Exoplanets and Stellar Physics

Abstract:

SWIFT is a visible light (650-1000nm) integral field spectorgaph fed by the Palomar extreme adaptive optics system PALM3K. With a subaperture spacing of 8cm, PALM3K is capable of delivering diffraction limited performance even in the visible. With SWIFT providing spatially resolved spectroscopy at R=4000, this provides a truly unique facility for high resolution science in three dimensions. We present here some results from the first year of PALM3K+SWIFT science. We also report on our experience of operating a small field of view instrument (1"x0.5") with a high performance AO system, and hope the lessons learned will provide valuable input to designing successful and productive AO plus Instrument combinations for ELTs.

Abstract:

We present Hubble Space Telescope near-infrared transmission spectroscopy of the transiting hot-Jupiter HAT-P-1b. We observed one transit withWide Field Camera 3 using the G141 lowresolution grism to cover thewavelength range 1.087-1.678μm. 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 planetto-star radius ratio of Rp/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 δλ = 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 5s 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 1000K isothermal model, as well as with that predicted by a planetary-averaged temperature model. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

We present an optical to near-infrared transmission spectrum of the hot JupiterHAT-P-1b, based on Hubble Space Telescope observations, covering the spectral regime from 0.29 to 1.027μm with Space Telescope Imaging Spectrograph (STIS), which is coupled with a recent Wide Field Camera 3 (WFC3) transit (1.087 to 1.687μm). 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 0.55μm, with a strong blueward slope into the near-ultraviolet. We detect atmospheric sodium absorption at a 3.3σ 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 ~0.85μm. 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. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

With the first ELTs around the corner it is becoming ever more important to determine observational strategies and assess the prospective success of observing programs prior to making the observations. To this end, scientific simulations need to become more refined to understand the criteria required for a specific science case. We address the science simulations for HARMONI, an AO assisted first light integral field spectrograph (IFS) for the E-ELT. AO point spread functions (PSFs) vary markedly as a function of wavelength and type of AO system used, so there is need to create detailed PSFs across all IFS wavelength channels for accurate simulations. Detailed AO simulations have shown that for LTAO on the E-ELT, Strehl ratios can vary from 0.5% in V-band up to 75% in K-band. Using a single PSF for an entire datacube (especially with large instantaneous wavelength coverage) could introduce misleading features into simulated observations using HARMONI. We have developed a method to parameterise detailed PSFs using analytical models, which can then be interpolated as a function of wavelength. This allows us to create accurate, but computationally inexpensive, AO PSF datacubes for HARMONI simulations. This shall be developed to cover LTAO, SCAO and GLAO/no-AO PSFs.

Abstract:

We report Gemini-North Gemini Multi-Object Spectrograph observations of the inflated hot Jupiter HAT-P-32b during two primary transits. We simultaneously observed two comparison stars and used differential spectrophotometry to produce multiwavelength light curves. 'White' light curves and 29 'spectral' light curves were extracted for each transit and analysed to refine the system parameters and produce transmission spectra from 520 to 930 nm in ̃ 14 nm bins. The light curves contain time-varyingwhite noise as well as time-correlated noise, and we used a Gaussian process model to fit this complex noise model. Common mode corrections derived from the white light-curve fits were applied to the spectral light curves which significantly improved our precision, reaching typical uncertainties in the transit depth of ̃ 2 × 10-4, corresponding to about half a pressure scale height. The low-resolution transmission spectra are consistent with a featureless model, and we can confidently rule out broad features larger than about one scale height. The absence of Na/K wings or prominent TiO/VO features is most easily explained by grey absorption from clouds in the upper atmosphere, masking the spectral features. However, we cannot confidently rule out clear atmosphere models with low abundances (̃ 10-3 solar) of TiO, VO or even metal hydrides masking the Na and K wings. A smaller scale height or ionization could also contribute to muted spectral features, but alone are unable to account for the absence of features reported here ©2013 The Authors.