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| Paper: |
The Puzzling K and Early-M Giants: A Summary of Precise Radial-Velocity Results for 15 Stars |
| Volume: |
185, Precise Stellar Radial Velocities, IAU Colloquium 170 |
| Page: |
193 |
| Authors: |
Larson, A. M.; Yang, S. L. S.; Walker, G. A. H. |
| Abstract: |
Nearly a decade ago, ``yellow giants'' were introduced as a new class of low-amplitude radial-velocity variable stars. In this report we discuss results for 14 spectral type K and M giants based on long-term monitoring using both the hydrogen-fluoride (HF) and iodine-cell techniques. We compare these results with those of published data for 3 additional stars (γ Cephei, β Geminorum, and β Ophiuchi), and discuss possible implications for the underlying physical mechanism(s). From data obtained using the HF technique we find a number of stars with significant (> 99% confidence level) periods. For single-period stars: gamma2 Delphini, P = 526.0 plus or minus 11.0 d, K = 11.6 plus or minus 2.2 ms-1; β Andromedae, P = 715.0 plus or minus 36.0 d, K = 323.0 plus or minus 39.0 ms-1; and α Hydrae, P = 848.4 plus or minus 14.94 d (a transient period), K = 127.5 plus or minus 13.0 ms-1. For multi-period stars: α Tauri, P1 = 647.93 plus or minus 4.62 d, K1 = 14.9 plus or minus 10.6 ms-1, P2 = 1.8358 plus or minus 0.048 d, K2 = 32.0 plus or minus 5.0 ms -1; β Pegasi, P1 = 409.18 plus or minus 7.2 d, K1 = 1043.1 plus or minus 74.0 ms-1, P2 = 104.44 plus or minus 0.52 d, K2 = 623.47 plus or minus 48.0 ms-1 (a photometrically variable star); and epsilon Pegasi (K supergiant), P1 = 65.223 plus or minus 0.065 d, K1 = 415.8 plus or minus 59.0 ms -1, P2 = 46.285 plus or minus 0.019 d, K2 = 559.08 plus or minus 57.0 ms-1, P3 = 10.721 plus or minus 0.002 d, K3 = 410.34 plus or minus 66.0 ms-1. From data obtained using both the HF and iodine-cell techniques, we find δ Sagittarii, P = 5.3581 plus or minus 0.0008 d, K = 51.36 plus or minus 3.8 ms -1. Finally, we report on data obtained from observations using the iodine-cell: HR 152, P = 19.959plus or minus 0.012 d, K = 140.8 plus or minus 17.0 ms -1 (the only significant period present in the data). We contrast these stars with stars of similar spectral types that show no significant periods: α Cassiopeiae, α Ursae Majoris, α Arietis, β Ursae Minoris, and γ Draconis. We also discuss incomplete but tantalizing results for α Ceti. |
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