395 research outputs found
Kn 26, a New Quadrupolar Planetary Nebula
Once classified as an emission line source, the planetary nebula (PN) nature
of the source Kn 26 has been only recently recognized in digital sky surveys.
To investigate the spectral properties and spatio-kinematical structure of Kn
26, we have obtained high spatial-resolution optical and near-IR narrow-band
images, high-dispersion long-slit echelle spectra, and intermediate-resolution
spectroscopic observations. The new data reveal an hourglass morphology typical
of bipolar PNe. A detailed analysis of its morphology and kinematics discloses
the presence of a second pair of bipolar lobes, making Kn 26 a new member of
the subclass of quadrupolar PNe. The time-lap between the ejection of the two
pairs of bipolar lobes is much smaller than their dynamical ages, implying a
rapid change of the preferential direction of the central engine. The chemical
composition of Kn 26 is particularly unusual among PNe, with a low N/O ratio
(as of type II PNe) and a high helium abundance (as of type I PNe), although
not atypical among symbiotic stars. Such an anomalous chemical composition may
have resulted from the curtail of the time in the Asymptotic Giant Branch by
the evolution of the progenitor star through a common envelope phase.Comment: 9 pages, 5 figures, accepted for publication in A&
NGC 6309, a Planetary Nebula that Shifted from Round to Multipolar
We present new narrow-band Ha, [N II], and [O III] high-resolution images of
the quadrupolar planetary nebula (PN) NGC 6309 that show in great detail its
bipolar lobes and reveal new morphological features. New high- and
low-dispersion long-slit spectra have been obtained to help in the
investigation of the new nebular components. The images and spectra unveil two
diffuse blobs, one of them located at 55 arcsec from the central star along the
NE direction (PA= +71) and the other at 78 arcsec in the SW direction (PA=
-151). Therefore, these structures do not share the symmetry axes of the inner
bipolar outflows. Their radial velocities relative to the system are quite low:
+3 and -4 km/s, respectively. Spectroscopic data confirm a high [O III] to Ha
ratio, indicating that the blobs are being excited by the UV flux from the
central star. Our images convincingly show a spherical halo 60 arcsec in
diameter encircling the quadrupolar nebula. The expansion velocity of this
shell is low, 66 km/s. The software SHAPE has been used to construct a
morpho-kinematic model for the ring and the bipolar flows that implies an age
of 4,000 yrs, the expansion of the halo sets a lower limit for its age 46,000
yrs, and the very low expansion of the blobs suggests they are part of a large
structure corresponding to a mass ejection that took place 150,000 yrs ago. In
NGC 6309 we have direct evidence of a change in the geometry of mass-loss, from
spherical in the halo to axially-symmetric in the two pairs of bipolar lobes.Comment: 8 pages, 7 figures, Accepted for publication in MNRA
Optical and Infrared Imaging and Spectroscopy of the Multiple-Shell Planetary Nebula NGC 6369
NGC 6369 is a double-shell planetary nebula (PN) consisting of a bright
annular inner shell with faint bipolar extensions and a filamentary envelope.
We have used ground- and space-based narrow-band optical and near-IR images,
broad-band mid-IR images, optical long-slit echelle spectra, and mid-IR spectra
to investigate its physical structure. These observations indicate that the
inner shell of NGC 6369 can be described as a barrel-like structure shape with
polar bubble-like protrusions, and reveal evidence for H2 and strong polycyclic
aromatic hydrocarbons (PAHs) emission from a photo-dissociative region (PDR)
with molecular inclusions located outside the bright inner shell.
High-resolution HST narrow-band images reveal an intricate excitation structure
of the inner shell and a system of "cometary" knots. The knotty appearance of
the envelope, the lack of kinematical evidence for shell expansion and the
apparent presence of emission from ionized material outside the PDR makes us
suggest that the envelope of NGC 6369 is not a real shell, but a flattened
structure at its equatorial regions. We report the discovery of irregular knots
and blobs of diffuse emission in low-excitation and molecular line emission
that are located up to 80" from the central star, well outside the main nebular
shells. We also show that the filaments associated to the polar protrusions
have spatial extents consistent with post-shock cooling regimes, and likely
represent regions of interaction of these structures with surrounding material.Comment: 14 pages, 13 figures. Accepted for publication in MNRA
Disruption of the with no lysine kinase-STE20-proline alanine-rich kinase pathway reduces the hypertension induced by angiotensin II
Optimization of Starburst99 for Intermediate-Age and Old Stellar Populations
We have incorporated the latest release of the Padova models into the
evolutionary synthesis code Starburst99. The Padova tracks were extended to
include the full asymptotic giant branch (AGB) evolution until the final
thermal pulse over the mass range 0.9 to 5 solar mass. With this addition,
Starburst99 accounts for all stellar phases that contribute to the integrated
light of a stellar population with arbitrary age from the extreme ultraviolet
to the near-infrared. AGB stars are important for ages between 0.1 and 2 Gyr,
with their contribution increasing at longer wavelengths. We investigate
similarities and differences between the model predictions by the Geneva and
the Padova tracks. The differences are particularly pronounced at ages > 1 Gyr,
when incompleteness sets in for the Geneva models. We also perform detailed
comparisons with the predictions of other major synthesis codes and found
excellent agreement. Our synthesized optical colors are compared to
observations of old, intermediate-age, and young populations. Excellent
agreement is found for the old globular cluster system of NGC 5128 and for old
and intermediate-age clusters in NGC 4038/39. In contrast, the models fail for
red supergiant dominated populations with sub-solar abundances. This failure
can be traced back to incorrect red supergiant parameters in the stellar
evolutionary tracks. Our models and the synthesis code are publicly available
as version 5.0 of Starburst99 at http://www.stsci.edu/science/starburst99/.Comment: The revised Starburst99 code discussed in this paper will replace the
current version 4.0 on our Starburst99 website by December 31, 2004. Accepted
for publication in ApJ; 39 pages, 23 figures, 5 table
Role of KLHL3 and dietary K<sup>+</sup> in regulating KS-WNK1 expression
This is the author accepted manuscript. The final version is available from the American Physiological Society via the DOI in this recordThe physiological role of the shorter isoform of WNK1 that is exclusively expressed in the kidney (KS-WNK1), with particular abundance in the distal convoluted tubule, remains elusive. KS-WNK1 despite lacking the kinase domain, is nevertheless capable of stimulating the NaCl cotransporter (NCC), apparently through activation of WNK4. It has recently been shown that a less severe form of the Familial Hyperkalemic Hypertension featuring only hyperkalemia is caused by missense mutations in the WNK1 acidic domain that preferentially affect CUL3-KLHL3 E3-induced degradation of KS-WNK1, rather than that of the full-length WNK1 (L-WNK1). Here we show that L-WNK1 is indeed less impacted by the CUL3-KLHL3 E3 ligase complex compared to KS-WNK1. We demonstrate that the unique 30 amino acid amino N-terminal fragment of KS-WNK1 is essential for its activating effect on NCC and recognition by KLHL3. We identify specific amino acid residues in this region critical for the functional effect of KS-WNK1 and KLHL3 sensitivity. To further explore this, we generated KLHL3-R528H knock-in mice that mimic human mutations causing Familial Hyperkalemic Hypertension. These mice revealed that the KLHL3 mutation specifically increased expression of KS-WNK1 in the kidney. We also observed that in wild type mice, expression of KS-WNK1 is only detectable after exposure to low potassium diet. These findings provide new insights into the regulation and function of KS-WNK1 by the CUL3-KLHL3 complex in DCT and indicate that this pathway is regulated by dietary K+ levels.National Institutes of Health (NIH)Conacyt MexicoPAPIIT UNAML'OréalMedical Research Council (MRC
Models for Massive Stellar Populations with Rotation
We present and discuss evolutionary synthesis models for massive stellar
populations generated with the Starburst99 code in combination with a new set
of stellar evolution models accounting for rotation. The new stellar evolution
models were compiled from several data releases of the Geneva group and cover
heavy-element abundances ranging from twice solar to one fifth solar. The
evolution models were computed for rotation velocities on the zero-age
main-sequence of 0 and 300 km/s and with the latest revision of stellar
mass-loss rates. Since the mass coverage is incomplete, in particular at
non-solar chemical composition, our parameter study is still preliminary and
must be viewed as exploratory. Stellar population properties computed with
Starburst99 and the new evolution models show some marked differences in
comparison with models obtained using earlier tracks. Since individual stars
now tend to be more luminous and bluer when on the blue side of the
Hertzsprung-Russell diagram, the populations mirror this trend. For instance,
increases by factors of two or more are found for the light-to-mass ratios at
ultraviolet to near-infrared wavelengths, as well as for the output of hydrogen
ionizing photons. If these results are confirmed once the evolution models have
matured, recalibrations of certain star-formation and initial mass function
indicators will be required.Comment: Accepted for publication in Ap
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