31,446 research outputs found
Spectroscopic Observations of Planetary Nebulae in the Northern Spur of M31
We present spectroscopy of three planetary nebulae (PNe) in the Northern Spur
of the Andromeda Galaxy (M31) obtained with the Double Spectrograph on the 5.1
m Hale Telescope at the Palomar Observatory. The samples are selected from the
observations of Merrett et al. Our purpose is to investigate formation of the
substructures of M31 using PNe as a tracer of chemical abundances. The [O III]
4363 auroral line is detected in the spectra of two objects, enabling
temperature determinations. Ionic abundances are derived from the observed
collisionally excited lines, and elemental abundances of nitrogen, oxygen, and
neon as well as sulphur and argon are estimated. Correlations between oxygen
and the alpha-element abundance ratios are studied, using our sample and the
M31 disk and bulge PNe from the literature. In one of the three PNe, we
observed relatively higher oxygen abundance compared to the disk sample in M31
at similar galactocentric distances. The results of at least one of the three
Northern Spur PNe might be in line with the proposed possible origin of the
Northern Spur substructure of M31, i.e. the Northern Spur is connected to the
Southern Stream and both substructures comprise the tidal debris of the
satellite galaxies of M31.Comment: 5 tables, 17 figures; accepted for publication in Ap
Understanding the white-light flare on 2012 March 9 : Evidence of a two-step magnetic reconnection
We attempt to understand the white-light flare (WLF) that was observed on
2012 March 9 with a newly constructed multi-wavelength solar telescope called
the Optical and Near-infrared Solar Eruption Tracer (ONSET). We analyzed WLF
observations in radio, H-alpha, white-light, ultraviolet, and X-ray bands. We
also studied the magnetic configuration of the flare via the nonlinear
force-free field (NLFFF) extrapolation and the vector magnetic field observed
by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory (SDO). Continuum emission enhancement clearly appeared at the 3600
angstrom and 4250 angstrom bands, with peak contrasts of 25% and 12%,
respectively. The continuum emission enhancement closely coincided with the
impulsive increase in the hard X-ray emission and a microwave type III burst at
03:40 UT. We find that the WLF appeared at one end of either the sheared or
twisted field lines or both. There was also a long-lasting phase in the H-alpha
and soft X-ray bands after the white-light emission peak. In particular, a
second, yet stronger, peak appeared at 03:56 UT in the microwave band. This
event shows clear evidence that the white-light emission was caused by
energetic particles bombarding the lower solar atmosphere. A two-step magnetic
reconnection scenario is proposed to explain the entire process of flare
evolution, i.e., the first-step magnetic reconnection between the field lines
that are highly sheared or twisted or both, and the second-step one in the
current sheet, which is stretched by the erupting flux rope. The WLF is
supposed to be triggered in the first-step magnetic reconnection at a
relatively low altitude.Comment: 4 pages, 4 figures, published in A&A Lette
Nodeless superconductivity in IrPtTe with strong spin-orbital coupling
The thermal conductivity of superconductor IrPtTe
( = 0.05) single crystal with strong spin-orbital coupling was measured down
to 50 mK. The residual linear term is negligible in zero magnetic
field. In low magnetic field, shows a slow field dependence. These
results demonstrate that the superconducting gap of IrPtTe is
nodeless, and the pairing symmetry is likely conventional s-wave, despite the
existence of strong spin-orbital coupling and a quantum critical point.Comment: 5 pages, 4 figure
Tailoring microstructure and texture of annealed Al-Mn alloy through the variation of homogenization and prior cold deformation strain
The grain structures and crystallographic textures desired for various applications of aluminium alloys are usually modified by recrystallization during annealing. In this study, the interactions between recrystallization and precipitation were investigated using the same Al-Mn alloy but with different homogenization procedures (which gives different microchemistries in terms of solute level and second phase particle state) and prior cold
deformation strains, both of which are easy to realize in industrial practice. The results show that recrystallization and precipitation kinetics are both promoted at large deformations but their mutual interactions also exis
The Temporal and Spectral Characteristics of "Fast Rise and Exponential Decay" Gamma-Ray Burst Pulses
In this paper we have analyzed the temporal and spectral behavior of 52 Fast
Rise and Exponential Decay (FRED) pulses in 48 long-duration gamma-ray bursts
(GRBs) observed by the CGRO/BATSE, using a pulse model with two shape
parameters and the Band model with three shape parameters, respectively. It is
found that these FRED pulses are distinguished both temporally and spectrally
from those in long-lag pulses. Different from these long-lag pulses only one
parameter pair indicates an evident correlation among the five parameters,
which suggests that at least 4 parameters are needed to model burst
temporal and spectral behavior. In addition, our studies reveal that these FRED
pulses have correlated properties: (i) long-duration pulses have harder spectra
and are less luminous than short-duration pulses; (ii) the more asymmetric the
pulses are the steeper the evolutionary curves of the peak energy () in
the spectrum within pulse decay phase are. Our statistical
results give some constrains on the current GRB models.Comment: 18 pages, 7 figures, accepted for publication in the Astrophysical
Journa
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