372 research outputs found
Rat brain 5-HT_(1C) receptors are encoded by a 5-6 kbase mRNA size class and are functionally expressed in injected Xenopus oocytes
Injection of rat brain RNA into Xenopus laevis oocytes induces synthesis of receptors that show an electrophysiological response to bath application of serotonin. While there are at least 4 pharmacologically distinct subtypes of 5-HT binding sites in the rat brain, we find that the pharmacological characteristics of the predominant electrophysiologically active receptor synthesized in Xenopus oocytes are most consistent with those of the 5-HT_(1C) subtype. Additional electrophysiologically active 5-HT receptor types could not be detected. Injection of mRNA isolated from a number of rat brain regions shows that the choroid plexus is particularly enriched for 5-HT_(1C) mRNA. Oocytes injected with RNA isolated from this region respond 16 or 8 times more strongly to serotonin than do oocytes injected with RNA isolated from cortex or substantia nigra, respectively. In addition, by fractionation of rat brain mRNA through agarose gels, we have identified a single RNA size class of about 5â6 kbase that encodes this serotonin receptor
Rat brain 5-HT_(1C) receptors are encoded by a 5-6 kbase mRNA size class and are functionally expressed in injected Xenopus oocytes
Injection of rat brain RNA into Xenopus laevis oocytes induces synthesis of receptors that show an electrophysiological response to bath application of serotonin. While there are at least 4 pharmacologically distinct subtypes of 5-HT binding sites in the rat brain, we find that the pharmacological characteristics of the predominant electrophysiologically active receptor synthesized in Xenopus oocytes are most consistent with those of the 5-HT_(1C) subtype. Additional electrophysiologically active 5-HT receptor types could not be detected. Injection of mRNA isolated from a number of rat brain regions shows that the choroid plexus is particularly enriched for 5-HT_(1C) mRNA. Oocytes injected with RNA isolated from this region respond 16 or 8 times more strongly to serotonin than do oocytes injected with RNA isolated from cortex or substantia nigra, respectively. In addition, by fractionation of rat brain mRNA through agarose gels, we have identified a single RNA size class of about 5â6 kbase that encodes this serotonin receptor
Crossing the `Yellow Void' -- Spatially Resolved Spectroscopy of the Post- Red Supergiant IRC+10420 and Its Circumstellar Ejecta
IRC +10420 is one of the extreme hypergiant stars that define the empirical
upper luminosity boundary in the HR diagram. During their post--RSG evolution,
these massive stars enter a temperature range (6000-9000 K) of increased
dynamical instability, high mass loss, and increasing opacity, a
semi--forbidden region, that de Jager and his collaborators have called the
`yellow void'. We report HST/STIS spatially resolved spectroscopy of IRC +10420
and its reflection nebula with some surprising results. Long slit spectroscopy
of the reflected spectrum allows us to effectively view the star from different
directions. Measurements of the double--peaked Halpha emission profile show a
uniform outflow of gas in a nearly spherical distribution, contrary to previous
models with an equatorial disk or bipolar outflow. Based on the temperature and
mass loss rate estimates that are usually quoted for this object, the wind is
optically thick to the continuum at some and possibly all wavelengths.
Consequently the observed variations in apparent spectral type and inferred
temperature are changes in the wind and do not necessarily mean that the
underlying stellar radius and interior structure are evolving on such a short
timescale. To explain the evidence for simultaneous outflow and infall of
material near the star, we propose a `rain' model in which blobs of gas
condense in regions of lowered opacity outside the dense wind. With the
apparent warming of its wind, the recent appearance of strong emission, and a
decline in the mass loss rate, IRC +10420 may be about to shed its opaque wind,
cross the `yellow void', and emerge as a hotter star.Comment: To appear in the Astronomical Journal, August 200
Spitzer Space Telescope Infrared Imaging and Spectroscopy of the Crab Nebula
We present 3.6, 4.5, 5.8, 8.0, 24, and 70 micron images of the Crab Nebula
obtained with the Spitzer Space Telescope IRAC and MIPS cameras, Low- and
High-resolution Spitzer IRS spectra of selected positions within the nebula,
and a near-infrared ground-based image made in the light of [Fe II]1.644
micron. The 8.0 micron image, made with a bandpass that includes [Ar II]7.0
micron, resembles the general morphology of visible H-alpha and near-IR [Fe II]
line emission, while the 3.6 and 4.5 micron images are dominated by continuum
synchrotron emission. The 24 micron and 70 micron images show enhanced emission
that may be due to line emission or the presence of a small amount of warm dust
in the nebula on the order of less than 1% of a solar mass. The ratio of the
3.6 and 4.5 micron images reveals a spatial variation in the synchrotron power
law index ranging from approximately 0.3 to 0.8 across the nebula. Combining
this information with optical and X-ray synchrotron images, we derive a
broadband spectrum that reflects the superposition of the flatter spectrum jet
and torus with the steeper diffuse nebula, and suggestions of the expected
pileup of relativistic electrons just before the exponential cutoff in the
X-ray. The pulsar, and the associated equatorial toroid and polar jet
structures seen in Chandra and HST images (Hester et al. 2002) can be
identified in all of the IRAC images. We present the IR photometry of the
pulsar. The forbidden lines identified in the high resolution IR spectra are
all double due to Doppler shifts from the front and back of the expanding
nebula and give an expansion velocity of approximately 1264 km/s.Comment: 21 pages, 4 tables, 16 figure
The UV Scattering Halo of the Central Source Associated with Eta Carinae
We have made an extensive study of the UV spectrum of Eta Carinae, and find
that we do not directly observe the star and its wind in the UV. Because of
dust along our line of sight, the UV light that we observe arises from
bound-bound scattering at large impact parameters. We obtain a reasonable fit
to the UV spectrum by using only the flux that originates outside 0.033". This
explains why we can still observe the primary star in the UV despite the large
optical extinction -- it is due to the presence of an intrinsic coronagraph in
the Eta Carinae system, and to the extension of the UV emitting region. It is
not due to peculiar dust properties alone. We have computed the spectrum of the
purported companion star, and show that it could only be directly detected in
the UV spectrum preferentially in the Far Ultraviolet Spectroscopic Explorer
(FUSE) spectral region (912-1175 Ang.). However, we find no direct evidence for
a companion star, with the properties indicated by X-ray studies and studies of
the Weigelt blobs, in UV spectra. This might be due to reprocessing of the
companion's light by the dense stellar wind of the primary. Broad FeII and
[FeII] emission lines, which form in the stellar wind, are detected in spectra
taken in the SE lobe, 0.2" from the central star. The wind spectrum shows some
similarities to the spectra of the B & D Weigelt blobs, but also shows some
marked differences in that high excitation lines, and lines pumped by Ly-alpha,
are not seen. The detection of the broad lines lends support to our
interpretation of the UV spectrum, and to our model for Eta Carinae.Comment: To appear in ApJ. 57 pages with 18 figure
Numerical models of collisions between core-collapse supernovae and circumstellar shells
Recent observations of luminous Type IIn supernovae (SNe) provide compelling
evidence that massive circumstellar shells surround their progenitors. In this
paper we investigate how the properties of such shells influence the SN
lightcurve by conducting numerical simulations of the interaction between an
expanding SN and a circumstellar shell ejected a few years prior to core
collapse. Our parameter study explores how the emergent luminosity depends on a
range of circumstellar shell masses, velocities, geometries, and wind mass-loss
rates, as well as variations in the SN mass and energy. We find that the shell
mass is the most important parameter, in the sense that higher shell masses (or
higher ratios of M_shell/M_SN) lead to higher peak luminosities and higher
efficiencies in converting shock energy into visual light. Lower mass shells
can also cause high peak luminosities if the shell is slow or if the SN ejecta
are very fast, but only for a short time. Sustaining a high luminosity for
durations of more than 100 days requires massive circumstellar shells of order
10 M_sun or more. This reaffirms previous comparisons between pre-SN shells and
shells produced by giant eruptions of luminous blue variables (LBVs), although
the physical mechanism responsible for these outbursts remains uncertain. The
lightcurve shape and observed shell velocity can help diagnose the approximate
size and density of the circumstellar shell, and it may be possible to
distinguish between spherical and bipolar shells with multi-wavelength
lightcurves. These models are merely illustrative. One can, of course, achieve
even higher luminosities and longer duration light curves from interaction by
increasing the explosion energy and shell mass beyond values adopted here.Comment: Accepted for publication in MNRAS. Tables of numerical results (SN
lightcurves and velocities) to be published online. (Updated to fix figures
The Structure of the Homunculus. II. Modeling the physical conditions in Eta Car's molecular shell
We present models that reproduce the observed double-shell structure of the
Homunculus Nebula around eta Carinae, including the stratification of infrared
H2 and [FeII] emission seen in data obtained with the Phoenix spectrograph on
Gemini South, as well as the corresponding stratified grain temperature seen in
thermal-infrared data. Tuning the model to match the observed shell thickness
allows us to determine the threshold density which permits survival of H2. An
average hydrogen density of n_H=(0.5-1)x10^7 cm-3 in the outer zone is required
to allow H2 to exist at all latitudes in the nebula, and for Fe+ to recombine.
This gives independent confirmation of the very large mass of the Homunculus,
indicating a total of roughly 15--35 Msun (although we note reasons why the
lower end of this range is favored). At the interface between the atomic and
molecular zones, we predict a sharp drop in the dust temperature, in agreement
with the bimodal dust color temperatures observed in the two zones. In the
outer molecular shell, the dust temperature drops to nearly the blackbody
temperature, and becomes independent of grain size because of self-shielding at
shorter UV wavelengths and increased heating at longer wavelengths. This
relaxes constraints on large grain sizes suggested by near-blackbody color
temperatures. Finally, from the strength of infrared [FeII] emission in the
inner shell we find that the gas-phase Fe abundance is roughly solar. This is
astonishing in such a dusty object, where one normally expects gaseous iron to
be depleted by two orders of magnitude.Comment: 18 pages, 5 figures. Accepted by Ap
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