Woo-Baik Lee

The Intrinsic Shapes of Low Surface Brightness Dwarf Irregular Galaxies and Comparison to Other Types of Dwarf Galaxies

In this paper, we measure the ellipticities of 30 low surface brightness (LSB) dwarf irregular (dI) galaxies and compare the ellipticity distribution with that of 80 dwarf elliptical (dEs) and 62 blue-compact dwarfs (BCDs). We find that the ellipticity distribution of LSB dIs is very similar to that of BCDs, and marginally different from that of dEs. We then determine the distribution of intrinsic shapes of dI galaxies and compare this to the distributions of other types of dwarf galaxies under various assumptions. First, we assume that LSB dIs are either all oblate or all prolate, and use a nonparametric analysis to find the best-fitting distribution of intrinsic shapes. With this assumption, we find that the scarcity of nearly circular LSB dIs implies, at the 99% confidence level, that they cannot be a population of randomly oriented oblate or prolate objects, implying that LSB dIs are highly unlikely to be disk-shaped systems. Next, we assume that dIs are triaxial, and use a parametric analysis to find permissible distributions of intrinsic shapes. We find that if the intrinsic axis ratios β and γ are distributed according to a Gaussian with means β0 and γ0 and a common standard deviation of σ, the best-fitting set of parameters for LSB dIs is (β0, γ0, σ) = (0.66, 0.50, 0.15), and the best fit for BCDs is (β0, γ0, σ) = (0.66, 0.55, 0.16), while the best fit for dEs is (β0, γ0, σ) = (0.78, 0.69, 0.24). The dIs and BCDs thus have very similar shape distributions, given this triaxial hypothesis, while the dEs peak at a somewhat more spherical shape. Therefore, our results provide strong observational evidence to support the evolutionary scenario in which the three types of dwarf galaxy have a close relation with each other.

Abundances in the Planetary Nebula IC 5217

High-resolution optical wavelength spectroscopic data were secured in the optical wavelengths, 3700–10050 A, for the planetary nebula IC 5217 with the Hamilton Echelle Spectrograph at Lick Observatory. These optical spectra have been analyzed along with the near-UV and UV archive data. Diagnostic analyses indicate a nebular physical condition with electron temperature of about 10,700 K (from the [O III] lines) and the density of N = 5000 cm-1. Ionic concentrations have been derived with the representative diagnostics, and with the aid of a photoionization model construction, we derived the elemental abundances. Contrary to the previous studies found in the literature, He and C appear to be depleted compared to the average planetary nebula and to the Sun (and S marginally so), while the remaining elements appear to be close to the average value. IC 5217 may have evolved from an O-rich progenitor, and the central star temperature of IC 5217 is likely to be 92,000 K.

Spectroscopic Observation of the Planetary Nebula IC 4846

A high-dispersion optical (3700-10100 A) spectrum was secured with the Hamilton echelle spectrograph at the coude focus of the 120 inch (3 m) Shane telescope at Lick Observatory, with the goal of deriving chemical abundances for the compact planetary nebula IC 4846. We also remeasured the UV spectra from the IUE archive. Diagnostics indicate that the entire planetary nebula may be represented by an electron density N 9000 cm–3 and electron temperature T 10,500 K. However, diagnostics seem to imply that the [O ii] and [S ii] zone electron temperatures are higher than the [O iii] radiating strata. The electron density of the [O ii] and [S ii] zone might be higher as well (for which N 20,000 cm–3). The photoionization model, which represents most of the observed line intensities, seems to confirm this physical condition, although the actual situation may be much more complicated. On the basis of the semiempirical ionization correction method and the photoionization model calculation, we derived the chemical abundances in this planetary nebula. Our optical data were compared with the image-tube scanner data from Aller & Czyzak. Apparently, there is a long-term spectral line variation in IC 4846. Chemical abundances derived in the present study agree, within 30%, with those previously estimated in Aller & Czyzak, except for carbon; the C, N, O, and Ne ratios are lower than both the average planetary nebula and the solar abundance. IC 4846 is a metal-deficient planetary nebula that may have evolved from a Population II progenitor.

Photometric Studies of CW Cephei

Three-filter observations of the hot, detached close binary CW Cephei are used as the basis for light curves dating to the mid-1980s. The ephemeris of apsidal rotation is improved as a result of a lengthier time base. The light-curve synthesis converges to essentially the same orbital and stellar parameters that have been accepted for almost 40 years. For the first time, emphasis is given to a new type of complication confusing the apsidal rotation behavior, and it is shown that this complication is photometric and not dynamical. In addition, we find that the light curve is itself beset by substantial complications, which may be associated with the rather feeble stellar winds.

CCD Photometry of Low Mass Ratio Contact Binary FP Boo - IV

We present new B, V, and R CCD photometric light curves for the low mass ratio contact binary FP Boo. A new photometric solution and absolute physical dimensions of the system were derived by applying the Wilson-Devinney program to our observed light curves and to previously published Rucinski et al.`s radial velocity curves. From the H-R diagram of 24 low mass ratio contact binary system including FP Boo, the evolutionary stage of FP Boo was found to coincide with those of the general low mass ratio contact binary systems. The light curves obtained in this season show a small asymmetry in their shapes.

CCD PHOTOMETRY OF CONTACT BINARY WZ Cephei

We present the full BVR light curves and five times of minima of WZ Cep to provides a complete photometric solution and to confirm the long term variation of the light curves. Our light curves show symmetry while previous light curves of Hoffmann (1984) show a high degree of asymmetry (the O`Connell effect). The BVR light curves were analyzed by the method of Wilson-Devinney Differential Correction. Our photometric results show a good agreement with those of Djurasevic et al. (1998).

Starspot Parameters of the W UMa Type Eclipsing Binary SW Lacertae

We present UBV photometry of SW Lac and analyse its light–curve to deduce starspot parameters for this star.

IMPROVED LIGHT CURVES OF LMC ECLIPSING BINARIES

We present accurate BV light curves and continuum energy curves of the EROS eclipsing binaries in the Large Magellanic Cloud to find accurate binary parameters as well as their distances. The observations have been carried out using the 2.1 meter telescope in CASLEO Argentina during Feb. 1-10, 2003. We have concentrated CCD direct observations upon EROS field 1 and 2 to improve the accuracy of light curves of eclipsing binaries in the fields. The spectroscopic observations have been also carried out using the simple dispersion method to get continuum energy curves between wavelengths of 4000-8000 A for several EROS eclipsing binaries. At first, we determined a combined temperature of both components of each binary system using the continuum. Then, the combined temperature was resolved using the first estimation of the light curve solution. Finally, we determined the photometric solutions of several binaries in the Large Magellanic Cloud.

Magnetic Activities of Near Contact Binaries

The light curves of 19 NCBs, whose X-ray luminosities are greater than those of normal late type main-sequence stars, have been analyzed by the spot model for their magnetic activities. 14 systems have a cool spot while one system has a hot spot on the secondary system. Their chromospheric activities have been investigated by measureing Mg II emissionline of the IUE high resolution spectra.

Progress Report for the KAO 1.0 meter Robotic Telescope

Korea Astronomy Observatory (KAO) is working to rebuild a 1.0-m robotic telescope in collaboration with a company (Astronomical Consultants & Equipment, Inc. or ACE). The telescope is being totally refurbished to make a fully automatic telescope which can operate in both interactive an fully autonomous robotic modes. This paper describes the design concepts and the work completed. The telescope is an f/7.5 Ritchey-Chretien system mounted on an equatorial fork with friction drives capable of high slewing (5°/s 2 ) and high resolution tracking. The control software manages the entire telescope, instruments and observatory. In interactive local and remote modes the observer can manually enter coordinates or retrieve them from a database. In robotic mode the telescope controller downloads requests from users and creates a schedule. The telescope will be equipped with a CCD camera and will be available over the internet.