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Articles de revues sur le sujet « Radial velocitie »

Auteur : Grafiati

Publié le 9 mars 2023

Mis à jour le 10 mars 2023

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1

Walker, G. A. H., J. Amor, S. Yang et B. Campbell. « Precise Radial Velocities and Radial Velocity Standards ». Symposium - International Astronomical Union 111 (1985) : 587–89. http://dx.doi.org/10.1017/s0074180900079547.

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By imposing absorption lines of HF in stellar spectra we can measure changes in r.v. with a precision of ~10m/s from a single spectrum, provided stellar line profiles are not distorted by atmospheric motions. The precision of absolute radial velocities is currently limited to ~100m/s by knowledge of rest wavelengths. Representative results are presented from our three, active PRV programs: velocity variations of δ Scuti stars; a search for unseen companions to late-type stars; and routine observations of certain IAU velocity ‘standards’.

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Deconto-Machado, A., R. A. Riffel, G. S. Ilha, S. B. Rembold, T. Storchi-Bergmann, R. Riffel, J. S. Schimoia et al. « Ionised gas kinematics in MaNGA AGN ». Astronomy & ; Astrophysics 659 (mars 2022) : A131. http://dx.doi.org/10.1051/0004-6361/202140613.

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Context. Feedback from active galactic nuclei (AGNs) in general seems to play an important role in the evolution of galaxies, although the impact of AGN winds on their host galaxies is still unknown in the absence of a detailed analysis. Aims. We aim to analyse the kinematics of a sample of 170 AGN host galaxies as compared to those of a matched control sample of non-active galaxies from the MaNGA survey in order to characterise and estimate the extents of the narrow-line region (NLR) and of the kinematically disturbed region (KDR) by the AGN. Methods. We defined the observed NLR radius (rNLR, o) as the farthest distance from the nucleus within which both [O III]/Hβ and [N II]/Hα ratios fall in the AGN region of the BPT diagram, and the Hα equivalent width was required to be larger than 3.0 Å. The extent of the KDR (rKDR, o) is defined as the distance from the nucleus within which the AGN host galaxies show a more disturbed gas kinematics than the control galaxies. Results. The AGN [O III]λ5007 luminosity ranges from 1039 to 1041 erg s−1, and the kinematics derived from the [O III] line profiles reveal that, on average, the most luminous AGNs (L[O III] > 3.8 × 1040 erg s−1) possess higher residual differences between the gaseous and stellar velocities and velocitie dispersions than their control galaxies in all the radial bins. Spatially resolved NLRs and KDRs were found in 55 and 46 AGN host galaxies, with corrected radii 0.2 < rKDR, c < 2.3 kpc and 0.4 < rNLR, c < 10.1 kpc and a relation between the two given by log rKDR, c = (0.53 ± 0.12) log rNLR, c + (1.07 ± 0.22), respectively. On average, the extension of the KDR corresponds to about 30% of that of the NLR. Assuming that the KDR is due to an AGN outflow, we have estimated ionised gas mass outflow rates that range between 10−5 and ∼1 M⊙ yr−1, and kinetic powers that range from 1034 to 1040 erg s−1. Conclusions. Comparing the power of the AGN ionised outflows with the AGN luminosities, they are always below the 0.05 LAGN model threshold for having an important feedback effect on their respective host galaxies. The mass outflow rates (and power) of our AGN sample correlate with their luminosities, populating the lowest AGN luminosity range of the correlations previously found for more powerful sources.

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Petersburg, Ryan R., J. M. Joel Ong, Lily L. Zhao, Ryan T. Blackman, John M. Brewer, Lars A. Buchhave, Samuel H. C. Cabot et al. « An Extreme-precision Radial-velocity Pipeline : First Radial Velocities from EXPRES ». Astronomical Journal 159, n^o 5 (1 avril 2020) : 187. http://dx.doi.org/10.3847/1538-3881/ab7e31.

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Philip, A. G. Davis, J. Andersen, A. Batten, M. Duflot, D. Hube, M. Mayor et J. Sahade. « 30. Radial Velocities ». Transactions of the International Astronomical Union 19, n^o 1 (1985) : 375–82. http://dx.doi.org/10.1017/s0251107x00006428.

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This report covers the period June 1981 to June 1984. and includes some material from IAU Colloquium No. 88, October, 1984.). The field of radial velocities has undergone a renaissance in the last few years as the new radial velocity machines have come into use. Not only can stars of much fainter magnitudes be reached, but the precision of the measured radial velocity has been increased by orders of magnitude. Instead of speaking of velocities accurate to kilometers per second it is now possible to measure velocities to tens of meters per second. Research programs, involving these new techniques are now underway involving the study of hundreds, and in some cases, thousands of faint stars.

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Sartoretti, P., D. Katz, M. Cropper, P. Panuzzo, G. M. Seabroke, Y. Viala, K. Benson et al. « Gaia Data Release 2 ». Astronomy & ; Astrophysics 616 (août 2018) : A6. http://dx.doi.org/10.1051/0004-6361/201832836.

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Context. The Gaia Data Release 2 (DR2) contains the first release of radial velocities complementing the kinematic data of a sample of about 7 million relatively bright, late-type stars. Aims. This paper provides a detailed description of the Gaia spectroscopic data processing pipeline, and of the approach adopted to derive the radial velocities presented in DR2. Methods. The pipeline must perform four main tasks: (i) clean and reduce the spectra observed with the Radial Velocity Spectrometer (RVS); (ii) calibrate the RVS instrument, including wavelength, straylight, line-spread function, bias non-uniformity, and photometric zeropoint; (iii) extract the radial velocities; and (iv) verify the accuracy and precision of the results. The radial velocity of a star is obtained through a fit of the RVS spectrum relative to an appropriate synthetic template spectrum. An additional task of the spectroscopic pipeline was to provide first-order estimates of the stellar atmospheric parameters required to select such template spectra. We describe the pipeline features and present the detailed calibration algorithms and software solutions we used to produce the radial velocities published in DR2. Results. The spectroscopic processing pipeline produced median radial velocities for Gaia stars with narrow-band near-IR magnitude GRVS ≤ 12 (i.e. brighter than V ~ 13). Stars identified as double-lined spectroscopic binaries were removed from the pipeline, while variable stars, single-lined, and non-detected double-lined spectroscopic binaries were treated as single stars. The scatter in radial velocity among different observations of a same star, also published in Gaia DR2, provides information about radial velocity variability. For the hottest (Teff ≥ 7000 K) and coolest (Teff ≤ 3500 K) stars, the accuracy and precision of the stellar parameter estimates are not sufficient to allow selection of appropriate templates. The radial velocities obtained for these stars were removed from DR2. The pipeline also provides a first-order estimate of the performance obtained. The overall accuracy of radial velocity measurements is around ~200–300 m s−1, and the overall precision is ~1 km s−1; it reaches ~200 m s−1 for the brightest stars.

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Katz, D., P. Sartoretti, M. Cropper, P. Panuzzo, G. M. Seabroke, Y. Viala, K. Benson et al. « Gaia Data Release 2 ». Astronomy & ; Astrophysics 622 (février 2019) : A205. http://dx.doi.org/10.1051/0004-6361/201833273.

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Context. For Gaia DR2, 280 million spectra collected by the Radial Velocity Spectrometer instrument on board Gaia were processed, and median radial velocities were derived for 9.8 million sources brighter than GRVS = 12 mag. Aims. This paper describes the validation and properties of the median radial velocities published in Gaia DR2. Methods. Quality tests and filters were applied to select those of the 9.8 million radial velocities that have the quality to be published in Gaia DR2. The accuracy of the selected sample was assessed with respect to ground-based catalogues. Its precision was estimated using both ground-based catalogues and the distribution of the Gaia radial velocity uncertainties. Results. Gaia DR2 contains median radial velocities for 7 224 631 stars, with Teff in the range [3550, 6900] K, which successfully passed the quality tests. The published median radial velocities provide a full-sky coverage and are complete with respect to the astrometric data to within 77.2% (for G ≤ 12.5 mag). The median radial velocity residuals with respect to the ground-based surveys vary from one catalogue to another, but do not exceed a few 100 m s−1. In addition, the Gaia radial velocities show a positive trend as a function of magnitude, which starts around GRVS ~ 9 mag and reaches about + 500 m s−1 at GRVS = 11.75 mag. The origin of the trend is under investigation, with the aim to correct for it in Gaia DR3. The overall precision, estimated from the median of the Gaia radial velocity uncertainties, is 1.05 km s−1. The radial velocity precision is a function of many parameters, in particular, the magnitude and effective temperature. For bright stars, GRVS ∈ [4, 8] mag, the precision, estimated using the full dataset, is in the range 220–350 m s−1, which is about three to five times more precise than the pre-launch specification of 1 km s−1. At the faint end, GRVS = 11.75 mag, the precisions for Teff = 5000 and 6500 K are 1.4 and 3.7 km s−1, respectively.

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Faizal, Mohd, Md Seri Suzairin, Mohd Al-Hafiz et Vijay Raj Raghavan. « CFD Studies on Velocity Distribution of Air in a Swirling Fluidized Bed ». Advanced Materials Research 468-471 (février 2012) : 25–29. http://dx.doi.org/10.4028/www.scientific.net/amr.468-471.25.

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This paper presents computational fluid dynamics (CFD) studies to characterize air velocity distribution for various bed configurations in a swirling fluidized bed (SFB). Unlike conventional fluidized beds, a SFB provides radial mixing which is desirable is fluidization. Three velocities components were observed, the tangential velocity, radial velocity and axial velocity. These velocities were created as a result of using annular blade type distributor which mimics the turbine blades. In actual industrial applications, the axial velocity will create fluidization while the tangential velocity provides swirling effect. The presence of radial velocity can be explained as a consequence of centrifugal force generated by the swirling gas. Understanding these velocity distributions will enable optimization of the annular blade distributor design towards a high efficient fluidized bed system.

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Griffin, R. F. « Photoelectric radial velocities, Paper XIV. Variation of the radial velocity of ε Cygni ». Monthly Notices of the Royal Astronomical Society 267, n^o 1 (mars 1994) : 69–76. http://dx.doi.org/10.1093/mnras/267.1.69.

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Lv, Xiao Shi, Guang Yong Wang et Jia Qi Guo. « The Study of the Influence of the Incident Angle, Frequency and Diameter on Blasting Vibration Velocity of the Underground Chamber ». Applied Mechanics and Materials 90-93 (septembre 2011) : 1555–65. http://dx.doi.org/10.4028/www.scientific.net/amm.90-93.1555.

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Based on model tests, the wave function expansion method was used to study scattering on the interaction of explosive stress waves and the underground chamber, and analyze the influence of the incident angle, frequency and diameter on blasting vibration velocity of underground chamber. It is obtained that when the cavern was under the plane waves of the vault, the radial vibration velocity of the vault is the largest among the four measured data, and it is the most intense vibrating place. When the incidence direction offsets from the vault to the horizontal direction on the left, the radial velocity facing burst are all larger than the radial velocity back of the burst. When the incident direction is on the dome, the tangential vibration velocity will increase first and then decrease from the vault to the side wall. When the incident direction is at the haunch, the tangential vibration velocity in the corner should be noticed. With increasing of the frequency, the radial vibration velocity and tangential vibration velocity increase accordingly. At the forward part of the burst, the larger the chamber diameter is, the bigger the radial and tangential velocities are. At the back side of the burst, the bigger the chamber diameter is, the smaller the radial and tangential vibration velocities are.

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Xiao, Qingnong, Ying-Hwa Kuo, Juanzhen Sun, Wen-Chau Lee, Eunha Lim, Yong-Run Guo et Dale M. Barker. « Assimilation of Doppler Radar Observations with a Regional 3DVAR System : Impact of Doppler Velocities on Forecasts of a Heavy Rainfall Case ». Journal of Applied Meteorology 44, n^o 6 (1 juin 2005) : 768–88. http://dx.doi.org/10.1175/jam2248.1.

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Abstract In this paper, the impact of Doppler radar radial velocity on the prediction of a heavy rainfall event is examined. The three-dimensional variational data assimilation (3DVAR) system for use with the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) is further developed to enable the assimilation of radial velocity observations. Doppler velocities from the Korean Jindo radar are assimilated into MM5 using the 3DVAR system for a heavy rainfall case that occurred on 10 June 2002. The results show that the assimilation of Doppler velocities has a positive impact on the short-range prediction of heavy rainfall. The dynamic balance between atmospheric wind and thermodynamic fields, based on the Richardson equation, is introduced to the 3DVAR system. Vertical velocity (w) increments are included in the 3DVAR system to enable the assimilation of the vertical velocity component of the Doppler radial velocity observation. The forecast of the hydrometeor variables of cloud water (qc) and rainwater (qr) is used in the 3DVAR background fields. The observation operator for Doppler radial velocity is developed and implemented within the 3DVAR system. A series of experiments, assimilating the Korean Jindo radar data for the 10 June 2002 heavy rainfall case, indicates that the scheme for Doppler velocity assimilation is stable and robust in a cycling mode making use of high-frequency radar data. The 3DVAR with assimilation of Doppler radial velocities is shown to improve the prediction of the rainband movement and intensity change. As a result, an improved skill for the short-range heavy rainfall forecast is obtained. The forecasts of other quantities, for example, winds, are also improved. Continuous assimilation with 3-h update cycles is important in producing an improved heavy rainfall forecast. Assimilation of Doppler radar radial velocities using the 3DVAR background fields from a cycling procedure produces skillful rainfall forecasts when verified against observations.

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Fekel, Francis C. « The Status of Early-Type Radial-Velocity Standards ». International Astronomical Union Colloquium 170 (1999) : 378–82. http://dx.doi.org/10.1017/s0252921100048806.

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AbstractA search for constant velocity B and A stars for use as early-type radial-velocity standards has continued for 15 years. For the past decade observations of over two dozen stars have been obtained with the KPNO coudé feed telescope, spectrograph, and a CCD detector. Mean velocities are given for 26 B and A stars plus HR 5447, an F2 V star. Unfortunately, most of the early and mid B-type stars have variable velocities. However, a number of slowly rotating, late B and A-type stars that have constant velocities are identified. From 53 velocities covering nearly 20 years, a preliminary orbit for the early-A star HR 8641 = o Peg has been determined. It has a period of 10.8 years and a total velocity amplitude of 2.4 km s−1.

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Cummings, I. N., J. B. Hearnshaw, P. M. Kilmartin et A. C. Gilmore. « High precision radial-velocity measurements of late-type evolved stars ». International Astronomical Union Colloquium 170 (1999) : 204–10. http://dx.doi.org/10.1017/s0252921100048569.

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AbstractHigh dispersion spectra for 44 southern evolved stars of spectral type K or M have been obtained. From these observations relative radial velocities of 50 m/s precision have been obtained by the method of digital cross-correlation. This method of achieving precise relative radial velocities for late-type stars, and the problems encountered in its use, are discussed. Using this method, statistically significant radial-velocity variations have been found. Two of the observed stars have their precise radial velocities presented and the potential mechanisms of their variation examined.

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Feast, M. W., T. D. Kinman et B. S. Lasker. « Planetary Nebulae and the Galactic Bulge ». Symposium - International Astronomical Union 131 (1989) : 167. http://dx.doi.org/10.1017/s007418090013774x.

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Fifteen new PN have been discovered in the region of Baade's Windows using an objective prism technique. Absolute spectrophotometry, excitation classes, radii and radial velocities have been obtained. Radial velocities were also measured for eight other PN in this region. After correction for solar motion and the circular velocity at the sun, the radial velocities of bulge PN (Vc) with |b| < 5°.5 show good evidence for a rotation of the bulge. If Vc=α + βΔℓ then,

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Grenier, S., M. O. Baylac, L. Rolland, R. Burnage, F. Arenou, D. Briot, F. Delmas et al. « Radial velocities ». Astronomy and Astrophysics Supplement Series 137, n^o 3 (juin 1999) : 451–56. http://dx.doi.org/10.1051/aas:1999489.

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Ozawa, Katsusuke, Jun Murotsuki, Susumu Miyashita, Jin Muromoto, Hideyuki Hasegawa, Hiroshi Kanai et Nobuo Yaegashi. « Assessing Fetal Cardiac Function by Measuring Myocardial Radial Velocity Using the Phased-Tracking Method ». Fetal Diagnosis and Therapy 38, n^o 2 (2015) : 126–34. http://dx.doi.org/10.1159/000371514.

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Objective: This study aimed to assess the cardiac function of healthy and pathological fetuses by measuring radial velocity using phased tracking (PT). Based on phase differences, PT allows the displacement of a specified point to be detected with improved spatial and temporal resolution. Methods: PT was used to assess cardiac radial velocity in the basal free wall of the left and right ventricles in 134 healthy fetuses, 10 second-trimester intrauterine growth-restricted (IUGR) fetuses, and 10 recipient twins with twin-to-twin transfusion syndrome (TTTS). Maximum velocities were measured in systole and early diastole. Results: Maximum radial velocity was successfully measured in 126 healthy fetuses (94%) at gestational ages of 16-40 weeks. Systolic and early diastolic maximum velocities increased with gestational age in both ventricles. As compared with controls, IUGR fetuses had significantly lower early diastolic maximum velocities in the right ventricle, and recipient twins with TTTS had significantly lower systolic and early diastolic maximum velocities in both ventricles. Conclusions: PT demonstrated right ventricular diastolic dysfunction in second-trimester IUGR fetuses as well as systolic and diastolic dysfunctions in both ventricles in recipient twins with TTTS. PT could be useful for evaluating fetal cardiac radial function.

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Akalin, A., et S. Engin. « A Study of Ultraviolet Spectra of Delta Sagittae ». Symposium - International Astronomical Union 151 (1992) : 273–75. http://dx.doi.org/10.1017/s0074180900122272.

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High resolution spectrum of the VV Cephei type star δ Sge (M2 II + A0 V) observed with the IUE satellite between 1979–1985 have been analysed. The radial velocity curves of non blended absorption features have been formed. Observed radial velocities are compared with the theoretical radial velocity curve due to orbital motion. We found that observed radial velocity variation is the resultant of radial velocity of hotter component and wind velocity around this star. The wind is perturbed by hotter component. Matching the UV continuum fluxes obtained from IUE high resolution spectra to fluxes of Kurucz model atmospheres yields Te=11000±500 °K. Thus the spectral type of hot component was found as A0.

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Madsen, Søren, Lennart Lindegren et Dainis Dravins. « Radial Velocities Without Spectroscopy ». International Astronomical Union Colloquium 170 (1999) : 77–81. http://dx.doi.org/10.1017/s0252921100048399.

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AbstractWe discuss non-spectroscopic (astrometric) ways to determine radial velocities and their potentials in future astrometric missions. Radial-velocity accuracies are presented, based on Hipparcos parallax and proper motion data for several open clusters.

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Mayor, Michel, Michèle Gerbaldi, Suzanne Grenier et Hugo Levato. « Radial Velocities for the Stars of the HIPPARCOS Mission ». Highlights of Astronomy 9 (1992) : 433–36. http://dx.doi.org/10.1017/s153929960000945x.

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A large fraction if not all of the programmes related to the study of the galactic structure, its kinematics and chemical evolution will require the knowledge of the third component of the velocity: the stellar radial velocity. But we will also need the radial velocity to be able to determine the true distribution of masses in the solar neighborhood (corrected by the crossing time of the stars in the sampled sphere). The radial velocity will allow the determination of the statistical parallax for a sample of stars lying beyond 100 parsec. At the very beginning of the development of the Hipparcos space mission, the very need for ground-based, complementary measurements has been recognized. However, in spite of the existence of new kinds of techniques or detectors, the task to provide radial velocities for the somewhat 118’000 stars of the Hipparcos Input Catalogue is quite enormous. All presently published stellar radial velocities determined since the beginning of this century represent at the most 20 to 25% of the total number of stars to be measured!

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Doi, Takao, C. R. O'Dell et Patrick Hartigan. « Internal Velocities in the Orion Nebula : Large Radial Velocity Features ». Astronomical Journal 127, n^o 6 (juin 2004) : 3456–78. http://dx.doi.org/10.1086/386351.

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Lindegren, Lennart, et Dainis Dravins. « Astrometric radial velocities for nearby stars ». Astronomy & ; Astrophysics 652 (août 2021) : A45. http://dx.doi.org/10.1051/0004-6361/202141344.

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Context. Under certain conditions, stellar radial velocities can be determined from astrometry, without any use of spectroscopy. This enables us to identify phenomena, other than the Doppler effect, that are displacing spectral lines. Aims. The change of stellar proper motions over time (perspective acceleration) is used to determine radial velocities from accurate astrometric data, which are now available from the Gaia and HIPPARCOS missions. Methods. Positions and proper motions at the epoch of HIPPARCOS are compared with values propagated back from the epoch of the Gaia Early Data Release 3. This propagation depends on the radial velocity, which obtains its value from an optimal fit assuming uniform space motion relative to the solar system barycentre. Results. For 930 nearby stars we obtain astrometric radial velocities with formal uncertainties better than 100 km s−1; for 55 stars the uncertainty is below 10 km s−1, and for seven it is below 1 km s−1. Most stars that are not components of double or multiple systems show good agreement with available spectroscopic radial velocities. Conclusions. Astrometry offers geometric methods to determine stellar radial velocity, irrespective of complexities in stellar spectra. This enables us to segregate wavelength displacements caused by the radial motion of the stellar centre-of-mass from those induced by other effects, such as gravitational redshifts in white dwarfs.

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Scarfe, C. D. « The Zero-Point of the IAU Standard Velocity System ». Symposium - International Astronomical Union 111 (1985) : 583–86. http://dx.doi.org/10.1017/s0074180900079535.

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Radial velocities of bright IAU standards have been obtained photographically over the past decade using the long camera of the DAO 1.2 meter telescope's coudé spectrograph. Most of the stars observed have been found to be constant in velocity to better than 0.15 km/s over that interval. The mean velocities agree with the IAU velocities, on the average, within 0.10 km/s, although mean velocities of some individual stars differ considerably more than this from the IAU value. A preliminary determination of the zero point of the long camera system, and hence of the IAU system, has been made from observations of the asteroid Vesta, whose actual radial velocity has been calculated from its orbital elements.

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Espinoza, Néstor, Diana Kossakowski et Rafael Brahm. « juliet : a versatile modelling tool for transiting and non-transiting exoplanetary systems ». Monthly Notices of the Royal Astronomical Society 490, n^o 2 (7 octobre 2019) : 2262–83. http://dx.doi.org/10.1093/mnras/stz2688.

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ABSTRACT Here we present juliet, a versatile tool for the analysis of transits, radial velocities, or both. juliet is built over many available tools for the modelling of transits, radial velocities, and stochastic processes (here modelled as Gaussian Processes; GPs) in order to deliver a tool/wrapper which can be used for the analysis of transit photometry and radial-velocity measurements from multiple instruments at the same time, using nested sampling algorithms which allows it to not only perform a thorough sampling of the parameter space, but also to perform model comparison via Bayesian evidences. In addition, juliet allows us to fit transiting and non-transiting multiplanetary systems, and to fit GPs which might share hyperparameters between the photometry and radial velocities simultaneously (e.g. stellar rotation periods), which might be useful for disentangling stellar activity in radial-velocity measurements. Nested Sampling, Importance Nested Sampling, and Dynamic Nested Sampling is performed with publicly available codes which in turn give juliet multithreading options, allowing it to scale the computing time of complicated multidimensional problems. We make juliet publicly available via GitHub.

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Fang, Ying-Chih, Thomas J. Weingartner, Rachel A. Potter, Peter R. Winsor et Hank Statscewich. « Quality Assessment of HF Radar–Derived Surface Currents Using Optimal Interpolation ». Journal of Atmospheric and Oceanic Technology 32, n^o 2 (février 2015) : 282–96. http://dx.doi.org/10.1175/jtech-d-14-00109.1.

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AbstractThis study investigates the applicability of the optimal interpolation (OI) method proposed by Kim et al. for estimating ocean surface currents from high-frequency radar (HFR) in the northeastern Chukchi Sea, where HFR siting is dictated by power availability rather than optimal locations. Although the OI technique improves data coverage when compared to the conventional unweighted least squares fit (UWLS) method, biased solutions can emerge. The quality of the HFR velocity estimates derived by OI is controlled by three factors: 1) the number of available incorporating radials (AR), 2) the ratio of the incorporating radials from multiple contributing site locations [ratio of overlapping radial velocities (ROR) or radar geometry], and 3) the positive definiteness [condition number (CN)] of the correlation matrix. Operationally, ROR does not require knowledge of the angle covariance matrix used to compute the geometric dilution of precision (GDOP) in the UWLS method and can be computed before site selection to optimize coverage or after data processing to assess data quality when applying the OI method. The Kim et al. method is extended to examine sensitivities to data gaps in the radial distribution and the effects on OI estimates.

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Milone, Alejandra A. E., David W. Latham, Robert D. Mathieu, Jon A. Morse et Robert J. Davis. « Can Evolution in Close Binaries Account for the Blue Stragglers in M67 ? » Symposium - International Astronomical Union 151 (1992) : 473–74. http://dx.doi.org/10.1017/s0074180900122752.

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For the past 9 years we have been monitoring the radial velocities of 13 blue stragglers in the old open cluster M67. For the 9 blue stragglers with rotational velocities no larger than about 100 km s−1 we have used the CfA digital speedometers to measure more than 500 radial velocities. To get reliable velocity correlations we use synthetic rotating templates computed from a grid of Kurucz model atmospheres. Four of the blue stragglers rotate too rapidly to allow successful velocity correlations with the CfA instruments. For three of these we have used a CCD spectrograph at Kitt Peak and similar reduction procedures (Morse et al. 1991.

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Kim, Sung Yong. « Quality Assessment Techniques Applied to Surface Radial Velocity Maps Obtained from High-Frequency Radars ». Journal of Atmospheric and Oceanic Technology 32, n^o 10 (octobre 2015) : 1915–27. http://dx.doi.org/10.1175/jtech-d-14-00207.1.

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AbstractThis paper presents examples of the data quality assessment of surface radial velocity maps obtained from shore-based single and multiple high-frequency radars (HFRs) using statistical and dynamical approaches in a hindcast mode. Since a single radial velocity map contains partial information regarding a true current field, archived radial velocity data embed geophysical signals, such as tides, wind stress, and near-inertial and low-frequency variance. The spatial consistency of the geophysical signals and their dynamic relationships with driving forces are used to conduct the quality assurance and quality control of radial velocity data. For instance, spatial coherence, tidal amplitudes and phases, and wind-radial transfer functions are used to identify a spurious range and azimuthal bin. The uncertainty and signal-to-noise ratio of radial data are estimated with the standard deviation and cross correlation of paired radials sampled at nearby grid points that belong to two different radars. This review paper can benefit HFR users and operators and those who are interested in analyzing HFR-derived surface radial velocity data.

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Barnes, T. G., et T. J. Moffett. « Radial Velocities of Classical Cepheids ». International Astronomical Union Colloquium 82 (1985) : 32–33. http://dx.doi.org/10.1017/s0252921100109005.

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Approximately 2000 radial velocities of 88 classical Cepheids have been observed using a photoelectric radial velocity meter. During the same time interval, these same Cepheids were intensively observed in the BVRI bandpasses, as reported elsewhere in these proceedings. This provides a homogeneous set of phase-locked radial velocity and photometric data which are useful in several contexts. We present here a sample of these results which will be published in their entirety elsewhere.

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Dravins, D., L. Lindegren, S. Madsen et J. Holmberg. « Astrometric Radial Velocities From Hipparcos ». Highlights of Astronomy 11, n^o 1 (1998) : 564. http://dx.doi.org/10.1017/s153929960002219x.

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AbstractSpace astrometry now permits accurate determinations of stellar radial motion, without using spectroscopy. Although the feasibility of deducing astrometric radial velocities from geometric projection effects was realized already by Schlesinger (1917), only with Hipparcos has it become practical. Such a program has now been carried out for the moving clusters of Ursa Major, Hyades, and Coma Berenices. Realized inaccuracies reach about 300 m/s (Dravins et al. 1997).Discrepancies between astrometric and spectroscopic radial velocities reveal effects (other than stellar motion) that affect wavelength positions of spectral lines. Such are caused by stellar surface convection, and by gravitational redshifts. A parallel program (Gullberg & Dravins 1997) is analyzing high-precision spectroscopic radial velocities for different spectral lines in these stars, using the ELODIE radial-velocity instrument atHaute-Provence.

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Xu, Qin, et Kang Nai. « An Adaptive Dealiasing Method Based on Variational Analysis for Radar Radial Velocities Scanned with Small Nyquist Velocities ». Journal of Atmospheric and Oceanic Technology 29, n^o 12 (1 décembre 2012) : 1723–29. http://dx.doi.org/10.1175/jtech-d-12-00145.1.

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Abstract Previous velocity–azimuth display (VAD)-based methods of dealiasing folded radial velocities have relied heavily on the VAD uniform-wind assumption and, thus, can fail when the uniform-wind assumption becomes poor around azimuthal circles in a vertical layer and the Nyquist velocity is small (≤12 m s−1). By using the two-step, alias-robust variational (AR-Var) analysis in place of the alias-robust VAD (AR-VAD) analysis for the reference check, the previous AR-VAD-based dealiasing method is improved to an AR-Var-based dealiasing method adaptively for radar radial velocities scanned with small Nyquist velocities. The method has been tested with severely aliased velocity data scanned by the Oklahoma KTLX radar. The robustness and satisfactory performance of the AR-Var-based dealiasing are exemplified by the results obtained for a severe winter ice storm scanned with the Nyquist velocity reduced to 11.51 m s−1.

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Minniti, Dante. « Kinematics of the Galactic Bulge : the velocity ellipsoid ». Symposium - International Astronomical Union 153 (1993) : 315–16. http://dx.doi.org/10.1017/s007418090012340x.

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Carrera, R., L. Casamiquela, J. Carbajo-Hijarrubia, L. Balaguer-Núñez, C. Jordi, M. Romero-Gómez, S. Blanco-Cuaresma et al. « OCCASO ». Astronomy & ; Astrophysics 658 (25 janvier 2022) : A14. http://dx.doi.org/10.1051/0004-6361/202141832.

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Context. Open clusters (OCs) are widely used as test particles to investigate a variety of astrophysical phenomena, from stellar evolution to Galactic evolution. Gaia and the complementary massive spectroscopic surveys are providing an unprecedented wealth of information about these systems. Aims. The Open Cluster Chemical Abundances from Spanish Observatories (OCCASO) survey aims to complement all this work by determining OCs’ accurate radial velocities and chemical abundances from high-resolution, R ≥ 60 000, spectra. Methods. Radial velocities were obtained by cross-correlating the observed spectra with a library of synthetic spectra that covers early M to A spectral types. Results. We provide radial velocities for 336 stars including several Gaia benchmark stars and objects belonging to 51 open clusters. The internal uncertainties of the derived radial velocities go from 10 m s−1 to 21 m s−1 as a function of the instrumental configuration used. The derived radial velocities, together with the Gaia proper motions, were used to investigate the cluster membership of the observed stars. After this careful membership analysis, we obtained average velocities for 47 open clusters. To our knowledge, this is the first radial velocity determination for five of these clusters. Finally, the radial velocities, proper motions, distances and ages were used to investigate the kinematics of the observed clusters and in the integration of their orbits.

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Yuan, Yue, Ping Wang, Di Wang et Junzhi Shi. « A Velocity Dealiasing Scheme Based on Minimization of Velocity Differences between Regions ». Advances in Meteorology 2020 (20 février 2020) : 1–12. http://dx.doi.org/10.1155/2020/6157636.

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The velocity dealiasing is an essential work of automatic weather phenomenon identification, nowcasting, and disaster monitoring based on radial velocity data. The noise data, strong wind shear, and isolated echo region in the Doppler radar radial velocity data severely interfere with the velocity dealiasing algorithm. This paper proposes a two-step velocity dealiasing algorithm based on the minimization of velocity differences between regions to solve this problem. The first step is to correct aliased velocities by minimizing the sum of gradients in every region to eliminate abnormal velocity gradients between points. The interference of noise data and strong wind shear can be reduced by minimizing the whole gradients in a region. The second step is to dealiase velocities by the velocity differences between different isolated regions. The velocity of an unknown isolated region is determined by the velocities of all known regions. This step improves the dealiasing results of isolated regions. In this paper, 604 volume scan samples, including typhoons, squall lines, and heavy precipitation, were used to test the algorithm. The statistical results and analysis show that the proposed algorithm can dealiase the velocity field with a high probability of detection and a low false alarm rate.

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Cudworth, Kyle, et Ruth C. Peterson. « Astrometric Distances of Globular Clusters ». Symposium - International Astronomical Union 126 (1988) : 523–24. http://dx.doi.org/10.1017/s0074180900042923.

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With high-precision radial velocities and proper motions, one can equate the proper motion and radial velocity dispersions to obtain astrometric distances independent of any standard candles. We discuss the method and the small distance it yields to M 22.

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Sachkov, M. E. « Cepheid Radial Velocities and Phase Lag ». International Astronomical Union Colloquium 176 (2000) : 240–41. http://dx.doi.org/10.1017/s0252921100057651.

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AbstractOur systematic measurements (since 1987) of radial velocities of northern Cepheids with a correlation spectrometer allowed us to make a detailed study of shapes of VR curves. This is a preliminary analysis of the phase lag between Cepheid radial velocity and light curves.

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Walker, Gordon A. H. « Precise Radial Velocities ». International Astronomical Union Colloquium 135 (1992) : 67–72. http://dx.doi.org/10.1017/s025292110000614x.

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AbstractCurrent techniques for the detection of long-term, low-amplitude (<50 m s−1), radial velocity variations are briefly reviewed together with some of their most successful programs. In the era of 8- to 10-m telescopes we must strive for a precision of < 1ms−1.

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Madsen, Søren, Dainis Dravins et Lennart Lindegren. « Astrometric radial velocities ». Astronomy & ; Astrophysics 381, n^o 2 (janvier 2002) : 446–63. http://dx.doi.org/10.1051/0004-6361:20011458.

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Habing, H. J. « Do maser stars trace a rotating Galactic bar ? » Proceedings of the International Astronomical Union 3, S242 (mars 2007) : 356–60. http://dx.doi.org/10.1017/s1743921307013373.

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AbstractI have analyzed the radial velocities in two large samples of maser stars that cover the Galactic plane from l = +40deg to l = −40deg through the Galactic Centre. I compare a diagram of longitude versus radial velocity as observed with a diagram obtained from the calculation of orbits in a simple, but realistic potential containing a weak, rotating bar. Almost all stars belong to the Galactic disk but there is a small sample with high velocities close to the Galactic Centre and in the so-called forbidden quadrants. These velocities cannot be explained by a combination of pure Galactic rotation and a modest dispersion in velocity. An acceptable explanation is one in which the stars of this small sample move up and down a rotating Galactic bar.

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37

Bonifacio, P., P. Molaro, V. Adibekyan, D. Aguado, Y. Alibert, C. Allende Prieto, E. Caffau et al. « ESPRESSO highlights the binary nature of the ultra-metal-poor giant HE 0107−5240 ». Astronomy & ; Astrophysics 633 (janvier 2020) : A129. http://dx.doi.org/10.1051/0004-6361/201935833.

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Context. The vast majority of the known stars of ultra low metallicity ([Fe/H] < −4.5) are known to be enhanced in carbon, and belong to the “low-carbon band” (A(C) = log(C/H)+12 ≤ 7.6). It is generally, although not universally, accepted that this peculiar chemical composition reflects the chemical composition of the gas cloud out of which these stars were formed. The first ultra-metal-poor star discovered, HE 0107−5240, is also enhanced in carbon and belongs to the “low-carbon band”. It has recently been claimed to be a long-period binary, based on radial velocity measurements. It has also been claimed that this binarity may explain its peculiar composition as being due to mass transfer from a former AGB companion. Theoretically, low-mass ratios in binary systems are much more favoured amongst Pop III stars than they are amongst solar-metallicity stars. Any constraint on the mass ratio of a system of such low metallicity would shed light on the star formation mechanisms in this metallicity regime. Aims. We acquired one high precision spectrum with ESPRESSO in order to check the reality of the radial velocity variations. In addition we analysed all the spectra of this star in the ESO archive obtained with UVES to have a set of homogenously measured radial velocities. Methods. The radial velocities were measured using cross correlation against a synthetic spectrum template. Due to the weakness of metallic lines in this star, the signal comes only from the CH molecular lines of the G-band. Results. The measurement obtained in 2018 from an ESPRESSO spectrum demonstrates unambiguously that the radial velocity of HE 0107−5240 has increased from 2001 to 2018. Closer inspection of the measurements based on UVES spectra in the interval 2001–2006 show that there is a 96% probability that the radial velocity correlates with time, hence the radial velocity variations can already be suspected from the UVES spectra alone. Conclusions. We confirm the earlier claims of radial velocity variations in HE 0107−5240. The simplest explanation of such variations is that the star is indeed in a binary system with a long period. The nature of the companion is unconstrained and we consider it is equally probable that it is an unevolved companion or a white dwarf. Continued monitoring of the radial velocities of this star is strongly encouraged.

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Boubert, D., J. Strader, D. Aguado, G. Seabroke, S. E. Koposov, J. L. Sanders, S. Swihart, L. Chomiuk et N. W. Evans. « Lessons from the curious case of the ‘fastest’ star in Gaia DR2 ». Monthly Notices of the Royal Astronomical Society 486, n^o 2 (29 janvier 2019) : 2618–30. http://dx.doi.org/10.1093/mnras/stz253.

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Abstract Gaia DR2 5932173855446728064 was recently proposed to be unbound from the Milky Way based on the $-614.3\pm 2.5\, \mathrm{km}\, \mathrm{s}^{-1}$ median radial velocity given in Gaia DR2. We obtained eight epochs of spectroscopic follow-up and find a very different median radial velocity of $-56.5 \pm 5.3\, \mathrm{km}\, \mathrm{s}^{-1}$. If this difference were to be explained by binarity, then the unseen companion would be an intermediate-mass black hole; we therefore argue that the Gaia DR2 radial velocity must be in error. We find it likely that the spectra obtained by Gaia were dominated by the light from a star $4.3\, \mathrm{arcsec}$ away, and that, due to the slitless, time delay integration nature of Gaia spectroscopy, this angular offset corresponded to a spurious $620\, \mathrm{km}\, \mathrm{s}^{-1}$ shift in the calcium triplet of the second star. We argue that such unanticipated alignments between stars may account for 105 of the 202 stars with radial velocities faster than $500\, \mathrm{km}\, \mathrm{s}^{-1}$ in Gaia DR2 and propose a quality cut to exclude stars that are susceptible. We propose further cuts to remove stars where the colour photometry is suspect and stars where the radial velocity measurement is based on fewer than four transits, and thus produce an unprecedentedly clean selection of Gaia radial velocities for use in studies of Galactic dynamics.

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Jeffers, S. V., P. Schöfer, A. Lamert, A. Reiners, D. Montes, J. A. Caballero, M. Cortés-Contreras et al. « CARMENES input catalogue of M dwarfs ». Astronomy & ; Astrophysics 614 (juin 2018) : A76. http://dx.doi.org/10.1051/0004-6361/201629599.

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CARMENES is a spectrograph for radial velocity surveys of M dwarfs with the aim of detecting Earth-mass planets orbiting in the habitable zones of their host stars. To ensure an optimal use of the CARMENES guaranteed time observations, in this paper we investigate the correlation of activity and rotation for approximately 2200 M dwarfs, ranging in spectral type from M0.0 V to M9.0 V. We present new high-resolution spectroscopic observations with FEROS, CAFE, and HRS of approximately 500 M dwarfs. For each new observation, we determined its radial velocity and measured its Hα activity index and its rotation velocity. Additionally, we have multiple observations of many stars to investigate if there are any radial velocity variations due to multiplicity. The results of our survey confirm that early-M dwarfs are Hα inactive with low rotational velocities and that late-M dwarfs are Hα active with very high rotational velocities. The results of this high-resolution analysis comprise the most extensive catalogue of rotation and activity in M dwarfs currently available.

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Hatzidimitriou, D., R. D. Cannon et M. R. S. Hawkins. « Structure and kinematics in the northeastern outer parts of the SMC ». Symposium - International Astronomical Union 148 (1991) : 107–8. http://dx.doi.org/10.1017/s0074180900200132.

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We present preliminary results from a study of the radial velocities of red horizontal branch stars in the north-eastern outer parts of the Small Magellanic Cloud (SMC). The sample is located in an area with a large line-of-sight depth of 15 kpc. It is suggested that there is a correlation between line-of-sight distance and radial velocity for these stars, with the more distant ones showing significantly higher velocities.

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Irwin, Alan W., Bruce Campbell, C. L. Morbey, G. A. H. Walker et S. Yang. « Long-Period Radial-Velocity Variations of Arcturus ». International Astronomical Union Colloquium 106 (1989) : 144. http://dx.doi.org/10.1017/s0252921100062771.

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We have measured the relative radial velocity of Arcturus using the HF absorption cell technique on 43 occasions from 1981 through 1985. The range of our velocities is 500 m s-1, which is much larger than our estimated internal errors (typically 10 m s-1). This confirms the radial velocity variability of Arcturus that has been previously reported by our group and others based on shorter observational time spans.

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Pilecki, Bogumil, Piotr Konorski et Marek Gorski. « RaveSpan - Radial Velocity and Spectrum Analyzer ». Proceedings of the International Astronomical Union 7, S282 (juillet 2011) : 301–2. http://dx.doi.org/10.1017/s174392131102761x.

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AbstractThe RV analysis tool integrates widely used methods of radial velocity determination (CCF, TODCOR, BF) in an easy to use graphical environment. No advanced knowledge of these methods is required to use it. The obtained velocities may be immediately analyzed with the same tool as it comprises flexible fitting of orbital parameters, which includes the third body influence and pulsational velocities of the components. These features together help to establish the most accurate combination of templates, spectrum range, and method. Scripting functionality is to be implemented in the future.

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Demers, S., L. Grondin†, M. J. Irwin et W. E. Kunkel. « Radial velocities of clusters between the Magellanic Clouds ». Symposium - International Astronomical Union 148 (1991) : 473–74. http://dx.doi.org/10.1017/s0074180900201198.

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Radial velocities of 20 stars members of young clusters and associations located in the inter-Cloud region within 2h < R.A. < 5h tend to be lower than the HI velocities in the same direction. The stellar velocities do not show a pronounced velocity gradiant as observed for the HI from the SMC to the LMC. This suggests that the stellar components belong to the SMC wing. Our photometry and spectroscopy support the view that one of the stars at 4h20m is a foreground HB star.

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Halbwachs, J. L., M. Mayor et S. Udry. « Multiplicity among solar-type stars ». Astronomy & ; Astrophysics 619 (novembre 2018) : A81. http://dx.doi.org/10.1051/0004-6361/201833377.

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Context. The statistical properties of binary stars are clues for understanding their formation process. A radial velocity survey was carried on amongst nearby G-type stars and the results were published in 1991. Aims. The survey of radial velocity measurements was extended towards K-type stars. Methods. A sample of 261 K-type stars was observed with the spectrovelocimeter CORAVEL (COrrelation RAdial VELocities). Those stars with a variable radial velocity were detected on the basis of the P(Χ2) test. The orbital elements of the spectroscopic binaries were then derived. Results. The statistical properties of binary stars were derived from these observations and published in 2003. We present the catalogue of the radial velocity measurements obtained with CORAVEL for all the K stars of the survey and the orbital elements derived for 34 spectroscopic systems. In addition, the catalogue contains eight G-type spectroscopic binaries that have received additional measurements since 1991 and for which the orbital elements are revised or derived for the first time.

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Eroglu, H., et N. Chigier. « Initial Drop Size and Velocity Distributions for Airblast Coaxial Atomizers ». Journal of Fluids Engineering 113, n^o 3 (1 septembre 1991) : 453–59. http://dx.doi.org/10.1115/1.2909517.

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Initial drop size and velocity distributions, after complete disintegration of coaxial liquid jets, were determined by phase Doppler measurements. The measured radial distributions of Sauter mean diameter (SMD) were compared with the photographs of the disintegrating liquid jet. The SMD distribution was found to be strongly affected by the structure and behavior of the preceding liquid intact jet. The results showed that SMD increases with increasing liquid supply pressure as well as with decreasing air supply pressure. The axial measurement stations were determined from the photographs of the coaxial liquid jet at very short distances (1–2 mm) downstream of the observed break-up locations. The droplets accelerated at these regions under the influence of the air velocity. Smaller droplets were found to reach higher velocities because of their larger drag-to-momentum ratio. In general, minimum droplet mean velocities were found at the center, and the maximum velocities were near the spray boundary. Size velocity correlations show that the velocity of larger drops did not change with drop size. Drop rms velocity distributions have double peaks whose radial positions coincide with the maximum mean velocity gradients.

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Xu, Qin, Yuan Jiang et Liping Liu. « Fitting Parametric Vortices to Aliased Doppler Velocities Scanned from Hurricanes ». Monthly Weather Review 142, n^o 1 (1 janvier 2014) : 94–106. http://dx.doi.org/10.1175/mwr-d-12-00362.1.

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Abstract An alias-robust least squares method that produces less errors than established methods is developed to produce reference radial velocities for automatically correcting raw aliased Doppler velocities scanned from hurricanes. This method estimates the maximum tangential velocity VM and its radial distance RM from the hurricane vortex center by fitting a parametric vortex model directly to raw aliased velocities at and around each selected vertical level. In this method, aliasing-caused zigzag discontinuities in the relationship between the observed and true radial velocities are formulated into the cost function by applying an alias operator to the entire analysis-minus-observation term to ensure the cost function to be smooth and concave around the global minimum. Simulated radar velocity observations are used to examine the cost function geometry around the global minimum in the space of control parameters (VM, RM). The results show that the global minimum point can estimate the true (VM, RM) approximately if the hurricane vortex center location is approximately known and the hurricane core and vicinity areas are adequately covered by the radar scans, and the global minimum can be found accurately by an efficient descent algorithm as long as the initial guess is in the concave vicinity of the global minimum. The method is used with elaborated refinements for automated dealiasing, and this utility is highlighted by an example applied to severely aliased radial velocities scanned from a hurricane.

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Xu, Qin, Valery melnikov@noaa.gov et Kang Nai. « A Dual-PRF Scan Mode and Adaptive Doppler-Velocity Dealiasing to Increase Radar Clear-Air Velocity Data Coverage and Usability ». Journal of Energy and Power Technology 04, n^o 04 (13 octobre 2022) : 1–16. http://dx.doi.org/10.21926/jept.2204034.

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By using long pulses with extended dwelling time, lowered pulse repetition frequency (PRF) and reduced Nyquist velocity, the radar measurement capability can be enhanced to increase clear-air Doppler velocity data coverage (which is beneficial for radar wind analysis and data assimilation and motivated our previous study). This potential capability is further explored (beyond our previous study) by not only modifying the existing operational clear-air scan mode with a lowered PRF and reduced the Nyquist velocity (to nearly 12 m/s) but also coupling this low-PRF scan with a high-PRF scan into a new dual-PRF scan mode. With this dual-PRF scan mode, the velocities from the high-PRF scan can be used to dealias the raw velocities from the low-PRF scan. Doppler velocities collected by using the low-PRF scan in this dual-PRF scan mode exhibit enhanced clear-air data coverage but encounter increased difficulties in dealiasing beyond the radial range covered by the high-PRF scan. To overcome the encountered difficulties, the previously developed alias-robust variational method for analyzing severely aliased radar velocity observations with small Nyquist velocities is further improved adaptively, so reliable reference radial velocities can be obtained and used to dealias the low-PRF scanned raw velocities on range circles beyond those covered by the high-PRF scan.

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Ilyin, I. V., et R. Duemmler. « Precise Radial-velocity Measurements with a Cassegrain Spectrograph, II : Radial-velocity Determination and Applications ». International Astronomical Union Colloquium 170 (1999) : 68–72. http://dx.doi.org/10.1017/s0252921100048375.

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AbstractWe present our measurements of radial velocities of two stars suspected to have a substellar companion by using observations made with a cassegrain échelle spectrograph. The stability issues and details of the data reduction are discussed in Ilyin & Duemmler (paper I, these proceedings). The results obtained here show that relatively high accuracy of radial velocity determinations is also attainable for cassegrain spectrographs.

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Deepak et Bacham E. Reddy. « Radial Velocity Comparison of Gaia DR2 and RAVE DR5 Survey : A Systematic Offset in Radial Velocities among a Group of Highly Accurate Radial Velocity Stars ». Astronomical Journal 156, n^o 4 (1 octobre 2018) : 170. http://dx.doi.org/10.3847/1538-3881/aadcde.

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Boyarchuk, A. A., T. S. Belyakina, A. E. Tarasov et N. Tomov. « The Observations of AG PEG During 1985–87 ». International Astronomical Union Colloquium 103 (1988) : 257. http://dx.doi.org/10.1017/s0252921100103562.

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AbstractThe light curves in UBVRI and profiles of the emission lines of Hα, HeII 5411 and HeI 5876, 6678 obtained during 1985–87. The radial velocities of the emission lines HeI 6678 and HeII 5411 demonstrated clear periodic variations in antiphase with the radial velocity defined for the absorption line.

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