91 research outputs found
Seeing, Wind and Outer Scale Effects on Image Quality at the Magellan Telescopes
We present an analysis of the science image quality obtained on the twin 6.5
metre Magellan telescopes over a 1.5 year period, using images of ~10^5 stars.
We find that the telescopes generally obtain significantly better image quality
than the DIMM-measured seeing. This is qualitatively consistent with
expectations for large telescopes, where the wavefront outer scale of the
turbulence spectrum plays a significant role. However, the dominant effect is
found to be wind speed with Magellan outperforming the DIMMs most markedly when
the wind is strongest. Excluding data taken during strong wind conditions (>10
m/s), we find that the Magellan telescopes still significantly outperform the
DIMM seeing, and we estimate the site to have L_0 ~ 25 m on average. We also
report on the first detection of a negative bias in DIMM data. This is found to
occur, as predicted, when the DIMM is affected by certain optical aberrations
and the turbulence profile is dominated by the upper layers of the atmosphere.Comment: Accepted for publication in PASP. 10 pages, 12 figures
MagAO: Status and on-sky performance of the Magellan adaptive optics system
MagAO is the new adaptive optics system with visible-light and infrared
science cameras, located on the 6.5-m Magellan "Clay" telescope at Las Campanas
Observatory, Chile. The instrument locks on natural guide stars (NGS) from
0 to 16 -band magnitude, measures turbulence
with a modulating pyramid wavefront sensor binnable from 28x28 to 7x7
subapertures, and uses a 585-actuator adaptive secondary mirror (ASM) to
provide flat wavefronts to the two science cameras. MagAO is a mutated clone of
the similar AO systems at the Large Binocular Telescope (LBT) at Mt. Graham,
Arizona. The high-level AO loop controls up to 378 modes and operates at frame
rates up to 1000 Hz. The instrument has two science cameras: VisAO operating
from 0.5-1 m and Clio2 operating from 1-5 m. MagAO was installed in
2012 and successfully completed two commissioning runs in 2012-2013. In April
2014 we had our first science run that was open to the general Magellan
community. Observers from Arizona, Carnegie, Australia, Harvard, MIT, Michigan,
and Chile took observations in collaboration with the MagAO instrument team.
Here we describe the MagAO instrument, describe our on-sky performance, and
report our status as of summer 2014.Comment: 13 pages, 11 figures, to appear in Proc. SPIE 9148-
Optical Properties of (162173) 1999 JU3: In Preparation for the JAXA Hayabusa 2 Sample Return Mission
We investigated the magnitude-phase relation of (162173) 1999 JU3, a target
asteroid for the JAXA Hayabusa 2 sample return mission. We initially employed
the international Astronomical Union's H-G formalism but found that it fits
less well using a single set of parameters. To improve the inadequate fit, we
employed two photometric functions, the Shevchenko and Hapke functions. With
the Shevchenko function, we found that the magnitude-phase relation exhibits
linear behavior in a wide phase angle range (alpha = 5-75 deg) and shows weak
nonlinear opposition brightening at alpha< 5 deg, providing a more reliable
absolute magnitude of Hv = 19.25 +- 0.03. The phase slope (0.039 +- 0.001
mag/deg) and opposition effect amplitude (parameterized by the ratio of
intensity at alpha=0.3 deg to that at alpha=5 deg, I(0.3)/I(5)=1.31+-0.05) are
consistent with those of typical C-type asteroids. We also attempted to
determine the parameters for the Hapke model, which are applicable for
constructing the surface reflectance map with the Hayabusa 2 onboard cameras.
Although we could not constrain the full set of Hapke parameters, we obtained
possible values, w=0.041, g=-0.38, B0=1.43, and h=0.050, assuming a surface
roughness parameter theta=20 deg. By combining our photometric study with a
thermal model of the asteroid (Mueller et al. in preparation), we obtained a
geometric albedo of pv = 0.047 +- 0.003, phase integral q = 0.32 +- 0.03, and
Bond albedo AB = 0.014 +- 0.002, which are commensurate with the values for
common C-type asteroids.Comment: 27 pages, 4 figure, accepted for publication in the Astrophysical
Journa
Do the photometric colors of Type II-P Supernovae allow accurate determination of host galaxy extinction?
We present infrared photometry of SN 1999em, plus optical photometry,
infrared photometry, and optical spectroscopy of SN 2003hn. Both objects were
Type II-P supernovae. The V-[RIJHK] color curves of these supernovae evolved in
a very similar fashion until the end of plateau phase. This allows us to
determine how much more extinction the light of SN 2003hn suffered compared to
SN 1999em. Since we have an estimate of the total extinction suffered by SN
1999em from model fits of ground-based and space-based spectra as well as
photometry of SN 1999em, we can estimate the total extinction and absolute
magnitudes of SN 2003hn with reasonable accuracy. Since the host galaxy of SN
2003hn also produced the Type Ia SN 2001el, we can directly compare the
absolute magnitudes of these two SNe of different types.Comment: 24 pages, 6 figure
First results of site testing program at Mt. Shatdzhatmaz in 2007 - 2009
We present the first results of the site testing performed at
Mt.~Shatdzhatmaz at Northern Caucasus, where the new Sternberg astronomical
institute 2.5-m telescope will be installed. An automatic site monitor
instrumentation and functionality are described together with the methods of
measurement of the basic astroclimate and weather parameters. The clear night
sky time derived on the basis of 2006 -- 2009 data amounts to 1340 hours per
year. Principle attention is given to the measurement of the optical turbulence
altitude distribution which is the most important characteristic affecting
optical telescopes performance. For the period from November 2007 to October
2009 more than 85\,000 turbulence profiles were collected using the combined
MASS/DIMM instrument. The statistical properties of turbulent atmosphere above
the summit are derived and the median values for seeing ~arcsec
and free-atmosphere seeing ~arcsec are determined.
Together with the estimations of isoplanatic angle ~arcsec and
time constant \tau_0 = 2.58 \mbox{ ms}, these are the first representative
results obtained for Russian sites which are necessary for development of
modern astronomical observation techniques like adaptive optics.Comment: Accepted for publication in MNRAS, 17 pages, 15 figure
H-alpha Spectral diversity of type II supernovae
We present a spectroscopic analysis of the H-alpha profiles of hydrogen-rich
type II supernovae. A total of 52 type II supernovae having well sampled
optical light curves and spectral sequences were analyzed. Concentrating on the
H-alpha P-Cygni profile we measure its velocity from the FWHM of emission and
the ratio of absorption to emission (a/e) at a common epoch at the start of the
recombination phase, and search for correlations between these spectral
parameters and photometric properties of the V-band light curves. Testing the
strength of various correlations we find that a/e appears to be the dominant
spectral parameter in terms of describing the diversity in our measured
supernova properties. It is found that supernovae with smaller a/e have higher
H-alpha velocities, more rapidly declining light curves from maximum, during
the plateau and radioactive tail phase, are brighter at maximum light and have
shorter optically thick phase durations. We discuss possible explanations of
these results in terms of physical properties of type II supernovae,
speculating that the most likely parameters which influence the morphologies of
H-alpha profiles are the mass and density profile of the hydrogen envelope,
together with additional emission components due to circumstellar interaction.Comment: Accepted for publication in ApJ letters. 9 pages, 3 figures, 2 table
UBVRIz Light Curves of 51 Type II Supernovae
We present a compilation of UBV RIz light curves of 51 type II supernovae
discovered during the course of four different surveys during 1986 to 2003: the
Cerro Tololo Supernova Survey, the Calan/Tololo Supernova Program (C&T), the
Supernova Optical and Infrared Survey (SOIRS), and the Carnegie Type II
Supernova Survey (CATS). The photometry is based on template-subtracted images
to eliminate any potential host galaxy light contamination, and calibrated from
foreground stars. This work presents these photometric data, studies the color
evolution using different bands, and explores the relation between the
magnitude at maximum brightness and the brightness decline parameter (s) from
maximum light through the end of the recombination phase. This parameter is
found to be shallower for redder bands and appears to have the best correlation
in the B band. In addition, it also correlates with the plateau duration, being
thus shorter (longer) for larger (smaller) s values.Comment: 110 pages, 9 Figures, 6 Tables, accepted in A
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