745 research outputs found
"Pricing Convertible Bonds with Default Risk: A Duffie-Singleton Approach"
We propose a new method to value convertible bonds(CBs). In particular, we explicitly take default risk into consideration based on Duffie-Singleton(1999), and provide a consistent and practical method for relative pricing of securities issued by a firm such as CBs, non-convertible corporate bonds and equities. Moreover, we show numerical examples using Japanese CBs' data, and compare our model with other practical models.
Infrared Spectroscopy of CO Ro-vibrational Absorption Lines toward the Obscured AGN IRAS 08572+3915
We present high-resolution spectroscopy of gaseous CO absorption in the
fundamental ro-vibrational band toward the heavily obscured active galactic
nucleus (AGN) IRAS 08572+3915. We have detected absorption lines up to highly
excited rotational levels (J<=17). The velocity profiles reveal three distinct
components, the strongest and broadest (delta_v > 200 km s-1) of which is due
to blueshifted (-160 km s-1) gas at a temperature of ~ 270 K absorbing at
velocities as high as -400 km s-1. A much weaker but even warmer (~ 700 K)
component, which is highly redshifted (+100 km s-1), is also detected, in
addition to a cold (~ 20 K) component centered at the systemic velocity of the
galaxy. On the assumption of local thermodynamic equilibrium, the column
density of CO in the 270 K component is NCO ~ 4.5 x 10^18 cm-2, which in fully
molecular gas corresponds to a H2 column density of NH2 ~ 2.5 x 10^22 cm-2. The
thermal excitation of CO up to the observed high rotational levels requires a
density greater than nc(H2) > 2 x 10^7 cm-3, implying that the thickness of the
warm absorbing layer is extremely small (delta_d < 4 x 10-2 pc) even if it is
highly clumped. The large column densities and high radial velocities
associated with these warm components, as well as their temperatures, indicate
that they originate in molecular clouds near the central engine of the AGN.Comment: 13 pages, 7 figures, accepted for publication in PASJ (Vol.65 No.1
2013/02/25
Multi-Color Coronagraph Experiment in a Vacuum Testbed with a Binary Shaped Pupil Mask
We conducted a number of multi-band coronagraph experiments using a vacuum
chamber and a binary-shaped pupil mask which in principle should work at all
wavelengths, in the context of the research and development on a coronagraph to
observe extra-solar planets (exoplanets) directly. The aim of this work is to
demonstrate that subtraction of Point Spread Function (PSF) and multi-band
experiments using a binary-shaped pupil mask coronagraph would help improve the
contrast in the observation of exoplanets. A checkerboard mask, a kind of
binary-shaped pupil mask, was used. We improved the temperature stability by
installing the coronagraph optics in a vacuum chamber, controlling the
temperature of the optical bench, and covering the vacuum chamber with thermal
insulation layers. We evaluated how much the PSF subtraction contributes to the
high contrast observation by subtracting the images obtained through the
coronagraph. We also carried out multi- band experiments in order to
demonstrate a more realistic observation using Super luminescent Light Emitting
Diodes (SLEDs) with center wavelengths of 650nm, 750nm, 800nm and 850nm. A
contrast of 2.3x10-7 was obtained for the raw coronagraphic image and a
contrast of 1.3x10-9 was achieved after PSF subtraction with a He-Ne laser at
632.8nm wavelength. Thus, the contrast was improved by around two orders of
magnitude from the raw contrast by subtracting the PSF. We achieved contrasts
of 3.1x10-7, 1.1x10-6, 1.6x10-6 and 2.5x10-6 at the bands of 650nm, 750nm,
800nm and 850nm, respectively, in the multi-band experiments. The results show
that contrast within each of the wavelength bands was significantly improved
compared with non-coronagraphic optics. We demonstrated PSF subtraction is
potentially beneficial for improving contrast of the coronagraph, and this
coronagraph produces a significant improvement in contrast with multi-band
light sources.Comment: 14 pages, 7 figures, accepted for publication in PAS
AKARI IRC 2.5-5 um Spectroscopy of Infrared Galaxies over a Wide Luminosity Range
We present the result of a systematic infrared 2.5-5 um spectroscopic study
of 22 nearby infrared galaxies over a wide infrared luminosity range (10 <
log(L_IR / Lsun) < 13) obtained from AKARI Infrared Camera (IRC). The unique
band of the AKARI IRC spectroscopy enables us to access both the 3.3 um
polycyclic aromatic hydrocarbon (PAH) emission feature from star forming
activity and the continuum of torus-dust emission heated by an active galactic
nucleus (AGN). Applying our AGN diagnostics to the AKARI spectra, we discover
14 buried AGNs. The large fraction of buried AGNs suggests that AGN activity
behind the dust is almost ubiquitous in ultra-/luminous infrared galaxies
(U/LIRGs). We also find that both the fraction and energy contribution of
buried AGNs increase with infrared luminosity from 10 < log(L_IR / Lsun) < 13,
including normal infrared galaxies with log (L_IR / Lsun) < 11. The energy
contribution from AGNs in the total infrared luminosity is only ~7% in LIRGs
and ~20% in ULIRGs, suggesting that the majority of the infrared luminosity
originates from starburst activity. Using the PAH emission, we investigate the
luminosity relation between star formation and AGN. We find that these infrared
galaxies exhibit higher star formation rates than optically selected Seyfert
galaxies with the same AGN luminosities, implying that infrared galaxies could
be an early evolutionary phase of AGN.Comment: 13 pages, 8 figures, accepted for publication in Ap
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