170 research outputs found
What mechanisms dominate the activity of Geminid Parent (3200) Phaethon?
A long-term sublimation model to explain how Phaethon could provide the
Geminid stream is proposed. We find that it would take Myr or more for
Phaethon to lose all of its internal ice (if ever there was) in its present
orbit. Thus, if the asteroid moved from the region of a 5:2 or 8:3 mean motion
resonance with Jupiter to its present orbit less than Myr ago, it may have
retained much of its primordial ice. The dust mantle on the sublimating body
should have a thickness of at least m but the mantle could have been less
than m thick years ago. We find that the total gas production rate
could have been as large as then, and the gas flow could
have been capable of lifting dust particles of up to a few centimeters in size.
Therefore, gas production during the past millennium could have been sufficient
to blow away enough dust particles to explain the entire Geminid stream. For
present-day Phaethon, the gas production is comparatively weak. But strong
transient gas release with a rate of is
expected for its south polar region when Phaethon moves from to
mean anomaly near perihelion. Consequently, dust particles with radii
of can be blown away to form a dust tail. In addition, we find
that the large surface temperature variation of K near perihelion can
generate sufficiently large thermal stress to cause fracture of rocks or
boulders and provide an efficient mechanism to produce dust particles on the
surface. The time scale for this process should be several times longer than
the seasonal thermal cycle, thereby dominating the cycle of appearance of the
dust tail.Comment: 10 pages, 5 figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
The Evidence for a Binary origin of the Young Planetary Nebula HB 12
The young planetary nebulae play an important role in stellar evolution when
intermediate- to low-mass stars (0.8 8 M) evolve from the
proto-planetary nebulae phase to the planetary nebulae phase. Many young
planetary nebulae display distinct bipolar structures as they evolve away from
the proto-planetary nebulae phase. One possible cause of their bipolarity could
be due to a binary origin of its energy source. Here we report our detailed
investigation of the young planetary nebula, Hubble 12, which is well-known for
its extended hourglass-like envelope. We present evidence with time-series
photometric observations the existence of an eclipsing binary at the center of
Hubble 12. Low-resolution spectra of the central source show, on the other
hand, absorption features such as CN, G-band & Mg b{\arcsec}, which can be
suggestive of a low-mass nature of the secondary component.Comment: 9 pages, 11 figures, Accepted for publication in A
Transit of asteroids across the 7/3 Kirkwood gap under the Yarkovsky effect
Many asteroids in the main belt are continuously pushed by Yarkovsky effect
into regions of different mean motion resonances (MMRs) and then ejected out.
They are considered as the principal source of near-Earth objects. We
investigate in this paper the effects of the 7/3 MMR with Jupiter (J7/3 MMR) on
the transportation of asteroids from Koronis and Eos families that reside
respectively on the inner and outer side of the resonance. The fraction of
asteroids that make successful crossing through the resonance and the escaping
rate from the resonance are found to depend on the Yarkovsky drifting rate, the
initial inclination and the migrating direction. The excitation of eccentricity
and inclination due to the combined influence from both the resonance and
Yarkovsky effect is discussed. Only the eccentricity can be pumped up
considerably, and it is attributed mainly to the resonance. In the
observational data, family members are also found in the resonance and on the
opposite side of the resonance with respect to the corresponding family centre.
The existence of these family members is explained using our results of
numerical simulations. Finally, the replenishment of asteroids in the J7/3 MMR
and the transportation of asteroids by it are discussed.Comment: 10 pages, 10 figures. Accepted by A&
The Planetary System of Upsilon Andromedae
The bright F8 V solar-type star upsilon Andromedae has recently been reported
to have a system of three planets of Jovian masses. In order to investigate the
orbital stability and mutual gravitational interactions among these extrasolar
planets, both forward and backward integrations from the latest observed
orbital elements for all three planets' orbits have been performed under the
coplanar assumption. We reconfirm that the middle and the outer planet have
strong interaction leading to large time variations in the eccentricities of
these planets, which was shown by the previous studies. However, we discuss the
validity of the ignorance of the innermost planet. We argue that this planetary
system is likely to be stable and oscillate around current orbital elements
since it was formed.
We suggest that one possible way to produce these orbital elements: the
innermost planet has very low eccentricity but the outermost planet has high
eccentricity could be the interaction with the protostellar disc.Comment: The version accepted by A&A, 16 pages, AAS style fil
Flare-associated type III radio bursts and dynamics of the EUV jet from SDO/AIA and RHESSI observations
We present a detailed description of the interrelation between the Type III
radio bursts and energetic phenomena associated with the flare activities in
Active region AR 11158 at 07:58 UT on 2011, Feb. 15. The timing of the Type-III
radio burst measured by the radio wave experiment on the Wind/WAVE and an array
of ground-based radio telescopes, coincided with an EUV jet and hard X-ray
emission observed by SDO/AIA and RHESSI., respectively. There is clear evidence
that the EUV jet shares the same source region as the hard X-ray emission. The
temperature of the jet, as determined by multiwavelength measurements of AIA,
suggests that type III emission is associated with hot, 7 MK, plasma at the
jet's footpoint.Comment: 5 figure
- âŠ