Publications of the Astronomical Society of the Pacific

Bryson, Stephen T.; Jenkins, Jon M.; Gilliland, Ronald L.; Twicken, Joseph D.; Clarke, Bruce; Rowe, Jason; Caldwell, Douglas; Batalha, Natalie; Mullally, Fergal; Haas, Michael R.; Tenenbaum, Peter

doi: 10.1086/671767pmid: N/A

The Kepler Mission was launched on 2009 March 6 to perform a photometric survey of more than 100,000 dwarf stars to search for Earth-size planets with the transit technique. The reliability of the resulting planetary candidate list relies on the ability to identify and remove false positives. Major sources of astrophysical false positives are planetary transits and stellar eclipses on background stars. We describe several new techniques for the identification of background transit sources that are separated from their target stars, indicating an astrophysical false positive. These techniques use only Kepler photometric data. We describe the concepts and construction of these techniques in detail as well as their performance and relative merits.

Gullikson, Kevin; Endl, Mike

doi: 10.1086/672272pmid: N/A

With about 700 confirmed extrasolar planets, it is time to move beyond discovery and towards characterization. Perhaps the most basic parameter of an extrasolar planet is its mass; however, this is very difficult to determine if the planet does not transit the star. The radial velocity technique, still the most fruitful method of discovering planets in the solar neighborhood, can only determine a minimum planet mass. We investigate a method using the near-future IGRINS near infrared spectrograph to detect the orbital motion of the planet itself. We simulate several observations of a star with an orbiting planet, and search for the spectral signature of the planet by cross-correlating against planet model spectra. A detection appears as a strong peak in the cross-correlation function, and gives the radial velocity of the planet at the time of observation. This, combined with the motion of the star from traditional radial velocity planet search programs, can determine the actual planet mass. We find that the IGRINS instrument can detect the spectral signature from large planets on very close orbits (so-called Hot Jupiters), and that the detections can provide tight constraints on the true planet mass.

Stevens, Daniel J.; Gaudi, B. Scott

doi: 10.1086/672572pmid: N/A

Given the radial velocity (RV) detection of an unseen companion, it is often of interest to estimate the probability that the companion also transits the primary star. Typically, one assumes a uniform distribution for the cosine of the inclination angle i of the companion’s orbit. This yields the familiar estimate for the prior transit probability of ∼R∗/a, given the primary radius R∗ and orbital semimajor axis a, and assuming small companions and a circular orbit. However, the posterior transit probability depends not only on the prior probability distribution of i but also on the prior probability distribution of the companion mass Mc, given a measurement of the product of the two (the minimum mass Mc sin i) from an RV signal. In general, the posterior can be larger or smaller than the prior transit probability. We derive analytic expressions for the posterior transit probability assuming a power-law form for the distribution of true masses, , for integer values -3 ≤ α ≤ 3. We show that for low transit probabilities, these probabilities reduce to a constant multiplicative factor fα of the corresponding prior transit probability, where fα in general depends on α and an assumed upper limit on the true mass. The prior and posterior probabilities are equal for α = -1. The posterior transit probability is ∼1.5 times larger than the prior for α = -3 and is ∼4/π times larger for α = -2, but is less than the prior for α≥0, and can be arbitrarily small for α > 1. We also calculate the posterior transit probability in different mass regimes for two physically-motivated mass distributions of companions around Sun-like stars. We find that for Jupiter-mass planets, the posterior transit probability is roughly equal to the prior probability, whereas the posterior is likely higher for Super-Earths and Neptunes (10 M⊕ - 30 M⊕) and Super-Jupiters (3 MJup - 10 MJup), owing to the predicted steep rise in the mass function toward smaller masses in these regimes. We therefore suggest that companions with minimum masses in these regimes might be better-than-expected targets for transit follow-up, and we identify promising targets from RV-detected planets in the literature. Finally, we consider the uncertainty in the transit probability arising from uncertainties in the input parameters, and the effect of ignoring the dependence of the transit probability on the true semimajor axis on i.

Guyon, Olivier; Mennesson, Bertrand; Serabyn, Eugene; Martin, Stefan

doi: 10.1086/671816pmid: N/A

A scheme to optimally design a beam combiner is discussed for any predetermined fixed geometry nulling interferometer aimed at detection and characterization of exoplanets with multiple telescopes or a single telescope (aperture masking). We show that considerably higher order nulls can be achieved with 1D (one-dimensional) interferometer geometries than possible with 2D (two-dimensional) geometries with the same number of apertures. Any 1D interferometer with N apertures can achieve a 2(N - 1)-order null, while the order of the deepest null for a random 2D aperture geometry interferometer is the order of the Nth term in the Taylor expansion of ei(x2+y2) around x = 0, y = 0 (2nd order null for N = 2,3; 4th order null for N = 4,5,6). We also show that an optimal beam combiner for nulling interferometry relies on only 0 or π phase shifts. Examples of nulling interferometer designs are shown to illustrate these findings.

Kopon, Derek; Close, Laird M.; Males, Jared R.; Gasho, Victor

doi: 10.1086/672091pmid: N/A

We present the novel design, laboratory verification, and on-sky performance of our advanced triplet atmospheric dispersion corrector (ADC), an important component of the Magellan Adaptive Optics system (MagAO), which recently achieved first light in December 2012. High-precision broadband (0.5–1.0  μm) atmospheric dispersion correction at visible wavelengths is essential both for wavefront sensing (WFS) on fainter guide stars, and for performing visible AO science using our VisAO science camera. At 2 airmasses (60° from zenith) and over the waveband 500–1000 nm, our triplet design produces a 57% improvement in geometric rms spot size, a 33% improvement in encircled energy at 20″ radius, and a 62% improvement in Strehl ratio when compared to a conventional doublet design. This triplet design has been fabricated, tested in the lab, and integrated into the MagAO WFS and the VisAO science camera. We present on-sky results of the ADC in operation with the MagAO system. We also present a zero-beam-deviation triplet ADC design, which will be important to future AO systems that require precise alignment of the optical axis over a large range of airmasses in addition to diffraction-limited broadband dispersion correction.

Coppejans, R.; Gulbis, A. A. S.; Kotze, M. M.; Coppejans, D. L.; Worters, H. L.; Woudt, P. A.; Whittal, H.; Cloete, J.; Fourie, P.

doi: 10.1086/672156pmid: N/A

Two identical new instruments, the Sutherland High-speed Optical Cameras (SHOC), have been developed for use on the South African Astronomical Observatory’s (SAAO) 1.9, 1.0 and 0.75 m telescopes at Sutherland. The SHOC systems are fast-frame-rate, accurately-timed, high-quality, visible-wavelength imagers. Each system consists of a camera, global positioning system (GPS), control computer and peripherals. The primary component is an Andor iXon X3 888 UVB camera, utilizing a 1024 × 1024 pixel, frame-transfer, thermoelectrically-cooled, back-illuminated CCD. One of SHOC’s most important features is that it can achieve frame rates of between 1 and 20 frames/s during normal operation (dependent on binning and subframing) with microsecond timing accuracy on each frame (achieved using frame-by-frame GPS triggering). Frame rates can be increased further, and fainter targets observed, by making use of SHOC’s electron-multiplying (EM) modes. SHOC is therefore ideally suited to time domain astronomy where high frame rates and extremely accurate timing are critical. Here, we present details of the instrument components, characteristics measured during commissioning, science demonstrations, and development plans. Attention is specifically given to exploration of the signal-to-noise (S/N) parameter space as a function of EM and conventional modes. These results enable observers to optimize instrumental settings for their observations and clearly demonstrate the advantages and potential pitfalls of the EM modes.

Akeson, R. L.; Chen, X.; Ciardi, D.; Crane, M.; Good, J.; Harbut, M.; Jackson, E.; Kane, S. R.; Laity, A. C.; Leifer, S.; Lynn, M.; McElroy, D. L.; Papin, M.; Plavchan, P.; Ramírez, S. V.; Rey, R.; von Braun, K.; Wittman, M.; Abajian, M.; Ali, B.; Beichman, C.; Beekley, A.; Berriman, G. B.; Berukoff, S.; Bryden, G.; Chan, B.; Groom, S.; Lau, C.; Payne, A. N.; Regelson, M.; Saucedo, M.; Schmitz, M.; Stauffer, J.; Wyatt, P.; Zhang, A.

doi: 10.1086/672273pmid: N/A

We describe the contents and functionality of the NASA Exoplanet Archive, a database and toolset funded by NASA to support astronomers in the exoplanet community. The current content of the database includes interactive tables containing properties of all published exoplanets, Kepler planet candidates, threshold-crossing events, data validation reports and target stellar parameters, light curves from the Kepler and CoRoT missions and from several ground-based surveys, and spectra and radial velocity measurements from the literature. Tools provided to work with these data include a transit ephemeris predictor, both for single planets and for observing locations, light curve viewing and normalization utilities, and a periodogram and phased light curve service. The archive can be accessed at http://exoplanetarchive.ipac.caltech.edu.

Fraser, Wesley C.; Gwyn, Stephen; Trujillo, Chad; Stephens, Andrew W.; Kavelaars, J. J.; Brown, Michael E.; Bianco, Federica B.; Boyle, Richard P.; Brucker, Melissa J.; Hetherington, Nathan; Joner, Michael; Keel, William C.; Langill, Phil P.; Lister, Tim; McMillan, Russet J.; Young, Leslie

doi: 10.1086/672001pmid: N/A

Here we present observations of seven large Kuiper Belt objects. From these observations, we extract a point source catalog with ∼0.01″ precision, and astrometry of our target Kuiper Belt objects with 0.04–0.08″ precision within that catalog. We have developed a new technique to predict the future occurrence of stellar occultations by Kuiper Belt objects. The technique makes use of a maximum likelihood approach which determines the best-fit adjustment to cataloged orbital elements of an object. Using simulations of a theoretical object, we discuss the merits and weaknesses of this technique compared to the commonly adopted ephemeris offset approach. We demonstrate that both methods suffer from separate weaknesses, and thus together provide a fair assessment of the true uncertainty in a particular prediction. We present occultation predictions made by both methods for the seven tracked objects, with dates as late as 2015. Finally, we discuss observations of three separate close passages of Quaoar to field stars, which reveal the accuracy of the element adjustment approach, and which also demonstrate the necessity of considering the uncertainty in stellar position when assessing potential occultations.

Meng, Zeyang; Zhou, Xu; Zhang, Hui; Zhou, Jilin; Wang, Songhu; Ma, Jun; Zhang, Tianmeng; Fan, Zhou; Zou, Hu

doi: 10.1086/672090pmid: N/A

During the Polar Night of 2008 at Dome A site (Antarctica), the Chinese Small Telescope ARray (CSTAR) gathered i-band photometric information (a total of over 300,000 images) of the 20 deg2 sky vicinity around the South Pole automatically and continuously. Within all the acquired images, we carry out an elaborate series of analyses and study the origin and influence of the ghost images in each frame. The point source catalog has also been amended by removing the ghost image effects from the real overlapped stars. This work provides a generalized ghost reduction pipeline and improves the photometric precision of the stars in the CSTAR FOV for the future search for transiting exoplanets.