Single site observations of TESS single transit detections

Abstract

Context. 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. To simulate the number of TESS transit detections during its 2 year mission with a particular emphasis on single transits. Additionally, to determine the feasibility of ground-based follow-up observations from a single site. Methods. A distribution of planets is simulated around the ∼ 4 million stars in the TESS Candidate Target List. These planets are tested for detectable transits and characterised. Based on simulated parameters the single transit detections are 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 3 (82±18 and 25±7 respectively) a factor which only grows as longer period detections are considered. Therefore, based on the results of 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 just 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.

An examination of the effect of the TESS extended mission on southern hemisphere monotransits

“…Due to the all-sky nature of TESS, as well as its relatively short baselines for much of the sky, it produces a large yield of mono-transiting systems: planets which will exhibit only a single transit during TESS observations. The predicted yield of these monotransits has been estimated in Cooke et al (2018) and Villanueva Jr. et al (2018). Recently it has been announced that the TESS mission will be extended, and as part of the extension plans it is envisaged that TESS will re-observe the southern ecliptic hemisphere in the fourth year of its mission (see NASA 2019 senior review 2 and NASA response 3 ).…”

CHEOPS observations of TESS primary mission monotransits

“…These systems are distributed across the sky as shown in Figure 2 with period and planetary radius distributions as shown in Figures 5 and 6. For more details of the TESS monotransit population see Cooke et al (2018) and Cooke et al (2019). We have then explored the feasibility of using CHEOPS to re-observe these monotransiting systems.…”

“…Planets are generated around these stars based on occurrence rates as functions of radius and period from Dressing & Charbonneau (2015) (M-stars) and Fressin et al (2013) (AFGK-stars). We determine transit parameters as in Cooke et al (2018) using equations from Winn (2010) and Barclay et al (2018).…”

“…This method involves taking the timestamps from actual TESS data for each available sector, stripping out data points with systematics and only simulating observations at the remaining times. This produces a more realistic observing strategy than was used in 1 http://archive.stsci.edu/tess/tic_ctl.html Cooke et al (2018). The improvement between the method employed here and the Cooke et al (2019) implementation of this method is that data for more TESS sectors is available.…”

“…These are targets identified as transiting planets by the TESS primary mission but with only one observed transit. Without the ability to fold multiple transits these systems require significant effort to properly characterise but are of interest since they are generally have longer periods than other TESS detections (those that exhibit multiple transits) (Cooke et al 2018). Better characterisation of these systems is vital to help develop our E-mail: b.cooke@warwick.ac.uk understanding of how planetary characteristics vary with orbital separation (Nottale et al 2004;Jones et al 2004;Alibert et al 2013).…”