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天文館

臺北天文館學報(出版品)

臺北天文館學報 第3期(English)

JTAM VOL. 3 (2005)


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FieldAuthorTitle
galaxy,
radio astronomy
Chang Mean-Ti, Hwang Chorng-YuanSecondary Electrons on Ultraluminous Infrared Galaxies(pdf檔案)
galaxyYu Po-Chieh, Hwang Chorng-YuanInvestigation of Hidden Broad-line Region and Non-hidden Broad-line Region Seyfert 2 Galaxies(pdf檔案)
galaxy,
X-ray astronomy
Huang Zhen-Yuan, Chen Lin-WenA Multi-wavelength Study of X-ray Jets in Active Galaxies(pdf檔案)
stellar cluster,
Milky Way
Chen Chin-Wei, Chen Wen-PingMorphology of Galactic Globular Clusters(pdf檔案)
nebula,
stellar cluster
Hui-Chen Chen, Ko Chung-MingOpen clusters in a dispersing cloud(pdf檔案)
binary,
X-ray astronomy
Hu Chin-Pin, Chou YiParameterization Studies of the Properties of the X-ray Dip for Low Mass X-ray Binary X 1916-053(pdf檔案)
solar system,
binary,
optical astronomy
Hu Juei-Hwa, Ip Wing-HuenSearch for exoplanets and variable stars in open clusters(pdf檔案)
stars,
X-ray astronomy
Pu Hung-YiMagnetic Inclination and Viewing Geometry of Neutron Stars Inferred From Their X-ray Emission(pdf檔案)
solar systemLin Hsing-WenA Theoretical Simulation of Black Drop Effect: Transit of Mercury and Venus(pdf檔案)
solar system,
optical astronomy
Wu Yu-Li, Ip Wing-HuenThe rotation period and surface colors of the large EKBOs(Quaoar, Ixion,2004DW)(pdf檔案)

Title: Secondary Electrons on Ultraluminous Infrared Galaxies

Author: Chang Mean-Ti, Hwang Chorng-Yuan

Keywords: galaxy, cosmic rays, ULIGs

Abstract:
   We investigate the role of secondary electrons in ultraluminous infrared galaxies (ULIGs). The radio emission in ULIGs is believed to be produced by synchrotron radiation of relativistic electrons. Nonetheless, the sources of these relativistic electrons are still unclear. Most of the ULIGs usually have enhanced star formation rates and also possess a huge of amount of molecular clouds, which are usually concentrated in a small central region (<= 1 kpc). Since the production rates of the secondary electrons are proportional to the cosmic ray fluxes and the density of the ambient gas, the radio emission of the secondary electrons in ULIGs might be important. We assume a steady-state model for the secondary electrons generated from the interaction of the cosmic-ray hadrons with dense molecular clouds in ULIGs. We estimate the contribution of the secondary electrons in ULIGs by comparing observational results with theoretical calculations for the radio emission in these sources. We find that, for some ULIGs, radio contribution from synchrotron radiation of secondary electrons is significant.

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>Title: Investigation of Hidden Broad-line Region and Non-hidden Broad-line Region Seyfert 2 Galaxies

Author: Yu Po-Chieh, Hwang Chorng-Yuan

Keywords: Galaxies: Active, Nuclei, Seyfert

Abstract:
   We investigate and compare some properties of hidden broad-line region (HBLR) Seyfert 2 and non-HBLR Seyfert 2 galaxies, including near-infrared, [OIII] emission nuclear dust morphology, and dust mass. We obtain optical images from Hubble Space Telescope to probe the nuclear dust structures of these galaxies within 1 kpc regions and dust masses inside the 1 kpc regions (M1kpc) are estimated from obscuration levels. Dust morphology shows no significant difference between HBLR and non-HBLR Seyfert 2 galaxies, this is significantly in contrast to the results of previous studies. We also compare the dust obscuration levels in host galaxies of HBLR and non-HBLR Sy2s using some properties, such as nuclear dust mass and mass ratio M1kpc/MTotal. At last, we compare the near-infrared colors of HBLR and non-HBLR Seyfert 2 galaxies and the results show that they are dominated by different mechanisms.

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Title: A Multi-wavelength Study of X-ray Jets in Active Galaxies

Author: Huang Zhen-Yuan, Chen Lin-Wen

Keywords: X-ray jets, AGN, radiation mechanisms

Abstract:
   To probe the high-energy origin of AGN jets, a series of analysis incorporating all available X-ray jet data with a synthesis model are carried out, in which the model includes synchrotron radiation, synchrotron self-Compton emission (SSC), and inverse Compton scattering off CMB photons (IC/CMB) – the main radiation mechanisms of X-ray jets as current consensus suggests. It has been demonstrated that synchrotron- dominated and inverse-Compton-dominated jets can be separated into two groups by comparison of broadband spectral indices; using the similar technique but with a more sophisticated analysis, we have further estimated the possible contributions respectively from the three mechanisms to the observed fluxes of our samples. Our analysis shows that the SSC mechanism is responsible for most optical emission while the IC/CMB model is the major contributor in X-ray; subsequently, the Doppler boosting factor and magnetic field of jets are constrained by the contribution fractions of the three mechanisms. Moreover, with the constrained beaming factors, the de-projected distance of each sample is calculated to determine the emission nature of jet propagation. There is an interesting trend showing that the synchrotron emission declines out to 100 kpc away from AGN cores and incidentally most of the optical and X-ray emission produced by SSC appears significantly at around the same scale. This could be the first evidence to indicate the average transportation limit of high-energy emission from jets.

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Title: Morphology of Galactic Globular Clusters

Author: Chen Chin-Wei, Chen Wen-Ping

Keywords: globular cluster, tidal force, tidal distortion, halo, morphology

Abstract:
   We study the morphology of the halo of 110 Galactic globular clusters with the 2MASS Point Source Catalog. Morphological parameters such as the flattening and average radius of the halo of each globular cluster were estimated by fitting the effective density contours with ellipses. The globular clusters in our sample in general have spherical halos, with a median flattening (f=1-b/a) of 0.1, equivalent to an aspect ratio of 0.9. Those closer to the Galactic bulge show more circularized shapes and have smaller physical sizes. Among the most 6 elongated globular clusters with f >=0.3 (1) Arp 2 and Pal 12 are known to be associated with the streamer of the Sagittarius dwarf galaxy, (2) Pal 5 is being cannibalized by the Milky Way, (3) UKS 1 and NGC 6355 are known bulge globular clusters, and (4) NGC 2419 is a halo member with a Galactocentric distance ~ 90 kpc. Furthermore, the distortion of the two bulge GC, NGC 6293 and NGC 6440, suspected by Nordquist et al. (1999) has been detected. We discuss possible mechanisms which might have caused the flattening of globular clusters.

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Title: Open clusters in a dispersing cloud

Author: Hui-Chen Chen, Ko Chung-Ming

Keywords: N-body problem, molecular cloud, simulation, open cluster

Abstract:
   Stellar clusters are born within giant molecular clouds. The survival rate of infant clusters is low (Lada and Lada 2003). The reason is alluded to cloud dispersion. Adopting the code NBODY2 developed by Aarseth, we study the behaviour of an open cluster in a dispersing molecular cloud. It is expected that the cluster may be destroyed or evaporated when the cloud disperses rapidly. However, we find that the cluster may not be disrupted completely even if the dispersion rate of the molecular cloud is fairly large (0.6 million years compared with respect to the lifetime of the molecular clouds, 20 to 50 million years).

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B>Title: Parameterization Studies of the Properties of the X-ray Dip for Low Mass X-ray Binary X 1916-053

Author: Hu Chin-Pin, Chou Yi

Keywords: X-ray binary, close binary, accretion disk, superhump, negative superhump, dip

Abstract:
   X 1916-053 is an ultra-compact Low Mass X-ray Binary (LMXB) composed of a neutron star and a white dwarf. The period of recurrent X-ray dips and optical modulations are slightly and significantly different with each other.
   We have developed new methods to parameterize the dip to systematically study its variation to further understand the binary and accretion disk behavior. A 4.87 days periodic variation of the dip width, probably due to the nodal precession of the accretion disk, is clearly seen in the RXTE 1998 observations. The signal of the beat frequency of disk nodal precession and the orbital period is marginally detected in the RXTE 1996 data with epoch folding period search method. From the negative superhump model, the mass ratio can be estimated of q=0.045 with 1:3 resonance disk radius, which is larger than the mass ratio predicted by the superhump model or Roche-lobe filling secondary but in the same order.
   Combined with more than 24 years' historical data, we found an orbital period derivative and established a quadratic ephemeris for the X-ray dips. The period derivative seems inconsistent with the prediction of standard model of orbital evolution. On the other hand, the radiation driven model may be proper to interpret the period derivative although the large mass outflow predicted by this model has never been observed in this system.
   From the statistic of dip phase of primary and secondary dips, we concluded that the primary dips are more stable than the secondary dips, which implies that the bulge which cause the primary dips should be on the outer edge of accretion disk instead of in the 1/2 ring.

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Title: Search for exoplanets and variable stars in open clusters

Author: Hu Juei-Hwa, Ip Wing-Huen

Keywords: exoplanets, variable star, open cluster

Abstract:
   We present results of the search for exoplanets and variable stars in open cluster fields, NGC 2324, NGC 2374, NGC 2420, with the Lulin One-meter Telescope (LOT). Our main scientific goal is to use time series CCD photometry survey to detect exoplanets via transit effects. Such detection technique demands high-precision photometry now being implemented and gradually improved at Lulin. The secondary scientific goal is to discover and study variable stars with the same data set and similar data analysis methods.
Two variable candidates have been found in the NGC 2324 star field and four variable candidates in the NGC 2374 star field but no transit events detected. In the NGC 2420, no varable has been found.

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Title: Magnetic Inclination and Viewing Geometry of Neutron Stars Inferred From Their X-ray Emission

Author: Pu Hung-Yi

Keywords: gravitation, methods: numerical, radiation mechanisms: thermal, stars: neutron

Abstract:
   To investigate a possible reason of the difference between the radio-quiet neutron stars and radio pulsars, I constrained the possible ranges of magnetic inclination angle α and the observer's viewing angle ζ for several radio-quiet neutron stars with X-ray thermal emission. With a given surface temperature distribution of a neutron star and assuming the surface emission is described by Planck function, the model light curves and spectra were calculated. As α and ζ are parameters in the model, the possible range of these two angles for radio-quiet neutron stars can be inferred by comparing the computed flux and pulsed fraction with the observed ones. The calculation included photon path bending and gravitational redshift. The result shows no significant sign of the different distribution in the α-ζ plane for radio-quiet neutron stars and radio pulsars.

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Title: A Theoretical Simulation of Black Drop Effect: Transit of Mercury and Venus

Author: Lin Hsing-Wen

Keywords: Black drop effect, PSF (point-spread function), transit of Venus, Contact II, Contact III, Solar limb darkening

Abstract:
   Black drop effect is a phenomenon which happens at the transit of Mercury or Venus. It makes us difficult to resolute the shadow of inner planet and solar limb, so we can't measure the duration time of the transit exactly. An optical theoretical simulation is applied to calculate the black drop effect, and we discover the major cause of black drop effect is Point-spread function (PSF) of the telescope. The other factors that may affect the black drop phenomenon, including solar limb darkening, enhance the effect. Now, we know that the black drop effect is an optical effect, which depends on the resolution of the telescopes. If the telescope has high resolution, in other words the PSF of the telescope is sharp, the black drop effect would be unobvious. Otherwise, the black drop would be notable. Because all of the telescopes can not avoid the black drop effect, we must pay attention to its influence on observations.

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Title: The rotation period and surface colors of the large EKBOs(Quaoar, Ixion,2004DW)

Author: Wu Yu-Li, Ip Wing-Huen

Keywords: KBOs, rotation period, surface color, Quaoar, Ixion, 2004DW, cometary activity

Abstract:
   We have observed three bright Kuiper-belt objects (KBOs), Quaoar, Ixion, and 2004DW, with the 1-meter telescope at Lulin Observatory. The period of Quaoar is 0.381 days determined from the PDM method. For determining the surface color of our objects, we adopt two methods: (1)using standard star correction to obtain the extinction coefficient of each filter to correct the airmass effect and (2) R-V-R-B-R series exposure. With the series exposure method, we have determined the surface colors of Quaoar are B-V=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. We find no faint coma in our objects, Quaoar, Ixion and 2004DW.

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