Where is the best site on Earth? Dome A, B, C and F, and Ridges A and B

1. 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 arXiv:0905.4156 submitted to PASP 16/05/09 2009年6月24日(水) みさゼミ　雑誌紹介 M2 沖田博文

2. Abstract The Antarctic plateau contains the best sites on Earth. Where is the best on Antarctica? to compare .. Boundary layer thickness Cloud cover Auroral emission Airglow Atmospheric thermal backgrounds Precipitable water vapor (PWV) temperature thermal backgrounds Free-atmosphere seeing South Pole Dome A Dome C Dome F Ridge A Ridge B All Antarctic sites are compromised for optical work by airglowand aurorae. Dome A is the best site overall. Dome F is remarkably good site. ‘OH hole’ exists in Spring at Dome C

3. Introduction This analysis combines, Satellite data published results atmospheric model Dome F Ridge A Dome A Dome B South Pole Ridge B Dome C

4. 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. Swain&Gallee(2006)

5. Boundary layer characteristics(2) ○Surface Wind Speed Dome F offers the most quiescent conditions, followed by Dome A /Ridge B, and Dome C. Swain&Gallee(2006) Parish&Bromwich (2007) van Lipzig+(2004)

6. Cloud cover(1) 0.0 Average seasonal cloud cover map, July 2002 – July 2007 Spring Summer The least cloud cover occurs during the winter (and spring?). 1.0 Fall Winter from an analysis of Aqua MODerate-resolution Imaging Spectroradiometer (MODIS) image, by Cloud and Earths Rediant Energy Experiment (CERES)

7. Cloud cover(2) 0.0 Nighttime fractional cloud cover from satellite instruments for 18 Sep. 11 Nov. 2003. 1.0 (a)GLAS (b)Aqua CERES-MODIS from the Ice, Cloud, and Elevation Satellite Geoscience Laser Altimeter System (GLAS)

8. Cloud cover(3) The opaque cloudiness was nearly non-existent over all of the sites. opaque cloud all cloud 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.

9. Aurorae and sky brightness(1) solar activity geomagnetic latitude (Λ) Magnetic Local Time(MLT) Auroral activity 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.

10. Aurorae and sky brightness(2) Kp=6 Kp=4 Kp=2 Kp=0 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.

11. Airglow OI OI 557.7nm and 630nm NO2 500-650nm OH 700-2300nm WINDII satellite allow predictions to be made for OI and OH emission. OH OI emission is very strong in Antarctica. OH emission , the Antarctic winter value are ～30% higher, but ‘OH hole’ exist on October, with6 time lessthan at temperate sites. as far from the Pole as possible = Dome C Liu+(2008)

12. 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. Mauna Kea South Pole Dome A For theKdark window, the useable passband at Dome A is about 15% wider than that at Dome C. Lawrence(2004)

13. Precipitable water vapor MAR model MHS experiment on the NOAA-18 satellite The best location is between Dome A, and Dome F Swain&Gallee(2006)

14. Surface temperature 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. Swain&Gallee(2006) Observed temperature form the Aqua/MODIS data for 2004-207

15. 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 of pressurelevel(600,500,400,300,200, 150,100,70,50,30,20,10mb)

16. Free atmosphere seeing(2) The best free seeing is atSouth Pole

17. Conclusions

19. First time-series optical photometry from Antarctica 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 2008A&A.490.287 2009年6月24日(水) みさゼミ　雑誌紹介 M2 沖田博文

20. Abstract The polar location telescope achieve long and continuous time-series photometry. Approximately 13,000 CCD frame (continuous 243hours) taken in July 2007 V841 Cen chromospherically active, spotted binary star V1034 Cen non-radially pulsating δ-Scuit star ・Spot filling factor is 44% ・Temperature difference photosphere – spot is 750+/-100K ・Rotation period 5.8854+/-0.0026days ・0.2-day fundamental period is known ・Found a total of 23 further periods The data quality is 3-4 times better than ever because there is low scintillation noise at Dome C.

21. Introduction(1) Time-series photometry is a powerful tool to understand cosmic variabilities and their many underlying physical mechanisms. different instrument/ detector/calibration × ・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.

22. Introduction(2) δScuti stars ・・・　have a complex surface oscillation spectrum (V1034 Cen) → internal stellar structure Spotted stars・・・　Magnetic spots, tracers of the internal dynamo activity (V841 Cen) → spot size / temperature CCD FOV

23. Target stars V841 Cen ・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 ? V1034 Cen ・A9IV δ-Sct star ・period of 0.235 days

24. Instrument 25cm f/12 Cassegrain, parallactic mount 1m above the ground moved by two extreme environment stepper motors sIRAIT 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 CCD camera at Dome C http://www-luan.unice.fr/~mekarnia/hivernage/fevrier.html

25. Problems encountered ・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.

26. Data(1) 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, respectively. σ(R)0.0042 σ(V)0.003 sky + detector limit scintillation noise at Dome C

27. Data(2) 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).

28. 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 5.8854 days synchronized to within 2% Lithium abundance an Older system?

29. Result and discussion(2) ○The pulsation spectrum of V1034 Cen 24 are ranked

30. 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)

31. Result and discussion(4)

32. Conclusions 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 Dome C.