arXiv subjects

Marc J. Kuchner

Publications and source records attributed to Marc J. Kuchner.

103 records · Page 6Linked to original sources

arXiv2004

The Dynamical Influence of a Planet at Semimajor Axis 3.4 AU on the Dust Around Epsilon Eridani

Precise-Doppler experiments suggest that a massive (m sin i=0.86 M_J) planet orbits at semimajor axis a=3.4 AU around Epsilon Eridani, a nearby star with a massive debris disk. The dynamical perturbations from such a planet would mold the distribution of dust around this star. We numerically integrated the orbits of dust grains in this system to predict the central dust cloud structure. For a supply of grains that begin in low-inclination, low-eccentricity orbits at 15 AU, the primary feature of the dust distribution is a pair of dense clumps, containing dust particles trapped in mean-motion resonances of the form n:1. These clumps appear to revolve around the star once every two planet revolutions. Future observations with the IRAM Plateau de Bure Interferometer, the SMA, or ALMA could detect these clumps, confirming the existence of the planet and revealing its location.

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arXiv2004

A Unified View of Coronagraph Image Masks

The last few years have seen a variety of new image mask designs for diffraction-limited coronagraphy. Could there still be useful designs as yet undiscovered? To begin to answer this question, I survey and unify the Fraunhofer theory of coronagraph image masks in the context of a one-dimensional classical coronagraph. I display a complete solution to the problem of removing on-axis light assuming an unapodized entrance aperture and I introduce the attenuation function, a measure of a generic coronagraph's off-axis performance. With these tools, I demonstrate that the masks proposed so far form a nearly complete library of image masks that are useful for detecting faint extrasolar planets.

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arXiv2003

Detection of Close-In Extrasolar Giant Planets Using the Fourier-Kelvin Stellar Interferometer

We evaluate the direct detection of extrasolar giant planets with a two-aperture nulling infrared interferometer, working at angles $θ<λ/2B$, and using a new `ratio-of-two-wavelengths' technique. Simple arguments suggest that interferometric detection and characterization should be quite possible for planets much closer than the conventional inner working angle, or angular resolution limit. We show that the peak signal from a nulling infrared interferometer of baseline ($\lesssim 40$ meters) will often occur `inside the null', and that the signal variations from path-difference fluctuations will cancel to first order in the ratio of two wavelengths. Using a new interferometer simulation code, we evaluate the detectability of all the known extrasolar planets as observed using this two-color method with the proposed {\it Fourier Kelvin Stellar Interferometer (FKSI)}. In its minimum configuration {\it FKSI} uses two 0.5-meter apertures on a 12.5-meter baseline, and a $\pm 20^{\circ}$ field-of-regard. We predict that $\sim 7$ known extrasolar planets are directly detectable using {\it FKSI}, with low-resolution spectroscopy ($R \sim 20$) being possible in the most favorable cases. Spaceborne direct detection of extrasolar giant planets is possible with $\sim 12$ meter baselines, and does not require the much longer baselines provided by formation flying.

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arXiv2003

Volatile-Rich Earth-Mass Planets in the Habitable Zone

A small planet is not necessarily a terrestrial planet. Planets that form beyond the snow line with too little mass to seed rapid gas accretion (<~ 10 Earth masses) should be rich in volatile ices like water and ammonia. Some of these planets should migrate inward by interacting with a circumstellar disk or with other planets. Such objects can retain their volatiles for billions of years or longer at ~1 AU as their atmospheres undergo slow hydrodynamic escape. These objects could appear in future surveys for extrasolar Earth analogs.

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arXiv2003

The Geometry of Resonant Signatures in Debris Disks with Planets

Using simple geometrical arguments, we paint an overview of the variety of resonant structures a single planet with moderate eccentricity (e < ~0.6) can create in a dynamically cold, optically thin dust disk. This overview may serve as a key for interpreting images of perturbed debris disks and inferring the dynamical properties of the planets responsible for the perturbations. We compare the resonant geometries found in the solar system dust cloud with observations of dust clouds around Vega and other stars and we discuss a new model for the asymmetries in the Epsilon Eridani cloud.

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arXiv2003

Notch Filter Masks: Practical Image Masks for Planet-Finding Coronagraphs

An ideal coronagraph with a band-limited image mask can efficiently image off-axis sources while removing identically all of the light from an on-axis source. However, strict mask construction tolerances limit the utility of this technique for directly imaging extrasolar terrestrial planets. We present a variation on the basic band-limited mask design--a family of ``notch filter'' masks--that mitigates this problem. These robust and trivially achromatic masks can be easily manufactured by cutting holes in opaque material.

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arXiv2002

Long-Term Dynamics and the Orbital Inclinations of the Classical Kuiper Belt Objects

We numerically integrated the orbits of 1458 particles in the region of the classical Kuiper Belt (41 AU < a < 47 AU) to explore the role of dynamical instabilities in sculpting the inclination distribution of the classical Kuiper Belt Objects (KBOs). We find that the selective removal of low-inclination objects by overlapping secular resonances (nu_17 and nu_18) acts to raise the mean inclination of the surviving population of particles over 4 billion years of interactions with Jupiter, Saturn, Uranus and Neptune, though these long-term dynamical effects do not themselves appear to explain the discovery of KBOs with inclinations near 30 degrees. Our integrations also imply that after 3 billion years of interaction with the massive planets, high inclination KBOs more efficiently supply Neptune-encountering objects, the likely progenitors of short-period comets, Centaurs, and scattered KBOs. The secular resonances at low inclinations may indirectly cause this effect by weeding out objects unprotected by mean motion resonances during the first 3 billion years.

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arXiv2002

Halting Planet Migration in the Evacuated Centers of Protoplanetary Disks

Precise Doppler searches for extrasolar planets find a surfeit of planets with orbital periods of 3-4 days, and no planets with orbital periods less than 3 days. The circumstellar distance, R_0, where small grains in a protoplanetary disk reach sublimation temperature (~1500 K) corresponds to a period of ~6 days. Interior to R_0, turbulent accretion due to magneto-rotational instability may evacuate the disk center. We suggest that planets with orbital periods of 3-4 days are so common because migrating planets halt once this evacuated region contains the sites of their exterior 2:1 Lindblad resonances.

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arXiv2002

A Coronagraph with a Band-Limited Mask for Finding Terrestrial Planets

Several recent designs for planet-finding telescopes use coronagraphs operating at visible wavelengths to suppress starlight along the telescope's optical axis while transmitting any off-axis light from circumstellar material. We describe a class of graded coronagraphic image masks that can, in principle, provide perfect elimination of on-axis light, while simultaneously maximizing the Lyot stop throughput and angular resolution. These ``band-limited'' masks operate on the intensity of light in the image plane, not the phase. They can work with almost any entrance pupil shape, provided that the entrance pupil transmissivity is uniform, and can be combined with an apodized Lyot stop to reduce the sensitivity of the coronagraph to imperfections in the image mask. We discuss some practical limitations on the dynamic range of coronagraphs in the context of a space-based terrestrial planet finder (TPF) telescope, and emphasize that fundamentally, the optical problem of imaging planets around nearby stars is a matter of precision fabrication and control, not Fraunhofer diffraction theory.

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arXiv2000

A Search for Resonant Structures in the Zodiacal Cloud with COBE DIRBE: The Mars Wake and Jupiter's Trojan Clouds

We searched the COBE DIRBE Sky and Zodi Atlas for a wake of dust trailing Mars and for Trojan dust near Jupiter's L5 Lagrange point. We compare the DIRBE images to a model Mars wake based on the empirical model of the Earth's wake as seen by the DIRBE and place a 3-sigma upper limit on the fractional overdensity of particles in the Mars wake of 18% of the fractional overdensity trailing the Earth. We place a 3-sigma upper limit on the effective emitting area of large (10-100 micron diameter) particles trapped at Jupiter's L5 Lagrange point of 6 x 10^17 cm^2, assuming that these large dust grains are distributed in space like the Trojan asteroids. We would have detected the Mars wake if the surface area of dust in the wake scaled simply as the mass of the planet times the Poynting-Robertson time scale.

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arXiv2000

Keck Speckle Imaging of the White Dwarf G29-38: No Brown Dwarf Companion Detected

The white dwarf Giclas 29-38 has attracted much attention due to its large infrared excess and the suggestion that excess might be due to a companion brown dwarf. We observed this object using speckle interferometry at the Keck telescope, obtaining diffraction-limited resolution (55 milliarcseconds) at K band, and found it unresolved. Assuming the entire K band excess is due to a single point-like companion, we place an upper limit on the binary separation of 30 milliarcseconds, or 0.42 AU at the star's distance of 14.1 pc. This result, combined with astroseismological data and other images of G29-38, supports the hypothesis that the source of the near-infrared excess is not a cool companion but a dust cloud.

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arXiv2000

An 11.6 Micron Keck Search For Exozodiacal Dust

We have begun an observational program to search nearby stars for dust disks that are analogous to the disk of zodiacal dust that fills the interior of our solar system. We imaged six nearby main-sequence stars with the Keck telescope at 11.6 microns, correcting for atmosphere-induced wavefront aberrations and deconvolving the point spread function via classical speckle analysis. We compare our data to a simple model of the zodiacal dust in our own system based on COBE/DIRBE observations and place upper limits on the density of exozodiacal dust in these systems.

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arXiv2000

A Search for Exozodiacal Dust and Faint Companions Near Sirius, Procyon, and Altair with the NICMOS Coronagraph

We observed Sirius, Altair, and Procyon with the NICMOS Coronagraph on the Hubble Space Telescope to look for scattered light from exozodiacal dust and faint companions within 10 AU from these stars. We did not achieve enough dynamic range to surpass the upper limits set by IRAS on the amount of exo-zodiacal dust in these systems, but we did set strong upper limits on the presence of nearby late-type and sub-stellar companions.

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