scholarly journals Precise Radial Velocities of F, G, K Dwarfs

1988 ◽  
Vol 132 ◽  
pp. 79-81
Author(s):  
Bruce Campbell ◽  
Gordon A. H. Walker
Keyword(s):  
Radial Velocities ◽  
Absorption Lines ◽  
Spectroscopic Binaries ◽  
Brown Dwarf ◽  
Dwarf Stars ◽  
Low Level ◽  
The Past ◽  
Velocity Variations

We have monitored changes in the radial velocities of 24 bright F, G and K dwarf stars (known spectroscopic binaries excluded) for the past six years at CFHT by imposing the absorption lines of HF gas in the spectra to act as wavelength fiducials. The average external error in the δ(velocities) which are based on some 16 stellar lines is 13 m/s corresponds to 0.6 micron in the spectrum or 0.04 of a diode spacing per line. Reductions are complete for 16 stars. There is no evidence for brown dwarf companions in the sample. Two previously unknown spectroscopic binaries were found, and seven stars show indications of significant, long-term, low-level velocity variations which could be interpreted as purturbations by companions of a few Jupiter masses with periods greater than 12 years except for γ Cep, which may have a period of 2.7 years, and ε Eri. Observing time has been guaranteed for at least two more years at CFHT.

scholarly journals Precise Radial Velocities

1992 ◽  
Vol 135 ◽  
pp. 67-72
Author(s):  
Gordon A.H. Walker
Keyword(s):  
Radial Velocity ◽  
Radial Velocities ◽  
Velocity Variations ◽  
Low Amplitude

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.

scholarly journals The Onset of Quasi-Periodic Variations in Be Stars

1993 ◽  
Vol 134 ◽  
pp. 223-225
Author(s):  
T. Kogure ◽  
M. Mon ◽  
M. Suzuki
Keyword(s):  
Sudden Onset ◽  
Radial Velocities ◽  
Emission Lines ◽  
Absorption Lines ◽  
Close Binaries ◽  
Be Stars ◽  
Early Type ◽  
Stable Period ◽  
Long Term Variations

We present some evidence of the quasi-periodic long-term variations (QPLV) in the violet-to-red ratio of double-peaked emission lines (V/R variation) and/or in the radial velocities of shell absorption lines for some Be stars. Although the V/R variations are rather prevailing phenomena among Be stars, the QPLV is remarkable by the following characteristics: (1)The QPLV appears as a sudden onset of repeated V/R variations after a long (10 years), almost stable period, and it persists for a few or several periods in ten or more years.(2)The period and amplitude of V/R variations change from cycle to cycle and from star to star. The variations of radial velocities (RV) of shell absorption lines are usually nearly parallel with the V/R variations.(3)The QPLV appears usually in early type Be stars with large rotational velocities, regardless whether the stars are normal Be or shell stars, and whether they are close-binaries or single stars.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2020 ◽  
Vol 636 ◽  
pp. A36 ◽  
Author(s):  
M. Lafarga ◽  
I. Ribas ◽  
C. Lovis ◽  
M. Perger ◽  
M. Zechmeister ◽  
...  
Keyword(s):  
Template Matching ◽  
Signal To Noise Ratio ◽  
Standard Procedure ◽  
Radial Velocities ◽  
Absorption Lines ◽  
High Signal ◽  
M Dwarfs ◽  
Inverse Slope ◽  
Dwarf Stars ◽  
M Dwarf Stars

Context. For years, the standard procedure to measure radial velocities (RVs) of spectral observations consisted in cross-correlating the spectra with a binary mask, that is, a simple stellar template that contains information on the position and strength of stellar absorption lines. The cross-correlation function (CCF) profiles also provide several indicators of stellar activity. Aims. We present a methodology to first build weighted binary masks and, second, to compute the CCF of spectral observations with these masks from which we derive radial velocities and activity indicators. These methods are implemented in a python code that is publicly available. Methods. To build the masks, we selected a large number of sharp absorption lines based on the profile of the minima present in high signal-to-noise ratio (S/N) spectrum templates built from observations of reference stars. We computed the CCFs of observed spectra and derived RVs and the following three standard activity indicators: full-width-at-half-maximum as well as contrast and bisector inverse slope. Results. We applied our methodology to CARMENES high-resolution spectra and obtain RV and activity indicator time series of more than 300 M dwarf stars observed for the main CARMENES survey. Compared with the standard CARMENES template matching pipeline, in general we obtain more precise RVs in the cases where the template used in the standard pipeline did not have enough S/N. We also show the behaviour of the three activity indicators for the active star YZ CMi and estimate the absolute RV of the M dwarfs analysed using the CCF RVs.

scholarly journals Activity in the circumstellar envelope of the Be/shell star ζ Tau

1994 ◽  
Vol 162 ◽  
pp. 372-373
Author(s):  
Yulian Guo ◽  
Lin Huang ◽  
Jinxin Hao
Keyword(s):  
Radial Velocity ◽  
Orbital Period ◽  
Absorption Lines ◽  
Circumstellar Envelope ◽  
Cyclic Variation ◽  
Spectroscopic Binary ◽  
Velocity Variations ◽  
Shell Star

ζ Tau is a well-known V/R-variable shell star. It is a single-lined spectroscopic binary with an orbital period of 133 days (Harmanec 1984, and Jarad 1987). Delplace (1970) found that the long-term radial velocity variations of the Balmer shell absorption lines are cyclic in 1960–67. Subsequently, similar behaviour has been observed and studied by several authors (Delplace and Chambon 1976, Hubert-Delplace et al 1983, Harmanec 1984, and Guo and Cao 1987). Mon et al (1992) showed that the cyclic variation had terminated and the star seems to have entered a new quiet phase around 1982.

scholarly journals International Yield Spillovers

2021 ◽  
Vol 2021 (001) ◽  
pp. 1-59
Author(s):  
Don H. Kim ◽  
◽  
Marcelo Ochoa ◽  
Keyword(s):  
Euro Area ◽  
Daily Variation ◽  
Low Level ◽  
The Past ◽  
Term Premia ◽  
Foreign Shocks ◽  
The U.S

This paper investigates spillovers from foreign economies to the U.S. through changes in longterm Treasury yields. We document a decline in the contribution of U.S. domestic news to the variance of long-term Treasury yields and an increased importance of overnight yield changes—a rough proxy for the contribution of foreign shocks to U.S. yields—over the past decades. Using a model that identifies U.S., Euro area, and U.K. shocks that move global yields, we estimate that foreign (non-U.S.) shocks account for at least 20 percent of the daily variation in long-term U.S. yields in recent years. We argue that spillovers occur in large part through bond term premia by showing that a low level of foreign yields relative to U.S. yields predicts a decline in distant forward U.S. yields and higher returns on a strategy that is long on a long-term Treasury security and short on a long-term foreign bond.

Searching for periodic variations in radial velocities after the removal of orbital motions of spectroscopic binaries

2020 ◽  
Author(s):  
Noriyuki Katoh ◽  
Yoichi Itoh ◽  
Bun’ei Sato
Keyword(s):  
Binary Systems ◽  
Orbital Motion ◽  
Periodic Variation ◽  
Radial Velocities ◽  
Doppler Signal ◽  
Spectroscopic Binaries ◽  
Residual Velocity ◽  
Significant Evidence ◽  
Velocity Variations ◽  
Unknown Component

ABSTRACT This study focuses on periodic variations of radial velocities (RVs) after removing the orbital motion of 33 spectroscopic binaries. The RVs were monitored from 2003 to 2012 and published in Katoh et al. (2013, AJ, 145, 41). Their RV precision was determined to be ∼10 m s−1 utilizing an I2 cell. We investigated the periodic variation using a generalzied Lomb–Scargle algorithm and found periodic variations in the residual velocities of seven binary systems. The residual-velocity variations are mostly generated by stellar activity rather than the orbital motion of a possible companion. For eight binaries, we found significant evidence of a second signal, with velocity dispersions greater than three times the RV uncertainty. We find these residual-velocity variations inconsistent with a Doppler signal induced by the orbital motion of an unknown component. For the remaining 18 binaries, we did not detect significant variations of residual-velocity.

scholarly journals An Extension of the Search for Spectroscopic Binaries in M3

1985 ◽  
Vol 113 ◽  
pp. 99-101
Author(s):  
Carlton P. Pryor ◽  
David W. Latham ◽  
Martha L. Hazen-Liller
Keyword(s):  
Radial Velocity ◽  
Globular Cluster ◽  
Convincing Evidence ◽  
Time Span ◽  
Radial Velocities ◽  
Spectroscopic Binaries ◽  
Spectroscopic Binary ◽  
Velocity Variations ◽  
Cluster Modelling

We have obtained 295 new radial velocities for the 112 giants in the globular cluster M3 previously observed by Gunn and Griffin. Our velocities have a typical accuracy of 0.8 km/s per measurement and have been combined with the Gunn and Griffin data in order to search for radial velocity variations over a time span of ten years. We find no convincing evidence that any of the giants observed are spectroscopic binaries with one notable exception, von Zeipel 164, which we believe is the first spectroscopic binary to be found in a globular cluster. Modelling of the velocity variations that would be expected in our data for a variety of binary populations confirms Gunn and Griffin's conclusion that binaries with separations of less than 10 AU must occur much less frequently among the giants of M3 than among the population I field stars.

scholarly journals Search for Long-Period Radial Velocity Variations in Some Be Stars

1982 ◽  
Vol 98 ◽  
pp. 155-159
Author(s):  
L. Pastori ◽  
E. Antonello ◽  
M. Fracassini ◽  
L.E. Pasinetti
Keyword(s):  
Radial Velocity ◽  
Radial Velocities ◽  
Be Stars ◽  
Long Period ◽  
Be Star ◽  
Velocity Variations ◽  
Periodogram Analysis

Some astronomers have suggested long period phenomena in the Be stars: Hubert (1971), Delplace and Hubert (1975), Feinstein (1975), Harmanec et al. (1976), Pustylnik (1976). In particular, Fracassini et al. (1977) have made a periodogram analysis of the radial velocities (RV) of the Be star o And from 1900 to 1976, to connect the shell appearance with eventual long-term RV variations. In the present study all the RV of seven Be stars, found in the literature from the beginning of the century up to now, have been assembled and analysed in the same way as o And, in order to find out long period phenomena (duplicity, variability, shell activity, etc…). A brief review on the studied stars may be found in Harmanec et al. (1980).

Commission 30: Radial Velocities: (Vitesses Radiales)

2000 ◽  
Vol 24 (1) ◽  
pp. 338-345
Author(s):  
J.B. Hearnshaw ◽  
A.A. Tokovinin ◽  
W.D. Cochran ◽  
F.C. Fekel ◽  
T. Mazeh ◽  
...  
Keyword(s):  
Variable Stars ◽  
Radial Velocities ◽  
Stellar Atmospheres ◽  
Spectroscopic Binaries ◽  
Electromagnetic Spectrum ◽  
Stellar Rotation ◽  
New Members ◽  
The Past ◽  
Pulsating Variable Stars ◽  
Wide Range

Commission 30 has 120 members in 28 countries who are active in the area of radial velocities. During the past triennium 11 new members have joined the commission. The work of the commission covers a wide range of topics all of which concern the application of the Doppler effect to astronomical objects, including galaxies and the interstellar medium as well as stars, and in all wavelength ranges of the electromagnetic spectrum. Although the commission focuses mainly on stellar and galaxy radial velocities, it is noted that stellar rotation, spectroscopic binaries, extrasolar planet searches, pulsating variable stars, asteroseismology and turbulence in stellar atmospheres are also included.

41. Diffusion Badges as a Long-Term, Low-Level Method of Ambient Air Analysis

2005 ◽  
Author(s):  
K. Parker ◽  
S. Rose-Pehrsson ◽  
D. Kidwell
Keyword(s):  
Ambient Air ◽  
Air Analysis ◽  
Low Level ◽  
Level Method
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