1,051 research outputs found
The Effect of Dust Extinction on the Observed Properties of Galaxies in the Near-Infrared
Galaxies behind the Milky Way suffer size reduction and dimming due to their
obscuration by dust in the disk of our Galaxy. The degree of obscuration is
wavelength dependent. It decreases towards longer wavelengths. Compared to the
optical, the Near InfraRed (NIR) band extinction is only
that of the band. This makes NIR surveys well suited for galaxy surveys
close to the Galactic Plane where extinction is severe.
While Galactic obscuration is less prominent in the NIR it is not negligible.
In this paper we derive empirical relations to correct isophotal radii and
magnitudes of galaxies observed in the NIR for foreground absorption. We
simulate extinction in the , and bands on 64 (unobscured) galaxies
from the 2MASS Large Galaxy Atlas \citep{jarrett}. We propose two methods for
the extinction correction, the first is optimized to provide the most accurate
correction and the second provides a convenient statistical correction that
works adequately in lower extinction regions. The optimized correction utilizes
the galaxy surface brightness, either the disk central surface brightness,
, or the combined disk plus bulge central surface brightness, elliptical
and disk/spiral Hubble types. A detailed comparison between the different
methods and their accuracy is provided.Comment: 9 pages, 8 figures and 8 tables. Accepted by the MNRAS: Accepted 2009
September 18. Received 2009 September 18; in original form 2009 July 1
The Distance to the Galactic Center Derived From Infrared Photometry of Bulge Red Clump Stars
On the basis of the near infrared observations of bulge red clump stars near
the Galactic center, we have determined the galactocentric distance to be R_0 =
7.52 +- 0.10 (stat) +- 0.35 (sys) kpc. We observed the red clump stars at |l| <
1.0 deg and 0.7 deg < |b| < 1.0 deg with the IRSF 1.4 m telescope and the
SIRIUS camera in the H and Ks bands. After extinction and population
corrections, we obtained (m - M)_0 = 14.38 +- 0.03 (stat) +- 0.10 (sys). The
statistical error is dominated by the uncertainty of the intrinsic local red
clump stars' luminosity. The systematic error is estimated to be +- 0.10
including uncertainties in extinction and population correction, zero-point of
photometry, and the fitting of the luminosity function of the red clump stars.
Our result, R_0 = 7.52 kpc, is in excellent agreement with the distance
determined geometrically with the star orbiting the massive black hole in the
Galactic center. The recent result based on the spatial distribution of
globular clusters is also consistent with our result. In addition, our study
exhibits that the distance determination to the Galactic center with the red
clump stars, even if the error of the population correction is taken into
account, can achieve an uncertainty of about 5%, which is almost the same level
as that in recent geometrical determinations.Comment: 14 pages, 4 figures, accepted by Ap
Zernike Phase Contrast Cryo-Electron Microscopy and Tomography for Structure Determination at Nanometer and Subnanometer Resolutions
Zernike phase contrast cryo-electron microscopy (ZPC-cryoEM) is an emerging technique that is capable of producing higher image contrast than conventional cryoEM. By combining this technique with advanced image processing methods, we achieved subnanometer resolution for two biological specimens: 2D bacteriorhodopsin crystal and epsilon15 bacteriophage. For an asymmetric reconstruction of epsilon15 bacteriophage, ZPC-cryoEM can reduce the required amount of data by a factor of ~3, compared with conventional cryoEM. The reconstruction was carried out to 13 Å resolution without the need to correct the contrast transfer function. New structural features at the portal vertex of the epsilon15 bacteriophage are revealed in this reconstruction. Using ZPC cryo-electron tomography (ZPC-cryoET), a similar level of data reduction and higher resolution structures of epsilon15 bacteriophage can be obtained relative to conventional cryoET. These results show quantitatively the benefits of ZPC-cryoEM and ZPC-cryoET for structural determinations of macromolecular machines at nanometer and subnanometer resolutions.National Institutes of Health (U.S.) (Grant P41RR002250)National Institutes of Health (U.S.) (Grant R01AI0175208)National Institutes of Health (U.S.) (Grant PN1EY016525)Robert Welch Foundation (Q1242
Phase contrast electron microscopy: development of thin-film phase plates and biological applications
Phase contrast transmission electron microscopy (TEM) based on thin-film phase plates has been developed and applied to biological systems. Currently, development is focused on two techniques that employ two different types of phase plates. The first technique uses a Zernike phase plate, which is made of a uniform amorphous carbon film that completely covers the aperture of an objective lens and can retard the phase of electron waves by π/2, except at the centre where a tiny hole is drilled. The other technique uses a Hilbert phase plate, which is made of an amorphous carbon film that is twice as thick as the Zernike phase plate, covers only half of the aperture and retards the electron wave phase by π. By combining the power of efficient phase contrast detection with the accurate preservation achieved by a cryotechnique such as vitrification, macromolecular complexes and supermolecular structures inside intact bacterial or eukaryotic cells may be visualized without staining. Phase contrast cryo-TEM has the potential to bridge the gap between cellular and molecular biology in terms of high-resolution visualization. Examples using proteins, viruses, cyanobacteria and somatic cells are provided
An X-ray Imaging Study of the Stellar Population in RCW49
We present the results of a high-resolution X-ray imaging study of the
stellar population in the Galactic massive star-forming region RCW49 and its
central OB association Westerlund 2. We obtained a 40 ks X-ray image of a
17'x17' field using the Chandra X-ray Observatory and deep NIR images using the
Infrared Survey Facility in a concentric 8'3x8'3 region. We detected 468 X-ray
sources and identified optical, NIR, and Spitzer Space Telescope MIR
counterparts for 379 of them. The unprecedented spatial resolution and
sensitivity of the X-ray image, enhanced by optical and infrared imaging data,
yielded the following results: (1) The central OB association Westerlund 2 is
resolved for the first time in the X-ray band. X-ray emission is detected from
all spectroscopically-identified early-type stars in this region. (2) Most
(86%) X-ray sources with optical or infrared identifications are cluster
members in comparison with a control field in the Galactic Plane. (3) A loose
constraint (2--5 kpc) for the distance to RCW49 is derived from the mean X-ray
luminosity of T Tauri stars. (4) The cluster X-ray population consists of
low-mass pre--main-sequence and early-type stars as obtained from X-ray and NIR
photometry. About 30 new OB star candidates are identified. (5) We estimate a
cluster radius of 6'--7' based on the X-ray surface number density profiles.
(6) A large fraction (90%) of cluster members are identified individually using
complimentary X-ray and MIR excess emission. (7) The brightest five X-ray
sources, two Wolf-Rayet stars and three O stars, have hard thermal spectra.Comment: 19 pages, 17 figures, 4 tables. ApJ in pres
Synergistic Formation of Radicals by Irradiation with Both Vacuum Ultraviolet and Atomic Hydrogen: A Real-Time In Situ Electron Spin Resonance Study
We report on the surface modification of polytetrafluoroethylene (PTFE) as an
example of soft- and bio-materials that occur under plasma discharge by
kinetics analysis of radical formation using in situ real-time electron spin
resonance (ESR) measurements. During irradiation with hydrogen plasma,
simultaneous measurements of the gas-phase ESR signals of atomic hydrogen and
the carbon dangling bond (C-DB) on PTFE were performed. Dynamic changes of the
C-DB density were observed in real time, where the rate of density change was
accelerated during initial irradiation and then became constant over time. It
is noteworthy that C-DBs were formed synergistically by irradiation with both
vacuum ultraviolet (VUV) and atomic hydrogen. The in situ real-time ESR
technique is useful to elucidate synergistic roles during plasma surface
modification.Comment: 14 pages, 4 figure
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