Detection Of Stellar Flares Via Photometry And Confirmation Of An Exoplanet

The detection and characterization of extra-solar planets?exoplanets?is one of the hottest fields in the past thirty years.Since the detection of the first exoplanet around sun-like stars,the formation,evolution,and habitability of exoplanets have been en-thusiastically studied by astronomers.The habitability of a planet,which is the only known vessel of life,is directly linked to the distance between itself and its host star?whether the planet is in the habitable zone of its host star?and the physical properties of the planet?whether the planet is Earth-like?.Moreover,the irradiation the planet receives from its host star is also an important factor on the habitability of the planet.It is therefore crucial to study the long-term and eruptive short-term radiation change of the host star.By studying the abrupt eruptive phenomenon on the surfaces of stars,namely stellar flares,this thesis searches for statistical properties of stellar flares in the optical band,getting ready for future study of planetary habitability.Being unpredictable beforehand,large field-of-view and long baseline photometry is one of the most important methods in studying stellar flares.While the Kepler spacecraft has provided more than 4,000 exoplanets,the high-precision working mode,namely the long cadence mode,inevitably suffers from undersampling which hinders the detailed study of stellar flares.Since 2015,our group joined the astronomical observation carried out in Antarc-tica that utilized the extraordinary condition and the advantage of polar nights and started the CHinese Exoplanet Survey Program from Antarctica?CHESPA?.By using the CSTAR 2008 data set,the AST3-II 2016 data set,as well as the radial velocity data taken by the Australian AAT telescope in 2015,the detection and characterization of stellar flares and the confirmation of an exoplanet candidate are carried out.The detailed results are listed as follows.In the second chapter,based on the features of the CSTAR 2008 data set,a robust and reliable method of flare-detection is developed.Using this method,fifteen stellar flares on thirteen sources are found,with two of them being known variables,including one active X-ray emitter.As for the properties of stellar flares,we define the flare skewness parameter that describes the ratio between the energy dissipation time and the energy injection time during a flare event.A linear relation between the duration and the decay time of a flare is found.Using simple math transformation,a typical value for the skewness parameter is calculated to be 3.67 for the flaring sources detected in this work.By fitting for the primary and secondary flares of one of the flare event on2MASS J174728.65-884609.43,the parameters of individual flares are obtained.In the third chapter,based on the detection method introduced in Chapter 2,a more comprehensive and adaptive flare detection method is developed,using which 20reliable stellar flare events are found.The fitting method in Chapter 2 is also improved to fit for the actual flare peak missed by the observation data.Based on the fitting result,flare parameters such as duration,amplitude,energy,and skewness are also calculated.Comparing to the work in Chapter 2,by more accurately defining the start,end,and peak time of a flare event,the skewness parameter is also updated to be 3.0 for the sources in this work.Combining with the distance data given by the Gaia satellaite,the i-band energy is calculated for all flares,with the smallest one being 10³⁴erg and the most energetic one being 10³⁸.It is also found that the average energy released by flares on giant stars are larger than those on dwarf stars,with one case being energetic enough that it could permanently destroy the atmosphere of any putative planets close to it.In the fourth chapter,by combining the 2008 data set of the CSTAR telescope and the radial velocity data taken in 2015 by the AAT telescope,a joint RV-transit fit is carried out,whose result shows that CEC-8 b is highly likely to be an inflated hot Jupiter,with its density being only one tenth of that of Jupiter.A comparison with all500-plus exoplanets with known densities in the NASA Exoplanet Archive shows that CEC-8 b is one of ten least dense planets.CEC-8 b is also considered to be a good target for atmospheric study due to its similarities with other inflated hot Jupiters.Finally,in the fifth chapter,I will briefly summarize all works I have involved in and look to the future.