Measurements of Venus dayside winds with CFHT/ESPaDOnS and VLT/UVES

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1 Measurements of Venus dayside winds with CFHT/ESPaDOnS and VLT/UVES Characterization of cloud top dynamics of Venus with ground-based Doppler velocimetry P. Machado(1,2), T. Widemann (1,3), D. Luz (2), J.Peralta (2) 1 - Paris Observatory/LESIA, (pedro.machado@obspm.fr) 2 - CAAUL- Observatório Astronómico de Lisboa 3 - Université de Versailles-Saint-Quentin-en-Yvelines, France

2 We applied the technique of Doppler velocimetry to the solar Fraunhofer lines (visible) in high resolution spectra obtained with VLT (8m) + UVES (R~100,000). VLT Telescope at Paranal, Chile. UVES echelle This technique allows to determine Doppler shifts with a high precision (absolute accelerometry, Connes, 1985). The spectrograph analyses the solar radiation scattered by the upper cloud layer, where τ~1, located at about 70 km altitude, where the retrograde zonal super-rotation reaches its maximum velocity. High resolution spectrograph UVES

3 slit parallel to the rotation axis latitudinal gradient slit parallel to equator, spatial variability in local time (longitude) The method allows to simultaneously characterize the zonal wind spatial and temporal variations across the dayside. In both cases it is possible to detect non-zonal components (meridional, SS-AS)

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5 Topographic map of the Zonal Wind (absolute)

6 VLT/UVES results (Icarus - Machado et al., 2012) Synthesis of vertical and horizontal observations PL 2 PL 1 PL 3

7 VLT/UVES results (Machado et al., 2012) Comparison from Ground based Doppler velocimetry and cloud tracking Galileu and VIRTIS UV results Machado et al. EPSC Madrid Sep , 2012

8 Synthesis of vertical and horizontal observations PL 2 PL 1 PL 3

9 Canada-France-Hawaii-Telescope ESPaDOnS spectropolarimeter Feb. 15, 2009 Date : 15Feb09 Instrument : ESPaDOnS spectropolarimeter mounted at 3.6-m CFHT nm single exposures, R = 80,000 Relative stability 5-10 m/s rms 1.6 arc sec.

10 Solar lines, cloud top (70 km) n deg = 74 : sqrt (chi2/(n deg -1)) : = : v equator = ( /- 11.0) m/s

11 VIRTIS-M cloud top tracking v eq = - (102 ± 10) m/s (Sánchez-Lavega et al., 2008) Ground-based Doppler - sequential 2-4 Jul : v eq = - (104 ± 10) m/s (Widemann et al., 2008) Ground-based Doppler long slit May 2007 : v eq = -(106 ± 21) m/s to -(127 ± 14) m/s (Machado et al., 2012) Coherence between ground-based and VEx cloud tracking for the background longitudinally averaged) zonal circulation

12 Feb dayside cloud top instantaneous zonal wind Zonal velocity temporal variation, by latitude stretchs Feb. 15, 2009UT

13 Feb dayside cloud top instantaneous zonal wind Zonal velocity temporal variation, by latitude stretchs Feb. 15, 2009UT

14 Feb dayside cloud top instantaneous zonal wind Zonal velocity temporal variation, by latitude stretchs Feb. 15, 2009UT Machado et al. EPSC Madrid Sep , 2012

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16 Zonal time-averaged Latitude v_zonal sigma2 chi2min

17 Zonal temporal variation #Temps Latitude v_zonal sigma2_p sigma2_m reference_temp Significant variation from 70.0 ± 21 m/s to 143 ± 43 m/s (2 ) at 45.0 N in a 3h25m interval in northern mid-latitude jet region.

18 2-regime fit of meridional wind component at cloud top along meridians ELong. v_zonal v_merid sigma2_z sigma2_s Marginal detection of a meridional regime along three sequential data meridians assuming a sinus function, 0 at 0 and 90 deg, max at 45 deg

19 Conclusion VLT/UVES : Mean zonal wind -(106 21) m/s to -(127 14) m/s at latitudes between 18N and 34S. Moderate jets near 50 S and 50 N. Small scale wind variations with local time. First ground-based characterization of the latitudinal profile of zonal wind, first zonal wind field map in the visible CFHT/ESPaDOnS : mean zonal wind cloud top consistent with other techniques: v equator = / m/s. Spatial and teporal variability (bands of ) by inversion of Doppler wind field parallel to the equator. Marginal meridional model flow detected at = 30 (23 13) m/s Doppler velocimetry allows to derive the absolute wind s velocity value and correlate them with winds determined from cloud tracking in the VEx VIRTIS-M and VMC UV images, and their temporal variation.

20 Observatoire de Paris LESIA Machado et al. EPSC Madrid Sep , 2012 The End

21 Shift retrieval: example relative shift curve : Å Reference Point Å Northern Region Southern Region Machado et al. EPSC Madrid Sep , 2012

22 Machado et al. EPSC Madrid Sep , 2012

23 With ESPaDOnS, the complete optical spectrum, from 370 to 1050 nm, is collected over 40 spectral orders in a single exposure at a resolution of about 80,000 (Donati et al., 1997). Our choice of observing dates offers the best compromise between the need to (i) maximize the angular diameter of Venus and spatial resolution on the disk, and (ii) minimize Venus phase angle and illuminated fraction as we work on the dayside only. Observations February 2011 Machado et al. EPSC Madrid Sep , 2012

24 Coordinated Ground and Spatial observations We present an analysis of Venus Doppler winds at cloud tops based on observations made at the Canada France Hawaii 3.6-m telescope (CFHT) with the ESPaDOnS visible spectrograph. These observations consisted of high-resolution spectra of Fraunhofer lines in the visible range ( μm) to measure the winds at cloud tops using the Doppler shift of solar radiation scattered by cloud top particles in the observer s direction (Widemann et al., 2007, 2008). The observations were made during February 2011 and were coordinated with Visual Monitoring Camera (VMC) observations by Venus Express. Machado et al. EPSC Madrid Sep , 2012