Analyzing JWST/NIRSpec Hydrogen Line Detections at TWA 27B: Constraining Accretion Properties and Geometry

Abstract

Hydrogen lines from forming planets are crucial for understanding planet formation. However, the number of planetary hydrogen line detections is still limited. Recent JWST/NIRSpec observations have detected Paschen and Brackett hydrogen lines at TWA 27 B (2M1207b). TWA 27 B is classified as a planetary-mass companison (PMC) rather than a planet due to its large mass ratio to the central object ($\approx 5M_{\mathrm{J}}$ compared to $25M_{\mathrm{J}}$). Nevertheless, TWA 27 B's hydrogen line emission is expected to be same as for planets, given its small mass. We aim to constrain the accretion properties and accretion geometry of TWA 27 B, contributing to our understanding of hydrogen line emission mechanism common to both PMCs and planets. We conduct spectral fitting of four bright hydrogen lines (Pa-$\alpha$, Pa-$\beta$, Pa-$\gamma$, Pa-$\delta$) with an accretion-shock emission model tailored for forming planets. We estimate the mass accretion rate at $\dot{M}\approx 3\times 10^{-9}{M}_{\mathrm{J}}{\mathrm{yr}}^{-1}$ with our fiducial parameters, though this is subject to an uncertainty of up to factor of ten. Our analysis also indicates a dense accretion flow, $n\gtrsim 10^{13}\mathrm{c}{\mathrm{m}}^{-3}$ just before the shock, implying a small accretion-shock filling factor $f_{\mathrm{f}}$ on the planetary surface ($f_{\mathrm{f}}\lesssim 5\times 10^{-4}$). This finding suggests that magnetospheric accretion is occurring at TWA 27 B. Additionally, we carry out a comparative analysis of hydrogen-line emission color to identify the emission mechanism, but the associated uncertainties proved too large for definitive conclusions. This underscores the need for further high-precision observational studies to elucidate these emission mechanisms fully.

14 pages, 6 figures, Accepted for publication in the Astronomical Journal

References in corpus (48)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• A Giant Planet Candidate near a Young Brown Dwarf
• 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
• The Optical to Mid-Infrared Extinction Law Based on the APOGEE, Gaia DR2, Pan-STARRS1, SDSS, APASS, 2MASS and WISE Surveys
• UV excess measures of accretion onto young very low-mass stars and brown dwarfs
• Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and Optical Spectra
• The Structure of Spiral Shocks Excited by Planetary-mass Companions
• Accreting Circumplanetary Disks: Observational Signatures
• Enabling New Flexibility in the SUNDIALS Suite of Nonlinear and Differential/Algebraic Equation Solvers
• Magellan Adaptive Optics Imaging of PDS 70: Measuring the Mass Accretion Rate of a Young Giant Planet within a Gapped Disk
• Images of Embedded Jovian Planet Formation At A Wide Separation Around AB Aurigae
• Circumplanetary disk or circumplanetary envelope?
• On the Terminal Rotation Rates of Giant Planets
• Origins of the H, He I, and Ca II Line Emission in Classical T Tauri Stars
• 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
• Accretion Properties of PDS 70b with MUSE
• Modeling the Halpha line emission around classical T Tauri stars using magnetospheric accretion and disk wind models
• Hubble Space Telescope UV and H$\alpha$ Measurements of the Accretion Excess Emission from the Young Giant Planet PDS 70 b
• Magnetospheric Accretion as a Source of H$\alpha$ Emission from Proto-planets around PDS 70
• The widest H$\alpha$ survey of accreting protoplanets around nearby transition disks
• Mean gas opacity for circumstellar environments and equilibrium temperature degeneracy
• The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits. III. The frequency of brown dwarfs and giant planets as companions to solar-type stars
• Comparison of planetary Hα-emission models: A new correlation with accretion luminosity
• Constraints on the formation mechanism of the planetary mass companion of 2MASS 1207334-393254
• Strong H$\alpha$ emission and signs of accretion in a circumbinary planetary mass companion from MUSE
• HST/WFC3 H$\alpha$ Direct-Imaging Detection of a Point-like Source in the Disk Cavity of AB Aur
• JWST/NIRSpec Observations of the Planetary Mass Companion TWA 27B
• Accreting protoplanets: Spectral signatures and magnitude of gas and dust extinction at H alpha
• Near-infrared Accretion Signatures from the Circumbinary Planetary Mass Companion Delorme 1 (AB)b
• Searching for proto-planets with MUSE
• The Giant Accreting Protoplanet Survey (GAPlanetS) -- Results from a Six Year Campaign to Image Accreting Protoplanets
• Emission line variability of young 10-30 Mjup companions : I. The case of GQ Lup b and GSC 06214-00210 b
• Searching for H${}_{\alpha }$-emitting sources in the gaps of five transitional disks. SPHERE/ZIMPOL high-contrast imaging
• Resolved near-UV hydrogen emission lines at 40-Myr super-Jovian protoplanet Delorme 1 (AB)b: Indications of magnetospheric accretion
• The Planetary Accretion Shock. III. Smoothing-free 2.5D simulations and calculation of H alpha emission
• Hydrodynamic Model of H$\alpha$ Emission from Accretion Shocks of Proto-Giant Planet and Circumplanetary Disk
• The influence of frequency-dependent radiative transfer on the structures of radiative shocks
• Keck/OSIRIS Pa$\beta$ high-contrast imaging and updated constraints on PDS~70b
• Constraining accretion signatures of exoplanets in the TW Hya transitional disk
• Revisiting the Helium and Hydrogen Accretion Indicators at TWA 27B: Weak Mass Flow at Near-Freefall Velocity
• Magnetic Fields and Accreting Giant Planets around PDS 70

Cited by in corpus (5)

• Evidence for Variable Accretion onto PDS 70 c and Implications for Protoplanet Detections
• JWST/MIRI observations of the young TWA 27 system: hydrocarbon disk chemistry, silicate clouds, evidence for a CPD
• Occurrence rates of accreting companions from a new method for computing emission-line survey sensitivity: application to the H-alpha Giant Accreting Protoplanet Survey
• Stellar halo subtraction alternative for accreting companions' characterization with integral field spectroscopy: Analytical and on-sky demonstration on the PDS70, HTLup, and YSES1 systems
• Semianalytical Accretion-Tracer Emission: Forming Planets Are Intrinsically Faint