1,110 research outputs found
A New Interpretation for the Second Peak of T Coronae Borealis Outbursts: A Tilting Disk around a Very Massive White Dwarf
A new interpretation for the second peak of T Coronae Borealis (T CrB)
outbursts is proposed based on a thermonuclear runaway (TNR) model. The system
consists of a very massive white dwarf (WD) with a tilting accretion disk and a
lobe-filling red-giant. The first peak of the visual light curve of T CrB
outbursts is well reproduced by the TNR model on a WD close to the
Chandrasekhar mass (), while the second peak
is reproduced by the combination of the irradiated M-giant and the irradiated
tilting disk. The derived fitting parameters are the WD mass , the M-giant companion mass
( is acceptable), the inclination angle of the orbit i \sim
70 \arcdeg, and the tilting angle of the disk i_{\rm prec} \sim 35 \arcdeg.
These parameters are consistent with the recently derived binary parameters of
T CrB.Comment: 6 pages including 2 figures, to be published in ApJ Letter
A Theoretical Light-Curve Model for the Recurrent Nova V394 Coronae Austrinae
A theoretical light curve for the 1987 outburst of V394 Coronae Austrinae
(V394 CrA) is modeled to obtain various physical parameters of this recurrent
nova. We then apply the same set of parametersto a quiescent phase and confirm
that these parameters give a unified picture of the binary. The early visual
light curve (1-10 days after the optical maximum) is well reproduced by a
thermonuclear runaway model on a very massive WD close to the Chandrasekhar
limit (1.37 +- 0.01 M_sun). The ensuing plateau phase (10-30 days) is also
reproduced by the combination of a slightly irradiated MS and a fully
irradiated flaring-up disk with a radius ~1.4 times the Roche lobe size. The
best fit parameters are the WD mass 1.37 M_sun, the companion mass 1.5 M_sun
(0.8-2.0 M_sun is acceptable), the inclination angle of the orbit i~65-68
degree, and the flaring-up rim ~0.30 times the disk radius. The envelope mass
at the optical peak is estimated to be ~6 x 10^{-6} M_sun, which indicates an
average mass accretion rate of 1.5 x 10^{-7} M_sun yr^{-1} during the quiescent
phase between the 1949 and 1987 outbursts. In the quiescent phase, the observed
light curve can be reproduced with a disk size of 0.7 times the Roche lobe size
and a rather slim thickness of 0.05 times the accretion disk size at the rim.
About 0.5 mag sinusoidal variation of the light curve requires the mass
accretion rate higher than ~1.0 x 10^{-7} M_sun yr^{-1}, which is consistent
with the above estimation from the 1987 outburst. These newly obtained
quantities are exactly the same as those predicted in a new progenitor model of
Type Ia supernovae.Comment: 9 pages including 4 figures, to appear in the Astrophysical Journal,
Part
Nucleosynthesis in Baryon-Rich Outflows Associated With Gamma-Ray Bursts
Robust generation of gamma-ray bursts (GRBs) implies the formation of
outflows with very low baryon loads and highly relativistic velocities, but
more baryon-rich, slower outflows are also likely to occur in most GRB central
engine scenarios, either as ``circum-jet winds'' or ``failed GRBs''. Here we
study the possibility of nucleosynthesis within such baryon-rich outflows by
conducting detailed reaction network calculations in the framework of the basic
fireball model. It is shown that high baryon load fireballs attaining mildly
relativistic velocities can synthesize appreciable quantities of heavy neutron
capture elements with masses up to the platinum peak and beyond. Small but
interesting amounts of light elements such as deuterium and boron can also be
produced. Depending on the neutron excess and baryon load, the combination of
high entropy, rapid initial expansion and gradual expansion at later times can
cause the reaction flow to reach the fission regime, and its path can be
intermediate between those of the - and -processes (``-process''). The
nucleosynthetic signature of these outflows may be observable in the companion
stars of black hole binary systems and in the most metal-poor stars,
potentially offering an important probe of the inner conditions of the GRB
source. Contribution to the solar abundances for some heavy elements may also
be possible. The prospects for further developments in various directions are
discussed.Comment: ApJ, in press; 11 pages, 3 figure
A new clue to the transition mechanism between optical high and low states of the supersoft X-ray source RX J0513.9-6951, implied from the recurrent nova CI Aquilae 2000 outburst model
We have found a new clue to the transition mechanism between optical
high/X-ray off and optical low/X-ray on states of the LMC supersoft X-ray
source RX J0513.9-6951. A sharp ~1 mag drop is common to the CI Aql 2000
outburst. These drops are naturally attributed to cessation of optically thick
winds on white dwarfs. A detailed light-curve analysis of CI Aql indicates that
the size of a disk drastically shrinks when the wind stops. This causes ~1-2
mag drop in the optical light curve. In RX J0513.9-6951, the same mechanism
reproduces sharp ~1 mag drop from optical high to low states. We predict this
mechanism also works on the transition from low to high states. Interaction
between the wind and the companion star attenuates the mass transfer and drives
full cycles of low and high states.Comment: 9 pages including 5 figures, to appear in the Astrophysical Journa
Helium Nova on a Very Massive White Dwarf -- A Light Curve Model of V445 Puppis (2000) Revised
V445 Pup (2000) is a unique object identified as a helium nova. Color indexes
during the outburst are consistent with those of free-free emission. We present
a free-free emission dominated light curve model of V445 Pup on the basis of
the optically thick wind theory. Our light curve fitting shows that (1) the
white dwarf (WD) mass is very massive (M_WD \gtrsim 1.35 M_\sun), and (2) a
half of the accreted matter remains on the WD, both of which suggest that the
increasing WD mass. Therefore, V445 Pup is a strong candidate of Type Ia
supernova progenitor. The estimated distance to V445 Pup is now consistent with
the recent observational suggestions, 3.5 < d < 6.5 kpc. A helium star
companion is consistent with the brightness of m_v=14.5 mag just before the
outburst, if it is a little bit evolved hot (\log T (K) \gtrsim 4.5) star with
the mass of M_He \gtrsim 0.8 M_\sun. We then emphasize importance of
observations in the near future quiescent phase after the thick circumstellar
dust dissipates away, especially its color and magnitude to specify the nature
of the companion star. We have also calculated helium ignition masses for
helium shell flashes against various helium accretion rates and discussed the
recurrence period of helium novae.Comment: 8 pages including 12 figures, to appear in Ap
Negative phototaxis in the photosymbiotic sea anemone Aiptasia as a potential strategy to protect symbionts from photodamage
Photosymbiotic cnidarians generally seek bright environments so that their symbionts can be photosynthetically active. However, excess light may result in a breakdown of symbiosis due to the accumulation of photodamage in symbionts causing symbiont loss (bleaching). It is currently unknown if photosymbiotic cnidarians sense light only to regulate spawning time and to facilitate predation, or whether they also use their light-sensing capacities to protect their symbionts from photodamage. In this study, we examined how the sea anemone Aiptasia changes its behaviour when exposed to excess light. We reveal that Aiptasia polyps, when carrying symbionts, contract their bodies when exposed to high light intensities and subsequently migrate away in a direction perpendicular to the light source. Interestingly, this negative phototaxis was only evident under blue light and absent upon UV, green and red light exposure. Non-symbiotic Aiptasia did not exhibit this light response. Our study demonstrates that photosymbiotic Aiptasia polyps display negative phototactic behaviour in response to blue light, and that they also can perceive its direction, despite lacking specialized eye structures. We postulate that Aiptasia uses blue light, which penetrates seawater efficiently, as a general proxy for sunlight exposure to protect its symbionts from photodamage
Stimulation of cannabinoid receptor agonist 2-arachidonylglycerol by chronic ethanol and its modulation by specific neuromodulators in cerebellar granule neurons
AbstractIn an earlier study, we reported that chronic ethanol (EtOH) stimulates the formation of anandamide in human SK-N-SH cells. In the present study, we investigated the effect of chronic EtOH on the formation of yet another cannabinoid receptor (CB1) agonist, 2-arachidonylglycerol (2-AG), in cerebellar granule neurons (CGNs). The formation of 2-[3H]AG without any stimulation was more pronounced in the older cultures than in younger cultures. Exposure of CGNs to EtOH led to a significant increase in the level of 2-[3H]AG (P<0.05). Incubation with the anandamidehydrolase inhibitor phenylmethylsulfonyl fluoride and EtOH did result in an additive increase in 2-[3H]AG, but did not with E-6-(bromomethylene)tetrahydro-3-(1-naphthelenyl)-2H-pyran-2-one. The formation of 2-[3H]AG was enhanced by ionomycin in both the control and EtOH-exposed CGNs, and the ionomycin-stimulated 2-[3H]AG synthesis was inhibited by the intracellular chelating agent 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid. Further, glutamate increased the formation of 2-[3H]AG only in control CGNs. MK-801 inhibited the EtOH-induced 2-[3H]AG synthesis, suggesting the participation of intracellular Ca2+ in EtOH-induced 2-[3H]AG synthesis. The dopamine receptor (D2) agonist did not modify the 2-AG synthesis in either the control or EtOH-exposed CGNs. However, the D2 receptor antagonist inhibited the EtOH-induced formation of 2-[3H]AG. The EtOH-induced 2-[3H]AG formation was inhibited by SR141716A and pertussis toxin, suggesting the CB1 receptor- and Gi/o-protein-mediated regulation of 2-AG. The observed increase in 2-AG level in CGNs is possibly a mechanism for neuronal adaptation to the continuous presence of EtOH. These findings indicate that some of the pharmacological actions of EtOH may involve alterations in the endocannabinoid signaling system
A Theoretical Light-Curve Model for the 1999 Outburst of U Scorpii
A theoretical light curve for the 1999 outburst of U Scorpii is presented in
order to obtain various physical parameters of the recurrent nova. Our U Sco
model consists of a very massive white dwarf (WD) with an accretion disk and a
lobe-filling, slightly evolved, main-sequence star (MS). The model includes a
reflection effect by the companion and the accretion disk together with a
shadowing effect on the companion by the accretion disk. The early visual light
curve (t ~ 1-15 days after maximum) is well reproduced by a thermonuclear
runaway model on a very massive WD close to the Chandrasekhar limit (M_{WD}=
1.37 \pm 0.01 M_\odot), in which optically thick winds blowing from the WD play
a key role in determining the nova duration. The duration of the strong wind
phase (t~0-17 days) is very consistent with the BeppoSAX supersoft X-ray
detection at t~19-20 days because supersoft X-rays are self-absorbed by the
massive wind. The envelope mass at the peak is estimated to be ~3x10^{-6}
M_\odot, which is indicating an average mass accretion rate ~2.5x10^{-7}
M_\odot yr^{-1} during the quiescent phase between 1987 and 1999. These
quantities are exactly the same as those predicted in a new progenitor model of
Type Ia supernovae.Comment: 7 pages, 3 figures, to appear in ApJL, vol. 52
Taking Stock of Reality: Biased Perceptions of the Costs of Romantic Partners’ Sacrifices
When romantic partners sacrifice their own self-interest to benefit the relationship, the sacrificer or recipient may—for various reasons—be biased in how they perceive the costs that the sacrificer incurs. In Study 1, romantic couples (N = 125) rated their own and their partner’s costs after a conversation about a sacrifice in the laboratory, followed by extensive experience sampling in their natural environment. In Study 2, a preregistered experiment, individuals (N = 775) imagined a scenario in which they, their partner, or an unknown person sacrificed and rated the associated costs and benefits. Both studies demonstrated a consistent discrepancy between perceptions of own and partner sacrifice, driven primarily by people underestimating their own sacrifice costs and overestimating the benefits (Study 2). Results across studies showed that this underestimation bias helps people to feel better and feel more satisfied in the relationship when giving up their own goals and preferences for the relationship
- …