The Study of Optical Variations of LMXB with LOT – XTE J1118+480 (KV UMa)
| Autor: | Ting-Chang Yang, 楊庭彰 |
|---|---|
| Rok vydání: | 2004 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 93 We observed the low mass X-ray binary (LMXB) -- XTE J1118+480 in optical band with Lulin One-meter Telescope for its timing series properties. Zurita et al. (2002) found XTE J1118+480 still revealed superhump phenomenon near the quiescent state in 2001. We try to observe it with LOT to verify if there are superhumps in the fully quiescent state, and to distinguish if the source is a permanent superhump or late superhump system. We use and setup the standard procedures, including data reductions and the CL scripts for the photometry, to accelerate the processes for the photometric data. Differential photometry is applied to measure the intensity variations of the target star, so the selection for proper comparison stars is rather important. We propose some suggestions for selecting the comparison stars to avoid the disturbances for the timing series analysis. The companion star of LMXB is dominated in the optical observation. Because of proper geometry relation between the binary and observor, the light curve will show ellipsoidal modulation. Ellipsoidal modulation implies the orbital period of the binary system. We can derive the orbital period from our observation for about one and half years, and discuss about the evolution of the orbital period. We mainly use Lomb-Scargle (LS) power spectrum for the periodicity analysis, and derive the signal frequency error from Monte Carlo simulation. For the observation from 2003 to 2004, the observation data is divided into five data sets, and the best estimated orbital period is about 0.16993349 +/- 0.00000090 day by the phase analysis method. The result is consistent with that of Zurita et al. (2002). It is verified that there are no significant change for the orbital period (.P~ 0) during the 2001-2004 observation. The result is consistent with the small period change (.P/ P~ 10^-7 to 10^-8 yr^-1) of LMXB system. We can fit an first order approximated model of ellipsoidal modulation with the best estimated orbital period. Subtracting the modeled light curve from the origin one, there maybe superhump signals left in the residual light curves. But after our analysis of power spectrum, there is no significant detection near the superhump frequency and its harmonics of Zurita et al. (2002). Thus, we can not detect superhump signals with LOT from more than one year observations. From the variation shape of the light curves, we consider that the accretion disk of the system contributes too less intensity for the optical light curve, so the superhump signals can not be detected. We can not conclude that if XTE J1118+480 is a late superhump or permanent superhump system. It maybe need better instruments or analytical methods to improve this. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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