1,202 research outputs found
Detecting the progenitors of core collapse supernovae
The masses and the evolutionary states of the progenitors of core-collapse
supernovae are not well constrained by direct observations. Stellar evolution
theory generally predicts that massive stars with initial masses less than
about 30M_sol should undergo core-collapse when they are cool M-type
supergiants. However the only two detections of a SN progenitor before
explosion are SN1987A and SN1993J, and neither of these was an M-type
supergiant. Attempting to identify the progenitors of supernovae is a difficult
task, as precisely predicting the time of explosion of a massive star is
impossible for obvious reasons. There are several different types of supernovae
which have different spectral and photometric evolution, and how exactly these
are related to the evolutionary states of the progenitor stars is not currently
known. I will describe a novel project which may allow the direct
identification of core-collapse supernovae progenitors on pre-explosion images
of resolved, nearby galaxies. This project is now possible with the excellent
image archives maintained by several facilities and will be enhanced by the new
initiatives to create Virtual Observatories, the earliest of which ASTROVIRTEL
is already producing results.Comment: To appear in the Euroconference proceedings of "The Evolution of
Galaxies II. Basic Building Blocks", held in La Renunion, October 2001, eds.
M. Sauvage, et al., 5 pages inc. 2 figs, (Kluwer
Observational constraints on the progenitors of core-collapse supernovae : the case for missing high mass stars
Over the last 15 years, the supernova community has endeavoured to identify
progenitor stars of core-collapse supernovae in high resolution archival images
of their galaxies.This review compiles results (from 1999 - 2013) in a distance
limited sample and discusses the implications. The vast majority of the
detections of progenitor stars are of type II-P, II-L or IIb with one type Ib
progenitor system detected and many more upper limits for progenitors of Ibc
supernovae (14). The data for these 45 supernovae progenitors illustrate a
remarkable deficit of high luminosity stars above an apparent limit of Log L ~=
5.1 dex. For a typical Salpeter IMF, one would expect to have found 13 high
luminosity and high mass progenitors. There is, possibly, only one object in
this time and volume limited sample that is unambiguously high mass (the
progenitor of SN2009ip). The possible biases due to the influence of
circumstellar dust and sample selection methods are reviewed. It does not
appear likely that these can explain the missing high mass progenitor stars.
This review concludes that the observed populations of supernovae in the local
Universe are not, on the whole, produced by high mass (M > ~18Msun) stars.
Theoretical explosions of model stars also predict that black hole formation
and failed supernovae tend to occur above M > ~18Msun. The models also suggest
there are islands of explodability for stars in the 8-120Msun range. The
observational constraints are quite consistent with the bulk of stars above M >
~18Msun collapsing to form black holes with no visible supernovae. (Abridged).Comment: Invited review article for Publications of the Astronomical Society
of Australia, to be published in a special PASA collection on "SN1987A and
Supernovae in the Local Universe". This is the accepted version, after
referee review. Additional minor corrections to match proofs. (25 pages
The Progenitor of SN 2005cs in the Whirlpool Galaxy
The progenitor of SN 2005cs, in the galaxy M51, is identified in
pre-explosion HST ACS WFC imaging. Differential astrometry, with post-explosion
ACS HRC F555W images, permitted the identification of the progenitor with an
accuracy of 0.006". The progenitor was detected in the F814W pre-explosion
image with I=23.3+/-0.2, but was below the detection thresholds of the F435W
and F555W images, with B<24.8 and V<25 at 5-sigma. Limits were also placed on
the U and R band fluxes of the progenitor from pre-explosion HST WFPC2 F336W
and F675W images. Deep images in the infra-red from NIRI on the Gemini-North
telescope were taken 2 months prior to explosion, but the progenitor is not
clearly detected on these. The upper limits for the JHK magnitudes of the
progenitor were J<21.9,H<21.1 and K<20.7. Despite having a detection in only
one band, a restrictive spectral energy distribution of the progenitor star can
be constructed and a robust case is made that the progenitor was a red
supergiant with spectral type between mid-K to late-M. The spectral energy
distribution allows a region in the theoretical HR diagram to be determined
which must contain the progenitor star. The initial mass of the star is
constrained to be M(ZAMS)=9+3/-2 M_solar, which is very similar to the
identified progenitor of the type II-P SN 2003gd, and also consistent with
upper mass limits placed on five other similar SNe. The upper limit in the deep
K-band image is significant in that it allows us to rule out the possibility
that the progenitor was a significantly higher mass object enshrouded in a dust
cocoon before core-collapse. This is further evidence that the trend for type
II-P SNe to arise in low to moderate mass red supergiants is real.Comment: Accepted (31/08/05) for publication in MNRAS Letter
The Disappearance of the Progenitors of Supernovae 1993J and 2003gd
Using images from the Hubble Space Telescope (HST) and the Gemini Telescope
we confirm the disappearance of the progenitors of two Type II supernovae
(SNe), and evaluate the presence of other stars associated with them. We find
that the progenitor of SN 2003gd, an M-supergiant star, is no longer observed
at the SN location, and determine its intrinsic brightness using image
subtraction techniques. The progenitor of SN 1993J, a K-supergiant star, is
also no longer present, but its B-supergiant binary companion is still
observed. The disappearance of the progenitors confirms that these two SNe were
produced by Red Supergiants.Comment: Science, in press, published online 19/03/09, 28 pages (MS+SOM)
(high-res figures available at
http://www.dark-cosmology.dk/~justyn/research/
Chemical composition of B-type supergiants in the OB8, OB10, OB48, OB78 associations of M31
Absolute and differential chemical abundances are presented for the largest
group of massive stars in M31 studied to date. These results were derived from
intermediate resolution spectra of seven B-type supergiants, lying within four
OB associations covering a galactocentric distance of 5 - 12 kpc. The results
are mainly based on an LTE analysis, and we additionally present a full
non-LTE, unified model atmosphere analysis of one star (OB78-277) to
demonstrate the reliability of the differential LTE technique. A comparison of
the stellar oxygen abundance with that of previous nebular results shows that
there is an offset of between ~0.15 - 0.4 dex between the two methods which is
critically dependent on the empirical calibration adopted for the R23 parameter
with [O/H]. However within the typical errors of the stellar and nebular
analyses (and given the strength of dependence of the nebular results on the
calibration used) the oxygen abundances determined in each method are fairly
consistent. We determine the radial oxygen abundance gradient from these stars,
and do not detect any systematic gradient across this galactocentric range. We
find that the inner regions of M31 are not, as previously thought, very 'metal
rich'. Our abundances of C, N, O, Mg, Si, Al, S and Fe in the M31 supergiants
are very similar to those of massive stars in the solar neighbourhood.Comment: 15 pages, 9 figures and 9 tables. Submitted to A&A April 200
The VLT-FLAMES Survey of Massive Stars: Observations centered on the Magellanic Cloud clusters NGC 330, NGC 346, NGC 2004, and the N11 region
We present new observations of 470 stars using the Fibre Large Array
Multi-Element Spectrograph (FLAMES) instrument in fields centered on the
clusters NGC 330 and NGC 346 in the Small Magellanic Cloud (SMC), and NGC 2004
and the N11 region in the Large Magellanic Cloud (LMC). A further 14 stars were
observed in the N11 and NGC 330 fields using the Ultraviolet and Visual Echelle
Spectrograph (UVES) for a separate programme. Spectral classifications and
stellar radial velocities are given for each target, with careful attention to
checks for binarity. In particular we have investigated previously unexplored
regions around the central LH9/LH10 complex of N11, finding ~25 new O-type
stars from our spectroscopy. We have observed a relatively large number of
Be-type stars that display permitted Fe II emission lines. These are primarily
not in the cluster cores and appear to be associated with classical Be-type
stars, rather than pre main-sequence objects. The presence of the Fe II
emission, as compared to the equivalent width of H, is not obviously
dependent on metallicity. We have also explored the relative fraction of Be- to
normal B-type stars in the field-regions near to NGC 330 and NGC 2004, finding
no strong evidence of a trend with metallicity when compared to Galactic
results. A consequence of service observations is that we have reasonable
time-sampling in three of our FLAMES fields. We find lower limits to the binary
fraction of O- and early B-type stars of 23 to 36%. One of our targets
(NGC346-013) is especially interesting with a massive, apparently hotter, less
luminous secondary component.Comment: 35 pages, 17 figures (some reduced in size). Replacement copy,
includes an erratum on the final page. A copy with full res. & embedded
figures is at http://www.roe.ac.uk/~cje/flamesMC.ps.g
Pan-STARRS and PESSTO search for an optical counterpart to the LIGO gravitational-wave source GW150914
We searched for an optical counterpart to the first gravitational-wave source discovered by LIGO (GW150914), using a combination of the Pan-STARRS1 wide-field telescope and the Public ESO Spectroscopic Survey of Transient Objects (PESSTO) spectroscopic follow-up programme. As the final LIGO sky maps changed during analysis, the total probability of the source being spatially coincident with our fields was finally only 4.2 per cent. Therefore, we discuss our results primarily as a demonstration of the survey capability of Pan-STARRS and spectroscopic capability of PESSTO. We mapped out 442 deg^2 of the northern sky region of the initial map. We discovered 56 astrophysical transients over a period of 41 d from the discovery of the source. Of these, 19 were spectroscopically classified and a further 13 have host galaxy redshifts. All transients appear to be fairly normal supernovae (SNe) and AGN variability and none is obviously linked with GW150914. We illustrate the sensitivity of our survey by defining parametrized light curves with time-scales of 4, 20 and 40 d and use the sensitivity of the Pan-STARRS1 images to set limits on the luminosities of possible sources. The Pan-STARRS1 images reach limiting magnitudes of i_(P1) = 19.2, 20.0 and 20.8, respectively, for the three time-scales. For long time-scale parametrized light curves (with full width half-maximum â40 d), we set upper limits of M_i †â17.2^(â0.9)_(+1.4) if the distance to GW150914 is D_L = 400 ± 200 Mpc. The number of Type Ia SN we find in the survey is similar to that expected from the cosmic SN rate, indicating a reasonably complete efficiency in recovering SN like transients out to D_L = 400 ± 200 Mpc
SN 1996cr: Confirmation of a Luminous Type IIn Supernova in the Circinus Galaxy
We have recently confirmed SN 1996cr as a late-time type IIn supernova (SN)
via VLT spectroscopy and isolated its explosion date to ~1 yr using archival
optical imaging. We briefly touch upon here the wealth of optical, X-ray, and
radio archival observations available for this enigmatic source. Due to its
relative proximity (3.8 +/-0.6 Mpc), SN 1996cr ranks among the brightest X-ray
and radio SNe ever detected and, as such, may offer powerful insights into the
structure and composition of type IIn SNe. We also find that SN 1996cr is
matched to GRB 4B 960202 at a 2-3 sigma confidence level, making it perhaps the
third GRB to be significantly associated with a type II SN. We speculate on
whether SN 1996cr could be an off-axis or ``failed'' GRB.Comment: 3 pages, 1 figure, poster proceeding for "Supernova 1987A: 20 Years
After: Supernovae and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W.
Weiler, and R. McCra
Late-time spectral line formation in Type IIb supernovae, with application to SN 1993J, SN 2008ax, and SN 2011dh
We investigate line formation processes in Type IIb supernovae (SNe) from 100
to 500 days post-explosion using spectral synthesis calculations. The modeling
identifies the nuclear burning layers and physical mechanisms that produce the
major emission lines, and the diagnostic potential of these. We compare the
model calculations with data on the three best observed Type IIb SNe to-date -
SN 1993J, SN 2008ax, and SN 2011dh. Oxygen nucleosynthesis depends sensitively
on the main-sequence mass of the star and modeling of the [O I] 6300, 6364
lines constrains the progenitors of these three SNe to the M_ZAMS=12-16 M_sun
range (ejected oxygen masses 0.3-0.9 M_sun), with SN 2011dh towards the lower
end and SN 1993J towards the upper end of the range. The high ejecta masses
from M_ZAMS >= 17 M_sun progenitors give rise to brighter nebular phase
emission lines than observed. Nucleosynthesis analysis thus supports a scenario
of low/moderate mass progenitors for Type IIb SNe, and by implication an origin
in binary systems. We demonstrate how oxygen and magnesium recombination lines
may be combined to diagnose the magnesium mass in the SN ejecta. For SN 2011dh,
a magnesium mass of of 0.02-0.14 M_sun is derived, which gives a Mg/O
production ratio consistent with the solar value. Nitrogen left in the He
envelope from CNO-burning gives strong [N II] 6548, 6583 emission lines that
dominate over H-alpha emission in our models. The hydrogen envelopes of Type
IIb SNe are too small and dilute to produce any noticeable H-alpha emission or
absorption after ~150 days, and nebular phase emission seen around 6550 A is in
many cases likely caused by [N II] 6548, 6583. Finally, the influence of
radiative transport on the emergent line profiles is investigated...(abridged)Comment: Published versio
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