http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
THE BRIGHTEST STARS IN GALAXIES AS DISTANCE INDICATORS
LYO A-RAN,LEE MYUNG GYOON The Korean Astronomical Society 1997 Journal of The Korean Astronomical Society Vol.30 No.1
The brightest stars in galaxies have been used as distance indicators since Hubble. However, the accuracy of the brightest stars for distance estimates has been controversial. Recently, Rozanski & Rowan-Robinson [1994 : MNRAS, 271, 530] argued large errors of this method for the distance determination : 0.58 mag and 0.90 mag, respectively, for the brightest red stars and the brightest blue stars, while Karachentsev & Tikhonov [1994 : A&A, 286, 718] suggested much smaller errors in the distance determination than the former: 0.37 mag for the brightest red stars and 0.46 mag for the brightest blue stars. The reasons for these conflicting results are not yet known. In this study we have investigated the accuracy of this method using a sample of 17 galaxies for which Cepheid distances are known and reliable photometry of the brightest stars are available. We have obtained the calibrations of the relations between the mean luminosities of the three blue and red brightest supergiants (BSGs and RSGs, respectively) and the total luminosities of the parent galaxies: $<M_{v(3)RSG}>= 0.21M_B^T- 3.84, \sigma(M_v) = 0.37 mag,\;and\;\delta_{\mu0}=0.47$ mag for the brightest red supergiants, and $<M_{B(3)BSG}>= 0.30M_B^T -3.02, \sigma(M_B)\;=\;0.55 mag,\;and\; \delta_{\mu0}=0.79mag$ for the brightest blue supergiants. Also it is found that the errors in the distance determination are reduced by a factor of two, as the observing wavelengths increase from B-band to K-band. In conclusion, the brightest red supergiants are considered to be useful for determining the distances to resolved late-type galaxies.
Inner Warm Disk of ESO H<i>α</i>279a Revealed by NA i and CO Overtone Emission Lines
Lyo, A-Ran,Kim, Jongsoo,Lee, Jae-Joon,Kim, Kyoung-Hee,Kang, Jihyun,Byun, Do-Young,Mace, Gregory,Sokal, Kimberly R.,Park, Chan,Chun, Moo-Young,Oh, Heeyoung,Yu, Young Sam,Oh, Jae Sok,Jeong, Ueejeong,Kim American Astronomical Society 2017 The Astrophysical Journal Vol.844 No.1
<P>We present an analysis of near-infrared, high-resolution spectroscopy toward the flat-spectrum young stellar object (YSO) ESO H alpha 279a (similar to 1.5M(circle dot)) in the Serpens star-forming region at a distance of 429 pc. Using the Immersion GRating INfrared Spectrometer (IGRINS; R approximate to 45,000), we detect emission lines originating from the accretion channel flow, jet, and inner disk. Specifically, we identify hydrogen Brackett series recombination, [Fe II], [Fe III], [Fe IV], Ca I, Na I, H-2, H2O, and CO overtone emission lines. By modeling five bands of CO overtone emission lines and the symmetric double-peaked line profile for Na I emission lines, we find that ESO H alpha 279a has an actively accreting Keplerian disk. From our Keplerian disk model, we find that Na I emission lines originate between 0.04 and 1.00 au, while the CO overtone emission lines are from the outer part of the disk, in the range between 0.22 and 3.00 au. The model reveals that the neutral atomic Na gas is a good tracer of the innermost region of the actively accreting disk. We derive a mass accretion rate of 2-10 x 10-7 Me yr(-1). from the measured Br gamma emission luminosity of 1.78(+/- 0.31) x 10(31) erg s(-1).</P>
UNBIASED WATER AND METHANOL MASER SURVEYS OF NGC 1333
Lyo, A-Ran,Kim, Jongsoo,Byun, Do-Young,Lee, Ho-Gyu American Institute of Physics 2014 The Astronomical journal Vol.148 No.5
<P>We present the results of unbiased 22 GHz H<SUB>2</SUB>O water and 44 GHz class I CH<SUB>3</SUB>OH methanol maser surveys in the central 7' × 10' area of NGC 1333 and two additional mapping observations of a 22 GHz water maser in a ~3' × 3' area of the IRAS4A region. In the 22 GHz water maser survey of NGC 1333 with a sensitivity of σ ~ 0.3 Jy, we confirmed the detection of masers toward H<SUB>2</SUB>O(B) in the region of HH 7-11 and IRAS4B. We also detected new water masers located ~20'' away in the western direction of IRAS4B or ~25'' away in the southern direction of IRAS4A. We could not, however, find young stellar objects or molecular outflows associated with them. They showed two different velocity components of ~0 and ~16 km s<SUP>–1</SUP>, which are blue- and redshifted relative to the adopted systemic velocity of ~7 km s<SUP>–1</SUP> for NGC 1333. They also showed time variabilities in both intensity and velocity from multi-epoch observations and an anti-correlation between the intensities of the blue- and redshifted velocity components. We suggest that the unidentified power source of these masers might be found in the earliest evolutionary stage of star formation, before the onset of molecular outflows. Finding this kind of water maser is only possible through an unbiased blind survey. In the 44 GHz methanol maser survey with a sensitivity of σ ~ 0.5 Jy, we confirmed masers toward IRAS4A2 and the eastern shock region of IRAS2A. Both sources are also detected in 95 and 132 GHz methanol maser lines. In addition, we had new detections of methanol masers at 95 and 132 GHz toward IRAS4B. In terms of the isotropic luminosity, we detected methanol maser sources brighter than ~5 × 10<SUP>25</SUP> erg s<SUP>–1</SUP> from our unbiased survey.</P>
Matsumoto, Naoko,Hirota, Tomoya,Sugiyama, Koichiro,Kim, Kee-Tae,Kim, Mikyoung,Byun, Do-Young,Jung, Taehyun,Chibueze, James O.,Honma, Mareki,Kameya, Osamu,Kim, Jongsoo,Lyo, A-Ran,Motogi, Kazuhito,Oh, C IOP Publishing 2014 ASTROPHYSICAL JOURNAL LETTERS - Vol.789 No.1
<P>We have carried out the first very long baseline interferometry (VLBI) imaging of a 44 GHz class I methanol maser (70-61A(+)) associated with a millimeter core MM2 in a massive star-forming region IRAS 18151-1208 with KaVA (KVN and VERA Array), which is a newly combined array of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We have succeeded in imaging compact maser features with a synthesized beam size of 2.7 milliarcseconds x 1.5 milliarcseconds (mas). These features are detected at a limited number of baselines within the length of shorter than approximate to 650 km corresponding to 100 M. in the uv-coverage. The central velocity and the velocity width of the 44 GHz methanol maser are consistent with those of the quiescent gas rather than the outflow traced by the SiO thermal line. The minimum component size among the maser features is similar to 5 mas x 2 mas, which corresponds to the linear size of similar to 15 AU x 6 AU assuming a distance of 3 kpc. The brightness temperatures of these features range from similar to 3.5 x 10(8) to 1.0 x 10(10) K, which are higher than the estimated lower limit from a previous Very Large Array observation with the highest spatial resolution of similar to 50 mas. The 44 GHz class I methanol maser in IRAS 18151-1208 is found to be associated with the MM2 core, which is thought to be less evolved than another millimeter core MM1 associated with the 6.7 GHz class II methanol maser.</P>
THE LONGEVITY OF CIRCUMSTELLAR DISKS: THE η CHAMAELEONTIS CLUSTER
LYO A-RAN,LAWSON W. A. The Korean Astronomical Society 2005 Journal of The Korean Astronomical Society Vol.38 No.2
We have analysed near-infrared JHKL observations of the members of the $\approx$9 Myr-old $\eta$ Chamaeleontis cluster. Using (J - H)/(K - L) and (H - K)/(K - L) IR colour-colour diagrams for the brightest 15 members of the cluster, we find the fraction of stellar systems with near-IR excess emission was 0.60 $\pm$ 0.13 (2$\sigma$). For the CTT and WTT star population, we also find a strong correlation between the IR excess and Ha emission which is also known as an accretion indicator. The (K - L) excess of these stars appears to indicate a wide range of star-disk activity; from a CTT star with high levels of accretion, to CTT - WTT transitional objects with evidence for some on-going accretion, and WTT stars with weak or absent IR excesses. Among the brightest 15 members, four stars (RECX 5, 9, 11 and ECHA J0843.3-7905) with IR excesses ${\Delta}$(K - L) > 0.4 mag and strong or variable optical emission were identified as likely experiencing on-going mass accretion from their circumstellar disks which we confirmed their accretion disks from the optical high-resolution echelle spectroscopic study. The result-ing accretion fraction of 0.27 $\pm$ 0.13 (2$\sigma$) suggests that the accretion phase, in addition to the disks themselves, can endure for at least ${\~}$10 Myr.
MILLIMETER OBSERVATIONS OF THE TRANSITION DISK AROUND HD 135344B (SAO 206462)
Lyo, A-Ran,Ohashi, Nagayoshi,Qi, Chunhua,Wilner, David J.,Su, Yu-Nung American Institute of Physics 2011 The Astronomical journal Vol.142 No.5
<P>We present ~1'' resolution 1.3 mm dust continuum and spectral line (<SUP>12</SUP>CO and <SUP>13</SUP>CO J = 2-1) observations of the transitional disk system HD 135344B obtained with the Submillimeter Array. The disk shows a Keplerian rotation pattern with an inclination of ~11°, based on the spatially and spectrally resolved <SUP>12</SUP>CO and <SUP>13</SUP>CO emission. The data show clear evidence for both dust and gas surface density reductions in the inner region of the disk (radius <img entity='lsim' SRC='http://ej.iop.org/icons/Entities/lsim.gif' ALT='lsim' ALIGN='BASELINE' /> 50 AU) from the continuum and <SUP>13</SUP>CO J = 2-1 data, respectively. The presence of this inner cavity in both the dust and gas is more consistent with clearing by giant planet formation than by photoevaporation or by grain growth. There is also an indication of global CO gas depletion in the disk, as the mass estimated from <SUP>13</SUP>CO emission (~3.8 × 10<SUP>–4</SUP> M<SUB>☉</SUB>) is about two orders of magnitude lower than that derived from the 1.3 mm continuum (~2.8 × 10<SUP>–2</SUP> M<SUB>☉</SUB>).</P>