
Radial Velocities ◽  
Surface Gravity ◽  
Absolute Accuracy ◽  
Paper Briefly ◽  
Order Of Magnitude ◽  
The Absolute

AbstractWe are developing methods to reach high absolute accuracy in spectroscopic radial velocities for stars of different spectral types. The basic idea is to remove the effects from convection and surface gravity that cause large systematic errors, in order to improve the absolute accuracy of radial velocities by one order of magnitude. This paper briefly describes observations and methodology in computing the radial velocities.

scholarly journals Itemformaat, differensiële itemskeefheid en die faktorstruktuur van 'n selfvoltooïngsvraelys

1999 ◽  
Vol 25 (2) ◽  
Author(s):  
C. Swart ◽  
G. Roodt ◽  
J. M. Schepers
Keyword(s):  
Factor Analysis ◽  
Random Sample ◽  
Financial Institution ◽  
Test Construction ◽  
Second Order ◽  
Order Factor ◽  
The Empirical Analysis ◽  
Existing Data ◽  
Second Order Factor Analysis

The purpose of this study was twofold: Firstly an existing Workvalues questionnaire was evaluated against criteria for test construction; and secondly the role of differential item skewness in the grouping of second order factors, within this Workvalues questionnaire, was empirically investigated. The existing data of the Workvalues questionnaire, consisting of 110 items on a random sample of 8000 respondents, within a financial institution, was used for the empirical analysis. A first- and second order factor analysis was done on the items of the 2099 completed quiestionnaires. Three clearly differentiated second order factors with seemingly acceptable internal consistencies were identified. The results indicated that the items of the first second order factor, grouped together on the base of differential skewness. The items of the second and third scale were less skew and could be interpreted. Opsomming Die doel van hierdie studie was tweeledig: Eerstens is 'n bestaande Werkwaardesvraelys teenoor kriteria vir toetskonstruksie geevalueer; en tweedens is die rol van differensiele itemskeefheid in die groepering van tweedeordefaktore van hierdie Werkwaardesvraelys empiries ondersoek. Die bestaande datastel van die Werkwaardesvraelys se 110 items, op 'n ewekansige steekproef van 8000 respondente in 'n finansiele instelling, is vir die empiriese ontleding gebruik. 'n Eerste- en tweedeordefaktorontleding is ten opsigte van die items van 2099 voltooide vraelyste uitgevoer en drie duidelik gedifferensieerde tweedeordefaktore met öenskynlike, aanneemlike interne konstanthede het na vore gekom. Resultate dui daarop dat items van die eerste tweedeordefaktor gegroepeer het op grond van differensiële skeefheid. Die items van die tweede en derde skaal was minder skeef en kon vertolk word.

Numerical Investigation Into Parameters Influencing the Installation of Suction Caissons in Sand

2008 ◽  
Author(s):  
Mostafa Zeinoddini ◽  
Woorya H. Shariati ◽  
Mahmood Nabipour
Keyword(s):  
Numerical Investigation ◽  
Friction Angle ◽  
Order Effect ◽  
Reduction Factor ◽  
Second Order ◽  
Strength Reduction Factor ◽  
Dilatancy Angle ◽  
Linear Effect ◽  
Full Penetration ◽  
Suction Caissons

This paper reports results from a numerical investigation into the suction caissons penetration in sand. Two dimensional axisymmetric models have first been calibrated and verified against several laboratory and field test data from other researchers. Soil nonlinearities and soil/caisson interactions have been taken into account. The verified models have then been used to evaluate the effects from various soil/structure characteristics on the performance of the suction caissons during the installation phase in sand. The results of the current study show that the total installation force required for the full penetration of the caisson has a second order relationship with the soil/caisson interface strength reduction factor. The soil cohesion has also been found to have a second order effect on the total installation force. The soil internal friction angle, and the soil modulus of elasticity have each been noticed to present an increasing linear effect on the total installation force. It has also been observed that while the caisson diameter remains constant, with an increase in the caisson length the total installation force almost linearly increases. This is the same when the caisson length is kept constant but its diameter increases. Dilatancy angle and Poisson’s ratio have been realized to have a second order monotically increasing effect on the total installation force.

scholarly journals Correcting HIRES/Keck radial velocities for small systematic errors

2018 ◽  
Vol 484 (1) ◽  
pp. L8-L13 ◽  
Author(s):  
Lev Tal-Or ◽  
Trifon Trifonov ◽  
Shay Zucker ◽  
Tsevi Mazeh ◽  
Mathias Zechmeister
Keyword(s):  
Systematic Errors ◽  
Radial Velocities
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