Attaining Doppler Precision of 3 M s-1

Butler, R. P.; Marcy, G. W.; Williams, Eric; McCarthy, C.; Dosanjh, P.; Vogt, Steven S.

doi:10.1086/133755

Cited by 1,105 publications

(1,025 citation statements)

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“…The RV measurements were calibrated using an iodine absorption cell (Butler et al 1996), and their reduction is described in Marcy et al (2014). They are listed in Table 5, with their epoch in BJD UTC and their 1σ internal errors.…”

Section: Hires Observationsmentioning

confidence: 99%

The Kepler-454 System: A Small, Not-Rocky Inner Planet, a Jovian World, and a Distant Companion

Gettel

Charbonneau

Dressing

et al. 2016

ApJ

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Kepler-454 (KOI-273) is a relatively bright (V = 11.69 mag), Sun-like star that hosts a transiting planet candidate in a 10.6 day orbit. From spectroscopy, we estimate the stellar temperature to be 5687±50 K, its metallicity to be [m/H] = 0.32±0.08, and the projected rotational velocity to be v sin i<2.4 km s −1 . We combine these values with a study of the asteroseismic frequencies from short cadence Kepler data to estimate the stellar mass to be M 1.028 0.03 0.04 -+  , the radius to be 1.066±0.012 R e , and the age to be 5.25 1.39Gyr. We estimate the radius of the 10.6 day planet as 2.37±0.13 R ⊕ . Using 63 radial velocity observations obtained with the HARPS-N spectrograph on the Telescopio Nazionale Galileo and 36 observations made with the HIRES spectrograph at the Keck Observatory, we measure the mass of this planet to be 6.8±1.4 M ⊕ . We also detect two additional nontransiting companions, a planet with a minimum mass of 4.46±0.12 M J in a nearly circular 524 day orbit and a massive companion with a period >10 years and mass >12.1 M J . The 12 exoplanets with radii <2.7 R ⊕ and precise mass measurements appear to fall into two populations, with those <1.6 R ⊕ following an Earth-like composition curve and larger planets requiring a significant fraction of volatiles. With a density of 2.76±0.73 g cm −3 , Kepler-454b lies near the mass transition between these two populations and requires the presence of volatiles and/or H/He gas.

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Section: Hires Observationsmentioning

confidence: 99%

The Kepler-454 System: A Small, Not-Rocky Inner Planet, a Jovian World, and a Distant Companion

Gettel

Charbonneau

Dressing

et al. 2016

ApJ

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“…The stellar effective temperature and iron abundance were obtained by fitting stellar-atmosphere models 21 to iodine-free HIRES spectra 9 , subject to a constraint on the surface gravity based on stellar-evolutionary models 22 . We estimated the stellar mass and radius from empirically calibrated relationships between those spectroscopic parameters 23 .…”

Section: Planetary Propertiesmentioning

confidence: 99%

A rocky composition for an Earth-sized exoplanet

Howard

Sanchis-Ojeda

Marcy

et al. 2013

Nature

195

157

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Planets with sizes between that of Earth (with radius R ⊕ ) and Neptune (about 4 R ⊕ ) are now known to be common around Sun-like stars 1,2,3 . Most such planets have been discovered through the transit technique, by which the planet's size can be determined from the fraction of starlight blocked by the planet as it passes in front of its star. Measuring the planet's mass-and hence its density, which is a clue to its composition-is more difficult. Planets of size 2-4 R ⊕ have proven to have a wide range of densities, implying a diversity of compositions 4,5 , but these measurements did not extend down to planets as small as Earth. Here we report Doppler spectroscopic measurements of the mass of the Earth-sized planet Kepler-78b, which orbits its host star every 8.5 hours (ref. 6). Given a radius of 1.20 ± 0.09 R ⊕ and mass of 1.69 ± 0.41 M ⊕ , the planet's mean density of 5.3 ± 1.8 g cm -3 is similar to the Earth's, suggesting a composition of rock and iron.Kepler-78 is one of approximately 150,000 stars whose brightness was precisely measured at 30-minute intervals for four years by the NASA Kepler spacecraft 7 . This star is somewhat smaller, less massive, and younger than the Sun (Table 1). Every 8.5 hours the star's brightness declines by 0.02% as the planet Kepler-78b transits (passes in front of) the stellar disk. The planet's radius was originally measured 6 to be 1.16 !!.!" !!.!" R ⊕ . The mass could not be measured, although masses >8 M ⊕ could be ruled out because the planet's gravity would have deformed the star and produced brightness variations that were not detected.We measured the mass of Kepler-78b by tracking the line-of-sight component of the host star's motion (the radial velocity, RV) due to the gravitational force of the planet. The RV analysis is challenging not only because the signal is expected to be small (~1-3 m s -1 ) but also because the apparent Doppler shifts due to rotating starspots are much larger (~50 m s -1 peak-to-peak). Nevertheless the detection proved to be possible, thanks to the precisely known orbital period and phase of Kepler-78b that cleanly separated the timescale of spot variations (P rot ≈ 12.5 days) from the much shorter timescale of the planetary orbit (P ≈ 8.5 hours). We adopted a strategy of intensive Doppler measurements spanning 6-8 hours per night, long enough to cover nearly the entire orbit and short enough for the spot variations to be nearly frozen out.We measured RVs using optical spectra of Kepler-78 that we obtained from the High Resolution Echelle Spectrometer (HIRES) 8 on the 10-m Keck I Telescope. These Doppler shifts were computed relative to a template spectrum with a standard algorithm 9 that uses a spectrum of molecular iodine superposed on the stellar spectrum as a reference for the wavelength scale and instrumental profile of HIRES (Supplementary Table 1). Exposures lasted 15-30 minutes depending on conditions and produced RVs with 1.5-2.0 m s -1 uncertainties. The time series of RVs spans 38 days, with large velocity offsets between nights ...

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“…In addition, in order to construct a solar template spectrum needed for the velocity extraction, 50 solar spectra without the iodine cell were acquired followed immediately by 50 flat fields through the iodine cell -these were used to determine the spectrograph pointspread function. A detailed account of the observations required for the iodine method was provided by Butler et al (1996). All the spectra were obtained with a resolution of 120 000.…”

Section: Solar Observationsmentioning

confidence: 99%

Stellar Observations Network Group: The prototype is nearly ready

Grundahl

Christensen‐Dalsgaard

Pallé

et al. 2013

Proc. IAU

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Abstract. The prototype telescope and instruments for the Stellar Observations Network Group (SONG) are nearing completion at the Observatorio del Teide on Tenerife. In this contribution we describe the current status (autumn 2013) of the telescope and its instrumentation. Preliminary performance characteristics are presented for the high-resolution spectrograph based on daytime observations of the Sun and a 4 hour test series obtained for the sub-giant β Aquilae.

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Attaining Doppler Precision of 3 M s-1

Cited by 1,105 publications

References 16 publications

The Kepler-454 System: A Small, Not-Rocky Inner Planet, a Jovian World, and a Distant Companion

The Kepler-454 System: A Small, Not-Rocky Inner Planet, a Jovian World, and a Distant Companion

A rocky composition for an Earth-sized exoplanet

Stellar Observations Network Group: The prototype is nearly ready

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