314 research outputs found
Optical Night-Sky Brightness at Mauna Kea over the Course of a Complete Sunspot Cycle
We have produced a data base of V-band and B-band night-sky brightness
measurements rather evenly spread out over the course of a whole sunspot cycle
from September 1985 to August 1996. Almost all the data were obtained at the
2800-m level of Mauna Kea using the same telescope, same photomultiplier tube,
filters, and diaphragm, thus minimizing various sources of systematic error and
allowing an estimate of the sources of random error. The yearly V-band averages
of observed sky brightness ranged from 21.287 to 21.906 magnitudes per square
arc second. The color of the sky is = 0.930 and does not change
discernibly over the course of the sunspot cycle. After correcting the V-band
data to the zenith, we find that the airglow component varied a factor of 4.5
over the course of the solar cycle. Once the 11-year solar cycle effect is
removed from the data, the most significant contribution to the scatter of
individual data points appears to be the short term variations on time scales
of tens of minutes like those observed by the Whole Earth Telescope project.Comment: 27 pages AAS-style (v 4.0) Latex, 5 figures, to be published in
Publications of the Astronomical Society of the Pacifi
Recommended from our members
A high resolution millimetre and submillimetre study of W3
The continuum bolometer receiver on the James Clerk Maxwell telescope has been used to map the dense core of the star formation region W3 with a spatial resolution of 15-20 arcsec. At 350 and 800 μm, the region appears as two principal peaks around the known IR sources IRS4 and IRS5, while at 1100 μm, a further peak is noted which is interpreted as being due to free-free emission around IRS2. Taking into account the free-free contribution to the intensity, the continuum dust emission from the region is found to be consistent with optically thin emission at all of the three wavelengths considered. Values for the dust optical depth, hydrogen column density, mass, and central density have been obtained for each of the main peaks
Optical Sky Brightness at Cerro Tololo Inter-American Observatory from 1992 to 2006
We present optical UBVRI sky brightness measures from 1992 through 2006. The
data are based on CCD imagery obtained with the CTIO 0.9-m, 1.3-m, and 1.5-m
telescopes. The B- and V-band data are in reasonable agreement with
measurements previously made at Mauna Kea, though on the basis of a small
number of images per year there are discrepancies for the years 1992 through
1994. Our CCD-based data are not significantly different than values obtained
at Cerro Paranal. We find that the yearly averages of V-band sky brightness are
best correlated with the 10.7-cm solar flux taken 5 days prior to the sky
brightness measures. This implies an average speed of 350 km/sec for the solar
wind. While we can measure an enhancement of the night sky levels over La
Serena 10 degrees above the horizon, at elevation angles above 45 degrees we
find no evidence that the night sky brightness at Cerro Tololo is affected by
artificial light of nearby towns and cities.Comment: 24 pages, 5 figures, to be published in the June, 2007, issue of the
Publications of the Astron. Society of the Pacifi
A Physical Model for SN 2001ay, a normal, bright, extremely slowly declining Type Ia supernova
We present a study of the peculiar Type Ia supernova 2001ay (SN 2001ay). The
defining features of its peculiarity are: high velocity, broad lines, and a
fast rising light curve, combined with the slowest known rate of decline. It is
one magnitude dimmer than would be predicted from its observed value of
Delta-m15, and shows broad spectral features. We base our analysis on detailed
calculations for the explosion, light curves, and spectra. We demonstrate that
consistency is key for both validating the models and probing the underlying
physics. We show that this SN can be understood within the physics underlying
the Delta-m15 relation, and in the framework of pulsating delayed detonation
models originating from a Chandrasekhar mass, white dwarf, but with a
progenitor core composed of 80% carbon. We suggest a possible scenario for
stellar evolution which leads to such a progenitor. We show that the unusual
light curve decline can be understood with the same physics as has been used to
understand the Delta-m15 relation for normal SNe Ia. The decline relation can
be explained by a combination of the temperature dependence of the opacity and
excess or deficit of the peak luminosity, alpha, measured relative to the
instantaneous rate of radiative decay energy generation. What differentiates SN
2001ay from normal SNe Ia is a higher explosion energy which leads to a shift
of the Ni56 distribution towards higher velocity and alpha < 1. This result is
responsible for the fast rise and slow decline. We define a class of SN
2001ay-like SNe Ia, which will show an anti-Phillips relation.Comment: 35 pages, 14 figures, ApJ, in pres
Gamma Doradus Stars: Defining a New Class of Pulsating Variables
In this paper we describe a new class of pulsating stars, the prototype of
which is the bright, early, F-type dwarf, Gamma Doradus. These stars typically
have between 1 and 5 periods ranging from 0.4 to 3 days with photometric
amplitudes up to 0.1 in Johnson V. The mechanism for these observed variations
is high-order, low-degree, non-radial, gravity-mode pulsation. Gamma Doradus
stars exhibit variability on a time scale that is an order of magnitude slower
than Delta Scuti stars. They may offer additional insight into stellar physics
when they are better understood (e.g., they may represent the cool portion of
an "iron opacity instability strip" currently formed by the Beta Cephei stars,
the SPB stars, and the subdwarf B stars; they may also offer insight into the
presence of g-modes in solar-like stars).Comment: 15 pages, 1 ps figure. Accepted for publication in PAS
SALT2: using distant supernovae to improve the use of Type Ia supernovae as distance indicators
We present an empirical model of Type Ia supernovae spectro-photometric
evolution with time. The model is built using a large data set including
light-curves and spectra of both nearby and distant supernovae, the latter
being observed by the SNLS collaboration. We derive the average spectral
sequence of Type Ia supernovae and their main variability components including
a color variation law. The model allows us to measure distance moduli in the
spectral range 2500-8000 A with calculable uncertainties, including those
arising from variability of spectral features. Thanks to the use of
high-redshift SNe to model the rest-frame UV spectral energy distribution, we
are able to derive improved distance estimates for SNe Ia in the redshift range
0.8<z<1.1. The model can also be used to improve spectroscopic identification
algorithms, and derive photometric redshifts of distant Type Ia supernovae.Comment: Accepted for publication in A&A. Data and source code available at :
http://supernovae.in2p3.fr/~guy/salt
- …