* Astronomy

Members Login
Post Info TOPIC: HD 149026 extrasolar planet


L

Posts: 131433
Date:
HD 149026b
Permalink  
 


Title: Analysis of Exoplanet HD 149026b Using BLISS Mapping
Authors: Kevin B. Stevenson, Joseph Harrington, Jonathan Fortney, Thomas J. Loredo, Ryan A. Hardy, Sarah Nymeyer, William C. Bowman, Patricio Cubillos, M. Oliver Bowman, Matthew Hardin

The dayside of HD 149026b is near the edge of detectability by the Spitzer Space Telescope. We report on eleven secondary-eclipse events at 3.6, 4.5, 3 x 5.8, 4 x 8.0, and 2 x 16 {\mu}m plus three primary transit events at 8.0 {\mu}m. Multiple observations at the longer wavelengths improved eclipse-depth signal-to-noise ratios by up to a factor of two and improved estimates of the planet-to-star radius ratio (Rp/Rs = 0.0517 ±0.0005). We also identify no significant deviations from a circular orbit and, using this model, report an improved period of 2.8758916 ±0.0000014 days. Chemical-equilibrium models find no indication of a temperature inversion in the dayside atmosphere of HD 149026b. Our best-fit model favours large amounts of CO and CO2, moderate heat redistribution (f=0.5), and a strongly enhanced metallicity. Brightness temperatures range from 1600 to 2000 K. These analyses use BiLinearly-Interpolated Subpixel Sensitivity (BLISS) mapping, a new technique to model two position-dependent systematics (intrapixel variability and pixelation). BLISS mapping outperforms previous methods in both speed and goodness of fit and does not require any free parameters. We also present an orthogonalization technique for linearly-correlated parameters that accelerates the convergence of Markov chains that employ the Metropolis random walk sampler.

Read more (2281kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: The 8 Micron Phase Variation of the Hot Saturn HD 149026b
Authors: Heather A. Knutson, David Charbonneau, Nicolas B. Cowan, Jonathan J. Fortney, Adam P. Showman, Eric Agol, Gregory W. Henry

We monitor the star HD 149026 and its Saturn-mass planet at 8.0 micron over slightly more than half an orbit using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We find an increase of 0.0227% ±0.0066% (3.4 sigma significance) in the combined planet-star flux during this interval. The minimum flux from the planet is 45% ±19% of the maximum planet flux, corresponding to a difference in brightness temperature of 480 ±140 K between the two hemispheres. We derive a new secondary eclipse depth of 0.0411% ±0.0076% in this band, corresponding to a dayside brightness temperature of 1440 ±150 K. Our new secondary eclipse depth is half that of a previous measurement (3.0 sigma difference) in this same bandpass by Harrington et al. (2007). We re-fit the Harrington et al. (2007) data and obtain a comparably good fit with a smaller eclipse depth that is consistent with our new value. In contrast to earlier claims, our new eclipse depth suggests that this planet's dayside emission spectrum is relatively cool, with an 8 micron brightness temperature that is less than the maximum planet-wide equilibrium temperature. We measure the interval between the transit and secondary eclipse and find that that the secondary eclipse occurs 20.9 +7.2 / -6.5 minutes earlier (2.9 sigma) than predicted for a circular orbit, a marginally significant result. This corresponds to e*cos(omega) = -0.0079 +0.0027 / -0.0025 where e is the planet's orbital eccentricity and omega is the argument of pericenter.

Read more (191kb, PDF)

__________________


L

Posts: 131433
Date:
HD 149026 b
Permalink  
 


With its giant rocky core and thick envelope of gas, the planet HD 149026b appears to break the rules of solar system evolution. But now two researchers think they've finally explained how this "hot Saturn" came about, and their findings reinforce the standard model of solar system formation that astronomers have been developing for nearly 2 decades.

Read more

__________________


L

Posts: 131433
Date:
HD 149026b
Permalink  
 


Title: Near-infrared transit photometry of the exoplanet HD 149026b
Authors: Joshua A. Carter, Joshua N. Winn, Ronald Gilliland, Matthew J. Holman

The transiting exoplanet HD 149026b is an important case for theories of planet formation and planetary structure, because the planet's relatively small size has been interpreted as evidence for a highly metal-enriched composition. We present observations of 4 transits with the Near Infrared Camera and Multi-Object Spectrometer on the Hubble Space Telescope, within a wavelength range of 1.1--2.0 \mu m. Analysis of the light curve gives the most precise estimate yet of the stellar mean density,
ho_\star = 0.497^{+0.042}_{-0.057} g cm^{-3}. By requiring agreement between the observed stellar properties (including
ho_\star) and stellar evolutionary models, we refine the estimate of the stellar radius: R_\star = 1.541^{+0.046}_{-0.042} R_\sun. We also find a deeper transit than has been measured at optical and mid-infrared wavelengths. Taken together, these findings imply a planetary radius of R_p = 0.813^{+0.027}_{-0.025} R_Jup, which is larger than earlier estimates. Models of the planetary interior still require a metal-enriched composition, although the required degree of metal enrichment is reduced. It is also possible that the deeper NICMOS transit is caused by wavelength-dependent absorption by constituents in the planet's atmosphere, although simple model atmospheres do not predict this effect to be strong enough to account for the discrepancy. We use the 4 newly-measured transit times to compute a refined transit ephemeris.

Read more  (545kb. PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Discovering the Growth Histories of Exoplanets: The Saturn Analog HD 149026b
Authors: Sarah E. Dodson-Robinson (1), Peter Bodenheimer (2) ((1) NASA Exoplanet Science Institute/Caltech, (2) UCO/Lick Observatory)

The transiting "hot Saturn" HD 149026b, which has the highest mean density of any confirmed planet in the Neptune-Jupiter mass range, has challenged theories of planet formation since its discovery in 2005. Previous investigations could not explain the origin of the planet's 67 Earth-mass solid core without invoking catastrophes such as gas giant collisions or heavy planetesimal bombardment launched by neighboring planets. Here we show that HD 149026b's large core can be successfully explained by the standard core accretion theory of planet formation. The keys to our reconstruction of HD 149026b are (1) applying a model of the solar nebula to describe the protoplanet nursery; (2) placing the planet initially on a long-period orbit at Saturn's heliocentric distance of 9.5 AU; and (3) adjusting the solid mass in the HD 149026 disk to twice that of the solar nebula in accordance with the star's heavy element enrichment. We show that the planet's migration into its current orbit at 0.042 AU is consistent with our formation model. Our study of HD 149026b demonstrates that it is possible to discover the growth history of any planet with a well-defined core mass that orbits a solar-type star.

Read more (343kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: A Precise Estimate of the Radius of HD 149026b
Authors: Philip Nutzman, David Charbonneau, Joshua N. Winn, Heather A. Knutson, Jonathan J. Fortney, Matthew J. Holman, Eric Agol

We present Spitzer 8 micron transit observations of the extrasolar planet system HD 149026. At this wavelength, transit light curves are weakly affected by stellar limb-darkening, allowing for a simpler and more accurate determination of planetary parameters. We measure a planet-star radius ratio of R_p/R_s = 0.05158 ± 0.00077, and in combination with ground-based data and independent constraints on the stellar mass and radius, we derive an orbital inclination of i = 85.4 +0.9/-0.8 deg. and a planet radius of 0.755 ± 0.040 Jupiter radii. These measurements further support models in which the planet is greatly enriched in heavy elements.

Read more (`26kb, PDF)

__________________


L

Posts: 131433
Date:
RE: HD 149026 extrasolar planet
Permalink  
 


Title: A Precise Estimate of the Radius of the Exoplanet HD 149026b from Spitzer Photometry
Authors: Philip Nutzman, David Charbonneau, Joshua N. Winn, Heather A. Knutson, Jonathan J. Fortney, Matthew J. Holman, Eric Agol

We present Spitzer 8 micron transit observations of the extrasolar planet HD 149026b. At this wavelength, transit light curves are weakly affected by stellar limb-darkening, allowing for a simpler and more accurate determination of planetary parameters. We measure a planet-star radius ratio of Rp/Rs = 0.05158 ± 0.00077, and in combination with ground-based data and independent constraints on the stellar mass and radius, we derive an orbital inclination of i = 85.4 +0.9/-0.8 degrees and a planet radius of Rp = 0.755 ± 0.040 R_jup. These measurements further support models in which the planet is greatly enriched in heavy elements.

Read more (119kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Five New Transits of the Super-Neptune HD 149026
Authors: Joshua N. Winn, Gregory W. Henry, Guillermo Torres, Matthew J. Holman

We present new photometry of HD 149026 spanning five transits of its "super-Neptune" planet. In combination with previous data, we improve upon the determination of the planet-to-star radius ratio: R_p/R_star = 0.0491^{+0.0018}_{-0.0005}. We find the planetary radius to be 0.71 ± 0.05 R_Jup, in accordance with previous theoretical models invoking a high metal abundance for the planet. The limiting error is the uncertainty in the stellar radius. Although we find agreement among four different ways of estimating the stellar radius, the uncertainty remains at 7%. We also present a refined transit ephemeris and a constraint on the orbital eccentricity and argument of pericenter, e cos(omega) = -0.0014 ± 0.0012, based on the measured interval between primary and secondary transits.

Read more (112kb, PDF)

__________________


L

Posts: 131433
Date:
HD 149026b
Permalink  
 


 It's a pretty good bet that even the crew of the Starship Enterprise wouldn't have had a category for HD 149026b. The planet is among the densest yet discovered, and new research shows it's by far the hottest and blackest. If the latest discoveries are any indication, lots of surprises await astronomers searching for alien worlds.
Since the first extrasolar planet was confirmed in 1995, astronomers have marvelled at the diversity of the 230-plus known worlds orbiting other suns. They have found planets that circle super-dense neutron stars  and that somehow survived or reconstituted themselves after a supernova. They have begun to detect and analyze rocky planets with atmospheres that possibly could support life. And a group has just clocked winds on a Jupiter-sized world blowing more than 30 times faster than the strongest winds on Earth, exceeding 10,000 kilometres per hour. The list of the weird grows almost weekly.

Read more

__________________


L

Posts: 131433
Date:
RE: HD 149026 extrasolar planet
Permalink  
 


Title: The formation of HD 149026 b
Authors: C. Broeg, G. Wuchterl

Today, many extrasolar planets have been detected. Some of them exhibit properties quite different from the planets in our solar system and they have eluded attempts to explain their formation. One such case is HD 149026 b. It was discovered by Sato et al. (2005) . A transit-determined orbital inclination results in a total mass of 114 earth masses. The unusually small radius can be explained by a condensible element core with an inferred mass of 67 earth masses for the best fitting theoretical model.
In the core accretion model, giant planets are assumed to form around a growing core of condensible materials. With increasing core mass, the amount of gravitationally bound envelope mass increases. This continues up to the so-called critical core mass -- the largest core allowing a hydrostatic envelope. For larger cores, the lack of static solutions forces a dynamic evolution of the protoplanet in the process accreting large amounts of gas or ejecting the envelope. This would prevent the formation of HD 149026 b.
By studying all possible hydrostatic equilibria we could show that HD 149026 b can remain hydrostatic up to the inferred heavy core. This is possible if it is formed in-situ in a relatively low-pressure nebula. This formation process is confirmed by fluid-dynamic calculations using the environmental conditions as determined by the hydrostatic models.
We present a quantitative in-situ formation scenario for the massive core planet HD 149026 b. Furthermore we predict a wide range of possible core masses for close-in planets like HD 149026 b. This is different from migration where typical critical core masses should be expected.

Read more (325kb, PDF)

__________________
1 2  >  Last»  | Page of 2  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard