142 research outputs found
Carbon Monoxide in the Cassiopeia A Supernova Remnant
We report the likely detection of near-infrared 2.29 m first overtone
Carbon Monoxide (CO) emission from the young supernova remnant Cassiopeia A
(Cas A). The continuum-subtracted CO filter map reveals CO knots within the
ejecta-rich reverse shock. We compare the first overtone CO emission with that
found in the well-studied supernova, SN 1987A and find 30 times less CO
in Cas A. The presence of CO suggests that molecule mixing is small in the SN
ejecta and that astrochemical processes and molecule formation may continue at
least ~300 years after the initial explosion.Comment: Accepted for the publication in ApJ Lette
Detection of CO and Dust Emission in Near-Infrared Spectra of SN 1998S
Near-infrared spectra (0.95 -- 2.4 micron) of the peculiar Type IIn supernova
1998S in NGC 3877 from 95 to 355 days after maximum light are presented. K-band
data taken at days 95 and 225 show the presence of the first overtone of CO
emission near 2.3 micron, which is gone by day 355. An apparent extended blue
wing on the CO profile in the day 95 spectrum could indicate a large CO
expansion velocity (~2000 -- 3000 km/s). This is the third detection of
infrared CO emission in nearly as many Type II supernovae studied, implying
that molecule formation may be fairly common in Type II events, and that the
early formation of molecules in SN 1987A may be typical rather than
exceptional. Multi-peak hydrogen and helium lines suggest that SN 1998S is
interacting with a circumstellar disk, and the fading of the red side of this
profile with time is suggestive of dust formation in the ejecta, perhaps
induced by CO cooling. Continuum emission that rises towards longer wavelengths
(J -> K) is seen after day 225 with an estimated near-infrared luminosity >~
10^40 erg/s. This may be related to the near-infrared excesses seen in a number
of other supernovae. If this continuum is due to free-free emission, it
requires an exceptionally shallow density profile. On the other hand, the shape
of the continuum is well fit by a 1200 +- 150 K blackbody spectrum possibly due
to thermal emission from dust. Interestingly, we observe a similar 1200 K
blackbody-like, near-infrared continuum in SN 1997ab, another Type IIn
supernova at an even later post-maximum epoch (day 1064+). A number of dust
emission scenarios are discussed, and we conclude that the NIR dust continuum
is likely powered by the interaction of SN 1998S with the circumstellar medium.Comment: 38 Pages, 12 Figures, Submitted to The Astronomical Journa
Low Carbon Abundance in Type Ia Supernovae
We investigate the quantity and composition of unburned material in the outer
layers of three normal Type Ia supernovae (SNe Ia): 2000dn, 2002cr and 20 04bw.
Pristine matter from a white dwarf progenitor is expected to be a mixture of
oxygen and carbon in approximately equal abundance. Using near-infrared (NIR,
0.7-2.5 microns) spectra, we find that oxygen is abundant while carbon is
severely depleted with low upper limits in the outer third of the ejected mass.
Strong features from the OI line at rest wavelength = 0.7773 microns are
observed through a wide range of expansion velocities approx. 9,000 - 18,000
km/s. This large velocity domain corresponds to a physical region of the
supernova with a large radial depth. We show that the ionization of C and O
will be substantially the same in this region. CI lines in the NIR are expected
to be 7-50 times stronger than those from OI but there is only marginal
evidence of CI in the spectra and none of CII. We deduce that for these three
normal SNe Ia, oxygen is more abundant than carbon by factors of 100 - 1,000.
MgII is also detected in a velocity range similar to that of OI. The presence
of O and Mg combined with the absence of C indicates that for these SNe Ia,
nuclear burning has reached all but the extreme outer layers; any unburned
material must have expansion velocities greater than 18,000 km/s. This result
favors deflagration to detonation transition (DD) models over pure deflagration
models for SNe Ia.Comment: accepted for publication in Ap
Eleven years of radio monitoring of the Type IIn supernova SN 1995N
We present radio observations of the optically bright Type IIn supernova SN
1995N. We observed the SN at radio wavelengths with the Very Large Array (VLA)
for 11 years. We also observed it at low radio frequencies with the Giant
Metrewave Radio Telescope (GMRT) at various epochs within years since
explosion. Although there are indications of an early optically thick phase,
most of the data are in the optically thin regime so it is difficult to
distinguish between synchrotron self absorption (SSA) and free-free absorption
(FFA) mechanisms. However, the information from other wavelengths indicates
that the FFA is the dominant absorption process. Model fits of radio emission
with the FFA give reasonable physical parameters. Making use of X-ray and
optical observations, we derive the physical conditions of the shocked ejecta
and the shocked CSM.Comment: 22 pages, 2 tables, 13 figures, Accepted for publication in
Astrophysical Journa
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
A Spitzer Space Telescope Study of SN 2002hh: An Infrared Echo from a Type IIP Supernova
We present late-time (590-994 days) mid-IR photometry of the normal but highly reddened Type IIP supernova SN 2002hh. Bright, cool, slowly fading emission is detected from the direction of the supernova. Most of this flux appears not to be driven by the supernova event but instead probably originates in a cool, obscured star formation region or molecular cloud along the line of sight. We also show, however, that the declining component of the flux is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR emission could also be coming from newly condensed dust and/or an ejecta/CSM impact, but their contributions are likely to be small. For the case of a CSM-IR echo, we infer a dust mass of as little as 0.036 M☉ with a corresponding CSM mass of 3.6(0.01/rdg) M☉, where rdg is the dust-to-gas mass ratio. Such a CSM would have resulted from episodic mass loss whose rate declined significantly about 28,000 years ago. Alternatively, an IR echo from a surrounding, dense, dusty molecular cloud might also have been responsible for the fading component. Either way, this is the first time that an IR echo has been clearly identified in a Type IIP supernova. We find no evidence for or against the proposal that Type IIP supernovae produce large amounts of dust via grain condensation in the ejecta. However, within the CSM-IR echo scenario, the mass of dust derived implies that the progenitors of the most common of core-collapse supernovae may make an important contribution to the universal dust content
A Spitzer Space Telescope study of SN 2002hh: an infrared echo from a Type IIP supernova
We present late-time (590-994 d) mid-IR photometry of the normal, but
highly-reddened Type IIP supernova SN 2002hh. Bright, cool, slowly-fading
emission is detected from the direction of the supernova. Most of this flux
appears not to be driven by the supernova event but instead probably originates
in a cool, obscured star-formation region or molecular cloud along the
line-of-sight. We also show, however, that the declining component of the flux
is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR
emission could also be coming from newly-condensed dust and/or an ejecta/CSM
impact but their contributions are likely to be small. For the case of a CSM-IR
echo, we infer a dust mass of as little as 0.036 M(solar) with a corresponding
CSM mass of 3.6(0.01/r(dg))M(solar) where r(dg) is the dust-to-gas mass ratio.
Such a CSM would have resulted from episodic mass loss whose rate declined
significantly about 28,000 years ago. Alternatively, an IR echo from a
surrounding, dense, dusty molecular cloud might also have been responsible for
the fading component. Either way, this is the first time that an IR echo has
been clearly identified in a Type IIP supernova. We find no evidence for or
against the proposal that Type IIP supernovae produce large amounts of dust via
grain condensation in the ejecta. However, within the CSM-IR echo scenario, the
mass of dust derived implies that the progenitors of the most common of
core-collapse supernovae may make an important contribution to the universal
dust content.Comment: 41 pages, 11 figures, 4 tables, accepted for publication in
Astrophysical Journal (References corrected
Nucleosynthesis in Two-Dimensional Delayed Detonation Models of Type Ia Supernova Explosions
The nucleosynthetic characteristics of various explosion mechanisms of Type
Ia supernovae (SNe Ia) is explored based on three two-dimensional explosion
simulations representing extreme cases: a pure turbulent deflagration, a
delayed detonation following an approximately spherical ignition of the initial
deflagration, and a delayed detonation arising from a highly asymmetric
deflagration ignition. Apart from this initial condition, the deflagration
stage is treated in a parameter-free approach. The detonation is initiated when
the turbulent burning enters the distributed burning regime. This occurs at
densities around g cm -- relatively low as compared to existing
nucleosynthesis studies for one-dimensional spherically symmetric models. The
burning in these multidimensional models is different from that in
one-dimensional simulations as the detonation wave propagates both into
unburned material in the high density region near the center of a white dwarf
and into the low density region near the surface. Thus, the resulting yield is
a mixture of different explosive burning products, from carbon-burning products
at low densities to complete silicon-burning products at the highest densities,
as well as electron-capture products synthesized at the deflagration stage. In
contrast to the deflagration model, the delayed detonations produce a
characteristic layered structure and the yields largely satisfy constraints
from Galactic chemical evolution. In the asymmetric delayed detonation model,
the region filled with electron capture species (e.g., Ni, Fe) is
within a shell, showing a large off-set, above the bulk of Ni
distribution, while species produced by the detonation are distributed more
spherically (abridged).Comment: Accepted by the Astrophysical Journal. 15 pages, 14 figures, 4 table
A Spitzer Space Telescope Study of SN 2003gd: Still No Direct Evidence that Core-Collapse Supernovae are Major Dust Factories
We present a new, detailed analysis of late-time mid-infrared (IR)
observations of the Type II-P supernova (SN) 2003gd. At about 16 months after
the explosion, the mid-IR flux is consistent with emission from 4 x 10^(-5)
M(solar) of newly condensed dust in the ejecta. At 22 months emission from
point-like sources close to the SN position was detected at 8 microns and 24
microns. By 42 months the 24 micron flux had faded. Considerations of
luminosity and source size rule out the ejecta of SN 2003gd as the main origin
of the emission at 22 months. A possible alternative explanation for the
emission at this later epoch is an IR echo from pre-existing circumstellar or
interstellar dust. We conclude that, contrary to the claim of Sugerman et al.
(2006, Science, 313, 196), the mid-IR emission from SN 2003gd does not support
the presence of 0.02 M(solar) of newly formed dust in the ejecta. There is, as
yet, no direct evidence that core-collapse supernovae are major dust factories.Comment: 26 pages, 2 figures, 2 tables, accepted for publication in
Astrophysical Journa
Dust and the type II-Plateau supernova 2004dj
We present mid-infrared (MIR) spectroscopy of a Type II-plateau supernova, SN
2004dj, obtained with the Spitzer Space Telescope, spanning 106--1393 d after
explosion. MIR photometry plus optical/near-IR observations are also reported.
An early-time MIR excess is attributed to emission from non-silicate dust
formed within a cool dense shell (CDS). Most of the CDS dust condensed between
50 d and 165 d, reaching a mass of 0.3 x 10^{-5} Msun. Throughout the
observations much of the longer wavelength (>10 microns) part of the continuum
is explained as an IR echo from interstellar dust. The MIR excess strengthened
at later times. We show that this was due to thermal emission from warm,
non-silicate dust formed in the ejecta. Using optical/near-IR line-profiles and
the MIR continua, we show that the dust was distributed as a disk whose radius
appeared to be slowly shrinking. The disk radius may correspond to a grain
destruction zone caused by a reverse shock which also heated the dust. The
dust-disk lay nearly face-on, had high opacities in the optical/near-IR
regions, but remained optically thin in the MIR over much of the period
studied. Assuming a uniform dust density, the ejecta dust mass by 996 d was 0.5
+/- 0.1) x 10^{-4} Msun, and exceeded 10^{-4}Msun by 1393 d. For a dust density
rising toward the center the limit is higher. Nevertheless, this study suggests
that the amount of freshly-synthesized dust in the SN 2004dj ejecta is
consistent with that found from previous studies, and adds further weight to
the claim that such events could not have been major contributors to the cosmic
dust budget.Comment: ApJ in press; minor changes c.f. v
- …