6,232 research outputs found
On the Progenitor and Supernova of the SN 2002cx-like Supernova 2008ge
We present observations of supernova (SN) 2008ge, which is spectroscopically
similar to the peculiar SN 2002cx, and its pre-explosion site that indicate
that its progenitor was probably a white dwarf. NGC 1527, the host galaxy of SN
2008ge, is an S0 galaxy with no evidence of star formation or massive stars.
Astrometrically matching late-time imaging of SN 2008ge to pre-explosion HST
imaging, we constrain the luminosity of the progenitor star. Since SN 2008ge
has no indication of hydrogen or helium in its spectrum, its progenitor must
have lost its outer layers before exploding, requiring that it be a white
dwarf, a Wolf-Rayet star, or a lower-mass star in a binary system. Observations
of the host galaxy show no signs of individual massive stars, star clusters, or
H II regions at the SN position or anywhere else, making a Wolf-Rayet
progenitor unlikely. Late-time spectroscopy of SN 2008ge show strong [Fe II]
lines with large velocity widths compared to other members of this class at
similar epochs. These previously unseen features indicate that a significant
amount of the SN ejecta is Fe (presumably the result of radioactive decay of
56Ni generated in the SN), further supporting a thermonuclear explosion.
Placing the observations of SN 2008ge in the context of observations of other
objects in the class of SN, we suggest that the progenitor was most likely a
white dwarf.Comment: 9 pages, 6 figures, accepted by A
Exact asymptotics for the stationary distribution of a Markov chain: A production model
We derive rough and exact asymptotic expressions for the station- ary distribution π of a Markov chain arising in a queueing/production context. The approach we develop can also handle "cascades", which are situations where the uid limit of the large deviation path from the origin to the increasingly rare event is nonlinear. Our approach considers a process that starts at the rare event. In our production ex- ample, we can have two sequences of states that asymptotically lie on the same line, yet π has different asymptotics on the two sequences
CDS wide slit time-series of EUV coronal bright points
Wide slit (90" x 240" ) movies of four Extreme Ultraviolet coronal bright points (BPs) obtained with the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SoHO) have been inspected. The wavelet analysis of the He I 584.34 Å, O V 629.73 Å and Mg VII/IX 368 Å time-series confirms the oscillating nature of the BPs, with periods ranging between 600 and 1100 s. In one case we detect periods as short as 236 s. We suggest that these oscillations are the same as those seen in the chromospheric network and that a fraction of the network bright points are most likely the cool footpoints of the loops comprising coronal bright points. These oscillations are interpreted in terms of global acoustic modes of the closed magnetic structures associated with BPs
Residential mobility in divided societies: How individual religion and geographical context influenced housing moves in Northern Ireland 2001–2011
Residential segregation is pervasive in many societies. People making residential moves in these divided contexts may increase or decrease segregation levels. In this paper, the divided society of Northern Ireland is used as an example to explore how residential mobility relates to residential segregation by religion. Survey evidence for this country consistently shows a preference for mixed neighbourhoods, yet actual patterns of geographical mobility suggest people move to same‐religion areas. The paper uses the Northern Ireland Longitudinal Study (NILS) to explore the individual and contextual factors that influence the destinations of internal migrants by religion between 2001 and 2011. How they move up or down the contextual ‘religion ladder’ of localities is modelled with reference to both their individual socio‐demographic and neighbourhood characteristics in 2001. It is found that there are still individual religious differentials in people's destinations. Catholics, for instance, are more likely than Protestants to move to more Catholic areas, suggesting that individual religion remains important despite the Peace Process. Some possible reasons for this are considered with a partial explanation being found in the geographical patterning of the population. Existing patterns of residential segregation constrain moves in religious space for the majority of people. It is concluded, nevertheless, that an individual's religion remains a considerable factor contrary to expectations
On the Progenitor System of the Type Iax Supernova 2014dt in M61
We present pre-explosion and post-explosion Hubble Space Telescope images of
the Type Iax supernova (SN Iax) 2014dt in M61. After astrometrically aligning
these images, we do not detect any stellar sources at the position of the SN in
the pre-explosion images to relatively deep limits (3 sigma limits of M_F438W >
-5.0 mag and M_F814W > -5.9 mag). These limits are similar to the luminosity of
SN 2012Z's progenitor system (M_F435W = -5.43 +/- 0.15 and M_F814W = -5.24 +/-
0.16 mag), the only probable detected progenitor system in pre-explosion images
of a SN Iax, and indeed, of any white dwarf supernova. SN 2014dt is consistent
with having a C/O white-dwarf primary/helium-star companion progenitor system,
as was suggested for SN 2012Z, although perhaps with a slightly smaller or
hotter donor. The data are also consistent with SN 2014dt having a low-mass red
giant or main-sequence star companion. The data rule out main-sequence stars
with M_init > 16 M_sun and most evolved stars with M_init > 8 M_sun as being
the progenitor of SN 2014dt. Hot Wolf-Rayet stars are also allowed, but the
lack of nearby bright sources makes this scenario unlikely. Because of its
proximity (D = 12 Mpc), SN 2014dt is ideal for long-term monitoring, where
images in ~2 years may detect the companion star or the luminous bound remnant
of the progenitor white dwarf.Comment: 5 pages, 3 figures, submitted to ApJ
Martin boundary of a reflected random walk on a half-space
The complete representation of the Martin compactification for reflected
random walks on a half-space is obtained. It is shown that the
full Martin compactification is in general not homeomorphic to the ``radial''
compactification obtained by Ney and Spitzer for the homogeneous random walks
in : convergence of a sequence of points to a
point of on the Martin boundary does not imply convergence of the sequence
on the unit sphere . Our approach relies on the large
deviation properties of the scaled processes and uses Pascal's method combined
with the ratio limit theorem. The existence of non-radial limits is related to
non-linear optimal large deviation trajectories.Comment: 42 pages, preprint, CNRS UMR 808
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