1,185 research outputs found
Star formation in Seyfert galaxies
An analysis of the IRAS data for a sample of classical (optically selected) Seyfert galaxies is presented. The IRAS fluxes at 25 micron, 60 micron, and 100 micron are found to be uncorrelated or only very weakly correlated with the UV/Optical continuum flux and the near and mid IR flux at 3.5 and 10 microns. To investigate the possibility that star formation accounts for the far IR flux, the IRAS measurements for the Seyfert galaxies are compared to IRAS observations of a sample of normal spiral galaxies, and a sample of Starburst galaxies. It is shown that the far IR luminosities and far IR colors of Seyfert galaxies are indistinguishable from those of the Starburst galaxies. Besides, normal galaxies are an order of magnitude less luminous than both the Seyfert and the Starburst galaxies. This indicates that star formation produces the bulk of the far infrared emission in Seyfert galaxies
Evidence for the existence of neurotoxic esterase in neural and lymphatic tissue of the adult hen,
Hen brain and spinal cord contain a number of esterases that hydrolyze phenyl valerate (PV). Most of this activity is sensitive to inhibition by micromolar concentrations of paraoxon. Included among the paraoxon-resistant esterases is neurotoxic esterase (NTE), which is inhibited in vivo and in vitro by certain organophosphorus compounds, such as mipafox, which cause delayed neurotoxicity. Since published information on the NTE content of non-neural tissues was heretofore lacking, a comprehensive study was undertaken of the occurrence of this enzyme in tissues of the adult hen (Gallus gallus domesticus), the species of choice in the study of organophosphorus-induced delayed neurotoxicity. Complete differential titration curves of PV esterase activity were obtained by preincubation of each tissue homogenate with a wide range of concentrations of paraoxon, a non-neurotoxic compound, plus or minus mipafox, a neurotoxic compound, followed by PV esterase assay. Brain NTE activity was determined to be 2426 +/- 104 nmoles [middle dot] min-1 [middle dot] (g wet weight)-1 (mean +/- S.E.M.). Titration of other tissues resulted in the following NTE activities, expressed as percentages of brain NTE activity: spinal cord (21%), peripheral nerve (1.7%), gastrocnemius muscle (0%), pectoralis muscle (0%), heart (14%), liver (0%), kidney (0%), spleen (70%), spleen lymphocytes (26%), and blood lymphocytes (24%). Using an abbreviated procedure, erythrocytes and plasma showed no NTE activity. These results indicate that NTE has limited distribution among the tissues of the adult hen and is present in lymphatic as well as neural tissue.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24034/1/0000283.pd
V5856 Sagittarii/2016: Broad Multi-Epoch Spectral Coverage of a Sustained High Luminosity Nova
Nova V5856 Sagittarii is unique for having remained more than nine magnitudes
above its pre-outburst brightness for more than six years. Extensive visible
and IR spectra from the time of outburst to the present epoch reveal separate
emitting regions with distinct spectral characteristics. Permitted emission
lines have both broad and narrow components, whereas the forbidden line
profiles are almost entirely broad. The permitted line components frequently
display P Cygni profiles indicating high optical depth, whereas the broad
components do not show detectable absorption. The densities and velocities
deduced from the spectra, including differences in the O I 7773 and 8446 lines,
are not consistent with an on-going wind. Instead, the prolonged high
luminosity and spectral characteristics are indicative of a post-outburst
common envelope that enshrouds the binary, and is likely the primary source of
the visible and IR emission.Comment: 27 pages; 13 figures. Accepted for publication in the Ap
DPP6 regulation of dendritic morphogenesis impacts hippocampal synaptic development
Dipeptidyl-peptidase 6 is an auxiliary subunit of Kv4-mediated A-type K+ channels that, in addition to enhancing channel surface expression, potently accelerates their kinetics. The dipeptidyl-peptidase 6 gene has been associated with a number of human central nervous system disorders including autism spectrum disorders and schizophrenia. Here we employ knockdown and genetic deletion of dipeptidyl-peptidase 6 to reveal its importance for the formation and stability of dendritic filopodia during early neuronal development. We find that the hippocampal neurons lacking dipeptidyl-peptidase 6 show a sparser dendritic branching pattern along with fewer spines throughout development and into adulthood. In electrophysiological and imaging experiments, we show that these deficits lead to fewer functional synapses and occur independently of the potassium channel subunit Kv4.2. We report that dipeptidyl-peptidase 6 interacts with a filopodia-associated myosin as well as with fibronectin in the extracellular matrix. dipeptidyl-peptidase 6 therefore has an unexpected but important role in cell adhesion and motility, impacting the hippocampal synaptic development and function
Dust Emission Features in NGC 7023 between 0.35 and 2.5 micron: Extended Red Emission (0.7 micron) and Two New Emission Features (1.15 and 1.5 micron)
We present 0.35 to 2.5 micron spectra of the south and northwest filaments in
the reflection nebula NGC 7023. These spectra were used to test the theory of
Seahra & Duley that carbon nanoparticles are responsible for Extended Red
Emission (ERE). Our spectra fail to show their predicted second emission band
at 1.0 micron even though both filaments exhibit strong emission in the
familiar 0.7 micron ERE band. The northwest filament spectrum does show one,
and possibly two, new dust emission features in the near-infrared. We clearly
detect a strong emission band at 1.5 micron which we tentatively attribute to
beta-FeSi_2 grains. We tentatively detect a weaker emission band at 1.15 micron
which coincides with the location expected for transitions from the conduction
band to mid-gap defect states of silicon nanoparticles. This is added evidence
that silicon nanoparticles are responsible for ERE as they already can explain
the observed behavior of the main visible ERE band.Comment: 9 pages, color figures, accepted to the ApJ, color and b/w versions
available at http://dirty.as.arizona.edu/~kgordon/papers/ere_1um.htm
Changes in the red giant and dusty environment of the recurrent nova RS Ophiuchi following the 2006 eruption
We present near-infrared spectroscopy of the recurrent nova RS Ophiuchi (RS Oph) obtained on several occasions after its latest outburst in 2006 February. The 1–5 μm spectra are dominated by the red giant, but the H i, He i and coronal lines present during the eruption are present in all our observations. From the fits of the computed infrared spectral energy distributions to the observed fluxes, we find Teff= 4200 ± 200 K for the red giant. The first overtone CO bands at 2.3 μm, formed in the atmosphere of the red giant, are variable. The spectra clearly exhibit an infrared excess due to dust emission longward of 5 μm; we estimate an effective temperature for the emitting dust shell of 500 K, and find that the dust emission is also variable, being beyond the limit of detection in 2007. Most likely, the secondary star in RS Oph is intrinsically variable
Direct Analysis of Spectra of the Peculiar Type Ia Supernova 2000cx
The Type Ia SN 2000cx exhibited multiple peculiarities, including a lopsided
B-band light-curve peak that does not conform to current methods for using
shapes of light curves to standardize SN Ia luminosities. We use the
parameterized supernova synthetic-spectrum code SYNOW to study line
identifications in the photospheric-phase spectra of SN 2000cx. Previous work
established the presence of Ca II infrared-triplet features forming above
velocity about 20,000 km/s, much higher than the photospheric velocity of about
10,000 km/s. We find Ti II features forming at the same high velocity.
High-velocity line formation is partly responsible for the photometric
peculiarities of SN 2000cx: for example, B-band flux blocking by Ti II
absorption features that decreases with time causes the B light curve to rise
more rapidly and decline more slowly than it otherwise would.
SN 2000cx contains an absorption feature near 4530 A that may be H-beta,
forming at the same high velocity. The lack of conspicuous H-alpha and P-alpha
signatures does not necessarily invalidate the H-beta identification if the
high-velocity line formation is confined to a clump that partly covers the
photosphere and the H-alpha and P-alpha source functions are elevated relative
to that of resonance scattering. The H-beta identification is tentative. If it
is correct, the high-velocity matter must have come from a nondegenerate
companion star.Comment: 41 pages including 21 figures, accepted by Ap
Visible and Near-Infrared Spectrophotometry of the Deep Impact Ejecta of Comet 9P/Tempel 1
We have obtained optical spectrophotometry of the evolution of comet
9P/Tempel 1 after the impact of the Deep Impact probe, using the Supernova
Integral Field Spectrograph (SNIFS) at the UH 2.2m telescope, as well as
simultaneous optical and infrared spectra using the Lick
Visible-to-Near-Infrared Imaging Spectrograph (VNIRIS) spectrograph. The
spatial distribution and temporal evolution of the "violet band" CN (0-0)
emission and of the 630 nm [OI] emission was studied. We found that CN emission
centered on the nucleus increased in the two hours after impact, but that this
CN emission was delayed compared to the light curve of dust-scattered sunlight.
The CN emission also expanded faster than the cloud of scattering dust. The
emission of [OI] at 630 nm rose similarly to the scattered light, but then
remained nearly constant for several hours after impact. On the day following
the impact, both CN and [OI] emission concentrated on the comet nucleus had
returned nearly to pre-impact levels. We have also searched for differences in
the scattering properties of the dust ejected by the impact compared to the
dust released under normal conditions. Compared to the pre-impact state of the
comet, we find evidence that the color of the comet was slightly bluer during
the post-impact rise in brightness. Long after the impact, in the following
nights, the comet colors returned to their pre-impact values. This can be
explained by postulating a change to a smaller particle size distribution in
the ejecta cloud, in agreement with the findings from mid-infrared observatons,
or by postulating a large fraction of clean ice particles, or by a combination
of these two.Comment: 28 pages of text and 8 figures. Paper is accepted for publication in
Icaru
Detection of Near-IR CO Absorption Bands in R Coronae Borealis Stars
R Coronae Borealis (RCB) stars are hydrogen-deficient, carbon-rich pulsating
post-AGB stars that experience massive irregular declines in brightness caused
by circumstellar dust formation. The mechanism of dust formation around RCB
stars is not well understood. It has been proposed that CO molecules play an
important role in cooling the circumstellar gas so that dust may form. We
report on a survey for CO in a sample of RCB stars. We obtained H- and K-band
spectra including the first and second overtone CO bands for eight RCB stars,
the RCB-like star, DY Per and the final-helium-flash star, FG Sge. The first
and second overtone CO bands were detected in the cooler (T(eff)<6000 K) RCB
stars, Z Umi, ES Aql, SV Sge and DY Per. The bands are not present in the
warmer (T(eff)>6000 K) RCB stars, R CrB, RY Sgr, SU Tau, XX Cam. In addition,
first overtone bands are seen in FG Sge, a final-helium-flash star that is in
an RCB-like phase at present. Effective temperatures of the eight RCB stars
range from 4000 to 7250 K. The observed photospheric CO absorption bands were
compared to line-blanketed model spectra of RCB stars. As predicted by the
models, the CO bands are strongest in the coolest RCB stars and not present in
the warmest. No correlation was found between the presence or strength of the
CO bands and dust formation activity in the stars.Comment: 13 oages, 3 figures, AJ in pres
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