Journal articles on the topic 'Transits'
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1
Oddo, Dominic, Diana Dragomir, Alexis Brandeker, Hugh P. Osborn, Karen Collins, Keivan G. Stassun, Nicola Astudillo-Defru, et al. "Characterization of a Set of Small Planets with TESS and CHEOPS and an Analysis of Photometric Performance." Astronomical Journal 165, no. 3 (February 28, 2023): 134. http://dx.doi.org/10.3847/1538-3881/acb4e3.
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Abstract The radius valley carries implications for how the atmospheres of small planets form and evolve, but this feature is visible only with highly precise characterizations of many small planets. We present the characterization of nine planets and one planet candidate with both NASA TESS and ESA CHEOPS observations, which adds to the overall population of planets bordering the radius valley. While five of our planets—TOI 118 b, TOI 262 b, TOI 455 b, TOI 560 b, and TOI 562 b—have already been published, we vet and validate transit signals as planetary using follow-up observations for four new TESS planets, including TOI 198 b, TOI 244 b, TOI 444 b, and TOI 470 b. While a three times increase in primary mirror size should mean that one CHEOPS transit yields an equivalent model uncertainty in transit depth as about nine TESS transits in the case that the star is equally as bright in both bands, we find that our CHEOPS transits typically yield uncertainties equivalent to between two and 12 TESS transits, averaging 5.9 equivalent transits. Therefore, we find that while our fits to CHEOPS transits provide overall lower uncertainties on transit depth and better precision relative to fits to TESS transits, our uncertainties for these fits do not always match expected predictions given photon-limited noise. We find no correlations between number of equivalent transits and any physical parameters, indicating that this behavior is not strictly systematic, but rather might be due to other factors such as in-transit gaps during CHEOPS visits or nonhomogeneous detrending of CHEOPS light curves.
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Zuckerman, Anna, James R. A. Davenport, Steve Croft, Andrew Siemion, and Imke de Pater. "The Breakthrough Listen Search for Intelligent Life: Detection and Characterization of Anomalous Transits in Kepler Lightcurves." Astronomical Journal 167, no. 1 (December 13, 2023): 20. http://dx.doi.org/10.3847/1538-3881/acfa6c.
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Abstract Never before has the detection and characterization of exoplanets via transit photometry been as promising and feasible as it is now, due to the increasing breadth and sensitivity of time domain optical surveys. Past works have made use of phase-folded stellar lightcurves in order to study the properties of exoplanet transits because this provides the highest signal that a transit is present at a given period and ephemeris. Characterizing transits on an individual, rather than phase-folded, basis is much more challenging due to the often low signal-to-noise ratio of lightcurves, missing data, and low sampling rates. However, by phase folding a lightcurve we implicitly assume that all transits have the same expected properties, and lose all information about the nature and variability of the transits. We miss the natural variability in transit shapes, or even the deliberate or inadvertent modification of transit signals by an extraterrestrial civilization (for example, via laser emission or orbiting megastructures). In this work, we develop an algorithm to search stellar lightcurves for individual anomalous (in timing or depth) transits, and we report the results of that search for 218 confirmed transiting exoplanet systems from Kepler.
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Heller, René, and Michael Hippke. "Signal preservation of exomoon transits during light curve folding." Astronomy & Astrophysics 657 (January 2022): A119. http://dx.doi.org/10.1051/0004-6361/202142403.
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In the search for moons around extrasolar planets (exomoons), astronomers are confronted with a stunning observation. Although 3400 of the 4500 exoplanets were discovered with the transit method and although there are well over 25 times as many moons than planets known in the Solar System (two of which are larger than Mercury), no exomoon has been discovered to date. In the search for exoplanet transits, stellar light curves are usually phase-folded over a range of trial epochs and periods. This approach, however, is not applicable in a straightforward manner to exomoons. Planet-moon transits either have to be modeled in great detail (including their orbital dynamics, mutual eclipses, etc.), which is computationally expensive, or key simplifications have to be assumed in the modeling. One such simplification is to search for moon transits outside of the planetary transits. The question we address in this report is how much in-transit data of an exomoon remains uncontaminated by the near-simultaneous transits of its host planet. We develop an analytical framework based on the probability density of the sky-projected apparent position of an exomoon relative to its planet and test our results with a numerical planet-moon transit simulator. For exomoons with planet-moon orbital separations similar to the Galilean moons, we find that only a small fraction of their in-transit data is uncontaminated by planetary transits: 14% for Io, 20% for Europa, 42% for Ganymede, and 73% for Callisto. The signal-to-noise ratio (S/N) of an out-of-planetary-transit folding technique is reduced compared to a full photodynamical model to about 38% (Io), 45% (Europa), 65% (Ganymede), and 85% (Callisto), respectively. For the Earth’s Moon, we find an uncontaminated data fraction of typically just 18% and a resulting S/N reduction to 42%. These values are astonishingly small and suggest that the gain in speed for any exomoon transit search algorithm that ignores the planetary in-transit data comes at the heavy price of losing a substantial fraction of what is supposedly a tiny signal in the first place. We conclude that photodynamical modeling of the entire light curve has substantial, and possibly essential, advantages over folding techniques of exomoon transits outside the planetary transits, in particular for small exomoons comparable to those of the Solar System.
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Wittrock, Justin M., Stefan Dreizler, Michael A. Reefe, Brett M. Morris, Peter P. Plavchan, Patrick J. Lowrance, Brice-Olivier Demory, et al. "Transit Timing Variations for AU Microscopii b and c." Astronomical Journal 164, no. 1 (June 30, 2022): 27. http://dx.doi.org/10.3847/1538-3881/ac68e5.
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Abstract We explore the transit timing variations (TTVs) of the young (22 Myr) nearby AU Mic planetary system. For AU Mic b, we introduce three Spitzer (4.5 μm) transits, five TESS transits, 11 LCO transits, one PEST transit, one Brierfield transit, and two transit timing measurements from Rossiter–McLaughlin observations; for AU Mic c, we introduce three TESS transits. We present two independent TTV analyses. First, we use EXOFASTv2 to jointly model the Spitzer and ground-based transits and obtain the midpoint transit times. We then construct an O − C diagram and model the TTVs with Exo-Striker. Second, we reproduce our results with an independent photodynamical analysis. We recover a TTV mass for AU Mic c of 10.8 − 2.2 + 2.3 M ⊕. We compare the TTV-derived constraints to a recent radial velocity (RV) mass determination. We also observe excess TTVs that do not appear to be consistent with the dynamical interactions of b and c alone or due to spots or flares. Thus, we present a hypothetical nontransiting “middle-d” candidate exoplanet that is consistent with the observed TTVs and candidate RV signal and would establish the AU Mic system as a compact resonant multiplanet chain in a 4:6:9 period commensurability. These results demonstrate that the AU Mic planetary system is dynamically interacting, producing detectable TTVs, and the implied orbital dynamics may inform the formation mechanisms for this young system. We recommend future RV and TTV observations of AU Mic b and c to further constrain the masses and confirm the existence of possible additional planet(s).
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Castellano, T., L. Doyle, and D. McIntosh. "The Visibility of Earth Transits." Symposium - International Astronomical Union 202 (2004): 445–47. http://dx.doi.org/10.1017/s0074180900218457.
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The recent photometric detection of planetary transits of the solar-like star HD 209458 at a distance of 47 parsecs suggest that transits can reveal the presence of Jupiter-size planetary companions in the solar neighborhood (Charbonneau et al. 2000; Henry et al. 2000). Recent space-based transit searches have achieved photometric precision within an order of magnitude of that required to detect the much smaller transit signal of an earth-size planet across a solar-size star. Laboratory experiments in the presence of realistic noise sources have shown that CCDs can achieve photometric precision adequate to detect the 9.6 E-5 dimming of the Sun due to a transit of the Earth (Borucki et al. 1997; Koch et al. 2000). Space-based solar irradiance monitoring has shown that the intrinsic variability of the Sun would not preclude such a detection (Borucki, Scargle, Hudson 1985). Transits of the Sun by the Earth would be detectable by observers that reside within a narrow band of sky positions near the ecliptic plane, if the observers possess current Earth epoch levels of technology and astronomical expertise. A catalog of solar-like stars that satisfy the geometric condition for Earth transit visibility are presented.
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Tingley, Brandon. "Transits in Poorly Sampled Data – Gaia and Beyond." Proceedings of the International Astronomical Union 4, S253 (May 2008): 386–87. http://dx.doi.org/10.1017/s1743921308026719.
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AbstractGaia, an ESA cornerstone mission, will obtain of the order of 100 high-precision photometric observations over five years for tens of millions of stars with V < 17. The vast number of red dwarfs in this data set, with their correspondingly deep (high S/N) transits, makes it worthwhile to explore the possibility of detecting transits in such data. Searching for transits under these circumstances requires a very different approach from that used for a normal, highly-sampled transit survey if the search is to be performed in a reasonable amount of time. It should be possible to identify a portion of the transiting Hot Jupiter/M dwarf systems in the data set, if the photometry is as stable and precise as specified by design. This same approach could be applied to ground-based transit searches – a transit survey targeted at red dwarfs with Jupiter-sized companions.
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Jin, Haitao, Fengjun Jin, Jiao’e Wang, Wei Sun, and Libo Dong. "Competition and Cooperation between Shared Bicycles and Public Transit: A Case Study of Beijing." Sustainability 11, no. 5 (March 3, 2019): 1323. http://dx.doi.org/10.3390/su11051323.
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As an eco-friendly transportation mode, shared bicycles provide a new option for public transit users in urban areas. China’s bicycle-sharing market began flourishing in July 2016 and reached a plateau in 2017. How shared bicycles influenced public transit systems during this period is an interesting topic. A case study of Beijing is conducted. This study aims to identify the competitive and cooperative influences of shared bicycles on public transit by exploring the changes in public transit trip distances before and after the upsurge in bicycle-sharing. A histogram shifting method is introduced to examine the influences of shared bicycles on public transit services from a travel distance perspective. A spatial correlation of bicycling usage and public transit changes is calculated using units of gridded cell spaces. The results show: (1) overall transit usage continued growing after the shared bicycles market reached a plateau; (2) short public transits within 2 km decreased while transfers within 2 km increased; and (3) the decrease of short transits and increase of transfers within 3 km were spatially highly correlated to the usage of shared bicycles. Hence, the role of bicycle-sharing systems is competitive for existing public transit systems during short trips and cooperative for connecting transits.
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Schneider, Glenn, Jay M. Pasachoff, and Leon Golub. "Space Studies of the Black-Drop Effect at a Mercury Transit." Highlights of Astronomy 13 (2005): 70–72. http://dx.doi.org/10.1017/s1539299600015100.
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AbstractTransits of Mercury and Venus across the face of the Sun are rare. The 20th century had 15 transits of Mercury and the 21st century will have 14, the two most recent occurring on 15 November 1999 and 7 May 2003. We report on our observations and analysis of a black-drop effect at the 1999 and 2003 transits of Mercury seen in high spatial resolution optical imaging with NASA’s Transition Region and Coronal Explorer (TRACE) spacecraft. We have separated the primary contributors to this effect, solar limb darkening and broadening due to the instrumental point spread function, for the 1999 event. The observations are important for understanding historical observations of transits of Venus, which in the 18th and 19th centuries were basic for the determination of the scale of the solar system. Our observations are in preparation for the 8 June 2004 transit of Venus, the first to occur since 1882. Only five transits of Venus have ever been seen – in 1639, 1761, 1769, 1874, and 1882. These events occur in pairs, whose members are separated by 8 years, with an interval between pairs of 105 or 122 years. Nobody alive has ever seen a transit of Venus.
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Hrudková, Marie, Ian Skillen, Chris Benn, Don Pollacco, Neale Gibson, Yogesh Joshi, Petr Harmanec, and Simon Tulloch. "Searching for transit timing variations in transiting exoplanet systems." Proceedings of the International Astronomical Union 4, S253 (May 2008): 446–49. http://dx.doi.org/10.1017/s1743921308026896.
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AbstractSearching for transit timing variations in the known transiting exoplanet systems can reveal the presence of other bodies in the system. Here we report such searches for two transiting exoplanet systems, TrES-1 and WASP-2. Their new transits were observed with the 4.2m William Herschel Telescope located on La Palma, Spain. In a continuing programme, three consecutive transits were observed for TrES-1, and one for WASP-2 during September 2007. We used the Markov Chain Monte Carlo simulations to derive transit times and their uncertainties. The resulting transit times are consistent with the most recent ephemerides and no conclusive proof of additional bodies in either system was found.
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Dvash, Elad, Yam Peleg, Shay Zucker, and Raja Giryes. "Shallow Transits—Deep Learning. II. Identify Individual Exoplanetary Transits in Red Noise using Deep Learning." Astronomical Journal 163, no. 5 (April 27, 2022): 237. http://dx.doi.org/10.3847/1538-3881/ac5ea2.
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Abstract In a previous paper, we introduced a deep learning neural network that should be able to detect the existence of very shallow periodic planetary transits in the presence of red noise. The network in that feasibility study would not provide any further details about the detected transits. The current paper completes this missing part. We present a neural network that tags samples that were obtained during transits. This is essentially similar to the task of identifying the semantic context of each pixel in an image—an important task in computer vision, called “semantic segmentation,” which is often performed by deep neural networks. The neural network we present makes use of novel deep learning concepts such as U-Nets, Generative Adversarial Networks, and adversarial loss. The resulting segmentation should allow further studies of the light curves that are tagged as containing transits. This approach toward the detection and study of very shallow transits is bound to play a significant role in future space-based transit surveys such as PLATO, which are specifically aimed to detect those extremely difficult cases of long-period shallow transits. Our segmentation network also adds to the growing toolbox of deep learning approaches that are being increasingly used in the study of exoplanets; but, so far mainly for vetting transits, rather than their initial detection.
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Alapini, Aude, and Suzanne Aigrain. "Reconstruction of the transit signal in the presence of stellar variability." Proceedings of the International Astronomical Union 3, S249 (October 2007): 89–92. http://dx.doi.org/10.1017/s174392130801644x.
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AbstractIntrinsic stellar variability can hinder the detection of shallow transits, particularly in space-based data. Therefore, this variability has to be filtered out before running the transit search. Unfortunately, filtering out the low frequency signal of the stellar variability also modifies the transit shape. This results in errors in the measured transit depth and duration used to derive the planet radius, and orbital inclination. We present an evaluation of the magnitude of this effect based on 20 simulated light curves from the CoRoT blind exercise 2 (BT2). We then present an iterative filter which uses the strictly periodic nature of the transits to separate them from other forms of variability, so as to recover the original transit shape before deriving the planet parameters. On average with this filter, we improve the estimation of the transit depth and duration by 15% and 10% respectively.
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Strange, Sharan. "Transits." Callaloo 13, no. 3 (1990): 389. http://dx.doi.org/10.2307/2931317.
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Keene, John. "Transits." Callaloo 16, no. 3 (1993): 515. http://dx.doi.org/10.2307/2932235.
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Llama, J., A. A. Vidotto, M. Jardine, K. Wood, and R. Fares. "Bow shocks and winds around HD 189733b." Proceedings of the International Astronomical Union 9, S302 (August 2013): 245–46. http://dx.doi.org/10.1017/s1743921314002191.
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AbstractAsymmetries in exoplanet transits are a useful tool for developing our understanding of magnetic activity on both stars and planets outside our Solar System. Near-UV observations of the WASP-12 system have revealed asymmetries in the timing of the transit when compared with the optical light curve. In this proceedings we review a number of reported asymmetries and present work simulating near-UV transits for the hot-Jupiter hosting star HD 189733.
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Cherdwongsung, P., S. Awiphan, P. Kittara, K. Matan, and N. Nakharutai. "Detectability of exomoons by examining the signals from a model of transiting exoplanets with moons." Journal of Physics: Conference Series 2145, no. 1 (December 1, 2021): 012009. http://dx.doi.org/10.1088/1742-6596/2145/1/012009.
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Abstract Exomoons are natural satellites of exoplanets. Nowadays, none has been confirmed. However, a number of detection techniques have been proposed, including Transit Timing Variations (TTV) and Transit Duration Variations (TDV) techniques. From a recent study, fitting observed transit with the traditional photocentric fitting model shows unique features around the primary and secondary exomoon transits in TDV and transit depth signals, which might reduce the detectability. The aim of this work is to retrieve the variation of TTV, TDV and transit depth signals of exomoon systems with the photocentric fitting model. One year star-planet-moon transit light curves are simulated with LUNA algorithm and fit with TransitFit. The results show that neglecting the TDV and transit depth data with phase around exomoon’s primary and secondary transits improve the exomoon detectability by a factor of ten and the systems with large moon orbital semi-major axis with nearly edge-on orbit around low mass stars can be detected.
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Fatheddin, Hossein, and Sedighe Sajadian. "Singular Spectrum Analysis of Exoplanetary Transits." Astronomical Journal 168, no. 2 (July 15, 2024): 71. http://dx.doi.org/10.3847/1538-3881/ad582f.
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Abstract Transit photometry is currently the most efficient and sensitive method for detecting extrasolar planets (exoplanets) and a large majority of confirmed exoplanets have been detected with this method. The substantial success of space-based missions such as NASA’s Kepler/K2 and Transiting Exoplanet Survey Satellite has generated a large and diverse sample of confirmed and candidate exoplanets. Singular spectrum analysis (SSA) provides a useful tool for studying photometric time series and exoplanetary transits. SSA is a technique for decomposing a time series into a sum of its main components, where each component is a separate time series that incorporates specific information from the behavior of the initial time series. SSA can be implemented for extracting important information (such as main trends and signals) from the photometry data or reducing the noise factors. The detectability and accurate characterization of an exoplanetary transit signal is principally determined by its signal-to-noise ratio (S/N). Stellar variability of the host star, small planet to star radius ratio, background noises from other sources in the field of observations and instrumental noise can cause lower S/Ns and consequently, more complexities or inaccuracies in the modeling of the transit signals, which in turn leads to the inaccurate inference of the astrophysical parameters of the planetary object. Therefore, implementing SSA leads to a more accurate characterization of exoplanetary transits and is also capable of detecting transits with low S/Ns (S/N < 10). In this paper, after discussing the principles and properties of SSA, we investigate its applications for studying photometric transit data and detecting low S/N exoplanet candidates.
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Cooke, Benjamin F., Don Pollacco, Richard West, James McCormac, and Peter J. Wheatley. "Single site observations of TESS single transit detections." Astronomy & Astrophysics 619 (November 2018): A175. http://dx.doi.org/10.1051/0004-6361/201834014.
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Context. The Transiting Exoplanet Survey Satellite (TESS) has been successfully launched and has begin data acquisition. To expedite the science that may be performed with the resulting data it is necessary to gain a good understanding of planetary yields. Given the observing strategy employed by TESS the probability of detecting single transits in long period systems is increased. These systems require careful consideration. Aims. We aim to simulate the number of TESS transit detections during its two-year mission with a particular emphasis on single transits. We also aim to determine the feasibility of ground-based follow-up observations from a single site. Methods. A distribution of planets was simulated around the approximately four million stars in the TESS candidate target list. These planets were tested for detectable transits and characterised. Based on simulated parameters the single transit detections were further analysed to determine which are amenable to ground-based follow-up. Results. TESS will discover an approximate lower bound of 4700 planets with around 460 being single transits. A large fraction of these will be observable from a single ground-based site. This paper finds that, in a single year, approximately 1000 transit events of around 320 unique TESS single transit detections are theoretically observable. Conclusions. As we consider longer period exoplanets, the need for exploring single transit detections increases. For periods ≳45 days the number of single transit detections outnumber multitransits by a factor of three (82 ± 18 and 25 ± 7, respectively) a factor which only grows as longer period detections are considered. Therefore, based on this paper, it is worth expending the extra effort required to follow-up these more challenging, but potentially very rewarding, discoveries. Additionally, we conclude that a large fraction of these targets can be theoretically observed from a single ground-based site. However, further work is required to determine whether these follow-up efforts are feasible when accounting for target specific criteria.
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Henriksen, Jens H., Søren Møller, Stefan Fuglsang, and Flemming Bendtsen. "Detection of early central circulatory transits in patients with cirrhosis by gamma variate fit of indicator dilution profiles." American Journal of Physiology-Gastrointestinal and Liver Physiology 288, no. 4 (April 2005): G677—G684. http://dx.doi.org/10.1152/ajpgi.00201.2004.
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Patients with cirrhosis have hyperdynamic circulation with abnormally distributed blood volume and widespread arteriovenous communications. We aimed to detect possible very early (i.e., before 4 s) and early (i.e., after 4 s) central circulatory transits and their potential influence on determination of central and arterial blood volume (CBV). Thirty-six cirrhotic patients and nineteen controls without liver disease undergoing hemodynamic catheterization were given central bolus injections of albumin with different labels. Exponential and gamma variate fits were applied to the indicator dilution curves, and the relations between flow, circulation times, and volumes were established according to kinetic principles. No significant very early central circulatory transits were identified. In contrast, early (i.e., 4 s to maximal) transits corresponding to a mean of 5.1% (vs. 0.8% in controls; P < 0.005) of cardiac output (equivalent to 0.36 vs. 0.05 l/min; P < 0.01) were found in cirrhotic patients. These early transits averaged 7.7 vs. 12.7 and 17.2 s of ordinary central transits of cirrhotic patients and controls, respectively ( P < 0.001). Early transits were directly correlated to the alveolar-arterial oxygen difference in the cirrhotic patients ( r = 0.46, P < 0.01) but not in controls ( r = 0.04; not significant). There was good agreement between the CBV determined by the conventional indicator dilution method and that determined by separation of early and ordinary transits by the gamma variate fit method (1.51 vs. 1.53 liter; not significant). In conclusion, no very early central circulatory transits were identified in cirrhotic patients. A significant part of the cardiac output undergoes an early transit, probably through pulmonary shunts or areas with low ventilation-perfusion ratios in cirrhotic patients. Composite determination of CBV by the gamma variate fit method is in close agreement with established kinetic methods. The study provides further evidence of abnormal central circulation in cirrhosis.
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Llama, J., A. A. Vidotto, M. Jardine, K. Wood, and R. Fares. "The Shocking Variability Of Exoplanet Transits." Proceedings of the International Astronomical Union 8, S299 (June 2013): 262–65. http://dx.doi.org/10.1017/s1743921313008521.
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AbstractAsymmetries in exoplanet transits are proving to be a useful tool for furthering our understanding of magnetic activity on both stars and planets outside our Solar System. Near-UV observations of the WASP- 12 system have revealed asymmetries in the timing of the transit when compared with the optical light curve. In this paper we review a number of reported asymmetries and present work simulating near-UV transits for the hot-Jupiter hosting star HD 189733.
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Szabó, Gy M., Z. Garai, A. Brandeker, D. Gandolfi, T. G. Wilson, A. Deline, G. Olofsson, et al. "Transit timing variations of AU Microscopii b and c." Astronomy & Astrophysics 659 (March 2022): L7. http://dx.doi.org/10.1051/0004-6361/202243076.
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Here we report large-amplitude transit timing variations (TTVs) for AU Microcopii b and c as detected in combined TESS (2018, 2020) and CHEOPS (2020, 2021) transit observations. AU Mic is a young planetary system with a debris disk and two transiting warm Neptunes. A TTV on the order of several minutes was previously reported for AU Mic b, which was suggested to be an outcome of mutual perturbations between the planets in the system. In 2021, we observed AU Mic b (five transits) and c (three transits) with the CHEOPS space telescope to follow-up the TTV of AU Mic b and possibly detect a TTV for AU Mic c. When analyzing TESS and CHEOPS 2020−2021 measurements together, we find that a prominent TTV emerges with a full span of ≥23 min between the two TTV extrema. Assuming that the period change results from a periodic process –such as mutual perturbations– we demonstrate that the times of transits in the summer of 2022 are expected to be 30−85 min later than predicted by the available linear ephemeris.
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Gilbert, Gregory J. "Accurate Modeling of Grazing Transits Using Umbrella Sampling." Astronomical Journal 163, no. 3 (February 4, 2022): 111. http://dx.doi.org/10.3847/1538-3881/ac45f4.
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Abstract Grazing transits present a special problem for statistical studies of exoplanets. Even though grazing planetary orbits are rare (due to geometric selection effects), for many low to moderate signal-to-noise ratio cases, a significant fraction of the posterior distribution is nonetheless consistent with a grazing geometry. A failure to accurately model grazing transits can therefore lead to biased inferences even for cases where the planet is not actually on a grazing trajectory. With recent advances in stellar characterization, the limiting factor for many scientific applications is now the quality of available transit fits themselves, and so the time is ripe to revisit the transit fitting problem. In this paper, we model exoplanet transits using a novel application of umbrella sampling and a geometry-dependent parameter basis that minimizes covariances between transit parameters. Our technique splits the transit fitting problem into independent Monte Carlo sampling runs for the grazing, nongrazing, and transition regions of the parameter space, which we then recombine into a single joint posterior probability distribution using a robust weighting scheme. Our method can be trivially parallelized and so requires no increase in the wall clock time needed for computations. Most importantly, our method produces accurate estimates of exoplanet properties for both grazing and nongrazing orbits, yielding more robust results than standard methods for many common star–planet configurations.
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Moges, Kassa. "Impacts of Public Transit on Economic Sustainability: A Case of Addis Ababa Light Rail Transit, Ethiopia." Journal of African Development Studies 7, no. 2 (July 27, 2022): 22–36. http://dx.doi.org/10.56302/jads.v7i2.3108.
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Sustainability of urban public transits is widely accepted but, there are diversified opinions and debates regarding modes of public transit. It is an unanswered whether road-based or rail-based public transport is more sustainable for rapidly growing cities like Addis Ababa. This study is done to empirically evaluate the economic sustainability impacts by Addis Ababa light rail transit (AA-LRT) using performance indicators like travel time, travel cost andemployment generation. Likely, it investigates whether AA-LRT is more economically sustainable or not, compared to other road-based public transits such as City-buses and Midi-buses and compared to the situation before the start of AA- LRT operation. Samples for onboard surveys were selected from transit users and experts through proportional quota sampling. Empirical quasi experiment, multi-criteria analysis and comparative impactanalysis approaches were used together with Paired-samples t-test, One way ANOVA, Ordinal and Logistic Regression. Findings indicate AA-LRT is really producing economic benefits such as travel time savings and affordable travel costs since 2015. Benefits are found to be more economically sustainable in AA-LRT than other road-based public transits. Furthermore, travel time and travel cost benefits in the post-AA-LRT period are better than situations before the start of AA-LRT in 2015. Thus, AA-LRT makes a more significant contribution to economic sustainability. However, it has little weaknesses like inadequate crossing facilities, overcrowded and delayed trips, troubled transfer, fare, and ticket system. To enhance the economic sustainability and address shortcomings, new designs like overhead crossings; expansion of rail network coverage; increasing number of trains and speed; integration among transits; implementation of flat fare and improving ticket system arerecommended.
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Fernández-Lajús, Eduardo, Yamila Miguel, Andrea Fortier, and Romina P. Di Sisto. "Monitoring and analyzing exoplanetary transits from Argentina." Proceedings of the International Astronomical Union 6, S276 (October 2010): 416–17. http://dx.doi.org/10.1017/s174392131102059x.
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AbstractPhotometric observations of transits can be used to derive physical and orbital parameters of the system, like the planetary and stellar radius, orbital inclination and mean density of the star. Furthermore, monitoring possible periodic variations in transit timing of planets is important, since small changes can be caused by the presence of other planets or moons in the system. On the other hand, long term changes in the transit length can be due to the orbital precession of the planets. For these reasons we started an observational program dedicated to observe transits of known exoplanets with the aim of contributing to a better understanding of these planetary systems. In this work we present our first results obtained using the observational facilities in Argentina including the 2.15 telescope at CASLEO.
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Petrucci, Romina, Emiliano Jofré, Martín Schwartz, Andrea Buccino, and Pablo Mauas. "TTVs study in southern stars." Proceedings of the International Astronomical Union 7, S286 (October 2011): 441–44. http://dx.doi.org/10.1017/s1743921312005236.
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AbstractIn this contribution we present 4 complete planetary transits observed with the 40-cm telescope “Horacio Ghielmetti” located in San Juan(Argentina). These objects correspond to a continuous photometric monitoring program of Southern planet host-stars that we are carrying out since mid-2011. The goal of this project is to detect additional planetary mass objects around stars with known transiting-planets through Transit Timing Variations (TTVs). For all 4 transits the depth and duration are in good agreement with the values published in the discovery papers.
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Iglesias Álvarez, Santiago, Enrique Díez Alonso, María Luisa Sánchez Rodríguez, Javier Rodríguez Rodríguez, Fernando Sánchez Lasheras, and Francisco Javier de Cos Juez. "One-Dimensional Convolutional Neural Networks for Detecting Transiting Exoplanets." Axioms 12, no. 4 (March 31, 2023): 348. http://dx.doi.org/10.3390/axioms12040348.
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The transit method is one of the most relevant exoplanet detection techniques, which consists of detecting periodic eclipses in the light curves of stars. This is not always easy due to the presence of noise in the light curves, which is induced, for example, by the response of a telescope to stellar flux. For this reason, we aimed to develop an artificial neural network model that is able to detect these transits in light curves obtained from different telescopes and surveys. We created artificial light curves with and without transits to try to mimic those expected for the extended mission of the Kepler telescope (K2) in order to train and validate a 1D convolutional neural network model, which was later tested, obtaining an accuracy of 99.02% and an estimated error (loss function) of 0.03. These results, among others, helped to confirm that the 1D CNN is a good choice for working with non-phased-folded Mandel and Agol light curves with transits. It also reduces the number of light curves that have to be visually inspected to decide if they present transit-like signals and decreases the time needed for analyzing each (with respect to traditional analysis).
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del Ser, D., O. Fors, and J. Núñez. "TFAW: Wavelet-based signal reconstruction to reduce photometric noise in time-domain surveys." Astronomy & Astrophysics 619 (November 2018): A86. http://dx.doi.org/10.1051/0004-6361/201730671.
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Context. There have been many efforts to correct systematic effects in astronomical light curves to improve the detection and characterization of planetary transits and astrophysical variability. Algorithms such as the trend filtering algorithm (TFA) use simultaneously-observed stars to measure and remove systematic effects, and binning is used to reduce high-frequency random noise. Aims. We present TFAW, a wavelet-based modified version of TFA. First, TFAW aims to increase the periodic signal detection and second, to return a detrended and denoised signal without modifying its intrinsic characteristics. Methods. We modified TFA’s frequency analysis step adding a stationary wavelet transform filter to perform an initial noise and outlier removal and increase the detection of variable signals. A wavelet-based filter was added to TFA’s signal reconstruction to perform an adaptive characterization of the noise- and trend-free signal and the underlying noise contribution at each iteration while preserving astrophysical signals. We carried out tests over simulated sinusoidal and transit-like signals to assess the effectiveness of the method and applied TFAW to real light curves from TFRM. We also studied TFAW’s application to simulated multiperiodic signals. Results. TFAW improves the signal detection rate by increasing the signal detection efficiency (SDE) up to a factor ∼2.5× for low S/R light curves. For simulated transits, the transit detection rate improves by a factor ∼2 − 5× in the low-S/R regime compared to TFA. TFAW signal approximation performs up to a factor ∼2× better than bin averaging for planetary transits. The standard deviations of simulated and real TFAW light curves are ∼40% better compared to TFA. TFAW yields better MCMC posterior distributions and returns lower uncertainties, less biased transit parameters and narrower (by approximately ten times) credibility intervals for simulated transits. TFAW is also able to improve the characterization of multiperiodic signals. We present a newly-discovered variable star from TFRM.
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Ducrot, E., M. Gillon, L. Delrez, E. Agol, P. Rimmer, M. Turbet, M. N. Günther, et al. "TRAPPIST-1: Global results of the Spitzer Exploration Science Program Red Worlds." Astronomy & Astrophysics 640 (August 2020): A112. http://dx.doi.org/10.1051/0004-6361/201937392.
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Context. With more than 1000 h of observation from Feb. 2016 to Oct. 2019, the Spitzer Exploration Program Red Worlds (ID: 13067, 13175 and 14223) exclusively targeted TRAPPIST-1, a nearby (12 pc) ultracool dwarf star, finding that it is orbited by seven transiting Earth-sized planets. At least three of these planets orbit within the classical habitable zone of the star, and all of them are well-suited for a detailed atmospheric characterization with the upcoming JWST. Aims. The main goals of the Spitzer Red Worlds program were (1) to explore the system for new transiting planets, (2) to intensively monitor the planets’ transits to yield the strongest possible constraints on their masses, sizes, compositions, and dynamics, and (3) to assess the infrared variability of the host star. In this paper, we present the global results of the project. Methods. We analyzed 88 new transits and combined them with 100 previously analyzed transits, for a total of 188 transits observed at 3.6 or 4.5 μm. For a comprehensive study, we analyzed all light curves both individually and globally. We also analyzed 29 occultations (secondary eclipses) of planet b and eight occultations of planet c observed at 4.5 μm to constrain the brightness temperatures of their daysides. Results. We identify several orphan transit-like structures in our Spitzer photometry, but all of them are of low significance. We do not confirm any new transiting planets. We do not detect any significant variation of the transit depths of the planets throughout the different campaigns. Comparing our individual and global analyses of the transits, we estimate for TRAPPIST-1 transit depth measurements mean noise floors of ~35 and 25 ppm in channels 1 and 2 of Spitzer/IRAC, respectively. We estimate that most of this noise floor is of instrumental origins and due to the large inter-pixel inhomogeneity of IRAC InSb arrays, and that the much better interpixel homogeneity of JWST instruments should result in noise floors as low as 10 ppm, which is low enough to enable the atmospheric characterization of the planets by transit transmission spectroscopy. Our analysis reveals a few outlier transits, but we cannot conclude whether or not they correspond to spot or faculae crossing events. We construct updated broadband transmission spectra for all seven planets which show consistent transit depths between the two Spitzer channels. Although we are limited by instrumental precision, the combined transmission spectrum of planet b to g tells us that their atmospheres seem unlikely to be CH4-dominated. We identify and model five distinct high energy flares in the whole dataset, and discuss our results in the context of habitability. Finally, we fail to detect occultation signals of planets b and c at 4.5 μm, and can only set 3-σ upper limits on their dayside brightness temperatures (611 K for b 586 K for c).
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Bryant, Edward M., Daniel Bayliss, Alexandre Santerne, Peter J. Wheatley, Valerio Nascimbeni, Elsa Ducrot, Artem Burdanov, et al. "A transit timing variation observed for the long-period extremely low-density exoplanet HIP 41378 f." Monthly Notices of the Royal Astronomical Society: Letters 504, no. 1 (April 16, 2021): L45—L50. http://dx.doi.org/10.1093/mnrasl/slab037.
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ABSTRACT HIP 41378 f is a temperate 9.2 ± 0.1 R⊕ planet with period of 542.08 d and an extremely low density of 0.09 ± 0.02 g cm−3. It transits the bright star HIP 41378 (V = 8.93), making it an exciting target for atmospheric characterization including transmission spectroscopy. HIP 41378 was monitored photometrically between the dates of 2019 November 19 and 28. We detected a transit of HIP 41378 f with NGTS, just the third transit ever detected for this planet, which confirms the orbital period. This is also the first ground-based detection of a transit of HIP 41378 f. Additional ground-based photometry was also obtained and used to constrain the time of the transit. The transit was measured to occur 1.50 h earlier than predicted. We use an analytic transit timing variation (TTV) model to show the observed TTV can be explained by interactions between HIP 41378 e and HIP 41378 f. Using our TTV model, we predict the epochs of future transits of HIP 41378 f, with derived transit centres of TC, 4 = $2459\,355.087^{+0.031}_{-0.022}$ (2021 May) and TC, 5 = $2459\,897.078^{+0.114}_{-0.060}$ (2022 November).
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Almenara, Jose Manuel, Hans J. Deeg, Carlos Lázaro, and María Jesús Arévalo. "An algorithm for the detection of transits of planets around eclipsing binaries in CoRoT." Proceedings of the International Astronomical Union 4, S253 (May 2008): 382–85. http://dx.doi.org/10.1017/s1743921308026707.
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AbstractWe present a matched filter algorithm to detect transits of planets that orbit both components of close eclipsing binaries in CoRoT targets. The formation of binary systems surrounded by disks is one of the most common outcomes of stellar formation; their detection would therefore constitute an important discovery. In an eclipsing binary system, the binary-planet alignment gives raised transit probabilities and the special transit shapes from circumbinary planets provide a unique identifier for their planetary nature; the problems of false alarms are largely avoided. CoRoT data have unprecedented time coverage and photometric precision that make them especially suitable for the search of transits of planets across eclipsing binaries. No reliable detections of circumbinary planets have been reported yet, and their discovery would constitute a new class of planets.
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Estrela, Raissa, Adriana Valio, and Sourav Palit. "Characterization of stellar activity using transits and its impact on habitability." Proceedings of the International Astronomical Union 15, S354 (June 2019): 461–66. http://dx.doi.org/10.1017/s1743921320000174.
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AbstractStellar magnetic field is the driver of activity in stars and can trigger spots, energetic flares, coronal plasma ejections and ionized winds. These phenomena play a crucial role in understanding the internal mechanisms of the star, but can also have potential effects in orbiting planets. During the transit of a planet, spots can be occulted producing features imprinted in the transit light curve. Here, we modelled these features to characterize the physical properties of the spots (radius, intensity, and location). In addition, we monitor spots signatures on multiple transits to estimate magnetic cycles length of Kepler stars. Flares have also been observed during transits in active stars. We derive the properties of the flares and analyse their UV impact on possible living organisms in planets orbiting in the habitable zone.
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Akinsanmi, B., S. C. C. Barros, N. C. Santos, A. C. M. Correia, P. F. L. Maxted, G. Boué, and J. Laskar. "Detectability of shape deformation in short-period exoplanets." Astronomy & Astrophysics 621 (January 2019): A117. http://dx.doi.org/10.1051/0004-6361/201834215.
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Context. Short-period planets are influenced by the extreme tidal forces of their parent stars. These forces deform the planets causing them to attain nonspherical shapes. The nonspherical shapes, modeled here as triaxial ellipsoids, can have an impact on the observed transit light-curves and the parameters derived for these planets. Aims. We investigate the detectability of tidal deformation in short-period planets from their transit light curves and the instrumental precision needed. We also aim to show how detecting planet deformation allows us to obtain an observational estimate of the second fluid Love number from the light curve, which provides valuable information about the internal structure of the planet. Methods. We adopted a model to calculate the shape of a planet due to the external potentials acting on it and used this model to modify the ellc transit tool. We used the modified ellc to generate the transit light curve for a deformed planet. Our model is parameterized by the Love number; therefore, for a given light curve we can derive the value of the Love number that best matches the observations. Results. We simulated the known cases of WASP-103b and WASP-121b which are expected to be highly deformed. Our analyses show that instrumental precision ≤50 ppm min−1 is required to reliably estimate the Love number and detect tidal deformation. This precision can be achieved for WASP-103b in ∼40 transits using the Hubble Space Telescope and in ∼300 transits using the forthcoming CHEOPS instrument. However, fewer transits will be required for short-period planets that may be found around bright stars in the TESS and PLATO survey missions. The unprecedented precisions expected from PLATO and JWST will permit the detection of shape deformation with a single transit observation. However, the effects of instrumental and astrophysical noise must be considered as they can increase the number of transits required to reach the 50 ppm min−1 detection limit. We also show that improper modeling of limb darkening can act to bury signals related to the shape of the planet, thereby leading us to infer sphericity for a deformed planet. Accurate determination of the limb darkening coefficients is therefore required to confirm planet deformation.
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Aigrain, Suzanne. "Probing the Physics of Planets and Stars with Transit Data." Proceedings of the International Astronomical Union 7, S285 (September 2011): 105. http://dx.doi.org/10.1017/s1743921312000361.
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SummaryVirtually all exoplanet detection and characterisation methods are based on time-domain data. This invited talk gave an overview of some recent results in the field, highlighting some of the time-series-specific challenges encountered along the way. In particular it focussed on planetary transits: how to detect shallow, rare transits in noisy data, and how to model them with extreme accuracy to extract information about the transiting planet's atmosphere. Space-based transit surveys also constitute an extraordinary goldmine of information on stellar variability, and the talk touched briefly upon some recent statistical work in that field.
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Lienhard, F., D. Queloz, M. Gillon, A. Burdanov, L. Delrez, E. Ducrot, W. Handley, et al. "Global analysis of the TRAPPIST Ultra-Cool Dwarf Transit Survey." Monthly Notices of the Royal Astronomical Society 497, no. 3 (July 15, 2020): 3790–808. http://dx.doi.org/10.1093/mnras/staa2054.
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ABSTRACT We conducted a global analysis of the TRAPPIST Ultra-Cool Dwarf Transit Survey – a prototype of the SPECULOOS transit search conducted with the TRAPPIST-South robotic telescope in Chile from 2011 to 2017 – to estimate the occurrence rate of close-in planets such as TRAPPIST-1b orbiting ultra-cool dwarfs. For this purpose, the photometric data of 40 nearby ultra-cool dwarfs were reanalysed in a self-consistent and fully automated manner starting from the raw images. The pipeline developed specifically for this task generates differential light curves, removes non-planetary photometric features and stellar variability, and searches for transits. It identifies the transits of TRAPPIST-1b and TRAPPIST-1c without any human intervention. To test the pipeline and the potential output of similar surveys, we injected planetary transits into the light curves on a star-by-star basis and tested whether the pipeline is able to detect them. The achieved photometric precision enables us to identify Earth-sized planets orbiting ultra-cool dwarfs as validated by the injection tests. Our planet-injection simulation further suggests a lower limit of 10 per cent on the occurrence rate of planets similar to TRAPPIST-1b with a radius between 1 and 1.3 R⊕ and the orbital period between 1.4 and 1.8 d.
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Lobodenko, M., Ya V. Pavlenko, I. Kulyk, A. Nahurna, M. Solomakha, and O. Baransky. "COMPARATIVE ANALYSIS OF OBSERVATIONS OF THE SELECTED EXOPLANET TRANSITS OBTAINED AT THE KYIV COMET STATION WITH THE DATABASE OF THE ORBITAL TELESCOPES TESS AND KEPLER." Odessa Astronomical Publications 35 (December 14, 2022): 44–49. http://dx.doi.org/10.18524/1810-4215.2022.35.268007.
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We present a comparative analysis of observations of the selected exoplanet transits obtained at the Kyiv Comet station with the database of the TESS (Transiting Exoplanet Survey Satellite) and Kepler space telescopes. The light curves obtained by the TESS and Kepler orbital telescopes were processed using a program based on the Python package Lightcurve 2.3v which is freely available in the MUST archive (Barbara A. Mikulski Archive for Space Telescopes). The ground based observations were carried out with the 70-cm telescope AZT- 8 (Lisnyky). Photometric processing of the ground based observation was performed by using the Muniwin program. The light curves and parameters of the observed transits as well as the exoplanet orbital parameters obtained from ground based observations were published in the ETD (Exoplanet Transit Database). Determined transit parameters were compared with the results of the TESS command, which are stored in the MUST archive. Here we presents a comparison of the parameters of transit phenomena (period, depth, transit duration) and some orbital parameters obtained from two independent sets of observations, terrestrial and orbital, performed in different epochs.
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Chouqar, J., Z. Benkhaldoun, A. Jabiri, J. Lustig-Yaeger, A. Soubkiou, and A. Szentgyorgyi. "Properties of sub-Neptune atmospheres: TOI-270 system." Monthly Notices of the Royal Astronomical Society 495, no. 1 (May 2, 2020): 962–70. http://dx.doi.org/10.1093/mnras/staa1198.
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ABSTRACT We investigate the potential for the James Webb Space Telescope (JWST) to detect and characterize the atmospheres of the sub-Neptunian exoplanets in the TOI-270 system. Sub-Neptunes are considered more likely to be water worlds than gas dwarfs. We model their atmospheres using three atmospheric compositions – two examples of hydrogen-dominated atmospheres and a water-dominated atmosphere. We then simulate the infrared transmission spectra of these atmospheres for JWST instrument modes optimized for transit observation of exoplanet atmospheres: NIRISS, NIRSpec, and MIRI. We then predict the observability of each exoplanet’s atmosphere. TOI-270c and d are excellent targets for detecting atmospheres with JWST transmission spectroscopy, requiring only 1 transit observation with NIRISS, NIRSpec, and MIRI; higher signal-to-noise ratio can be obtained for a clear H-rich atmosphere. Fewer than three transits with NIRISS and NIRSpec may be enough to reveal molecular features. Water-dominated atmospheres require more transits. Water spectral features in water-dominated atmospheres may be detectable with NIRISS in two or three transits. We find that the detection of spectral features in a cloudy, H-rich atmosphere does not require integrations as long as those required for the water-dominated atmosphere, which is consistent with the differences in atmospheric mean molecular weight. TOI-270c and d could be prime targets for JWST transit observations of sub-Neptune atmospheres. These results provide useful predictions for observers who may propose to use JWST to detect and characterize the TOI-270 planet atmospheres.
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Emilio, Marcelo, Rock Bush, Jeff Kuhn, and Isabelle Scholl. "Solar astrometry with planetary transits." Proceedings of the International Astronomical Union 15, S354 (June 2019): 481–93. http://dx.doi.org/10.1017/s1743921320004068.
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AbstractPlanetary transits are used to measure the solar radius since the beginning of the 18th century and are the most accurate direct method to measure potentially long-term variation in the solar size. Historical measures present a range of values dominated by systematic errors from different instruments and observers. Atmospheric seeing and black drop effect contribute as error sources for the precise timing of the planetary transit ground observations. Both Solar and Heliospheric Observatory (SOHO) and Solar Dynamics Observatory (SDO) made observations of planetary transits from space to derive the solar radius. The International Astronomical Union approved the resolution B3 in 2015, defining a nominal solar radius of precisely 695,700 km. In this work, we show that this value is off by more than 300 km, which is one order of magnitude higher than the error of the most recent solar radius observations.
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Shiltsev, Vladimir. "Venus transits." Physics World 25, no. 06 (June 2012): 21. http://dx.doi.org/10.1088/2058-7058/25/06/28.
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Jenkins, James S., Joseph Harrington, Ryan C. Challener, Nicolás T. Kurtovic, Ricardo Ramirez, Jose Peña, Kathleen J. McIntyre, et al. "Proxima Centauri b is not a transiting exoplanet." Monthly Notices of the Royal Astronomical Society 487, no. 1 (May 11, 2019): 268–74. http://dx.doi.org/10.1093/mnras/stz1268.
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Abstract We report Spitzer Space Telescope observations during predicted transits of the exoplanet Proxima Centauri b. As the nearest terrestrial habitable-zone planet we will ever discover, any potential transit of Proxima b would place strong constraints on its radius, bulk density, and atmosphere. Subsequent transmission spectroscopy and secondary-eclipse measurements could then probe the atmospheric chemistry, physical processes, and orbit, including a search for biosignatures. However, our photometric results rule out planetary transits at the 200 ppm level at 4.5 $\mu$m, yielding a 3σ upper radius limit of 0.4 R⊕ (Earth radii). Previous claims of possible transits from optical ground- and space-based photometry were likely correlated noise in the data from Proxima Centauri’s frequent flaring. Our study indicates dramatically reduced stellar activity at near-to-mid infrared wavelengths, compared to the optical. Proxima b is an ideal target for space-based infrared telescopes, if their instruments can be configured to handle Proxima’s brightness.
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Borsato, L., G. Piotto, D. Gandolfi, V. Nascimbeni, G. Lacedelli, F. Marzari, N. Billot, et al. "Exploiting timing capabilities of the CHEOPS mission with warm-Jupiter planets." Monthly Notices of the Royal Astronomical Society 506, no. 3 (June 24, 2021): 3810–30. http://dx.doi.org/10.1093/mnras/stab1782.
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ABSTRACT We present 17 transit light curves of seven known warm-Jupiters observed with the CHaracterising ExOPlanet Satellite (CHEOPS). The light curves have been collected as part of the CHEOPS Guaranteed Time Observation (GTO) program that searches for transit-timing variation (TTV) of warm-Jupiters induced by a possible external perturber to shed light on the evolution path of such planetary systems. We describe the CHEOPS observation process, from the planning to the data analysis. In this work, we focused on the timing performance of CHEOPS, the impact of the sampling of the transit phases, and the improvement we can obtain by combining multiple transits together. We reached the highest precision on the transit time of about 13–16 s for the brightest target (WASP-38, G = 9.2) in our sample. From the combined analysis of multiple transits of fainter targets with G ≥ 11, we obtained a timing precision of ∼2 min. Additional observations with CHEOPS, covering a longer temporal baseline, will further improve the precision on the transit times and will allow us to detect possible TTV signals induced by an external perturber.
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Carpintero, D. D., and M. Melita. "An alternative stable solution for the Kepler-419 system, obtained with the use of a genetic algorithm." Astronomy & Astrophysics 620 (November 30, 2018): A88. http://dx.doi.org/10.1051/0004-6361/201731997.
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Context. The mid-transit times of an exoplanet may be nonperiodic. The variations in the timing of the transits with respect to a single period, that is, the transit timing variations (TTVs), can sometimes be attributed to perturbations by other exoplanets present in the system, which may or may not transit the star. Aims. Our aim is to compute the mass and the six orbital elements of an nontransiting exoplanet, given only the central times of transit of the transiting body. We also aim to recover the mass of the star and the mass and orbital elements of the transiting exoplanet, suitably modified in order to decrease the deviation between the observed and the computed transit times by as much as possible. Methods. We have applied our method, based on a genetic algorithm, to the Kepler-419 system. Results. We were able to compute all 14 free parameters of the system, which, when integrated in time, give transits within the observational errors. We also studied the dynamics and the long-term orbital evolution of the Kepler-419 planetary system as defined by the orbital elements computed by us, in order to determine its stability.
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Halim, Maisarah Abdul, Nur Aulia Rosni, and Teh Bor Tsong. "Conceptual Framework for Maximizing Service Catchment Area Between Rail Transit and Feeder Service Using Spatial Temporal Regression Technique." IOP Conference Series: Earth and Environmental Science 1240, no. 1 (September 1, 2023): 012010. http://dx.doi.org/10.1088/1755-1315/1240/1/012010.
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Abstract The move towards a more sustainable transport mode is crucial in the Klang Valley by incorporating feeder services to rail network stations. Feeder services will complement the expanding rail transits network and deliver connectivity for areas not covered within rail stations. Past literatures found that feeder services were ineffective during rail breakdown as feeder service was not going or stopping to where it was intended to. Feeder service can be allocated more effectively if we have better idea of targeted service area. Urban planners now have access to a variety of urban analytics because of technological advancements and the rise of smart cities. Data generated are produced across numerous locations and at diverse time scales, providing a significant possibility for data mining to uncover insightful information when both space and time are considered. This study will attempt to assess the community’s accessibility to rail transit through feeder service in Klang Valley. In achieving this a conceptual framework is developed within the objectives of this study which are firstly, to identify built environment factors that influence ridership around transit stations. Secondly, to determine the spatial -temporal relationship between built environment and transit ridership of feeder service and rail transits. Next, the station-level spatial and temporal variability of ridership data between feeder service to rail network is examined. Finally, as the main finding of this study, a framework in maximizing a service catchment transportation service for feeder service and rail transit will be developed. In doing that, the conceptual framework approach is by addressing numerical analytical technique in geographic data, by using spatial temporal regression. This study aspires to provide planning departments and transit agencies with useful guidance to execute targeted policies and develop a sustainable and efficient feeder service coverage area to support rail transits by looking at both spatial and temporal scales.
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Smith, Alexis M. S., and Szilárd Csizmadia. "A CHEOPS Search for Massive, Long-period Companions to the Warm Jupiter K2-139 b." Astronomical Journal 164, no. 1 (June 28, 2022): 21. http://dx.doi.org/10.3847/1538-3881/ac704c.
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Abstract K2-139 b is a warm Jupiter with an orbital period of 28.4 days, but only three transits of this system have previously been observed–in the long-cadence mode of K2–limiting the precision with which the orbital period can be determined and future transits predicted. We report photometric observations of four transits of K2-139 b with ESA’s CHaracterising ExOPlanet Satellite (CHEOPS), conducted with the goal of measuring the orbital obliquity via spot-crossing events. We jointly fit these CHEOPS data alongside the three previously-published transits from the K2 mission, considerably increasing the precision of the ephemeris of K2-139 b. The transit times for this system can now be predicted for the next decade with a 1σ precision less than 10 minutes, compared to over one hour previously, allowing the efficient scheduling of observations with Ariel. We detect no significant deviation from a linear ephemeris, allowing us to exclude the presence of a massive outer planet orbiting with a period less than 150 days, or a brown dwarf with a period less than one year. We also determine the scaled semimajor axis, the impact parameter, and the stellar limb darkening with improved precision. This is driven by the shorter cadence of the CHEOPS observations compared to that of K2, and validates the subexposure technique used for analyzing long-cadence photometry. Finally, we note that the stellar spot configuration has changed from the epoch of the K2 observations; unlike the K2 transits, we detect no evidence of spot-crossing events in the CHEOPS data.
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Vissapragada, Shreyas, Gudmundur Stefánsson, Michael Greklek-McKeon, Antonija Oklopčić, Heather A. Knutson, Joe P. Ninan, Suvrath Mahadevan, et al. "A Search for Planetary Metastable Helium Absorption in the V1298 Tau System." Astronomical Journal 162, no. 5 (November 1, 2021): 222. http://dx.doi.org/10.3847/1538-3881/ac1bb0.
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Abstract Early in their lives, planets endure extreme amounts of ionizing radiation from their host stars. For planets with primordial hydrogen and helium-rich envelopes, this can lead to substantial mass loss. Direct observations of atmospheric escape in young planetary systems can help elucidate this critical stage of planetary evolution. In this work, we search for metastable helium absorption—a tracer of tenuous gas in escaping atmospheres—during transits of three planets orbiting the young solar analog V1298 Tau. We characterize the stellar helium line using HET/HPF, and find that it evolves substantially on timescales of days to months. The line is stable on hour-long timescales except for one set of spectra taken during the decay phase of a stellar flare, where absoprtion increased with time. Utilizing a beam-shaping diffuser and a narrowband filter centered on the helium feature, we observe four transits with Palomar/WIRC: two partial transits of planet d (P = 12.4 days), one partial transit of planet b (P = 24.1 days), and one full transit of planet c (P = 8.2 days). We do not detect the transit of planet c, and we find no evidence of excess absorption for planet b, with ΔR b/R ⋆ < 0.019 in our bandpass. We find a tentative absorption signal for planet d with ΔR d/R ⋆ = 0.0205 ± 0.054, but the best-fit model requires a substantial (−100 ± 14 minutes) transit-timing offset on a two-month timescale. Nevertheless, our data suggest that V1298 Tau d may have a high present-day mass-loss rate, making it a priority target for follow-up observations.
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Rabus, M., R. Alonso, H. J. Deeg, J. A. Belmonte, J. M. Almenara, R. L. Gilliland, and T. M. Brown. "Transit timing variability in TrES-1." Proceedings of the International Astronomical Union 4, S253 (May 2008): 432–35. http://dx.doi.org/10.1017/s1743921308026859.
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AbstractWe observed several transits of the exoplanet TrES-1 distributed over four years from 2004 to 2007. On the basis of these observations and additional published data, we present a mid-transit time analysis. The aim is to find indications of the presence of a third body by analysing the difference between the calculated and observed transit times.
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Mallonn, M., K. Poppenhaeger, T. Granzer, M. Weber, and K. G. Strassmeier. "Detection capability of ground-based meter-sized telescopes for shallow exoplanet transits." Astronomy & Astrophysics 657 (January 2022): A102. http://dx.doi.org/10.1051/0004-6361/202140599.
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Meter-sized ground-based telescopes are frequently used today for the follow-up of extrasolar planet candidates. While the transit signal of a Jupiter-sized object can typically be detected to a high level of confidence with small telescope apertures as well, the shallow transit dips of planets with the size of Neptune and smaller are more challenging to reveal. We employ new observational data to illustrate the photometric follow-up capabilities of meter-sized telescopes for shallow exoplanet transits. We describe in detail the capability of distinguishing the photometric signal of an exoplanet transit from an underlying trend in the light curve. The transit depths of the six targets we observed, Kepler-94b, Kepler-63b, K2-100b, K2-138b, K2-138c, and K2-138e, range from 3.9 ppt down to 0.3 ppt. For five targets of this sample, we provide the first ground-based photometric follow-up. The timing of three targets is precisely known from previous observations, and the timing of the other three targets is uncertain and we aim to constrain it. We detect or rule out the transit features significantly in single observations for the targets that show transits of 1.3 ppt or deeper. The shallower transit depths of two targets of 0.6 and 0.8 ppt were detected tentatively in single light curves, and were detected significantly by repeated observations. Only for the target of the shallowest transit depth of 0.3 ppt were we unable to draw a significant conclusion despite combining five individual light curves. An injection-recovery test on our real data shows that we detect transits of 1.3 ppt depth significantly in single light curves if the transit is fully covered, including out-of-transit data toward both sides, in some cases down to 0.7 ppt depth. For Kepler-94b, Kepler-63b, and K2-100b, we were able to verify the ephemeris. In the case of K2-138c with a 0.6 ppt deep transit, we were able to refine it, and in the case of K2-138e, we ruled out the transit in the time interval of more than ±1.5 σ of its current literature ephemeris.
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Jontof-Hutter, Daniel, Paul A. Dalba, and John H. Livingston. "TESS Observations of Kepler Systems with Transit Timing Variations." Astronomical Journal 164, no. 2 (July 7, 2022): 42. http://dx.doi.org/10.3847/1538-3881/ac7396.
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Abstract We identify targets in the Kepler field that may be characterized by transit timing variations and are detectable by the Transiting Exoplanet Survey Satellite (TESS). Despite the reduced signal-to-noise ratio of TESS transits compared to Kepler, we recover 48 transits from 13 systems in Sectors 14, 15, 26, 40 and 41. We find strong evidence of a nontransiting perturber orbiting Kepler-396 (KOI-2672) and explore two possible cases of a third planet in that system that could explain the measured transit times. We update the ephemerides and mass constraints where possible at KOI-70 (Kepler-20), KOI-82 (Kepler-102), KOI-94 (Kepler-89), KOI-137 (Kepler-18), KOI-244 (Kepler-25), KOI-245 (Kepler-37), KOI-282 (Kepler-130), KOI-377 (Kepler-9), KOI-620 (Kepler-51), KOI-806 (Kepler-30), KOI-1353 (Kepler-289), and KOI-1783 (Kepler-1662).
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Grosson, Theodore A., and Christopher M. Johns-Krull. "Color Dependence of Planetary Transit Depths due to Large Starspots and Dust Clouds: Application to PTFO 8-8695." Research Notes of the AAS 5, no. 11 (November 16, 2021): 264. http://dx.doi.org/10.3847/2515-5172/ac391d.
Full textAbstract:
Abstract Although thousands of exoplanets have now been discovered, there is still a significant lack of observations of young planets only a few Myr old. Thus there is little direct evidence available to differentiate between various models of planet formation. The detection of planets of this age would provide much-needed data that could help constrain the planet formation process. To explore what transit observations of such planets may look like, we model the effects of large starspots and dust clouds on the depths of exoplanet transits across multiple wavelengths. We apply this model to the candidate planet PTFO 8-8695b, whose depths vary significantly across optical and infrared wavelengths. Our model shows that, while large starspots can significantly increase the color dependence of planetary transits, a combination of starspots and a large cloud surrounding the planet is required to reproduce the observed transit depths across four wavelengths.
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Chen, G., E. Pallé, H. Parviainen, H. Wang, R. van Boekel, F. Murgas, F. Yan, et al. "An enhanced slope in the transmission spectrum of the hot Jupiter WASP-104b." Monthly Notices of the Royal Astronomical Society 500, no. 4 (November 20, 2020): 5420–35. http://dx.doi.org/10.1093/mnras/staa3555.
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ABSTRACT We present the optical transmission spectrum of the hot Jupiter WASP-104b based on one transit observed by the blue and red channels of the Double Spectrograph (DBSP) at the Palomar 200-inch telescope and 14 transits observed by the MuSCAT2 four-channel imager at the 1.52-m Telescopio Carlos Sánchez. We also analyse 45 additional K2 transits, after correcting for the flux contamination from a companion star. Together with the transit light curves acquired by DBSP and MuSCAT2, we are able to revise the system parameters and orbital ephemeris, confirming that no transit timing variations exist. Our DBSP and MuSCAT2 combined transmission spectrum reveals an enhanced slope at wavelengths shorter than 630 nm and suggests the presence of a cloud deck at longer wavelengths. While the Bayesian spectral retrieval analyses favour a hazy atmosphere, stellar spot contamination cannot be completely ruled out. Further evidence, from transmission spectroscopy and detailed characterization of the host star’s activity, is required to distinguish the physical origin of the enhanced slope.
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Burrows, Adam. "New Insights into Extrasolar Giant Planets." Symposium - International Astronomical Union 202 (2004): 255–60. http://dx.doi.org/10.1017/s0074180900218020.
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In this contribution, I summarize recent theoretical attempts to understand important diagnostic aspects of close-in extrasolar giant planets, in particular transits and albedos. The potential scientific returns of the anticipated direct detection of “EGPs” in transit and/or in reflection are significant.
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Lin, Zifan, Ryan J. MacDonald, Lisa Kaltenegger, and David J. Wilson. "Differentiating modern and prebiotic Earth scenarios for TRAPPIST-1e: high-resolution transmission spectra and predictions for JWST." Monthly Notices of the Royal Astronomical Society 505, no. 3 (June 3, 2021): 3562–78. http://dx.doi.org/10.1093/mnras/stab1486.
Full textAbstract:
ABSTRACT The TRAPPIST-1 system is a priority target for terrestrial exoplanet characterization. TRAPPIST-1e, residing in the habitable zone, will be observed during the James Webb Space Telescope (JWST) GTO Program. Here, we assess the prospects of differentiating between prebiotic and modern Earth scenarios for TRAPPIST-1e via transmission spectroscopy. Using updated TRAPPIST-1 stellar models from the Mega-MUSCLES survey, we compute self-consistent model atmospheres for a 1 bar prebiotic Earth scenario and two modern Earth scenarios (1 and 0.5 bar eroded atmosphere). Our modern and prebiotic high-resolution transmission spectra ($0.4\!-\! 20\, \rm{\mu m}$ at R ∼100 000) are made available online. We conduct a Bayesian atmospheric retrieval analysis to ascertain the molecular detectability, abundance measurements, and temperature constraints achievable for both scenarios with JWST. We demonstrate that JWST can differentiate between our prebiotic and modern Earth scenarios within 20 NIRSpec Prism transits via CH4 abundance measurements. However, JWST will struggle to detect O3 for our modern Earth scenario to $\gt 2\, \sigma$ confidence within the nominal mission lifetime (∼ 80 transits over 5 yr). The agnostic combination of N2O and/or O3 offers better prospects, with a predicted detection significance of $2.7\, \sigma$ with 100 Prism transits. We show that combining MIRI LRS transits with Prism data provides little improvement to atmospheric constraints compared to observing additional Prism transits. Though biosignatures will be challenging to detect for TRAPPIST-1e with JWST, the abundances for several important molecules – CO2, CH4, and H2O – can be measured to a precision of ≲ 0.7 dex (a factor of 5) within a 20 Prism transit JWST program.