We report Doppler measurements of the stars HD 187085 and HD 20782 which indicate two high eccentricity low-mass companions to the stars. We find HD 187085 has a Jupiter-mass companion with a ∼1000-d ...orbit. Our formal ‘best-fitting’ solution suggests an eccentricity of 0.47, however, it does not sample the periastron passage of the companion and we find that orbital solutions with eccentricities between 0.1 and 0.8 give only slightly poorer fits (based on rms and χ2ν) and are thus plausible. Observations made during periastron passage in 2007 June should allow for the reliable determination of the orbital eccentricity for the companion to HD 187085. Our data set for HD 20782 does sample periastron and so the orbit for its companion can be more reliably determined. We find the companion to HD 20782 has M sin i= 1.77 ± 0.22 MJup, an orbital period of 595.86 ± 0.03 d and an orbit with an eccentricity of 0.92 ± 0.03. The detection of such high-eccentricity (and relatively low-velocity amplitude) exoplanets appears to be facilitated by the long-term precision of the Anglo-Australian Planet Search. Looking at exoplanet detections as a whole, we find that those with higher eccentricity seem to have relatively higher velocity amplitudes indicating higher mass planets and/or an observational bias against the detection of high-eccentricity systems.
We discuss how to read a planet's spectrum to assess its habitability and search for the signatures of a biosphere. After a decade rich in giant exoplanet detections, observation techniques have ...advanced to a level where we now have the capability to find planets of less than 10 Earth masses (M(Earth)) (so-called "super Earths"), which may be habitable. How can we characterize those planets and assess whether they are habitable? This new field of exoplanet search has shown an extraordinary capacity to combine research in astrophysics, chemistry, biology, and geophysics into a new and exciting interdisciplinary approach to understanding our place in the Universe. The results of a first-generation mission will most likely generate an amazing scope of diverse planets that will set planet formation, evolution, and our planet into an overall context.
We report precise Doppler measurements of the stars HD 216437, HD 196050 and HD 160691 obtained with the Anglo-Australian Telescope using the UCLES spectrometer together with an iodine cell as part ...of the Anglo-Australian Planet Search. Our measurements reveal periodic Keplerian velocity variations that we interpret as evidence for planets in orbit around these solar type stars. HD 216437 has a period of 1294 ± 250 d, a semi-amplitude of 38 ± 3 m s−1 and an eccentricity of 0.33 ± 0.09. The minimum (M sin i) mass of the companion is 2.1 ± 0.3 MJUP and the semi-major axis is 2.4 ± 0.5 au. HD 196050 has a period of 1300 ± 230 d, a semi-amplitude of 49 ± 8 m s−1 and an eccentricity of 0.19 ± 0.09. The minimum mass of the companion is 2.8 ± 0.5 MJUP and the semi-major axis is 2.4 ± 0.5 au. We also report further observations of the metal-rich planet bearing star HD 160691. Our new solution confirms the previously reported planet and shows a trend indicating a second, longer-period companion. These discoveries add to the growing numbers of mildly eccentric, long-period extrasolar planets around metal-rich Sun-like stars.
New Planets around Three G Dwarfs O’Toole, Simon J; Butler, R. Paul; Tinney, C. G ...
Astrophysical journal/The Astrophysical journal,
05/2007, Volume:
660, Issue:
2
Journal Article
Peer reviewed
Open access
Doppler velocity measurements from the Anglo-Australian Planet Search reveal planetary mass companions to HD 23127, HD 159868, and a possible second planetary companion to HD 154857. These stars are ...all G dwarfs. The companions are all in eccentric orbits with periods ranging from 1.2 to >9.3 yr, minimum (Msin t) masses ranging from 1.5 to >4.5 M sub(J), and semimajor axes between 1 and >4.5 AU. The orbital parameters are updated for the inner planet to HD 154857, while continued monitoring of the outer companion is required to confirm its planet status.
Multiple Companions to HD 154857 and HD 160691 McCarthy, Chris; Butler, R. Paul; Tinney, C. G ...
Astrophysical journal/The Astrophysical journal,
12/2004, Volume:
617, Issue:
1
Journal Article
Peer reviewed
Open access
Precise Doppler measurements from the Anglo-Australian Telescope (AAT) UCLES spectrometer reveal two companions to both HD 154857 and HD 160691. The inner companion to HD 154857 has a period of 398 ...days, an eccentricity of 0.51, and a minimum mass of 1.8M sub(J). An outer companion has a period much longer than 2 yr and is currently detected only as a linear trend of 14 m s super(-1) yr super(-1). The inner companion to HD 160691, previously announced from AAT data, has a period of 645 days, an eccentricity of 0.20, and a minimum mass of 1.7M sub(J). For the outer planet, whose orbit is less well constrained, a two-Keplerian fit yields a period of 8.2 yr, an eccentricity of 0.57, and a minimum mass of 3.1M sub(J). With these orbital parameters, its maximum separation from the star of 0".4 makes it a viable target for direct imaging.
We report the detection of three new low-mass planets from the Anglo-Australian Planet Search. The three parent stars of these planets are chromospherically quiet main-sequence G dwarfs with ...metallicities ranging from roughly solar (HD 117618 and HD 208487) to metal enriched (HD 102117). The orbital periods range from 20.8 to 130 days, the minimum masses from roughly 0.5M sub(Sat) to 0.5M sub(Jup), and the eccentricities from 0.08 to 0.37, with the planet in the smallest orbit (HD 102117) having the smallest eccentricity. With semiamplitudes of 10.6-19 m s super(-1), these planets induce Doppler amplitudes similar to those of Jupiter analogs, albeit with shorter periods. Many of the most interesting future Doppler planets will be detected at these semiamplitude levels, placing a premium on measurement precision. The detection of such amplitudes in data extending back 6 yr gives confidence in the Anglo-Australian Planet Search's ability to detect Jupiter analogs as our time baseline extends to 12 yr. We discuss the criticality of such detections for the design of the next generation of extremely large telescopes and also highlight prospects for suitable observing strategies to push to below 1 m s super(-1) precisions for bright stars in a search for sub-Neptunian planets.
After Earth's origin, our host star, the Sun, was shining 20-25% less brightly than today. Without greenhouse-like conditions to warm the atmosphere, our early planet would have been an ice ball, and ...life may never have evolved. But life did evolve, which indicates that greenhouse gases must have been present on early Earth to warm the planet. Evidence from the geological record indicates an abundance of the greenhouse gas CO(2). CH(4) was probably present as well; and, in this regard, methanogenic bacteria, which belong to a diverse group of anaerobic prokaryotes that ferment CO(2) plus H(2) to CH(4), may have contributed to modification of the early atmosphere. Molecular oxygen was not present, as is indicated by the study of rocks from that era, which contain iron carbonate rather than iron oxide. Multicellular organisms originated as cells within colonies that became increasingly specialized. The development of photosynthesis allowed the Sun's energy to be harvested directly by life-forms. The resultant oxygen accumulated in the atmosphere and formed the ozone layer in the upper atmosphere. Aided by the absorption of harmful UV radiation in the ozone layer, life colonized Earth's surface. Our own planet is a very good example of how life-forms modified the atmosphere over the planets' lifetime. We show that these facts have to be taken into account when we discover and characterize atmospheres of Earth-like exoplanets. If life has originated and evolved on a planet, then it should be expected that a strong co-evolution occurred between life and the atmosphere, the result of which is the planet's climate.
On the Double-Planet System around HD 83443 Butler, R. Paul; Marcy, Geoffrey W; Vogt, Steven S ...
Astrophysical journal/The Astrophysical journal,
10/2002, Volume:
578, Issue:
1
Journal Article
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