Supernovae represent the violent explosions of massive stars which have reached the end of their life-cycle. These massive explosions where the
bulk of a star's material is ejected into space and the interstellar medium are characterized with luminosities which easily can exceed that of
the host galaxy for a brief period of a few weeks or even months. This ejection of material including heavy elements is both vital and critical
for new generations of stars and exoplanets.
Supernovae are classified into one of two primary types. White dwarfs which gain matter via accretion have their cores collapse once they approach the Chandrasekhar limit of 1.38 solar masses, thus yielding a Type Ia supernova. Accretion of matter can be accomplished by a variety of means including via a close binary star companion or a merger with another white dwarf. In contrast, type Ib and Ic involve large stars which have exhausted their available fuel and collapse due to gravity. Type II supernovae involve much more massive stars (at least nine solar masses) where the nuclear fusion follows a steady path from lighter to progressively heavier elements (such as hydrogen to helium which is then converted to carbon etc) and until nuclear fusion is no longer possible at the core due to the iron and nickel that has been accumulated, thus leading to a huge core collapse and an ensuing stellar explosion.
Spectroscopy has also played a key role in identifying the type of supernova one observes and, in fact, now forms the basis for their classification. More specifically, type Ia supernovae are characterized without any hydrogen emission lines in their spectra and in contrast to type II which exhibit strong hydrogen emission lines. Furthermore, type I are further subdivided on the basis of the presence of a silicon line (615nm, type Ia), a helium line (type Ib) or neither one (type Ic) in their spectra.
Many supernovae leave behind them spectacular gas clouds and stellar remnants (neutrinos) which cover multiple full moons in width across the sky. Regrettably, for residents of the northern hemisphere, only four supernova remnants (SNR) are visible and, more specifically, the Crab Nebula (M1) in Taurus, the massive Veil complex (NGC 6960, 6974, 6979, 6992, 6995) in Cygnus, the Jellyfish Nebula (IC 433) in Gemini and Simeis 147 (aka Shajn 147, Sh 2-240) also in Taurus. The most recognized supernova remnant is perhaps the Crab nebula in Taurus which is believed to have exploded in 1054 AD as documented by Chinese astronomers of the time whereas Simeis 147 is especially dim and represents one of the faintest objects in the sky.
In contrast to supernovae where the star is ultimately destroyed, novae represent precisely the opposite scenario where the explosions involved and the consequent release of matter into space involve the (white dwarf) star remaining intact. Once enough material has been accredited from a nearby companion red dwarf, one will observe a new explosion and outburst. Some of the brightest novae observed during the past one hundred years or so are available here.
Note: For the CBAT announcement involving Nova Delphini 2013, click here whereas spectroscopic details are available here and here. Further details from the International Variable Star Index are available here whereas an AAVSO finder chart is available here. For the latest AAVSO light curve and associated observations, click here.
Note: Differential photometry yields a magnitude estimate of 6.08 + 0.01 using SAO 88610 (mag 8.043 (V) as per GSC-ACT) for the reference star and SAO 88584 as the check star for August 15.0111 UT. Nova Delphini 2013 reached a maximum magnitude of 4.3 approximately on August 16.45 UT (further details here).
Nova Delphini 2013
RA / Dec:
20h 23m 30.73s /
+20° 46' 04.1"
H-a / CO
Aug 15, 2013
03:14 - 03:18 UT+3
AP 305/f3.8 Riccardi-Honders
AP 1200GTO GEM
SBIG LRGB CCD filters
1.21" per pixel