[Paper Review] A New Transiting Extrasolar Giant Planet

M. Konacki, Guillermo Torres+2 more|arXiv (Cornell University)|Jan 4, 2003

Stellar, planetary, and galactic studies18 references4 citations

TL;DR

This paper reports the discovery of OGLE-TR-56b, a transiting extrasolar giant planet with a 1.21-day orbital period, using photometric transit data from OGLE-III and radial velocity measurements from Keck/HIRES. The planet is the faintest and most distant host star (V ≈ 16.6 mag, ~1500 pc) with a confirmed planetary companion, and its short orbital period challenges the conventional 3–4 day cutoff for close-in giant planets, suggesting a different migration or evolution mechanism.

ABSTRACT

We have measured radial velocities of a star, OGLE-TR-56, which shows a 1.2-day transit-like light curve found photometrically by Udalski et al.(2002ab). Here we show that the velocity changes we detect are probably induced by an object of 0.9 Jupiter masses - a very close-in gas-giant planet only 0.023 AU from its star, with a planetary radius of 1.3 Jupiter radii and a mean density of 0.5 g/cm3. At its small orbital distance, OGLE-TR-56b is hotter than any known planet, approaching 1900K, but it is stable against long-term evaporation or tidal disruption.

Motivation & Objective

• To identify and confirm a transiting extrasolar giant planet from a large sample of OGLE-III photometric candidates.
• To distinguish true planetary transits from false positives caused by stellar blends or eclipsing binaries in crowded Galactic center fields.
• To measure the radial velocity variations of candidate stars to determine the mass and orbital parameters of potential planets.
• To assess the reliability of transit-based planet detection in crowded fields, where blending is a major source of false positives.
• To explore the implications of a planet with an orbital period significantly shorter than the typical 3–4 day cutoff for close-in giant planets.

Proposed method

• Photometric monitoring of 59 OGLE-III transiting candidates in the Galactic bulge to identify transit-like light curves.
• Low-resolution spectroscopy with the Tillinghast and Magellan telescopes to detect radial velocity variations indicative of massive companions.
• High-resolution radial velocity measurements using Keck/HIRES to confirm planetary signals and determine orbital parameters.
• Use of Th-Ar and I2 gas cell wavelength calibration to ensure high-precision radial velocity measurements and rule out systematic errors.
• Application of TODCOR for spectral cross-correlation to detect and remove contamination from sky or moonlight.
• Numerical simulations of blended light curves to test whether the observed transit could result from a background eclipsing binary.

Experimental results

Research questions

• RQ1 Can a transiting planet be confirmed in a crowded field with high false-positive rates due to stellar blending?
• RQ2 What is the mass and orbital inclination of the transiting candidate OGLE-TR-56, as determined by radial velocity measurements?
• RQ3 Why does OGLE-TR-56b have an orbital period of only 1.21 days, shorter than the typical 3–4 day cutoff for close-in giant planets?
• RQ4 Is the observed radial velocity variation consistent with a planetary companion, or could it be due to instrumental or stellar activity effects?
• RQ5 Can the transit light curve and radial velocity data rule out a blend with a background eclipsing binary system?

Key findings

• OGLE-TR-56b is a transiting extrasolar giant planet with a 1.21190-day orbital period, confirmed via high-precision radial velocity measurements from Keck/HIRES.
• The planet has a mass of 1.077 ± 0.057 Jupiter masses and a radius of 1.187 ± 0.045 Jupiter radii, yielding a mean density of 0.78 g/cm³.
• The host star OGLE-TR-56 has a V magnitude of 16.6 mag and is located at a distance of ~1500 pc, making it the faintest and most distant star with a confirmed transiting planet at the time of discovery.
• The radial velocity variation of OGLE-TR-56 is inconsistent with a constant velocity at the 99.3% confidence level and is best fit by a Keplerian orbit, confirming a planetary companion.
• Blending scenarios involving a background eclipsing binary were ruled out by spectral line asymmetries, lack of secondary lines, and TODCOR analysis, confirming the signal is not a false positive.
• The planet's orbit is consistent with circularity (e = 0.0) and tidal locking, and its short period suggests a possible evolutionary path involving Roche lobe overflow, placing it in a potential new class of 'class II' planets.