Showing papers by "Seung-Lee Kim published in 2003"

New sx phoenicis stars in the globular cluster m53

Abstract: Through time-series CCD photometry of the metal-poor globular cluster M53 we have discovered eight new SX Phoenicis–type stars (labeled "SXP1" to "SXP8"). All the new SX Phoenicis stars are located in the blue straggler star region of the color-magnitude diagram of M53. One of these stars (SXP2) is found to have very closely separated pulsation frequencies: f1/f2 = 0.9595, where f1 and f2 are the primary and secondary frequencies, respectively. This may be due to excitation of nonradial modes. Six of these SX Phoenicis stars are considered to be pulsating in the fundamental mode. They show a tight linear correlation between the period and luminosity. We derive a period-luminosity relation for the fundamental mode for the period range of -1.36 < log P(days) < -1.15: V = -3.010(±0.262) log P + 15.310(±0.048) with an rms scatter of 0.038, corresponding to MV = -3.010 log P - 1.070 for an adopted distance modulus of (m - M)V = 16.38.

A Period Study and Light Synthesis for the W Ursae Majoris Type Binary SS Arietis

Abstract: Numerous new CCD measures of the cool overcontact binary SS Arietis are compiled into six well-covered light curves. The confusing history of the binary's period variability is laid out in order to consider the diverse interpretations that have been presented previously. It is concluded that the period activity can be ascribed to no fewer than three separate causes. There is some little support for a magnetic cycle functioning in phase with one of the components of the period variability. The three light curves from 1996 have responded satisfactorily to a modern synthesis code, and the characterization of the binary characterization is better constrained than was the case from earlier light-curve studies. Light curves from 1999 have not been so satisfactorily represented. Conditioning the light-curve results with published radial velocities has very little effect on the light-curve parameters. It does, however, reveal a curious distribution of the velocity residuals, and we offer some possible interpretations. Low-level spot activity is also modeled. There is no evidence of a third star contributing significant light to the system.

New SX Phoenicis Stars in the Globular Cluster M53

Abstract: Through time-series CCD photometry of the metal-poor globular cluster M53, we have discovered eight new SX Phoenicis type stars (labeled from SXP1 to SXP8). All the new SX Phoenicis stars are located in the blue straggler star region of a color-magnitude diagram of M53. One of these stars (SXP2) is found to have very closely separated pulsation frequencies: $f_1/f_2 = 0.9595$ where $f_1$ and $f_2$ are primary and secondary frequencies. This may be due to excitation of non-radial modes. Six of these SX Phoenicis stars are considered to be pulsating in the fundamental mode. They show a tight linear correlation between the period and luminosity. We derive a period - luminosity relation for the fundamental mode for the period range of $-1.36 =-3.010(\pm0.262)Log P + 15.310(\pm0.048)$ with an rms scatter of 0.038, corresponding to $ =-3.010 Log P - 1.070$ for an adopted distance modulus of $(m-M)_V=16.38$ (Harris 1996).

Search for variable stars in the open cluster NGC 2539

Abstract: We present UBVI absolute and V-band time-series CCD photometric results for the intermediate-age open cluster NGC 2539. From the empirical zero-age main sequence and theoretical isochrone fitting in color-color and color-magnitude diagrams, we estimated the physical parameters of this cluster as follows: the color excess of E(B - V) = 0.06′0.03, the distance modulus of (V - M V ) 0 = 10.2′0.1 and the age of log t=8.8 (∼630 Myr). By carefully examining the time-series images, we discovered seven new variable stars in the observed cluster field. Considering the light curves, periods and positions on the color-magnitude diagram, we classified them as five eclipsing binary stars, one δ Scuti star and one y Doradus candidate. The y Doradus candidate might not be a cluster member because it is located redder by about Δ(B-V) = 0.2 than the cool edge of y Doradus instability strip.