The HARPS-TERRA project I. Description of the algorithms, performance and new measurements on a few remarkable stars observed by HARPS
TL;DR: In this paper, the authors proposed an algorithm to obtain precision RV measurements using least-squares matching of each observed spectrum to a high signal-to-noise ratio template derived from the same observations.
Abstract: Doppler spectroscopy has uncovered or confirmed all the known planets orbiting nearby stars. Two main techniques are used to obtain precision Doppler measurements at optical wavelengths. The first approach is the gas cell method, which consists on the least-squares matching of the spectrum of Iodine imprinted on the spectrum of the star. The second method relies on the construction of a stabilized spectrograph externally calibrated in wavelength. The most precise stabilized spectrometer in operation is HARPS, operated by ESO in La Silla Observatory/Chile. The Doppler measurements obtained with HARPS are typically obtained using the Cross-Correlation Function technique (CCF). It consists of multiplying the stellar spectrum with a weighted binary mask and finding the minimum of such product as a function of the Doppler shift. It is known that CCF is suboptimal in exploiting the Doppler information in the stellar spectrum. Here, we describe an algorithm to obtain precision RV measurements using least-squares matching of each observed spectrum to a high signal-to-noise ratio template derived from the same observations. Such algorithm is implemented in our software called HARPS-TERRA (Template Enhanced Radial velocity Re-analysis Application). New radial velocity measurements on a representative sample of stars observed by HARPS is used to illustrate the benefits of the proposed method. We show that, compared to CCF, template matching provides a significant improvement in accuracy, specially when applied to M dwarfs.
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Queen Mary University of London1, Spanish National Research Council2, Open University3, Carnegie Institution for Science4, University of Göttingen5, University of Texas at Austin6, University of Chile7, University of Hertfordshire8, University of Warsaw9, Max Planck Society10, University of Montpellier11, Weizmann Institute of Science12, Heidelberg University13
TL;DR: Observations reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units.
Abstract: At a distance of 1.295 parsecs, the red dwarf Proxima Centauri (α Centauri C, GL 551, HIP 70890 or simply Proxima) is the Sun's closest stellar neighbour and one of the best-studied low-mass stars. It has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun and a mass of about 12 per cent of the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is about 83 days (ref. 3) and its quiescent activity levels and X-ray luminosity are comparable to those of the Sun. Here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface.
1,052 citations
Book•
01 May 2011TL;DR: In this paper, the authors present an overview of the solar system and its evolution, including the formation and evolution of stars, asteroids, and free-floating planets, as well as their internal and external structures.
Abstract: 1. Introduction 2. Radial velocities 3. Astrometry 4. Timing 5. Microlensing 6. Transits 7. Imaging 8. Host stars 9. Brown dwarfs and free-floating planets 10. Formation and evolution 11. Interiors and atmospheres 12. The Solar System Appendixes References Index.
527 citations
TL;DR: In this article, the authors proposed a new method to solve the problem of space-time anomaly detection in astronomy and astronomy postdoctoral fellowship (Award AST-1602597).
Abstract: National Science Foundation (U.S.). Astronomy and Astrophysics Postdoctoral Fellowship (Award AST-1602597)
281 citations
Cites methods from "The HARPS-TERRA project I. Descript..."
...We use a 5th-order Legendre polynomial to account for the continuum mismatch (e.g Anglada-Escudé & Butler 2012)....
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DOI•
01 May 2011TL;DR: An overview of the processes described in this chapter is as follows in this paper, where the authors start with star formation in molecular clouds, and then gravitationally accumulate their mantles of ice and/or gas.
Abstract: PLANETARY SYSTEMS, the solar system amongst them, are believed to form as inevitable and common byproducts of star formation For orientation, an overview of the processes described in this chapter is as follows The present paradigm starts with star formation in molecular clouds Brown dwarfs are formed as the lowmass tail of this process, although some may be formed as a high-mass tail of planet formation Gas and dust in the collapsing molecular cloud which does not fall directly onto the protostar resides in a relatively long-lived accretion disk which provides the environment for the subsequent stages of planet formation Terrestrial-mass planets are formed within the disk through the progressive agglomeration of material denoted, as it grows in size, as dust, rocks, planetesimals and protoplanets A similar process typically occurring further out in the disk results in the cores of giant planets, which then gravitationally accumulate their mantles of ice and/or gas As the planet-forming bodies grow in mass, growth and dynamics become more dominated by gravitational interactions Towards the final phases, and before the remaining gas is lost through accretion or dispersal, the gas provides a viscous medium at least partially responsible for planetary migration Some migration also occurs during these later stages as a result of gravitational scattering between the (proto-)planets and the residual sea of planetesimals The final structural stabilisation of the planetary system may be affected by planet–planet interactions, until a configuration emerges which may be dynamically stable over billions of years The current observational data for exoplanet systems is broadly compatible with this overall picture Other constraints come from a substantial body of detailed observations of the solar system (Chapter 12) Context and present paradigm An understanding of howplanets formis essential in understanding and interpreting the considerable range of observed planetary system architectures and dynamics Today, the most widely considered solar nebula theory holds that planet formation in the solar system, and by inference in other exoplanet systems, follows on from the process of star formation and accretion disk formation, through the agglomeration of residual material as the protoplanetary disk collapses and evolves
251 citations
University of Southern Queensland1, University of Toulouse2, Centre national de la recherche scientifique3, University of Göttingen4, University of Montpellier5, University of St Andrews6, Harvard University7, Federal University of Rio Grande do Norte8, Janssen Pharmaceutica9, Max Planck Society10, Bulgarian Academy of Sciences11, National Autonomous University of Mexico12, University of Liège13
TL;DR: In this article, the authors presented the results of a major high-resolution spectropolarimetric BCool project magnetic survey of 170 solar-type stars, including 67 stars with surface magnetic fields.
Abstract: We present the results of a major high-resolution spectropolarimetric BCool project magnetic survey of 170 solar-type stars. Surface magnetic fields were detected on 67 stars, with 21 classified as mature solar-type stars, a result that increases by a factor of 4 the number of mature solar-type stars on which magnetic fields have been observed. In addition, a magnetic fieldwasdetectedfor3outof18ofthesubgiantstarssurveyed.ForthepopulationofK-dwarfs, the mean value of |Bl| (|Bl|mean) was also found to be higher (5.7 G) than |Bl|mean measured for the G-dwarfs (3.2 G) and the F-dwarfs (3.3 G). For the sample as a whole, |Bl|mean increases with rotation rate and decreases with age, and the upper envelope for |Bl| correlates well with the observed chromospheric emission. Stars with a chromospheric S-index greater than about 0.2 show a high magnetic field detection rate and so offer optimal targets for future studies. This survey constitutes the most extensive spectropolarimetric survey of cool stars undertaken to date, and suggests that it is feasible to pursue magnetic mapping of a wide range of moderately active solar-type stars to improve our understanding of their surface fields and
191 citations
References
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Queen Mary University of London1, Spanish National Research Council2, Open University3, Carnegie Institution for Science4, University of Göttingen5, University of Texas at Austin6, University of Chile7, University of Hertfordshire8, University of Warsaw9, Max Planck Society10, University of Montpellier11, Weizmann Institute of Science12, Heidelberg University13
TL;DR: Observations reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units.
Abstract: At a distance of 1.295 parsecs, the red dwarf Proxima Centauri (α Centauri C, GL 551, HIP 70890 or simply Proxima) is the Sun's closest stellar neighbour and one of the best-studied low-mass stars. It has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun and a mass of about 12 per cent of the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is about 83 days (ref. 3) and its quiescent activity levels and X-ray luminosity are comparable to those of the Sun. Here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface.
1,052 citations
TL;DR: In this article, the authors present a catalog of nearby exoplanets, which contains the 172 known low-mass companions with orbits established through radial velocity and transit measurements around stars within 200 pc, including five previously unpublished ex-oplanets orbiting the stars HD 11964, HD 66428, HD 99109, HD 107148 and HD 164922.
Abstract: We present a catalog of nearby exoplanets. It contains the 172 known low-mass companions with orbits established through radial velocity and transit measurements around stars within 200 pc. We include five previously unpublished exoplanets orbiting the stars HD 11964, HD 66428, HD 99109, HD 107148, and HD 164922. We update orbits for 83 additional exoplanets, including many whose orbits have not been revised since their announcement, and include radial velocity time series from the Lick, Keck, and Anglo-Australian Observatory planet searches. Both these new and previously published velocities are more precise here due to improvements in our data reduction pipeline, which we applied to archival spectra. We present a brief summary of the global properties of the known exoplanets, including their distributions of orbital semimajor axis, minimum mass, and orbital eccentricity.
968 citations
"The HARPS-TERRA project I. Descript..." refers background or methods or result in this paper
...Let us note that, because the data used in (Butler et al. 2006) was restricted to fewer measurements, the orbital solution presented there (only RV) was already quite different from the one reported by Hatzes et al. (2000) and Benedict et al. (2006)....
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...The six data sets available to the date are provided in the current distribution of SYSTEMIC and were extracted from Benedict et al. (2006) and Butler et al. (2006)....
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...ǫ Eridani is a K3V star of approximately 0.82 M⊙ (Butler et al. 2006) and a close neigh- bor to the Sun (3.2 pc). ǫ Eridani was first reported to be RV variable by (Campbell et al. 1988) and (Walker et al. 1995) explicitly reported a possible variability with a period between 5 and 10 years....
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...The obtained solution is significantly different to the one reported by Hatzes et al. (2000), Benedict et al. (2006) or Butler et al. (2006)....
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Book•
01 May 2011TL;DR: In this paper, the authors present an overview of the solar system and its evolution, including the formation and evolution of stars, asteroids, and free-floating planets, as well as their internal and external structures.
Abstract: 1. Introduction 2. Radial velocities 3. Astrometry 4. Timing 5. Microlensing 6. Transits 7. Imaging 8. Host stars 9. Brown dwarfs and free-floating planets 10. Formation and evolution 11. Interiors and atmospheres 12. The Solar System Appendixes References Index.
527 citations
TL;DR: In this article, an analysis of 11 years of precision radial velocity measurements of 76 nearby solar-type stars from the Lick radial velocity survey is presented, where the authors report on variability, periodicity, and long-term velocity trends.
Abstract: We present an analysis of 11 yr of precision radial velocity measurements of 76 nearby solar-type stars from the Lick radial velocity survey. For each star, we report on variability, periodicity, and long-term velocity trends. Our sample of stars contains eight known companions with mass less than 8 (M p sin i) Jupiter masses six of which were discovered at Lick. For the remaining stars, we place upper limits (M J ), on the companion mass as a function of orbital period. For most stars, we can exclude companions with velocity amplitude m s~1 at the 99% level, or for orbital radii K Z 20 M p sin i Z 0.7M J (a/AU)1@2 a ( 5 AU. We examine the implications of our results for the observed distribution of mass and orbital radius of companions. We show that the combination of intrinsic stellar variability and measurement errors most likely explains why all con—rmed companions so far have m s~1. The —nite duration of the K Z 40 observations limits detection of Jupiter-mass companions to AU. Thus it remains possible that the a ( 3 majority of solar-type stars harbor Jupiter-mass companions much like our own, and if so these com- panions should be detectable in a few years. It is striking that more massive companions with are rare at orbital radii 4¨6 AU; we could have detected such objects in D90% of stars, M p sin i ( 3M J yet found none. The observed companions show a ii piling-up ˇˇ toward small orbital radii, and there is a paucity of con—rmed and candidate companions with orbital radii between D0.2 and D1 AU. The small number of con—rmed companions means that we are not able to rule out selection eUects as the cause of these features. We show that the traditional method for detecting periodicities, the Lomb-Scargle perio- dogram, fails to account for statistical —uctuations in the mean of a sampled sinusoid, making it non- robust when the number of observations is small, the sampling is uneven, or for periods comparable to or greater than the duration of the observations. We adopt a ii —oating-mean ˇˇ periodogram, in which the zero point of the sinusoid is allowed to vary during the —t. We discuss in detail the normalization of the periodogram and the probability distribution of periodogram powers. We stress that the three diUer- ent prescriptions in the literature for normalizing the periodogram are statistically equivalent and that it is not possible to write a simple analytic form for the false alarm probability, making Monte Carlo methods essential. Subject headings: binaries: spectroscopicmethods: statisticalplanetary systems
366 citations
"The HARPS-TERRA project I. Descript..." refers background in this paper
...A 6.9 years periodicity was first reported in Cumming et al. (1999) but, at that time, it was considered suspicious given the high chromospheric activity on the star....
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TL;DR: In this article, a spectral window function is used to compare the amplitude and phase of predicted aliases with peaks present in the spectral window to distinguish true periods from aliases, and the authors apply it to confirm prior alias distinctions for the planets GJ 876 d and HD 75898 b.
Abstract: Radial velocity measurements of stellar reflex motion have revealed many extrasolar planets, but gaps in the observations produce aliases, spurious frequencies that are frequently confused with the planets' orbital frequencies. In the case of Gl 581 d, the distinction between an alias and the true frequency was the distinction between a frozen, dead planet and a planet possibly hospitable to life. To improve the characterization of planetary systems, we describe how aliases originate and present a new approach for distinguishing between orbital frequencies and their aliases. Our approach harnesses features in the spectral window function to compare the amplitude and phase of predicted aliases with peaks present in the data. We apply it to confirm prior alias distinctions for the planets GJ 876 d and HD 75898 b. We find that the true periods of Gl 581 d and HD 73526 b/c remain ambiguous. We revise the periods of HD 156668 b and 55 Cnc e, which were afflicted by daily aliases. For HD 156668 b, the correct period is 1.2699 days and the minimum mass is (3.1 ± 0.4) M ⊕. For 55 Cnc e, the correct period is 0.7365 days—the shortest of any known planet—and the minimum mass is (8.3 ± 0.3) M ⊕. This revision produces a significantly improved five-planet Keplerian fit for 55 Cnc, and a self-consistent dynamical fit describes the data just as well. As radial velocity techniques push to ever-smaller planets, often found in systems of multiple planets, distinguishing true periods from aliases will become increasingly important.
299 citations
"The HARPS-TERRA project I. Descript..." refers background in this paper
...This is characteristic of long period signals aliased with the seasonal availability of the star (see Dawson & Fabrycky 2010, for a detailed discussion of the yearly alias)....
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