Peter Nisenson

Evidence for Multiple Companions to υ Andromedae

The bright F8 V star t Andromedae was previously reported to have a 4.6 day Doppler velocity periodicity, consistent with having a Jupiter-mass companion orbiting at 0.059 AU. Follow-up obser- vations by both the Lick and Advanced Fiber-Optic Echelle spectrometer (AFOE) planet survey pro- grams con—rm this periodicity and reveal additional periodicities at 241 and 1267 days. These periodicities are consistent with Keplerian orbital motion and imply two additional companions orbiting at 0.83 and 2.5 AU, with minimum (M sin i) masses of 2.0 and 4.6 respectively. Non-Keplerian M JUP , explanations for the observed Doppler velocity variations, including radial and nonradial pulsations, rotational modulation of surface features, and stellar magnetic cycles, are examined. These explanations seem unlikely based on the observed photometric and chromospheric stability of the star. This putative three-planet system is found to be dynamically stable by both analytic techniques and numerical simula- tions. The outer two companions both reside in eccentric orbits, as do all nine known extrasolar planet candidates in distant orbits. If real, this multiple-planet system is the —rst around a main-sequence star, and its study should oUer insights into planet formation, planet-planet interactions, and the observed eccentricities of planetary orbits. Subject headings: binaries: spectroscopicplanetary systemsstars: individual (t Andromedae)

A Planet Orbiting the Star ρ Coronae Borealis

We report the discovery of near-sinusoidal radial velocity variations of the G0V star ρ CrB, with period 39.6 days and amplitude 67 m s-1. These variations are consistent with the existence of an orbital companion in a circular orbit. Adopting a mass of 1.0 M☉ for the primary, the companion has minimum mass about 1.1 Jupiter masses and orbital radius about 0.23 AU. Such an orbital radius is too large for tidal circularization of an initially eccentric orbit during the lifetime of the star, and hence we suggest that the low eccentricity is primordial, as would be expected for a planet formed in a dissipative circumstellar disk.

Detection of Earth-like Planets Using Apodized Telescopes

The mission of NASAs Terrestrial Planet Finder (TPF) is to find Earth-like planets orbiting other stars and characterize the atmospheres of these planets using spectroscopy. Because of the enormous brightness ratio between the star and the reflected light from the planet, techniques must be found to reduce the brightness of the star. The current favorite approach to doing this is with interferometry: interfering the light from two or more separated telescopes with a π phase shift, nulling out the starlight. While this technique can, in principle, achieve the required dynamic range, building a space interferometer that has the necessary characteristics poses immense technical difficulties. In this paper, we suggest a much simpler approach to achieving the required dynamic range. By simply adjusting the transmissive shape of a telescope aperture, the intensity in large regions around the stellar image can be reduced nearly to zero. This approach could lead to construction of a TPF using conventional technologies, requiring space optics on a much smaller scale than the current TPF approach.

An Upper Limit on the Reflected Light from the Planet Orbiting the Star τ Bootis

The planet orbiting ??Boo at a separation of 0.046 AU could produce a reflected light flux as bright as 1 × 10-4 relative to that of the star. A spectrum of the system will contain a reflected light component which varies in amplitude and Doppler shift as the planet orbits the star. Assuming the secondary spectrum is primarily the reflected stellar spectrum, we can limit the relative reflected light flux to be less than 5 × 10-5. This implies an upper limit of 0.3 for the planetary geometric albedo near 480?nm, assuming a planetary radius of 1.2 RJup. This albedo is significantly less than that of any of the giant planets of the solar system and is not consistent with certain published theoretical predictions.

THE AFOE: A SPECTROGRAPH FOR PRECISION DOPPLER STUDIES

The Advanced Fiber Optic Echelle (AFOE) is a fiber-fed echelle spectrograph designed for the measurement of stellar Doppler shifts. Using a 2k x 2k CCD detector, it samples about 55% of the wavelength range between 450 nm and 700 nm (20 echelle orders) at a single shot, with spectral resolution R = 32000 to 70000 at 500 nm, depending on the slit width employed. The AFOE employs a number of devices to assure that the calibrations necessary for accurate Doppler measurements can be properly performed. The most important of these are: (1) coupling to the telescope via a double-scrambling optical fiber system; (2) continuous calibration of the wavelength scale and point-spread function by means of an atomic emission lamp entering the spectrograph via a separate fiber and/or a molecular iodine absorption cell; (3) availability of fiber-coupled sunlight for regular calibration against the solar spectrum; (4) appropriate mechanical design and active thermal control, yielding good mechanical stability. The AFOE is coupled to the Tillinghast 1.5-m telescope at the F. L. Whipple Observatory. It presently achieves S/N = 500 in the continuum near 500 nm in 60s when observing Arcturus (alpha-Boo, mV = -0.04). This noise level sets a limit of about 0.7 ms-1 to the Doppler precision attainable in this length of observing time. Currently, our actual frame-to-frame repeatability is worse than the photon noise limited value by about a factor of 3 for this bright star, and about 1.5 for stars with mV = 4. Work is continuing to refine data processing methods so that the ultimate noise limit may be approached more closely, and to improve the spectrographs relatively low efficiency.

Partial atmospheric correction with adaptive optics

Adaptive optics has seen only limited application in astronomical facilities, despite its significant potential for improving seeing conditions and increasing observing efficiency and productivity. Expense and technological difficulty appear to be the reasons that this is the case. Correction of large apertures requires hundreds of active elements in both the wave-front sensor and the adaptive mirror. We have performed some one-dimensional numerical simulations to test atmospheric wave-front correction when the active element is not matched to the correlation scale in the pupil. The results demonstrate that substantial seeing improvement can be obtained with an adaptive optical system having a limited number of active elements.

A High-Eccentricity Low-Mass Companion to HD 89744

HD 89744 is an F7 V star with a mass of 1.4 M middle dot in circle, an effective temperature of 6166 K, an age of 2.0 Gyr, and metallicity &sqbl0;Fe&solm0;H&sqbr0;=0.18. The radial velocity of the star has been monitored with the Advanced Fiber-Optic Echelle 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 companions periastron passage in the fall of 1999. As a result, we have determined the stars orbital wobble to have a period P=256 days, an orbital amplitude K=257 m s-1, and an eccentricity e=0.7. From the stellar mass, we infer that the companion has a minimum mass m2sini=7.2 MJ in an orbit with a semimajor axis a2=0.88 AU. The eccentricity of the orbit, among the highest known for extrasolar planets, continues the trend that extrasolar planets with semimajor 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 extrasolar planets tend to have high metallicity.

Asymmetries in the atmosphere of Mira

A two-dimensional high angular resolution study of ο Ceti (Mira), carried out at four epochs from 1983 November to 1988 November using speckle interferometry techniques, detected asymmetries in the extended atmosphere of this pulsating star. The reconstructed speckle images show that the strength and the shape of this asymmetry changes as a function of wavelength and time. The position angles of the major axes of the asymmetries at different epochs are determined and the axes are measured accurately as a function of wavelength. The origin of the observed asymmetries has not yet been identified. Plausible causes include instabilities in the pulsating atmosphere, nonspherical pulsation, or the interaction with the nearby companion

Speckle imaging with the PAPA detector

A new 2-D photon-counting camera, the PAPA (precision analog photon address) detector has been built, tested, and used successfully for the acquisition of speckle imaging data. The camera has 512 × 512 pixels and operates at count rates of at least 200,000/sec. In this paper we present technical details on the camera and include some of the laboratory and astronomical results which demonstrate the detectors capabilities.

Real Time Optical Processing with Bi 12 SiO 20 PROM

Use of the Itek PROM, a Pockels effect real time electrooptic image modulator, in optical processing systems is discussed. Applications include an incoherent-to-coherent converter for word/character recognition systems; on-line Vander Lugt type Fourier plane filters for real time cross correlation; a block data composer for holographic memories; and an active storage array for a parallel optical digital computer.