• 천문학회보
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• 제38권1호
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• pp.72.1-72.1
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• 2013

Camera for QUasars in EArly uNiverse (CQUEAN) is an optical CCD camera, developed by Center for Exploration of Origin of the Universe (CEOU), which is now searching for high red shift quasar candidates. It has been operated since 2010, attached to the 2.1m Otto Struve telescope at the McDonald Observatory, USA. Based on the previous operation experiences, we present CQUEAN II system design which has a new filter wheel allowing with 20 narrow band filters. In addition, the auto guiding system will be rearranged and the interfacing units between the telescope and the instrument will become stabilized.

• 천문학회보
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• 제36권1호
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• pp.53.1-53.1
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• 2011

We investigate the radial properties of the narrow-line region (NLR) in two radio-quiet quasars, PG1012+008 and PG1307+085, using the spectra obtained with the FORS1 at the Very Large Telescope. These high quality spectra with seeing < 0.6" enable us to extract seven two-pixel (0.4") spectra as a function of the radial distance from the accretion disk. In contrast to [OIII] narrow-band imaging, which can be contaminated by starbursts, shock-ionized gas, and tidal tails, we use emission-line diagnostic to determine the true size of the AGN-excited NLR. In this poster, we present the results based on the radial variance of $H{\beta}$ to [OIII] ${\lambda}5007$ ratio. For both targets, the [OIII] emission line exhibits a blue wing, suggesting an outflow of gas. In the case of PG1307+085, the blue wing disappears at the distance of 1". We will discuss the properties of the NLR in detail.

• 천문학회지
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• 제50권1호
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• pp.1-5
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• 2017

Like Hipparcos, Gaia is designed to give absolute parallaxes, independent of any astrophysical reference system. And indeed, Gaia's internal zero-point error for parallaxes is likely to be smaller than any individual parallax error. Nevertheless, due in part to mechanical issues of unknown origin, there are many astrophysical questions for which the parallax zero-point error ${\sigma}({\pi}_0)$ will be the fundamentally limiting constraint. These include the distance to the Large Magellanic Cloud and the Galactic Center. We show that by using the photometric parallax estimates for RR Lyrae stars (RRL) within 8kpc, via the ultra-precise infrared period-luminosity relation, one can independently determine a hyper-precise value for ${\pi}_0$. Despite their paucity relative to bright quasars, we show that RRL are competitive due to their order-of-magnitude improved parallax precision for each individual object relative to bright quasars. We show that this method is mathematically robust and well-approximated by analytic formulae over a wide range of relevant distances.

• 천문학회보
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• 제46권2호
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• pp.44.2-44.2
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• 2021

Detecting lensed quasar systems and estimating their time delays using the unresolved joint light curves can be the next frontier among the cosmological probes in the near future. One can get the independent measurement of the Hubble constant from the time delays but without requiring the systems to be resolved a priori followed by monitoring the image light curves using high-resolution telescopes for years. In this work, we propose a novel technique that can identify lensed quasars only using the observed unresolved light curves and without assuming a template or any prior information. Following a set of conservative selection criteria that gives zero false-positive outcome, we can accurately estimate the time delay for almost all the lensed systems with marginal noise in the data. For the case of noisy data, our approach can still correctly identify a substantial number of lensed systems with high certainty and measure the time delay accurately.

• 천문학회지
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• 제29권spc1호
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• pp.103-104
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• 1996

• 천문학회보
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• 제35권1호
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• pp.77.2-77.2
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• 2010

A high redshift quasar is useful to investigate the early part of our universe. Since they are one of the brightest objects in the early universe, they can provide us with clues of the growth of super massive black holes and the early metal enrichment history. To discover the high redshift quasars, we designed a survey of wide area and moderate depth; Infrared Medium-deep Survey (IMS), a J-band imaging survey of ~200 $deg^2$ area where the multi-wavelength data sets exist. To obtain the J-band data, we are using the United Kingdom Infra-Red Telescope (UKIRT), and so far we have covered ~20 $deg^2$ with Y- or J-bands over three observing runs during 2009. We used color-color diagrams of multi-wavelength bands including i, z, Y, J, K, $3.6{\mu}m$ and $4.5{\mu}m$ to select high redshift quasars. The major challenge in the selection is many M/L/T dwarfs, low redshift galaxies, and instrumental defects that can be mistaken as a high redshift quasar. We describe how such contaminating sources can be excluded by adopting multiple color-color diagrams and eye-ball inspections. So far, our selection reveals two quasar candidates at z~7.

• 천문학회보
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• 제35권1호
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• pp.38.2-38.2
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• 2010

We report the current status of CQUEAN (Camera for QUasars in EArly uNiverse) development. CQUEAN is an optical CCD camera which uses a 1024*1024 pixel deep-depletion CCD. It has an enhanced QE than conventional CCD at wavelength band around 1${\mu}m$, thus it will be an efficient tool for observation of quasars at z > 7. It will be attached to the 2.1m telescope at McDonald Observatory, USA. A telescope interface containing a focal reducer is being designed to secure a larger field of view at the cassegrain focus of 2.1m telescope. Instrument control software will be written with python on linux platform. We are carrying out lab tests to investigate the characteristics of the system components in order to maximize the observational efficiency. Preliminary results of the tests will be presented. CQUEAN is expected to see the first light during summer season of 2010.

• 천문학회보
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• 제35권2호
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• pp.37.1-37.1
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• 2010

A high redshift quasar is useful to investigate the early part of our universe. Since they are one of the brightest objects in the early universe, they can provide us with clues of the growth of super massive black holes and the early metal enrichment history. To discover the high redshift quasars, we designed a survey of wide area and moderate depth; Infrared Medium-deep Survey (IMS), a J-band imaging survey of ~200 deg2 area where the multi-wavelength data sets exist. To obtain the J-band data, we are using the United Kingdom Infra-Red Telescope (UKIRT), and so far we have covered~40 deg2 with Y- or J-bands over 36 observing nights. We used color-color diagrams of multi-wavelength bands including i, z, Y, J, K, $3.6{\mu}m$ and $4.5{\mu}m$ to select high redshift quasars. The major challenge in the selection is many M/L/T dwarfs, low redshift galaxies, and instrumental defects that can be mistaken as a high redshift quasar. We describe how such contaminating sources can be excluded by adopting multiple color-color diagrams and eye-ball inspections. So far, our selection reveals one quasar candidates at z~7 and a few candidates at z~6. In this poster presentation, we will update the current status of the quasar selection in the IMS fields.

• 천문학회지
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• 제44권4호
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• pp.115-123
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• 2011

To perform imaging observations of optically red objects such as high redshift quasars and brown dwarfs, the Center for the Exploration of the Origin of the Universe (CEOU) recently developed an optical CCD camera, Camera for QUasars in EArly uNiverse (CQUEAN), which is sensitive at 0.7-1.1 ${\mu}m$. To enable observations with long exposures, we develop an auto-guiding system for CQUEAN. This system consists of an off-axis mirror, a baffle, a CCD camera, a motor and a differential decelerator. To increase the number of available guiding stars, we design a rotating mechanism for the off-axis guiding camera. The guiding field can be scanned along the 10 arcmin ring offset from the optical axis of the telescope. Combined with the auto-guiding software of the McDonald Observatory, we confirm that a stable image can be obtained with an exposure time as long as 1200 seconds.

• 천문학회보
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• 제43권2호
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• pp.36.2-36.2
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• 2018

Cosmic reionization era in the early universe was playing a leading part on making the present universe we know. However, we have not been able to reveal the main contributor to the cosmic reionization to date. Faint quasars have been mentioned as the alternative due to the uncertainty of the faint end slope of the quasars luminosity function. With the availability of the deep (~25mag) images from Subaru Hyper Suprime-Cam (HSC) Strategic Program survey, we have tried to find more quasar with low luminosity in the ELAIS-N1 field. Faint quasar candidates were selected from several multi-band color cut criteria based on the track of the simulated quasar at z ~ 5. The Infrared Medium-deep Survey (IMS) and The UKIRT Infrared Deep Sky Survey (UKIDSS) - Deep Extragalactic Survey (DXS) provide J band information which is used to cover the relatively long wavelength range of quasar spectra. To search the reliable candidates with possible Lyman break, medium-band observation was performed by the SED camera for QUasars in EArly uNiverse(SQUEAN) in the McDonald observatory and Seoul National University 4k Camera(SNUCAM) in the Maidanak observatory. Photometric redshifts of the observed candidates were estimated from chi-square minimization. Also, we predicted the importance of the faint quasar to the cosmic reionization from the expected number density of the faint quasar.