Abstract
We investigate the X-ray and UV emission from the contact binary star KIC 9832227, which was observed with XMM-Newton for one orbital cycle. The binary is detected with an average X-ray ...luminosity of 3.4 × 10
30
erg s
−1
. The X-ray emission is restricted to energies below 3 keV and originates from a multitemperature plasma with temperatures up to 1 keV. The X-ray spectrum has at least two distinct components, a cooler, mostly steady component, and a hotter component exhibiting significant variability. The variable X-ray emission appears to originate from a compact flare near the contact region between the two stars that is being eclipsed by the secondary. We analyze the eclipse profile to constrain the location, size, and density of the flaring region. The remaining X-ray emission is not eclipsed and could originate from the polar region on the primary star or an extended corona. The UV emission exhibits the same nearly sinusoidal modulation at half the orbital period that is observed at longer wavelengths. The primary and secondary eclipses have slightly different depths, which is generally attributed to starspot activity. Using simulations of the UV light curve with stellar atmosphere models, we deduce the presence of a starspot near the polar region of the primary, and we determine the time of primary eclipse.
Abstract
Contact binary star systems represent the long-lived penultimate phase of binary evolution. Population statistics of their physical parameters inform an understanding of binary evolutionary ...pathways and end products. We use light curves and new optical spectroscopy to conduct a pilot study of ten (near) contact systems in the long-period (
P
> 0.5 days) tail of close binaries in the Kepler field. We use PHOEBE light-curve models to compute Bayesian probabilities on five principal system parameters. Mass ratios and third-light contributions measured from spectra agree well with those inferred from the light curves. Pilot study systems have extreme mass ratios
q
< 0.32. Most are triples. Analysis of the unbiased sample of 783 0.15 d <
P
< 2 days (near) contact binaries results in 178 probable contact systems, 114 probable detached systems, and 491 ambiguous systems for which we report best-fitting and 16th-/50th-/84th-percentile parameters. Contact systems are rare at periods
P
> 0.5 days, as are systems with
q
> 0.8. There exists an empirical mass ratio lower limit
q
min
(
P
)
≈ 0.05–0.15 below which contact systems are absent, supporting a new set of theoretical predictions obtained by modeling the evolution of contact systems under the constraints of mass and angular momentum conservation. Premerger systems should lie at long periods and near this mass ratio lower limit, which rises from
q
= 0.044 for
P
= 0.74 days to
q
= 0.15 at
P
= 2.0 days. These findings support a scenario whereby nuclear evolution of the primary (more massive) star drives mass transfer to the primary, thus moving systems toward extreme
q
and larger
P
until the onset of the Darwin instability at
q
min
precipitates a merger.
We present the first identification of a candidate precursor for an imminent red nova. Our prediction is based on the example of the precursor to the red nova V1309 Sco, which was retrospectively ...found to be a contact binary with an exponentially decreasing period. We explore the use of this distinctive timing signature to identify precursors, developing the observational and analysis steps needed. We estimate that our Galaxy has roughly 1-10 observable precursors. Specifically, we lay out the observational case for KIC 9832227, which we identified as a tentative candidate two years ago (Molnar et al. 2015, AAS Meeting #225 Abstracts 415.05). Orbital timing over the past two years has followed the tentative exponential fit. As of late 2015, the period time derivative went beyond the range found in other systems ( ), a necessary criterion for a serious candidate. We estimate time of merger is the year 2022.2 0.7. Double absorption line spectra confirm directly the 0.458-day light-curve is the orbital period of a contact binary system and yield a mass ratio . Closer analysis of the Kepler timing data shows evidence of a component C with orbital period days and . An alternative interpretation of the long-term timing trend, that is, a light travel-time delay due to the orbit around a distant component D, is ruled out by the spectroscopic data for any nondegenerate star. Additional measurements are needed to test further the merging hypothesis and to use fully this fortuitous opportunity.
The transparency of two-dimensional (2D) materials to intermolecular interactions of crystalline materials has been an unresolved topic. Here we report that remote atomic interaction through 2D ...materials is governed by the binding nature, that is, the polarity of atomic bonds, both in the underlying substrates and in 2D material interlayers. Although the potential field from covalent-bonded materials is screened by a monolayer of graphene, that from ionic-bonded materials is strong enough to penetrate through a few layers of graphene. Such field penetration is substantially attenuated by 2D hexagonal boron nitride, which itself has polarization in its atomic bonds. Based on the control of transparency, modulated by the nature of materials as well as interlayer thickness, various types of single-crystalline materials across the periodic table can be epitaxially grown on 2D material-coated substrates. The epitaxial films can subsequently be released as free-standing membranes, which provides unique opportunities for the heterointegration of arbitrary single-crystalline thin films in functional applications.
► Spin vector and model shape for Asteroid (832) Karin from rotation lightcurves. ► First spin vector determination for largest member of a very young asteroid family. ► Observational constraints for ...family formation models that include spin. ► Senses of spin for the 20 largest Karin cluster members are markedly nonrandom.
Studies of asteroid families constrain models of asteroid collisions and evolution processes, and the Karin cluster within the Koronis family is among the youngest families known (Nesvorný, D., Bottke, Jr., W.F., Dones, L., Levison, H.F. 2002. Nature 417, 720–722). (832) Karin itself is by far the largest member of the Karin cluster, thus knowledge of Karin’s spin vector is important to constrain family formation and evolution models that include spin, and to test whether its spin properties are consistent with the Karin cluster being a very young family. We observed rotation lightcurves of Karin during its four consecutive apparitions in 2006–2009, and combined the new observations with previously published lightcurves to determine its spin vector orientation and preliminary model shape. Karin is a prograde rotator with a period of (18.352±0.003) h, spin obliquity near (42±5)°, and pole ecliptic longitude near either (52±5)° or (230±5)°. The spin vector and shape results for Karin will constrain models of family formation that include spin properties; in the meantime we briefly discuss Karin’s own spin in the context of those of other members of the Karin cluster and the parent body’s siblings in the Koronis family.
•We develop and test a time-efficient epoch method for spin sense determination.•We apply our method to 21 Flora-region asteroids.•We use the spin sense distribution to constrain Flora spin–orbit ...evolution models.•We measure the SDSS colors of several large inner main belt asteroids.
The Flora asteroid family’s size and location on the inner edge of the main belt make it a likely source of NEOs and terrestrial planet impactors; however, reliable determination of Flora membership is inhibited by the family’s age and the presence of a high density of background objects. Dykhuis et al. (Dykhuis et al. 2014. Icarus 243, 111–128) identified the Flora family as the product of a 950-My-old collision dispersed in semimajor axis as a result of the Yarkovsky effect, and defined the family’s membership and extent in orbital parameter space. The observed preponderance of prograde rotators at semimajor axes greater than that of (8) Flora is consistent with the predictions of the single-collision Yarkovsky dispersion model.
Here we extend the available rotational property data for the Flora family via a survey of 21 Flora-region asteroids, using a time-efficient modification of the “epoch method” to determine prograde/retrograde spin sense. Five of the survey asteroids are shown to be prograde; five are shown to be retrograde; six are shown to have spin axes in or near their orbital planes; and five represent other cases for which spin axis information was not determined. The high-semimajor axis component of the Flora family is found to have only prograde and in-plane rotators, consistent with model predictions of Yarkovsky dispersion. Moreover, we confirm a wide range of ecliptic latitudes of the spin axes among these prograde rotators, consistent with models of family evolution in which a significant fraction of the members are captured in spin–orbit resonance. Near the “center” of the family (near the semimajor axis location of (8) Flora), the spin directions are mixed, with a slight preference for retrograde rotators, placing constraints on the efficiency of YORP-cycle spin reorientation for the family.
In addition to our spin sense survey, we also report new measurements of the Sloan colors of a number of large inner main belt asteroids.
Plasma-based ambient desorption/ionization (ADI) sources for mass spectrometry (MS) often use helium as the primary discharge gas due to the large reaction cross section of excited helium species ...with atmospheric gases, which ultimately leads to efficient reagent-ion formation. However, some studies have shown that mixed-gas plasmas provide unique advantages. For instance, our group showed that a helium‑oxygen flowing atmospheric-pressure afterglow (He:O2-FAPA) source yielded enhanced ion signals for small polar analytes, but compounds with aromatic rings underwent chemical modification to produce pyrylium species. Here, it is shown that the addition of H2 to the helium FAPA gas significantly decreased the reagent-ion signals, but analyte-ion signal was not affected to the same degree. In addition, mass spectra obtained with He:H2-FAPA were chemically cleaner with fewer ions stemming from analyte species and produced less oxidation of analytes. Addition of nitrogen increased the abundance of negative reagent ions (e.g., NO2− and NO3−) which led to enhanced ion signal for RDX. To better understand these unique advantages of a mixed-gas FAPA, the impact of molecular-gas (O2, N2, or H2) addition on the optical-emission spectra from the discharge was also measured. Spatially resolved emission was obtained from the anode- and negative-glow regions. In general, addition of small fractions (~0.1%) of molecular gases decreased helium and OH emission intensities. Atomic oxygen and hydrogen emission increased with the addition of O2 and H2, respectively. Furthermore, emission characteristics of N2, N2+, and NO with respect to molecular gas composition on He-FAPA were measured. Fundamental plasma parameters, such as OH rotational temperature (Trot), were also calculated for these mixed-gas systems.
Display omitted
•Adding molecular gases to FAPA results in unique plasma chemistries (observed with MS).•Oxygen addition increases reagent-ion density and analyte-ion signal for small polar analytes.•H2:He FAPA produces chemically cleaner mass spectra of analytes, but with lower signal.•Optical analysis of mixed-gas FAPA show significant quenching of excited species important for MS.
The ascomycetous fungus Nectria haematococca, (asexual name Fusarium solani), is a member of a group of >50 species known as the "Fusarium solani species complex". Members of this complex have ...diverse biological properties including the ability to cause disease on >100 genera of plants and opportunistic infections in humans. The current research analyzed the most extensively studied member of this complex, N. haematococca mating population VI (MPVI). Several genes controlling the ability of individual isolates of this species to colonize specific habitats are located on supernumerary chromosomes. Optical mapping revealed that the sequenced isolate has 17 chromosomes ranging from 530 kb to 6.52 Mb and that the physical size of the genome, 54.43 Mb, and the number of predicted genes, 15,707, are among the largest reported for ascomycetes. Two classes of genes have contributed to gene expansion: specific genes that are not found in other fungi including its closest sequenced relative, Fusarium graminearum; and genes that commonly occur as single copies in other fungi but are present as multiple copies in N. haematococca MPVI. Some of these additional genes appear to have resulted from gene duplication events, while others may have been acquired through horizontal gene transfer. The supernumerary nature of three chromosomes, 14, 15, and 17, was confirmed by their absence in pulsed field gel electrophoresis experiments of some isolates and by demonstrating that these isolates lacked chromosome-specific sequences found on the ends of these chromosomes. These supernumerary chromosomes contain more repeat sequences, are enriched in unique and duplicated genes, and have a lower G+C content in comparison to the other chromosomes. Although the origin(s) of the extra genes and the supernumerary chromosomes is not known, the gene expansion and its large genome size are consistent with this species' diverse range of habitats. Furthermore, the presence of unique genes on supernumerary chromosomes might account for individual isolates having different environmental niches.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Over the last 15 to 20 years several high quality, high resolution data have been taken with the very large array (VLA). These data exhibit a wide range of ring opening angles (
|
B
|
=
0
to 26°) and ...wavelengths (
λ
=
0.7
to 20 cm). At these wavelengths the primary flux from the rings is scattered saturnian thermal emission, with a small contribution coming from the ring particles' own thermal emission. Much of the data do show signs of asymmetries due to wakes either on the ansae or the portion of the rings which occult the planet. As in previous work, we use our Monte Carlo radiative transfer code including idealized wakes Dunn, D.E., Molnar, L.A., Fix, J.D., 2002. Icarus 160, 132–160; Dunn, D.E., Molnar, L.A., Niehof, J.T., de Pater, I., Lissauer, J.L., 2004. Icarus 171, 183–198 to model the relative contributions of the scattered and thermal radiation emanating from the rings and compare the results to that seen in the data. Although the models do give satisfactory fits to all of our data, we find that no single model can simulate the data at all different
|
B
|
and
λ. We find that one model works best for moderate and low
|
B
|
and another one at higher
|
B
|
. The main difference between these models is the ratio of the wake width to their separation. We similarly find that the 2 cm data require higher density wakes than the longer wavelength data, perhaps caused by a preponderance of somewhat smaller ring material in the wakes. We further find evidence for an increase in the physical temperature of the rings with increasing
|
B
|
. Continuous observations are required to determine whether the above results regarding variations in wake parameters with
|
B
|
and
λ are indeed caused by these parameters, or instead by changes over time.
We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of
λ3.6 cm. The moderate ring opening angle (
B≈15°) allows us to explore direct ...transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132–160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae.
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