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Register a new userMolecular Signatures in the Near Infrared Dayside Spectrum of HD 189733b
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We have measured the dayside spectrum of HD 189733b between 1.5 and 2.5 microns using the NICMOS instrument on the Hubble Space Telescope. The emergent spectrum contains significant modulation, which we attribute to the presence of molecular bands seen in absorption. We find that water (H2O), carbon monoxide (CO), and carbon dioxide (CO2) are needed to explain the observations, and we are able to estimate the mixing ratios for these molecules. We also find temperature decreases with altitude in the ~0.01 < P < ~1 bar region of the dayside near-infrared photosphere and set an upper limit to the dayside abundance of methane (CH4) at these pressures.
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We report on the measurement of the 7.5-14.7 micron spectrum for the transiting extrasolar giant planet HD 189733b using the Infrared Spectrograph on the Spitzer Space Telescope. Though the observations comprise only 12 hours of telescope time, the continuum is well measured and has a flux ranging from 0.6 mJy to 1.8 mJy over the wavelength range, or 0.49 +/- 0.02% of the flux of the parent star. The variation in the measured fractional flux is very nearly flat over the entire wavelength range and shows no indication of significant absorption by water or methane, in contrast with the predictions of most atmospheric models. Models with strong day/night differences appear to be disfavored by the data, suggesting that heat redistribution to the night side of the planet is highly efficient.
The study of exoplanetary atmospheres is key to understand the differences between their physical, chemical and dynamical processes. Up to now, the bulk of atmospheric characterization analysis has been conducted on transiting planets. On some sufficiently bright targets, high-resolution spectroscopy (HRS) has also been successfully tested for non-transiting planets. We study the dayside of the non-transiting planet HD 102195b using the GIANO spectrograph mounted at TNG, demonstrating the feasibility of atmospheric characterization measurements and molecular detection for non-transiting planets with the HRS technique using 4-m class telescopes. The Doppler-shifted planetary signal changes on the order of many km/s during the observations, in contrast with the telluric absorption which is stationary in wavelength, allowing us to remove the contamination from telluric lines while preserving the features of the planetary spectrum. The emission signal from HD 102195bs atmosphere is then extracted by cross-correlating the residual spectra with atmospheric models. We detect molecular absorption from water vapor at 4.4$sigma$ level. We also find convincing evidence for the presence of methane, which is detected at the 4.1$sigma$ level. The two molecules are detected with a combined significance of 5.3$sigma$, at a semi-amplitude of the planet radial velocity $K_P=128pm 6$ km/s. We estimate a planet true mass of $M_P=0.46pm 0.03~M_J$ and orbital inclination between 72.5 and 84.79$^{circ}$ (1$sigma$). Our analysis indicates a non-inverted atmosphere for HD 102195b, as expected given the relatively low temperature of the planet, inefficient to keep TiO/VO in gas phase. Moreover, a comparison with theoretical expectations and chemical model predictions corroborates our methane detection and suggests that the detected $CH_4$ and $H_2O$ signatures could be consistent with a low C/O ratio.
High-resolution spectroscopy (R $ge$ 20,000) at near-infrared wavelengths can be used to investigate the composition, structure, and circulation patterns of exoplanet atmospheres. However, up to now it has been the exclusive dominion of the biggest telescope facilities on the ground, due to the large amount of photons necessary to measure a signal in high-dispersion spectra. Here we show that spectrographs with a novel design - in particular a large spectral range - can open exoplanet characterisation to smaller telescope facilities too. We aim to demonstrate the concept on a series of spectra of the exoplanet HD 189733 b taken at the Telescopio Nazionale Galileo with the near-infrared spectrograph GIANO during two transits of the planet. In contrast to absorption in the Earths atmosphere (telluric absorption), the planet transmission spectrum shifts in radial velocity during transit due to the changing orbital motion of the planet. This allows us to remove the telluric spectrum while preserving the signal of the exoplanet. The latter is then extracted by cross-correlating the residual spectra with template models of the planet atmosphere computed through line-by-line radiative transfer calculations, and containing molecular absorption lines from water and methane. By combining the signal of many thousands of planet molecular lines, we confirm the presence of water vapour in the atmosphere of HD 189733 b at the 5.5-$sigma$ level. This signal was measured only in the first of the two observing nights. By injecting and retrieving artificial signals, we show that the non-detection on the second night is likely due to an inferior quality of the data. The measured strength of the planet transmission spectrum is fully consistent with past CRIRES observations at the VLT, excluding a strong variability in the depth of molecular absorption lines.
We present analysis of XMM-Newton Optical Monitor observations in the near-ultraviolet of HD 189733, covering twenty primary transits of its hot Jupiter planet. The transit is clearly detected with both the UVW2 and UVM2 filters, and our fits to the data reveal transit depths in agreement with that observed optically. The measured depths correspond to radii of $1.059^{+0.046}_{-0.050}$ and $0.94^{+0.15}_{-0.17}$ times the optically-measured radius (1.187 R$_{rm J}$ at 4950 r{A}) in the UVW2 and UVM2 bandpasses, respectively. We also find no statistically significant variation in the transit depth across the 8 year baseline of the observations. We rule out extended broadband absorption towards or beyond the Roche lobe at the wavelengths investigated, although observations with higher spectral resolution are required to determine if absorption out to those distances from the planet is present in individual near-UV lines.
Using the NICMOS instrument on the Hubble Space Telescope, we have measured the dayside spectrum of HD 209458b between 1.5--2.5 microns. The emergent spectrum is dominated by features due to the presence of methane (CH4) and water vapor (H2O), with smaller contributions from carbon dioxide (CO2). Combining this near-infrared spectrum with existing mid-infrared measurements shows the existence of a temperature inversion and confirms the interpretation of previous photometry measurements. We find a family of plausible solutions for the molecular abundance and detailed temperature profile. Observationally resolving the ambiguity between abundance and temperature requires either (1) improved wavelength coverage or spectral resolution of the dayside emission spectrum, or (2) a transmission spectrum where abundance determinations are less sensitive to the temperature structure.
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