ABSTRACT
Among highly irradiated exoplanets, some have been found to undergo significant hydrodynamic expansion traced by atmospheric escape. To better understand these processes in the context of ...planetary evolution, we propose NIGHT (the Near-Infrared Gatherer of Helium Transits). NIGHT is a high-resolution spectrograph dedicated to surveying and temporally monitoring He i triplet absorption at 1083 nm in stellar and planetary atmospheres. In this paper, we outline our scientific objectives, requirements, and cost-efficient design. Our simulations, based on previous detections and modelling using the current exoplanet population, determine our requirements and survey targets. With a spectral resolution of 70 000 on a 2-m telescope, NIGHT can accurately resolve the helium triplet and detect 1 per cent peak absorption in 118 known exoplanets in a single transit. Additionally, it can search for 3σ temporal variations of 0.4 per cent in 66 exoplanets in-between two transits. These are conservative estimates considering the ongoing detections of transiting planets amenable to atmospheric characterization. We find that instrumental stability at 40 m s−1, less stringent than for radial velocity monitoring, is sufficient for transmission spectroscopy in He i. As such, NIGHT can utilize mostly off-the-shelf components, ensuring cost-efficiency. A fibre-fed system allows for flexibility as a visitor instrument on a variety of telescopes, making it ideal for follow-up observations after JWST or ground-based detections. Over a few years of surveying, NIGHT could offer detailed insights into the mechanisms shaping the hot Neptune desert and close-in planet population by significantly expanding the statistical sample of planets with known evaporating atmospheres. First light is expected in 2024.
The quest for extrasolar planets and their characterization as well as studies of fundamental physics on cosmological scales rely on capabilities of high-resolution astronomical spectroscopy. A ...central requirement is a precise wavelength calibration of astronomical spectrographs allowing for extraction of subtle wavelength shifts from the spectra of stars and quasars. Here, we present an all-fiber, 400 nm wide near-infrared frequency comb based on electro-optic modulation with 14.5 GHz comb line spacing. Tests on the high-resolution, near-infrared spectrometer GIANO-B show a photon-noise limited calibration precision of < 10 cms as required for Earth-like planet detection. Moreover, the presented comb provides detailed insight into particularities of the spectrograph such as detector inhomogeneities and differential spectrograph drifts. The system is validated in on-sky observations of a radial velocity standard star (HD221354) and telluric atmospheric absorption features. The advantages of the system include simplicity, robustness and turn-key operation, features that are valuable at the observation sites.
A new family of planets is considered which is in between the rocky terrestrial planets and the gaseous giants, “Ocean-Planets.” We present the possible formation, composition and internal structure ...of these putative planets. We consider their oceans, as well as their possible Exobiology interest. These exoplanets should be detectable by Space missions such as Eddington, Kepler, and possibly COROT (launch scheduled in 2006). They have a density lower than that of rocky planets. Their rather large radius would make them attractive targets for exoplanet spectroscopic missions such as Darwin/TPF, all the more because a robust biosignature appears to exist.
Since 1998, a planet-search program around main sequence stars within 50 pc in the southern hemisphere has been carried out with the CORALIE echelle spectrograph at La Silla Observatory. With an ...observing time span of more than 14 years, the CORALIE survey is now able to unveil Jovian planets on Jupiter's period domain. This growing period-interval coverage is important for building formation and migration models since observational constraints are still weak fir periods beyond the ice line. Long-term, precise Doppler measurements with the CORALIE echelle spectrograph, together with a few additional observations made with the HARPS spectrograph on the ESO 3.6m telescope, reveal radial velocity signatures of massive planetary companions on long-period orbits. In this paper we present seven new planets orbiting HD27631, HD98649, HD 106515A, HD166724, HD196067, HD219077, and HD220689, together with the CORALIE orbital parameters for three already known planets around HD10647, HD30562, and HD86226. Finally, the hosts of these long period planets show no metallicity excess.
Context. Since 1998, a planet-search around main sequence stars within 50 pc in the southern hemisphere has been underway with the CORALIE spectrograph at La Silla Observatory. Aims. With an ...observing time span of more than 20 yr, the CORALIE survey is able to detect long-term trends in data with masses and separations large enough to select ideal targets for direct imaging. Detecting these giant companion candidates will allow us to start bridging the gap between radial-velocity-detected exoplanets and directly imaged planets and brown dwarfs. Methods. Long-term precise Doppler measurements with the CORALIE spectrograph reveal radial-velocity signatures of massive planetary companions and brown dwarfs on long-period orbits. Results. In this paper, we report the discovery of new companions orbiting HD 181234, HD 13724, HD 25015, HD 92987 and HD 50499. We also report updated orbital parameters for HD 50499b, HD 92788b and HD 98649b. In addition, we confirm the recent detection of HD 92788c. The newly reported companions span a period range of 15.6–40.4 yr and a mass domain of 2.93–26.77 MJup, the latter of which straddles the nominal boundary between planets and brown dwarfs. Conclusions. We report the detection of five new companions and updated parameters of four known extrasolar planets. We identify at least some of these companions to be promising candidates for imaging and further characterisation.
Context. The study of Earth-mass extrasolar planets via the radial-velocity technique and the measurement of the potential cosmological variability of fundamental constants call for ...very-high-precision spectroscopy at the level of δλ/λ < 10−9. Only an accurate wavelength calibration of the spectrograph can guarantee that the aimed precision is achieved over a multi-exposure and multi-epoch data set. Wavelength accuracy is obtained by providing two fundamental ingredients: 1) an absolute and information-rich wavelength source and 2) the ability of the spectrograph and its data reduction of transferring the reference scale (wavelengths) to a measurement scale (detector pixels) in a repeatable manner. Aims. The goal of this work is to improve the wavelength calibration accuracy of the HARPS spectrograph by combining the absolute spectral reference provided by the emission lines of a thorium-argon hollow-cathode lamp (HCL) with the spectrally rich and precise spectral information of a Fabry-Pérot-based calibration source. Methods. On the basis of calibration frames acquired each night since the Fabry-Pérot etalon was installed on HARPS in 2011, we constructed a combined wavelength solution that fits simultaneously the thorium emission lines and the Fabry-Pérot lines. The combined fit was anchored to the absolute thorium wavelengths, which provide the “zero-point” of the spectrograph, while the Fabry-Pérot lines were used to improve the (spectrally) local precision. The obtained wavelength solution was verified for auto-consistency and tested against a solution obtained using the HARPS laser-frequency comb (LFC). Results. The combined thorium+Fabry-Pérot wavelength solution shows significantly better performances compared to the thorium-only calibration. In both cases, the residuals of the LFC line positions to the fitted wavelength solution follow a Gaussian distribution with an rms value of about 14 m s−1 for the combined solution, and twice as large for the thorium-only solution (29 m s−1). Given these positive results, we have applied the new calibrations to scientific frames and tested the radial-velocity residual on three well-known stars: HD 10700, HD 20794, and HD 69830. In all three cases the radial-velocity (RV) scatter could be reduced compared to the measurements using the previous calibration. Conclusions. The richness of the Fabry-Pérot spectrum helps to improve the wavelength calibration using thorium-argon lamps or extending the wavelength domain of LFCs with limited operational range. The presented techniques will therefore be used in the new HARPS and HARPS-N pipeline, and will be exported to the ESPRESSO spectrograph.
Planets less massive than about 10
M
Earth
are expected to have no massive H–He atmosphere and a cometary composition (∼50% rocks, 50% water, by mass) provided they formed beyond the snowline of ...protoplanetary disks. Due to inward migration, such planets could be found at any distance between their formation site and the star. If migration stops within the habitable zone, this may produce a new kind of planets, called
ocean-planets. Ocean-planets typically consist in a silicate core, surrounded by a thick ice mantle, itself covered by a 100 km-deep ocean. The possible existence of ocean-planets raises important astrobiological questions: Can life originate on such body, in the absence of continent and ocean–silicate interfaces? What would be the nature of the atmosphere and the geochemical cycles? In this work, we address the fate of
hot ocean-planets produced when migration ends at a closer distance. In this case the liquid/gas interface can disappear, and the hot H
2O envelope is made of a supercritical fluid. Although we do not expect these bodies to harbor life, their detection and identification as water-rich planets would give us insight as to the abundance of hot and, by extrapolation, cool ocean-planets. The water reservoir of these planets seems to be weakly affected by gravitational escape, provided that they are located beyond some minimum distance, e.g. 0.04 AU for a 5-Earth-mass planet around a Sun-like star. The swelling of their water atmospheres by the high stellar flux is expected not to significantly increase the planets' radii. We have studied the possibility of detecting and characterizing these hot ocean-planets by measuring their mean densities using transit missions in space—CoRoT (CNES) and
Kepler (NASA)—in combination with Doppler velocimetry from the ground—HARPS (ESO) and possible future instruments. We have determined the domain in the stellar magnitude, orbital distance plane where discrimination between ocean-planets and rocky planets is possible with these instruments. The brightest stars of the mission target lists and the planets closest to their stars are the most favorable cases. Full advantage of high precision photometry by CoRoT, and particularly
Kepler, can be obtained only if a new generation of Doppler instruments is built.
The ESPRI project relies on the astrometric capabilities offered by the PRIMA facility of the Very Large Telescope Interferometer for discovering and studying planetary systems. We give a ...comprehensive overview of the instrument infrastructure and present the observation strategy for dual-field relative astrometry in the infrared K-band. We describe the differential delay lines, a key component of the PRIMA facility that was delivered by the ESPRI consortium, and discuss their performance within the facility. This paper serves as reference for future ESPRI publications and fir the users of the PRIMA facility. Observations of bright visual binaries were used to test the observation procedures and to establish the instrument's astrometilc precision and accuracy. Our observations led to defining corrective actions required to make the facility ready for carrying out the ESPIC search fir extrasolar planets.
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