Studying young stellar objects with near-IR non-redundant aperture masking and millimeter interferometry

Abstract

Circumstellar disks and outflows play a central role in the growth of low-mass (M < 2 M_sun) stars and the formation of planetary systems. These disks are ubiquitous at young ages (< 1 Myr), as they are naturally formed during the gravitational collapse of protostellar cores due to the conservation of angular momentum. Circumstellar disks feed the forming stars and provide an environment for small grains to eventually grow into rocky planets and the cores of giant planets at a wide range of stellocentric distances ( ~0.1-100 au). In parallel to the growth solids in the disk, bipolar outflows and winds are generated on similar physical scales. Outflows carry angular momentum away and help the accretion of circumstellar material onto the central object. They also play an important role in the dissipation of the envelope that marks the transition from the Class I (a deeply embedded protostar) to Class II stage (an optically visible T Tauri star). Eventually, the primordial disk disperses, leaving a star surrounded by a remnant debris (Class III) object and likely a system of planetesimals and planets. This thesis incorporates high-sensitivity millimeter-wavelength interferometry and near-infrared Non-Redundant Mask (NRM) Interferometry to assess molecular outflow and disks properties in Class I-II objects. It explores the physical mechanisms dispersing the disk and envelope system (e.g., outflows and dynamical interactions in binary systems) and the properties of protoplanetary disks as a function of stellar mass at an age of 2-3 Myr.

We investigate the properties of the Class I molecular outflows present in HBC 494 and V883 Ori, two young stellar objects experiencing episodic events of extreme accretion known as FU Ori outbursts. These outflows help to disperse the surrounding envelope at very early stages while removing angular momentum from the disk. We estimate the kinematic properties and describe physical structures of the outflows using the 12CO and 13CO emissions lines. Similarly, the C18O emission line is used to describe envelope material from both sources. An outstanding result is the wide-opening angle of the outflow cavities of ~150 deg. for both sources. Outflows masses in both FUors are on the same order of magnitude, while V883 Ori shows an outflow component that is much slower (characteristic velocity of only 0.65 km s^-1) than seen in other FUors such as HBC 494. To date, interferometric studies of FUors are scarce and more observations needed in order to compare with other objects at a similar sensitivity and resolution. In addition, using NRM, we searched for binary companions to objects previously classified as Transitional Disks (TD, disks with inner opacity holes) in nearby (d < 300 pc) star-forming regions (Ophiuchus, Taurus-Auriga, and IC348) and investigate the interaction with (sub)stellar companions as a possible mechanism for the depletion of their inner disks. We implement a new method of completeness correction using a combination of randomly sampled binary orbits and Bayesian inference. We find that ~ 0.38 +/- 0.09 of the TDs are actually circumbinary disks, while the remaining objects are transitional disks where the inner holes are the result of other internal processes such as photoevaporation, and/or planet-disk interactions.

Finally, we present an ALMA 1.3 mm survey of Class II sources in the benchmark 2-3 Myr stellar cluster IC 348 to investigate the properties of disks at the time 50% of the disks have already been completely dispersed. We find that the detection rate in 1.3 mm continuum is a strong function of stellar mass. Most targets with masses 0.3 < M_sun remain undetected down to a 3-sigma sensitivity of 0.45 mJy, corresponding to a disk dust mass of ~0.9 M_earth. A stacking analysis of the non-detections suggests that the typical dust mass around most 2-3 Myr old M-type stars is 0.2 M_earth (or 0.07 M_JUP of gas + dust, assuming a standard gas to dust mass ratio of 100). A Bayesian analysis is used to statistically compare IC 348 to other star-forming regions. As a general result, this analysis shows that IC 348 disks are a factor of 5 fainter on average than in Taurus, Cha I, and Lupus. While IC 348 and sigma Ori have similar distributions. On the other hand, Upper Sco disks are definitely fainter on average than IC 348. The resulting cumulative distribution functions confirm a clear evolution (depletion of mm-sized grains) of the circumstellar disks in these regions over a period of 1-10 Myr.