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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 is being 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 four unit telescopes of the VLT can be combined. The Principal Investigator is Francesco Pepe.
ESPRESSO builds 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 benefits 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. 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 detects 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-size rocky planets around stars as faint as V ≈ 9 (CODEX on the E-ELT) 
For calibration, ESPRESSO uses a laser frequency comb (LFC), with backup of two ThAr lamps. It features 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. After being shipped to Chile, installed at the VLT, ESPRESSO saw its first light there on 27 November 2017, in 1-UT mode, observing the star Tau Ceti; the first star observed in the 4-UT mode was on February 3, 2018.
ESPRESSO has been opened to the astronomical community in the 1-UT mode (one single telescope used), and is producing scientific data since October 24, 2018. On quiet stars it has already demonstrated radial-velocity precision of 25 cm/s over a full night. However, there have been some problems, for example, in light collecting efficiency which was around 30% lower than expected and required. And so, some fine tuning, including replacing the parts causing the efficiency problem and subsequent re-testing, were to be done on the instrument before the full 4-UT mode was open to the scientific community in April 2019.[needs update] A problem was discovered in the ESPRESSO charge-couple device controllers, digital imaging hardware, where a differential nonlinearity issue has reduced the resolution obtainable more severely than was previously feared. The ESO detector team that determined the source of the problem is currently, as of June 2019,[update] working on a new version of the associated hardware in order to remedy this hopefully temporary setback.
On Aug 29 2019, the ESPRESSO ETC was updated to reflect the gain in transmission after the technical mission of July. This gain in flux was of, in average, ≈50% in flux in the UHR and HR modes and of ≈40% in the MR.
- The measurement of high precision radial velocities of solar type stars for the search for rocky planets in the habitable zone of their star.
- The measurement of the variation of the physical constants
- The analysis of the chemical composition of stars in nearby galaxies.
ESPRESSO is being developed by a consortium consisting on the European Southern Observatory (ESO) and seven scientific institutes:
- Centre for Astrophysics of the University of Porto (Portugal)
- Faculdade de Ciências da Universidade de Lisboa, CAAUL & LOLS (Portugal)
- Trieste Astronomical Observatory (Italy)
- Brera Astronomical Observatory (Italy)
- Instituto de Astrofísica de Canarias (Spain)
- Physics Institute of the University of Bern (Switzerland)
- University of Geneva (Switzerland)
- Institute of Astrophysics and Space Sciences (Portugal)
|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|
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|
|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|
MK-type stars with planets in the habitable zone
|Wikimedia Commons has media related to ESPRESSO.|
- CODEX spectrograph
- CORALIE spectrograph
- Doppler spectroscopy
- ELODIE spectrograph
- EXPRES spectograph
- HIRES spectrograph
- List of extrasolar planets
- SOPHIE échelle spectrograph
- "ESO - Espresso". Retrieved 2012-10-24.
- http://www.eso.org/public/usa/announcements/ann16073/ ESPRESSO Sees Light at the End of the Tunnel
- http://www.media.inaf.it/2016/10/17/prima-luce-espresso-coude-lab/ ESPRESSO vede la luce in fondo al “tunnel”
- "ESPRESSO - Searching for other Worlds". Centro de Astrofísica da Universidade do Porto. 2010-10-16. Archived from the original on 2010-10-17. Retrieved 2010-10-16.
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The first observation was for the star Tau Ceti. It was done using the UT1 of the VLT, the observations made on the four united telescopes will be done later.
- https://www.eso.org/public/unitedkingdom/news/eso1806/ ESO’s VLT Working as 16-metre Telescope for First Time
- Bratschi, Pierre (2018-02-14). "ESPRESSO: first time with the 4 UTs of the VLT". NCCR PlanetS. National Centre of Competence in Research PlanetS. Retrieved 2018-11-07.
... first light of ESPRESSO with the four VLT 8.2-meter Unit Telescopes (4UT mode) took place on Saturday February 3rd, 2018... star observed by ESPRESSO with the 4UT mode was the so-called Pepe star
- Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations, ESO
- Barbara, Vonarburg (2018-11-28). "Fine-tuning Espresso". NCCR PlanetS. National Centre of Competence in Research PlanetS. Retrieved 2018-12-28.
ESPRESSO has been opened to the astronomical community and finally started operations on the 24th of October 2018.
- "ESPRESSO News and Press Releases". European Southern Observatory. 2019-06-05. Retrieved 2019-06-21.
An issue with the ESPRESSO CCD controllers has recently been identified.
- "ESO - News". www.eso.org. Retrieved 2019-11-12.
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