62 research outputs found
56Ni dredge-up in Supernova 1987A
We use early-time observations of He I 10830 \AA to measure the extent of
upward mixing of radioactive material in SN 1987A. This work develops and
extends the work of Graham (1988), and places constraints on actual explosion
models. The presence of the He I 10830 \AA (2s^{3}S--2p^{3}P) line at
days post-explosion implies re-ionisation by -rays from upwardly-mixed
radioactive material produced during the explosion. Using the unmixed explosion
model 10H (Woosley 1988) as well as mixed versions of it, we estimated the
-ray energy deposition by applying a purely absorptive radiative
transfer calculation. The deposition energy was used to find the ionisation
balance as a function of radius, and hence the 2sS population density
profile. This was then applied to a spectral synthesis model and the synthetic
spectra were compared with the observations. Neither model 10H nor the mixed
version, 10HMM, succeeded in reproducing the observed He I 10830 \AA line. The
discrepancy with the data found for 10HMM is particularly significant, as this
model has successfully reproduced the X-ray and -ray observations and
the UVOIR light curve. We find that a match to the He I line profile is
achieved by reducing the extent of mixing in 10HMM. Our reduced-mixing models
also reproduce the observed -ray line light curves and the iron-group
velocities deduced from late-time infrared line profiles. We suggest that the
He I line method provides a more sensitive measure of the extent of mixing in a
type II supernova explosion.Comment: 18 pages, 5 figures, accepted for publication in MNRAS (uses epsf.sty
- included
The origin of the high velocity circumstellar gas around SN 1998S
Modelling of high resolution Balmer line profiles in the early-time spectra
of SN 1998S shows that the inferred fast (roughly 400 km/s) circumstellar (CS)
gas on days 23 and 42 post-explosion is confined to a narrow, negative velocity
gradient shell just above the photosphere. This gas may be identified with a
slow (v < 40 km/s) progenitor wind accelerated at the ejecta-wind interface. In
this scenario, the photosphere coincides with a cool dense shell formed in the
reverse shock. Acceleration by radiation from the supernova or by a
shock-accelerated relativistic particle precursor are both possible
explanations for the observed fast CS gas. An alternative, equally plausible
scenario is that the fast CS gas is accelerated within shocked clouds engulfed
by the outer shock, as it propagates through the intercloud wind.Comment: 9 pages, 6 figures. MNRAS, accepted. Typos added, acknowledgments
correcte
56Ni dredge-up in the type IIp Supernova 1995V
We present contemporary infrared and optical spectra of the plateau type II
SN 1995V in NGC 1087 covering four epochs, approximately 22 to 84 days after
shock breakout. The data show, for the first time, the infrared spectroscopic
evolution during the plateau phase of a typical type II event. In the optical
region P Cygni lines of the Balmer series and of metals lines were identified.
The infrared (IR) spectra were largely dominated by the continuum, but P Cygni
Paschen lines and Brackett gamma lines were also clearly seen. The other
prominent IR features are confined to wavelengths blueward of 11000 \AA and
include Sr II 10327, Fe II 10547, C I 10695 and He I 10830 \AA. We demonstrate
the presence of He I 10830 \AA on days 69 and 85. The presence of this line at
such late times implies re-ionisation. A likely re-ionising mechanism is
gamma-ray deposition following the radioactive decay of 56Ni. We examine this
mechanism by constructing a spectral model for the He I 10830 \AA line based on
explosion model s15s7b2f of Weaver & Woosley (1993). We find that this does not
generate the observed line owing to the confinement of the 56Ni to the central
zones of the ejecta. In order to reproduce the He I line, it was necessary to
introduce additional upward mixing of the 56Ni, with 10^{-5} of the total
nickel mass reaching above the helium photosphere. In addition, we argue that
the He I line-formation region is likely to have been in the form of pure
helium clumps in the hydrogen envelope.Comment: Accepted for publication in MNRAS, 32 pages including 11 figures
(uses psfig.sty - included
Circumstellar Na I and Ca II lines in type IIP supernovae and SN 1998S
We study a possibility of detection of circumstellar absorption lines of Na I
D and Ca II H,K in spectra of type IIP supernovae at the photospheric
epoch. The modelling shows that the circumstellar lines of Na I doublet will
not be seen in type IIP supernovae for moderate wind density, e.g.,
characteristic of SN 1999em, whereas rather pronounced Ca II lines with P Cygni
profile should be detectable. A similar model is used to describe Na I and Ca
II circumstellar lines seen in SN 1998S, type IIL with a dense wind. We show
that line intensities in this supernova are reproduced, if one assumes an
ultraviolet excess, which is caused primarily by the comptonization of
supernova radiation in the shock wave.Comment: To be published in Astronomy Letter
Optical and Infrared Spectroscopy of the type IIn SN 1998S : Days 3-127
We present contemporary infrared and optical spectroscopic observations of
the type IIn SN 1998S for the period between 3 and 127 days after discovery. In
the first week the spectra are characterised by prominent broad emission lines
with narrow peaks superimposed on a very blue continuum(T~24000K). In the
following two weeks broad, blueshifted absorption components appeared in the
spectra and the temperature dropped. By day 44, broad emission components in H
and He reappeared in the spectra. These persisted to 100-130d, becoming
increasingly asymmetric. We agree with Leonard et al. (2000) that the broad
emission lines indicate interaction between the ejecta and circumstellar
material (CSM) and deduce that progenitor of SN 1998S appears to have gone
through at least two phases of mass loss, giving rise to two CSM zones.
Examination of the spectra indicates that the inner zone extended to <90AU,
while the outer CSM extended from 185AU to over 1800AU. Analysis of high
resolution spectra shows that the outer CSM had a velocity of 40-50 km/s.
Assuming a constant velocity, we can infer that the outer CSM wind commenced
more than 170 years ago, and ceased about 20 years ago, while the inner CSM
wind may have commenced less than 9 years ago. During the era of the outer CSM
wind the outflow was high, >2x10^{-5}M_{\odot}/yr corresponding to a mass loss
of at least 0.003M_{\odot} and suggesting a massive progenitor. We also model
the CO emission observed in SN 1998S. We deduce a CO mass of ~10^{-3} M_{\odot}
moving at ~2200km/s, and infer a mixed metal/He core of ~4M_{\odot}, again
indicating a massive progenitor.Comment: 22 pages, 14 figures, accepted in MNRA
Supernova 1996L: evidence of a strong wind episode before the explosion
Observations of the type II SN 1996L reveal the presence of a slowly
expanding (V~700$ km/s) shell at ~ 10^(16) cm from the exploding star. Narrow
emission features are visible in the early spectra superposed on the normal SN
spectrum. Within about two months these features develop narrow symmetric
P-Cygni profiles. About 100 days after the explosion the light curve suddenly
flattens, the spectral lines broaden and the Halpha flux becomes larger than
what is expected from a purely radioactive model. These events are interpreted
as signatures of the onset of the interaction between the fast moving ejecta
and a slowly moving outer shell of matter ejected before the SN explosion. At
about 300 days the narrow lines disappear and the flux drops until the SN fades
away, suggesting that the interaction phase is over and that the shell has been
swept away. Simple calculations show that the superwind episode started 9 yr
before the SN explosion and lasted 6 yr, with an average dM/dt=10^(-3)
M_solar/yr. Even at very late epochs (up to day 335) the typical forbidden
lines of [OI], CaII], [FeII] remain undetected or very weak. Spectra after day
270 show relatively strong emission lines of HeI. These lines are narrower than
other emission lines coming from the SN ejecta, but broader than those from the
CSM. These high excitation lines are probably the result of non-thermal
excitation and ionization caused by the deposition of the gamma-rays emitted in
the decay of radioactive material mixed in the He layer.Comment: 8 pages, 6 figures, Latex, To appear in M.N.R.A.
Optical and infrared observations of the Type IIP SN2002hh from day 3 to 397
We present optical and infrared (IR) observations of the type IIP SN2002hh
from 3 to 397 days after explosion. The optical spectroscopic (4-397d) and
photometric (3-278d) data are complemented by spectroscopic (137-381d) and
photometric (137-314d) data acquired at IR wavelengths. This is the first time
L-band spectra have ever been successfully obtained for a supernova at a
distance beyond the Local Group. The VRI light curves in the first 40 days
reveal SN2002hh to be a SN IIP (plateau) - the most common of all core-collapse
supernovae. SN2002hh is one of the most highly extinguished supernovae ever
investigated. To provide a good match between its early-time spectrum and a
coeval spectrum of the Type IIP SN1999em, as well as maintaining consistency
with KI interstellar absorption, we invoke a 2-component extinction model. One
component is due to the combined effect of the interstellar medium of our Milky
Way Galaxy and the SN host galaxy, while the other component is due to a "dust
pocket" where the grains have a mean size smaller than in the interstellar
medium. The early-time optical light curves of SNe 1999em and 2002hh are
generally well-matched, as are the radioactive tails of these two SNe and
SN1987A. The late-time similarity of the SN2002hh optical light curves to those
of SN1987A, together with measurements of the optical/IR luminosity and [FeII]
1.257mu emission indicate that 0.07 +- 0.02 Msun of Ni 56 was ejected by
SN2002hh. [... ABRIDGED...] From the [OI] 6300,6364 A doublet luminosity we
infer a 16-18 Msun main-sequence progenitor star. The progenitor of SN2002hh
was probably a red supergiant with a substantial, dusty wind.Comment: 32 pages, 30 figures, accepted for publication in MNRA
On the source of the late-time infrared luminosity of SN 1998S and other type II supernovae
We present late-time near-infrared (NIR) and optical observations of the type
IIn SN 1998S. The NIR photometry spans 333-1242 days after explosion, while the
NIR and optical spectra cover 333-1191 days and 305-1093 days respectively. The
NIR photometry extends to the M'-band (4.7 mu), making SN 1998S only the second
ever supernova for which such a long IR wavelength has been detected. The shape
and evolution of the H alpha and HeI 1.083 mu line profiles indicate a powerful
interaction with a progenitor wind, as well as providing evidence of dust
condensation within the ejecta. The latest optical spectrum suggests that the
wind had been flowing for at least 430 years. The intensity and rise of the HK
continuum towards longer wavelengths together with the relatively bright L' and
M' magnitudes shows that the NIR emission was due to hot dust newly-formed in
supernovae may provide the ejecta and/or pre-existing dust in the progenitor
circumstellar medium (CSM). [ABRIDGED] Possible origins for the NIR emission
are considered. Significant radioactive heating of ejecta dust is ruled out, as
is shock/X-ray-precursor heating of CSM dust. More plausible sources are (a) an
IR-echo from CSM dust driven by the UV/optical peak luminosity, and (b)
emission from newly-condensed dust which formed within a cool, dense shell
produced by the ejecta shock/CSM interaction. We argue that the evidence
favours the condensing dust hypothesis, although an IR-echo is not ruled out.
Within the condensing-dust scenario, the IR luminosity indicates the presence
of at least 0.001 solar masses of dust in the ejecta, and probably considerably
more. Finally, we show that the late-time intrinsic (K-L') evolution of type II
supernovae may provide a useful tool for determining the presence or absence of
a massive CSM around their progenitor stars.Comment: 23 pages, 15 figures, to be published in MNRA
Constraints on gamma-ray burst and supernova progenitors through circumstellar absorption lines. (II): Post-LBV Wolf-Rayet stars
Van Marle et al. (2005) showed that circumstellar absorption lines in early
Type Ib/c supernova and gamma-ray burst afterglow spectra may reveal the
progenitor evolution of the exploding Wolf-Rayet star. While the quoted paper
deals with Wolf-Rayet stars which evolved through a red supergiant stage, we
investigate here the initially more massive Wolf-Rayet stars which are thought
to evolve through a Luminous Blue Variable (LBV) stage. We perform hydrodynamic
simulations of the evolution of the circumstellar medium around a 60 Msol star,
from the main sequence through the LBV and Wolf-Rayet stages, up to core
collapse. We then compute the column density of the circumstellar matter as a
function of radial velocity, time and angle. This allows a comparison with the
number and blue-shifts, of absorption components in the spectra of LBVs,
Wolf-Rayet stars, Type Ib/c supernovae and gamma-ray burst afterglows. Our
simulation for the post-LBV stage shows the formation of various absorption
components, which are, however, rather short lived; they dissipate on time
scales shorter than 50,000yr. As the LBV stage is thought to occur at the
beginning of core helium burning, the remaining Wolf-Rayet life time is
expected to be one order of magnitude larger. When interpreting the absorption
components in the afterglow spectrum of GRB-021004 as circumstellar, it can be
concluded that the progenitor of this source did most likely not evolve through
an LBV stage. However, a close binary with late common-envelope phase (Case C)
may produce a circumstellar medium that closely resembles the LBV to Wolf-Rayet
evolution, but with a much shorter Wolf-Rayet period.Comment: accepted for publication by A&
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