279 research outputs found
Searching for a Companion Star of Tycho's Type Ia Supernova with Optical Spectroscopic Observations
We report our first results of photometric and spectroscopic observations for
Tycho's supernova remnant (SNR Tycho) to search for the companion star of a
type Ia supernova (SN Ia). From photometric observations using Suprime-Cam on
the Subaru Telescope, we have picked up stars brighter than 22 mag (in
-band) for spectroscopy, which are located within a circular region with the
radius of 30" around the center of SNR Tycho. If the ejecta of young supernova
remnants, such as SNR Tycho, have a sufficient amount of Fe I, we should be
able to detect absorption lines at 3720 \AA and 3860 \AA associated with
transitions from the ground state of Fe I in the spectrum of the companion
star. To identify the companion star of a SN Ia using these characteristic
absorption lines of Fe I, we made optical low-resolution spectroscopy of their
targets using FOCAS on the Subaru Telescope. In our spectroscopic observations,
we obtained spectra of 17 stars in the SNR Tycho region and compare them with
template stellar spectra. We detect significant absorption lines from two stars
at 3720 \AA. Since widths of their absorption lines are broad, it is likely
that the detected absorptions are due to Fe I in the expanding ejecta of SNR
Tycho. However, none of stars exhibits a clear red wing in the observed
profiles of the absorption, though a star in the background of the SNR should
show it. Hence, we suggest another interpretation that the detected absorption
lines might be caused by the peculiarity of stars. A star named Tycho(E) has
the absorption line at 3720 \AA and its projected position is close to the
center of SNR Tycho. Based on our observations, Tycho(E) is a new candidate as
the companion star of Tycho's supernova.Comment: 17 pages, 28 figures, accepted for publication in PAS
The Maximum Effect of Thermal Instability on Galactic Outflows
We have investigated steady, radial gas outflows (or winds) from galaxies and
the development of thermal instability in the hot gas. In order to see the
maximum influence of the instability on the global structure of the galactic
outflows, we study inhomogeneous comoving flows and the non-linear fate of the
fluctuations in the flows. We compare the results with solutions for
homogeneous flows. In the case of supersonic flows, the global structure of
inhomogeneous flows is not much different from that of homogeneous flows.
However, detailed investigation shows that the average density of inhomogeneous
flows decreases faster than that of homogeneous flows, because local thermal
instability removes overdense regions in the inhomogeneous flows and reduces
the mass flux. We also find that when the gravity of a galaxy is strong, the
cold clouds formed from the removed gas are distributed in the galactic halo.
In the case of subsonic flows, the form of inhomogeneous flows is different
from that of homogeneous flows near the regions where the flows terminate. The
density rise appearing near the regions where the homogeneous flows terminate
is not seen in the inhomogeneous flows because the local thermal instability
decreases the mass flux. The cold clouds formed through thermal instability in
the inhomogeneous flow almost all coast to the same maximum radius.Comment: 19 pages, 6 figures; to appear in Ap
Evolution of Multiphase Hot Interstellar Medium in Elliptical Galaxies
We present the results of a variety of simulations concerning the evolution
of multiphase (inhomogeneous) hot interstellar medium (ISM) in elliptical
galaxies. We assume the gases ejected from stars do not mix globally with the
circumferential gas. The ejected gas components evolve separately according to
their birth time, position, and origin. We consider cases where supernova
remnants (SNRs) mix with local ISM. The components with high metal abundance
and/or high density cool and drop out of the hot ISM gas faster than the other
components because of their high metal abundance and/or density. This makes the
average metal abundance of the hot ISM low. Furthermore, since the metal
abundance of mass-loss gas decreases with radius, gas inflow from outer region
makes the average metal abundance of the hot ISM smaller than that of mass-loss
gas in the inner region. As gas ejection rate of stellar system decreases, mass
fraction of mass-loss gas ejected at outer region increases in a galaxy. If the
mixing of SNRs is ineffective, our model predicts that observed [Si/Fe] and
[Mg/Fe] should decrease towards the galactic center because of strong iron
emission by SNRs. In the outer region, where the cooling of time of the ISM is
long, the selective cooling is ineffective and most of gas components remain
hot. Thus, the metal abundance of the ISM in this region directly reflects that
of the gas ejected from stars. Our model shows that supernovae are not
effective heating sources in the inner region of elliptical galaxies, because
most of the energy released by them radiates. Therefore, cooling flow is
established even if the supernova rate is high. Mixing of SNRs with ambient ISM
makes the energy transfer between supernova explosion and ambient ISM more
effective.Comment: 21 pages (AASTeX), 14 figures, accepted for publication in The
Astrophysical Journa
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