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ESPRESSO (Echelle SPectrograph for Rocky Exoplanet- and Stable Spectroscopic Observations)is a third-generation, fiber fed, cross-dispersed, echelle spectrograph mounted on the European Southern Observatory's Very Large Telescope (VLT). The unit saw its first light on September 25, 2016.
ESPRESSO is the successor of a line of echelle spectrometers that include CORAVEL, Elodie, Coralie, and HARPS. It measures changes in the light spectrum with great sensitivity, and will be used to search for Earth-size rocky exoplanets via the radial velocity method. For example, Earth induces a radial-velocity variation of 9 cm/s on the 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, located in the VLT Combined-Coude Laboratory 70 meters away from the telescope, where the light from up to 4 Unit Telescopes of the VLT can be combined. The Principal Investigator is Francesco Pepe.
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 by 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 spectrographs worldwide with such accuracy.[ citation needed ] The ESPRESSO would greatly exceed this capability making detection of Earth-size planets from ground-based instruments possible. Commissioning of ESPRESSO at the VLT started late 2017.
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 detect extremely faint objects.
For example, for G2V type stars:
ESPRESSO will focus the observations on the best-suited candidates: non-active, non-rotating, quiet G dwarfs to red 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 Th Ar 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.
All design work was completed and finalised by April 2013, with the manufacturing phase of the project commencing thereafter.ESPRESSO was tested on June 3, 2016,. ESPRESSO first light occurred on September 25, 2016, during which they spotted various objects, among them the star 60 Sgr A. and after being shipped to Chile and installed at the VLT, ESPRESSO saw its first light there on 27 November 2017. ESPRESSO is currently in testing phase, but by December 2018 it will officially begin its mission proper.
The main scientific objectives for ESPRESSO are:
ESPRESSO is being developed by a consortium consisting on the European Southern Observatory (ESO) and seven scientific institutes:
|Sky aperture||4 arcsec|
|λ coverage||380 nm-686 nm|
|λ precision||5 m/s|
|RV stability||< 10 cm/s|
|4-VLT mode (D = 16 m) with RV = 1 m/s|
|Planet Mass||Distance |
|Radial velocity |
|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.|
|Planet||Planet Type ||Semimajor Axis |
|Orbital Period || Radial velocity |
|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|
|Proxima Centauri b||Habitable planet (potentially)||0.05||11.19 days||1.38||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|
|Type|| RHAB |
| RV |
| Period |
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