High-precision spectrophotometry is highly desirable in detecting and characterizing close-in extrasolar planets to learn about their makeup and temperature. For such a goal, a modest-size telescope with a simple low-resolution spectroscopic instrument is potentially as good as or better than a complex general-purpose spectrograph since calibration and removal of systematic errors are expected to dominate. We use a transmission grating placed in front of an imaging CCD camera on Steward Observatory's Kuiper 1.5 m telescope to provide a high signal-to-noise ratio, low-dispersion visible spectrum of the star HD 209458. We attempt to detect the reflected light signal from the extrasolar planet HD 209458b by differencing the signal just before and after secondary occultation. We present a simple data reduction method and explore the limits of ground-based low-dispersion spectrophotometry with a diffraction grating. Reflected light detection levels of 0.1% are achievable for 5000-7000 Å, too coarse for useful limits on extrasolar planets but potentially useful for determining spectra of short-period binary systems with large (∆mvis=6) brightness ratios. Limits on the precision are set by variations in atmospheric seeing in the low-resolution spectrum. Calibration of this effect can be carried out by measurement of atmospheric parameters from the observations themselves, which may allow the precision to be limited by the noise due to photon statistics and atmospheric scintillation effects.
Publications of the Astronomical Society of the Pacific
- Pub Date:
- March 2003
- stars: individual (HD 209458);
- Techniques: Spectroscopic;
- 34 pages and 17 figures. Accepted for publication in PASP