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ESPRESSO (Echelle SPectrograph for Rocky Exoplanet- and Stable Spectroscopic Observations) is a third-generation, fiber fed, cross-dispersed, echelle spectrograph for the European Southern Observatory's Very Large Telescope (VLT) is the successor of a line of echelle spectrometers (CORAVEL, Elodie, Coralie, HARPS). It measures changes in the light spectrum with great sensitivity, and will be used to search for Earth-like planets via the radial velocity method. For example, our Earth induces a radial-velocity variation of 9 cm/s on our Sun; this gravitational "wobble" causes minute variations in the color of sunlight, invisible to the human eye but detectable by the instrument. The telescope light is fed to the instrument via a Coude-Train optical system and fibers. ESPRESSO is located in the VLT Combined-Coude Laboratory (incoherent focus) where a front-end unit can combine the light from up to 4 Unit Telescopes (UT) of the VLT.
ESPRESSO is scheduled to begin scientific operations in 2017.
ESPRESSO will build on the foundations laid by the High Accuracy Radial Velocity Planet Searcher (HARPS) instrument at the 3.6-metre telescope at ESO’s La Silla Observatory. ESPRESSO will benefit not only from the much larger combined light-collecting capacity of the four 8.2-metre VLT Unit Telescopes, but also from improvements in the stability and calibration accuracy that are now possible (for example, laser frequency comb technology). The requirement is to reach 10 cm/s, but the aimed goal is to obtain a precision level of a few cm/s. This would mean a large step forward over current radial-velocity spectrographs like ESO's HARPS. The HARPS instrument can attain a precision of 97 cm/s (3.5 km/h), with an effective precision of the order of 30 cm/s, making it one of only two instruments worldwide with such accuracy. The ESPRESSO would greatly exceed this capability making detection of earth-like planets from ground based instruments possible. Installation and commissioning of ESPRESSO at the VLT is foreseen in 2016.
The instrument is capable of operating in 1-UT mode (using one of the telescopes) and in 4-UT mode. In 4-UT mode, in which all the four 8-m telescopes are connected incoherently to form a 16-m equivalent telescope, the spectrograph will reach extremely faint objects.
For example (for G2V type stars):
- Rocky planets around stars as faint as V ~ 9 in (in 1-UT mode)
- Neptune mass planets around stars as faint as V ~ 12 (in 4-UT mode )
- Earth-like planets around stars as faint as V ~ 9 (CODEX on the E-ELT) (2025)
ESPRESSO will focus the observations on the best-suited candidates: non-active, non-rotating, quiet G to M dwarfs. It will operate at the peak of its efficiency for a spectral type up to M4-type stars.
ESPRESSO will use as calibration a laser frequency comb (LFC), with backup of two ThAr lamps. It will have three instrumental modes: singleHR, singleUHR and multiMR. In the singleHR mode ESPRESSO can be fed by any of the four UTs.
- Opened to the Scientific Community by 2017
- Schedule: First light on Telescope: Second Part of 2016
- Preliminary Acceptance Europe, October 2015
- Final Design Review, May 2013
- Preliminary Design Review, November 2011
- Kick-off Meeting, January 2011
- Phase A Study Review Meeting, March 2010
The main scientific drivers for ESPRESSO are:
- The measurement of high precision radial velocities of solar type stars for search for rocky planets.
- The measurement of the variation of the physical constants (search for possible variations of the constants of nature at different times and in different directions through the study of the light from very distant quasars).
- The analysis of the chemical composition of stars in nearby galaxies.
ESPRESSO is being developed by a consortium consisting of ESO and seven further scientific institutes:
- Centro de Astrofísica da Universidade do Porto (Portugal).
- Faculdade de Ciências da Universidade de Lisboa, CAAUL & LOLS (Portugal).
- INAF–Osservatorio Astronomico di Trieste (Italy).
- INAF–Osservatorio Astronomico di Brera (Italy).
- Instituto de Astrofísica de Canarias (Spain).
- Physikalisches Institut der Universität Bern (Switzerland).
- Université de Genève (Switzerland).
Comparison between ESPRESSO and CODEX
|Telescope||VLT (8m)||E-ELT (39m)|
|Sky aperture||1 arcsec||0.80 arcsec|
|λ coverage||380nm-780nm nm||380–680 nm|
|λ precision||5 m/s||1 m/s|
|RV stability||< 10 cm/s||< 2 cm/s|
|4-VLT mode (D = 16 m) with RV = 1 m/s|
Radial velocity comparison tables
|Super-Earth (5 M⊕)||0.1||1.4 m/s|
|Alpha Centauri Bb (1.13 ± 0.09 M⊕)||0.04||0.51 m/s||(1)|
|Super-Earth (5 M⊕)||1||0.45 m/s|
|Source: Luca Pasquini, power-point presentation, 2009 Notes: (1) Most precise vradial measurements ever recorded. ESO's HARPS spectrograph was used.|
|51 Pegasi b||Hot Jupiter||0.05||4.23 days||55.9||First-generation spectrograph|
|55 Cancri d||Gas giant||5.77||14.29 years||45.2||First-generation spectrograph|
|Jupiter||Gas giant||5.20||11.86 years||12.4||First-generation spectrograph|
|Gliese 581c||Super-Earth||0.07||12.92 days||3.18||Second-generation spectrograph|
|Saturn||Gas giant||9.58||29.46 years||2.75||Second-generation spectrograph|
|Alpha Centauri Bb||Terrestrial planet||0.04||3.23 days||0.510||Second-generation spectrograph|
|Neptune||Ice giant||30.10||164.79 years||0.281||Third-generation spectrograph|
|Earth||Habitable planet||1.00||365.26 days||0.089||Third-generation spectrograph (likely)|
|Pluto||Dwarf planet||39.26||246.04 years||0.00003||Not detectable|
MK-type stars with planets in the habitable zone
- CORALIE spectrograph
- Doppler spectroscopy
- ELODIE spectrograph
- List of extrasolar planets
- SOPHIE échelle spectrograph
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