The HARPS search for southern extra-solar planets

Santos, N. C.; Mortier, A.; Faria, J. P.; Dumusque, X.; Adibekyan, V.; Delgado-Mena, E.; Figueira, P.; Benamati, L.; Boisse, I.; Cunha, Diana; Silva, J. Gomes da; Curto, G. Lo; Lovis, C.; Martins, J. H. C.; Mayor, M.; Melo, C.; Oshagh, M.; Pepe, F.; Queloz, D.; Santerne, A.; Ségransan, D.; Sozzetti, A.; Sousa, S. G.; Udry, S.

doi:10.1051/0004-6361/201423808

Cited by 101 publications

(113 citation statements)

References 73 publications

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“…Saar & Donahue 1997;Queloz et al 2000;Santos et al 2010;Dumusque et al 2012;Kane et al 2016), even for stars with a low activity level (e.g. Santos et al 2014). The analysis of the generalized Lomb Scargle (GLS) periodograms of the residuals (O−C) of radial velocities after removing the two Keplerians reveals some power near 30 days (Fig.…”

Section: Radial-velocity Fittingmentioning

confidence: 94%

An extreme planetary system around HD 219828

Santos

Santerne

Faria

et al. 2016

A&A

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Context. With about 2000 extrasolar planets confirmed, the results show that planetary systems have a whole range of unexpected properties. This wide diversity provides fundamental clues to the processes of planet formation and evolution. Aims. We present a full investigation of the HD 219828 system, a bright metal-rich star for which a hot Neptune has previously been detected. Methods. We used a set of HARPS, SOPHIE, and ELODIE radial velocities to search for the existence of orbiting companions to HD 219828. The spectra were used to characterise the star and its chemical abundances, as well as to check for spurious, activity induced signals. A dynamical analysis is also performed to study the stability of the system and to constrain the orbital parameters and planet masses. Results. We announce the discovery of a long period (P = 13.1 yr) massive (m sin i = 15.1 M Jup ) companion (HD 219828 c) in a very eccentric orbit (e = 0.81). The same data confirms the existence of a hot Neptune, HD 219828 b, with a minimum mass of 21 M ⊕ and a period of 3.83 days. The dynamical analysis shows that the system is stable, and that the equilibrium eccentricity of planet b is close to zero. Conclusions. The HD 219828 system is extreme and unique in several aspects. First, ammong all known exoplanet systems it presents an unusually high mass ratio. We also show that systems like HD 219828, with a hot Neptune and a long-period massive companion are more frequent than similar systems with a hot Jupiter instead. This suggests that the formation of hot Neptunes follows a different path than the formation of their hot jovian counterparts. The high mass, long period, and eccentricity of HD 219828 c also make it a good target for Gaia astrometry as well as a potential target for atmospheric characterisation, using direct imaging or high-resolution spectroscopy. Astrometric observations will allow us to derive its real mass and orbital configuration. If a transit of HD 219828 b is detected, we will be able to fully characterise the system, including the relative orbital inclinations. With a clearly known mass, HD 219828 c may become a benchmark object for the range in between giant planets and brown dwarfs.

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Section: Radial-velocity Fittingmentioning

confidence: 94%

An extreme planetary system around HD 219828

Santos

Santerne

Faria

et al. 2016

A&A

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“…Moreover, we also analysed the Bisector Inverse Slope (BIS, Queloz et al 2001) of the CCF but we note that this diagnostic of line asymmetry loses sensitivity for very low stellar rotations such as the case we are studying here (e.g. Saar et al 1998;Santos et al 2003;Queloz et al 2009;Santos et al 2014).…”

Section: Stellar Activity and Line Profile Analysismentioning

confidence: 99%

“…However, stellar rotationally modulated active regions are known to induce RV signals not in phase with activity proxies (e.g. Queloz et al 2001;Santos et al 2014). In their detection paper, Lovis & Mayor (2007) used BIS and the Ca ii H&K lines as activity diagnostic tools to validate the candidate brown dwarf.…”

Section: Stellar Activity Photometry and Line Profile Analysismentioning

confidence: 99%

Planets around evolved intermediate-mass stars

Mena

Santos

Silva

et al. 2018

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Aims. The aim of this work is to search for planets around intermediate-mass stars in open clusters by using data from an extensive survey with more than 15 years of observations. Methods. We obtain high-precision radial velocities (RV) with the HARPS spectrograph for a sample of 142 giant stars in 17 open clusters. We fit Keplerian orbits when a significant periodic signal is detected. We also study the variation of stellar activity indicators and line-profile variations to discard stellar-induced signals.Results. We present the discovery of a periodic RV signal compatible with the presence of a planet candidate in the 1.15 Gyr open cluster IC4651 orbiting the 2.06 M star No. 9122. If confirmed, the planet candidate would have a minimum mass of 7.2M J and a period of 747 days. However, we also find that the FWHM of the CCF varies with a period close to the RV, casting doubts on the planetary nature of the signal. We also provide refined parameters for the previously discovered planet around NGC2423 No. 3 but show evidence that the BIS of the CCF is correlated with the RV during some of the observing periods. This fact advises us that this might not be a real planet and that the RV variations could be caused by stellar activity and/or pulsations. Finally, we show that the previously reported signal by a brown dwarf around NGC4349 No. 127 is presumably produced by stellar activity modulation. Conclusions. The long-term monitoring of several red giants in open clusters has allowed us to find periodic RV variations in several stars. However, we also show that the follow-up of this kind of stars should last more than one orbital period to detect long-term signals of stellar origin. This work warns that although it is possible to detect planets around red giants, large-amplitude, long-period RV modulations do exist in such stars that can mimic the presence of an orbiting planetary body. Therefore, we need to better understand how such RV modulations behave as stars evolve along the Red Giant Branch and perform a detailed study of all the possible stellar-induced signals (e.g. spots, pulsations, granulation) to comprehend the origin of RV variations.

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“…Indeed, these signals can even mimic planetary signals (e.g. Figueira et al 2010;Santos et al 2014;Robertson et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Uncovering the planets and stellar activity of CoRoT-7 using only radial velocities

Faria

Haywood

Brewer

et al. 2016

A&A

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Stellar activity can induce signals in the radial velocities of stars, complicating the detection of orbiting low-mass planets. We present a method to determine the number of planetary signals present in radial-velocity datasets of active stars, using only radial-velocity observations. Instead of considering separate fits with different number of planets, we use a birth-death Markov chain Monte Carlo algorithm to infer the posterior distribution for the number of planets in a single run. In a natural way, the marginal distributions for the orbital parameters of all planets are also inferred. This method is applied to HARPS data of CoRoT-7. We confidently recover the orbits of both CoRoT-7b and CoRoT-7c although the data show evidence for the presence of additional signals.

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The HARPS search for southern extra-solar planets

Cited by 101 publications

References 73 publications

An extreme planetary system around HD 219828

An extreme planetary system around HD 219828

Planets around evolved intermediate-mass stars

Uncovering the planets and stellar activity of CoRoT-7 using only radial velocities

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