A High-Eccentricity Low-Mass Companion to HD 89744

Abstract of the paper submitted to the Astrophysical Journal Letters:
"A High-Eccentricity Low-Mass Companion to HD 89744" by Korzennik, Brown, Fischer, Nisenson, Noyes.

Abstract

HD 89744 is an F7 V star with mass 1.4 M , effective temperature 6166 K, age 2.0 Gy and metallicity [Fe/H]= 0.18. The radial velocity of the star has been monitored with the AFOE spectrograph at the Whipple Observatory since 1996, and evidence has been found for a low mass companion. The data were complemented by additional data from the Hamilton spectrograph at Lick Observatory during the companion's periastron passage in fall 1999. As a result, we have determined the star's orbital wobble to have period P = 256 d, orbital amplitude K = 257 m/s, and eccentricity e = 0.7. From the stellar mass we infer that the companion has minimum mass m₂ sin i = 7.2 M_Jup in an orbit with semi-major axis a₂ = 0.88 AU. The eccentricity of the orbit, among the highest known for extra-solar planets, continues the trend that extra-solar planets with semi-major axes greater than about 0.15 AU tend to have much higher eccentricities than are found in our solar system. The high metallicity of the parent star reinforces the trend that parent stars of extra-solar planets tend to have high metallicity

The full text of the paper is available as a compressed (gzip) PostScript file (207 kB), or PDF file (387 kB).

Velocities

Plot of the radial velocity measurements

Fig. 1.: Radial velocity observations of HD 89744 with their respective uncertainties. Red circles denotes AFOE observations, and green circles Lick observations after applying an offset determined by the combined orbital fit. The Keplerian orbital fit is indicated by the dotted line.

Orbital Fit

Fig. 2.: Phase plot of the Keplerian orbital fit. Red circles denotes AFOE observations, green circles Lick observations.

Orbital Parameters

Orbital parameters resulting from a Keplerian fit to the combined data set. The last two rows of the table use the adopted value m₁ = 1.4 M_Sun:

           ___________________________________________________________
                                          |                           
             P  [day]                     |   256.0    +/-     0.7    
                                          |                           
             K  [m/s]                     |     257    +/-      14    
                                          |                           
             e                            |    0.70    +/-      0.02  
                                          |                           
             omega                        |     195    +/-      3     
                                          |                           
             To  [JD-2,450,000]           |     994    +/-      2     
           _______________________________|___________________________
                                          |            -7              
             f (m1 ; m2 ; i) [Msun]       |     1.64 10                
                                          |                           
             a1 sin  i [AU]               |     0.0043                 
           _______________________________|___________________________
                                          |                           
             RMS(residuals) [m/s]         |    20.5                   
                                          |                           
             reduced Chi                  |     1.6                  
                                          |                           
             NTot , NRej                  |      88,            1      
           _______________________________|___________________________
                                          |                           
             a2  [AU]                     |     0.88                   
                                          |                           
             m2 sin  i [Mjup]             |     7.2                  
           _______________________________|___________________________

Stellar Parameters

The physical parameters of the star HD 89744 (from scientific literature):

                 ____________________________________________
                                |                  | 
                  Mass [Msun]   |  1.4   +/-  0.09 | (1), (2)
                                |                  | 
                  Radius [Rsun] |  2.14  +/-  0.1  | (1)
                                |                  |
                  Teff [K]      | 6166   +/-  145  | (1)
                                |                  |
                  Mv            |  2.78            | (3)
                                |                  | 
                  Age [Gy]      |   2.04           | (2)
                                |                  | 
                  [Fe/H]        | 0.18             | (4)
                                |                  |
                  Prot [days]   |     9            | (5)
                                |                  |
                  v sini [km/s] |     8            | (6), (7)
                 ____________________________________________


                     (1) Prieto & Lambert, 2000
                     (2) Ng & Bertelli, 1998
                     (3) Perryman, 1997
                     (4) Edvardsson et al., 1993
                     (5) Baliunas, Sokoloff, & Soon, 1996
                     (6) Bernacca & Perinotto, 1970
                     (7) Uesugi & Fukuda, 1970

There is more on the AFOE's planet detection program.
__________________________________________________

Sylvain G. Korzennik (skorzennik@cfa.harvard.edu)

Last modified: Fri Mar 3 11:52:01 2000