Outcome of Six Candidate Transiting Planets from a TrES Field in Andromeda (original) (raw)
Related papers
2006
Ground-based wide-field surveys for nearby transiting gas giants are yielding far fewer true planets than astrophysical false positives, some of which are difficult to reject. Recent experience has highlighted the need for careful analysis to eliminate astronomical systems in which light from a faint eclipsing binary is blended with that from a bright star. During the course of the Transatlantic Exoplanet Survey, we identified a system presenting a transit-like periodic signal. We obtained the proper motion and infrared color of this target (GSC 03885À00829) from publicly available catalogs, which suggested this star is an F dwarf, supporting our transit hypothesis. This spectral classification was confirmed using spectroscopic observations from which we determined the stellar radial velocity. The star did not exhibit any signs of a stellar mass companion. However, subsequent multicolor photometry displayed a color-dependent transit depth, indicating that a blend was the likely source of the eclipse. We successfully modeled our initial photometric observations of GSC 03885À00829 as the light from a K dwarf binary system superimposed on the light from a late F dwarf star. High-dispersion spectroscopy confirmed the presence of light from a cool stellar photosphere in the spectrum of this system. With this candidate, we demonstrate both the difficulty in identifying certain types of false positives in a list of candidate transiting planets and our procedure for rejecting these imposters, which may be useful to other groups performing wide-field transit surveys.
Monthly Notices of the Royal Astronomical Society, 2008
Wide-field photometric surveys in search of transiting extrasolar planets are now numerous and have met with some success in finding hot Jupiters. These transiting planets have very short periods and very small semimajor axes, facilitating their discovery in such surveys. Transiting planets with longer periods present more of a challenge, since they transit their parent stars less frequently. This paper investigates the effects of observing windows on detecting transiting planets by calculating the fraction of planets with a given period that have zero, one (single), two (double), or 3 (multiple) transits occurring while observations are being taken. We also investigate the effects of collaboration by performing the same calculations with combined observing times from two wide-field transit survey groups. For a representative field of the 2004 observing season, both XO and SuperWASP experienced an increase in single and double transit events by up to 20-40 per cent for planets with periods 14 < P < 150 d when collaborating by sharing data. For the XO Project using its data alone, between 20-40 per cent of planets with periods 14-150 d should have been observed at least once. For the SuperWASP Project, 50-90 per cent of planets with periods between 14-150 d should have been observed at least once. If XO and SuperWASP combine their observations, 50-100 per cent of planets with periods less than 20 d should be observed three or more times. We find that in general widefield transit surveys have selected appropriate observing strategies to observe a significant fraction of transiting giant planets with semimajor axes larger than the hot Jupiter regime. The actual number of intermediate-period transiting planets that are detected depends upon their true semimajor axis distribution and the signal-to-noise ratio of the data. We therefore conclude that the investment of resources needed to investigate more sophisticated photometry calibrations or examine single and double transit events from wide-field surveys might be a worthwhile endeavour. The collaboration of different transit surveys by combining photometric data can greatly increase the number of transits observed for all semimajor axes. In addition, the increased number of data points can improve the signal-to-noise ratio of binned data, increasing the chances of detecting transiting extrasolar planets.
TrES Exoplanets and False Positives: Finding the Needle in the Haystack
2007
Our incomplete understanding of the formation of gas giants and of their mass-radius relationship has motivated ground-based, wide-field surveys for new transiting extrasolar giant planets. Yet, astrophysical false positives have dominated the yield from these campaigns. Astronomical systems where the light from a faint eclipsing binary and a bright star is blended, producing a transit-like light curve, are particularly difficult to eliminate. As part of the Trans-atlantic Exoplanet Survey, we have encountered numerous false positives and have developed a procedure to reject them. We present examples of these false positives, including the blended system GSC 03885-00829 which we showed to be a K dwarf binary system superimposed on a late F dwarf star. This transit candidate in particular demonstrates the careful analysis required to identify astrophysical false positives in a transit survey. From amongst these impostors, we have found two transiting planets. We discuss our follow-up observations of TrES-2, the first transiting planet in the Kepler field.
Astrophysical False Positives Encountered in Wide-Field Transit Searches
2004
Wide-field photometric transit surveys for Jupiter-sized planets are inundated by astrophysical false positives, namely systems that contain an eclipsing binary and mimic the desired photometric signature. We discuss several examples of such false alarms. These systems were initially identified as candidates by the PSST instrument at Lowell Observatory. For three of the examples, we present follow-up spectroscopy that demonstrates that these systems consist of (1) an M-dwarf in eclipse in front of a larger star, (2) two main-sequence stars presenting grazing-incidence eclipses, and (3) the blend of an eclipsing binary with the light of a third, brighter star. For an additional candidate, we present multi-color follow-up photometry during a subsequent time of eclipse, which reveals that this candidate consists of a blend of an eclipsing binary and a physically unassociated star. We discuss a couple indicators from publicly-available catalogs that can be used to identify which candida...
Characterisation of extrasolar planetary transit candidates
Astronomy & Astrophysics, 2010
The detection of transits is an efficient technique to uncover faint companions around stars. The full characterisation of the companions (M-type stars, brown dwarfs or exoplanets) requires high-resolution spectroscopy to measure properly masses and radii. With the advent of massive variability surveys over wide fields, the large number of possible candidates makes such a full characterisation for all of them impractical. We explore here a fast technique to pre-select the most promising candidates using either near-IR photometry or low resolution spectroscopy. We develop a new method based on the well-calibrated surface brightness relation along with the correlation between mass and luminosity for main sequence stars, so that not only can giant stars be excluded but also accurate effective temperatures and radii measured. The main source of uncertainty arises from the unknown dispersion of extinction at a given distance. We apply this technique to our observations of a sample of 34 stars extracted from the 62 low-depth transits identified by OGLE during their survey of some 10 5 stars in the Carina fields of the Galactic disc. We infer that at least 78% of the companions of the stars which are well characterised in this sample are not exoplanets. Stars OGLE-TR-105, OGLE-TR-109 and OGLE-TR-111 are the likeliest to host exoplanets and deserve high-resolution follow-up studies. Most recently, OGLE-TR-111 was confirmed as an exoplanet with M planet 0.53 ± 0.11 M Jup (Pont et al. 2004), confirming the efficiency of our method in pre-selecting reliable planetary transit candidates.
A Search for Transiting Extrasolar Planets from the Southern Hemisphere
Master of Science Thesis, Department of Astrophysics, University of New South Wales, 2008
To date, more than 300 planets orbiting stars other than our sun have been discovered using a range of observing techniques, with new discoveries occuring monthly. The work in this thesis focused on the detection of exoplanets using the transit method. Planets orbiting close to their host stars have a roughly 10 per cent chance of eclipsing (transiting) the star, with Jupiter-sized planets causing a one per cent dip in the flux of the star over a few hours. A wealth of orbital and physical information on the system can be extracted from these systems, including the planet density which is essential in constraining models of planetary formation. To detect these types of planets requires monitoring tens of thousands of stars over a period of months. To accomplish this, we conduct a wide-field survey using the 0.5-meter Automated Patrol Telescope (APT) at Siding Spring Observatory (SSO) in NSW, Australia. Once candidates were selected from the data-set, selection criteria were applied to separate the likely planet candidates from the false-positives. For this thesis, the methods and instrumentation used in attaining data and selecting planet candidates are discussed, as well as the results and analysis of the planet candidates selected from star fields observed from 2004-2007. Of the 65 planet candidates initially selected from the 25 target fields observed, only two were consistent with a planet transit. These candidates were later determined to be eclipsing binary stars based on follow up observations using the 40-inch telescope, 2.3-m telescope, and the 3.9-m Anglo-Australian Telescope, all located at SSO. Additionally, two planet candidates from the SuperWASP-North consortium were observed on the 40-inch telescope. Both proved to be eclipsing binary stars. While no planets were found, our search methods and results are consistent with successful transit surveys targeting similar fields with stars in a similar magnitude range and using similar methods.
The Astronomical Journal, 2016
The past two decades have seen a significant advancement in the detection, classification, and understanding of exoplanets and binaries. This is due, in large part, to the increase in use of small-aperture telescopes (<20 cm) to survey large areas of the sky to milli-mag precision with rapid cadence. The vast majority of the planetary and binary systems studied to date consists of main-sequence or evolved objects, leading to a dearth of knowledge of properties at early times (<50 Myr). Only a dozen binaries and one candidate transiting Hot Jupiter are known among pre-main-sequence objects, yet these are the systems that can provide the best constraints on stellar formation and planetary migration models. The deficiency in the number of wellcharacterized systems is driven by the inherent and aperiodic variability found in pre-main-sequence objects, which can mask and mimic eclipse signals. Hence, a dramatic increase in the number of young systems with high-quality observations is highly desirable to guide further theoretical developments. We have recently completed a photometric survey of threenearby (<150 pc) and young (<50 Myr) moving groups with a small-aperture telescope. While our survey reached the requisite photometric precision, the temporal coverage was insufficient to detect Hot Jupiters. Nevertheless, we discovered 346 pre-main-sequence binary candidates, including 74 high-priority objects for further study.
Interpreting and predicting the yield of transit surveys: giant planets in the OGLE fields
Astronomy and Astrophysics, 2007
Transiting extrasolar planets are now discovered jointly by photometric surveys and by radial velocimetry, allowing measurements of their radius and mass. We want to determine whether the different data sets are compatible between themselves and with models of the evolution of extrasolar planets. We further want to determine whether to expect a population of dense Jupiter-mass planets to be detected by future more sensitive transit surveys. We simulate directly a population of stars corresponding to the OGLE transit survey and assign them planetary companions based on a list of 153 extrasolar planets discovered by radial velocimetry. We use a model of the evolution and structure of giant planets that assumes that they are made of hydrogen and helium and of a variable fraction of heavy elements (between 0 and 100 M ⊕ ). The output list of detectable planets of the simulations is compared to the real detections. We confirm that the radial velocimetry and photometric survey data sets are compatible within the statistical errors, assuming that planets with periods between 1 and 2 days are approximately 5 times less frequent than planets with periods between 2 and 5 days. We show that evolution models fitting present observational constraints predict a lack of small giant planets with large masses. As a side result of the study, we identify two distinct populations of planets: those with short periods (P < 10d), which are only found in orbit around metal-rich stars with [Fe/H] >∼ −0.07, and those on longer orbits (P > 10d), for which the metallicity bias is less marked. We further confirm the relative absence of low-mass giant planets at small orbital distances. Testing these results and the underlying planetary evolution models requires the detection of a statistically significant number of transiting planets, which should be provided over the next few years by continued ground-based photometric surveys, the space missions CoRoT and Kepler, and combined radial velocity measurements.
A new transiting extrasolar giant planet
Arxiv preprint astro-ph/0301052, 2003
A conceptually simple and technologically feasible approach to finding planets orbiting other stars is to observe the periodic dimming of starlight due to a planet transiting in front of its star. Despite many intense photometric searches, no transiting planet had yet been discovered in this way. The only known transiting extrasolar planet, 1,2 HD 209458b, was first detected by precise radial velocity measurements. 2,3 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. 4,5 Here we show that the velocity changes we detect are probably induced by an object of 0.9 Jupiter masses-a very closein 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 cm −3. At its small orbital distance, OGLE-TR-56b is hotter than any known planet, approaching 1900 K, but it is stable against long-term evaporation or tidal disruption. As the planet with the tightest known orbit, OGLE-TR-56b will place strong constraints on planet formation and migration models. The advent of high-precision Doppler and timing techniques in the past decade has brought a rich bounty of giant planets 6-8 as well as smaller, terrestrial-mass pulsar planets. 9 To date over one hundred extrasolar giant planets have been found by different groups using precise radial velocity measurements. 8 Photometric observations of transiting planets, when combined with radial velocities, yield entirely new diagnostics: the planet size and mean density. 1,2 Transits supply the orbital inclination and a precise mass for the planet, and they additionally enable a number of follow-up studies. 10-13 Hence, a large number of transit searches are already underway or under development. 14 However, photometry alone cannot distinguish whether the occulting object is a gas giant planet (∼1-13 Jupiter masses), a brown dwarf (∼13-80 Jupiter masses) or a very late type dwarf star, because such objects have nearly constant radius over a range from ∼0.001 to 0.1 Solar masses. This critical parameter, the mass of the companion, can be determined from the amplitude of the radial velocity variation induced in the star. One of the most successful searches to date is the Optical Gravitational Lensing Experiment (OGLE), which uncovered 59 transiting candidates in three fields in the direction of the Galactic centre (OGLE-III), 4,5 with estimated sizes for the possible companions of ∼1-4 Jupiter radii. The large number of relatively faint (V = 14-18 mag) candidates to study led to our strategy of a preliminary spectroscopic reconnaissance to detect and
The EXPLORE Project. I. A Deep Search for Transiting Extrasolar Planets
The Astrophysical Journal, 2003
Searching for transits provides a very promising technique for finding close-in extra-solar planets. Transiting planets present the advantage of allowing one to determine physical properties such as mass and radius unambiguously. The EXPLORE (EXtra-solar PLanet Occultation REsearch) project is a transit search project carried out using wide-field CCD imaging cameras on 4-m class telescopes, and 8-10m class telescopes for radial velocity verification of the photometric candidates. We describe some of the considerations that go into the design of the EXPLORE transit search to maximize the discovery rate and minimize contaminating objects that mimic transiting planets. We show that high precision photometry (2 to 10 millimag) and high time sampling (few minutes) are crucial for sifting out contaminating signatures, such as grazing binaries. We have an efficient data reduction pipeline which allows us to completely reduce the data and search for transit candidates in less than one month after the imaging observations, allowing us to conduct same-semester radial velocity follow-up observations, reducing the phase uncertainty.