Geoffrey W. Marcy

Planets Orbiting Other Suns1,2

ABSTRACT After a century fraught with false claims, evidence for planets around other stars finally appears robust. Infrared imaging and spectroscopy of disks around stars foreshadow detailed models of the formation and evolution of planetary systems. Surveys of main‐sequence stars show that 5% harbor companions of (0.5–8)MJUP within 3 AU, peaked at lowest masses. Their orbits are either within 0.2 AU or eccentric, and occasionally both. These odd orbits suggest that dynamics with gas and planetesimals yield diverse systems and that stable, coplanar orbits of about nine giant and rocky planets may require special initial conditions. Far fewer stars (<1%) harbor (5–80)MJUP companions. This brown dwarf desert for companions stands in contrast to the abundant brown dwarfs that are freely floating.

Sub-Saturn Planetary Candidates of HD 16141 and HD 46375

Precision Doppler measurements from the Keck High-Resolution Echelle Spectrograph reveal periodic Keplerian velocity variations in the stars HD 16141 and HD 46375. HD 16141 (G5 IV) has a period of 75.8 days and a velocity amplitude of 11 m s-1, yielding a companion having Msini=0.22 M(JUP) and a semimajor axis of a=0.35 AU. HD 46375 (K1 IV-V) has a period of 3.024 days and a velocity amplitude of 35 m s-1, yielding a companion with Msini=0.25 M(JUP), a semimajor axis of a=0.041 AU, and an eccentricity of 0.04 (consistent with zero). These companions contribute to the rising planet mass function toward lower masses.Precision Doppler measurements from the Keck/HIRES spectrometer reveal periodic Keplerian velocity variations in the stars HD 16141 and HD 46375. HD 16141 (G5 IV) has a period of 75.8 d and a velocity amplitude of 11 m/s, yielding a companion having Msini = 0.22 Mjup and a semimajor axis, a = 0.35 AU. HD 46375 (K1 IV/V) has a period of 3.024 d and a velocity amplitude of 35 m/s, yielding a companion with Msini=0.25 Mjup, a semimajor axis of a = 0.041 AU, and an eccentricity of 0.04 (consistent with zero). These companions contribute to the rising planet mass function toward lower masses.

Limits on the magnetic flux of pre-main-sequence stars

We attempt to detect a magnetic field on the weak T Tauri star, TAP35, via the enhanced equivalent widths of Zeeman-broadened absorption lines. We synthesize 25 Fe I lines, having a range of Zeeman sensitivities, using an LTE Stokes line-transfer calculation. The oscillator strengths of all lines are empirically determined a priori using the same line-transfer code applied to the spectrum of the magnetically quiet star, τ Ceti. The Fe abundance of TAP35 was established by synthesizing lines that are insensitive to Zeeman splitting. We find that the equivalent widths, Weq, of Zeeman-sensitive lines in TAP35 are systematically enhanced relative to the Zeeman-insensitive lines, consistent with the presence of widespread, kilogauss fields. The excess Weq can be explained by a product of field strength and surface filling factor (B f) of 1 kiloGauss. A strong upper limit can be placed on the product of those two quantities, B f < 2 kG. This measurement bears on the physics of T Tauri coronae, chromospheres, dynamos, and accretion-disk boundary layers.

Physical realism in the analysis of stellar magnetic fields. III. Flux tubes and multicomponent atmospheres

Several important tests of likely systematic effects in the analysis of Zeeman broadening on cool stars have been performed. The effects of different atmospheric structures inside and outside of magnetic regions are considered, and the effects of field gradients within flux tubes and of errors in the assumed spectral type of a star are considered. It is found that substantial effects are possible which render the results of one-component analyses somewhat uncertain, with systematic errors potentially as great as 40 percent in the derived magnetic flux. However, it appears that two-component models consisting of quiet and flux tube regions may be oversimplified, since the predicted line profiles tend to be shallower than those observed. 39 refs.

The Lick Observatory Planet Search

1 Based on observations obtained at Lick Observatory, which is operated by the University of California. ABSTRACT We have constructed a precision Doppler technique with which we have detected 6 extrasolar planets to date. Doppler precision is achieved by inserting an iodine absorption cell in the telescope, providing a ducial wavelength scale against which to measure Doppler shifts. Our current precision is 3 m s ?1 , which corresponds to one part in one hundred million in wavelength, or 1/1000th of a pixel on the CCD detector. As of 1996 August, our survey of 120 stars has revealed six stars that show velocity variations consistent with Jupiter{mass companions in Keplerian orbits. These objects span a greater range of orbital radii and eccentricity than the planets in our own solar system. Three of these objects are 51 Peg{type planets with circular orbits having radii 0.15 AU or less. The other three objects have masses between 1.7 and 6.5 M JUP , eccentricities between 0.01 and 0.6, and semi{major axes between 0.4 and 2.1 AU. We have not found any objects having masses between 10 and 80 M JUP , the domain usually associated with brown dwarfs. These six new companions represent a new population of objects having extremely low masses, similar to that of Jupiter. We have begun a survey of an additional 400 stars using the Keck 10{m telescope, which will allow the detection of Neptune{mass planets.

Magnetic fields on K and M dwarfs

Of seven late K and early M dwarfs, six were observed to have magnetic fields. No relationship was seen between effective temperature and either field strength or filling factor. Magnetic flux was observed not to be constant over this range of effective temperature.