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NICMOS Spectroscopy of HD 189733bSpectral features corresponding to methane and water opacity were reported based on transmission spectroscopy of HD 189733b with Hubble/NICMOS. Recently, these data, and a similar data set for XO-1b, have been reexamined in Gibson et al. 2010, who claim they cannot reliably reproduce prior results. We examine the methods used by the Gibson team and identify two specific issues that could act to increase the formal uncertainties and to create instability in the minimization process. This would also be consistent with the GPA10 finding that they could not identify a way to select among the several instrument models they constructed. In the case of XO-1b, the Gibson team significantly changed the way in which the instrument model is defined (both with respect to the three approaches they used for HD 189733b, and the approach used by previous authors); this change, which omits the effect of the spectrum position on the detector, makes direct intercomparison of results difficult. In the experience of our group, the position of the spectrum on the detector is an important element of the instrument model because of the significant residual structure in the NICMOS spectral flat field. The approach of changing instrument models significantly complicates understanding the data reduction process and interpreting the results. Our team favors establishing a consistent method of handling NICMOS instrument systematic errors and applying it uniformly to data sets.
Document ID
20150005820
Acquisition Source
Jet Propulsion Laboratory
Document Type
Conference Paper
External Source(s)
Authors
Swain, Mark R.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Deroo, Pieter
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Vasisht, Gautam
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Date Acquired
April 17, 2015
Publication Date
October 11, 2010
Subject Category
Astronomy
Meeting Information
Meeting: IAU Symposium 276: The Astrophysics of Planetary Systems
Location: Torino
Country: Italy
Start Date: October 11, 2010
End Date: October 15, 2010
Sponsors: International Astronomical Union
Distribution Limits
Public
Copyright
Other
Keywords
infrared
exoplanet
spectroscopy

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