| Summary: | 碩士 === 國立中央大學 === 天文研究所 === 93 === We have observed three bright Kuiper-belt objects (KBOs), Quaoar, Ixion, and
2004DW, with the 1-meter telescope at Lulin Observatory. Two kinds of CCDs,
Ap8 and PI1300B, and standard Johnson BVR filters as the broad-band photometry
are used for the observations. The exposure time is 300 seconds in the R filter,
420 seconds in the V filter and 600 seconds in the B filter. Data reduction and
calibration are carried out with standard IRAF processes and aperture photometry.
The lightcurves of the objects are obtained by using differential photometry.
We adopt two methods to determine the rotation period of Quaoar. One is
Lomb normalized periodogram (LNP) and the other is phase dispersion minimization
(PDM). The period of Quaoar is 0.381 days determined from the PDM method.
Using the 1.5-meter telescope at Sierra Neved Observatory, Ortiz et al. (2003) also
observed Quaoar with no filter. They had observed Quaoar for 14 days and found
that the period of Quaoar is 0.36831±0.00001 days. Although our data points are
just a few and possess larger errors than theirs, our result is still in agreement with
Ortiz’s value.
For determining the surface color of our objects, we also adopt two methods:
(1) using standard star correction to obtain the extinction cofficient of each filter to
correct the airmass effect and (2) R-V-R-B-R series exposure. In series exposure,
adjacent B-V and V-R values are averaged to avoid the rotation effect and translation
fomulae are used to transfer insturment colors to standard colors. With the
series exposure method, we have determined the surface colors of Quaoar are BV=
1.095±0.037 and V-R=0.612±0.028. The results for Ixion are B-V=1.299±0.219
and V-R=0.723±0.157; those for 2004DW are 0.789±0.033 and V-R=0.427±0.028.
We have investigated the cometary activity of the objects. To obtain the radial
profiles of the objects, we first add their images together to imporve the S/N ratio
and then subtract the averaged sky background from them. We find no faint coma
in our objects, Quaoar, Ixion and 2004DW.
|
|---|
