M Stars in the Tw Hya Association: Stellar X-Rays and Disk Dissipation

Kastner, Joel H.; Principe, David A.; Punzi, Kristina; Stelzer, B.; Gorti, Uma; Pascucci, Ilaria; Argiroffi, C.

doi:10.3847/0004-6256/152/1/3

Cited by 31 publications

(33 citation statements)

References 68 publications

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“…Giant planet-hosting M dwarfs are more likely to be metal rich and the inventory of refractory solids would be double ([Fe/H > 0.3) in 4% of Kepler M dwarfs, according to the metallicities estimated by Gaidos et al (2016). These inventories do not address the issue of accretion time, an acute problem if M dwarfs disks dissipate more rapidly (Kastner et al 2016).…”

Section: Discussionmentioning

confidence: 99%

A minimum mass nebula for M dwarfs

Gaidos

2017

Monthly Notices of the Royal Astronomical Society: Letters

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Recently revealed differences in planets around M dwarf vs. solar-type stars could arise from differences in their primordial disks, and surveys of T Tauri stars find a correlation between stellar mass and disk mass. "Minimum" disks have been reconstructed for the Solar System and solar-type stars and here this exercise is performed for M dwarfs using Kepler-detected planets. Distribution of planet mass between current orbits produces a disk with total mass of ≈0.009M ⊙ and a power-law profile with index α = 2.2. Disk reconstruction from the output of a forward model of planet formation indicates that the effect of detection bias on disk profile is slight and that the observed scatter in planet masses and semi-major axes is consistent with a universal disk profile. This nominal M dwarf disk is more centrally concentrated than those inferred around the solar-type stars observed by Kepler, and the mass surface density beyond 0.02 AU is sufficient for in situ accretion of planets as single embryos. The mass of refractory solids within 0.5 AU is 5.6M ⊕ compared to 4M ⊕ for solar-type stars, in contrast with the trend with total disk mass. The total solids beyond 0.5 AU is sufficient for the core of at least one giant planet.

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Section: Discussionmentioning

confidence: 99%

A minimum mass nebula for M dwarfs

Gaidos

2017

Monthly Notices of the Royal Astronomical Society: Letters

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“…The count rates of RASS sources unambiguously associated with Table 1 stars were converted to fluxes assuming a conversion factor appropriate for young late-type stars, i.e., 6.3 × 10 −12 erg cm −2 count −1 (Kastner et al 2016a). The resulting X-ray fluxes were used to determine the stars' X-ray luminosities relative to bolometric, log (L X /L bol ), at the epoch of the RASS observations.…”

Section: Relative X-ray Luminositiesmentioning

confidence: 99%

Nearby Young, Active, Late-type Dwarfs in Gaia's First Data Release

Kastner

Sacco

Rodríguez

et al. 2017

ApJ

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The Galex Nearby Young Star Survey (GALNYSS) has yielded a sample of ∼2000 UV-selected objects that are candidate nearby (D < ∼150 pc), young (age ∼10-100 Myr), late-type stars. Here, we evaluate the distances and ages of the subsample of (19) GALNYSS stars with Gaia Data Release 1 (DR1) parallax distances D ≤ 120 pc. The overall youth of these 19 mid-K to early-M stars is readily apparent from their positions relative to the loci of main sequence stars and giants in Gaia-based color-magnitude and color-color diagrams constructed for all stars detected by Galex and the Wide-field Infrared Space Explorer for which parallax measurements are included in DR1. The isochronal ages of all 19 stars lie in the range ∼10-100 Myr. Comparison with Li-based age estimates indicates a handful of these stars may be young main-sequence binaries rather than pre-main sequence stars. Nine of the 19 objects have not previously been considered as nearby, young stars, and all but one of these are found at declinations north of +30• . The Gaia DR1 results presented here indicate that the GALNYSS sample includes several hundred nearby, young stars, a substantial fraction of which have not been previously recognized as having ages < ∼100 Myr.

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“…Ultraviolet (UV) and Xray radiation, which are created by hot gas accretion onto and activity in the protostellar atmosphere, can effectively enhance the populations of rovibrationallyexcited molecules, which create pathways for molecular dissociation (e.g. Glassgold & Najita 2001;Bergin et al 2004;Gorti & Hollenbach 2004;Glassgold et al 2004;Kamp et al 2005;Dullemond et al 2007;Güdel et al 2007;Kastner et al 2016). High-energy radiation may also help heat and regulate chemical processes in the disk atmosphere, leading to the production of atomic and molecular by-products (e.g.…”

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confidence: 99%

Signatures of Hot Molecular Hydrogen Absorption from Protoplanetary Disks. I. Non-thermal Populations

Hoadley

Arulanantham

Loyd

et al. 2017

ApJ

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The environment around protoplanetary disks (PPDs) regulates processes which drive the chemical and structural evolution of circumstellar material. We perform a detailed empirical survey of warm molecular hydrogen (H 2 ) absorption observed against H I-Lyα (Lyα: λ 1215.67Å) emission profiles for 22 PPDs, using archival Hubble Space Telescope (HST ) ultraviolet (UV) spectra to identify H 2 absorption signatures and quantify the column densities of H 2 ground states in each sightline. We compare thermal equilibrium models of H 2 to the observed H 2 rovibrational level distributions. We find that, for the majority of targets, there is a clear deviation in high energy states (T exc 20,000 K) away from thermal equilibrium populations (T(H 2 ) 3500 K). We create a metric to estimate the total column density of non-thermal H 2 (N(H 2 ) nLTE ) and find that the total column densities of thermal (N(H 2 )) and N(H 2 ) nLTE correlate for transition disks and targets with detectable C IV-pumped H 2 fluorescence. We compare N(H 2 ) and N(H 2 ) nLTE to circumstellar observables and find that N(H 2 ) nLTE correlates with X-ray and FUV luminosities, but no correlations are observed with the luminosities of discrete emission features (e.g., Lyα, C IV). Additionally, N(H 2 ) and N(H 2 ) nLTE are too low to account for the H 2 fluorescence observed in PPDs, so we speculate that this H 2 may instead be associated with a diffuse, hot, atomic halo surrounding the planet-forming disk. We create a simple photon-pumping model for each target to test this hypothesis and find that Lyα efficiently pumps H 2 levels with T exc ≥ 10,000 K out of thermal equilibrium.

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M Stars in the Tw Hya Association: Stellar X-Rays and Disk Dissipation

Cited by 31 publications

References 68 publications

A minimum mass nebula for M dwarfs

A minimum mass nebula for M dwarfs

Nearby Young, Active, Late-type Dwarfs in Gaia's First Data Release

Signatures of Hot Molecular Hydrogen Absorption from Protoplanetary Disks. I. Non-thermal Populations

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