Improving planet-finding spectrometers Crepp, Justin R
Science (American Association for the Advancement of Science),
11/2014, Letnik:
346, Številka:
6211
Journal Article
Recenzirano
Odprti dostop
Adaptive optics will enhance the precision of exoplanet surveys
Adaptive optics (AO) systems correct for optical wavefront errors introduced by Earth's turbulent atmosphere, turning initially blurry ...images into intense diffraction-limited concentrations of light. The implementation of AO systems on the world's largest telescopes has revolutionized essentially all areas of astronomy (
1
). Instruments that receive a well-corrected beam of light can operate as if observing from space and thus benefit from an order-of-magnitude higher spatial and spectral resolution (see the figure). Given the benefits of working with nonfuzzy images, it may therefore be surprising to learn that one of the most important techniques for finding extrasolar planets, the Doppler radial velocity method, still uses “seeing-limited” observations—that is, measurements obtained without AO correction.
Abstract
We used high-precision radial velocity measurements of FGKM stars to determine the occurrence of giant planets as a function of orbital separation spanning 0.03–30 au. Giant planets are more ...prevalent at orbital distances of 1–10 au compared to orbits interior or exterior of this range. The increase in planet occurrence at ∼1 au by a factor of ∼4 is highly statistically significant. A fall-off in giant planet occurrence at larger orbital distances is favored over models with flat or increasing occurrence. We measure
14.1
−
1.8
+
2.0
giant planets per 100 stars with semimajor axes of 2–8 au and
8.9
−
2.4
+
3.0
giant planets per 100 stars in the range 8–32 au, a decrease in occurrence with increasing orbital separation that is significant at the ∼2
σ
level. We find that the occurrence rate of sub-Jovian planets (0.1–1 Jupiter masses) is also enhanced for 1–10 au orbits. This suggests that lower-mass planets may share the formation or migration mechanisms that drive the increased prevalence near the water–ice line for their Jovian counterparts. Our measurements of cold gas giant occurrence are consistent with the latest results from direct imaging surveys and gravitational lensing surveys despite different stellar samples. We corroborate previous findings that giant planet occurrence increases with stellar mass and metallicity.
In this paper we search for distant massive companions to known transiting gas giant planets that may have influenced the dynamical evolution of these systems. We present new radial velocity ...observations for a sample of 51 planets obtained using the Keck HIRES instrument, and find statistically significant accelerations in fifteen systems. Six of these systems have no previously reported accelerations in the published literature: HAT-P-10, HAT-P-22, HAT-P-29, HAT-P-32, WASP-10, and XO-2. We combine our radial velocity fits with Keck NIRC2 adaptive optics (AO) imaging data to place constraints on the allowed masses and orbital periods of the companions responsible for the detected accelerations. The estimated masses of the companions range between 1-500 M sub(Jup), with orbital semi-major axes typically between 1-75 AU. A significant majority of the companions detected by our survey are constrained to have minimum masses comparable to or larger than those of the transiting planets in these systems, making them candidates for influencing the orbital evolution of the inner gas giant. We estimate a total occurrence rate of 51% + or - 10% for companions with masses between 1-13 M sub(Jup) and orbital semi-major axes between 1-20 AU in our sample. We find no statistically significant difference between the frequency of companions to transiting planets with misaligned or eccentric orbits and those with well-aligned, circular orbits. We combine our expanded sample of radial velocity measurements with constraints from transit and secondary eclipse observations to provide improved measurements of the physical and orbital characteristics of all of the planets included in our survey.
ABSTRACT Stellar companions can influence the formation and evolution of planetary systems, but there are currently few observational constraints on the properties of planet-hosting binary star ...systems. We search for stellar companions around 77 transiting hot Jupiter systems to explore the statistical properties of this population of companions as compared to field stars of similar spectral type. After correcting for survey incompleteness, we find that of hot Jupiter systems have stellar companions with semimajor axes between 50 and 2000 au. This is 2.9 times larger than the field star companion fraction in this separation range, with a significance of . In the 1-50 au range, only of hot Jupiters host stellar companions, compared to the field star value of , which is a difference. We find that the distribution of mass ratios for stellar companions to hot Jupiter systems peaks at small values and therefore differs from that of field star binaries which tend to be uniformly distributed across all mass ratios. We conclude that either wide separation stellar binaries are more favorable sites for gas giant planet formation at all separations, or that the presence of stellar companions preferentially causes the inward migration of gas giant planets that formed farther out in the disk via dynamical processes such as Kozai-Lidov oscillations. We determine that less than 20% of hot Jupiters have stellar companions capable of inducing Kozai-Lidov oscillations assuming initial semimajor axes between 1 and 5 au, implying that the enhanced companion occurrence is likely correlated with environments where gas giants can form efficiently.
Doppler-based planet surveys have discovered numerous giant planets but are incomplete beyond several AU. At larger star-planet separations, direct planet detection through high-contrast imaging has ...proven successful, but this technique is sensitive only to young planets and characterization relies upon theoretical evolution models. Here we demonstrate that radial velocity measurements and high-contrast imaging can be combined to overcome these issues. The presence of widely separated companions can be deduced by identifying an acceleration (long-term trend) in the radial velocity of a star. By obtaining high spatial resolution follow-up imaging observations, we rule out scenarios in which such accelerations are caused by stellar binary companions with high statistical confidence. We report results from an analysis of Doppler measurements of a sample of 111 M-dwarf stars with a median of 29 radial velocity observations over a median time baseline of 11.8 yr. By targeting stars that exhibit a radial velocity acceleration ("trend") with adaptive optics imaging, we determine that 6.5% + or - 3.0% of M-dwarf stars host one or more massive companions with 1 < m/M sub(J) < 13 and 0 < a < 20 AU. These results are lower than analyses of the planet occurrence rate around higher-mass stars. We find the giant planet occurrence rate is described by a double power law in stellar mass M and metallicity F identical with Fe/H such that f(M, F) = 0.039 super(+0.056) sub(-0.028) M super(0.8+1.1-0.9)10 super((3.8+ or -1.2))F. Our results are consistent with gravitational microlensing measurements of the planet occurrence rate; this study represents the first model-independent comparison with microlensing observations.
Correlations between stellar properties and the occurrence rate of exoplanets can be used to inform the target selection of future planet-search efforts and provide valuable clues about the ...planet-formation process. We analyze a sample of 1266 stars drawn from the California Planet Survey targets to determine the empirical functional form describing the likelihood of a star harboring a giant planet as a function of its mass and metallicity. Our stellar sample ranges from M dwarfs with masses as low as0.2 M
⊙
0.2
M
⊙
to intermediate-mass subgiants with masses as high as1.9 M
⊙
1.9
M
⊙
. In agreement with previous studies, our sample exhibits a planet-metallicity correlation at all stellar masses; the fraction of stars that harbor giant planets scales as
f ∝ 101.2Fe/H
f
∝
10
1.2
Fe
/
H
. We can rule out a flat metallicity relationship among our evolved stars (at 98% confidence), which argues that the high metallicities of stars with planets is not likely due to convective envelope “pollution.” Our data also rule out a constant planet occurrence rate forFe/H < 0
Fe
/
H
<
0
, indicating that giant planets continue to become rarer at sub-Solar metallicities. We also find that planet occurrence increases with stellar mass (
f ∝ M
⋆
f
∝
M
⋆
), characterized by a rise from 3% around M dwarfs (0.5 M
⊙
0.5
M
⊙
) to 14% around A stars (2 M
⊙
2
M
⊙
), at Solar metallicity. We argue that the correlation between stellar properties and giant planet occurrence is strong supporting evidence of the core-accretion model of planet formation.
ABSTRACT The mass and age of substellar objects are degenerate parameters leaving the evolutionary state of brown dwarfs ambiguous without additional information. Theoretical models are normally used ...to help distinguish between old, massive brown dwarfs and young, low-mass brown dwarfs but these models have yet to be properly calibrated. We have carried out an infrared high-contrast imaging program with the goal of detecting substellar objects as companions to nearby stars to help break degeneracies in inferred physical properties such as mass, age, and composition. Rather than using imaging observations alone, our targets are pre-selected based on the existence of dynamical accelerations informed from years of stellar radial velocity (RV) measurements. In this paper, we present the discovery of a rare benchmark brown dwarf orbiting the nearby (d = 18.69 0.19 pc), solar-type (G9V) star HD 4747 (Fe/H = −0.22 0.04) with a projected separation of only = 11.3 0.2 au (θ = 0 6). Precise Doppler measurements taken over 18 years reveal the companion's orbit and allow us to place strong constraints on its mass using dynamics ( ). Relative photometry (ΔKs = 9.05 0.14, , ) indicates that HD 4747 B is most likely a late-type L-dwarf and, if near the L/T transition, an intriguing source for studying cloud physics, variability, and polarization. We estimate a model-dependent mass of for an age of Gyr based on gyrochronology. Combining astrometric measurements with RV data, we calculate the companion dynamical mass ( ) and orbit (e = 0.740 0.002) directly. As a new mass, age, and metallicity benchmark, HD 4747 B will serve as a laboratory for precision astrophysics to test theoretical models that describe the emergent radiation of brown dwarfs.
An Earth-Sized Planet in the Habitable Zone of a Cool Star Quintana, Elisa V.; Barclay, Thomas; Raymond, Sean N. ...
Science (American Association for the Advancement of Science),
04/2014, Letnik:
344, Številka:
6181
Journal Article
Recenzirano
Odprti dostop
The quest for Earth-like planets is a major focus of current exoplanet research. Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too ...close to their host star to allow liquid water on their surfaces. We present the detection of Kepler-186f, a 1.11 ± 0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47 ± 0.05 solar-radius star. The intensity and spectrum of the star's radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form.
ABSTRACT We conducted a Doppler survey at Keck combined with NIRC2 K-band adaptive optics (AO) imaging to search for massive, long-period companions to 123 known exoplanet systems with one or two ...planets detected using the radial velocity (RV) method. Our survey is sensitive to Jupiter-mass planets out to 20 au for a majority of stars in our sample, and we report the discovery of eight new long-period planets, in addition to 20 systems with statistically significant RV trends that indicate the presence of an outer companion beyond 5 au. We combine our RV observations with AO imaging to determine the range of allowed masses and orbital separations for these companions, and account for variations in our sensitivity to companions among stars in our sample. We estimate the total occurrence rate of companions in our sample to be 52 5% over the range 1-20 MJup and 5-20 au. Our data also suggest a declining frequency for gas giant planets in these systems beyond 3-10 au, in contrast to earlier studies that found a rising frequency for giant planets in the range 0.01-3 au. This suggests either that the frequency of gas giant planets peaks between 3 and 10 au, or that outer companions in these systems have a different semi-major axis distribution than the overall population of gas giant planets. Our results also suggest that hot gas giants may be more likely to have an outer companion than cold gas giants. We find that planets with an outer companion have higher average eccentricities than their single counterparts, suggesting that dynamical interactions between planets may play an important role in these systems.
We report the discovery and confirmation of a transiting circumbinary planet (PH1b) around KIC 4862625, an eclipsing binary in the Kepler field. The planet was discovered by volunteers searching the ...first six Quarters of publicly available Kepler data as part of the Planet Hunters citizen science project. Transits of the planet across the larger and brighter of the eclipsing stars are detectable by visual inspection every ~ 137 days, with seven transits identified in Quarters 1-11. The physical and orbital parameters of both the host stars and planet were obtained via a photometric-dynamical model, simultaneously fitting both the measured radial velocities and the Kepler light curve of KIC 4862625. The 6.18 + or - 0.17 R sub(+ in circle) planet orbits outside the 20 day orbit of an eclipsing binary consisting of an F dwarf (1.734 + or - 0.044 R sub(middot in circle), 1.528 + or - 0.087 M sub(middot in circle)) and M dwarf (0.378 + or - 0.023 R sub(middot in circle), 0.408 + or - 0.024 M sub(middot in circle)). For the planet, we find an upper mass limit of 169 M sub(+ in circle) (0.531 Jupiter masses) at the 99.7% confidence level. With a radius and mass less than that of Jupiter, PH1b is well within the planetary regime. Outside the planet's orbit, at ~ 1000 AU, a previously unknown visual binary has been identified that is likely bound to the planetary system, making this the first known case of a quadruple star system with a transiting planet.
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