1,108 research outputs found
Chandra Observations of a Young Embedded Magnetic B Star in the rho Ophiuchus Cloud
This paper reports on an analysis of two Chandra X-ray observations of the
young magnetic B star rho Ophiuchus S1. X-ray emission from the star was
detected in both observations. The average flux was almost the same in both,
but during each observation the flux showed significant time variations by a
factor of two on timescales of 20-40 ks. Each spectrum could be fit by either
an absorbed power-law model with a photon index of ~3 or a thin-thermal plasma
model with a temperature of ~2 keV and an extremely low metal abundance (<~0.1
solar). The spectrum of the first observation has a weak-line feature at about
6.8 keV, which might correspond to highly ionized iron Kalpha. In contrast, the
spectrum of the second observation apparently shows a weak edge absorption
component at E~4 keV. The continuum emission and log LX/Lbol ~ -6 are similar
to those of young intermediate-mass stars (Herbig Ae/Be stars), although the
presence of a strong magnetic field (inferred from the detection of non-thermal
radio emission) has drawn an analogy between rho Ophiuchus S1 and magnetic
chemically peculiar (MCP) stars. If the X-ray emission is thermal, the small
abundances that we derived might be related to the inverse first-ionization
potential (FIP) effect, though there is no significant trend as a function of
FIP from our model fits. If the emission is non-thermal, it might be produced
by high-energy electrons in the magnetosphere.Comment: 13 pages, 6 figures, To appear in the October issue of PASJ (vol.55,
No. 5
Millimeter Interferometric HCN(1-0) and HCO+(1-0) Observations of Luminous Infrared Galaxies
We present the results on millimeter interferometric observations of four
luminous infrared galaxies (LIRGs), Arp 220, Mrk 231, IRAS 08572+3915, and VV
114, and one Wolf-Rayet galaxy, He 2-10, using the Nobeyama Millimeter Array
(NMA). Both the HCN(1-0) and HCO+(1-0) molecular lines were observed
simultaneously and their brightness-temperature ratios were derived.
High-quality infrared L-band (2.8-4.1 micron) spectra were also obtained for
the four LIRGs to better constrain their energy sources deeply buried in dust
and molecular gas. When combined with other LIRGs we have previously observed
with NMA, the final sample comprised nine LIRGs (12 LIRGs' nuclei) with
available interferometric HCN(1-0) and HCO+(1-0) data-sufficient to investigate
the overall trend in comparison with known AGNs and starburst galaxies. We
found that LIRGs with luminous buried AGN signatures at other wavelengths tend
to show high HCN(1-0)/HCO+(1-0) brightness-temperature ratios as seen in
AGN-dominated galaxies, while the Wolf-Rayet galaxy He 2-10 displays a small
ratio. An enhanced HCN abundance in the interstellar gas surrounding a strongly
X-ray-emitting AGN, as predicted by some chemical calculations, is a natural
explanation of our results.Comment: 43 pages, 11 figures, accepted for publication in Astronomical
Journal. Higher resolution version is available at
http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN2/HCN2.pd
Vibrationally excited HC3N in NGC 4418
We investigate the molecular gas properties of the deeply obscured luminous
infrared galaxy NGC 4418. We address the excitation of the complex molecule
HC3N to determine whether its unusually luminous emission is related to the
nature of the buried nuclear source. We use IRAM 30m and JCMT observations of
rotational and vibrational lines of HC3N to model the excitation of the
molecule by means of rotational diagrams. We report the first confirmed
extragalactic detection of vibrational lines of HC3N. We detect 6 different
rotational transitions ranging from J=10-9 to J=30-29 in the ground vibrational
state and obtain a tentative detection of the J=38-37 line. We also detect 7
rotational transitions of the vibrationally excited states v6 and v7, with
angular momenta ranging from J=10-9 to 28-27. The energies of the upper states
of the observed transitions range from 20 to 850 K. In the optically thin
regime, we find that the rotational transitions of the vibrational ground state
can be fitted for two temperatures, 30 K and 260 K, while the vibrationally
excited levels can be fitted for a rotational temperature of 90 K and a
vibrational temperature of 500 K. In the inner 300 pc of NGC 4418, we estimate
a high HC3N abundance, of the order of 10^-7. The excitation of the HC3N
molecule responds strongly to the intense radiation field and the presence of
warm, dense gas and dust at the center of NGC 4418. The intense HC3N line
emission is a result of both high abundances and excitation. The properties of
the HC3N emitting gas are similar to those found for hot cores in Sgr B2, which
implies that the nucleus (< 300 pc) of NGC 4418 is reminiscent of a hot core.
The potential presence of a compact, hot component (T=500 K) is also discussed
A survey for Fe 6.4 keV emission in young stellar objects in rho Oph: the strong fluorescence from Elias 29
We report the results of a search for 6.4 keV Fe fluorescent emission in
Young Stellar Objects (YSOs) with measured accretion luminosities in the rho
Oph cloud, using all existing chandra and XMM-Newton observations of the
region. A total of nine such YSOs have X-ray data with sufficiently high S/N
for the 6.4 keV line to be potentially detected if present. A positive
detection of the Fe 6.4 keV line is reported for one object, Elias 29, in both
the XMM-Newton and the chandra data. The 6.4 keV line is detected in Elias 29
both during quiescent and flaring emission, unlikely all previously reported
detections of 6.4 keV Fe fluorescence in YSOs which were made during intense
flaring. The observed equivalent width of the fluorescent line is large, at
W_alpha approx 140 eV, ruling out fluorescence from diffuse circumstellar
material. It is also larger than expected for simple reflection from a
solar-composition photosphere or circumstellar disk, but it is compatible with
being due to fluorescence from a centrally illuminated circumstellar disk. The
X-ray spectrum of Elias 29 is also peculiar in terms of its high (ionized) Fe
abundance, as evident from the very intense Fe xxv 6.7 keV line emission; we
speculate on the possible mechanism leading to the observed high abundance.Comment: Accepted by A&
Distribution of dust clouds around the central engine of NGC 1068
We studied the distribution of dust clouds around the central engine of NGC
1068 based on shifted-and-added 8.8 - 12.3 micron (MIR) multi-filter images and
3.0 - 3.9 micron (L-band) spectra obtained with the Subaru Telescope. In a
region of 100 pc (1.4") around the central peak, we successfully constructed
maps of color temperatures and emissivities of the MIR and L-band continua as
well as the 9.7 micron and 3.4 micron dust features with spatial resolutions of
26 pc (0.37") in the MIR and 22 pc (0.3") in the L-band. Our main results are:
1) color temperature of the MIR continuum scatters around the thermal
equilibrium temperature with the central engine as the heat source while that
of the L-band continuum is higher and independent upon distance from the
central engine; 2) the peak of the 9.7 micron silicate absorption feature is
shifted to a longer wavelength at some locations; 3) the ratio of the optical
depths of the dust features is different from the Galactic values and show
complicated spatial distribution; and 4) there is a pie shaped warm dust cloud
as an enhancement in the emissivity of the MIR continuum extending about 50 pc
to the north from the central engine. We speculate that material falls into the
central engine through this cloud.Comment: 26 pages, 9 figures. Accepted for publication on Ap
Near-infrared and Millimeter Constraints on the Nuclear Energy Source of the Infrared Luminous Galaxy NGC 4418
We present near-infrared and millimeter investigations of the nucleus of the
infrared luminous galaxy NGC 4418, which previous observations suggest
possesses a powerful buried AGN. We found the following main results: (1) The
infrared K-band spectrum shows CO absorption features at 2.3-2.4 micron owing
to stars and very strong H2 emission lines. The luminosity ratios of H2
emission lines are suggestive of a thermal origin, and the equivalent width of
the H2 1-0 S(1) line is the second largest observed to date in an external
galaxy, after the well-studied strong H2-emitting galaxy NGC 6240. (2) The
infrared L-band spectrum shows a clear polycyclic aromatic hydrocarbon (PAH)
emission feature at 3.3 micron, which is usually found in star-forming
galaxies. The estimated star-formation luminosity from the observed PAH
emission can account for only a small fraction of the infrared luminosity. (3)
Millimeter interferometric observations of the nucleus reveal a high HCN (1-0)
to HCO+ (1-0) luminosity ratio of 1.8, as has been previously found in pure
AGNs. (4) The measurements of HCN (1-0) luminosity using a single-dish
millimeter telescope show that the HCN (1-0) to infrared luminosity ratio is
slightly larger than the average, but within the scattered range, for other
infrared luminous galaxies. All of these results can be explained by the
scenario in which, in addition to energetically-insignificant, weakly-obscured
star-formation at the surface of the nucleus, a powerful X-ray emitting AGN
deeply buried in dust and high density molecular gas is present.Comment: 31 pages, 9 figures, Accepted for publication in Astronomical Journal
(2004 November issue
Autoinhibition regulates the motility of the C. elegans intraflagellar transport motor OSM-3
OSM-3 is a Kinesin-2 family member from Caenorhabditis elegans that is involved in intraflagellar transport (IFT), a process essential for the construction and maintenance of sensory cilia. In this study, using a single-molecule fluorescence assay, we show that bacterially expressed OSM-3 in solution does not move processively (multiple steps along a microtubule without dissociation) and displays low microtubule-stimulated adenosine triphosphatase (ATPase) activity. However, a point mutation (G444E) in a predicted hinge region of OSM-3's coiled-coil stalk as well as a deletion of that hinge activate ATPase activity and induce robust processive movement. These hinge mutations also cause a conformational change in OSM-3, causing it to adopt a more extended conformation. The motility of wild-type OSM-3 also can be activated by attaching the motor to beads in an optical trap, a situation that may mimic attachment to IFT cargo. Our results suggest that OSM-3 motility is repressed by an intramolecular interaction that involves folding about a central hinge and that IFT cargo binding relieves this autoinhibition in vivo. Interestingly, the G444E allele in C. elegans produces similar ciliary defects to an osm-3–null mutation, suggesting that autoinhibition is important for OSM-3's biological function
Energy Diagnoses of Nine Infrared Luminous Galaxies Based on 3--4 Micron Spectra
The energy sources of nine infrared luminous galaxies (IRLGs) are diagnosed
based on their ground-based 3--4 m spectra. Both the equivalent width of
the 3.3 m polycyclic aromatic hydrocarbon (PAH) emission feature and the
3.3 m PAH to far-infrared luminosity ratio () are
analyzed. Assuming nuclear compact starburst activity in these sources produces
the 3.3 m PAH emission as strongly as that in starburst galaxies with
lower far-infrared luminosities, the followings results are found: For six
IRLGs, both the observed equivalent widths and the ratios
are too small to explain the bulk of their far-infrared luminosities by compact
starburst activity, indicating that active galactic nucleus (AGN) activity is a
dominant energy source. For the other three IRLGs, while the 3.3 m PAH
equivalent widths are within the range of starburst galaxies, the
ratios after correction for screen dust extinction are a
factor of 3 smaller. The uncertainty in the dust extinction correction
factor and in the scatter of the intrinsic ratios for
starburst galaxies do not allow a determination of the ultimate energy sources
for these three IRLGs.Comment: 29 pages, 2 figures, Accepted for publication in Ap
Bright X-ray flares in Orion young stars from COUP: evidence for star-disk magnetic fields?
We have analyzed a number of intense X-ray flares observed in the Chandra
Orion Ultradeep Project (COUP), a 13 days observation of the Orion Nebula
Cluster (ONC). Analysis of the flare decay allows to determine the size, peak
density and magnetic field of the flaring structure. A total of 32 events (the
most powerful 1% of COUP flares), have sufficient statistics for the analysis.
A broad range of decay times (from 10 to 400 ks) are present in the sample.
Peak flare temperatures are often very high, with half of the flares in the
sample showing temperatures in excess of 100 MK. Significant sustained heating
is present in the majority of the flares. The magnetic structures which are
found, are in a number of cases very long, with semi-lengths up to 10^12 cm,
implying the presence of magnetic fields of hundreds of G extending to
comparable distance from the stellar photosphere. These very large sizes for
the flaring structures ($ >> R_*) are not found in more evolved stars, where,
almost invariably, the same type of analysis results in structures with L <=
R_*. As the majority of young stars in the ONC are surrounded by disks, we
speculate that the large magnetic structures which confine the flaring plasma
are actually the same type of structures which channel the plasma in the
magnetospheric accretion paradigm, connecting the star's photosphere with the
accretion disk.Comment: Accepted to ApJS, COUP special issu
Infrared 3-4 Micron Spectroscopic Investigations of a Large Sample of Nearby Ultraluminous Infrared Galaxies
We present infrared L-band (3-4 micron) nuclear spectra of a large sample of
nearby ultraluminous infrared galaxies (ULIRGs).ULIRGs classified optically as
non-Seyferts (LINERs, HII-regions, and unclassified) are our main targets.
Using the 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission and
absorption features at 3.1 micron due to ice-covered dust and at 3.4 micron
produced by bare carbonaceous dust, we search for signatures of powerful active
galactic nuclei (AGNs) deeply buried along virtually all lines-of-sight. The
3.3 micron PAH emission, the signatures of starbursts, is detected in all but
two non-Seyfert ULIRGs, but the estimated starburst magnitudes can account for
only a small fraction of the infrared luminosities. Three LINER ULIRGs show
spectra typical of almost pure buried AGNs, namely, strong absorption features
with very small equivalent-width PAH emission. Besides these three sources, 14
LINER and 3 HII ULIRGs' nuclei show strong absorption features whose absolute
optical depths suggest an energy source more centrally concentrated than the
surrounding dust, such as a buried AGN. In total, 17 out of 27 (63%) LINER and
3 out of 13 (23%) HII ULIRGs' nuclei show some degree of evidence for powerful
buried AGNs, suggesting that powerful buried AGNs may be more common in LINER
ULIRGs than in HII ULIRGs. The evidence of AGNs is found in non-Seyfert ULIRGs
with both warm and cool far-infrared colors. These spectra are compared with
those of 15 ULIRGs' nuclei with optical Seyfert signatures taken for
comparison.The overall spectral properties suggest that the total amount of
dust around buried AGNs in non-Seyfert ULIRGs is systematically larger than
that around AGNs in Seyfert 2 ULIRGs.Comment: 56 pages, 9 figures, accepted for publication in ApJ (20 January
2006, vol 637 issue
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