Observatoire de Paris LESIA Centro de Astronomia e ... · VLT/UVES results (Icarus - Machado et al., 2012) Machado et al. EPSC Madrid Sep. 24-28, 2012 . Observatoire de Paris –

Observatoire de Paris – LESIA Centro de Astronomia e Astrofísica de Lisboa

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, ([email protected])

2 - CAAUL- Observatório Astronómico de Lisboa

3 - Université de Versailles-Saint-Quentin-en-Yvelines, France

mailto:[email protected]


VLT Telescope at Paranal, Chile.

High resolution spectrograph UVES

UVES echelle

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). 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.

Machado et al. EPSC Madrid Sep. 24-28, 2012


0.3“

5 1

2

3

4

10.33”

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)

slit parallel to the rotation axis latitudinal gradient

slit parallel to equator, spatial variability in local time (longitude).





Topographic map of the Zonal Wind (absolute)



Synthesis of vertical and horizontal observations

PL 1 PL 3

PL 2

VLT/UVES results (Icarus - Machado et al., 2012)



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



Synthesis of vertical and horizontal observations

PL 1 PL 3

PL 2


Date : 15Feb09 – Instrument : ESPaDOnS spectropolarimeter mounted at 3.6-m CFHT – 370-1050nm – single exposures, R = 80,000 Relative stability 5-10 m/s rms – 1.6 arc sec.

Canada-France-Hawaii-Telescope ESPaDOnS spectropolarimeter – Feb. 15, 2009




Solar lines, cloud top (70 km) ndeg = 74 : sqrt (chi2/(ndeg-1)) : = 4.03 2 : v equator = (110.1 +/- 11.0) m/s



VIRTIS-M cloud top tracking veq = - (102 ± 10) m/s

(Sánchez-Lavega et al., 2008) Ground-based Doppler - sequential 2-4 Jul. 2007 : veq = - (104 ± 10) m/s

(Widemann et al., 2008) Ground-based Doppler – long slit May 2007 : veq = -(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



Zonal velocity temporal variation, by latitude stretchs – Feb. 15, 2009UT

Feb. 15 2009 dayside cloud top instantaneous zonal wind












Zonal – time-averaged


Latitude v_zonal sigma2 chi2min 0.000 89.000 9.000 2.485 11.300 97.000 23.000 2.491 22.500 105.000 27.000 3.222 33.800 98.000 17.000 1.979 45.000 102.000 35.000 2.858 56.300 -3.000 54.000 1.888 -11.300 39.000 49.000 1.864 -22.500 91.000 24.000 2.551 -33.800 101.000 32.000 3.103 -45.000 124.000 46.000 6.228 -56.300 156.000 93.000 4.940


Zonal – temporal variation

#Temps Latitude v_zonal sigma2_p sigma2_m reference_temp 0.848 0.000 61.000 2.000 2.000 89.000 0.856 11.300 83.000 12.000 13.000 97.000 0.865 22.500 93.000 27.000 27.000 105.000 0.873 33.800 96.000 19.000 19.000 98.000 0.883 0.000 82.000 2.000 2.000 89.000 0.893 45.000 70.000 21.000 21.000 102.000 0.905 56.300 -35.000 82.000 82.000 -3.000 0.919 0.000 84.000 21.000 20.000 89.000 0.928 -11.300 39.000 49.000 49.000 39.000 0.937 -22.500 91.000 24.000 24.000 91.000 0.945 -33.800 101.000 32.000 31.000 101.000 0.954 0.000 86.000 7.000 7.000 89.000 0.963 -45.000 124.000 46.000 46.000 124.000 0.972 -56.300 156.000 93.000 97.000 156.000 0.980 0.000 96.000 25.000 25.000 89.000 0.988 0.000 153.000 56.000 55.000 89.000 0.996 11.300 118.000 44.000 45.000 97.000 1.006 22.500 137.000 49.000 49.000 105.000 1.013 33.800 127.000 67.000 67.000 98.000 1.022 0.000 118.000 36.000 36.000 89.000 1.029 45.000 143.000 43.000 43.000 102.000 1.037 56.300 16.000 76.000 76.000 -3.000


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.



2-regime fit of meridional wind

component at cloud top along meridians


ELong. v_zonal v_merid sigma2_z sigma2_s

30.000 129.000 23.000 63.000 13.000 36.294

45.000 103.000 18.000 18.000 15.000 54.443

70.000 75.000 4.000 11.000 17.000 56.110

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


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 = 110.1 +/- 11.0 m/s. • Spatial and teporal variability (bands of 11.25 ) 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.


Centro de Astronomia e Astrofísica de Lisboa Observatoire de Paris – LESIA

The End Machado et al. EPSC Madrid Sep. 24-28, 2012


1

5900-6700 Å

4800-5700 Å

Northern Region Southern Region

Reference Point

2007-05-27 22:50

Shift retrieval: example relative shift curve






•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


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 (0.37–1.05 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 19-20 February 2011 and were coordinated

with Visual Monitoring Camera (VMC) observations by Venus Express.


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Observatoire de Paris LESIA Centro de Astronomia e ... · VLT/UVES results (Icarus - Machado et al., 2012) Machado et al. EPSC Madrid Sep. 24-28, 2012 . Observatoire de Paris –