Precise radial velocity measurements of G and K giants

Setiawan, J.; Pasquini, L.; Silva, L. da; Hatzes, A. P.; Lühe, O. von der; Girardi, L.; Medeiros, J. R. De; Guenther, E. W.

doi:10.1051/0004-6361:20041042-1

Cited by 66 publications

(82 citation statements)

References 45 publications

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“…In addition, higher-temperature giants are unsuitable because they display few spectral lines and often complex atmospheric dynamics. Thus, the cluster must be sufficiently old, with main-sequence rotation slower than some 5-10 km s −1 , and must have a well developed red-giant branch with many cool giants that are good targets for radial-velocity measurements (e.g., Setiawan et al 2004).…”

Section: Radial Velocities In Open Clustersmentioning

confidence: 99%

“…The observation that dwarfs are dynamically hotter than giants might seem counter-intuitive, because giants are known to be intrinsic RV variables, with variations of up to a few hundreds m s −1 (e.g., Setiawan et al 2004), and their intrinsic RV variability will add to their RV dispersion. In addition, main-sequence stars have lower masses, and in the case of mass segregation the giants should be (as they are in M 67) mostly concentrated in the middle of the cluster, near the center of the potential well.…”

Section: Dynamically Hot Dwarfsmentioning

confidence: 99%

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Gravitational redshifts in main-sequence and giant stars

Pasquini

Melo

Chavero

et al. 2011

A&A

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Context. Precise analyses of stellar radial velocities is able to reveal intrinsic causes of the wavelength shifts of spectral lines (other than Doppler shifts due to radial motion), such as gravitational redshifts and convective blueshifts. Aims. Gravitational redshifts in solar-type main-sequence stars are expected to be some 500 m s −1 greater than those in giants. We search for this difference in redshifts among groups of open-cluster stars that share the same average space motion and thus have the same average Doppler shift. Methods. We observed 144 main-sequence stars and cool giants in the M 67 open cluster using the ESO FEROS spectrograph and obtained radial velocities by means of cross-correlation with a spectral template. Binaries and doubtful members were not analyzed, and average spectra were created for different classes of stars. Results. The M 67 dwarf and giant radial-velocity distributions are each well represented by Gaussian functions, which share the same apparent average radial velocity to within 100 m s −1 . In addition, dwarfs in M 67 appear to be dynamically hotter (σ = 0.90 km s −1 ) than giants (σ = 0.68 km s −1 ). Conclusions. We fail to detect any difference in the gravitational redshifts of giants and MS stars. This is probably because of the differential wavelength shifts produced by the different hydrodynamics of dwarf and giant atmospheres. Radial-velocity differences measured between unblended lines in averaged spectra vary with line-strength: stronger lines are more blueshifted in dwarfs than in giants, apparently removing any effect of the gravitational redshift. Synthetic high-resolution spectra are computed from three dimensional (3D) hydrodynamic model atmospheres for both giants and dwarfs, and synthetic wavelength shifts obtained. In agreement with observations, 3D models predict substantially smaller wavelength-shift differences than expected from gravitational redshifts only. The procedures developed could be used to test 3D models for different classes of stars, but will ultimately require high-fidelity spectra for measurements of wavelength shifts in individual spectral lines.

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Section: Radial Velocities In Open Clustersmentioning

confidence: 99%

Section: Dynamically Hot Dwarfsmentioning

confidence: 99%

Gravitational redshifts in main-sequence and giant stars

Pasquini

Melo

Chavero

et al. 2011

A&A

Self Cite

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“…Both classes of variables often exhibit pseudo-orbital variations caused by shock waves associated with the envelope pulsation (Udry et al 1998;Hatzes & Cochran 1998;Wood 2000;Hinkle et al 2002;Setiawan et al 2004;Derekas et al 2006;Soszyński 2007;Hekker et al 2008). For semi-regular variables, Hinkle et al (2002) obtain semi-amplitudes K between 1.6 and 3.1 km s −1 , whereas for Miras the semi-amplitudes may reach 20 km s −1 in the most extreme cases (Alvarez et al 2001).…”

Section: Photometric Variabilitymentioning

confidence: 99%

Spectroscopic binaries among Hipparcos M giants

Famaey¹,

Pourbaix²,

Frankowski³

et al. 2009

A&A

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Context. This paper is a follow-up on the vast effort to collect radial velocity data for stars belonging to the Hipparcos survey. Aims. We aim at extending the orbital data available for binaries with M giant primaries. The data presented in this paper will be used in the companion papers of this series to (i) derive the binary frequency among M giants and compare it to that of K giants (Paper II); and (ii) analyse the eccentricity -period diagram and the mass-function distribution (Paper III). Methods. Keplerian solutions are fitted to radial-velocity data. However, for several stars, no satisfactory solution could be found, even though the radial-velocity standard deviation is greater than the instrumental error, because M giants suffer from intrinsic radialvelocity variations due to pulsations. We show that these intrinsic radial-velocity variations can be linked with both the average spectral-line width and the photometric variability. Results. We present an extensive collection of spectroscopic orbits for M giants with 12 new orbits, plus 17 from the literature. On top of these, 1 preliminary orbit yielded an approximate value for the eccentricity and the orbital period. Moreover, to illustrate how the large radial-velocity jitter present in Mira and semi-regular variables may easily be confused with orbital variations, we also present examples of pseudo-orbital variations (in S UMa, X Cnc, and possibly in HD 115 521, a former IAU radial-velocity standard). Because of this difficulty, M giants involving Mira variables were excluded from our monitored sample. We finally show that the majority of M giants detected as X-ray sources are actually binaries. Conclusions. The data presented in this paper considerably increase the orbital data set for M giants, and will allow us to conduct a detailed analysis of the eccentricity -period diagram in a companion paper (Paper III).

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“…In addition, the pipeline uses the initial time of the observation instead of the central time, which also introduces another uncertainty, especially for long exposure observations. This issue was also mentioned by Setiawan et al (2000). This has led some groups to question the detections that were made using FEROS data before this problem was discovered, leading to the reanalysis of data taken with this instrument and the rejection of some systems (e.g.…”

Section: Introductionmentioning

confidence: 99%

RAFT – I. Discovery of new planetary candidates and updated orbits from archival FEROS spectra

Soto

Jenkins

Jones

2015

Monthly Notices of the Royal Astronomical Society

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A recent reanalysis of archival data has lead several authors to arrive at strikingly different conclusions for a number of planet-hosting candidate stars. In particular, some radial velocities measured using FEROS spectra have been shown to be inaccurate, throwing some doubt on the validity of a number of planet detections. Motivated by these results, we have begun the Reanalysis of Archival FEROS specTra (RAFT) program and here we discuss the first results from this work. We have reanalyzed FEROS data for the stars HD 11977, HD 47536, HD 70573, HD 110014 and HD 122430, all of which are claimed to have at least one planetary companion. We have reduced the raw data and computed the radial velocity variations of these stars, achieving a long-term precision of ∼ 10 m s −1 on the known stable star τ Ceti, and in good agreement with the residuals to our fits. We confirm the existence of planets around HD 11977, HD 47536 and HD 110014, but with different orbital parameters than those previously published. In addition, we found no evidence of the second planet candidate around HD 47536, nor any companions orbiting HD 122430 and HD 70573. Finally, we report the discovery of a second planet around HD 110014, with a minimum mass of 3.1 M Jup and a orbital period of 130 days. Analysis of activity indicators allow us to confirm the reality of our results and also to measure the impact of magnetic activity on our radial velocity measurements. These results confirm that very metal-poor stars down to [Fe/H]∼-0.7 dex, can indeed form giant planets given the right conditions.

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Precise radial velocity measurements of G and K giants

Cited by 66 publications

References 45 publications

Gravitational redshifts in main-sequence and giant stars

Gravitational redshifts in main-sequence and giant stars

Spectroscopic binaries among Hipparcos M giants

RAFT – I. Discovery of new planetary candidates and updated orbits from archival FEROS spectra

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