J. E. Stys

Space Telescope Science Institute, Baltimore, Maryland, United States

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Publications (5)15.79 Total impact

  • 01/2009;
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    ABSTRACT: We report on a V=11.2 early K dwarf, XO-2 (GSC 03413-00005), that hosts a Rp=0.98+0.03/-0.01 Rjup, Mp=0.57+/-0.06 Mjup transiting extrasolar planet, XO-2b, with an orbital period of 2.615857+/-0.000005 days. XO-2 has high metallicity, [Fe/H]=0.45+/-0.02, high proper motion, mu_tot=157 mas/yr, and has a common proper motion stellar companion with 31" separation. The two stars are nearly identical twins, with very similar spectra and apparent magnitudes. Due to the high metallicity, these early K dwarf stars have a mass and radius close to solar, Ms=0.98+/-0.02 Msolar and Rs=0.97+0.02/-0.01 Rsolar. The high proper motion of XO-2 results from an eccentric orbit (Galactic pericenter, Rper<4 kpc) well confined to the Galactic disk (Zmax~100 pc). In addition, the phase space position of XO-2 is near the Hercules dynamical stream, which points to an origin of XO-2 in the metal-rich, inner Thin Disk and subsequent dynamical scattering into the solar neighborhood. We describe an efficient Markov Chain Monte Carlo algorithm for calculating the Bayesian posterior probability of the system parameters from a transit light curve. Comment: 14 pages, 10 Figures, Accepted in ApJ. Negligible changes to XO-2 system properties. Removed Chi^2 light curve analysis section, and simplified MCMC light curve analysis discussion
    The Astrophysical Journal 05/2007; · 6.28 Impact Factor
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    ABSTRACT: A planet transits an 11th magnitude, G1V star in the constellation Corona Borealis. We designate the planet XO-1b, and the star, XO-1, also known as GSC 02041-01657. XO-1 lacks a trigonometric distance; we estimate it to be 200+-20 pc. Of the ten stars currently known to host extrasolar transiting planets, the star XO-1 is the most similar to the Sun in its physical characteristics: its radius is 1.0+-0.08 R_Sun, its mass is 1.0+-0.03 M_Sun, V sini < 3 km/s, and its metallicity [Fe/H] is 0.015+-0.04. The orbital period of the planet XO-1b is 3.941534+-0.000027 days, one of the longer ones known. The planetary mass is 0.90+-0.07 M_Jupiter, which is marginally larger than that of other transiting planets with periods between 3 and 4 days. Both the planetary radius and the inclination are functions of the spectroscopically determined stellar radius. If the stellar radius is 1.0+-0.08 R_Sun, then the planetary radius is 1.30+-0.11 R_Jupiter and the inclination of the orbit is 87.7+-1.2 degrees. We have demonstrated a productive international collaboration between professional and amateur astronomers that was important to distinguishing this planet from many other similar candidates.
    The Astrophysical Journal 06/2006; · 6.28 Impact Factor
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    ABSTRACT: The XO project's first objective is to find hot Jupiters transiting bright stars (i.e., V
    Publications of the Astronomical Society of the Pacific 01/2005; 117:783-795. · 3.23 Impact Factor
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    ABSTRACT: The XO project's first objective is to find hot Jupiters transiting bright stars, i.e. V < 12, by photometry. Two XO cameras have been operating since September 2003 on the 10,000-foot Haleakala summit on Maui. Each XO camera consists of a 200-mm f/1.8 lens coupled to a 1024x1024 pixel, thinned CCD operated in drift-scan (TDI) mode. By rotating the mount at 478 arcsec/second about the declination axis while tracking at the sidereal rate in right ascension, the XO system scans repeatedly from 0 to 63 degrees of declination; each strip's width is 0.5 hours of RA. In its first year, XO has observed 6.6 percent of the sky in total, within six strips centered at RA=0, 4, 8, 12, 16, and 20 hours. Autonomously operating, XO reads out 1 billion pixels per clear night, calibrates them photometrically and astrometrically, performs aperture photometry, archives the pixel data and transmits the photometric data to STScI for further analysis. From the first year of operation, the resulting database consists of photometry of more than 100,000 stars at more than 1000 epochs per star with differential photometric precision better than 1 percent per epoch. Analysis of those light curves produces transiting-Jupiter candidates requiring detailed follow up, culminating in spectroscopy to measure radial-velocity variation in order to differentiate genuine planets from the more numerous impostors, primarily binary and multiple stars. XO is funded primarily by the Origins program of NASA.