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.

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.

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 The Long-term Variation in the RV Tauri Star U Mon

1995 ◽  
Vol 155 ◽  
pp. 409-410 ◽  
Author(s):  
Karen R. Pollard ◽  
P. L. Cottrell
Keyword(s):  
High Resolution ◽  
Light Curve ◽  
Radial Velocity ◽  
Tauri Star ◽  
Short Term ◽  
Instability Strip ◽  
Term Variation ◽  
Velocity Variations

The RV Tauri stars are semiregular pulsating variables located in the brightest part of the Cepheid II instability strip. They have a characteristic light curve of alternating deep and shallow minima. A subset of the RV Tauri stars (the RVb subclass) exhibit long-term (500 to 2600 day) light and radial velocity variations. Although it is well established that the short-term variations are due to pulsations, the long-term behaviour is not well understood.BVRI photometry and high-resolution spectra of U Mon (the brightest member of the RVb subclass) were obtained at the Mt John University Observatory (MJUO) between 1990 Aug and 1994 May. The light and colour curves obtained clearly show the long-term variation in U Mon (Fig. 1(a) and (b)). The reddest colours occur slightly later than the long-term minimum in the light curve. The short-term light and colour variations are ‘damped’ at the long-term minimum.

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.

The radial-velocity variations of Polaris - A Cepheid leaving the instability strip?

1989 ◽  
Vol 98 ◽  
pp. 2249 ◽  
Author(s):  
Nadine Dinshaw ◽  
Jaymie M. Matthews ◽  
Gordon A. H. Walker ◽  
Grant M. Hill
Keyword(s):  
Radial Velocity ◽  
Instability Strip ◽  
Velocity Variations

scholarly journals Mode Discrimination in Nonradially Oscillating Stars From Light, Colour and Velocity Observations

1980 ◽  
Vol 58 ◽  
pp. 371-376
Author(s):  
L.A. Balona ◽  
R.S. Stobie
Keyword(s):  
Radial Velocity ◽  
Phase Difference ◽  
Spherical Harmonic ◽  
Amplitude Ratio ◽  
Harmonic Mode ◽  
Instability Strip ◽  
Nonradial Oscillation ◽  
Mode Discrimination ◽  
Velocity Variations

AbstractExpressions for the amplitudes and phases of the light, colour and radial velocity variations are derived for a star in nonradial oscillation. For stars in the cepheid instability strip the spherical harmonic mode of the oscillation can be obtained from the phase difference between the light and colour variations. For 3 Cep stars the mode can be estimated from the amplitude ratio of the light and colour variations.

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 The Light and Velocity Curve Bumps for BW Vulpeculae

1980 ◽  
Vol 58 ◽  
pp. 337-343
Author(s):  
William Dean Pesnell ◽  
Arthur N. Cox
Keyword(s):  
Light Curve ◽  
Radial Velocity ◽  
Velocity Curve ◽  
Resonance Mechanism ◽  
Outstanding Feature ◽  
Non Linear ◽  
Velocity Variations

BW Vulpeculae (HD 199140) is a well known Beta Cenhei star, with several unusual characteristics. It possesses the largest amplitude in both light and radial velocity variations, of any star in this classification. The most outstanding feature of the observations is a standstill or bump, on the light curve, accompanied by doubled lines in the radial velocity observations. In this paper, we have attempted to explain these phenomena with two different models. Firstly, the resonance mechanism, from Simon and Schmidt, and secondly, a non-linear calculation.

scholarly journals A Search for Radial Velocity Oscillations in Procyon

1988 ◽  
Vol 132 ◽  
pp. 83-86
Author(s):  
Ken G. Libbrecht
Keyword(s):  
High Resolution ◽  
Radial Velocity ◽  
Duty Cycle ◽  
New Technique ◽  
Absorption Cell ◽  
Velocity Measurements ◽  
Stellar Spectra ◽  
Iodine Absorption ◽  
A New Technique

I describe here a new technique for precision radial velocity measurements, using an iodine absorption cell in front of the slit of a high resolution spectrograph. A CCD in a continuous readout mode records a timeseries of stellar spectra with a duty cycle of unity. In January 1987, observations were obtained on two clear nights with bad seeing. No oscillations were detected in the data, but the technique shows promise for significantly better results under better conditions.

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