Stellar photospheric abundances as a probe of discs and planets

Jermyn, Adam S.; Kama, M.

doi:10.1093/mnras/sty429

Cited by 25 publications

(37 citation statements)

References 92 publications

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“…Here we compare our results to the carbon abundance of the HD 163296 star. Its stellar C/H ratio is measured as 1.5 +1.2 −0.7 ×10 −4 (Folsom et al 2012;Jermyn & Kama 2018) which is about half of that in the Sun (2.7 +0.3 −0.3 × 10 −4 , Asplund et al 2009). Therefore HD 163296 system started with relatively carbon poor materials than the ISM.…”

Section: Discussionmentioning

confidence: 98%

Excess C/H in Protoplanetary Disk Gas from Icy Pebble Drift Across the CO Snowline

Zhang

Bosman

Bergin

2020

ApJL

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The atmospheric composition of giant planets carries the information of their formation history. Superstellar C/H ratios are seen in atmospheres of Jupiter, Saturn, and various giant exoplanets. Also, giant exoplanets show a wide range of C/O ratio. To explain these ratios, one hypothesis is that protoplanets accrete carbon-enriched gas when a large number of icy pebbles drift across the CO snowline. Here we report the first direct evidence of an elevated C/H ratio in disk gas. We use two thermo-chemical codes to model the 13 C 18 O, C 17 O, and C 18 O (2-1) line spectra of the HD 163296 disk. We show that the gas inside the CO snowline (∼70 au) has a C/H ratio of 1-2 times higher than the stellar value. This ratio exceeds the expected value substantially, as only 25-60% of the carbon should be in gas at these radii. Although we cannot rule out the case of a normal C/H ratio inside 70 au, the most probable solution is an elevated C/H ratio of 2-8 times higher than the expectation. Our model also shows that the gas outside 70 au has a C/H ratio of 0.1× the stellar value. This picture of enriched C/H gas at the inner region and depleted gas at the outer region is consistent with numerical simulations of icy pebble growth and drift in protoplanetary disks. Our results demonstrate that the large-scale drift of icy pebble can occur in disks and may significantly change the disk gas composition for planet formation.

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Section: Discussionmentioning

confidence: 98%

Excess C/H in Protoplanetary Disk Gas from Icy Pebble Drift Across the CO Snowline

Zhang

Bosman

Bergin

2020

ApJL

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“…Their observable photosphere mass, of order 10 −10 M , can be entirely replaced on a timescale of days at disk accretion ratesṀ acc ∼ 10 −8 to 10 −7 M yr −1 (Jermyn & Kama 2018). Measuring the stellar surface composition is thus a tool for studying the elemental composition of material recently accreted from a circumstellar disk (the Contaminated Astars Method, CAM; Kama et al 2015;Jermyn & Kama 2018). Surface layers built up on the star from dustdepleted material in the protoplanetary disk stage form a small fraction of the total mass of the star, and are lost through diffusive and rotational mixing with the bulk of the star within a million years after the disk dissipates (Jermyn & Kama 2018).…”

Section: Discussionmentioning

confidence: 99%

“…Now let f ph be the mass fraction of accreted material in the photosphere of a star (Jermyn & Kama 2018). Then the observed stellar composition is related to the composition of the accreting material as…”

Section: Refractory Fraction Of An Elementmentioning

confidence: 99%

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Abundant Refractory Sulfur in Protoplanetary Disks

Kama

Shorttle

Jermyn

et al. 2019

ApJ

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Sulfur is one of the most abundant elements in the Universe, with important roles in astro-, geo-, and biochemistry. Its main reservoirs in planet-forming disks have previously eluded detection: gaseous molecules only account for < 1 % of total elemental sulfur, with the rest likely in either ices or refractory minerals. Mechanisms such as giant planets can filter out dust from gas accreting onto disk-hosting stars. For stars above 1.4 solar masses, this leaves a chemical signature on the stellar photosphere that can be used to determine the fraction of each element that is locked in dust. Here, we present an application of this method to sulfur, zinc, and sodium. We analyse the accretion-contaminated photospheres of a sample of young stars and find (89 ± 8) % of elemental sulfur is in refractory form in their disks. The main carrier is much more refractory than water ice, consistent with sulfide minerals such as FeS.

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“…Since young A stars (Herbig Ae stars) have only a thin convective zone at their surfaces, their surface composition provides a record of their recent accretion history (e.g. Jermyn & Kama 2018). Kama et al (2015) showed that the material Herbig Ae stars accreted from transition discs with large cavities was typically depleted in refractory elements by about a factor of 10 (but not carbon or oxygen), while stars accreting from normal, non-transition discs showed a solar composition.…”

Section: Introductionmentioning

confidence: 99%

Fingerprints of giant planets in the composition of solar twins

Booth

Owen

2020

Monthly Notices of the Royal Astronomical Society

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The Sun shows a ∼ 10 % depletion in refractory elements relative to nearby solar twins. It has been suggested that this depletion is a signpost of planet formation. The exoplanet statistics are now good enough to show that the origin of this depletion does not arise from the sequestration of refractory material inside the planets themselves. This conclusion arises because most sun-like stars host close-in planetary systems that are on average more massive than the Sun's. Using evolutionary models for the protoplanetary discs that surrounded the young Sun and solar twins we demonstrate that the origin of the depletion likely arises due to the trapping of dust exterior to the orbit of a forming giant planet. In this scenario a forming giant planet opens a gap in the gas disc, creating a pressure trap. If the planet forms early enough, while the disc is still massive, the planet can trap 100 M ⊕ of dust exterior to its orbit, preventing the dust from accreting onto the star in contrast to the gas. Forming giant planets can create refractory depletions of ∼ 5 − 15%, with the larger values occurring for initial conditions that favour giant planet formation (e.g. more massive discs, that live longer). The incidence of solar-twins that show refractory depletion matches both the occurrence of giant planets discovered in exoplanet surveys and "transition" discs that show similar depletion patterns in the material that is accreting onto the star.

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Stellar photospheric abundances as a probe of discs and planets

Cited by 25 publications

References 92 publications

Excess C/H in Protoplanetary Disk Gas from Icy Pebble Drift Across the CO Snowline

Excess C/H in Protoplanetary Disk Gas from Icy Pebble Drift Across the CO Snowline

Abundant Refractory Sulfur in Protoplanetary Disks

Fingerprints of giant planets in the composition of solar twins

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