Anatomy of the Class I protostar L1489 IRS with NOEMA - II. A disk replenished by a massive streamer

Abstract

(abridged) Streamers are newly identified channels that transport mass from large, molecular-cloud scales down to small, protoplanetary-disk scales. To better understand their impact on planet formation, it is essential to study their physical and chemical properties. In this framework, we aim to characterize the longest streamer identified in carbon chain emission within the Class I system L1489 IRS, connecting the nearby prestellar core L1489 to the young stellar object (YSO). We observed multiple transitions of C$_2$H, ortho-c-C$_3$H$_2$, and HC$_3$N in L1489 IRS with NOEMA and IRAM-30m at 3mm and 2mm. Using a variety of radiative transfer methods, including a hyperfine structure (HFS) fitting, rotational diagrams, and proposing a new self-consistent Markov chain Monte Carlo (MCMC) approach combined with the non-LTE RADEX code, we derived the column densities and abundances of those molecules, as well as the H$_2$ number density along the streamer. This enabled us to estimate its mass, infall rate, and its impact on the {star+disk} system's mass. We found lower limits on the streamer mass of $\geq(4.67-18.3)\times10^{-3}$ $M_\odot$ (i.e., $\geq0.65-2.57$ times the current disk mass) and an infall rate of $\geq(1.94-7.57)\times10^{-7}$ $M_\odot$ yr$^{-1}$, where the ranges correspond to the different molecular tracers. These values are consistent with those derived in similar Class I objects. This suggests that the disk could be fully replenished by streamer material. Given its mass, the streamer is likely at the origin of the external warped disk seen in this system, as predicted by numerical simulations. Moreover, the first investigations based on the C$_2$H/c-C$_3$H$_2$ and HC$_3$N/c-C$_3$H$_2$ abundance ratios suggest that the streamer chemistry may be inherited from the core. These results suggest, for the first time, that the chemical composition of a Class I object is [...]

Figures (12)

• Figure 1: Gallery of S/N maps from few of the observed lines used in this work. The line name is indicated on the top of each panel while their beam is shown in the lower right corner. The star indicates the position of L1489 IRS. The cyan contour corresponds to the targeted emission for the analysis (see Sect. \ref{['sec:data-preprocessing']}). The black cross indicates the position of the peak intensity of the core wu2019. Top to bottom: IRAM-30m observations of HC3N (first panel), single-field combined observations (IRAM-30m + NOEMA) of HC3N (second), C2H (third), and c-C3H2 (fourth), and mosaic combined observations of c-C3H2 (fifth).
• Figure 2: Excitation temperature (left column) and column density (right column) maps for C2H (top), ortho-c-C3H2 (middle), and HC3N (bottom), derived with methods described in the text. The beam displayed on the bottom left corner corresponds for C2H and c-C3H2 to the smoothed beam used in the analysis (see Sect. \ref{['sec:data-preprocessing']}), and to the original beam from NOEMA observations for HC3N (see Sect. \ref{['sec:results-hc3n']}).
• Figure 3: Rotational diagram of HC3N on observed IRAM-30m lines toward the streamer. Red points correspond to the observations while the blue dashed line correspond to the best linear fitting.
• Figure 4: Gallery of integrated intensity maps (in K km s$^{-1}$) of observed lines used in this work. The line name is indicated on the top of each panel while their beam is shown in the lower right corner. The star indicates the position of L1489 IRS. The cyan contour corresponds to the targeted emission for the analysis (see Sect. \ref{['sec:data-preprocessing']}). Top row: Single-field combined (IRAM-30m + NOEMA) observations of C2H. Middle row: IRAM-30m (columns 1 to 5) and combined (column 6) observations of HC3N. Bottom row: Mosaic (first and second column) and single-field (third and fourth column) combined observations of c-C3H2.
• Figure 5: Same as Fig. \ref{['fig:mom0-maps']}, but for the S/N maps of observed lines used in this work.