Disks and Jets in the Formation of Multiple Stellar Systems

The general goal of this thesis is to study the first stages of the star formation process in multiple systems. For that, we analyze two complementary aspects of multiple star formation: the simultaneous formation of protostars in a cluster, and the formation of an individual binary system. We use sensitive, high-resolution, and multifrequency continuum and line observations obtained with the Very Large Array (VLA) and the Atacama Large Millimeter/Submillimeter Array (ALMA). The centimeter VLA continuum observations allow us to detect the thermal free-free emission from ionized jets and photoevaporating disks, while the millimeter ALMA continuum emission traces the dust in the mid-plane of the disks and the line emission provides us means to study its kinematics. Additionally, the high angular resolution and sensitivity of our observations allow us to detect components of several possible multiple systems.

In the first place, we present multiwavelength (0.7 - 5 cm), multiepoch (1994 - 2015) VLA observations toward the region enclosing the bright far-IR sources FIR 3 (HOPS 370) and FIR 4 (HOPS 108) in the Orion Molecular Cloud (OMC) 2, in Orion. We report the detection of 10 radio sources, seven of them identified as young stellar objects (YSOs). We image a well-collimated radio jet with a thermal free-free core (VLA 11) associated with the Class I intermediate-mass protostar HOPS 370. The jet presents several knots (VLA 12N, 12C, 12S) of non-thermal radio emission (likely synchrotron from shock-accelerated relativistic electrons) at distances of ∼ 7500 - 12500 au from the protostar, in a region where other shock tracers have been previously identified. We show that these knots are moving away from the HOPS 370 protostar at ∼ 100 km/s. The Class 0 protostar HOPS 108, which we detect as an independent, kinematically decoupled radio source, falls in the path of these non-thermal radio knots. These results favor the previously proposed scenario where the formation of HOPS 108 has been triggered by the impact of the HOPS 370 outflow with a dense clump. However, HOPS 108 presents an apparent proper motion velocity of ∼30 km/s, similar to that of other runaway stars in Orion, whose origin is puzzling.

Later, we extend our study to the whole field of view of those observations, a 12.5'-long portion of the Integral Shaped Filament (ISF) which contains the whole OMC-2 region and the southernmost 2.5' of the OMC-3 region. We report 47 additional radio sources, 23 of which are presented here for the first time. For these 47 radio sources, we report the positions, flux densities, and spectral indices. We discuss the nature of the 47 reported radio sources by analyzing their radio spectral index, morphology, emission at other wavelength ranges, position relative to the ISF, and association with dust clumps. We conclude that, out of the 57 total radio sources in the field of view, 41 (72%) are very likely associated with the star-forming region, 6 are extragalactic background sources, and we are unsure about the association with the star-forming region of the remaining 10 sources. Of the 41 sources associated with the star-forming region, 36 are tracing the position of YSOs, 3 are tracing non-thermal emission from jet knots, one is tracing the shock-ionized wall of an outflow cavity, and one could be either a YSO or a jet knot. We unambiguously identify the radio continuum emission of the driving sources of the 9 previously reported molecular outflows in our field of view. In four of these sources, we clearly resolve the elongated morphology characteristic of radio jets. We detect thermal free-free emission from two Class III YSOs that may be tracing their associated photoevaporating disks. We find signs of variability in 13 radio sources, seven of which are also variable at shorter wavelengths (near-IR/optical/X-ray). We find 7 pairs of radio sources with a projected separation < 3000 au, that are potential binary systems; taking into account the additional sources detected at other wavelengths, we then identify a total of 17 potential multiple systems in our field of view within this separation range.

Finally, we study the close binary system SVS 13, with components separated 90 au. We detect at least two circumstellar disks of dust and gas, and one circumbinary disk with prominent spiral arms, that appears to be in the earliest stages of formation, associated with this protostellar system. Dust emission appears more intense and compact toward component VLA 4B, while VLA 4A seems to be associated with a larger amount of dust and with stronger molecular transitions. We are able to estimate rotational temperatures and molecular column densities, indicating warm temperatures and rich chemistry. Molecular transitions typical of hot corinos are detected toward both VLA 4A and VLA 4B. From the observed dust emission and the kinematical information, we estimate the orientation of the system, the stellar masses and the mass of their associated disks. Our analysis of the proper motions and the kinematics of the disks suggest that up to four stellar objects, one of them a visible star, could be present within a region of size <100 au. In summary, SVS 13 seems to be an excellent test-bed to test numerical simulations of the earliest stages in the formation of binary and multiple systems.