scholarly journals Radial-velocity Variations of Late-type Variables

1999 ◽  
Vol 170 ◽  
pp. 228-232
Author(s):  
Stephenson L.S. Yang ◽  
Gordon A.H. Walker ◽  
Ana M. Larson
Keyword(s):  
Radial Velocity ◽  
Hydrogen Fluoride ◽  
Absorption Cell ◽  
Late Type ◽  
Velocity Variations ◽  
Low Amplitude

AbstractLow-amplitude, radial-velocity variations of bright late-type stars were monitored at the 1.2-m telescope of the Dominion Astrophysical Observatory (DAO) with the hydrogen fluoride (HF) absorption-cell technique. Many of the stars appear to be semi-regular red variables (SRb and SRc) and irregular red variables (Lb). The radial-velocity amplitudes range from a few tens of meters per second to a few kilometers per second while the timescales of the variations appear to range from a few tens of days to a few hundreds of days. These irregular-looking velocities are analysed for multiperiodicities. There are also variations in the chromospheric Ca II 8662 index for a few of the variables.

scholarly journals The HF Precise Radial Velocity Programme at DAO

1993 ◽  
Vol 139 ◽  
pp. 383-383
Author(s):  
S. Yang ◽  
A. Larson ◽  
A.W. Irwin ◽  
C. Goodenough ◽  
G.A.H. Walker ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Hydrogen Fluoride ◽  
Radial Velocities ◽  
Absorption Cell ◽  
Late Type ◽  
Wavelength Calibration ◽  
Stellar Spectra ◽  
Preliminary Results ◽  
Yield Information ◽  
Low Amplitude

AbstractA programme to measure precise radial velocities of late-type stars is being carried out at the 1.22-m telescope of the Dominion Astrophysical Observatory (DAO). Wavelength-calibration fiducials are imposed directly on the stellar spectra by passing the starlight through a controlled hydrogen fluoride (HF) absorption cell placed in front of the coude spectrograph. Presently, the primary targets of the programme are bright G, K, and M giants. Preliminary results confirm the low-amplitude, radial-velocity (RV) variability of the yellow giants discovered at the Canada-Prance-Hawaii telescope using the HF technique. These yellow giants and additional bright candidates are now being continually monitored at DAO. Preliminary results also indicate that the “yellow giant” variability extends to the early-M giants. In addition to the RV variations, the data also yield information on the simultaneous variability of the Ca II λ8662 line, Teff, as well as the R - I index of the stars.

scholarly journals Extremely Low Amplitude Cepheids

1993 ◽  
Vol 139 ◽  
pp. 385-385
Author(s):  
R. Paul Butler
Keyword(s):  
Radial Velocity ◽  
Velocity Curve ◽  
Reference Star ◽  
Absorption Cell ◽  
Instability Strip ◽  
Iodine Absorption ◽  
Order Of Magnitude ◽  
Velocity Variations ◽  
Low Amplitude

AbstractSeveral photometric studies conducted in the 1970's indicate that at least half the stars in the Cepheid instability strip are stable at the level of 0.02 mag (Fernie & Hube 1971; Percy 1975; Fernie 1976; Percy, Baskerville, & Trevorrow 1979). A precision radial velocity survey of these “stable stars” is currently being conducted by the author. Radial velocity errors have been reduced to a few tens of meters per second with the use of an iodine absorption cell (Marcy & Butler 1992).Extremely low amplitude (200 m/s) periodic radial velocity variations have been found for HR 7796, an F8Ib supergiant (Butler 1992). Two and a half complete cycles have been monitored over three observing runs. The period is found to be 11.87 days. Observations of the reference star HR 509 (G8 V) taken on the same nights, show no periodicities and a scatter of just 20 m/s. Both the period and the shape of the velocity curve appear similar to a normal F8Ib Cepheid. If HR 7796 is a Cepheid, it is the smallest amplitude Cepheid by more than an order of magnitude.

Radial Velocity Variations in Cool Supergiants

1984 ◽  
Vol 88 ◽  
pp. 283-288
Author(s):  
Hugh C. Harris
Keyword(s):  
Radial Velocity ◽  
Main Sequence ◽  
Short Period ◽  
Cool Stars ◽  
Synchronous Rotation ◽  
Red Supergiants ◽  
Velocity Variations ◽  
Orbital Periods ◽  
Low Amplitude ◽  
Good Agreement

AbstractA survey of F, G, and W supergiants has been carried out with the DAO radial velocity spectrometer, an efficient instrument for detecting low-amplitude velocity variations in cool stars. Observations of 78 stars over five seasons show generally good agreement with OORAVEL results for spectroscopie binaries. The majority of supergiants show low-amplitude variability, with amplitudes typically 1 to 2 km s−1. The width of the cross-correlation profile has been measured for 58 supergiants. It reveals 14 stars with unusually broad lines, indicative of rotation velocities of 15 to 35 km s−1. Several have short-period binary companions and may be in synchronous rotation. The other broad-lined stars are apparently single or with long orbital periods; they may be making their first transition from the main sequence to become red supergiants.

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 Low-amplitude and long-period radial velocity variations in giants HD 3574, 63 Cygni, and HD 216946

2014 ◽  
Vol 566 ◽  
pp. A124
Author(s):  
B.-C. Lee ◽  
I. Han ◽  
M.-G. Park ◽  
A. P. Hatzes ◽  
K.-M. Kim
Keyword(s):  
Radial Velocity ◽  
Long Period ◽  
Velocity Variations ◽  
Low Amplitude

scholarly journals Starspot-Induced Radial Velocity Jitter During a Stellar Cycle

2012 ◽  
Vol 8 (S293) ◽  
pp. 382-384
Author(s):  
Heidi Korhonen ◽  
Jan Marie Andersen ◽  
Silva Järvinen
Keyword(s):  
Radial Velocity ◽  
High Activity ◽  
Activity Cycle ◽  
The Sun ◽  
Late Type ◽  
Cool Stars ◽  
Velocity Variations

AbstractLate-type stars exhibit cool regions on their surface, the stellar equivalent of sunspots. These dark starspots can also mimic the radial velocity variations caused by orbiting planets, making it at times difficult to distinguish between planets and activity signatures. The amount of spots on the Sun and other cool stars changes cyclically during an activity cycle, which has length varying from about a year to longer than the solar 11 years. In this work we investigate the influence of varying amount of starspots on the sparsely sampled radial velocity observations - which are the norm in the radial velocity studies searching for exoplanets on wide orbits. We study two simulated cases: one with a random spot configuration, and one where the spot occurrence is concentrated. In addition we use Doppler images of young solar analogue V889 Her as a high activity case.

scholarly journals The RV Variability of Yellow Giants

1993 ◽  
Vol 139 ◽  
pp. 384-384
Author(s):  
A.M. Larson ◽  
A.W. Irwin ◽  
S.L.S. Yang ◽  
C. Goodenough ◽  
G.A.H. Walker ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Hydrogen Fluoride ◽  
Absorption Cell ◽  
Select Group ◽  
Solar Type ◽  
Substellar Companions

AbstractThe hydrogen fluoride (HF) absorption cell technique has been used at the Canada-France-Hawaii Telescope for over a decade to monitor the radial velocity variability of nearby, solar-type stars in a search for substellar companions. As a complement to this program, we have also been monitoring a select group of G and K subgiants, giants and supergiants, which have all proved variable. We present here a brief summary of our analysis.

Application of the Telluric-Line Technique to Study Late-Type Stars for Radial-Velocity Variations

1999 ◽  
Vol 170 ◽  
pp. 48-51
Author(s):  
Robert Greimel ◽  
Stephenson L.S. Yang
Keyword(s):  
Radial Velocity ◽  
Line Profile ◽  
Radial Velocities ◽  
Early Type ◽  
Late Type ◽  
Reduction Procedure ◽  
Temporal Sampling ◽  
Velocity Variations ◽  
Convenient Technique ◽  
Telluric Line

AbstractAlthough the use of telluric lines as wavelength fiducials to measure radial velocities does not achieve as high a precision as other fiducial-imposition techniques, this very convenient technique can be used concurrently with other observing programs to increase the temporal sampling of target stars. We have been carrying out a program to monitor the line-profile variations of early-type non-radial pulsators at the Hα and He I 667.8-nm region. With the rather modest reciprocal dispersion of 1nm/mm and the use of a 4096-element CCD, the telluric lines in the 630-nm region are also available in the observed spectra. We decided to use these telluric lines as wavelength fiducials to monitor bright, latetype stars for radial-velocity variations. As an experiment, we have also decided to reduce the spectra using available simple IRAF tasks to see how high a velocity precision can be achieved with only minor tweaking. The precision certainly would not rival other precise techniques, but the convenience in both the observing and reduction procedure may enable more target stars to be monitored by more observers. Moreover, interesting results can still be obtained with a mere 100 m/s precision. The result for a few late-type stars which also have prior HF velocities will be presented.

scholarly journals Long-Period Radial-Velocity Variations of Arcturus

1989 ◽  
Vol 106 ◽  
pp. 144-144
Author(s):  
Alan W. Irwin ◽  
Bruce Campbell ◽  
C.L. Morbey ◽  
G.A.H. Walker ◽  
S. Yang
Keyword(s):  
Radial Velocity ◽  
Absorption Cell ◽  
Long Period ◽  
Velocity Variations

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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