Beschreibung: We present Hubble Space Telescope ( HST ) optical transmission spectra of the transiting hot-Jupiter WASP-12b, taken with the Space Telescope Imaging Spectrograph instrument. The resulting spectra cover the range 2900–10 300 Swhich we combined with archival Wide Field Camera 3 spectra and Spitzer photometry to cover the full optical to infrared wavelength regions. With high spatial resolution, we are able to resolve WASP-12A's stellar companion in both our images and spectra, revealing that the companion is in fact a close binary M0V pair, with the three stars forming a triple-star configuration. We derive refined physical parameters of the WASP-12 system, including the orbital ephemeris, finding the exoplanet's density is ~20 per cent lower than previously estimated. From the transmission spectra, we are able to decisively rule out prominent absorption by TiO in the exoplanet's atmosphere, as there are no signs of the molecule's characteristic broad features nor individual bandheads. Strong pressure-broadened Na and K absorption signatures are also excluded, as are significant metal-hydride features. We compare our combined broad-band spectrum to a wide variety of existing aerosol-free atmospheric models, though none are satisfactory fits. However, we do find that the full transmission spectrum can be described by models which include significant opacity from aerosols: including Rayleigh scattering, Mie scattering, tholin haze and settling dust profiles. The transmission spectrum follows an effective extinction cross-section with a power law of index α, with the slope of the transmission spectrum constraining the quantity α T  = –3528 ± 660 K, where T is the atmospheric temperature. Rayleigh scattering (α = –4) is among the best-fitting models, though requires low terminator temperatures near 900 K. Sub-micron size aerosol particles can provide equally good fits to the entire transmission spectrum for a wide range of temperatures, and we explore corundum as a plausible dust aerosol. The presence of atmospheric aerosols also helps to explain the modestly bright albedo implied by Spitzer observations, as well as the near blackbody nature of the emission spectrum. Ti-bearing condensates on the cooler night-side is the most natural explanation for the overall lack of TiO signatures in WASP-12b, indicating the day/night cold trap is an important effect for very hot Jupiters. These findings indicate that aerosols can play a significant atmospheric role for the entire wide range of hot-Jupiter atmospheres, potentially affecting their overall spectrum and energy balance.

Beschreibung: We present an optical to near-infrared transmission spectrum of the hot Jupiter HAT-P-1b, based on Hubble Space Telescope observations, covering the spectral regime from 0.29 to 1.027 μm with Space Telescope Imaging Spectrograph (STIS), which is coupled with a recent Wide Field Camera 3 (WFC3) transit (1.087 to 1.687 μm). We derive refined physical parameters of the HAT-P-1 system, including an improved orbital ephemeris. The transmission spectrum shows a strong absorption signature shortward of 0.55 μm, with a strong blueward slope into the near-ultraviolet. We detect atmospheric sodium absorption at a 3.3 significance level, but find no evidence for the potassium feature. The red data imply a marginally flat spectrum with a tentative absorption enhancement at wavelength longer than ~ 0.85 μm. The STIS and WFC3 spectra differ significantly in absolute radius level (4.3 ± 1.6 pressure scaleheights), implying strong optical absorption in the atmosphere of HAT-P-1b. The optical to near-infrared difference cannot be explained by stellar activity, as simultaneous stellar activity monitoring of the G0V HAT-P-1b host star and its identical companion show no significant activity that could explain the result. We compare the complete STIS and WFC3 transmission spectrum with theoretical atmospheric models which include haze, sodium and an extra optical absorber. We find that both an optical absorber and a supersolar sodium to water abundance ratio might be a scenario explaining the HAT-P-1b observations. Our results suggest that strong optical absorbers may be a dominant atmospheric feature in some hot Jupiter exoplanets.

Beschreibung: We measure the transmission spectrum of WASP-19b from three transits using low-resolution optical spectroscopy from the Hubble Space Telescope ( HST ) Space Telescope Imaging Spectrograph (STIS). The STIS spectra cover a wavelength range of 0.29–1.03 μm, with resolving power R  = 500. The optical data are combined with archival near-infrared data from the HST Wide Field Camera 3 (WFC3) G 141 grism, covering the wavelength range from 1.087 to 1.687 μm, with resolving power R  = 130. We reach signal-to-noise levels between 3000 and 11 000 in 0.1 μm bins when measuring the transmission spectra from 0.53–1.687 μm. WASP-19 is known to be a very active star, with the optical stellar flux varying by a few per cent over time. We correct the transit light curves for the effects of stellar activity using ground-based activity monitoring with the Cerro Tololo Inter-American Observatory. While we were not able to construct a transmission spectrum using the blue optical data because of the presence of large occulted starspots, we were able to use the spot crossings to help constrain the mean stellar spot temperature. To search for predicted features in the hot-Jupiter atmosphere, in addition to the transmission spectrum we also define spectral indices for differential radius ( R P / R * ) measurements to specifically search for the presence of TiO and alkali line features. Our measurements rule out TiO features predicted for a planet of WASP-19b's equilibrium temperature (2050 K) in the transmission spectrum at the 2.7–2.9 confidence level, depending on atmospheric model formalism. The WFC3 transmission spectrum shows strong absorption features due to the presence of H 2 O, which is detected at the 4 confidence level between 1.1 and 1.4 μm. The transmission spectra results indicate that WASP-19b is a planet with no or low levels of TiO and without a high C/O ratio. The lack of observable TiO features are possibly due to rainout, breakdown from stellar activity or the presence of other absorbers in the optical.

Beschreibung: We present Hubble Space Telescope near-infrared transmission spectroscopy of the transiting hot-Jupiter HAT-P-1b. We observed one transit with Wide Field Camera 3 using the G141 low-resolution grism to cover the wavelength range 1.087–1.678 μm. These time series observations were taken with the newly available spatial-scan mode that increases the duty cycle by nearly a factor of 2, thus improving the resulting photometric precision of the data. We measure a planet-to-star radius ratio of R p / R * = 0.117 09 ± 0.000 38 in the white light curve with the centre of transit occurring at 245 6114.345 ± 0.000 133 (JD). We achieve S/N levels per exposure of 1840 (0.061 per cent) at a resolution of = 19.2 nm ( R  ~ 70) in the 1.1173–1.6549 μm spectral region, providing the precision necessary to probe the transmission spectrum of the planet at close to the resolution limit of the instrument. We compute the transmission spectrum using both single target and differential photometry with similar results. The resultant transmission spectrum shows a significant absorption above the 5 level matching the 1.4 μm water absorption band. In solar composition models, the water absorption is sensitive to the ~1 m bar pressure levels at the terminator. The detected absorption agrees with that predicted by a 1000 K isothermal model, as well as with that predicted by a planetary-averaged temperature model.

Beschreibung: We are in the midst of a revolution in our understanding of planets in the Universe. In the last 20 years, 200-times more planets have been discovered beyond our solar system than reside within it. Astronomers are determining their properties, are finding correlations between a star’s type and its planet...

Beschreibung: Understanding a planet’s atmosphere is a necessary condition for understanding not only the planet itself, but also its formation, structure, evolution, and habitability. This requirement puts a premium on obtaining spectra and developing credible interpretative tools with which to retrieve vital planetary information. However, for exoplanets, these twin goals are...

Beschreibung: Using basic physical arguments, we derive by dimensional and physical analysis the characteristic masses and sizes of important objects in the universe in terms of just a few fundamental constants. This exercise illustrates the unifying power of physics and the profound connections between the small and the large in the...

Beschreibung: We report Hubble Space Telescope optical to near-infrared transmission spectroscopy of the hot-Jupiter WASP-6b, measured with the Space Telescope Imaging Spectrograph and Spitzer's InfraRed Array Camera. The resulting spectrum covers the range 0.29–4.5 μm. We find evidence for modest stellar activity of WASP-6 and take it into account in the transmission spectrum. The overall main characteristic of the spectrum is an increasing radius as a function of decreasing wavelength corresponding to a change of ( R p / R * ) = 0.0071 from 0.33 to 4.5 μm. The spectrum suggests an effective extinction cross-section with a power law of index consistent with Rayleigh scattering, with temperatures of 973 ± 144 K at the planetary terminator. We compare the transmission spectrum with hot-Jupiter atmospheric models including condensate-free and aerosol-dominated models incorporating Mie theory. While none of the clear-atmosphere models is found to be in good agreement with the data, we find that the complete spectrum can be described by models that include significant opacity from aerosols including Fe-poor Mg 2 SiO 4 , MgSiO 3 , KCl and Na 2 S dust condensates. WASP-6b is the second planet after HD 189733b which has equilibrium temperatures near ~1200 K and shows prominent atmospheric scattering in the optical.

Beschreibung: We present Hubble Space Telescope optical and near-IR transmission spectra of the transiting hot-Jupiter WASP-31b. The spectrum covers 0.3–1.7 μm at a resolution R  ~ 70, which we combine with Spitzer photometry to cover the full-optical to IR. The spectrum is dominated by a cloud deck with a flat transmission spectrum which is apparent at wavelengths 〉 0.52 μm. The cloud deck is present at high altitudes and low pressures, as it covers the majority of the expected optical Na line and near-IR H 2 O features. While Na  i absorption is not clearly identified, the resulting spectrum does show a very strong potassium feature detected at the 4.2 confidence level. Broadened alkali wings are not detected, indicating pressures below ~10 mbar. The lack of Na and strong K is the first indication of a sub-solar Na/K abundance ratio in a planetary atmosphere (ln[Na/K] = –3.3 ± 2.8), which could potentially be explained by Na condensation on the planet's night side, or primordial abundance variations. A strong Rayleigh scattering signature is detected at short wavelengths, with a 4 significant slope. Two distinct aerosol size populations can explain the spectra, with a smaller sub-micron size grain population reaching high altitudes producing a blue Rayleigh scattering signature on top of a larger, lower lying population responsible for the flat cloud deck at longer wavelengths. We estimate that the atmospheric circulation is sufficiently strong to mix micron size particles upwards to the required 1–10 mbar pressures, necessary to explain the cloud deck. These results further confirm the importance of clouds in hot Jupiters, which can potentially dominate the overall spectra and may alter the abundances of key gaseous species.