📝 Original Info
- Title: Benefits of Ground-Based Photometric Follow-Up for Transiting Extrasolar Planets Discovered with Kepler and CoRoT
- ArXiv ID: 0907.5193
- Date: 2015-05-13
- Authors: Researchers from original ArXiv paper
📝 Abstract
Currently, over forty transiting planets have been discovered by ground-based photometric surveys, and space-based missions like Kepler and CoRoT are expected to detect hundreds more. Follow-up photometric observations from the ground will play an important role in constraining both orbital and physical parameters for newly discovered planets, especially those with small radii (R_p less than approximately 4 Earth radii) and/or intermediate to long orbital periods (P greater than approximately 30 days). Here, we simulate transit light curves from Kepler-like photometry and ground-based observations in the near-infrared (NIR) to determine how jointly modeling space-based and ground-based light curves can improve measurements of the transit duration and planet-star radius ratio. We find that adding observations of at least one ground-based transit to space-based observations can significantly improve the accuracy for measuring the transit duration and planet-star radius ratio of small planets (R_p less than approximately 4 Earth radii) in long-period (~1 year) orbits, largely thanks to the reduced effect of limb darkening in the NIR. We also demonstrate that multiple ground-based observations are needed to gain a substantial improvement in the measurement accuracy for small planets with short orbital periods (~3 days). Finally, we consider the role that higher ground-based precisions will play in constraining parameter measurements for typical Kepler targets. Our results can help inform the priorities of transit follow-up programs (including both primary and secondary transit of planets discovered with Kepler and CoRoT), leading to improved constraints for transit durations, planet sizes, and orbital eccentricities.
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Deep Dive into Benefits of Ground-Based Photometric Follow-Up for Transiting Extrasolar Planets Discovered with Kepler and CoRoT.
Currently, over forty transiting planets have been discovered by ground-based photometric surveys, and space-based missions like Kepler and CoRoT are expected to detect hundreds more. Follow-up photometric observations from the ground will play an important role in constraining both orbital and physical parameters for newly discovered planets, especially those with small radii (R_p less than approximately 4 Earth radii) and/or intermediate to long orbital periods (P greater than approximately 30 days). Here, we simulate transit light curves from Kepler-like photometry and ground-based observations in the near-infrared (NIR) to determine how jointly modeling space-based and ground-based light curves can improve measurements of the transit duration and planet-star radius ratio. We find that adding observations of at least one ground-based transit to space-based observations can significantly improve the accuracy for measuring the transit duration and planet-star radius ratio of small pla
📄 Full Content
Over the past decade, ground-based photometry has discovered over forty planets that transit their host star. A majority of these known transiting planets have radii and masses that are comparable to Jupiter, and most have orbital periods that are less than five days.1 Currently, space-based planet searches (e.g., CoRoT and Kepler) are poised to extend the reach of the transit method to small planets (R p 4 R ⊕ ) and longer orbital periods (P 30 days). These systems present exciting opportunities for follow-up observations to characterize the physical properties of potentially rocky planets. As the number of known transiting planets grows, it will become increasingly important to make the best possible use of followup resources (Clarkson et al. 2007;O'Donovan et al. 2007;Pont et al. 2007;Latham et al. 2008). Indeed, merely confirming the planet candidates from CoRoT and Kepler will present a significant challenge, as the target stars will be fainter, the planets will be smaller, and the orbital periods will be longer than for the targets discovered in ground-based surveys. Highresolution imaging will be important for rejecting blends with background objects or wide binary companions. Moderate-resolution optical and infrared spectroscopy will be essential for rejecting spectroscopic binaries and hierarchical systems. Finally, at least several highprecision Doppler observations will be needed to confirm planet candidates and to measure planet masses and orbits (Gautier et al. 2007;Latham 2007;Brown & Latham 2008).
There will continue to be an important role for follow-up photometric observations. For ground-based transit searches, follow-up observations have routinely obtained higher quality photometry, provided more precise measurements of planet and orbital parameters, and served as the basis for transit timing variations. In this paper, we focus on yet another potential role for follow-up photometric observations. Due to an approximate degeneracy between the stellar limb darkening parameters and the impact parameter (the minimum distance from the center of the planet to the center of the stars when projected onto the sky plane; e.g., see also Pál 2008), white light observations provide only weak constraints on the impact parameter. The uncertainty in the impact parameter propagates to interfere with the measurement of the planet-star radius ratio and transit duration (Knutson et al. 2007). An accurate measurement of the radius ratio is critical for establishing the size, density, and composition of transiting planets. A precise measurement of the transit duration can constrain the stellar density (and hence the stellar size) for planets on circular orbits (e.g., Torres et al. 2008) and/or help to characterize the orbital eccentricity (e.g., Ford et al. 2008;Bakos et al. 2009). Thus, the near degeneracy between the impact parameter and stellar limb darkening model will affect all Kepler observations (and early CoRoT discoveries) that use a single, broad, white broadband filter, which can be severely affected by stellar limb darkening. Fortunately, ground-based follow-up photometry is routinely performed at near-infrared (NIR) wavelengths which are only minimally impacted by limb darkening (e.g., observing with a Sloan i ′ or z ′ filter; see Holman et al. 2006, for example, as well as §3.2 in this paper). Thus, NIR photometry (or space-based IR photometry; e.g., Nutzman et al. 2009) can enable a more precise measurement of the impact parameter, planet-star radius ratio, and transit duration (as shown in §3). Ground-based follow-up photometry may offer additional advantages for very high cadence observations to search for transit timing variations (Agol et al. 2005;Holman & Murray 2005;Ford & Holman 2007) and/or changes in the transit duration or shape that could be caused due to moons, rings, or tidal bulge (Kipping 2009;Ragozzine & Wolf 2009).
Our investigation of the potential contributions of ground-based transit follow-up observations is further motivated by the improving precision of ground-based photometry for transit follow-up applications. Once the host star and transit times are known, nearly routine ground-based transit follow-up observations can provide photometry with a precision of ∼1 millimagnitude (mmag) at a rate of ∼1 observation per minute for 11th and 12th magnitude stars, even with a relatively small observatory [e.g., 1.2m Fred L. Whipple Observatory (FLWO); Holman et al. 2006;Winn et al. 2007]. Recent observations with larger telescopes have achieved even higher photometric precisions for favorable planet-host stars, e.g., 0.39 mmag/min in z ′ -band for a V =12 star with the 2.2m University of Hawaii (UH) telescope (rescaled from the quoted precision for a V =12.7 star; Johnson et al. 2009) and 0.315 mmag/min in z-band for a V =12 star with the 6.5m Magellan telescope (rescaled from the quoted precision for a V =12.5 star; Winn et al. 2009). It is particularly noteworthy that differen
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