ESPRESSO

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ESPRESSO spectrograph concept at the Preliminary Design Review.
ESPRESSO spectrograph optical design at the Preliminary Design Review.

ESPRESSO (Echelle SPectrograph for Rocky Exoplanet- and Stable Spectroscopic Observations)[1] is a third-generation, fiber fed, cross-dispersed, echelle spectrograph for the European Southern Observatory's Very Large Telescope (VLT). 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.[2] 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.

Sensitivity

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,[3] 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),[4] with an effective precision of the order of 30 cm/s,[5] making it one of only two instruments worldwide with such accuracy.[citation needed] 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.[2]

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.[2][6][7]

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)[8]

Status

Engineering rendering of the ESPRESSO instrument[9]

The project is currently in its manufacturing phase. All design work is complete.[1]

  • 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

Scientific Objectives

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.

These science cases require an efficient, high-resolution, extremely stable and accurate spectrograph.

Consortium

ESPRESSO is being developed by a consortium consisting of ESO and seven further scientific institutes:

Comparison between ESPRESSO and CODEX

ESPRESSO CODEX
Telescope VLT (8m) E-ELT (39m)
Scope Rocky planets Earth-like
Sky aperture 1 arcsec 0.80 arcsec
R 150000 150000
λ coverage 350–730 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
Source:[8]

Radial velocity comparison tables

Planet Mass Distance
AU		 Radial velocity
(vradial)		 Note
Jupiter 1 28.4 m/s
Jupiter 5 12.7 m/s
Neptune 0.1 4.8 m/s
Neptune 1 1.5 m/s
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[10])
Super-Earth (5 M⊕) 1 0.45 m/s
Earth 0.04109589 0.30 m/s
Earth 1 0.09 m/s
Source: Luca Pasquini, power-point presentation, 2009[8] Notes: (1) Most precise vradial measurements ever recorded. ESO's HARPS spectrograph was used.[10][11]
Planets[8]
Planet Planet Type
 Semimajor Axis
(AU)		 Orbital Period
 Radial velocity
(m/s)		 Detectable by:
51 Pegasi b Hot Jupiter 0.05 4.23 days 55.9[12] First-generation spectrograph
55 Cancri d Gas giant 5.77 14.29 years 45.2[13] First-generation spectrograph
Jupiter Gas giant 5.20 11.86 years 12.4[14] First-generation spectrograph
Gliese 581c Super-Earth 0.07 12.92 days 3.18[15] 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[16] 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

Stellar mass
(M☉)		 Planetary mass
(M⊕)		 Lum.
(L0)		 Type RHAB
(AU)		 RV
(cm/s)		 Period
(days)
0.10 1.0 8×10−4 M8 0.028 168 6
0.21 1.0 7.9×10−3 M5 0.089 65 21
0.47 1.0 6.3×10−2 M0 0.25 26 67
0.65 1.0 1.6×10−1 K5 0.40 18 115
0.78 2.0 4.0×10−1 K0 0.63 25 209
Source: [17]

See also

References

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  8. ↑ 8.0 8.1 8.2 8.3 Lua error in package.lua at line 80: module 'strict' not found.
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