Atmosphere of HD 189733 Ab

Cloudy Atmosphere of the Extra-solar Planet HD189733b : A Possible Explanation of the Detected B-band Polarization
http://arxiv.org/abs/0807.1794

Abstract wrote:

The peak amplitude of linear polarization detected recently from an extrasolar hot giant planet HD 189733b, is a few times of $10^{-4}$, more than an order of magnitude higher than all theoretical predictions. Rayleigh scattering off $H_2$ and $He$ may although give rise to a planet-star flux ratio of the order of $10^{-4}$ in the blue band, it cannot account for the high polarization unless the planet has an unusually extended atmosphere. Therefore, it is suggested that the high polarization should be attributed to the presence of a thin cloud of sub-micron size dust grains in the upper visible atmosphere which supports the observational finding of an almost feature-less transmission spectrum in the optical with no indication of the expected alkaline absorption features. It is found that the polarimetry observation allows for a small eccentricity of the orbit that is predicted from the time delay of the secondary eclipse of the planet. The estimated longitude of the ascending node is $16^o\pm6$ which interestingly coincides with the observationally inferred location of the peak hemisphere-integrated brightness.

Interesting

What's really neat about these polarimetry observations is that they give you the longitude of the ascending node, which means for a transiting planet, the orbit can be fully specified in 3D.

Lazarus wrote:

What's really neat about these polarimetry observations is that they give you the longitude of the ascending node, which means for a transiting planet, the orbit can be fully specified in 3D.

Indeed, which has been done only for HD 189733 b so far.

Quote :

A ground-based near-infrared emission spectrum of the exoplanet HD 189733b p637
Infrared spectroscopy can probe the conditions and compositions of exoplanet atmospheres. Previous results relied on space-based telescopes that do not provide spectroscopic capability in the 2.4–5.2 μm spectral region. Here, ground-based observations of the dayside emission spectrum for HD 189733b are reported between 2.0–2.4 μm and 3.1–4.1 μm; an unexpected feature at around 3.25 μm is found that is difficult to explain with models that assume local thermodynamic equilibrium conditions, and is assigned to methane.
Mark R. Swain et al.

In Nature.

Observations from ground using NASA's Infrared Telescope Facility.

Links.

http://www.nature.com/nature/journal/v463/n7281/full/nature08775.html
http://www.nature.com/nature/journal/v463/n7281/edsumm/e100204-03.html

The relevant paper is now on Arxiv

A ground-based near-infrared emission spectrum of the exoplanet HD 189733b
http://arxiv.org/abs/1002.2453

The climate of HD 189733b from fourteen transits and eclipses measured by Spitzer
http://arxiv.org/abs/1007.4378

Abstract wrote:

We present observations of seven transits and seven eclipses of the transiting planet system HD 189733 taken with Spitzer IRAC at 8 microns. We use a new correction for the detector ramp variation with a double-exponential function. Our main findings are: (1) an upper limit on the variability of the day-side planet flux of 2.7% (68% confidence); (2) the most precise set of transit times measured for a transiting planet, with an average accuracy of 3 seconds; (3) a lack of transit-timing variations, excluding the presence of second planets in this system above 20% of the mass of Mars in low-order mean-motion resonance at 95% confidence; (4) a confirmation of the planet's phase variation, finding the night side is 64% as bright as the day side, as well as an upper limit on the night-side variability of 17% (68% confidence); (5) a better correction for stellar variability at 8 micron causing the phase function to peak 3.5 hrs before secondary eclipse, confirming that the advection and radiation timescales are comparable at the 8 micron photosphere; (6) variation in the depth of transit, which possibly implies variations in the surface brightness of the portion of the star occulted by the planet, posing a fundamental limit on non-simultaneous multi-wavelength transit absorption measurements of planet atmospheres; (7) a measurement of the infrared limb-darkening of the star, in agreement with stellar atmosphere models; ( an offset in the times of secondary eclipse of 69 sec, which is mostly accounted for by a 31 sec light travel time delay and 33 sec delay due to the shift of ingress and egress by the planet hot spot; this confirms that the phase variation is due to an offset hot spot on the planet; (9) a retraction of the claimed eccentricity of this system due to the offset of secondary eclipse; and (10) high precision measurements of the parameters of this system.

Abstract wrote:

a confirmation of the planet's phase variation, finding the night side is 64% as bright as the day side

wow, the night on that planet must be very clear, as clear as the day on Earth !

3.6 and 4.5 Micron Phase Curves and Evidence for Non-Equilibrium Chemistry in the Atmosphere of Extrasolar Planet HD 189733b

Further details about the best-studied extrasolar planet. Looks like there's some vertical mixing going on which breaks the assumption of the chemistry being in thermal equilibrium.

Atmospheric escape from HD 189733b observed in HI Lyman-alpha: detailed analysis of HST/STIS September 2011 observations
http://arxiv.org/abs/1301.6030

Quote :

Observations of transits of the hot giant exoplanet HD 189733b in the unresolved HI Lyman-alpha line show signs of hydrogen escaping the upper atmosphere of the planet. New resolved Lyman-alpha observations obtained with the STIS spectrograph onboard the Hubble Space Telescope in April 2010 and September 2011 confirmed that the planet is evaporating, and furthermore discovered significant temporal variations in the physical conditions of its evaporating atmosphere. Here we present a detailed analysis of the September 2011 observations of HD 189733b, when an atmospheric signature was detected. We present specific methods to find and characterize this absorption signature of escaping hydrogen in the Lyman-alpha line, and to calculate its false-positive probability, found to be 3.6%. Taking advantage of the spectral resolution and high sensitivity of the STIS spectrograph, we also present new results on temporal and spectro-temporal variability of this absorption feature. We also report the observation of HD 189733b in other lines (SiIII at 1206.5A, NV at 1240A). Variations in these lines could be explained either by early occultation by a bow-shock rich in highly ionized species, or by stellar variations.

http://arxiv.org/abs/1307.3239

The Deep Blue Color of HD189733b: Albedo Measurements with Hubble Space Telescope/Space Telescope Imaging Spectrograph at Visible Wavelengths

...

Spectrally resolved detection of sodium in the atmosphere of HD189733b with the HARPS spectrograph
http://arxiv.org/abs/1503.05581

Among other results, a blueshift in the Na-line seems to imply winds of 8±2 km/s.

Observing HD 189733 b from a plane:

Angerhausen et al. "First exoplanet transit observation with the Stratospheric Observatory for Infrared Astronomy: Confirmation of Rayleigh scattering in HD 189733 b with HIPO"
http://arxiv.org/abs/1507.01866

Spatially resolved eastward winds and rotation of HD189733b
http://arxiv.org/abs/1511.03689

Quote :

We measure wind velocities on opposite sides of the hot Jupiter HD189733b by modeling sodium absorption in high-resolution HARPS transmission spectra. Our model implicitly accounts for the Rossiter-McLaughlin effect, which we show can explain the high wind velocities suggested by previous studies. Our results reveal a strong eastward motion of the atmosphere of HD189733b, with a redshift of 2.3+1.3−1.5kms−1 on the leading limb of the planet and a blueshift of 5.3+1.0−1.4kms−1 on the trailing limb. These velocities can be understood as a combination of tidally locked planetary rotation and an eastward equatorial jet; closely matching the predictions of atmospheric circulation models. Our results show that the sodium absorption of HD189733b is intrinsically velocity broadened and so previous studies of the average transmission spectrum are likely to have overestimated the role of pressure broadening.

Similar science, different instrument.

Rotation and winds of exoplanet HD 189733 b measured with high-dispersion transmission spectroscopy
http://arxiv.org/abs/1512.05175

Quote :

Giant exoplanets orbiting very close to their parent star (hot Jupiters) are subject to tidal forces expected to synchronize their rotational and orbital periods on short timescales (tidal locking). However, spin rotation has never been measured directly for hot Jupiters. Furthermore, their atmospheres can show equatorial super-rotation via strong eastward jet streams, and/or high-altitude winds flowing from the day- to the night-side hemisphere. Planet rotation and atmospheric circulation broaden and distort the planet spectral lines to an extent that is detectable with measurements at high spectral resolution. We observed a transit of the hot Jupiter HD 189733 b around 2.3 {\mu}m and at a spectral resolution of R~105 with CRIRES at the ESO Very Large Telescope. After correcting for the stellar absorption lines and their distortion during transit (the Rossiter-McLaughlin effect), we detect the absorption of carbon monoxide and water vapor in the planet transmission spectrum by cross-correlating with model spectra. The signal is maximized (7.6{\sigma}) for a planet rotational velocity of (3.4+1.3−2.1) km/s, corresponding to a rotational period of (1.7+2.9−0.4) days. This is consistent with the planet orbital period of 2.2 days and therefore with tidal locking. We find that the rotation of HD 189733 b is longer than 1 day (3{\sigma}). The data only marginally (1.5{\sigma}) prefer models with rotation versus models without rotation. We measure a small day- to night-side wind speed of (−1.7+1.1−1.2) km/s. Compared to the recent detection of sodium blue-shifted by (8±2) km/s, this likely implies a strong vertical wind shear between the pressures probed by near-infrared and optical transmission spectroscopy.