Maciej Konacki

An extrasolar planet that transits the disk of its parent star

Planets orbiting other stars could in principle be found through the periodic dimming of starlight as a planet moves across—or ‘transits’—the line of sight between the observer and the star. Depending on the size of the planet relative to the star, the dimming could reach a few per cent of the apparent brightness of the star. Despite many searches, no transiting planet has been discovered in this way; the one known transiting planet—HD209458b—was first discovered using precise measurements of the parent stars radial velocity and only subsequently detected photometrically. Here we report radial velocity measurements of the star OGLE-TR-56, which was previously found to exhibit a 1.2-day transit-like light curve in a survey looking for gravitational microlensing events. The velocity changes that we detect correlate with the light curve, from which we conclude that they are probably induced by an object of around 0.9 Jupiter masses in an orbit only 0.023 au from its star. We estimate the planetary radius to be around 1.3 Jupiter radii and its density to be about 0.5 g cm-3. This object is hotter than any known planet (∼ 1,900 K), but is still stable against long-term evaporation or tidal disruption.

A Transiting Extrasolar Giant Planet around the Star OGLE-TR-10

We report a transiting extrasolar giant planet around the star OGLE-TR-10 (orbital period = 3.1 days), which was uncovered as a candidate by the OGLE team in their photometric survey toward the Galactic center. We observed OGLE-TR-10 spectroscopically over a period of 2 yr (2002-2004), using the HIRES instrument with an iodine cell on the Keck I telescope, and measured small radial velocity variations that are consistent with the presence of a planetary companion. This confirms the earlier identification of OGLE-TR-10b by our team and also recently by Bouchy and coworkers as a possible planet. In addition, in this paper we are able to rule out a blend scenario as an alternative explanation. From an analysis combining all available radial velocity measurements with the OGLE light curve, we find that OGLE-TR-10b has a mass of 0.57 ± 0.12MJ and a radius of 1.24 ± 0.09RJ. These parameters bear close resemblance to those of the first known transiting extrasolar planet, HD 209458b.

Testing Blend Scenarios for Extrasolar Transiting Planet Candidates. I. OGLE-TR-33: A False Positive

We report high-resolution spectroscopic follow-up observations of the faint transiting planet candidate OGLE-TR-33 (V = 14.7), located in the direction of the Galactic center. Small changes in the radial velocity of the star were detected that initially suggested the presence of a large planet or brown dwarf in orbit. However, further analysis revealed spectral line asymmetries that change in phase with the 1.95 day period, casting doubt on those measurements. These asymmetries make it more likely that the transit-like events in the light curve are the result of contamination from the light of an eclipsing binary along the same line of sight (referred to as a blend). We performed detailed simulations in which we generated synthetic light curves resulting from such blend scenarios and fitted them to the measured light curve. Guided by these fits and the inferred properties of the stars, we uncovered a second set of lines in our spectra that correspond to the primary of the eclipsing binary and explain the asymmetries. Using all the constraints from spectroscopy, we were then able to construct a model that satisfies all the observations and to characterize the three stars based on model isochrones. OGLE-TR-33 is fully consistent with being a hierarchical triple system composed of a slightly evolved F6 star (the brighter object) near the end of its main-sequence phase and an eclipsing binary with a K7-M0 star orbiting an F4 star. The application to OGLE-TR-33 of the formalism developed to fit light curves of transit candidates illustrates the power of such simulations for predicting additional properties of the blend and for guiding further observations that may serve to confirm that scenario, thereby ruling out a planet. Tests such as this can be very important for validating faint candidates.

Masses and Orbital Inclinations of Planets in the PSR B1257+12 System

We present measurements of the true masses and orbital inclinations of the two Earth-mass planets in the PSR B1257+12 system, based on the analysis of their mutual gravitational perturbations detectable as microsecond variations of the arrival times of radio pulses from the pulsar. The 6.2 ms pulsar, PSR B1257+12, has been regularly timed with the Arecibo telescope since late 1990. Assuming the standard pulsar mass of 1.4 M_☉, the derived masses of planets B and C are 4.3 ± 0.2 and 3.9 ± 0.2 M_⊕, respectively. The corresponding orbital inclinations of 53° ± 4° and 47° ± 3° (or 127° and 133°) imply that the two orbits are almost coplanar. This result, together with the known near 3 : 2 resonance between the orbits of the two planets, strongly supports the hypothesis of a disk origin of the PSR B1257+12 planetary system. The systems long-term stability is guaranteed by the low Earth-like masses of planets B and C.

New Data and Improved Parameters for the Extrasolar Transiting Planet OGLE-TR-56b

We report new spectroscopic observations with the Keck HIRES instrument of the recently discovered transiting planet OGLE-TR-56b. Our radial velocity measurements with errors of ~100 m s-1 show clear variations that are in excellent agreement with the phasing (period and epoch) derived from the OGLE transit photometry. Careful analysis of the spectral line bisectors, along with numerical simulations of blend scenarios, supports the argument for the planetary nature of the companion. The new data, combined with measurements from the previous season, allow an improved determination of the mass of the planet, Mp = MJup. All available OGLE photometry, including new measurements made during the 2003 season, have also been analyzed to derive an improved value for the planetary radius of Rp = RJup. We discuss the implications of these results for the theory of extrasolar planets.

Trojan Pairs in the HD 128311 and HD 82943 Planetary Systems

Two nearby stars, HD 128311 and HD 82943, are believed to host pairs of Jupiter-like planets involved in a strong first-order 2:1 mean motion resonance (MMR). In this work, we reanalyze available radial velocity (RV) measurements and demonstrate that it is also possible to explain the observed RV variations of the parent stars as being induced by a pair of Trojan planets (i.e., in a 1:1 MMR). We show that these Trojan configurations reside in extended zones of stability in which such systems can easily survive in spite of the large masses of the planets, large eccentricities, and nonzero mutual inclinations of their orbits. We also show that HD 82943 could harbor a previously unknown third planet of ~0.5MJ in ~2 AU orbit.

An extrasolar giant planet in a close triple-star system

Hot Jupiters are gas-giant planets orbiting with periods of 3–9 days around Sun-like stars. They are believed to form in a disk of gas and condensed matter at or beyond ∼2.7 astronomical units (au—the Sun–Earth distance) from their parent star. At such distances, there exists a sufficient amount of solid material to produce a core capable of capturing enough gas to form a giant planet. Subsequently, they migrate inward to their present close orbits. Here I report the detection of an unusual hot Jupiter orbiting the primary star of a triple stellar system, HD 188753. The planet has an orbital period of 3.35 days and a minimum mass of 1.14 times that of Jupiter. The primary stars mass is 1.06 times that of the Sun, 1.06 M[circdot]. The secondary star, itself a binary stellar system, orbits the primary at an average distance of 12.3 au with an eccentricity of 0.50. The mass of the secondary pair is 1.63 M[circdot]. Such a close and massive secondary would have truncated a disk around the primary to a radius of only ∼1.3 au (ref. 4) and might have heated it up to temperatures high enough to prohibit giant-planet formation, leaving the origin of this planet unclear.

Precision radial velocities of double-lined spectroscopic binaries with an iodine absorption cell

A spectroscopic technique employing an iodine absorption cell (I2) to superimpose a reference spectrum onto a stellar spectrum is currently the most widely adopted approach to obtain precision radial velocities of solar-type stars. It has been used to detect ~80 extrasolar planets out of ~130 known. Yet in its original version, it only allows us to measure precise radial velocities of single stars. In this paper, we present a novel method employing an I2 absorption cell that enables us to accurately determine radial velocities of both components of double-lined binaries. Our preliminary results, based on the data from the Keck I telescope and HIRES spectrograph, demonstrate that 20-30 m s-1 radial velocity precision can be routinely obtained for early type binaries (F3-F8). For later type binaries, the precision reaches ~10 m s-1. We discuss applications of the technique to stellar astronomy and searches for extrasolar planets in binary systems. In particular, we combine the interferometric data collected with the Palomar Testbed Interferometer with our preliminary precision velocities of the spectroscopic double-lined binary HD 4676 to demonstrate that with such a combination one can routinely obtain masses of the binary components accurate at least at the level of 1.0%.

Arecibo Timing and Single-Pulse Observations of Eighteen Pulsars

We present new results of timing and single-pulse measurements for 18 radio pulsars discovered in 1993-1997 by the Penn State/Naval Research Laboratory declination-strip survey conducted with the 305 m Arecibo Telescope at 430 MHz. Long-term timing measurements have led to significant improvements of the rotational and the astrometric parameters of these sources, including the millisecond pulsar, PSR J1709+2313, and the pulsar located within the supernova remnant S147, PSR J0538+2817. Single-pulse studies of the brightest objects in the sample have revealed an unusual bursting pulsar, PSR J1752+2359, two new drifting subpulse pulsars, PSR J1649+2533 and PSR J2155+2813, and another example of a pulsar with profile mode changes, PSR J1746+2540. PSR J1752+2359 is characterized by bursts of emission, which appear once every 3-5 minutes and decay exponentially on a ~45 s timescale. PSR J1649+2533 spends ~30% of the time in a null state with no detectable radio emission.

Timing Observations of Four Millisecond Pulsars with the Arecibo and Effelsberg Radio Telescopes

We present long-term timing observations of four millisecond radio pulsars with the 305 m Arecibo and the 100 m Effelsberg radiotelescopes. Our analysis of the combined pulse time-of-arrival data from the two telescopes has led to improvements of the precision of timing parameter determination for all the four pulsars. A new, much more significant measurement of a third-order spin frequency derivative of PSR B1257+12 adds to the existing evidence that a fourth, distant planet may orbit this pulsar. Proper motions have been measured for PSR J1640+2224, PSR B1953+29, and PSR J2229+2643. The derived low transverse velocities of these objects agree with the kinematic characteristics of the observed millisecond pulsar population. Exceptionally low spindown rates of PSR J1640+2224 and PSR J2229+2634 have been used to derive useful limits on the initial spin periods of these objects and on the variation of the gravitational constant G.