1,003 research outputs found
Sejong Open Cluster Survey (SOS). 0. Target Selection and Data Analysis
Star clusters are superb astrophysical laboratories containing cospatial and
coeval samples of stars with similar chemical composition. We have initiated
the Sejong Open cluster Survey (SOS) - a project dedicated to providing
homogeneous photometry of a large number of open clusters in the SAAO
Johnson-Cousins' system. To achieve our main goal, we have paid much
attention to the observation of standard stars in order to reproduce the SAAO
standard system.
Many of our targets are relatively small, sparse clusters that escaped
previous observations. As clusters are considered building blocks of the
Galactic disk, their physical properties such as the initial mass function, the
pattern of mass segregation, etc. give valuable information on the formation
and evolution of the Galactic disk. The spatial distribution of young open
clusters will be used to revise the local spiral arm structure of the Galaxy.
In addition, the homogeneous data can also be used to test stellar evolutionary
theory, especially concerning rare massive stars. In this paper we present the
target selection criteria, the observational strategy for accurate photometry,
and the adopted calibrations for data analysis such as color-color relations,
zero-age main sequence relations, Sp - Mv relations, Sp - Teff relations, Sp -
color relations, and Teff - BC relations. Finally we provide some data analysis
such as the determination of the reddening law, the membership selection
criteria, and distance determination.Comment: 21 pages, 16 figures, accepted for publication in J. of Korean
Astronomical Society (JKAS
An Optical and Infrared Photometric Study of the Young Open Cluster IC 1805 in the Giant H II Region W4
We present deep wide-field optical CCD photometry and mid-infrared
Spitzer/IRAC and MIPS 24micron data for about 100,000 stars in the young open
cluster IC 1805. The members of IC 1805 were selected from their location in
the various color-color and color-magnitude diagrams, and the presence of
Halpha emission, mid-infrared excess emission, and X-ray emission. The
reddening law toward IC 1805 is nearly normal (R_V = 3.05+/-0.06). However, the
distance modulus of the cluster is estimated to be 11.9+/-0.2 mag (d =
2.4+/-0.2 kpc) from the reddening-free color-magnitude diagrams, which is
larger than the distance to the nearby massive star-forming region W3(OH)
measured from the radio VLBA astrometry. We also determined the age of IC 1805
(tau_MSTO = 3.5 Myr). In addition, we critically compared the age and mass
scale from two pre-main-sequence evolution models. The initial mass function
with a Salpeter-type slope of Gamma = -1.3+/-0.2 was obtained and the total
mass of IC 1805 was estimated to be about 2700+/-200 M_sun. Finally, we found
our distance determination to be statistically consistent with the Tycho-Gaia
Astrometric Solution Data Release 1, within the errors. The proper motion of
the B-type stars shows an elongated distribution along the Galactic plane,
which could be explained by some of the B-type stars being formed in small
clouds dispersed by previous episodes of star formation or supernova
explosions.Comment: 45 pages, 32 figures, 9 tables, accepted for publication in ApJ
Reddening, distance, and stellar content of the young open cluster Westerlund 2
We present deep UBVIC photometric data of the young open cluster Westerlund 2. An abnormal reddening law of RV, cl = 4.14 ± 0.08 was found for the highly reddened early-type members (E(B−V)≧1.45E(B−V)≧1.45), whereas a fairly normal reddening law of RV, fg = 3.33 ± 0.03 was confirmed for the foreground early-type stars (E(B − V)fg < 1.05). The distance modulus was determined from zero-age main-sequence fitting to the reddening-corrected colour–magnitude diagram of the early-type members to be V0 − MV = 13.9 ± 0.14 (random error) +0.4−0.1−0.1+0.4 (the upper limit of systematic error) mag (d=6.0±0.4+1.2−0.3d=6.0±0.4−0.3+1.2 kpc). To obtain the initial mass function, pre-main-sequence (PMS) stars were selected by identifying the optical counterparts of Chandra X-ray sources and mid-infrared emission stars from the Spitzer GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) source catalogue. The initial mass function shows a shallow slope of Γ = −1.1 ± 0.1 down to log m = 0.7. The total mass of Westerlund 2 is estimated to be at least 7 400 M⊙. The age of Westerlund 2 from the main-sequence turn-on and PMS stars is estimated to be ≲ 1.5 Myr. We confirmed the existence of a clump of PMS stars located ∼1 arcmin north of the core of Westerlund 2, but we could not find any clear evidence for an age difference between the core and the northern clump
Reddening, Distance, and Stellar Content of the Young Open Cluster Westerlund 2
We present deep photometric data of the young open cluster
Westerlund 2. An abnormal reddening law of was found for
the highly reddened early-type members (), whereas a fairly
normal reddening law of was confirmed for the foreground
early-type stars (). The distance modulus was determined from
zero-age main-sequence (ZAMS) fitting to the reddening-corrected
colour-magnitude diagram of the early-type members to be
(random error) (the upper limit of systematic error) mag ( kpc). To obtain the initial mass function,
pre-main-sequence (PMS) stars were selected by identifying the optical
counterparts of Chandra X-ray sources and mid-infrared emission stars from the
Spitzer GLIMPSE source catalog. The initial mass function shows a shallow slope
of down to . The total mass of Westerlund 2
is estimated to be at least 7,400 . The age of Westerlund 2 from the
main-sequence turn-on and PMS stars is estimated to be 1.5 Myr. We
confirmed the existence of a clump of PMS stars located arcmin north of
the core of Westerlund 2, but we could not find any clear evidence for an age
difference between the core and the northern clump.Comment: 25 pages, 22 figures, 6 tables, accepted for publication in MNRA
Performance of the tuberculin skin test and interferon-γ release assay for detection of tuberculosis infection in immunocompromised patients in a BCG-vaccinated population
<p>Abstract</p> <p>Background</p> <p>Interferon-γ release assay (IGRA) may improve diagnostic accuracy for latent tuberculosis infection (LTBI). This study compared the performance of the tuberculin skin test (TST) with that of IGRA for the diagnosis of LTBI in immunocompromised patients in an intermediate TB burden country where BCG vaccination is mandatory.</p> <p>Methods</p> <p>We conducted a retrospective observational study of patients given the TST and an IGRA, the QuantiFERON-TB Gold In-Tube (QFT-IT), at Severance Hospital, a tertiary hospital in South Korea, from December 2006 to May 2009.</p> <p>Results</p> <p>Of 211 patients who underwent TST and QFT-IT testing, 117 (55%) were classified as immunocompromised. Significantly fewer immunocompromised than immunocompetent patients had positive TST results (10.3% vs. 27.7%, p 0.001), whereas the percentage of positive QFT-IT results was comparable for both groups (21.4% vs. 25.5%). However, indeterminate QFT-IT results were more frequent in immunocompromised than immunocompetent patients (21.4% vs. 9.6%, p 0.021). Agreement between the TST and QFT-IT was fair for the immunocompromised group (κ = 0.38), but moderate agreement was observed for the immunocompetent group (κ = 0.57). Indeterminate QFT-IT results were associated with anaemia, lymphocytopenia, hypoproteinemia, and hypoalbuminemia.</p> <p>Conclusion</p> <p>In immunocompromised patients, the QFT-IT may be more sensitive than the TST for detection of LTBI, but it resulted in a considerable proportion of indeterminate results. Therefore, both tests may maximise the efficacy of screening for LTBI in immunocompromised patients.</p
Microstructure and gas-sensing properties of thick film sensor using nanophase SnO 2 powder
Abstract The object of the present work apply the nanophase SnO 2 powder synthesized by inert gas condensation method (IGC) to thick film hydrogen sensor and to study the effect of microstructural changes of sensors on the sensing properties. SnO 2 gas sensors were printed using nanophase SnO 2 powder without any doping element by a silk screen printing method and subsequently sintered. Among the thick film sensors manufactured at various temperatures, the highest sensitivity was obtained in the sensor sintered at 600 • C, which exhibited its maximum sensitivity of 96% at 250 • C against the hydrogen concentration of 2500 ppm. The results were discussed in viewpoint of the pore structure and the crystallinity of the sensors
The starburst cluster westerlund 1: The initial mass function and mass segregation
Westerlund 1 is the most important starburst cluster in the Galaxy due to its massive star content. We have performed BVIC and JKS photometry to investigate the initial mass function (IMF). By comparing the observed color with the spectral-type-intrinsic-color relation, we obtain the mean interstellar reddening of 〈E(B-V)〉 = 4.19 ± 0.23 and 〈E(J-KS )〉 = 1.70 ± 0.21. Due to the heavy extinction toward the cluster, the zero-age main sequence fitting method based on optical photometry proved to be inappropriate for the distance determination, while the near-infrared photometry gave a reliable distance to the cluster - 3.8 kpc from the empirical relation. Using the recent theoretical stellar evolution models with rotation, the age of the cluster is estimated to be 5.0 ± 1.0 Myr. We derived the IMF in the massive part and obtained a fairly shallow slope of Γ = -0.8 ± 0.1. The integration of the IMF gave a total mass for the cluster in excess of 5.0 × 104 M⊙. The IMF shows a clear radial variation indicating the presence of mass segregation. We also discuss the possible star formation history of Westerlund 1 from the presence of red supergiants and relatively low luminosity yellow hypergiants
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