Where is the best site on Earth?
Dome A, B, C and F, and Ridges A and B
Will Saunders, Jon S. Lawrence, John W. V. Storey,
and Michael C.B. Ashley
submitted to PASP 16/05/09
The Antarctic plateau contains the best sites on Earth.
Where is the best on Antarctica?
to compare ..
Boundary layer thickness
Atmospheric thermal backgrounds
Precipitable water vapor (PWV)
temperature thermal backgrounds
All Antarctic sites are compromised for optical work by airglow and aurorae.
Dome A is the best site overall.
Dome F is remarkably good site.
‘OH hole’ exists in Spring at Dome C
This analysis combines,
Boundary layer characteristics(1)
○Boundary Layer Thickness
predicted wintertime median
boundary layer thickness
Dome F has the thinnest height at 18.5m,
Dome A is 21.7m, Ridge B is <24m,
Dome C is 27.7m.
The height is important for design and cost.
But, surface seeing is not perfectly correlated
with boundary layer thickness.
Boundary layer characteristics(2)
○Surface Wind Speed
Dome F offers the most quiescent conditions,
followed by Dome A /Ridge B, and Dome C.
Average seasonal cloud cover map,
July 2002 – July 2007
The least cloud cover occurs during
the winter (and spring?).
from an analysis of Aqua MODerate-resolution
Imaging Spectroradiometer (MODIS) image,
by Cloud and Earths Rediant Energy Experiment
Nighttime fractional cloud cover from
satellite instruments for 18 Sep. 11 Nov.
from the Ice, Cloud, and Elevation Satellite
Geoscience Laser Altimeter System (GLAS)
The opaque cloudiness was nearly
non-existent over all of the sites.
from the Cloud-Aerosol Lidar and Infrared
Pathfinder Satellite Observations (CALIPSO)
While Dome C has the least cloud cover,
it is only 4% less than Dome F.
Aurorae and sky brightness(1)
geomagnetic latitude (Λ)
Magnetic Local Time(MLT)
Aurorae brighten the sky most in U, B, V.
The strongest aurorae → 60°<|Λ|<75°, MLT=12
Using the auroral models of H91,
H91 give average solar activity level Kp, running from 1 to 6.
Aurorae and sky brightness(2)
Dome A, Dome C and Ridge B all have
remarkably similar, at a lebel ～23m/arcmin^2
The optical sky brightness at Dome F is
dominated by aurorae, most of the time.
557.7nm and 630nm
WINDII satellite allow predictions to be made
for OI and OH emission.
OI emission is very strong in Antarctica.
OH emission , the Antarctic winter value are
～30% higher, but ‘OH hole’ exist on October,
with 6 time less than at temperate sites.
as far from the Pole as possible = Dome C
Atmospheric thermal emission
The atmospheric thermal emission is determined both
by the total mass of each atmospheric component above site,
and its temperature profile.
Dome C is predicted to be brighter than
Dome A by about a factor of 2.
For the Kdark window, the useable
passband at Dome A is about 15%
wider than that at Dome C.
Precipitable water vapor
MHS experiment on the NOAA-18 satellite
The best location is between
Dome A, and Dome F
The coldest possible surface temperature is impress
the lowest telescope emission in the thermal infrared.
The ridge along Dome F – Dome A-ridge B defines
the coldest regions.
form the Aqua/MODIS
data for 2004-207
Free atmosphere seeing(1)
Estimating the seeing directly from meteorological data
is extremely uncertain because the turbulent layers
much thinner than the resolution.
We confident the best seeing will be associated with
the lowest wind speeds.
Assumption that |dV/dz| are proportional to the wind speeds.
NCAR/NCEP reanalysis data
Mean winter wind speed as a function
Free atmosphere seeing(2)
The best free seeing is at South Pole
First time-series optical photometry
sIRAIT monitoring of the RS CVn binary V841 Centauri
and the δ-Scuti star V1034 Centauri
K. G. Strassmeier, R. Briguglio, T. Granzer,
G. Tosti, I. DiVarano, I. Savanov, M. Bagaglia,
S. Castellini, A. Mancini, G. Nucciarelli, O. Straniero,
E. Distefano, S. Messina, G. Cutispoto
The polar location telescope achieve long and continuous time-series photometry.
Approximately 13,000 CCD frame (continuous 243hours) taken in July 2007
spotted binary star
・Spot filling factor is 44%
・0.2-day fundamental period is known
・Temperature difference photosphere ・Found a total of 23 further periods
– spot is 750+/-100K
・Rotation period 5.8854+/-0.0026days
The data quality is 3-4 times better than ever because there is low scintillation
noise at Dome C.
Time-series photometry is a powerful tool to understand cosmic variabilities and
their many underlying physical mechanisms.
・World-wide network telescope
・Polar site telescope
absent 24-hour day-night cycle
constantly stable atmosphere
A continuous 1500-hours night opens up a new window for science cases like
the search for extra-solar planets, for astroseismology, and for stellar rotation
and activity studies.
δScuti stars ・・・ have a complex surface oscillation spectrum
→ internal stellar structure
Spotted stars・・・ Magnetic spots, tracers of the internal dynamo activity
→ spot size / temperature
・single-lined spectroscopic binary with an active K1 subgiant
・strong CaII H&K and Hαemission
・Lithium abundance log n=0.77 → comparably young system
・v sin i=33+/-2km/s
・The orbit is circular with a period of 5.998 days.
・The photometric (=rotational) period of the K1 subgiant is 5.929+/-0.024 days
→ the orbital motion and the stellar rotation are bound ?
・A9IV δ-Sct star
・period of 0.235 days
25cm f/12 Cassegrain, parallactic mount
1m above the ground
moved by two extreme environment stepper motors
MaxCam CCD by Finger Lakes Instruments
768×512 9μm pixel →FOV8’×5.3’, 0.65”/pixel
with filter wheel(U,B,V,R,I)
CCD temperature is set at -28℃+/-0.3℃
5℃+/-2℃ in the drivers box
at Dome C
・A spatially non-uniform gain of the CCD
→due to the controller or the environment ?
・Comparison stars are at least 4 mag fainter
→using the δ-Scuti star V1034 Cen as the comparison star for V841 Cen
・Suddenly decrease/increase the count
→due to the CCD controller ?
→exponentially resettled to the previous count rate within ～10 hours
・The telescope has pointing and tracking error
→Repositioning was done manually after an hour or so
→photometric aperture did not always enclose exactly the same pixels.
About 13,000 frame taken July6-16, 2007
consecutive BVR frames with 60s, 50s, 40s integration time respectively.
temperature around -72℃+/-2℃
seeing varied between 2.8” and 5-6”
photometric precision of sIRAIT for the
range 12.5m to 15.5m,
0.04m at 12.5m, and 0.4m at 15.5m
A simple linear fit to a 2.4-hour long V
and R data subset shows a standard
deviation of 3.0 and 4.2 mmag,
sky + detector limit
scintillation noise at Dome C
V841 Cen – V1034 Cen
It is possible to separate the light variability because of the star’s
significantly different variability periods and amplitudes (～6 times).
Result and discussion(1)
○The rotation period of V841 Cen
4 different period-search
・5.811 days ← Phase Dispersion Minimization
(Lafler&Kinman1965, Stellingwerf 1978)
・5.884 days ← Lomb-Scargle (Scargle 1982)
・5.8872 days ← Minimum String Length (Dworetsky1983)
・5.8854 days ← CLEAN algorithm (Roberts+1987)
rms of the four periods → 0.0026 days
The rotational period 5.998 days
The orbital period
synchronized to within 2%
an Older system?
Result and discussion(2)
○The pulsation spectrum of V1034 Cen
Result and discussion(3)
○A spot model for V841 Cen
New light-curve inversion code (Savanov&Strassmeier2008)
・stellar surface spot configuration from multi-color light curves
・spot-filling factor is a composite of a two temperature contribution
・Temperature 4390K(Nacascues+1998), 4700K(Flower1996)
・spectroscopic parallax → 63+26-13pc →Luminosity 2.3L◎
・projected rotational velocity 10+/-1km/s → radius Rsin i=1.16+/-0.12R◎
→ inclination 30°(4700K) or 26°(4400K)
f = 44+/-3% ΔT=750+/-100K
This would be needed to interpret the magnetic-flux emergence in such a binary
because the proximity of the companion star breaks the rotational symmetry
and cause a non-uniform surface flux distribution. (Holzwarth2004)
Result and discussion(4)
243 continuous hours of optical photometry
3mmag rms precision in V
a factor 3-4 betters ← scintillation noise smaller by a factor 3-4
We conclude that high-precision continuous photometry within the
turbulent grand layer just one meter above ground is feasible at