Discovery of a Substellar Companion to the K2 III Giant ι Draconis

Frink, S.; Mitchell, D.; Quirrenbach, A.; Fischer, Debra A.; Marcy, Geoffrey W.; Butler, R. Paul

doi:10.1086/341629

Cited by 199 publications

(196 citation statements)

References 20 publications

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“…Several stars with planetary-mass companions have already been discovered, mainly around red giants (Niedzielski et al 2007(Niedzielski et al , 2009aGettel et al 2012b,a). These findings supplement the slowly growing population of ∼50 planets currently known around evolved stars, discovered in such projects as the McDonald Observatory Planet Search , the Okayama Planet Search (Sato et al 2003), the Tautenburg Planet Search (Hatzes et al 2005), the Lick K-giant Survey (Frink et al 2002), the ESO FEROS planet search (Setiawan et al 2003a,b), the Retired A Stars and Their Companions (Johnson et al 2007), the CORALIE and HARPS search (Lovis & Mayor 2007), and the Boyunsen Planet Search (Lee et al 2011).…”

Section: Introductionsupporting

confidence: 66%

The Penn State-Toruń Centre for Astronomy Planet Search stars

Zieliński

Niedzielski

Wolszczan

et al. 2012

A&A

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Aims. We present basic atmospheric parameters (T eff , log g, v t , and [Fe/H]) as well as luminosities, masses, radii, and absolute radial velocities for 348 stars, presumably giants, from the ∼1000 star sample observed within the Penn State-Toruń Centre for Astronomy Planet Search with the High Resolution Spectrograph of the 9.2 m Hobby-Eberly Telescope. The stellar parameters (luminosities, masses, radii) are key to properly interpreting newly discovered low-mass companions, while a systematic study of the complete sample will create a basis for future statistical considerations concerning the appearance of low-mass companions around evolved low-and intermediate-mass stars. Methods. The atmospheric parameters were derived using a strictly spectroscopic method based on the LTE analysis of equivalent widths of Fe I and Fe II lines. With existing photometric data and the Hipparcos parallaxes, we estimated stellar masses and ages via evolutionary tracks fitting. The stellar radii were calculated from either estimated masses and the spectroscopic log g or from the spectroscopic T eff and estimated luminosities. The absolute radial velocities were obtained by cross-correlating spectra with a numerical template. Results. We completed the spectroscopic analysis for 332 stars, 327 of which were found to be giants. A simplified analysis was applied to the remaining 16 stars, which had incomplete data. The results show that our sample is composed of stars with effective temperatures ranging from 4055 K to 6239 K, with log g between 1.39 and 4.78 (5 dwarfs were identified). The estimated luminosities are between log L/L = −1.0 and 3 and lead to masses ranging from 0.6 to 3.4 M . Only 63 stars with masses larger than 2 M were found. The radii of our stars range from 0.6 to 52 R with the vast majority between 9−11 R . The stars in our sample are generally less metal-abundant than the Sun with median [Fe/H] = −0.15. The estimated uncertainties in the atmospheric parameters were found to be comparable to those reached in other studies. However, due to lack of precise parallaxes, the stellar luminosities and, in turn, the masses are far less precise, within 0.2 M in best cases and 0.3 M on average.

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Section: Introductionsupporting

confidence: 66%

The Penn State-Toruń Centre for Astronomy Planet Search stars

Zieliński

Niedzielski

Wolszczan

et al. 2012

A&A

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“…If confirmed, the determined orbit of the 1.8 M Jup mass planet is fairly eccentric, e = 0.25 ± 0.03, but, up to now, 6 out of 22 companions around K-giants show more than 0.2 eccentricity: e = 0.7 of ι Dra (Frink et al 2002), e = 0.2 of K1 III star HD 47536 (Setiawan et al 2003,b), e = 0.27 of K1 II-III star HD 13189 (Hatzes et al 2005), e = 0.43 of K1 III star 4 UMa (Döllinger et al 2007), e = 0.38 of K1.5 III star 42 Dra (Döllinger et al 2009), and e = 0.46 of K2 III star HD 110014 (de Medeiros et al 2009). The eccentricity for the planetary orbit of α Ari is therefore not unusual among K-giants, and such eccentric modulation is difficult to produce by surface variations or stellar oscillations.…”

Section: Resultsmentioning

confidence: 75%

“…This makes giant stars suitable targets for extrasolar planet detection with the RV method. Frink et al (2002) discovered the first planetary companion around the K-giant star ι Dra (K2 III), and thereafter, several companions around K-giant stars have been reported using the precise RV method (Setiawan 2003;Setiawan et al 2003;Mitchell et al 1234;Hatzes et al 2005Hatzes et al , 2006Reffert et al 2006;Johnson et al 2007Johnson et al , 2008Döllinger et al 2007Döllinger et al , 2009de Medrios et al 2009;and Sato et al 2007and Sato et al , 2008aand Sato et al ,b, 2010. However, in K-giants the velocity variations caused by planetary companions can be blended with the stellar pulsations and surface activities, which complicates identification of planetary companions.…”

Section: Introductionmentioning

confidence: 99%

A likely exoplanet orbiting the oscillating K-giantαArietis

Lee

Mkrtichian

Han

et al. 2011

A&A

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Aims. To search for extrasolar planets around intermediate-mass stars, we are conducting a precise RV survey around K-giants. Methods. We present high-accuracy RV measurements of α Ari made from November 2003 to February 2010. This star belongs to our sample of 55 K-giants studied for extrasolar planet and pulsation searches using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) attached to the 1.8-m telescope at Bohyunsan Optical Astronomy Observatory (BOAO) in Korea.Results. We find a planetary companion with long-period and low-amplitude radial velocity (RV) variations in oscillating K2 III star α Ari (HD 12929). We do not find the correlation between RV variations and chromospheric activity indicators (Ca II H & K region, Hα line). The bisector analysis also shows that the bisector velocity span (BVS) does not show any obvious correlation with RV variation but has periodic component that may be attributed to the rotation of the star. If the RV variation is indeed caused by a planetary companion, an orbital solution with a period of P = 381 days, a semi-amplitude of K = 41 m s −1 , and an eccentricity of e = 0.25 fits the data best. Assuming a possible stellar mass of M = 1.5 M , we estimate the minimum mass for the planetary companion of m 2 sin i = 1.8 M Jup with an orbital semi-major axis of 1.2 AU. Conclusions. Our finding of a likely exoplanet in α Ari supports searching for extrasolar planets around giant stars with multiperiodic oscillations.

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“…A highly eccentric orbital solution argues in favour of a planetary cause (see e.g. the case for the K2 III ι Dra; Frink et al 2002), but the small non-zero eccentricity calculated for the conjectured ν Oct planet (e ∼ 0.1) is no obstacle. Also, Ramm et al (2009) have assumed their RVs fit a Keplerian orbit (which in any case may be a significant oversimplification), so it is not surprising that some non-zero eccentricity has been derived.…”

Section: Pulsationsmentioning

confidence: 97%

Line-depth-ratio temperatures for the close binary ν Octantis: new evidence supporting the conjectured circumstellar retrograde planet

Ramm¹

2015

Monthly Notices of the Royal Astronomical Society

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We explore the possibly that either starspots or pulsations are the cause of a periodic radialvelocity signal (P ∼ 400 days) from the K-giant binary ν Octantis (P ∼ 1050 days, e ∼ 0.25), alternatively conjectured to have a retrograde planet. Our study is based on temperatures derived from 22 line-depth ratios (LDRs) for ν Oct and twenty calibration stars. Empirical evidence and stability modelling provide unexpected support for the planet since other standard explanations (starspots, pulsations and additional stellar masses) each have credibility problems. However, the proposed system presents formidable challenges to planet-formation and stability theories: it has by far the smallest stellar separation of any claimed planet-harbouring binary (a bin ∼ 2.6 AU) and an equally unbelievable separation ratio (a pl /a bin ∼ 0.5), hence the necessity that the circumstellar orbit be retrograde.The LDR analysis of 215 ν Oct spectra acquired between 2001-2007, from which the RV perturbation was first revealed, have no significant periodicity at any frequency. The LDRs recover the original 21 stellar temperatures with an average accuracy of 45 ± 25 K. The 215 ν Oct temperatures have a standard deviation of only 4.2 K. Assuming the host primary is not pulsating, the temperatures converted to magnitude differences strikingly mimic the very stable photometric Hipparcos observations 15 years previously, implying the long-term stability of the star and demonstrating a novel use of LDRs as a photometric gauge. Our results provide substantial new evidence that conventional starspots and pulsations are unlikely causes of the RV perturbation. The controversial system deserves continued attention, including with higher resolving-power spectra for bisector and LDR analyses.

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Discovery of a Substellar Companion to the K2 III Giant ι Draconis

Cited by 199 publications

References 20 publications

The Penn State-Toruń Centre for Astronomy Planet Search stars

The Penn State-Toruń Centre for Astronomy Planet Search stars

A likely exoplanet orbiting the oscillating K-giantαArietis

Line-depth-ratio temperatures for the close binary ν Octantis: new evidence supporting the conjectured circumstellar retrograde planet

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