• 제목/요약/키워드: space telescope

검색결과 944건 처리시간 0.026초

THE INFRARED MEDIUM-DEEP SURVEY. V. A NEW SELECTION STRATEGY FOR QUASARS AT z > 5 BASED ON MEDIUM-BAND OBSERVATIONS WITH SQUEAN

  • JEON, YISEUL;IM, MYUNGSHIN;PAK, SOOJONG;HYUN, MINHEE;KIM, SANGHYUK;KIM, YONGJUNG;LEE, HYE-IN;PARK, WOOJIN
    • 천문학회지
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    • 제49권1호
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    • pp.25-35
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    • 2016
  • Multiple color selection techniques are successful in identifying quasars from wide-field broadband imaging survey data. Among the quasars that have been discovered so far, however, there is a redshift gap at 5 ≲ z ≲ 5.7 due to the limitations of filter sets in previous studies. In this work, we present a new selection technique of high redshift quasars using a sequence of medium-band filters: nine filters with central wavelengths from 625 to 1025 nm and bandwidths of 50 nm. Photometry with these medium-bands traces the spectral energy distribution (SED) of a source, similar to spectroscopy with resolution R ~ 15. By conducting medium-band observations of high redshift quasars at 4.7 ≤ z ≤ 6.0 and brown dwarfs (the main contaminants in high redshift quasar selection) using the SED camera for QUasars in EArly uNiverse (SQUEAN) on the 2.1-m telescope at the McDonald Observatory, we show that these medium-band filters are superior to multi-color broad-band color section in separating high redshift quasars from brown dwarfs. In addition, we show that redshifts of high redshift quasars can be determined to an accuracy of Δz/(1 + z) = 0.002 - 0.026. The selection technique can be extended to z ~ 7, suggesting that the medium-band observation can be powerful in identifying quasars even at the re-ionization epoch.

Are Quasars Growing Fast in the Early Universe?: The Lowest Eddington Ratio Quasar at z~6

  • Kim, Yongjung;Im, Myungshin;Jeon, Yiseul;Kim, Minjin;Hyun, Minhee;Kim, Dohyeong;Kim, Jae-Woo;Taak, Yoon Chan;Yoon, Yongmin;Choi, Changsu;Hong, Jueun;Jun, Hyunsung David;Karouzos, Marios;Kim, Duho;Kim, Ji Hoon;Lee, Seong-Kook;Pak, Soojong;Park, Won-Kee
    • 천문학회보
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    • 제42권2호
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    • pp.44.3-45
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    • 2017
  • To date, luminous quasars at z ~ 6 have been found to be in maximal accretion with the Eddington ratios, ${\lambda}Edd$ ~ 1, suggesting enhanced nuclear activities in the early universe. However, this may not be the whole picture of supermassive black hole (SMBH) growth since previous studies have not reached on faint quasars that are more likely to harbor SMBHs with low ${\lambda}Edd$. To understand the accretion activities in quasars at high redshift, we obtained the deep near-infrared (NIR) spectrum of a quasar, IMS J2204+0112, one of the few faintest quasars that have been identified at z ~ 6. From the NIR spectrum, we find that IMS J2204+0112 harbors a SMBH with about a billion solar mass, with ${\log}({\lambda}Edd)=-0.91$. This is the lowest accretion rate found so far for quasars at z ~ 6, but a common value among quasars at z ~ 2. The inclusion of this object in the ${\lambda}Edd$ analysis gives the intrinsic ${\lambda}Edd$ distribution of z ~ 6 quasars, which is lower than previous results that are based on bright quasars, but it is still higher than ${\lambda}Edd$ of z ~ 2 quasars. Although the number statistics needs to be improved in future, the low peak ${\lambda}Edd$ value is consistent with the SMBH growth from a massive black hole seed (~ 105 Msun) or from a stellar mass black hole through short-duration super-Eddington accretion events (${\lambda}Edd$ > 10).

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Faint Quasar Candidates at z~5 in the ELAIS-N1 field

  • Shin, Suhyun;Im, Myungshin;Kim, Yongjung;Hyun, Minhee;Jeon, Yiseul;Kim, Minjin;Kim, Dohyeong;Kim, Jae-Woo;Taak, Yoon Chan;Yoon, Yongmin;Choi, Changsu;Hong, Jueun;Jun, Hyunsung David;Karouzos, Marios;Kim, Duho;Kim, Ji Hoon;Lee, Seong-Kook;Pak, Soojong;Park, Won-Kee
    • 천문학회보
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    • 제42권2호
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    • pp.74.2-74.2
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    • 2017
  • Faint quasars are important to test the possibility that quasars are the main contributor to the cosmic reionization. However, it has been difficult to find faint quasars due to the lack of deep, wide-field imaging data. In this poster, we present our efforts to find faint quasars in the ELAIS-N1 field through the deep data (iAB ~ 25) obtained by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. To select reliable quasar candidate, we also use the near-infrared (NIR) data of the Infrared Medium-deep Survey (IMS) and the UKIRT Infrared Deep Sky Survey (UKIDSS) - Deep Extragalactic Survey (DXS). Using multiple-band color cuts, we select high redshift quasar candidates. To confirm them as high redshift quasars, candidates are observed by the SED camera for QUasars in EArly uNiverse (SQUEAN) instrument in several medium band filters that can sample the redshifted Lyman break efficiency. The quasar sample will be used to study the growth of BH and stellar mass, the relation between the quasar activity and the host galaxy, and their contribution to the cosmic re-ionization.

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직경 1 m 비축포물면의 가공 및 평가 (Fabrication and Evaluation of Diameter 1 m Off-axis Parabolic mirror)

  • 양호순;이재협;전병혁;이윤우;이경묵;최세철;김종민
    • 한국광학회지
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    • 제19권4호
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    • pp.287-293
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    • 2008
  • 망원경의 조립 및 평가를 위해서는 평행광선을 만들어주는 시준장치가 반드시 필요하다. 최근에 고해상도 카메라의 초점거리가 길어짐에 따라 상대적으로 적은 부피를 차지하는 Cassegrain 형태의 시준장치가 많이 사용되고 있다. 하지만 이러한 형태는 적외선 광학계를 평가할 때 부경이 가지는 온도로 인하여 불필요한 열복사선을 방출하여 적외선 광학계의 평가 정밀도를 떨어뜨리게 된다. 본 논문에서는 직경이 800 mm이고 초점거리가 2 m인 적외선 광학계를 평가하기 위하여 초점거리는 6m이고 물리적인 직경 1 m, 유효 직경이 930 mm인 비축포물면을 Zerodur를 이용하여 가공하고 측정한 과정을 설명한다. 약 4개월간의 작업 끝에 면의 최종 파면수차는 30.4 nm rms($\lambda$/138, ${\lambda}=4.2\;{\mu}m$)를 얻어서 적외선 광학계뿐만 아니라 가시광 영역 광학계도 측정 가능한 성능을 보유하였다.

GG Tauri A: gas properties and dynamics from the cavity to the outer disk

  • Nguyen, Thi Phuong;Dutrey, Anne;Pham, Ngoc Diep;Chapillon, Edwige;Guilloteau, Stephane;Lee, Chang Won;Di Folco, Emmanuel;Majumdar, Liton;Bary, Jeff;Beck, Tracy L.;Coutens, Audrey;Denis-Alpizar, Otoniel;Melisse, Jean-Paul;Pietu, Vincent;Stoecklin, Thierry;Tang, Yei-Wen
    • 천문학회보
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    • 제46권2호
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    • pp.38.2-39
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    • 2021
  • I will presents the analysis of the gas properties of the protoplanetary disk surrounding the young low-mass (about 1.2Msun) triple star, GG Tau A. This work makes use of ALMA observations of rotational lines of CO (12CO, 13CO and C18O) together NOEMA observations of a few dozens of other molecules. While the CO emission gives information on the molecular layer close to the disk atmosphere, its less abundant isotopologues 13CO and C18O bring information much deeper in the molecular layer. I will present the analysis of the morphology and kinematics of the gas disk using the CO isotopologues. A radiative transfer model of the ring in CO isotopologues will also be presented. The subtraction of this model from the original data reveals the weak emission of the molecular gas lying inside the cavity. Thus, I am able to evaluate the properties of the gas inside the cavity, such as the gas dynamics, excitation conditions, and the amount of mass in the cavity. High angular resolution observations of CO reveals sprials induced by embedded planet(s) located near the 3:2:1 mean-motion resonance that help to explain the special morphology of the circumbinary disk. I also discuss some chemical properties of the GG Tau A disk. I report the first detection of H2S and C2S in a protoplanetary disk. The molecule abundance relative to 13CO of about twenties other molecules will also be given. In GG Tau A, the detections of rare molecules such as H2S and C2S have been probably possible because the disk is more massive (a factor about 3-5) than other disks where the molecules was searched. Such a large disk mass makes the system suitable to detect rare molecules and to study cold-chemistry in protoplanetary disks.

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Observation of the Cosmic Near-Infrared Background with the CIBER rocket

  • 김민규;;이형목;;;;;;;;;이대희;;;;;남욱원
    • 천문학회보
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    • 제37권1호
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    • pp.42-42
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    • 2012
  • The First stars (Pop.III stars) in the universe are expected to be formed between the recombination era at z - 1100 and the most distant quasar (z - 8). They have never been directly detected due to its faintness so far, but can be observed as a background radiation at around 1${\mu}m$ which is called the Cosmic Near-Infrared Background (CNB). Main part of the CNB is thought to be redshifted Lyman-alpha from gas clouds surrounding the Pop.III stars. Until now, the COBE (COsmic Background Explorer) and the IRTS (Infrared Telescope in Space) observed excess emission over the background due to galaxies. To confirm the COBE and the IRTS results and pursue more observational evidences, we carried out the sounding rocket experiment named the Cosmic Infrared Background ExpeRiment (CIBER). The CIBER is successfully launched on July 10, 2010 at White Sands Missile Range, New Mexico, USA. It consists of three kinds of instruments. We report the results obtained by LRS (Low Resolution Spectrometer) which is developed to fill the uncovered spectrum around 1${\mu}m$. LRS is a refractive telescope of 5.5 cm aperture with spectral resolution of 20 - 30 and wavelength coverage of 0.7 to 2.0${\mu}m$. After subtracting foreground components (zodiacal light, integrated star light and diffuse galactic light) from the sky brightness of observed five fields, there remained significant residual emission (even for the lower limit case) consistent with the IRTS and the COBE results. In addition, there exists a clear gap at 0.7 - 0.8${\mu}m$ in the CNB spectrum over the background due to galaxies according to recent results (Matsuoka et al. 2011; Mattila et al. 2011). The origin of the excess emission could be ascribed to the Pop.III stars with its active era of z = 7 - 10.

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HYPER SUPRIME-CAMERA SURVEY OF THE AKARI NEP WIDE FIELD

  • Goto, Tomotsugu;Toba, Yoshiki;Utsumi, Yousuke;Oi, Nagisa;Takagi, Toshinobu;Malkan, Matt;Ohayma, Youichi;Murata, Kazumi;Price, Paul;Karouzos, Marios;Matsuhara, Hideo;Nakagawa, Takao;Wada, Takehiko;Serjeant, Steve;Burgarella, Denis;Buat, Veronique;Takada, Masahiro;Miyazaki, Satoshi;Oguri, Masamune;Miyaji, Takamitsu;Oyabu, Shinki;White, Glenn;Takeuchi, Tsutomu;Inami, Hanae;Perason, Chris;Malek, Katarzyna;Marchetti, Lucia;Lee, HyungMoK;Im, Myung;Kim, Seong Jin;Koptelova, Ekaterina;Chao, Dani;Wu, Yi-Han;AKARI NEP Survey team;AKARIAll Sky Survey Team
    • 천문학논총
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    • 제32권1호
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    • pp.225-230
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    • 2017
  • The extragalactic background suggests half the energy generated by stars was reprocessed into the infrared (IR) by dust. At z~1.3, 90% of star formation is obscured by dust. To fully understand the cosmic star formation history, it is critical to investigate infrared emission. AKARI has made deep mid-IR observation using its continuous 9-band filters in the NEP field ($5.4deg^2$), using ~10% of the entire pointed observations available throughout its lifetime. However, there remain 11,000 AKARI infrared sources undetected with the previous CFHT/Megacam imaging (r ~25.9ABmag). Redshift and IR luminosity of these sources are unknown. These sources may contribute significantly to the cosmic star-formation rate density (CSFRD). For example, if they all lie at 1< z <2, the CSFRD will be twice as high at the epoch. We are carrying out deep imaging of the NEP field in 5 broad bands (g, r, i, z, and y) using Hyper Suprime-Camera (HSC), which has 1.5 deg field of view in diameter on Subaru 8m telescope. This will provide photometric redshift information, and thereby IR luminosity for the previously-undetected 11,000 faint AKARI IR sources. Combined with AKARI's mid-IR AGN/SF diagnosis, and accurate midIR luminosity measurement, this will allow a complete census of cosmic star-formation/AGN accretion history obscured by dust.

IRAS 15099-5856: Remarkable Mid-Infrared Source with Prominent Crystalline Silicate Emission

  • 구본철;;서경원;문대식;;;;;김현정;정웅섭;;임명신;이호규;이재준
    • 천문학회보
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    • 제35권1호
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    • pp.57-57
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    • 2010
  • We report the discovery of a bright mid-infrared (MIR) source with prominent crystalline silicate emission using the space telescope AKARI and Spitzer. This source, IRAS 15099-5856, has a spectacular morphology with a bright central compact source (CCS) surrounded by knots, spurs, and several extended (~4') arc-like filaments. The source is seen only in infrared at ${\geq}10{\mu}m$. The Spitzer MIR spectrum of the CCS shows prominent emission features from Mg-rich crystalline silicates and strong [Ne II] 12.88 ${\mu}m$ and several other faint ionic lines. We model the MIR spectrum as thermal emission from several independent dust components and compare their properties to those of the Herbig Be star HD 100546 which shows very similar MIR spectrum. Our molecular line observations reveal two molecular clouds around the source, but no associated dense molecular cores. We discuss two possible origins for IRAS 15099-5856; a deeply embedded massive young stellar object on the other side of the Galaxy and a disrupted, protoplanetary disk being photoevaporated by the UV radiation from the nearby O star Muzzio 10.

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SEARCH FOR EXOPLANETS AROUND NORTHERN CIRCUMPOLAR STARS III. LONG-PERIOD RADIAL VELOCITY VARIATIONS IN HD 18438 AND HD 158996

  • Bang, Tae-Yang;Lee, Byeong-Cheol;Jeong, Gwang-Hui;Han, Inwoo;Park, Myeong-Gu
    • 천문학회지
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    • 제51권1호
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    • pp.17-25
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    • 2018
  • Detecting exoplanets around giant stars sheds light on the later-stage evolution of planetary systems. We observed the M giant HD 18438 and the K giant HD 158996 as part of a Search for Exoplanets around Northern circumpolar Stars (SENS) and obtained 38 and 24 spectra from 2010 to 2017 using the high-resolution Bohyunsan Observatory Echelle Spectrograph (BOES) at the 1.8m telescope of Bohyunsan Optical Astronomy Observatory in Korea. We obtained precise RV measurements from the spectra and found long-period radial velocity (RV) variations with period 719.0 days for HD 18438 and 820.2 days for HD 158996. We checked the chromospheric activities using Ca $\text\tiny{II}$ H and $H{\alpha}$ lines, HIPPARCOS photometry and line bisectors to identify the origin of the observed RV variations. In the case of HD 18438, we conclude that the observed RV variations with period 719.0 days are likely to be caused by the pulsations because the periods of HIPPARCOS photometric and $H{\alpha}$ EW variations for HD 18438 are similar to that of RV variations in Lomb-Scargle periodogram, and there are no correlations between bisectors and RV measurements. In the case of HD 158996, on the other hand, we did not find any similarity in the respective periodograms nor any correlation between RV variations and line bisector variations. In addition, the probability that the real rotational period can be as longer than the RV period for HD 158996 is only about 4.3%. Thus we conclude that observed RV variations with a period of 820.2 days of HD 158996 are caused by a planetary companion, which has the minimum mass of 14.0 $M_{Jup}$, the semi-major axis of 2.1 AU, and eccentricity of 0.13 assuming the stellar mass of $1.8 M_{\odot}$. HD 158996 is so far one of the brightest and largest stars to harbor an exoplanet candidate.

Discovery of a Faint Quasar at z ~ 6 and Implications for Cosmic Reionization

  • Kim, Yongjung;Im, Myungshin;Jeon, Yiseul;Kim, Minjin;Choi, Changsu;Hong, Jueun;Hyun, Minhee;Jun, Hyunsung David;Karouzos, Marios;Kim, Dohyeong;Kim, Duho;Kim, Jae-Woo;Kim, Ji Hoon;Lee, Seong-Kook;Pak, Soojong;Park, Won-Kee;Taak, Yoon Chan;Yoon, Yongmin
    • 천문학회보
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    • 제41권1호
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    • pp.37.3-38
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    • 2016
  • Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of the universe. Confirmation of this scenario requires spectroscopic identification of faint quasars ($M_{1450}$ > -24 mag) at z > 6, but only a very small number of such quasars have been spectroscopically identified so far. Here, we report the discovery of a faint quasar IMS J220417.92+011144.8 at z ~ 6 in a $12.5deg^2$ region of the SA22 field of the Infrared Medium-deep Survey (IMS). The spectrum of the quasar shows a sharp break at ${\sim}8443{\AA}$, with emission lines redshifted to $z=5.944{\pm}0.002$ and rest-frame ultraviolet continuum magnitude $M_{1450}=-23.59{\pm}0.10$ AB mag. The discovery of IMS J220417.92+011144.8 is consistent with the expected number of quasars at z ~6 estimated from quasar luminosity functions based on previous observations of spectroscopically identified low-luminosity quasars. This suggest that the number of $M_{1450}$ ~ -23 mag quasars at z ~ 6 may not be high enough to fully account for the reionization of the universe. In addition, our study demonstrates that faint quasars in the early universe can be identified effectively with a moderately wide and deep near-infrared survey such as the IMS.

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