(unusually) the science
instrument. Photometric measurements were
recorded several times
per second.
Figure 7.
Predicted track of Quaoar
during an occultation
attempt on August 5,
2013. This event was
another “near-miss” at
Gemini South.
One of the challenges
of these observations
is that the catalogued
positions of many of the
stars are not sufficiently
precise to predict an
occultation with certainty. The team uses observations from the
Canada-France-Hawaii Telescope (CFHT)
Legacy Survey to make the predictions of
upcoming occultations, and then they only
observe events that have the highest probability of being successful. Despite these
efforts, to date no occultation event of the
large (1000-kilometer-diameter) Quaoar has
been observed. Nonetheless, as previously
mentioned, full analysis of the observations
obtained on July 13, 2013, at Gemini South
set useful limits on the atmosphere.
References:
Fraser, W., et al., The Astrophysical Journal Letters, 774: L18, 2013
Fraser, W., et al., The Publication of the Astronomical Society of the Pacific, 125: 1000, 2013
July 2013
Figure 8.
Images of the SN 2007gr
environment extracted
from the integral field
unit observations
corresponding to
Ha and V band. A
green circle marks
the supernova host
star cluster, and other
nearby star clusters
(SC-B, etc.) are noted.
32
Mass, Metallicity, and History of
Supernova Progenitors
laborators determine the properties of supernova progenitors through observations
of the stellar population at the host sites.
This study concentrates on the local environments of Type Ib and Ic supernovae — those
that do not show hydrogen in their spectra
and likely result from the core collapse of
massive stars, specifically, Wolf-Rayet stars.
Strong stellar winds or mass loss to a companion could strip the outer hydrogen layers
of a progenitor. Indeed, the team generally
found the Type Ic supernovae in more metal-rich environments than the Type Ibs. Furthermore, both types have higher metallicity
than Type II supernovae, which are also due
to core collapse of massive stars but have retained their hydrogen shells. The higher metallicity would promote mass loss through
stellar winds.
Another difference between the Types Ib
and Ic is that the latter are generally younger,
implying more massive stellar progenitors.
Some of the progenitors of both types are
less massive than about 25 times the Sun’s
mass and thus not massive enough to be
stripped Wolf-Rayet stars. T \