| Since the first exoplanet discovered in the late 20th century,exoplanet science has become one of the hottest area in astronomy.Currently,thousands of exoplanets have been discovered.The plenty of information brought by these exoplanets has led us to a deeper understanding of the formation and evolution of planetary systems.One of the hot issues in the field of exoplanet research is to find planets in habitable zone around other stars.It is not only to find another home for us,but also useful to answer the important scientific questions,such as "Where do we come from?"Currently,dozens of planets in habitable zone have been discovered.Unfortu-nately,most of these planets lack complete information of parameters,especially mass information.For example,the traditional radial velocity method can only measure the minimum mass of the planet.It brings difficulties for us to study the nature of these planets and habitability of the planets.We need a way to obtain planetary parameters accurately.As a traditional astronomical method,astrometry method plays an impor-tant role in determining planets' orbital elements and planetary mass.And astrometry measurements can simultaneously obtain planetary mass and planetary orbital param-eters.However,astrometry measurements of exoplanets require high detection preci-sion.In recent years,the detection precision of astrometry has been greatly improved.In 2013,the ESA launched the Gaia satellite,which increased the precision of astrom-etry measurements to the level of ?as,which made it possible for us to detect planetary systems.In order to make good use of future astrometry data,we study how to calculate the mass and orbit information of the planet from the celestial positions.We have built a data processing method to fit the orbital elements of each planet in the multiple planets system.It has been verified that this method can be used to obtain the orbital elements and mass information of the planet.However,we find that Gaia's current precision can provide more complete planetary parameters of jupiter-like planets within 500pc.But the detection precision is still not enough for terrestrial planets,especially for terrestrial planets in habitable zone.Because astrometric measurements can provide more comprehensive parameters of the planets,China is also planning the next generation of high-precision astrometric satellites,HEPS(Habitable ExoPlanets Survey).The precison of the HEPS satellite is designed to achieve sub-micro arcsecond precision,and its goal is to detect habitable terrestrial planets in a solar-like star system within 30pc from us.However,HEPS is expected to achieve high-precision observations only for a limited number of specific targets.Therefore,we simulated the astrometric signals of the planetary systems with al-ready found exoplanets near the solar system,and fit the planetary parameters using our fitting method.Our simulation results provide observational candidates for the future observation of HEPS.At the same time,we analyzed the factors affecting the detec-tion of habitable planets for different multi-planet systems.We find that the detected probability of a planet is related to the planet's signal-to-noise ratio,the time interval of observation,the duration of observation,and the other planets in the planetary system.We give an approximate expression of these influencing factors through simulation.This approximation can be used not only for the observation targets we provide for HEPS,but also for other observation targets to estimate the probability of detection of habitable planets,and even extend our analysis to the other astrometric projects,such as analysis of the results of the Gaia satellite detection.Based on the observation mode of HEPS,this paper simulates and fits the astro-nomical measurement signals of the planetary system in the habitable zone.By fitting the results,the source that is most suitable for HEPS observation is selected,and the fac-tors affecting the fitting results are analyzed.Based on these factors,we can optimize the observation strategy and offer important reference for future astrometric measure-ment plans and data processing methods.In Chapter 1,we review the history of detecting exoplanets in the habitable zone,especially the efforts made to study habitable planets.By comparing and analyzing various methods for detecting terrestrial planets in the habitable zone,the advantages of astrometry method in detecting exoplanets in the habitable zone is obvious.We will discuss the present status of astrometry and give a brief introduction to the future astrometry project.In Chapter 2,we introduce the astrometry signal of the stars caused by the plan-ets,the astrometry observation of the exoplanets,and the process which we process the astrometric data and calculate the parameters of the planetary orbits.We firstly es-tablish a model of stellar motion including the annual parallax and the proper motion of the stars.Combined with the error model of HEPS,we simulate the measured sig-nal of the celestial objects,and then establish a program using Monte Carlo simulation and Levenberg-Marquardt method.This process is quick and efficient to obtain the planetary orbital parameters.In Chapter 3,we use the astrometry signal simulation and planetary parameter inversion methods to the detection of terrestrial planets in the habitable zone around the solar-like stars.We firstly propose the use of planetary detect probability as the measurement of the quality of astrometry detection of a planet,and then we study the signal-to-noise ratio of the planet and the influence of other planets' mass and semi-major axis in the multi-planetary system.In Chapter 4,we will examine the real plane-tary systems in conjunction with Gaia DR2 data.By calculating the detecet probability of planets in the habitable zone in these systems,we provide observation candidates for future astrometric projects,such as HEPS.At the same time,we will study the effect of data sampling interval and observation duration on the probability of detection.In the end,we get an estimate of the detect probability of a planet in the habitable zone associated with the planet's signal-to-noise ratio,the mass and semi-major axis of the other planets in the system,and different observation strategies.Finally,in Chapter 5,I will summarize the work described above and discuss what important information astrometry method can provide,in addition to detecting planets in habitable zone,and what scientific problems of exoplanets it can help us to solve.By discussing these scientific questions,we summarize the important breakthroughs which astrometry method can make in the research field of exoplanets.Then I will discuss about the follow-up research plan. |
PDF Full Text Request