The Venus Twilight Experiment - Coconino Astronomical Society

The Venus Twilight Experiment - Coconino Astronomical Society

The Venus Twilight Experiment: probing the mesosphere in 2004 and 2012 Paolo Tanga1, T. Widemann2, A. Ambastha3, B. A. Babcock4, J. Berthier5, S. Bouley5, F. Braga-­‐
Ribas2, K. Brasch6, W. Burke7, F. Colas5, T. Fukuhara8, L. Fulham9, M. Imai8, M. Lu4, P. Machado2,10, L. Maquet5, J. M. Pasachoff4, J. Roberts11, G. Schneider12, W. Sheehan6, C. Sigismondi13, N. Thouvenin5, F. Vachier5, C. Veillet14 , X. Wang15 1Laboratoire Lagrange UMR7293, Univ. de Nice Sophia An>polis, CNRS, Observatoire de la Cote d'Azur, France, 2Observatoire de Paris/LESIA, CNRS, UPMC, Université Paris-­‐Diderot, France, 3Solar Observatory of Uidapur, India, 4Williams College, 5IMCCE/Obs. de Paris, France, 6Lowell Observatory, 7Coconino Astronomical Society,
8Hokkaido University, Japan, 9Moondarra Obs., Australia, 10CAAUL, Lisbon Observatory, Portugal, 11AIA, USA, 12Steward Observatory, Univ. of Arizona, 13ICRA, Italy, 14Canada France Hawaii Telescope, 15Huairou Solar Observing Sta>on, Na>onal Observatories of China, Chinese Academy of Science. The aureole is due to refracWon Simple model: Baum and Code (1953) – theory of refracWve stellar occultaWons Devia?on ω and a@enua?on of flux Φ are related to H and thickness of the refracWng layer Sky r1/2 : closest approach distance corresponding to Φ = 0.5 k : geometric parameter Sun Paolo Tanga – DPS Reno Oct 19 2012 2 Model features •  Transparent atmosphere •  Opaque layer: transiWon following the absorpWon profiles by Wilquet et al. 2008 τ = 1 at ro •  For a given geometry the aureole brightness depends upon: Δr = ro-­‐r1/2 H : scale height Paolo Tanga – DPS Reno Oct 19 2012 3 The aureole from 2004 to 2012: moWvaWons •  2004: –  confirmaWon of historical observaWons –  first photometry of the aureole –  measure of mesospheric scale height possible: Tanga, Widemann, Sicardy et al. Icarus 2012 (Dutch Open Telescope data) large range of laWtudes at the same Wme S. Rondi, coronagraph June 8, 2004 •  2012, goals: –  improve SNR + mulWple wavelengths –  exploit at best our last transit opportunity –  improve refracWon model Paolo Tanga – DPS Reno Oct 19 2012 4 Sites/expediWons F
10 nm filters OC
ard, n
g
i
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A 450 , 535 , 607 , 760 nm B V R I Paolo Tanga – DPS Reno Oct 19 2012 5 Longyearbyen, Norway Egress – I-­‐filter (760 nm) T. Widemann Nayoro, Japan Egress – V-­‐filter (760 nm) Mount-­‐Isa, Australia Egress – I-­‐filter (760 nm) F. Braga-­‐Ribas Tien Shan, Kazakhstan Egress – B-­‐filter (450 nm) Paolo Tanga – DPS Reno Oct 19 2012 Haleakala, Maui Ingress – B-­‐filter (450 nm) J. Pasachoff Udaipur, India Egress – R-­‐filter (607 nm) 6 P. Tanga, Laboratoire Lagrange, Obs. de la Côte d’Azur; Th. Widemann, LESIA, Obs. de Paris - Venus Twilight Experiment
Venus Twilight Experiment
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N Aureole at ingress, on June 5, 2012
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P. Tanga,Venus Twilight Coronagraph at Lowell Observatory, Arizona, USA
mardi 5 juin 12
Lowell obs., AZ Ingress – V-­‐band (535 nm) P. Tanga Paolo Tanga – DPS Reno Oct 19 2012 7 Aureole photometry, first results N f f = 0.5 Lowell – V band Haleakala – B band equator N V Normalized at the photospheric brightness at 1 Rv from the limb. Consistent with Ehrenreich et al. 2012 B Paolo Tanga – DPS Reno Oct 19 2012 8 Lightcurves at ingress 1st contact N 2nd contact 80° 0° 40° N 60° N Solar Dynamic Observatory, HMI 761 nm (P. Scherrer, J. Schou) Paolo Tanga – DPS Reno Oct 19 2012 9 2004 and 2012 – polar regions 2012 N 2nd contact 2004 1st contact 2004 data from Tanga et al., Icarus 2012 Paolo Tanga – DPS Reno Oct 19 2012 10 2004 and 2012 – low laWtudes 2004 2012 N 3rd contact 4th contact morning side Paolo Tanga – DPS Reno Oct 19 2012 11 1st contact Model: new perspecWves Polar region, 80° N 2nd contact Δr = 58 km, H = 7.3 km StraWficaWon required: •  Upper layer: –  high H –  Large alWtude range Δr = 20 km •  “deeper” layer –  Low H –  Thinner range Paolo Tanga – DPS Reno Oct 19 2012 12 Conclusions •  ConfirmaWon of the polar region (asymmetric) brightness peak -­‐ Δr = 58 km, H = 7.3 km •  Slightly red aureole consistent with Ehrenreich et al. 2012 •  Fainter aureole in 2012 wrt 2004 at mid/low-­‐laWtudes Related to variability in the mesosphere – extensive to global •  MulW-­‐layered model required in polar regions –  Involving deeper layers –  Possibility of retrieving a verWcal H profile (à temperature) –  Role of diffusion? Paolo Tanga – DPS Reno Oct 19 2012 13