The Infrared Emissions Of Debris Disks And Protoplanetary Disks

Circumstellar disks play an important role in the early stage stellar evolution and formation of planets. These disks can be detected most effectively through their infrared emission. AKARI/FIS Brigh Source Catalog (AKARIBSC) is a public unbiased all-sky far-infrared point source catalog covering a broad wave-length range from65to160μm, which provides unique dataset for searching of cirumstellar disks. The thesis presents our work on the searching debris disks and protoplanetary disks with AKARIBSC during my PhD study.The first work focuses on bright debris disk candidates detected with the AKARI/FIS. We cross-correlate the Hipparcos main-sequence star catalog with the AKARI/FIS Bright Source Catalog, and identify136stars (at>90%re-liability) with far-infrared detections at least in one band. After rejecting57stars classified as young stellar objects, Be stars and other type stars with known dusty disks or with potential contaminations, and4stars without infrared excess emission, we obtain a sample of75candidate stars with debris disks. Stars in our sample cover spectral types from B to K with most being early types. This represents a unique sample of luminous debris disks that derived uniformly from an all sky survey with a spatial resolution a factor of four better than the previ-ous such survey by IRAS. Moreover, by collecting the infrared photometric data from other public archives, almost three quarters of them have infrared excesses in more than one band, allowing the estimate of the dust temperatures. We fit the blackbody model to the broad band spectral energy distribution of these stars to derive the statistical distribution of the disk parameters. Four B stars with excesses in four or more bands require a double blackbody model, with the high one around100or200K, and the low one around40-50K.The other work present our effort on hunting for long-lived protoplanetary disks detected in AKARI/FIS. We cross-correlate the Hipparcos catalog with AKARI/FIS YSO catalog, and identified25far infrared emission stars. The reliability of the match is over90rejecting4stars classified as planetary nebular or red gaint star, we got21YSOs in the solar neighbor. The central objects cover spectral types from B to M. The Hipparcos parallaxes enable us to place the ob-jects in the H-R diagram, which can be used to determine their age by isochrones. Among these objects, two YSOs has been found to have age larger than10Myr. Optical to Infrared Spectra Energy Distribution of these two YSOs are consistent with those of type Ⅱ YSOs with protoplanetary disks. Furthermore, from the SED fitting with Liu’s theoretical models, the age of these two sources is constrained tol4.1±4.2Myr and16.8±4.4Myr, respectively. Therefore, two YSO candidates with long-lived protoplanetary disks have been detected in AKARI/FIS. The presence of long-lived of protoplanetary disks has significant implications for the formation of planets and their host stars.