Accretion onto the Embedded Protostar L1527 IRS: Insights from JWST NIRSpec and MIRI Observations

Abstract

Accretion is the primary driver of protostellar evolution, regulating mass assembly and shaping the physical and chemical environments of young stellar objects. Quantifying accretion in the Class 0 protostellar phase is particularly important, yet remains observationally challenging due to high extinction toward the central protostars. In this paper, we present JWST NIRSpec and MIRI/MRS IFU data towards the Class 0 protostar L1527 IRS. We extract one-dimensional spectra and find emission from atomic and molecular hydrogen, water, OH, and several ionic species. The atomic hydrogen lines, Br$α$, Pf$α$, and Pf$γ$ are the most critical to this study since they can be used as accretion diagnostics. The existence of these atomic hydrogen lines viewed in scattered light indicates that accretion is likely occurring magnetospherically rather than through a boundary layer. Moment 0 emission maps show that the hydrogen emission is co-spatial with the scattered light continuum with a strong east-west asymmetry which is not due to outflow shocks. We additionally present moment 0 maps of other detected species and discuss their emission morphology. By primarily analyzing the Br$α$ line, the strongest of our detected atomic hydrogen lines, we characterize the accretion onto L1527 IRS by estimating the accretion luminosity to be $0.4~\text{L}_\odot$ and the accretion rate to be around $1\times10^{-7}~ \text{M}_\odot \text{yr}^{-1}$. We lastly discuss the implications of our results with respect to both non-steady and asymmetric accretion possibly occurring in L1527 IRS.

Figures (14)

• Figure 1: Our extracted 1D spectrum of L1527 using NIRSpec and MIRI data. The various observing channels are highlighted with different colors. Below the spectrum we show the median collapsed spectral cubes to demonstrate the morphology of the continuum emission for each channel. We also plot the apertures we used to extract the 1D spectra from each channel as orange ellipses. The ALMA continuum position of the source is shown with the cyan star and the diffraction limited beam is shown as a grey circle (in future Figures as well). We fill out our spectral coverage by showing data from the JOYS program (in blue) presented in Devaraj et al. (Submitted)
• Figure 2: Top row: Continuum subtracted moment 0 maps for the three detected atomic hydrogen lines. The contours correspond to the local continuum emission. Bottom row: the corresponding line profiles for the atomic hydrogen lines along with the S/R of the line. The line profiles were extracted using the elliptical apertures shown in Figure \ref{['fig:full_spec']}. For Pf$\alpha$, only the eastern aperture was used as the western aperture introduced more noise than signal and thus made the line profile less clear. The gray dotted portion of the Pf $\gamma$ line profile is a nearby H$_2$ line that has been masked out.
• Figure 3: Comparison of the Pf$\alpha$ and Br$\alpha$ line profiles after the Pf$\alpha$ profile has been down-sampled to match the NIRSpec spectral resolution.
• Figure 4: Continuum subtracted moment 0 maps for a sample of our detected molecular hydrogen transitions with contours representing the local continuum.
• Figure 5: Top row: Continuum subtracted moment 0 maps for [Ar II], [Ne III], and [Fe II]. Bottom row: Continuum subtracted moment 1 maps for the same species. Pixels below the 3$\sigma$ level in the moment 0 maps have been masked out of the moment 1 maps. For both rows, the contours show the local continuum.