Lulin Observatory Research Articles

Photometric and spectroscopic observations of asteroid (21) Lutetia three months before the Rosetta fly-by

Context. On its journey to comet 67P/Churyumov-Gerasimenko, the International Rosetta Mission (ESA) was planned to fly-by two asteroids: (2867) Steins and (21) Lutetia. Although classified as an M-type asteroid because of its high albedo, its reflectance spectrum in the near and mid-infrared region, suggests a primitive composition, more typical of C-type asteroids. Results from ground-based observations are indicative of compositional variegation and of at least one significantly large crater on the surface of this asteroid.Aims. We analyse photometric and spectroscopic data of the asteroid, obtained from ground-based observations, to support the data taken by the spacecraft.Methods. We obtained uvbyIR i ′ photometric measurements covering the complete rotational period of the asteroid (about 8 h), using both the BUSCA instrument at the 2.2 m telescope in Calar Alto Observatory (CSIC-MPIA), and the 1 m telescope at Lulin Observatory (Taiwan, NCU). We also obtained visible and near-infrared spectra, covering the range 0.4–2.5 μ m, with CAFOS at the 2.2 m (Calar Alto) and NICS at the 3.6 m telescope TNG (“El Roque de los Muchachos” Observatory). The spectroscopic data were taken at different rotational phases to search for any significant inhomogeneities in the surface of the asteroid.Results. The simultaneous photometric lightcurves in five filters obtained with the BUSCA instrument, and the lightcurves obtained at Lulin Observatory reveal a brightness variation around a rotational phase 0.1. We took visible and near-infrared spectra at that rotational phase, and a different rotational phase for comparison. Differences in the visible spectral slope among the spectra are indicative of a crater as the most likely cause of this variation.

THE OUTBURST OF COMET 17P/HOLMES

Comet 17P/Holmes had a massive outburst at approximately 2007 October 23.8 and its total brightness reached maximum (from m = 17 to m = 2.5) around 2007 October 25, about 1.7 days (42 hr) after the event. Following the first report of this extraordinary cometary outburst, comprehensive observations were obtained at the Lulin Observatory until early 2008 January by using broadband filters and narrowband cometary filters. The separation velocity, as projected on the plane of the sky, between the nucleus and the coma blob produced by the outburst has been estimated to be 0.132 ± 0.004 km s −1 from October 25.8 to November 1.6. The expansion speed, also projected on the plane of the sky of the dust shell has been found to be constant at a rate of approximately 0.554 ± 0.005 km s −1 from October 25.8 to November 1.6. The color on December 10 is slightly redder than that of the Sun. Our narrowband observations provide information on the production rates of gas species on October 31: log Q (CN) = 27.103 and log Q (C2) = 27.349. The resulting abundance ratios show that the 17P can be classified as a typical comet in terms of composition.

Imaging polarimetry of Comet 9P/Tempel before and after the Deep Impact

The NASA's Deep Impact mission was the first impact experiment to a cometary nucleus. The target of the mission was Comet 9P/Tempel, one of the Jupiter family comets. The impact was performed on July 4th, 2005. Imaging polarimetric observations were carried out by Polarimetric Imager for COmets (PICO) mounted on the Lulin One-meter Telescope (LOT) at Lulin Observatory, Taiwan. Intensity and linear polarization degree maps were obtained on July 3–5, 2005. Impact ejecta plume was clearly recognized in the enhanced intensity map. Furthermore, arc-shaped region of high polarization was recognized in the polarization map. Dust grains in this region had larger expansion velocity than the grains which provided the brightest area in the intensity map. comparing our results with the MIR spectroscopy obtained by Subaru Telescope we conclude that very small carbonaceous grains might be responsible for the region of high polarization.

Photometry and imaging of comet C/2004 Q2 (Machholz) at Lulin and La Silla

Aims. We have investigated the development of the dust and gas coma of the comet C/2004 Q2 (Machholz) from December 2004 to January 2005 using observations obtained at the Lulin Observatory, Taiwan and the European Southern Observatory at La Silla, Chile. Methods. We determined the dust-activity parameter Afρ and the dust color and derived Haser production rates and scale lengths of C2 and NH2. An image enhancement technique was applied to study the morphology of the gas and dust coma. Results. Two jets were observed in the coma distributions of C2 and CN of comet Machholz that were not formed in the dust coma. The jets showed a spiral-like structure and pointed at different position angles at different observing times. The formation of these jets can be explained by the presence of two active surface regions on a rotating cometary nucleus.

Surface heterogeneity of 2005 UD from photometric observations

Context. The recently discovered Apollo-type near-Earth asteroid 2005 UD has been suggested to be a fragment of (3200) Phaethon. Aims. To test this hypothesis, we carried out photometric observations of 2005 UD using the 1-m telescope at Lulin Observatory. Methods. Multi-color photometry was used to compare the surface properties of (3200) Phaethon and 2005 UD. Surface-color variation due to the rotation was also examined. Results. The time-resolved differential photometry showed clear brightness variation, and the lightcurve was fitted with a rotation period of 5.23 h and an amplitude of 0.44 mag. Using this rotational lightcurve, we derived the surface colors of 2005 UD. The surface of 2005 UD exhibits colors similar to those of F- and B-type asteroids, which is consistent with (3200) Phaethon. Furthermore, the (R - I) color of 2005 UD shows variation during the rotation of the body. Conclusions. The similarity of surface colors between (3200) Phaethon and 2005 UD observationally supports the hypothesis that 2005 UD is likely to be a fragment of (3200) Phaethon. A simple explanation for the inhomogeneity of the surface is that we see the surface and subsurface of the precursor object. Another explanation is the topographical structure that such as a large crater causes on this heterogeneous surface.

Very Early Multicolor Observations of the Plateau Phase of the GRB 041006 Afterglow

Observations of the optical afterglow of GRB 041006 with the Kiso Observatory 1.05 m Schmidt telescope, the Lulin Observatory 1.0 m telescope and the Xinglong Observatory 0.6 m telescope. Three-bands (B, V and R) of photometric data points were obtained on 2004 October 6, 0.025-0.329 days after the burst. These very early multi band light curves imply the existence of a color dependent plateau phase. The B-band light curve shows a clear plateau at around 0.03 days after the burst. The R band light curve shows the hint of a plateau, or a possible slope change, at around 0.1 days after the burst. The overall behavior of these multi-band light curves may be interpreted in terms of the sum of two separate components, one showing a monotonic decay the other exhibiting a rising and a falling phase, as described by the standard afterglow model.

Observations of dwarf planet (136199) Eris and other large TNOs on Lulin Observatory

To provide comprehensive observations and in-depth standy of the physical property of the trans-neptunian objects (TNOs), the Lulin Observatory in Taiwan has started a program to study the time variabilities of lightcurves of large TNOs and dwarf planets. Our initial results show that (50000) Quaoar has a significant brightness variation of Δ m ∼ 0.3 with a rotation period of about 18.84 h while (136199) Eris (formerly 2003 UB313) has very little brightness variation (Δ m ∼ 0.05). The rotation period of Eris is hence highly uncertain even though a periodicity of 3.55 h is suggested by our measurements.

Imaging polarimetry of Comet 9P/Tempel before and after the Deep Impact

The NASA's Deep Impact mission was the first impact experiment to a cometary nucleus. The target of the mission was Comet 9P/Tempel, one of the Jupiter family comets. The impact was performed on July 4th, 2005. Imaging polarimetric observations were carried out by Polarimetric Imager for COmets (PICO) mounted on the Lulin One-meter Telescope (LOT) at Lulin Observatory, Taiwan. Intensity and linear polarization degree maps were obtained on July 3–5, 2005. Impact ejecta plume was clearly recognized in the enhanced intensity map. Furthermore, arc-shaped region of high polarization was recognized in the polarization map. Dust grains in this region had larger expansion velocity than the grains which provided the brightest area in the intensity map. comparing our results with the MIR spectroscopy obtained by Subaru Telescope we conclude that very small carbonaceous grains might be responsible for the region of high polarization.

Search for small trans-Neptunian objects by the TAOS project

AbstractThe Taiwan-America Occultation Survey (TAOS) aims to determine the number of small icy bodies in the outer reach of the Solar System by means of stellar occultation. An array of 4 robotic small (D=0.5 m), wide-field (f/1.9) telescopes have been installed at Lulin Observatory in Taiwan to simultaneously monitor some thousand of stars for such rare occultation events. Because a typical occultation event by a TNO a few km across will last for only a fraction of a second, fast photometry is necessary. A special CCD readout scheme has been devised to allow for stellar photometry taken a few times per second. Effective analysis pipelines have been developed to process stellar light curves and to correlate any possible flux changes among all telescopes. A few billion photometric measurements have been collected since the routine survey began in early 2005. Our preliminary result of a very low detection rate suggests a deficit of small TNOs down to a few km size, consistent with the extrapolation of some recent studies of larger (30–100 km) TNOs.

Optical Afterglow Observations of the Unusual Short-Duration Gamma-Ray Burst GRB 040924

The 1 m telescope at Lulin Observatory and the 0.76 m Katzman Automatic Imaging Telescope at Lick Observatory were used to observe the optical afterglow of the short-duration (1.2-1.5 s) gamma-ray burst GRB 040924. This object has a soft high-energy spectrum, thus making it an exceptional case, perhaps actually belonging to the short-duration tail of the long-duration GRBs. Our data, combined with other reported measurements, show that the early R-band light curve can be described by two power laws with index α = -0.7 (at t = 16-50 minutes) and α = -1.06 (at later times). The rather small difference in the spectral indices can be explained more easily by an afterglow model invoking a cooling break than by one with a jet break.

Characteristics and Performance of the CCD Photometric System at Lulin Observatory

The Lulin One-meter Telescope at Lulin Observatory in Taiwan started open-use observations in January 2003. In order to evaluate the performance of the CCD photometric system, the characteristics and quality of the site, we ob- tained data of photometric standards as well as calibration data from February to November 2004. We report here the results of our analysis including the gain, readout noise, dark current and linearity of the CCD camera, and transformation coefficients, total throughputs, night sky brightnesses andlimiting magnitudes for UBV RI bands.

Low‐latitude ELF‐whistlers observed in Taiwan

Detections of ELF whistler‐like events at a low latitude location are reported. Events with frequencies between 60 and 100 Hz were recorded by the ELF station at the Lulin Observatory in Taiwan from August 26, 2003 to July 13, 2004. The most distinguished feature for these events is the frequency descent in the frequency‐time spectrograms, resembling terrestrial whistlers. Other notable features include (a) a long event duration averaging up to two minutes, (b) a daytime diurnal maximum occurring around 10 am, (c) a dominant magnetic field polarization in the north‐south direction with strength of a few to tens of pT, and (d) no detection of vertical electric fields. Similar events were only reported twice for the past thirty years: one at an auroral latitude site in Alaska and the other at a mid‐latitude site in California. Possible source mechanisms including magnetosheath lion roars and lightning‐generated whistlers are discussed.

The NCU Lu-Lin Observatory

AbstractThe NCU (National Central University) Lu-Lin observatory is located at Mt. Front Lu-Lin, 120°52′25”E and 23°28′07” N, a 2862-m peak in the Yu-Shan National Park. The construction of Lu-Lin observatory was finished on January 14, 1999. The initial assessment of Lu-Lin site started in 1989, after which a three-year project was founded by the National Science Council (NSC) to support a modern seeing monitoring program. The average seeing at Lu-Lin is about 1.39 arc-second with an average of 200 clear nights annually. The sky background is 20.72 mag/arcsec2 in V band and 21.22 mag/arcsec2 in B band.The Lu-Lin observatory is for both research and education. A homemade 76-cm Super Light Telescope (SLT) and four TAOS 50-cm robotic telescopes for a survey on Kuiper Belt Objects will be the two major research facilities. The pilot program for SLT consists of observations of time-varying astrophysical phenomena. The TAOS #1 telescope was installed at Lu-Lin in March 2000. A 90 KW/240 VAC power line and a water pipe system have been pulled to the site in early 2001. A wireless Network system through A-Li Shan has been operating at Lu-Lin observatory while a faster wireless Network system with 11.5 Mbit/sec bandwidth is under consideration and may be available in the near future for remote observing.