CHARACTERIZING THE COOL KOIs. III. KOI 961: A SMALL STAR WITH LARGE PROPER MOTION AND THREE SMALL PLANETS

By P. Muirhead, J. Johnson, K. Apps, J. Carter, Timothy Morton, D. Fabrycky, J. Pineda, M. Bottom, B. Rojas-Ayala, E. Schlawin and 14 more. 2012

176 citations recorded by the source corpus.

We characterize the star KOI 961, an M dwarf with transit signals indicative of three short-period exoplanets discovered by the Kepler mission. We proceed by comparing KOI 961 to Barnard's Star, a nearby, well-characterized mid-M dwarf. We compare colors, optical and near-infrared spectra, and find remarkable agreement between the two, implying similar effective temperatures and metallicities. Both are metal-poor compared to the Solar neighborhood, have low projected rotational velocity, high absolute radial velocity, large proper motion, and no quiescent Hα emission—all of which are consistent with being old M dwarfs. We combine empirical measurements of Barnard's Star and expectations from evolutionary isochrones to estimate KOI 961's mass (0.13 ± 0.05 M☉), radius (0.17 ± 0.04 R☉), and luminosity (2.40 × 10−3.0 ± 0.3 L☉). We calculate KOI 961's distance (38.7 ± 6.3 pc) and space motions, which, like Barnard's Star, are consistent with a high scale-height population in the Milky Way. We perform an independent multi-transit fit to the public Kepler light curve and significantly revise the transit parameters for the three planets. We calculate the false-positive probability for each planet candidate, and find a less than 1% chance that any one of the transiting signals is due to a background or hierarchical eclipsing binary, validating the planetary nature of the transits. The best-fitting radii for all three planets are less than 1 R⊕, with KOI 961.03 being Mars-sized (RP = 0.57 ± 0.18 R⊕), and they represent some of the smallest exoplanets detected to date.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/134dff9b1d1a6a7193fbbeca28b935961271d788

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In Astronomy and Astrophysics

1. D. Charbonneau
2. Timothy Morton
3. J. Johnson
4. Jon Fortney
5. J. Winn
6. E. Gaidos
7. G. Marcy
8. Andrew W. Howard

In Instrumentation

1. D. Charbonneau
2. Timothy Morton
3. J. Winn
4. J. Johnson
5. J. Southworth
6. E. Gaidos
7. Jon Fortney
8. G. Marcy

Citations in the corpus

• Revised Stellar Properties of Kepler Targets for the Q1-17 (DR25) Transit Detection Run (2016, methodology): “The input parameters were reversed back to the H14 catalog, which were based on Muirhead et al. (2012a).”
• CHARACTERIZING THE COOL KOIs. IV. KEPLER-32 AS A PROTOTYPE FOR THE FORMATION OF COMPACT PLANETARY SYSTEMS THROUGHOUT THE GALAXY (2012, methodology): “We combine the results of the above analyses with those of Borucki et al. (2011a), Muirhead et al. (2012a), and Fabrycky et al. (2012a) by weighted mean to obtain the final values used in this work presented in Table 2.”
• VALIDATION OF KEPLER'S MULTIPLE PLANET CANDIDATES. II. REFINED STATISTICAL FRAMEWORK AND DESCRIPTIONS OF SYSTEMS OF SPECIAL INTEREST (2014, methodology): “Adopting the Muirhead et al. (2012) result to break our degeneracy, we choose results from the empirical isochrone fitting and use the empirical stellar parameters for our estimates of planetary sizes given in Table 5.”
• SPECTRO-THERMOMETRY OF M DWARFS AND THEIR CANDIDATE PLANETS: TOO HOT, TOO COOL, OR JUST RIGHT? (2013, methodology): “Muirhead et al. (2012a) and Dressing & Charbonneau (2013) in Figure 12.”
• SOPHIE velocimetry of Kepler transit candidates VII. A false-positive rate of 35% for Kepler close-in giant candidates (2012, background): “…photometric precision reached by Kepler has permitted the discovery of the first validated transiting planet in the habitable zone (Borucki et al. 2012) out of the solar system as well as extrasolar planets with radii of about the size of the Earth (Fressin et al. 2012; Muirhead et al. 2012).”
• A PLATEAU IN THE PLANET POPULATION BELOW TWICE THE SIZE OF EARTH (2013, background): “As an extreme example, the interpretations of the three planets in the KOI-961 system (Muirhead et al. 2012) changed dramatically when HIRES spectra showed the star to be an M5 dwarf (0.2 R⊙ as opposed to 0.6 R⊙ listed in the KIC).”
• The Habitability of Planets Orbiting M-dwarf Stars (2016, methodology): “In the case of the first Earth-sized planets observed to transit an M dwarf, the authors employed a proxy star of the same spectral type with directly-measured properties (Muirhead et al., 2012).”
• FALSE POSITIVE PROBABILITIES FOR ALL KEPLER OBJECTS OF INTEREST: 1284 NEWLY VALIDATED PLANETS AND 428 LIKELY FALSE POSITIVES (2016, methodology): “This procedure has also been used in the literature to validate a number of Kepler planets (e.g., Muirhead et al. 2012; Dawson et al. 2012; Swift et al. 2013), and has also been ar X iv :1 60 5.”
• The Gaia–Kepler Stellar Properties Catalog. I. Homogeneous Fundamental Properties for 186,301 Kepler Stars (2020, methodology): “Alternatively, Jontof-Hutter et al. (2015) computed the stellar parameters of Kepler -138 by fitting the light curve constraint of ρ? as well as the spectroscopic constraints of Teff and [Fe/H] of Muirhead et al. (2012) to Dartmouth Stellar Evolution models.”
• KEPLER ECLIPSING BINARY STARS. III. CLASSIFICATION OF KEPLER ECLIPSING BINARY LIGHT CURVES WITH LOCALLY LINEAR EMBEDDING (2012, background): “The mission already yielded several exciting results, including the first ever discovery of transiting circumbinary planets (Doyle et al. 2011; Welsh et al. 2012) and the detection of several Earth sized planets (Gautier et al. 2012; Fressin et al. 2012; Muirhead et al. 2012).”
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• AN EFFICIENT AUTOMATED VALIDATION PROCEDURE FOR EXOPLANET TRANSIT CANDIDATES (2012, methodology): “An early version of this analysis, representing a halfway point between MJ11 and this work, was used to validate the KOI-961 planets (Muirhead et al. 2012).”
• THE OCCURRENCE OF POTENTIALLY HABITABLE PLANETS ORBITING M DWARFS ESTIMATED FROM THE FULL KEPLER DATASET AND AN EMPIRICAL MEASUREMENT OF THE DETECTION SENSITIVITY (2015, methodology): “Other authors further constrained the properties of particular planet host stars and associated planet candidates by acquiring followup spectroscopic and high resolution imaging observations (Johnson et al. 2012; Muirhead et al. 2012a,b; Ballard et al. 2013; Muirhead et al. 2013; Swift et al. 2013).”
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• NEAR-INFRARED METALLICITIES, RADIAL VELOCITIES, AND SPECTRAL TYPES FOR 447 NEARBY M DWARFS (2013, background): “For example, Muirhead et al. (2012a) and Muirhead et al. (2012b) exploited theK-band metallicity and temperature relations of Rojas-Ayala et al. (2012, hereafter R12) to estimate new planet properties for theKeplerObjects of Interest (KOIs) orbiting the coolestKepler stars and discovered the…”