CDROM/APJ/V466/P415 Spectroscopic Orbits for Three Binaries (Mazeh+ 1996) ================================================================================ Spectroscopic Orbits for Three Binaries with Low-Mass Companions and the Distribution of Secondary Masses Near the Substellar Limit Tsevi Mazeh, David W. Latham, and Robert P. Stefnik <1996, ApJ, 466, 415> =1996ApJ...466..415M ================================================================================ Abstract: We present orbital solutions for three low-amplitude spectroscopic binaries discovered in a sample of 20 solar-type IAU radial velocity standard stars observed with the Digital Speedometers at the Harvard- Smithsonian Center for Astrophysics. We update the orbital solutions for HD 114762 and HD 140913, and present a preliminary new solution for HD 29587. For all three orbits, the minimum mass for the secondary is less than 0.08 Msun, the borderline between stellar and substellar masses. We consider the probability that all three binaries have small enough inclination angles so that their companions are above the substellar limit. To do so, we treat the 20 IAU standards as a sample drawn from a population of binaries with a mass-ratio distribution that does not allow any substellar companions. We calculate the probability that such a sample could still have three binaries, with the low-amplitude orbits actually found within the IAU sample. We show that this probability is small, depending on the specific mass-ratio distribution. For example, a flat mass-ratio distribution that assumes there are no substellar companions can be excluded at a high confidence level, 99.7%. We further show that our three detections may imply that the secondary-mass distribution rises near the substellar limit. However, the observations do not yet allow us to distinguish whether the unseen companions of HD 114762, HD 140913, and HD 29587 have stellar or substellar masses. In particular, recent attempts to estimate the mass of the companion of HD 114762 based on assumptions about the intrinsic rotation of the primary are inconclusive, and the companion could easily have a mass as low as 0.02 Msun. We compare our three detections with the null results of four very precise radial velocity searches for substellar companions. The difference is indeed puzzling but can be accounted for if just a small fraction of the solar-type stars, of the order of a few percent, have companions with masses near the substellar limit. Keywords: binaries: spectroscopic -- stars: individual (HD 29587, HD 114762, HD 140913) -- stars: low-mass, brown dwarfs Description: The table reports all the individual velocities determined for the 20 solar-type stars listed in Table 1 of the printed paper. The data sets for each star are separated by a header giving the star name and the J2000 right ascension and declination. A blank line separates the data records for each star. File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- table.dat 40 3089 Individual velocities -------------------------------------------------------------------------------- Byte-per-byte Description of file: table.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- ----- Header record ----- 1- 9 A9 --- HD Henry Draper Catalog number 10-14 5X --- --- Blank 15-16 I2 h RAh Right ascension, J2000 17 1X --- --- Always ':' 18-19 I2 min RAm R.A. 20 1X --- --- Always ':' 21-24 F4.1 s RAs R.A. 25 1X --- --- Blank 26 A1 --- DE- Declination sign 27-28 I2 deg DEd Declination, J2000 29 A1 --- --- Always ':' 30-31 I2 arcmin DEm Dec. 32 A1 --- --- Always ':' 33-34 I2 arcsec DEs Dec. ----- Data records ----- 1-13 D13.5 day HJD Heliocentric Julian Date 14-16 3X --- --- Blank 17-21 F5.2 km/s Rv Barycentric radial velocity 22-23 2X --- --- Blank 24-28 F5.2 km/s e_Rv Internal estimate of velocity error 29-34 F6.1 --- TDR Tonry-Davis R value 35-40 F6.2 --- CC Peak value of the correlation coefficient -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 22-Oct-96