arXiv subjects

Ray Jayawardhana

Publications and source records attributed to Ray Jayawardhana.

At least 91 records · Page 5Linked to original sources

arXiv2013

Discovery of a Visual T-Dwarf Triple System and Binarity at the L/T Transition

We present new high contrast imaging of 8 L/T transition brown dwarfs using the NIRC2 camera on the Keck II telescope. One of our targets, the T3.5 dwarf 2MASS J08381155 + 1511155, was resolved into a hierarchal triple with projected separations of 2.5+/-0.5 AU and 27+/-5 AU for the BC and A(BC) components respectively. Resolved OSIRIS spectroscopy of the A(BC) components confirm that all system members are T dwarfs. The system therefore constitutes the first triple T-dwarf system ever reported. Using resolved photometry to model the integrated-light spectrum, we infer spectral types of T3, T3, and T4.5 for the A, B, and C components respectively. The uniformly brighter primary has a bluer J-Ks color than the next faintest component, which may reflect a sensitive dependence of the L/T transition temperature on gravity, or alternatively divergent cloud properties amongst components. Relying on empirical trends and evolutionary models we infer a total system mass of 0.034-0.104 Msun for the BC components at ages of 0.3-3 Gyr, which would imply a period of 12-21 yr assuming the system semi-major axis to be similar to its projection. We also infer differences in effective temperatures and surface gravities between components of no more than ~150 K and ~0.1 dex. Given the similar physical properties of the components, the 2M0838+15 system provides a controlled sample for constraining the relative roles of effective temperature, surface gravity, and dust clouds in the poorly understood L/T transition regime. Combining our imaging survey results with previous work we find an observed binary fraction of 4/18 or 22_{-8}^{+10}% for unresolved spectral types of L9-T4 at separations >~0.1 arcsec. This translates into a volume-corrected frequency of 13^{-6}_{+7}%, which is similar to values of ~9-12% reported outside the transition. (ABRIDGED)

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arXiv2013

A Combined VLT and Gemini Study of the Atmosphere of the Directly-Imaged Planet, beta Pictoris b

We analyze new/archival VLT/NaCo and Gemini/NICI high-contrast imaging of the young, self-luminous planet $β$ Pictoris b in seven near-to-mid IR photometric filters, using advanced image processing methods to achieve high signal-to-noise, high precision measurements. While $β$ Pic b's near-IR colors mimick that of a standard, cloudy early-to-mid L dwarf, it is overluminous in the mid-infrared compared to the field L/T dwarf sequence. Few substellar/planet-mass objects -- i.e. $κ$ And b and 1RXJ 1609B -- match $β$ Pic b's $JHK_{s}L^\prime$ photometry, and its 3.1 $μm$ and 5 $μm$ photometry are particularly difficult to reproduce. Atmosphere models adopting cloud prescriptions and large ($\sim$ 60 $μm$) dust grains fail to reproduce the $β$ Pic b spectrum. However, models incorporating thick clouds similar to those found for HR 8799 bcde but also with small (a few microns) modal particle sizes yield fits consistent with the data within uncertainties. Assuming solar abundance models, thick clouds, and small dust particles ($ $ = 4 $μm$) we derive atmosphere parameters of log(g) = 3.8 $\pm$ 0.2 and $T_{eff}$ = 1575--1650 $K$, an inferred mass of 7$^{+4}_{-3}$ $M_{J}$, and a luminosity of log(L/L$_{\odot}$) $\sim$ -3.80 $\pm$ 0.02. The best-estimated planet radius, $\approx$ 1.65 $\pm$ 0.06 $R_{J}$, is near the upper end of allowable planet radii for hot-start models given the host star's age and likely reflects challenges with constructing accurate atmospheric models. Alternatively, these radii are comfortably consistent with hot-start model predictions if $β$ Pic b is younger than $\approx$ 7 Myr, consistent with a late formation, well after its host star's birth $\sim$ 12$^{+8}_{-4}$ Myr ago.

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arXiv2013

A Multiplicity Census of Intermediate-Mass Stars in Scorpius-Centaurus

Stellar multiplicity properties have been studied for much of the range from the lowest to the highest stellar masses, but intermediate-mass stars from F-type to late A-type have received relatively little attention. Here we report on a Gemini/NICI snapshot imaging survey of 138 such stars in the young Scorpius-Centaurus (Sco-Cen) region, for the purpose of studying multiplicity with sensitivity down to planetary masses at wide separations. In addition to two brown dwarfs and a companion straddling the hydrogen burning limit we reported previously, here we present 26 new stellar companions and determine a multiplicity fraction within 0.1"--5.0" of 21+/-4%. Depending on the adopted semi-major axis distribution, our results imply a total multiplicity in the range of ~60--80%, which further supports the known trend of a smoothly continuous increase in the multiplicity fraction as a function of primary stellar mass. A surprising feature in the sample is a distinct lack of nearly equal-mass binaries, for which we discuss possible reasons. The survey yielded no additional companions below or near the deuterium-burning limit, implying that their frequency at >200 AU separations is not quite as high as might be inferred from previous detections of such objects within the Sco-Cen region.

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arXiv2013

Quick-MESS: A fast statistical tool for Exoplanet Imaging Surveys

Several tools have been developed in the past few years for the statistical analysis of the exoplanet search surveys, mostly using a combination of Monte-Carlo simulations or a Bayesian approach.Here we present the Quick-MESS, a grid-based, non-Monte Carlo tool aimed to perform statistical analyses on results from and help with the planning of direct imaging surveys. Quick-MESS uses the (expected) contrast curves for direct imaging surveys to assess for each target the probability that a planet of a given mass and semi-major axis can be detected. By using a grid-based approach Quick-MESS is typically more than an order of magnitude faster than tools based on Monte-Carlo sampling of the planet distribution. In addition, Quick-MESS is extremely flexible, enabling the study of a large range of parameter space for the mass and semi-major axes distributions without the need of re-simulating the planet distribution. In order to show examples of the capabilities of the Quick-MESS, we present the analysis of the Gemini Deep Planet Survey and the predictions for upcoming surveys with extreme-AO instruments.

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arXiv2013

Search for Rayleigh scattering in the atmosphere of GJ1214b

We investigate the atmosphere of GJ1214b, a transiting super-Earth planet with a low mean density, by measuring its transit depth as a function of wavelength in the blue optical portion of the spectrum. It is thought that this planet is either a mini-Neptune, consisting of a rocky core with a thick, hydrogen-rich atmosphere, or a planet with a composition dominated by water. Most observations favor a water-dominated atmosphere with a small scale-height, however, some observations indicate that GJ1214b could have an extended atmosphere with a cloud layer muting the molecular features. In an atmosphere with a large scale-height, Rayleigh scattering at blue wavelengths is likely to cause a measurable increase in the apparent size of the planet towards the blue. We observed the transit of GJ1214b in the B-band with the FOcal Reducing Spectrograph (FORS) at the Very Large Telescope (VLT) and in the g-band with both ACAM on the William Hershel Telescope (WHT) and the Wide Field Camera (WFC) at the Isaac Newton Telescope (INT). We find a planet-to-star radius ratio in the B-band of 0.1162+/-0.0017, and in the g-band 0.1180+/-0.0009 and 0.1174+/-0.0017 for the WHT & INT observations respectively. These optical data do not show significant deviations from previous measurements at longer wavelengths. In fact, a flat transmission spectrum across all wavelengths best describes the combined observations. When atmospheric models are considered a small scale-height water-dominated model fits the data best.

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arXiv2013

Optical Phase Curves of Kepler Exoplanets

We have conducted a comprehensive search for optical phase variations of all planet candidates with tight orbits in fifteen quarters of data from the Kepler space telescope. After correcting for systematics, we found eight systems that appear to show secondary eclipses as well as phase variations. Of these, five (Kepler-5, Kepler-6, Kepler-8, KOI-64 and KOI-2133) are new and three (TrES-2, HAT-P-7 and KOI-13) have previously published phase curves, albeit with many fewer observations. We model the full phase curve of each planet candidate, including the primary and secondary transits, and derive their albedos, day- and night-side temperatures, ellipsoidal variations and Doppler beaming. We find that KOI-64 and KOI-2133 have night-side temperatures well above their equilibrium values (while KOI-2133 also has an albedo >1), so we conclude that they are likely to be self-luminous objects rather than planets. The characteristics of the six other candidates are consistent with their being planets with low geometric albedos (<0.3). For TrES-2 and KOI-13, the Kepler bandpass appears to probe atmospheric layers hotter than the planet's equilibrium temperature. For KOI-13, we detect a never-before-seen third cosine harmonic with an amplitude of 6.7+/-0.3 ppm and a phase shift of -1.1+/-0.1 radians in the phase curve residual, which could be due to its spin-orbit misalignment. We report derived planetary parameters for all six planets, including masses from ellipsoidal variations and Doppler beaming, and compare our results to published values when available. Our results nearly double the number of Kepler exoplanets with measured phase curve variations, thus providing valuable new constraints on the properties of close-in hot Jupiters.

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arXiv2013

HST Spectral Mapping of L/T Transition Brown Dwarfs Reveals Cloud Thickness Variations

Most directly imaged giant exoplanets are fainter than brown dwarfs with similar spectra. To explain their relative underluminosity unusually cloudy atmospheres have been proposed. However, with multiple parameters varying between any two objects, it remained difficult to observationally test this idea. We present a new method, sensitive time-resolved Hubble Space Telescope near-infrared spectroscopy, to study two rotating L/T transition brown dwarfs (2M2139 and SIMP0136). The observations provide spatially and spectrally resolved mapping of the cloud decks of the brown dwarfs. The data allow the study of cloud structure variations while other parameters are unchanged. We find that both brown dwarfs display variations of identical nature: J- and H-band brightness variations with minimal color and spectral changes. Our light curve models show that even the simplest surface brightness distributions require at least three elliptical spots. We show that for each source the spectral changes can be reproduced with a linear combination of only two different spectra, i.e. the entire surface is covered by two distinct types of regions. Modeling the color changes and spectral variations together reveal patchy cloud covers consisting of a spatially heterogenous mix of low-brightness, low-temperature thick clouds and brighter, thin and warm clouds. We show that the same thick cloud patches seen in our varying brown dwarf targets, if extended to the entire photosphere, predict near-infrared colors/magnitudes matching the range occupied by the directly imaged exoplanets that are cooler and less luminous than brown dwarfs with similar spectral types. This supports the models in which thick clouds are responsible for the near infrared properties of these underluminous exoplanets.

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arXiv2012

Discovery of Two Very Wide Binaries with Ultracool Companions and a New Brown Dwarf at the L/T Transition

We present the discovery and spectroscopic follow-up of a nearby late-type L dwarf (2M0614+3950), and two extremely wide very-low-mass binary systems (2M0525-7425AB and 2M1348-1344AB), resulting from our search for common proper motion pairs containing ultracool components in the Two Micron All Sky Survey (2MASS) and the Wide-field Infrared Survey Explorer (WISE) catalogs. The near-infrared spectrum of 2M0614+3950 indicates a spectral type L$9 \pm 1$ object residing at a distance of $26.0 \pm 1.8$ pc. The optical spectrum of 2M0525-7425A reveals an M$3.0 \pm 0.5$ dwarf primary, accompanied by a secondary previously classified as L2. The system has an angular separation of $\sim 44"$, equivalent to $\sim 2000 $AU at distance of $46.0 \pm 3.0$ pc. Using optical and infrared spectra, respectively, we classify the components of 2M1348-1344AB as M$4.5 \pm 0.5$ and T$5.5 \pm 1$. The angular separation of $\sim 68"$ is equivalent to $\sim 1400 $AU at a distance of $20.7 \pm 1.4$ pc. 2M1348-1344AB is one of only six very wide (separation $>$ 1000 AU) systems containing late T dwarfs known to date.

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arXiv2012

New Brown Dwarf Companions to Young Stars in Scorpius-Centaurus

We present the discoveries of three faint companions to young stars in the Scorpius-Centaurus region, imaged with the NICI instrument on Gemini South. We have confirmed all three companions through common proper motion tests. Follow-up spectroscopy has confirmed two of them, HIP 65423 B and HIP 65517 B, to be brown dwarfs, while the third, HIP 72099 B, is more likely a very low-mass star just above the hydrogen burning limit. The detection of wide companions in the mass range of ~40--100 Mjup complements previous work in the same region, reporting detections of similarly wide companions with lower masses, in the range of ~10--30 Mjup. Such low masses near the deuterium burning limit have raised the question of whether those objects formed like planets or stars. The existence of intermediate objects as reported here could represent a bridge between lower-mass companions and stellar companions, but in any case demonstrate that mass alone may not provide a clear-cut distinction for the formation of low-mass companions to stars.

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arXiv2012

Substellar Objects in Nearby Young Clusters (SONYC) VI: The planetary-mass domain of NGC1333

Within the SONYC - Substellar Objects in Nearby Young Clusters - survey, we investigate the frequency of free-floating planetary-mass objects (planemos) in the young cluster NGC1333. Building upon our extensive previous work, we present spectra for 12 of the faintest candidates from our deep multi-band imaging, plus seven random objects in the same fields, using MOIRCS on Subaru. We confirm seven new sources as young very low mass objects (VLMOs), with Teff of 2400-3100K and mid-M to early-L spectral types. These objects add to the growing census of VLMOs in NGC1333, now totaling 58. Three confirmed objects (one found in this study) have masses below 15 MJup, according to evolutionary models, thus are likely planemos. We estimate the total planemo population with 5-15 MJup in NGC1333 is <~8. The mass spectrum in this cluster is well approximated by dN/dM ~ M^-alpha, with a single value of alpha = 0.6+/-0.1 for M<0.6Msol, consistent with other nearby star forming regions, and requires alpha <~ 0.6 in the planemo domain. Our results in NGC1333, as well as findings in several other clusters by ourselves and others, confirm that the star formation process extends into the planetary-mass domain, at least down to 6 MJup. However, given that planemos are 20-50 times less numerous than stars, their contribution to the object number and mass budget in young clusters is negligible. Our findings disagree strongly with the recent claim from a microlensing study that free-floating planetary-mass objects are twice as common as stars - if the microlensing result is confirmed, those isolated Jupiter-mass objects must have a different origin from brown dwarfs and planemos observed in young clusters.

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arXiv2012

Large Amplitude Variations of an L/T Transition Brown Dwarf: Multi-Wavelength Observations of Patchy, High-Contrast Cloud Features

We present multiple-epoch photometric monitoring in the $J$, $H$, and $K_s$ bands of the T1.5 dwarf 2MASS J21392676+0220226 (2M2139), revealing persistent, periodic ($P=7.721\pm$0.005 hr) variability with a peak-to-peak amplitude as high as 26% in the $J$-band. The light curve shape varies on a timescale of days, suggesting that evolving atmospheric cloud features are responsible. Using interpolations between model atmospheres with differing cloud thicknesses to represent a heterogeneous surface, we find that the multi-wavelength variations and the near-infrared spectrum of 2M2139 can be reproduced by either (1)cool, thick cloud features sitting above a thinner cloud layer, or (2)warm regions of low condensate opacity in an otherwise cloudy atmosphere, possibly indicating the presence of holes or breaks in the cloud layer. We find that temperature contrasts between thick and thin cloud patches must be greater than 175 K and as high as 425 K. We also consider whether the observed variability could arise from an interacting binary system, but this scenario is ruled out. 2M2139 joins the T2.5 dwarf SIMP0136 discovered by Artigau and coworkers as the second L/T transition brown dwarf to display large-amplitude variability on rotational timescales, suggesting that the fragmentation of dust clouds at the L/T transition may contribute to the abrupt decline in condensate opacity and $J$-band brightening observed to occur over this regime.

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arXiv2012

Close Companions to Young Stars. I. A Large Spectroscopic Survey in Chamaeleon I and Taurus-Auriga

We present the results of a multiplicity survey of 212 T Tauri stars in the Chamaeleon I and Taurus-Auriga star-forming regions, based on high-resolution spectra from the Magellan Clay 6.5 m telescope. From these data, we achieved a typical radial velocity precision of ~80 m/s with slower rotators yielding better precision, in general. For 174 of these stars, we obtained multi-epoch data with sufficient time baselines to identify binaries based on radial velocity variations. We identified eight close binaries and four close triples, of which three and two, respectively, are new discoveries. The spectroscopic multiplicity fractions we find for Cha I (7%) and Tau-Aur (6%) are similar to each other, and to the results of field star surveys in the same mass and period regime. However, unlike the results from imaging surveys, the frequency of systems with close companions in our sample is not seen to depend on primary mass. Additionally, we do not find a strong correlation between accretion and close multiplicity. This implies that close companions are not likely the main source of the accretion shut down observed in weak-lined T Tauri stars. Our results also suggest that sufficient radial velocity precision can be achieved for at least a subset of slowly rotating young stars to search for hot Jupiter planets.

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arXiv2011

Substellar Objects in Nearby Young Clusters (SONYC) IV: A census of very low mass objects in NGC1333

SONYC -- Substellar Objects in Nearby Young Clusters -- is a program to investigate the frequency and properties of young substellar objects with masses down to a few times that of Jupiter. Here we present a census of very low mass objects in the ~1 Myr old cluster NGC1333. We analyze near-infrared spectra taken with FMOS/Subaru for 100 candidates from our deep, wide-field survey and find 10 new likely brown dwarfs with spectral types of M6 or later. Among them, there are three with >~M9 and one with early L spectral type, corresponding to masses of 0.006 to <~0.02 Msol, so far the lowest mass objects identified in this cluster. The combination of survey depth, spatial coverage, and extensive spectroscopic follow-up makes NGC1333 one of the most comprehensively surveyed clusters for substellar objects. In total, there are now 51 objects with spectral type M5 or later and/or effective temperature of 3200 K or cooler identified in NGC1333; 30-40 of them are likely to be substellar. NGC1333 harbours about half as many brown dwarfs as stars, which is significantly more than in other well-studied star forming regions, thus raising the possibility of environmental differences in the formation of substellar objects. The brown dwarfs in NGC1333 are spatially strongly clustered within a radius of ~1 pc, mirroring the distribution of the stars. The disk fraction in the substellar regime is <66%, lower than for the total population (83%) but comparable to the brown dwarf disk fraction in other 2-3 Myr old regions.

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arXiv2011

Substellar Objects in Nearby Young Clusters (SONYC) V: New brown dwarfs in rho Ophiuchi

SONYC - Substellar Objects in Nearby Young Clusters - is a survey program to investigate the frequency and properties of substellar objects with masses down to a few times that of Jupiter in nearby star-forming regions. For the ~1Myr old rho Ophiuchi cluster, in our earlier paper we reported deep, wide-field optical and near-infrared imaging using Subaru, combined with 2MASS and Spitzer photometry, as well as follow-up spectroscopy confirming three likely cluster members, including a new brown dwarf with a mass close to the deuterium-burning limit. Here we present the results of extensive new spectroscopy targeting a total of ~100 candidates in rho Oph, with FMOS at the Subaru Telescope and SINFONI at the ESO's Very Large Telescope. We identify 19 objects with effective temperatures at or below 3200 K, 8 of which are newly identified very-low-mass probable members of rho Oph. Among these eight, six objects have Teff <= 3000 K, confirming their likely substellar nature. These six new brown dwarfs comprise one fifth of the known substellar population in ρOph. We estimate that the number of missing substellar objects in our survey area is ~15, down to 0.003 - 0.03 MSun and for Av = 0 - 15. The upper limit on the low-mass star to brown dwarf ratio in rho Oph is 5.1 +- 1.4, while the disk fractions are ~40% and ~60% for stars and BDs, respectively. Both results are in line with those for other nearby star forming regions.

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arXiv2011

High-contrast Imaging Search for Planets and Brown Dwarfs around the Most Massive Stars in the Solar Neighborhood

There has been a long-standing discussion in the literature as to whether core accretion or disk instability is the dominant mode of planet formation. Over the last decade, several lines of evidence have been presented showing that core accretion is most likely the dominant mechanism for the close-in population of planets probed by radial velocity and transits. However, this does not by itself prove that core accretion is the dominant mode for the total planet population, since disk instability might conceivably produce and retain large numbers of planets in the far-out regions of the disk. If this is a relevant scenario, then the outer massive disks of B-stars should be among the best places for massive planets and brown dwarfs to form and reside. In this study, we present high-contrast imaging of 18 nearby massive stars, of which 15 are in the B2--A0 spectral type range and provide excellent sensitivity to wide companions. By comparing our sensitivities to model predictions of disk instability based on physical criteria for fragmentation and cooling, and using Monte-Carlo simulations for orbital distributions, we find that ~85 % of such companions should have been detected in our images on average. Given this high degree of completeness, stringent statistical limits can be set from the null-detection result, even with the limited sample size. We find that <32 % of massive stars form and retain disk instability planets, brown dwarfs and very low-mass stars of <100 Mjup within 300 AU, at 99 % confidence. These results, combined with previous findings in the literature, lead to the conclusion that core accretion is likely the dominant mode of planet formation.

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arXiv2011

Broadband Transmission Spectroscopy of the super-Earth GJ 1214b suggests a Low Mean Molecular Weight Atmosphere

We used WIRCam on CFHT to observe four transits of the super-Earth GJ 1214b in the near-infrared. For each transit we observed in two bands nearly-simultaneously by rapidly switching the WIRCam filter wheel back and forth for the duration of the observations. By combining all our J-band (~1.25 microns) observations we find a transit depth in this band of 1.338\pm0.013% - a value consistent with the optical transit depth reported by Charbonneau and collaborators. However, our best-fit combined Ks-band (~2.15 microns) transit depth is deeper: 1.438\pm0.019%. Formally our Ks-band transits are deeper than the J-band transits observed simultaneously by a factor of 1.072\pm0.018 - a 4-sigma discrepancy. The most straightforward explanation for our deeper Ks-band depth is a spectral absorption feature from the limb of the atmosphere of the planet; for the spectral absorption feature to be this prominent the atmosphere of GJ 1214b must have a large scale height and a low mean molecular weight. That is, it would have to be hydrogen/helium dominated and this planet would be better described as a mini-Neptune. However, recently published observations from 0.78 - 1.0 microns, by Bean and collaborators, show a lack of spectral features and transit depths consistent with those obtained by Charbonneau and collaborators. The most likely atmospheric composition for GJ 1214b that arises from combining all these observations is less clear; if the atmosphere of GJ 1214b is hydrogen/helium dominated then it must have either a haze layer that is obscuring transit depth differences at shorter wavelengths, or significantly different spectral features than current models predict. Our observations disfavour a water-world composition, but such a composition will remain a possibility until observations reconfirm our deeper Ks-band transit depth or detect features at other wavelengths. [Abridged]

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arXiv2011

Substellar Objects in Nearby Young Clusters (SONYC) III: Chamaeleon-I

SONYC - Substellar Objects in Nearby Young Clusters - is a survey program to investigate the frequency and properties of substellar objects with masses down to a few times that of Jupiter in nearby star-forming regions. In this third paper, we present our recent results in the Chamaeleon-I star forming region. We have carried out deep optical and near-infrared imaging in four bands (I, z, J, Ks) using VIMOS on the ESO Very Large Telescope and SOFI on the New Technology Telescope, and combined our data with mid-infrared data from the Spitzer Space Telescope. The survey covers ~0.25 sqdeg on the sky, and reaches completeness limits of 23.0 in the I-band, 18.3 in the J-band, and 16.7 in Ks-band. Follow-up spectroscopy of the candidates selected from the optical photometry (I <~ 21) was carried out using the multi-object spectrograph VIMOS on the VLT. We identify 13 objects consistent with M spectral types, 11 of which are previously known M-dwarfs with confirmed membership in the cluster. The 2 newly reported objects have effective temperatures above the substellar limit. We also present two new candidate members of Chamaeleon-I, selected from our JK photometry combined with the Spitzer data. Based on the results of our survey, we estimate that the number of missing very-low-mass members down to ~0.008 MSun and Av <= 5 is <= 7, i.e. <= 3% of the total cluster population according to the current census.

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arXiv2011

Discovery of a ~23 Mjup Brown Dwarf Orbiting ~700 AU from the Massive Star HIP 78530 in Upper Scorpius

We present the discovery of a substellar companion on a wide orbit around the ~2.5 Msun star HIP 78530, which is a member of the 5 Myr-old Upper Scorpius association. We have obtained follow-up imaging over two years and show that the companion and primary share common proper motion. We have also obtained JHK spectroscopy of the companion and confirm its low surface gravity, in accordance with the young age of the system. A comparison with Drift-Phoenix synthetic spectra indicates an effective temperature of 2800+/-200 K and a comparison with template spectra of young and old dwarfs indicates a spectral type of M8+/-1. The mass of the companion is estimated to be 19-26 Mjup based on its bolometric luminosity and the predictions of evolutionary models. The angular separation of the companion is 4.5", which at the distance of the primary star, 156.7 pc, corresponds to a projected separation of ~710 AU. This companion features one of the lowest mass ratios (~0.009) of any known companion at separations greater than 100 AU.

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