Comparison of planetary Hα-emission models: A new correlation with accretion luminosity

Abstract

Accreting planets have been detected through their hydrogen-line emission, specifically H$\alpha$. To interpret this, stellar-regime empirical correlations between the H$\alpha$ luminosity $L_{\mathrm{H}\alpha }$ and the accretion luminosity $L_{\mathrm{acc}}$ or accretion rate $\dot{M}$ have been extrapolated to planetary masses, however without validation. We present a theoretical $L_{\mathrm{acc}}$--$L_{\mathrm{H}\alpha }$ relationship applicable to a shock at the surface of a planet. We consider wide ranges of accretion rates and masses and use detailed spectrally-resolved, non-equilibrium models of the postshock cooling. The new relationship gives a markedly higher $L_{\mathrm{acc}}$ for a given $L_{\mathrm{H}\alpha }$ than fits to young stellar objects, because Ly-$\alpha$, which is not observable, carries a large fraction of $L_{\mathrm{acc}}$. Specifically, an $L_{\mathrm{H}\alpha }$ measurement needs ten to 100 times higher $L_{\mathrm{acc}}$ and $\dot{M}$ than previously predicted, which may explain the rarity of planetary H$\alpha$ detections. We also compare the $\dot{M}$--$L_{\mathrm{H}\alpha }$ relationships coming from the planet-surface shock or implied by accretion-funnel emission. Both can contribute simultaneously to an observed H$\alpha$ signal but at low (high) $\dot{M}$ the planetary-surface shock (heated funnel) dominates. Only the shock produces Gaussian line wings. Finally, we discuss accretion contexts in which different emission scenarios may apply, putting recent literature models in perspective, and also present $L_{\mathrm{acc}}$--$L_{\mathrm{line}}$ relationships for several other hydrogen lines.

arXiv comment13 pages, accepted to ApJL

References in corpus (43)

• Two accreting protoplanets around the young star PDS 70
• X-Shooter spectroscopy of young stellar objects in Lupus: Accretion properties of class II and transitional objects
• X-Shooter spectroscopy of young stellar objects: IV -- Accretion in low-mass stars and sub-stellar objects in Lupus
• Accreting Protoplanets in the LkCa 15 Transition Disk
• Star and protoplanetary disk properties in Orion's suburbs
• Characterization of exoplanets from their formation II: The planetary mass-radius relationship
• Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and Optical Spectra
• Distribution of Accreting Gas and Angular Momentum onto Circumplanetary Disks
• Accretion of Jupiter-mass Planets in the Limit of Vanishing Viscosity
• Meridional flows in the disk around a young star
• The Far-Ultraviolet Spectra of TW Hya. II. Models of H2 Fluorescence in a Disk
• X-shooter spectroscopy of young stellar objects: I - Mass accretion rates of low-mass T Tauri stars in σOrionis
• Accreting Circumplanetary Disks: Observational Signatures
• Magellan Adaptive Optics Imaging of PDS 70: Measuring the Mass Accretion Rate of a Young Giant Planet within a Gapped Disk
• Constraining the Nature of the PDS 70 Protoplanets with VLTI/GRAVITY
• Characterization of exoplanets from their formation III: The statistics of planetary luminosities
• Accretion onto Planetary Mass Companions of Low-Mass Young Stars
• On the Terminal Rotation Rates of Giant Planets
• Including Dust Coagulation in Hydrodynamic Models of Protoplanetary Disks: Dust Evolution in the Vicinity of a Jupiter-mass Planet
• A search for accreting young companions embedded in circumstellar disks: High-contrast H$\alpha$ imaging with VLT/SPHERE
• Theoretical Model of Hydrogen Line Emission from Accreting Gas Giants
• A Systematic Study of the Final Masses of Gas Giant Planets
• Accretion Properties of PDS 70b with MUSE
• Hubble Space Telescope UV and H$\alpha$ Measurements of the Accretion Excess Emission from the Young Giant Planet PDS 70 b
• Thermodynamics of Giant Planet Formation: Shocking Hot Surfaces on Circumplanetary Disks
• Magnetospheric Accretion as a Source of H$\alpha$ Emission from Proto-planets around PDS 70
• Observability of Forming Planets and their Circumplanetary Disks II. -- SEDs and Near-Infrared Fluxes
• The widest H$\alpha$ survey of accreting protoplanets around nearby transition disks
• The Planetary Accretion Shock: I. Framework for Radiation-hydrodynamical Simulations and First Results
• The Planetary Accretion Shock. II. Grid of Post-Shock Entropies and Radiative Shock Efficiencies for Non-Equilibrium Radiation Transport
• Global 3D radiation-hydrodynamic simulations of gas accretion: The opacity dependent growth of Saturn-mass planets
• Strong H$\alpha$ emission and signs of accretion in a circumbinary planetary mass companion from MUSE
• Detectability of embedded protoplanets from hydrodynamical simulations
• Hydrogen recombination line luminosities and -variability from forming planets
• A measure of the size of the magnetospheric accretion region in TW Hydrae
• Accretion Outbursts in Circumplanetary Disks
• On the structure and mass delivery towards circumplanetary discs
• The Planetary Luminosity Problem: "Missing Planets" and the Observational Consequences of Episodic Accretion
• Searching for proto-planets with MUSE
• Possible Signatures of Magnetospheric Accretion onto Young Giant Planets
• Disk-fed giant planet formation
• The Separation and H-alpha Contrasts of Massive Accreting Planets in the Gaps of Transitional Disks: Predicted H-alpha Protoplanet Yields for Adaptive Optics Surveys
• Observing the gas component of circumplanetary disks around wide-orbit planet-mass companions in the (sub)mm regime

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