scholarly journals High precision radial-velocity measurements of late-type evolved stars

1999 ◽  
Vol 170 ◽  
pp. 204-210 ◽  
Author(s):  
I.N. Cummings ◽  
J.B. Hearnshaw ◽  
P.M. Kilmartin ◽  
A.C. Gilmore
Keyword(s):  
Radial Velocity ◽  
High Precision ◽  
Spectral Type ◽  
Cross Correlation ◽  
Radial Velocities ◽  
High Dispersion ◽  
Late Type ◽  
Velocity Measurements ◽  
Evolved Stars ◽  
Type K

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.

scholarly journals Densified Pupil Spectrograph as High-precision Radial Velocimetry: From Direct Measurement of the Universe’s Expansion History to Characterization of Nearby Habitable Planet Candidates

2022 ◽  
Vol 163 (2) ◽  
pp. 63
Author(s):  
Taro Matsuo ◽  
Thomas P. Greene ◽  
Mahdi Qezlou ◽  
Simeon Bird ◽  
Kiyotomo Ichiki ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Direct Measurement ◽  
High Precision ◽  
Resolving Power ◽  
Line Of Sight ◽  
High Dispersion ◽  
Velocity Measurements ◽  
Habitable Planet ◽  
Airy Disk

Abstract The direct measurement of the universe’s expansion history and the search for terrestrial planets in habitable zones around solar-type stars require extremely high-precision radial-velocity measures over a decade. This study proposes an approach for enabling high-precision radial-velocity measurements from space. The concept presents a combination of a high-dispersion densified pupil spectrograph and a novel line-of-sight monitor for telescopes. The precision of the radial-velocity measurements is determined by combining the spectrophotometric accuracy and the quality of the absorption lines in the recorded spectrum. Therefore, a highly dispersive densified pupil spectrograph proposed to perform stable spectroscopy can be utilized for high-precision radial-velocity measures. A concept involving the telescope’s line-of-sight monitor is developed to minimize the change of the telescope’s line of sight over a decade. This monitor allows the precise measurement of long-term telescope drift without any significant impact on the Airy disk when the densified pupil spectra are recorded. We analytically derive the uncertainty of the radial-velocity measurements, which is caused by the residual offset of the lines of sight at two epochs. We find that the error could be reduced down to approximately 1 cm s−1, and the precision will be limited by another factor (e.g., wavelength calibration uncertainty). A combination of the high-precision spectrophotometry and the high spectral resolving power could open a new path toward the characterization of nearby non-transiting habitable planet candidates orbiting late-type stars. We present two simple and compact highly dispersed densified pupil spectrograph designs for cosmology and exoplanet sciences.

scholarly journals Precision versus Accuracy: some astrophysical and operational limitations

1999 ◽  
Vol 170 ◽  
pp. 52-57
Author(s):  
R. E. M. Griffin
Keyword(s):  
High Resolution ◽  
Wavelength Range ◽  
Spectral Type ◽  
Cross Correlation ◽  
Systematic Errors ◽  
Radial Velocities ◽  
High Dispersion ◽  
Low Level ◽  
Separate Category ◽  
Wide Wavelength Range

AbstractThe measurement of accurate radial velocities for A- or B-type dwarfs poses a separate category of problems: the small number of suitable lines, the wide wavelength range over which such lines are distributed, thermal broadening, rotational broadening, line distortions caused by rotating spots, spectrum variations due to obvious duplicity, and low-level velocity variations due to undetected companion spectra. Moreover, the fact that A- and B-type spectra fall into very distinct groups, each with its own sub-set of the above problems, means that it may be both difficult and unsatisfactory to specify velocity standards, since intrinsic uncertainties caused by differences in spectral type may exceed the measuring errors. The investigation summarized here into the nature and magnitude of some of these intrinsic errors employs wide spans of high-resolution, high-dispersion spectra of Sirius and Vega as ‘natural’ templates. Attention is also drawn to systematic errors which may arise (a) when modelling a cross-correlation ‘dip’ and (b) whenever a spectrum or a cross-correlation dip is measured in the unavoidable presence of another such spectrum or dip.

scholarly journals Comparison of Selected Methods for Radial Velocity Measurements

2006 ◽  
Vol 2 (S240) ◽  
pp. 486-489
Author(s):  
Štefan Parimucha ◽  
Petr Škoda
Keyword(s):  
Radial Velocity ◽  
Line Profile ◽  
Cross Correlation ◽  
Radial Velocities ◽  
Be Stars ◽  
Velocity Measurements ◽  
Stellar Spectra ◽  
Advantages And Disadvantages ◽  
Profile Fitting ◽  
Correlation Line

AbstractWe present a comparison of selected methods for measuring radial velocities in stellar spectra. We compare cross-correlation, line-profile fitting with Gauss, Lorentz and Voigt functions and a less-known mirroring method. We discuss their applicability and precision and indicate their advantages and disadvantages. The mirroring method proved to be useful for the analysis of Be stars, but is not implemented in any major astronomical packages.

scholarly journals Astrometric Radial Velocities From Hipparcos

1998 ◽  
Vol 11 (1) ◽  
pp. 564-564
Author(s):  
D. Dravins ◽  
L. Lindegren ◽  
S. Madsen ◽  
J. Holmberg
Keyword(s):  
Radial Velocity ◽  
High Precision ◽  
Radial Velocities ◽  
Radial Motion ◽  
Spectral Lines ◽  
Parallel Program ◽  
Stellar Surface ◽  
Space Astrometry ◽  
Stellar Motion ◽  
Surface Convection

Abstract Space 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.

scholarly journals Spectroscopic Orbit of the Eclipsing Binary BD +52°2009

1999 ◽  
Vol 170 ◽  
pp. 325-330
Author(s):  
B. Khalesseh
Keyword(s):  
Correlation Function ◽  
Light Curve ◽  
Radial Velocity ◽  
Physical Model ◽  
Cross Correlation ◽  
Cross Correlation Function ◽  
Physical Parameters ◽  
Mass Ratio ◽  
Velocity Measurements ◽  
Eclipsing Binary

AbstractNew radial velocity measurements of the Algol-type eclipsing binary BD +52 °2009, based on Reticon observations, are presented. The velocity measures are based on fitting theoretical profiles, generated by a physical model of the binary, to the observed cross-correlation function (ccf). Such profiles match this function very well, much better in fact than Gaussian profiles, which are generally used. Measuring the ccf’s with Gaussian profiles yields the following results: mp sin3i = 2.55 ± 0.05m⊙, ms sin3i = 1.14 ± 0.03m⊙, (ap + as) sin i = 7.34 ± 0.05R⊙, and mp/ms = 2.23 ± 0.05. However, measuring the ccf’s with theoretical profiles yields a mass ratio of 2.33 and following results: mp sin3i = 2.84 ± 0.05m⊙, ms sin3i = 1.22 ± 0.03m⊙, (ap + as) sin i = 7.56 ± 0.05R⊙. The system has a semi-detached configuration. By combining the solution of a previously published light curve with the spectroscopic orbit, one can obtain the following physical parameters: mp = 2.99m⊙, ms3 = 1.28m⊙, < Tp >= 9600K, < Ts >= 5400K, < Rp >= 2.35R⊙, < Rs >= 2.12R⊙. The system consists of an A0 primary and a G2 secondary.

scholarly journals Precise Radial Velocity Measurements with a Cassegrain Spectrograph, I: Wavelength calibration

1999 ◽  
Vol 170 ◽  
pp. 63-67
Author(s):  
I. V. Ilyin ◽  
R. Duemmler
Keyword(s):  
High Resolution ◽  
Radial Velocity ◽  
Cross Correlation ◽  
Time Dependent ◽  
Instrumental Effects ◽  
Velocity Measurements ◽  
Echelle Spectrograph ◽  
Optical Telescope ◽  
La Palma ◽  
Observational Strategy

AbstractWe briefly describe the instrumental effects which affect the accuracy of the radial velocity measurements. We have implemented several methods to correct for the instability effects and improve the accuracy of the measurements. These include modifications of the observational strategy and a time-dependent wavelength solution as well as a discussion of the error of the offset from cross-correlation. These methods are applied to observations obtained with the high resolution échelle spectrograph SOFIN mounted at the Cassegrain focus of the alt-azimuth 2.56-m Nordic Optical Telescope, La Palma, Canary Islands.

scholarly journals The empirical period-radius relation for pulsating stars: a synthesis based on photometric and radial velocity measurements

1986 ◽  
Vol 118 ◽  
pp. 273-274
Author(s):  
G. Burki
Keyword(s):  
Radial Velocity ◽  
Stellar Evolution ◽  
Variable Stars ◽  
Radial Velocities ◽  
Velocity Measurements ◽  
Pulsating Stars ◽  
Powerful Test ◽  
The Mean

The relation existing between the radius and the period for the pulsating stars of a given class constitutes a powerful test for the theory of stellar evolution and for the identification of the pulsation modes. In recent years, several authors have determined the mean radius of a lot of pulsating stars of various classes by applying the Baade-Wesselink method. Fig. 1 presents the resulting general logP - logR diagram grouping these determinations. The sources for the radii are given by Burki and Meylan (1986). The variable stars in known binaries have been excluded since the presence of a companion biases the radius calculation (Burki, 1984). The determinations marked by arrows are based on the radial velocities by CORAVEL (1m telescope at the Haute-Provence Observatory, France) or/and on the photometry in the Geneva system (40cm and 70cm telescopes at La Silla Observatory, Chile).

scholarly journals Proxima’s orbit around α Centauri

2017 ◽  
Vol 598 ◽  
pp. L7 ◽  
Author(s):  
P. Kervella ◽  
F. Thévenin ◽  
C. Lovis
Keyword(s):  
Radial Velocity ◽  
High Precision ◽  
Orbital Period ◽  
Triple System ◽  
Orbital Motion ◽  
The Sun ◽  
Proper Motions ◽  
Velocity Measurements ◽  
Degree Of Confidence ◽  
High Degree

Proxima and α Centauri AB have almost identical distances and proper motions with respect to the Sun. Although the probability of such similar parameters is, in principle, very low, the question as to whether they actually form a single gravitationally bound triple system has been open since the discovery of Proxima one century ago. Owing to HARPS high-precision absolute radial velocity measurements and the recent revision of the parameters of the α Cen pair, we show that Proxima and α Cen are gravitationally bound with a high degree of confidence. The orbital period of Proxima is ≈ 550 000 yr. With an eccentricity of 0.50+0.08-0.09, Proxima comes within 4.3+1.1-0.9 kau of α Cen at periastron, and is currently close to apastron (13.0+0.3-0.1 kau). This orbital motion may have influenced the formation or evolution of the recently discovered planet orbiting Proxima, as well as circumbinary planet formation around α Cen.

scholarly journals High Luminosity F-K Stars Motions and Hα Emissions

1980 ◽  
Vol 51 ◽  
pp. 170-170
Author(s):  
J. Smolinski ◽  
J.L. Climenhaga ◽  
B.L. Harris
Keyword(s):  
Radial Velocity ◽  
Radial Velocities ◽  
Emission Lines ◽  
High Dispersion ◽  
Common Phenomenon ◽  
Line Profiles ◽  
High Luminosity ◽  
Regular Time ◽  
Time Variations

AbstractChanges and differences in radial velocities between neutral and ionized metals have been found for three F5-type supergiants: HD 231195, HD 10494, and HD 17971. Fifteen high dispersion coudé spectrograms (6 Å/mm) were used and 33 to 165 lines were measured on each. Semi-regular time variations up to about 8 km s-1 in radial velocity have been found. In addition, Hα line profiles for 8 high luminosity F-K stars have been analyzed. All of the stars show Ha emissions, variable in time, which is probably a common phenomenon in very luminous stars. Metallic emission lines with low excitation potentials, in particular the Ca I 6572.8 and the Fe I 6574.2 lines, are present in 5 of these stars.

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