5,058 research outputs found
An HI interstellar bubble surrounding WR85 and RCW118
We analyze the distribution of the interstellar matter in the environs of the
Wolf-Rayet star LSS3982 (= WR85, WN6+OB?) linked to the optical ring nebula
RCW118. Our study is based on neutral hydrogen 21cm-line data belonging to the
Southern Galactic Plane Survey (SGPS).
The analysis of the HI data allowed the identification of a neutral hydrogen
interstellar bubble related to WR 85 and the 25' diameter ring nebula RCW118.
The HI bubble was detected at a systemic velocity of -21.5 km/s, corresponding
to a kinematical distance of 2.8+/-1.1 kpc, compatible with the stellar
distance. The neutral stucture is about 25' in radius or 21+/-8 pc, and is
expanding at 9+/-2 km/s. The associated ionized and neutral masses amount to
3000 Mo. The CO emission distribution depicts a region lacking CO coincident in
position and velocity with the HI structure. The 9'.3 diameter inner optical
nebula appears to be related to the approaching part of the neutral atomic
shell. The HI void and shell are the neutral gas counterparts of the optical
bubble and have very probably originated in the action of the strong stellar
wind of the central star during the O-type and WR phases on the surrounding
interstellar medium. The HI bubble appears to be in the momentun conserving
stage.Comment: 9 pages, 7 figures, accepted in MNRA
Effects of lattice distortion and Jahn–Teller coupling on the magnetoresistance of La0.7Ca0.3MnO3 and La0.5Ca0.5CoO3 epitaxial films
Studies of La0.7Ca0.3MnO3 epitaxial films on substrates with a range of lattice constants reveal two dominant contributions to the occurrence of colossal negative magnetoresistance (CMR) in these manganites: at high temperatures (T → TC, TC being the Curie temperature), the magnetotransport properties are predominantly determined by the conduction of lattice polarons, while at low temperatures (T ≪ TC/, the residual negative magnetoresistance is correlated with the substrate-induced lattice distortion which incurs excess magnetic domain wall scattering. The importance of lattice polaron conduction associated with the presence of Jahn–Teller coupling in the manganites is further verified by comparing the manganites with epitaxial films of another ferromagnetic perovskite, La0.5Ca0.5CoO3. Regardless of the differences in the substrate-induced lattice distortion, the cobaltite films exhibit much smaller negative magnetoresistance, which may be attributed to the absence of Jahn–Teller coupling and the high electron mobility that prevents the formation of lattice polarons. We therefore suggest that lattice polaron conduction associated with the Jahn–Teller coupling is essential for the occurrence of CMR, and that lattice distortion further enhances the CMR effects in the manganites
Scanning tunneling spectroscopic studies of the pairing state of cuprate superconductors
Quasiparticle tunneling spectra of both hole-doped (p-type) and electron-doped (n-type) cuprates are studied using a low-temperature scanning tunneling microscope. The results reveal that neither the pairing symmetry nor the pseudogap phenomenon is universal among all cuprates, and that the response of n-type cuprates to quantum impurities is drastically different from that of the p-type cuprates. The only ubiquitous features among all cuprates appear to be the strong electronic correlation and the nearest-neighbor antiferromagnetic Cu2+-Cu2+ coupling in the CuO2 planes
870 micron continuum observations of the bubble-shaped nebula Gum 31
We are presenting here a study of the cold dust in the infrared ring nebula
Gum 31. We aim at deriving the physical properties of the molecular gas and
dust associated with the nebula, and investigating its correlation with the
star formation in the region, that was probably triggered by the expansion of
the ionization front. We use 870 micron data obtained with LABOCA to map the
dust emission. The obtained LABOCA image was compared to archival IR,radio
continuum, and optical images. The 870 micron emission follows the 8 micron
(Spitzer), 250 micron, and 500 micron (Herschel) emission distributions showing
the classical morphology of a spherical shell. We use the 870 micron and 250
micron images to identify 60 dust clumps in the collected layers of molecular
gas using the Gaussclumps algorithm. The clumps have effective deconvolved
radii between 0.16 pc and 1.35 pc, masses between 70 Mo and 2800 Mo, and volume
densities between 1.1x10^3 cm^-3 and 2.04x10^5 cm^-3. The total mass of the
clumps is 37600 Mo. The dust temperature of the clumps is in the range from 21
K to 32 K, while inside the HII region reaches ~ 40 K. The clump mass
distribution is well-fitted by a power law dN/dlog(M/Mo) proportional to
M^(-alpha), with alpha=0.93+/-0.28. The slope differs from those obtained for
the stellar IMF in the solar neighborhood, suggesting that the clumps are not
direct progenitors of single stars/protostars. The mass-radius relationship for
the 41 clumps detected in the 870 microns emission shows that only 37% of them
lie in or above the high-mass star formation threshold, most of them having
candidate YSOs projected inside. A comparison of the dynamical age of the HII
region with the fragmentation time, allowed us to conclude that the collect and
collapse mechanism may be important for the star formation at the edge of Gum
31, although other processes may also be acting.Comment: 15 pages, 10 figures. Accepted for publication in A&
Molecular gas and star formation towards the IR dust bubble S24 and its environs
We present a multi-wavelength analysis of the infrared dust bubble S24, and
its environs, with the aim of investigating the characteristics of the
molecular gas and the interstellar dust linked to them, and analyzing the
evolutionary status of the young stellar objects (YSOs) identified there. Using
APEX data, we mapped the molecular emission in the CO(2-1), CO(2-1),
CO(2-1), and CO(3-2) lines in a region of about 5'x 5' in size
around the bubble. The cold dust distribution was analyzed using ATLASGAL and
Herschel images. Complementary IR and radio data were also used.The molecular
gas linked to the S24 bubble, G341.220-0.213, and G341.217-0.237 has velocities
between -48.0 km sec and -40.0 km sec. The gas distribution
reveals a shell-like molecular structure of 0.8 pc in radius bordering
the bubble. A cold dust counterpart of the shell is detected in the LABOCA and
Herschel images.The presence of extended emission at 24 m and radio
continuum emission inside the bubble indicates that the bubble is a compact HII
region. Part of the molecular gas bordering S24 coincides with the extended
infrared dust cloud SDC341.194-0.221. A cold molecular clump is present at the
interface between S24 and G341.217-0.237. As regards G341.220-0.213, the
presence of an arc-like molecular structure at the northern and eastern
sections of this IR source indicates that G341.220-0.213 is interacting with
the molecular gas. Several YSO candidates are found to be linked to the IR
extended sources, thus confirming their nature as active star-forming regions.
The total gas mass in the region and the H ambient density amount to 10300
M and 5900 cm, indicating that G341.220-0.213, G341.217-0.237,
and the S24 HII region are evolving in a high density medium. A triggering star
formation scenario is also investigated.Comment: 17 pages, 16 figures. Submitted to A&A. Revised according to the
referee repor
Principles for data analysis workflows
Traditional data science education often omits training on research
workflows: the process that moves a scientific investigation from raw data to
coherent research question to insightful contribution. In this paper, we
elaborate basic principles of a reproducible data analysis workflow by defining
three phases: the Exploratory, Refinement, and Polishing Phases. Each workflow
phase is roughly centered around the audience to whom research decisions,
methodologies, and results are being immediately communicated. Importantly,
each phase can also give rise to a number of research products beyond
traditional academic publications. Where relevant, we draw analogies between
principles for data-intensive research workflows and established practice in
software development. The guidance provided here is not intended to be a strict
rulebook; rather, the suggestions for practices and tools to advance
reproducible, sound data-intensive analysis may furnish support for both
students and current professionals
Spectroscopic Evidence for Anisotropic S-Wave Pairing Symmetry in MgB2
Scanning tunneling spectroscopy of superconducting MgB ( K)
were studied on high-density pellets and c-axis oriented films. The sample
surfaces were chemically etched to remove surface carbonates and hydroxides,
and the data were compared with calculated spectra for all symmetry-allowed
pairing channels. The pairing potential () is best described by an
anisotropic s-wave pairing model, with , where is the angle relative to the
crystalline c-axis, meV, and meV.Comment: 4 pages and 3 figures. Submitted to Physical Review Letters.
Corresponding author: Nai-Chang Yeh (e-mail: [email protected]
Molecular gas towards G18.8+1.8
This work aims at investigating the characteristics of the molecular gas
associated with the nebula G18.8+1.8, linked to the Wolf-Rayet star HD168206
(WR 113), and its relation to other components of its local interstellar
medium.
We carried out molecular observations of the 12CO(J=1-0) and (J=2-1) lines
with angular resolution of 44 arcsec and 22 arcsec using the SEST telescope.
Complementary NANTEN data of the 12CO(1-0) line were also used. The dust
emission was analyzed using Spitzer-IRAC images at 8.0 microns, and WISE data
at 3.4, 4.6, and 12.0 microns.
The SEST data allowed us to identify a molecular component (Cloud 3) having
velocities in the interval from ~ +30 to +36 km/s which is most probably linked
to the nebula. Morphological and kinematical properties suggest that Cloud 3
constitute a wind-blown molecular half-shell, which expands around WR113. The
ratio R_(2-1/1-0) and excitation temperatures indicate that the molecular gas
is being irradiated by strong UV radiation. The location of the inner optical
ring in the outer edge of Cloud 3 suggests that the stars SerOB2-1, -2, -3,
-63, and -64 are responsables for the ionization of Cloud 3 and the inner ring
nebula. A comparison between the spatial distribution of the molecular gas and
the PAH emission at 8 m indicates the existence of a PDR between the
ionized and the molecular gas.
A search for candidate young stellar objects (YSOs) in the region around
G18.8+1.8 based on available 2MASS, MSX, IRAS, and Spitzer-IRAC catalogs
resulted in the detection of about sixty sources, some of them projected onto
Cloud 3. Two small spots of clustered candidates YSOs are projected near the
outer border of Cloud 3, although a triggered stellar formation scenario is
doubtful.Comment: 12 pages, 9 figures, accepted for publication in A&
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