42 research outputs found
On geometry of fronts in wave propagations
We give a geometric description of (wave) fronts in wave propagation processes. The concrete form of the defining function of a wave front issuing from the initial algebraic variety is obtained with the aid of the Gauss-Manin systems associated with certain complete intersection singularities. In the case of propagation on the plane, we get restrictions on the types of possible cusps that can appear on the wave front
Period integrals associated to an affine Delsarte type hypersurface
We calculate the period integrals for a special class of affine hypersurfaces (deformed Delsarte hypersurfaces) in an algebraic torus by the aid of their Mellin transforms. A description of the relation between poles of Mellin transforms of period integrals and the mixed Hodge structure of the cohomology of the hypersurface is given. By interpreting the period integrals as solutions to Pochhammer hypergeometric differential equation, we calculate concretely the irreducible monodromy group of period integrals that correspond to the compactification of the affine hypersurface in a complete simplicial toric variety. As an application of the equivalence between oscillating integral for Delsarte polynomial and quantum cohomology of a weighted projective space , we establish an equality between its Stokes matrix and the Gram matrix of the full exceptional collection on
Stokes matrices for the quantum differential equations of some Fano varieties
The classical Stokes matrices for the quantum differential equation of
projective n-space are computed, using multisummation and the so-called
monodromy identity. Thus, we recover the results of D. Guzzetti that confirm
Dubrovin's conjecture for projective spaces. The same method yields explicit
formulas for the Stokes matrices of the quantum differential equations of
smooth Fano hypersurfaces in projective n-space and for weighted projective
spaces.Comment: 20 pages. Introduction has been changed. Small corrections in the
tex
The AKARI/IRC Mid-Infrared All-Sky Survey
Context : AKARI is the first Japanese astronomical satellite dedicated to
infrar ed astronomy. One of the main purposes of AKARI is the all-sky survey
performed with six infrared bands between 9 and 200um during the period from
2006 May 6 to
2007 August 28. In this paper, we present the mid-infrared part (9um and 18um
b ands) of the survey carried out with one of the on-board instruments, the
Infrar ed Camera (IRC). Aims : We present unprecedented observational results
of the 9 and 18um AKARI al l-sky survey and detail the operation and data
processing leading to the point s ource detection and measurements. Methods :
The raw data are processed to produce small images for every scan and point
sources candidates, above the 5-sigma noise level per single scan, are der
ived. The celestial coordinates and fluxes of the events are determined
statisti cally and the reliability of their detections is secured through
multiple detect ions of the same source within milli-seconds, hours, and months
from each other. Results : The sky coverage is more than 90% for both bands. A
total of 877,091 s ources (851,189 for 9um, 195,893 for 18um) are confirmed and
included in the cur rent release of the point source catalogue. The detection
limit for point source s is 50mJy and 90mJy for the 9um and 18um bands,
respectively. The position accu racy is estimated to be better than 2".
Uncertainties in the in-flight absolute flux calibration are estimated to be 3%
for the 9um band and 4% for the 18um ban d. The coordinates and fluxes of
detected sources in this survey are also compar ed with those of the IRAS
survey and found to be statistically consistent.Comment: Accepted for publication in AandA AKARI special issu
AKARI's infrared view on nearby stars : Using AKARI Infrared Camera All-Sky Survey, 2MASS, and Hipparcos catalog
--Results-- We found that the (B-V) v.s. (V-S9W) color-color diagram is
useful to identify the stars with infrared excess emerged from circumstellar
envelopes/disks. Be stars with infrared excess are well separated from other
types of stars in this diagram. Whereas (J-L18W) v.s. (S9W-L18W) diagram is a
powerful tool to classify several object-types. Carbon-rich asymptotic giant
branch (AGB) stars and OH/IR stars form distinct sequences in this color-color
diagram. Young stellar objects (YSOs), pre-main sequence (PMS) stars, post-AGB
stars and planetary nebulae (PNe) have largest mid-infrared color-excess, and
can be identified in infrared catalog. Finally, we plot L18W v.s. (S9W-L18W)
color-magnitude diagram, using the AKARI data together with Hipparcos
parallaxes. This diagram can be used to identify low-mass YSOs, as well as AGB
stars. We found that this diagram is comparable to the [24] vs ([8.0]-[24])
diagram of Large Magellanic Cloud sources using the Spitzer Space Telescope
data. Our understanding of Galactic objects will be used to interpret
color-magnitude diagram of stellar populations in nearby galaxies which Spitzer
Space Telescope has observed. --Conclusions-- Our study of the AKARI
color-color and color-magnitude will be used to explore properties of unknown
objects in future. In addition, our analysis highlights a future key project to
understand stellar evolution with circumstellar envelope, once the forthcoming
astronometrical data with GAIA are available.Comment: 14 pages, 11 figures, accepted for publication in A&A. High
resolution version is available at:
http://www.ir.isas.jaxa.jp/%7Eyita/allsky20100302.pdf (26Mb
The Peculiar Type Ib Supernova 2006jc: A WCO Wolf-Rayet Star Explosion
We present a theoretical model for Type Ib supernova (SN) 2006jc. We
calculate the evolution of the progenitor star, hydrodynamics and
nucleosynthesis of the SN explosion, and the SN bolometric light curve (LC).
The synthetic bolometric LC is compared with the observed bolometric LC
constructed by integrating the UV, optical, near-infrared (NIR), and
mid-infrared (MIR) fluxes. The progenitor is assumed to be as massive as
on the zero-age main-sequence. The star undergoes extensive mass
loss to reduce its mass down to as small as , thus becoming a WCO
Wolf-Rayet star. The WCO star model has a thick carbon-rich layer, in which
amorphous carbon grains can be formed. This could explain the NIR brightening
and the dust feature seen in the MIR spectrum. We suggest that the progenitor
of SN 2006jc is a WCO Wolf-Rayet star having undergone strong mass loss and
such massive stars are the important sites of dust formation. We derive the
parameters of the explosion model in order to reproduce the bolometric LC of SN
2006jc by the radioactive decays: the ejecta mass , hypernova-like
explosion energy ergs, and ejected Ni mass . We
also calculate the circumstellar interaction and find that a CSM with a flat
density structure is required to reproduce the X-ray LC of SN 2006jc. This
suggests a drastic change of the mass-loss rate and/or the wind velocity that
is consistent with the past luminous blue variable (LBV)-like event.Comment: 12 pages, 11 figures. Accepted for publication in the Astrophysical
Journa
Star-galaxy separation in the AKARI NEP Deep Field
Context: It is crucial to develop a method for classifying objects detected
in deep surveys at infrared wavelengths. We specifically need a method to
separate galaxies from stars using only the infrared information to study the
properties of galaxies, e.g., to estimate the angular correlation function,
without introducing any additional bias. Aims. We aim to separate stars and
galaxies in the data from the AKARI North Ecliptic Pole (NEP) Deep survey
collected in nine AKARI / IRC bands from 2 to 24 {\mu}m that cover the near-
and mid-infrared wavelengths (hereafter NIR and MIR). We plan to estimate the
correlation function for NIR and MIR galaxies from a sample selected according
to our criteria in future research. Methods: We used support vector machines
(SVM) to study the distribution of stars and galaxies in the AKARIs multicolor
space. We defined the training samples of these objects by calculating their
infrared stellarity parameter (sgc). We created the most efficient classifier
and then tested it on the whole sample. We confirmed the developed separation
with auxiliary optical data obtained by the Subaru telescope and by creating
Euclidean normalized number count plots. Results: We obtain a 90% accuracy in
pinpointing galaxies and 98% accuracy for stars in infrared multicolor space
with the infrared SVM classifier. The source counts and comparison with the
optical data (with a consistency of 65% for selecting stars and 96% for
galaxies) confirm that our star/galaxy separation methods are reliable.
Conclusions: The infrared classifier derived with the SVM method based on
infrared sgc- selected training samples proves to be very efficient and
accurate in selecting stars and galaxies in deep surveys at infrared
wavelengths carried out without any previous target object selection.Comment: 8 pages, 8 figure