Sebastian G. Els

Evidence for a Long-Period Planet Orbiting ϵ Eridani*

High-precision radial velocity (RV) measurements spanning the years 1980.8‐2000.0 are presented for the nearby (3.22 pc) K2 V star e Eri. These data, which represent a combination of six independent data sets taken with four different telescopes, show convincing variations with a period of …7 yr. A least-squares orbital solution using robust estimation yields orbital parameters of period yr, velocity amplitude m s 21 , ecP p 6.9 K p 19 centricity , projected companion mass , and semimajor axis

The Extrasolar Planet ϵ Eridani b: Orbit and Mass*

Hubble Space Telescope (HST) observations of the nearby (3.22 pc) K2 V star Eridani have been combined with ground-based astrometric and radial velocity data to determine the mass of its known companion. We model the astrometric and radial velocity measurements simultaneously to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size. Because of the long period of the companion, Eri b, we extend our astrometric coverage to a total of 14.94 yr (including the 3 yr span of the HST data) by including lower precision ground-based astrometry from the Allegheny Multichannel Astrometric Photometer. Radial velocities now span 1980.8-2006.3. We obtain a perturbation period, P = 6.85 ± 0.03 yr, semimajor axis α = 1.88 ± 0.20 mas, and inclination i = 301 ± 38. This inclination is consistent with a previously measured dust disk inclination, suggesting coplanarity. Assuming a primary mass M* = 0.83 M⊙, we obtain a companion mass M = 1.55MJ ± 0.24MJ. Given the relatively young age of Eri (~800 Myr), this accurate exoplanet mass and orbit can usefully inform future direct-imaging attempts. We predict the next periastron at 2007.3 with a total separation ρ = 03 at position angle P.A. = -27°. Orbit orientation and geometry dictate that Eri b will appear brightest in reflected light very nearly at periastron. Radial velocities spanning over 25 yr indicate an acceleration consistent with a Jupiter-mass object with a period in excess of 50 yr, possibly responsible for one feature of the dust morphology, the inner cavity.

Thirty Meter Telescope Site Testing I: Overview

As part of the conceptual and preliminary design processes of the Thirty Meter Telescope (TMT), the TMT site-testing team has spent the last five years measuring the atmospheric properties of five candidate mountains in North and South America with an unprecedented array of instrumentation. The site-testing period was preceded by several years of analyses selecting the five candidates: Cerros Tolar, Armazones and Tolonchar in northern Chile; San Pedro Martir in Baja California, Mexico; and the 13 North (13N) site on Mauna Kea, Hawaii. Site testing was concluded by the selection of two remaining sites for further consideration, Armazones and Mauna Kea 13N. It showed that all five candidates are excellent sites for an extremely large astronomical observatory and that none of the sites stands out as the obvious and only logical choice based on its combined properties. This is the first article in a series discussing the TMT site-testing project.

The planet search program at the ESO Coudé Echelle spectrometer - II. The

In this article we present the results of the planet search program carried out at the ESO Coudé Echelle Spectrometer (CES) for components A and B of the α Centauri system. Since November 1992 we have obtained high precision differential radial velocities (RV s) for both stars. We demonstrate that, after subtraction of the binary orbital motion, no additional residual RV signal is present within our detection limits, which could have been attributed to giant planets orbiting either of the two stars. We performed numerical simulations to determine the detection threshold of the CES survey for planets around both stars. In combination with known dynamical limitations for stable planetary orbits (Wiegert & Holman 1997) we can now set strong constraints on the existence of Jupiter-mass-type planets in the α Centauri system.

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The results of the characterization of precipitable water vapor in the atmospheric column carried out in the context of identifying potential sites for the deployment of the Thirty Meter Telescope (TMT) are pre- sented. Prior to starting the dedicated field campaign to look for a suitable site for the TMT, candidate sites were selected based on a climatology report utilizing satellite data that considered water vapor as one of the study vari- ables. These candidate sites are all of tropical or subtropical location at geographic areas dominated by high-pressure systems. The results of the detailed on-site study, spanning a period of 4 yr, from early 2004 until the end of 2007, confirmed the global mean statistics provided in the previous reports based on satellite data, and also confirmed that all the candidate sites are exceptionally good for astronomy research. At the locations of these sites, the atmospheric conditions are such that the higher the elevation of the site, the drier it gets. However, the data analysis shows that during winter, San Pedro Martir, a site about 230 m lower in elevation than Armazones, is drier than the Armazones site. This finding is attributed to the fact that Earths atmosphere is largely unsaturated, leaving room for regional variability; it is useful in illustrating the relevance of in situ atmospheric studies for understanding the global and seasonal variability of potential sites for astronomy research. The results also show that winter and spring are the driest seasons at all of the tested sites, with Mauna Kea (in the northern hemisphere) and Tolonchar (in the southern hemisphere) being the tested sites with the lowest precipitable water vapor in the atmospheric column and the highest atmospheric transmission in the near and mid-infrared bands. This is the tenth article in a series discussing the TMT site-testing project.

Centauri system: Limits for planetary companions

The results on the vertical distribution of optical turbulence above the five mountains which were investigated by the site testing for the Thirty Meter Telescope (TMT) are reported. On San Pedro Martir in Mexico; the 13 North site on Mauna Kea; and three mountains in northern Chile: Cerro Tolar, Cerro Armazones, and Cerro Tolonchar; MASS-DIMM turbulence profilers have been operated over at least two years. Acoustic turbulence profilers—SODARs—were also operated at these sites. The obtained turbulence profiles indicate that at all sites the lowest 200 m are the main source of the total seeing observed, with the Chilean sites showing a weaker ground layer than the other two sites. The two northern hemisphere sites have weaker turbulence at altitudes above 500 m, with 13N showing the weakest turbulence at 16 km, responsible for the large isoplanatic angle at this site. The influence of the jetstream and wind speeds close to the ground on the clear sky turbulence strength throughout the atmosphere are discussed, as well as seasonal and nocturnal variations. This is the sixth article in a series discussing the TMT site testing project.

Thirty Meter Telescope Site Testing X: Precipitable Water Vapor

In this article we present an analysis of the statistical and temporal properties of seeing and isoplanatic angle measurements obtained with combined Differential Image Motion Monitor (DIMM) and Multi-Aperture Scintillation Sensor (MASS) units at the Thirty Meter Telescope (TMT) candidate sites. For each of the five candidate sites we obtained multiyear, high-cadence, high-quality seeing measurements. These data allow for a broad and detailed analysis, giving us a good understanding of the characteristics of each of the sites. The overall seeing statistics for the five candidate sites are presented, broken into total seeing (measured by the DIMM), free-atmosphere seeing and isoplanatic angle (measured by the MASS), and ground-layer seeing (difference between the total and free-atmosphere seeing). We examine the statistical distributions of seeing measurements and investigate annual and nightly behavior. The properties of the seeing measurements are discussed in terms of the geography and meteorological conditions at each site. The temporal variability of the seeing measurements over timescales of minutes to hours is derived for each site. We find that each of the TMT candidate sites has its own strengths and weaknesses when compared against the other candidate sites. The results presented in this article form part of the full set of results that are used for the TMT site-selection process. This is the fifth article in a series discussing the TMT site-testing project.

Thirty Meter Telescope Site Testing VI: Turbulence Profiles

Differential image motion monitors (DIMMs) have become the industry standard for astronomical site characterization. The calibration of DIMMs is generally considered to be routine, but we show that particular care must be paid to this issue if high-accuracy measurements are to be achieved. In a side by side comparison of several DIMMs, we demonstrate that with proper care we can achieve an agreement between the seeing measurements of two DIMMS operating under the same conditions to better than +/-0.02 arc sec.

Thirty Meter Telescope Site Testing V: Seeing and Isoplanatic Angle

The optical turbulence conditions as measured between 2004 until end of 2008 above Cerro Tololo, their seasonal as well as nocturnal behavior are presented. A comparison with the MASS-DIMM system of the Thirty Meter Telescope site testing was conducted and identifies an artificially increased seeing component in the data collected by the CTIO DIMM system under northerly winds. Evidence is shown that this increased turbulence is caused by the telescope dome. A correction for this effect is attempted and applied to the CTIO DIMM data. The MASS data of this comparison campaign allow to set constraints on the general assumption of uniform turbulent layers above a site.

High-accuracy differential image motion monitor measurements for the Thirty Meter Telescope site testing program

Seeing stability is an important criterion of site characterization. Two sites, with the same seeing statistics, could in principle differ in their temporal stability and hence have their observatories perform differently. Temporal variability can, however, be defined in several ways, all of which may determine the performance of the observatories in different manner. In this paper, we propose three methods to measure variability each focusing on different applications: Selection (maximization of observation time), Image quality (seeing variation within a given integration time) and finally Scheduling (prediction of seeing fluctuation on a given time scale). We apply these methods to the seeing of the TMT candidate sites to determine their stability properties.