13 research outputs found
A faint type of supernova from a white dwarf with a helium-rich companion
Supernovae (SNe) are thought to arise from two different physical processes.
The cores of massive, short-lived stars undergo gravitational core collapse and
typically eject a few solar masses during their explosion. These are thought to
appear as as type Ib/c and II SNe, and are associated with young stellar
populations. A type Ia SN is thought to arise from the thermonuclear detonation
of a white dwarf star composed mainly of carbon and oxygen, whose mass
approaches the Chandrasekhar limit. Such SNe are observed in both young and old
stellar environments. Here we report our discovery of the faint type Ib SN
2005E in the halo of the nearby isolated galaxy, NGC 1032.
The lack of any trace of recent star formation near the SN location (Fig. 1),
and the very low derived ejected mass (~0.3 M_sun), argue strongly against a
core-collapse origin for this event. Spectroscopic observations and the derived
nucleosynthetic output show that the SN ejecta have high velocities and are
dominated by helium-burning products, indicating that SN 2005E was neither a
subluminous nor a regular SN Ia (Fig. 2). We have therefore found a new type of
stellar explosion, arising from a low-mass, old stellar system, likely
involving a binary with a primary white dwarf and a helium-rich secondary. The
SN ejecta contain more calcium than observed in any known type of SN and likely
additional large amounts of radioactive 44Ti. Such SNe may thus help resolve
fundamental physical puzzles, extending from the composition of the primitive
solar system and that of the oldest stars, to the Galactic production of
positrons.Comment: Revised to reflect published version in Nature, May 20th, 2010.
Additional data and analysis are include
Production of dust by massive stars at high redshift
The large amounts of dust detected in sub-millimeter galaxies and quasars at
high redshift pose a challenge to galaxy formation models and theories of
cosmic dust formation. At z > 6 only stars of relatively high mass (> 3 Msun)
are sufficiently short-lived to be potential stellar sources of dust. This
review is devoted to identifying and quantifying the most important stellar
channels of rapid dust formation. We ascertain the dust production efficiency
of stars in the mass range 3-40 Msun using both observed and theoretical dust
yields of evolved massive stars and supernovae (SNe) and provide analytical
expressions for the dust production efficiencies in various scenarios. We also
address the strong sensitivity of the total dust productivity to the initial
mass function. From simple considerations, we find that, in the early Universe,
high-mass (> 3 Msun) asymptotic giant branch stars can only be dominant dust
producers if SNe generate <~ 3 x 10^-3 Msun of dust whereas SNe prevail if they
are more efficient. We address the challenges in inferring dust masses and
star-formation rates from observations of high-redshift galaxies. We conclude
that significant SN dust production at high redshift is likely required to
reproduce current dust mass estimates, possibly coupled with rapid dust grain
growth in the interstellar medium.Comment: 72 pages, 9 figures, 5 tables; to be published in The Astronomy and
Astrophysics Revie