IRAM 04191+1522: a compact proto-brown dwarf binary candidate

Abstract

Very low-luminosity objects in nearby star-forming regions have been identified as promising proto-brown dwarf candidates. The study of their multiplicity can shed light on the dominant formation mechanism of these substellar objects. We aim at studying the multiplicity of the very low luminosity object IRAM 04191+1522. To do so, we have obtained 0.89mm ALMA observations with a very extended configuration, achieving an angular resolution of ~0.04 arcsec (6 au at 140 pc). We have complemented our data with new VLA observations, and ALMA archival data at 1.3mm. As a result, we resolve IRAM04191+1522 into a close binary candidate for the first time. The binary is detected in the ALMA continuum data with a projected separation of ~80 mas, or 11 au at a distance of 140 pc. The two sources are oriented in the East-West direction, with the eastern component being brighter and more extended than the western one, which is marginally resolved. The analysis of C18O(2-1) archival data reveals gaseous material in rotation around the binary, presumably from a circumbinary disk with ~27 au of radius centered on the faintest ALMA component. A fit of the position-velocity diagram allows us to estimate a total dynamical mass for the system of 50+-40 MJup. Therefore, we classify IRAM04191 as a tight proto-brown dwarf binary candidate. The VLA data reveals the detection of a single object closer to the western ALMA source, and with a spectral index consistent with a radio jet.

Figures (7)

• Figure 1: ALMA and VLA observations of IRAM04191. Left: 0.89 mm observations. The contours represent values of 5, 7, 8, 9, 10, 10.7-$\sigma$ (rms=6.6e-05 Jy/beam) drawn from the image smoothed with a Gaussian of FWHM corresponding to approximately one synthesized beam. Middle: 1.3 mm observations (robust of 0.5). The contours represent values of 4, 7, 10, 13,and 19-$\sigma$, with rms= 2.4e-05 Jy/beam. Right: VLA KKaQ image (robust of 1). The contours correspond to 3, 4, 6, 9, 12, 15, 18 times the $rms$ (5 $\mu$Jy/beam). The synthesized beams are displayed in the bottom left corner of each image. The white crosses represent the positions of the two detected sources at 1.3 mm.
• Figure 2: First-order moment of the C$^{18}$O (2--1) line. We have selected the channels that show emission closer to the central binary (see text), revealing the presence of rotating emission resembling a circumbinary disk. The synthesized beam is displayed at the bottom right (pink). We have overplotted with black contours the detection from the ALMA 1.3 mm observations, being 4, 7, 10, 13, 19 the $rms$ of the image, 2.4e-5 Jy/beam. The beam of the ALMA data is shown in the bottom-left corner (grey). The red and black '+' signs indicate the positions of the sources detected at 1.3 mm, as reported in Table B1.
• Figure 3: PV-diagram built along the major axis of the C$^{18}$O emission. The contours represent values of 3, 6 and 9-$\sigma$. We include the extracted velocities from the edge (pink and cyan) and ridge (blue and red) methods within SLAM, assuming a Keplerian rotation pattern.
• Figure 4: Dynamical mass ($M_{\rm dyn}$) vs $L_{\rm int}$ diagram adopted from Palau2024_review. Blue symbols represent protostars, VeLLOs and proto-BD candidates with $L_{\rm int}$ and $M_{\rm dyn}$ measurements, while the solid line represents the fit to the data. The shaded area corresponds to 2 (dark) and 5 times (light) the uncertainty of the fit. The dashed green lines delimit the region at the bottom left consistent with proto-BDs. We have represented IRAM 04191 with the dynamical mass derived in this work.
• Figure 5: 0.89 mm observations of IRAM04191 with robust of 0.5. Left: self-calibrated image. The contours represent 5, 9,13, 17, 21, 22, 23, 25, 27 times the $rms$ (4.9e-5 Jy/beam). Right: non self-calibrated image. The contours represent 4, 7, 10, 12, 15, 18, 21 times the $rms$ (4.5e-5 Jy/beam). The white crosses represent the position of the two sources detected in the 1.3 mm data.