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| Paper: |
A Program for the Analysis of Long-Period Binaries: The Case of γ Delphini |
| Volume: |
185, Precise Stellar Radial Velocities, IAU Colloquium 170 |
| Page: |
297 |
| Authors: |
Irwin, A. W.; Vandenberg, D. A.; Larson, A. M. |
| Abstract: |
At the University of Victoria and University of Washington we have started a programme to analyze long-period binaries that have been observed with both the precise-radial-velocity (PRV) and astrometric techniques. For this paper we define ``long period'' to mean a period substantially greater than the epoch range of the astrometric (and PRV) observations. In this special case only a small fraction of the orbit is observed so that random and systematic errors in the observations make it impossible to determine a reliable orbit from observations alone. We are specifically interested in systems where (1) the parallax, relative angular position, and relative proper motion yield reliable values for two components of both the position and velocity and where (2) measurements with the PRV technique yield reliable values of the difference in radial velocity and radial acceleration between the two members of the system. It should be possible to combine these 6 position, velocity, and acceleration components with the total mass of the system (as predicted by the theory of stellar interiors with abundance input from the theory of stellar atmospheres) to determine a consistent orbit, age, mass, radius (and surface gravity), effective temperature, and abundance for each star of the long-period binary. In other words we will be analyzing such binary systems as if they were open clusters but with additional constraints due to the parallax, astrometric and PRV observations. For our first analysis we will concentrate on the example of the γ Delphini binary consisting of a K1 IV primary (gamma2 Del) and an F7 V secondary (gamma1Del). The primary has been observed with the PRV technique and shows a significant radial acceleration as well as a periodic signature (P = 1.4 yr). At least three possible causes of this periodic signature are rotation, pulsation (either g-mode or r-mode), or a planetary companion. The results of our analysis should help to constrain these possibilities. For example, for all the orbit possibilities checked so far the minimum periastron distance is more than 1000 a.u. The semi-major axis of the possible planetary companion is 1.4 a.u. so it appears there is plenty of room in the system for the possible planetary companion of the primary to survive the perturbations caused by the γ Del secondary. |
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