LkCa 15: A YOUNG EXOPLANET CAUGHT AT FORMATION?

By A. Kraus, Michael J. Ireland. 2011

324 citations recorded by the source corpus.

Young and directly imaged exoplanets offer critical tests of planet-formation models that are not matched by radial velocity surveys of mature stars. These targets have been extremely elusive to date, with no exoplanets younger than 10–20 Myr and only a handful of direct-imaged exoplanets at all ages. We report the direct-imaging discovery of a likely (proto)planet around the young (∼2 Myr) solar analog LkCa 15, located inside a known gap in the protoplanetary disk (a “transitional disk”). Our observations use non-redundant aperture masking interferometry at three epochs to reveal a faint and relatively blue point source (, K′ − L′ = 0.98 ± 0.22), flanked by approximately co-orbital emission that is red and resolved into at least two sources (, K′ − L′ = 2.7 ± 0.3; , K′ − L′ = 1.94 ± 0.16). We propose that the most likely geometry consists of a newly formed (proto)planet that is surrounded by dusty material. The nominal estimated mass is ∼6 MJup according to the 1 Myr hot-start models. However, we argue based on its luminosity, color, and the presence of circumplanetary material that the planet has likely been caught at its epoch of assembly, and hence this mass is an upper limit due to its extreme youth and flux contributed by accretion. The projected separations (71.9 ± 1.6 mas, 100.7 ± 1.9 mas, and 88.2 ± 1.8 mas) and deprojected orbital radii (16, 21, and 19 AU) correspond to the center of the disk gap, but are too close to the primary star for a circular orbit to account for the observed inner edge of the outer disk, so an alternative explanation (i.e., additional planets or an eccentric orbit) is likely required. This discovery is the first direct evidence that at least some transitional disks do indeed host newly formed (or forming) exoplanetary systems, and the observed properties provide crucial insight into the gas giant formation process.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/deb3921a88f86a31f70dfb6a50445573620a851d

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Citations in the corpus

Protoplanetary disk lifetimes vs stellar mass and possible implications for giant planet populations (2015, background): “…between transitional disks and planets – as demonstrated by several resolved images of planetary mass companions within the gap or cavity (e.g. Huélamo et al. 2011; Kraus & Ireland 2012; Quanz et al. 2013; Close et al. 2014) – makes them a cornerstone for theories of planet formation and evolution.”
Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA (2015, background): “Planet candidates have been found in cavities of the transition disks T Cha (Huélamo et al. 2011), LkCa 15 (Kraus & Ireland 2012) and HD 100546 (Quanz et al. 2014), indicating planet clearing as a possible scenario.”
Kinematic Evidence for an Embedded Protoplanet in a Circumstellar Disk (2018, background): “…imaging have been reported in several discs: HD 100546 (Quanz et al. 2013a; Brittain et al. 2014; Quanz et al. 2015; Currie et al. 2015), LkCa 15 (Kraus & Ireland 2012; Sallum et al. 2015), HD 169142 (Quanz et al. 2013b; Biller et al. 2014; Reggiani et al. 2014), and MWC 758 (Reggiani et al.…”
A YOUNG PROTOPLANET CANDIDATE EMBEDDED IN THE CIRCUMSTELLAR DISK OF HD 100546 (2013, background): “…observations, a few low-mass companion candidates have been revealed in the gap of their host star’s transitional disks (e.g., LkCa15 b, T Cha b; Kraus & Ireland 2012; Huélamo et al. 2011), but in some cases scattered light from the disk rim or other disk structures may be a valid explanation…”
DISCOVERY OF A PROBABLE 4–5 JUPITER-MASS EXOPLANET TO HD 95086 BY DIRECT IMAGING (2013, background): “Also, the (proto-) planet candidates around LkCa 15 (Kraus & Ireland 2012) and HD100546 (Quanz et al. 2013) still require confirmations.”
A LIKELY CLOSE-IN LOW-MASS STELLAR COMPANION TO THE TRANSITIONAL DISK STAR HD 142527 (2012, background): “Indeed, observations using SAM have already yielded two planetary or brown dwarf candidate companions to transition disk stars (Huélamo et al. 2011; Kraus & Ireland 2012).”
THE GEMINI/NICI PLANET-FINDING CAMPAIGN: THE FREQUENCY OF PLANETS AROUND YOUNG MOVING GROUP STARS (2013, background): “…(1) members of young ( 10 Myr) starforming clusters or OB associations (e.g., Taurus and Upper Sco; Lafrenière et al. 2008; Todorov et al. 2010; Kraus & Ireland 2012), (2) members of nearby young moving groups (ages of 10–300 Myr, e.g., Lagrange et al. 2010; Chauvin et al. 2005a; Marois et…”
HOW EMPTY ARE DISK GAPS OPENED BY GIANT PLANETS (2013, background): “There are hints of gap clearing by planets in so-called “transitional” disks having optically thin cavities (e.g., Kraus and Ireland 2012; Debes et al. 2013; Quanz et al. 2013).”
DETECTION AND CHARACTERIZATION OF EXOPLANETS AND DISKS USING PROJECTIONS ON KARHUNEN–LOÈVE EIGENIMAGES (2012, background): “…structures orbiting nearby stars were 1Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD 21218, USA obtained relatively recently (Marois et al. 2008a; Kalas et al. 2008; Lagrange et al. 2009, 2010; Marois et al. 2010b; Kalas 2011; Janson et al. 2012; Kraus & Ireland 2012).”
Complex organic molecules in protoplanetary disks (2013, background): “…emission within a radius of ≈ 50 AU has reclassified this object as a transition disk (Piétu et al. 2006) in which planet formation is likely at Article number, page 16 of 34 Catherine Walsh et al.: Complex organic molecules in protoplanetary disks an advanced stage (Kraus & Ireland 2012).”
The star formation history and accretion-disc fraction among the K-type members of the Scorpius–Centaurus OB association (2016, background): “These samples have been indispensible for direct imaging of brown dwarf and planetary-mass companions (e.g., Kraus & Ireland 2012), imaging debris disks in scattered light (e.g., Kalas et al. 2015), exploring the star-disk interaction in young stars (e.g., Nguyen et al. 2009), and studying the…”
Discovery of a planetary-mass companion within the gap of the transition disk around PDS 70 (2018, background): “Regarding LkCa15, three companion candidates have been reported in the literature (Kraus & Ireland 2012; Sallum et al. 2015).”
Adaptive Optics for Astronomy (2012, background): “…for which the interferometric analysis leads to superior PSF calibration and speckle suppression, is now providing evidence that the central holes in the disks are due to the presence of a binary star (Kraus et al. 2012) or are carved by giant planets (Huélamo et al. 2011, Kraus & Ireland 2012).”
Resolved gas cavities in transitional disks inferred from CO isotopologs with ALMA (2015, background): “Planet candidates have been found in cavities of several transition disks (Kraus & Ireland 2012; Quanz et al. 2013, 2015).”
Imaging Extrasolar Giant Planets (2016, background): “For the youngest protoplanets embedded in their host stars’ circumstellar disks, accretion streams might dominate over thermal photospheric emission, complicating luminosity measurements and mass estimates (e.g., LkCa15 b and HD 100546 b; Kraus & Ireland 2012; Quanz et al. 2013).”
Rapid growth of gas-giant cores by pebble accretion (2012, background): “Our results predict that ice and gas giant planets, detectable with direct imaging surveys, will be abundant around young (∼1 Myr) stars.”