3,427 research outputs found
Antitrust and the Consumer Interest: The Fallacy of Parens Patriae and A Suggested New Approach
The exon junction complex is required for definition and excision of neighboring introns in Drosophila
Splicing of pre-mRNAs results in the deposition of the exon junction complex (EJC) upstream of exon-exon boundaries. The EJC plays crucial post-splicing roles in export, translation, localization, and nonsense-mediated decay of mRNAs. It also aids faithful splicing of pre-mRNAs containing large introns, albeit via an unknown mechanism. Here, we show that the core EJC plus the accessory factors RnpS1 and Acinus aid in definition and efficient splicing of neighboring introns. This requires prior deposition of the EJC in close proximity to either an upstream or downstream splicing event. If present in isolation, EJC-dependent introns are splicing-defective also in wild-type cells. Interestingly, the most affected intron belongs to the piwi locus, which explains the reported transposon desilencing in EJC-depleted Drosophila ovaries. Based on a transcriptome-wide analysis, we propose that the dependency of splicing on the EJC is exploited as a means to control the temporal order of splicing events
Photometric studies of three multiperiodic Beta Cephei stars: Beta CMa, 15 CMa and KZ Mus
We have carried out single and multi-site photometry of the three Beta Cephei
stars Beta and 15 CMa as well as KZ Mus. For the two stars in CMa, we obtained
270 h of measurement in the Stromgren uvy and Johnson V filters, while 150 h of
time-resolved Stromgren uvy photometry was acquired for KZ Mus. All three stars
are multi-periodic variables, with three (Beta CMa) and four (15 CMa, KZ Mus)
independent pulsation modes. Two of the mode frequencies of 15 CMa are new
discoveries and one of the known modes showed amplitude variations over the
last 33 years. Taken together, this explains the star's diverse behaviour
reported in the literature fully.
Mode identification by means of the amplitude ratios in the different
passbands suggests one radial mode for each star. In addition, Beta CMa has a
dominant l=2 mode while its third mode is nonradial with unknown l. The
nonradial modes of 15 CMa, which are l <= 3, form an almost equally split
triplet that, if physical, would imply that we see the star under an
inclination angle larger than 55 degrees. The strongest nonradial mode of KZ
Mus is l=2, followed by the radial mode and a dipole mode. Its weakest known
mode is nonradial with unknown l, confirming previous mode identifications for
the star's pulsations.
The phased light curve for the strongest mode of 15 CMa has a descending
branch steeper than the rising branch. A stillstand phenomenon during the rise
to maximum light is indicated. Given the low photometric amplitude of this
nonradial mode this is at first sight surprising, but it can be explained by
the mode's aspect angle.Comment: 12 pages, 11 figure
Discovery and analysis of p-mode and g-mode oscillations in the A-type primary of the eccentric binary HD 209295
We have discovered both intermediate-order gravity mode and low-order
pressure mode pulsation in the same star, HD 209295. It is therefore both a
Gamma Doradus and a Delta Scuti star, which makes it the first pulsating star
to be a member of two classes.
The star is a single-lined spectroscopic binary with an orbital period of
3.10575 d and an eccentricity of 0.352. Weak pulsational signals are found in
both the radial velocity and line-profile variations, allowing us to show that
the two highest-amplitude Gamma Doradus pulsation modes are consistent with l=1
and |m|=1.
In our 280 h of BVI multi-site photometry we detected ten frequencies in the
light variations, one in the Delta Scuti regime and nine in the Gamma Doradus
domain. Five of the Gamma Doradus frequencies are exact integer multiples of
the orbital frequency. This observation leads us to suspect they are tidally
excited. Results of theoretical modeling (stability analysis, tidal excitation)
were consistent with the observations.
We could not detect the secondary component of the system in infrared
photometry, suggesting that it may not be a main-sequence star. Archival data
of HD 209295 show a strong ultraviolet excess, the origin of which is not
known. The orbit of the primary is consistent with a secondary mass of M > 1.04
Msun indicative of a neutron star or a white dwarf companion.Comment: 18 pages, 18 figures, accepted for publication in MNRAS, shortened
abstrac
Particle decay branching ratios for states of astrophysical importance in 19Ne
We have measured proton and alpha-particle branching ratios of excited states
in 19Ne formed using the 19F(3He,t) reaction at a beam energy of 25 MeV. These
ratios have a large impact on the astrophysical reaction rates of
15O(alpha,gamma), 18F(p,gamma) and 18F(p,alpha), which are of interest in
understanding energy generation in x-ray bursts and in interpreting anticipated
gamma-ray observations of novae. We detect decay protons and alpha-particles
using a silicon detector array in coincidence with tritons measured in the
focal plane detector of our Enge split-pole spectrograph. The silicon array
consists of five strip detectors of the type used in the Louvain-Edinburgh
Detector Array, subtending angles from 130 degrees to 165 degrees with
approximately 14% lab efficiency. The correlation angular distributions give
additional confidence in some prior spin-parity assignments that were based on
gamma branchings. We measure Gamma_p/Gamma=0.387+-0.016 for the 665 keV proton
resonance, which agrees well with the direct measurement of Bardayan et al.Comment: 5 pages, 2 figures, 3 tables. Prepared using RevTex 4 and BibTex.
Further minor revisions, incl. fig. 1 font size increase, 1 table removal,
and minor changes to the tex
New measurements of magnetic fields of roAp stars with FORS1 at the VLT
Magnetic fields play a key role in the pulsations of rapidly oscillating Ap
(roAp) stars since they are a necessary ingredient of all pulsation excitation
mechanisms proposed so far. This implies that the proper understanding of the
seismological behaviour of the roAp stars requires knowledge of their magnetic
fields. However, the magnetic fields of the roAp stars are not well studied.
Here we present new results of measurements of the mean longitudinal field of
14 roAp stars obtained from low resolution spectropolarimetry with FORS1 at the
VLT.Comment: 5 pages, accepted for publication in A&
Constraints of a pulsation frequency on stellar parameters in the eclipsing spectroscopic binary system: V577 Oph
We present a preliminary spectroscopic analysis of the binary system V577Oph,
observed during the summer of 2007 on the 2.6m NOT telescope on La Palma. We
have obtained time series spectroscopic observations, which show clear binary
motion as well as radial velocity variations due to pulsation in the primary
star. By modelling the radial velocities we determine a full orbital solution
of the system, which yields M_A sin^3 i = 1.562 +/- 0.012 M_solar and M_B sin^3
i = 1.461 +/- 0.020 M_solar. An estimate of inclination from photometry yields
a primary mass of 1.6 M_solar. Using this derived mass, and the known pulsation
frequency we can impose a lower limit of 1 Gyr on the age of the system, and
constrain the parameters of the oscillation mode. We show that with further
analysis of the spectra (extracting the atmospheric parameters), tighter
constraints could be imposed on the age, metallicity and the mode parameters.
This work emphasizes the power that a single pulsation frequency can have for
constraining stellar parameters in an eclipsing binary system.Comment: Accepted by A
A multisite photometric study of two unusual Beta Cep stars: the magnetic V2052 Oph and the massive rapid rotator V986 Oph
We report a multisite photometric campaign for the Beta Cep stars V2052 Oph
and V986 Oph. 670 hours of high-quality differential photoelectric Stromgren,
Johnson and Geneva time-series photometry were obtained with eight telescopes
on five continents during 182 nights. Frequency analyses of the V2052 Oph data
enabled the detection of three pulsation frequencies, the first harmonic of the
strongest signal, and the rotation frequency with its first harmonic.
Pulsational mode identification from analysing the colour amplitude ratios
confirms the dominant mode as being radial, whereas the other two oscillations
are most likely l=4. Combining seismic constraints on the inclination of the
rotation axis with published magnetic field analyses we conclude that the
radial mode must be the fundamental. The rotational light modulation is in
phase with published spectroscopic variability, and consistent with an oblique
rotator for which both magnetic poles pass through the line of sight. The
inclination of the rotation axis is 54o <i< 58o and the magnetic obliquity 58o
<beta< 66o. The possibility that V2052 Oph has a magnetically confined wind is
discussed. The photometric amplitudes of the single oscillation of V986 Oph are
most consistent with an l=3 mode, but this identification is uncertain.
Additional intrinsic, apparently temporally incoherent, light variations of
V986 Oph are reported. Different interpretations thereof cannot be
distinguished at this point, but this kind of variability appears to be present
in many OB stars. The prospects of obtaining asteroseismic information for more
rapidly rotating Beta Cep stars, which appear to prefer modes of higher l, are
briefly discussed.Comment: 12 pages, 8 figures, MNRAS, in pres
M-Dwarf Fast Rotators and the Detection of Relatively Young Multiple M-Star Systems
We have searched the Kepler light curves of ~3900 M-star targets for evidence
of periodicities that indicate, by means of the effects of starspots, rapid
stellar rotation. Several analysis techniques, including Fourier transforms,
inspection of folded light curves, 'sonograms', and phase tracking of
individual modulation cycles, were applied in order to distinguish the
periodicities due to rapid rotation from those due to stellar pulsations,
eclipsing binaries, or transiting planets. We find 178 Kepler M-star targets
with rotation periods, P_rot, of < 2 days, and 110 with P_rot < 1 day. Some 30
of the 178 systems exhibit two or more independent short periods within the
same Kepler photometric aperture, while several have three or more short
periods. Adaptive optics imaging and modeling of the Kepler pixel response
function for a subset of our sample support the conclusion that the targets
with multiple periods are highly likely to be relatively young physical binary,
triple, and even quadruple M star systems. We explore in detail the one object
with four incommensurate periods all less than 1.2 days, and show that two of
the periods arise from one of a close pair of stars, while the other two arise
from the second star, which itself is probably a visual binary. If most of
these M-star systems with multiple periods turn out to be bound M stars, this
could prove a valuable way of discovering young hierarchical M-star systems;
the same approach may also be applicable to G and K stars. The ~5% occurrence
rate of rapid rotation among the ~3900 M star targets is consistent with spin
evolution models that include an initial contraction phase followed by magnetic
braking, wherein a typical M star can spend several hundred Myr before spinning
down to periods longer than 2 days.Comment: 17 pages, 12 figures, 2 tables; accepted for publication in The
Astrophysical Journa
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