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Title: Discovery of the secondary eclipse of HAT-P-11 b
Author: K. F. Huber, S. Czesla, J. H. M. M. Schmitt

We report the detection of the secondary eclipse of HAT-P-11 b, a Neptune-sized planet orbiting an active K4 dwarf. Using all available short-cadence data of the Kepler mission, we derive refined planetary ephemeris increasing their precision by more than an order of magnitude. Our simultaneous primary and secondary transit modelling results in improved transit and orbital parameters. In particular, the precise timing of the secondary eclipse allows to pin down the orbital eccentricity to 0.26459_{-0.00048}^{+0.00069}. The secondary eclipse depth of 6.09_{-1.11}^{+1.12} ppm corresponds to a 5.5sigma detection and results in a geometric albedo of 0.39±0.07 for HAT-P-11 b, close to Neptune's value, which may indicate further resemblances between these two bodies. Due to the substantial orbital eccentricity, the planetary equilibrium temperature is expected to change significantly with orbital position and ought to vary between 630° K and 950° K, depending on the details of heat redistribution in the atmosphere of HAT-P-11 b.

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Title: Water Vapour Absorption in the Clear Atmosphere of an exo-Neptune
Author: Jonathan Fraine, Drake Deming, Björn Benneke, Heather Knutson, Andrés Jordán, Néstor Espinoza, Nikku Madhusudhan, Ashlee Wilkins, Kamen Todorov

Transmission spectroscopy to date has detected atomic and molecular absorption in Jupiter-sized exoplanets, but intense efforts to measure molecular absorption in the atmospheres of smaller (Neptune-sized) planets during transits have revealed only featureless spectra. From this it was concluded that the majority of small, warm planets evolve to sustain high mean molecular weights, opaque clouds, or scattering hazes in their atmospheres, obscuring our ability to observe the composition of these atmospheres. Here we report observations of the transmission spectrum of HAT-P-11b (~4 Earth radii) from the optical to the infrared. We detected water vapour absorption at 1.4 micrometre wavelength. The amplitude of the water absorption (approximately 250 parts-per- million) indicates that the planetary atmosphere is predominantly clear down to ~1 mbar, and sufficiently hydrogen-rich to exhibit a large scale height. The spectrum is indicative of a planetary atmosphere with an upper limit of ~700 times the abundance of heavy elements relative to solar. This is in good agreement with the core accretion theory of planet formation, in which gas giant planets acquire their atmospheres by directly accreting hydrogen-rich gas from the protoplanetary nebulae onto a large rocky or icy core.

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Clear skies reveal water on distant Neptune-sized planet

A cloud-free atmosphere has allowed scientists to pick out signs of water vapour on a distant planet the size of Neptune: the smallest "exoplanet" ever to reveal its chemical composition.
Previously, only larger, Jupiter-like giants have been studied in this way.

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NASA Telescopes Find Clear Skies and Water Vapour on Exo-Neptune

Astronomers using data from three of NASA's space telescopes - Hubble, Spitzer, and Kepler - have discovered clear skies and steamy water vapour on a gaseous planet outside our solar system. The planet is about the size of Neptune, making it the smallest for which molecules of any kind have been detected.
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Title: Hint of 150 MHz radio emission from the Neptune-mass extrasolar transiting planet HAT-P-11b
Authors: A. Lecavelier des Etangs, S.K. Sirothia, Gopal-Krishna, P. Zarka

Since the radio-frequency emission from planets is expected to be strongly influenced by their interaction with the magnetic field and corona of the host star, the physics of this process can be effectively constrained by making sensitive measurements of the planetary radio emission. Up to now, however, numerous searches for radio emission from extrasolar planets at radio wavelengths have only yielded negative results. Here we report deep radio observations of the nearby Neptune-mass extrasolar transiting planet HAT-P-11b at 150 MHz, using the Giant Meterwave Radio Telescope (GMRT). On July 16, 2009, we detected a 3-sigma emission whose light curve is consistent with an eclipse when the planet passed behind the star. This emission is at a position 14 arcsec from the transiting exoplanet's coordinates; thus, with a synthetised beam of FWHM~16 arcsec, the position uncertainty of this weak radio signal encompasses the location of HAT-P-11. We estimate a 5% false positive probability that the observed radio light curve mimics the planet's eclipse light curve. If the faint signature is indeed a radio eclipse event associated with the planet, then its flux would be 3.87 mJy ± 1.29 mJy at 150 MHz. However, our equally sensitive repeat observations of the system on November 17, 2010 did not detect a significant signal in the radio light curve near the same position. This lack of confirmation leaves us with the possibility of either a variable planetary emission, or a chance occurrence of a false positive signal in our first observation. Deeper observations are required to confirm this hint of 150 MHz radio emission from HAT-P-11b.

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A network of small telescopes has bagged its smallest prize yet - and that's great news for astronomers.
HATNet's discovery of an extrasolar world only slightly bigger than Neptune helps prepare the way for an even more capable planet-hunter that could find alien Earths.
To date, more than 300 planets have been found orbiting other stars. Most of them were detected by measuring the gravitational wobble that the planet induces in its parent star. That method works great for huge planets, but not as well for smaller worlds.
The Harvard-Smithsonian Centre for Astrophysics' HATNet uses a different method: Six automated 4.3-inch telescopes in Hawaii and Arizona work together to watch for the ever-so-slight dimming of a star's light as a planet crosses in front of it.


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-- Edited by Blobrana on Saturday 2nd of January 2010 10:40:15 AM

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Astronomers at the Harvard-Smithsonian Center for Astrophysics have discovered a planet somewhat larger and more massive than Neptune orbiting a star 120 light-years from Earth. While Neptune has a diameter 3.8 times that of Earth and a mass 17 times Earth's, the new world (named HAT-P-11b) is 4.7 times the size of Earth and has 25 Earth masses.
HAT-P-11b was discovered because it passes directly in front of (transits) its parent star, thereby blocking about 0.4 percent of the star's light. This periodic dimming was detected by a network of small, automated telescopes known as "HATNet," which is operated by the Centre in Arizona and Hawaii. HAT-P-11b is the 11th extrasolar planet found by HATNet, and the smallest yet discovered by any of the several transit search projects underway around the world.

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Position(2000): RA = 19 50 50, Dec = +48 04 51

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HAT-P-11 b is located in the Cygnus constellation.

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Title: HAT-P-11b: A Super-Neptune Planet Transiting a Bright K Star in the Kepler Field
Authors: G. A. Bakos (1,2), G. Torres (1), A. Pál (1,4), J. Hartman (1), Géza Kovács (3), R. W. Noyes (1), D. W. Latham (1), D. D. Sasselov (1), B. Sipocz (1,4), G. A. Esquerdo (1), D. A. Fischer (5), J. A. Johnson (6), G. W. Marcy (7), R. P. Butler (8), H. Isaacson (5), A. Howard (7), S. Vogt (9), Gábor Kovács (1), J. Fernandez (1), A. Moór (3), R. P. Stefanik (1), J. Lázár (9), I. Papp (9), P. Sári (9), ((1) CfA, (2) NSF Fellow, (3) Konkoly Observatory, (4) ELTE, (5) SFSU, (6) IfA, (7) UC Berkeley, (8) Carnegie Institute of Washington, (9) UC Santa Cruz, (10) Hungarian Astronomical Association)

We report on the discovery of HAT-P-11b, the smallest radius transiting extrasolar planet (TEP), and the first hot Neptune discovered to date by transit searches. HAT-P-11b orbits the bright (V=9.59) and metal rich ([Fe=H] = +0.31 ±0.05) K4 dwarf star GSC 03561-02092 with P = 4.8878162 ±0.0000071 days and produces a transit signal with depth of 4.2 mmag; the shallowest found by transit searches that is due to a confirmed planet. We present a global analysis of the available photometric and radial-velocity data that result in stellar and planetary parameters, with simultaneous treatment of systematic variations. The planet, like its near-twin GJ 436b, is somewhat larger than Neptune (17 Mearth, 3.8 Rearth) both in mass Mp = 0.081 ±0.009 MJup (25.8 ±2.9 Mearth) and radius Rp = 0.422 ±0.014 RJup (4.73 ±0.16 Rearth). HAT-P-11b orbits in an eccentric orbit with e = 0.198 ±0.046 and omega = 355.2 ±17.3 deg, causing a reflex motion of its parent star with amplitude 11.6 ±1.2 m/s, a challenging detection due to the high level of chromospheric activity of the parent star. Our ephemeris for the transit events is Tc = 2454605.89132 ±0.00032 (BJD), with duration 0.0957 ±0.0012 d, and secondary eclipse epoch of 2454608.96 ±0.15 d (BJD). The basic stellar parameters of the host star are M* = 0.809 ±^0.020_0.027 Msun, R* = 0.752 ±0.021 Rsun and Teff = 4780 ±50 K. Importantly, HAT-P-11 will lie on one of the detectors of the forthcoming Kepler mission; this should make possible fruitful investigations of the detailed physical characteristic of both the planet and its parent star at unprecedented precision.

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