397 research outputs found
Search for the companions of Galactic SNe Ia
The central regions of the remnants of Galactic SNe Ia have been examined for
the presence of companion stars of the exploded supernovae. We present the
results of this survey for the historical SN 1572 and SN 1006. The spectra of
the stars are modeled to obtain Teff, log g and the metallicity. Radial
velocities are obtained with an accuracy of 5--10 km s. Implications for
the nature of the companion star in SNeIa follow.Comment: 8 pages, 2 Postscript figures. Appeared in "From Twilight to
Highlight: the Physics of Supernovae", ed. W. Hillebrandt & B. Leibundgut
(Springer), pp. 140-14
Neural network classification of gamma-ray bursts
From a cluster analysis it appeared that a three-class classification of GRBs could be preferable to just the classic separation of short/hard and long/soft GRBs (Balastegui A., Ruiz-Lapuente P. and Canal R. MNRAS 328 (2001) 283). A new classification of GRBs obtained via a neural network is presented, with a short/hard class, an intermediate-duration/soft class, and a long/soft class, the
latter being a brighter and more inhomogenous class than the intermediate duration one. A possible physical meaning of this new classification is also outlined
Type Ia supernova counts at high z: signatures of cosmological models and progenitors
Determination of the rates at which supernovae of Type Ia (SNe Ia) occur in
the early Universe can give signatures of the time spent by the binary
progenitor systems to reach explosion and of the geometry of the Universe.
Observations made within the Supernova Cosmology Project are already providing
the first numbers. Here it is shown that, for any assumed SNe Ia progenitor,
SNe Ia counts up to are useful tests of the SNe Ia
progenitor systems and cosmological tracers of a possible non-zero value of the
cosmological constant, . The SNe Ia counts at high redshifts compare
differently with those at lower redshifts depending on the cosmological model.
Flat --dominated universes would show a more significant
increase of the SNe Ia counts at than a flat,
universe. Here we consider three sorts of universes: a flat universe with
, , ;
an open universe with , ,
; and a flat, --dominated universe with , , ). On the
other hand, the SNe Ia counts from one class of binary progenitors (double
degenerate systems) should not increase steeply in the to range,
contrary to what should be seen for other binary progenitors. A measurement of
the SNe Ia counts up to is within reach of ongoing SNe Ia searches
at high redshifts.Comment: 16 pages, incl. 2 figures. To appear in ApJ (Letters
No surviving evolved companions to the progenitor of supernova SN 1006
Type Ia supernovae are thought to occur as a white dwarf made of carbon and
oxygen accretes sufficient mass to trigger a thermonuclear explosion. The
accretion could occur slowly from an unevolved (main-sequence) or evolved
(subgiant or giant) star, that being dubbed the single-degenerate
channel, or rapidly as it breaks up a smaller orbiting white dwarf (the double-
degenerate channel). Obviously, a companion will survive the explosion
only in the single-degenerate channel. Both channels might contribute to
the production of type Ia supernovae but their relative proportions
still remain a fundamental puzzle in astronomy. Previous searches for remnant
companions have revealed one possible case for SN 1572, though that has
been criticized. More recently, observations have restricted surviving
companions to be small, main-sequence stars, ruling out giant
companions, though still allowing the single-degenerate channel. Here we report
the result of a search for surviving companions to the progenitor of SN
1006. None of the stars within 4' of the apparent site of the explosion
is associated with the supernova remnant, so we can firmly exclude all giant
and subgiant companions to the progenitor. Combined with the previous results,
less than 20 per cent of type Iae occur through the single degenerate channel.Comment: Published as a letter in Nature (2012 September 27
Type Ia Supernova Scenarios and the Hubble Sequence
The dependence of the Type Ia supernova (SN Ia) rate on galaxy type is
examined for three currently proposed scenarios: merging of a
Chandrasekhar--mass CO white dwarf (WD) with a CO WD companion, explosion of a
sub--Chandrasekhar mass CO WD induced by accretion of material from a He star
companion, and explosion of a sub--Chandrasekhar CO WD in a symbiotic system.
The variation of the SNe Ia rate and explosion characteristics with time is
derived, and its correlation with parent population age and galaxy redshift is
discussed. Among current scenarios, CO + He star systems should be absent from
E galaxies. Explosion of CO WDs in symbiotic systems could account for the SNe
Ia rate in these galaxies. The same might be true for the CO + CO WD scenario,
depending on the value of the common envelope parameter. A testable prediction
of the sub--Chandrasekhar WD model is that the average brightness and kinetic
energy of the SN Ia events should increase with redshift for a given Hubble
type. Also for this scenario, going along the Hubble sequence from E to Sc
galaxies SNe Ia events should be brighter on average and should show larger
mean velocities of the ejecta. The observational correlations strongly suggest
that the characteristics of the SNe Ia explosion are linked to parent
population age. The scenario in which WDs with masses below the Chandrasekhar
mass explode appears the most promising one to explain the observed variation
of the SN Ia rate with galaxy type together with the luminosity--expansion
velocity trend.Comment: 16 pages uuencoded compressed Postscript, 2 figures included. ApJ
Letters, in pres
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