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

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

The frequency of binary star interlopers amongst transitional discs

Using Non-Redundant Mask interferometry (NRM), we searched for binary companions to objects previously classified as transitional discs (TD). These objects are thought to be an evolutionary stage between an optically thick disc and optically thin disc. We investigate the presence of a stellar companion as a possible mechanism of material depletion in the inner region of these discs, which would rule out an ongoing planetary formation process in distances comparable to the binary separation. For our detection limits, we implement a new method of completeness correction using a combination of randomly sampled binary orbits and Bayesian inference. The selected sample of 24 TDs belongs to the nearby and young star-forming regions: Ophiuchus (˜130 pc), Taurus-Auriga (˜140 pc) and IC348 (˜220 pc). These regions are suitable to resolve faint stellar companions with moderate to high confidence levels at distances as low as 2 au from the central star. With a total of 31 objects, including 11 known TDs and circumbinary discs from the literature, we have found that a fraction of 0.38 ± 0.09 of the SEDs of these objects are likely due to the tidal interaction between a close binary and its disc, while the remaining SEDs are likely the result of other internal processes such as photoevaporation, grain growth, planet-disc interactions. In addition, we detected four companions orbiting outside the area of the truncation radii and propose that the IR excesses of these systems are due to a disc orbiting a secondary companion

The ALMA Early Science View of FUor/EXor objects. IV. Misaligned Outflows in the Complex Star-forming Environment of V1647 Ori and McNeil's Nebula

We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the star-forming environment surrounding V1647 Ori, an outbursting FUor/EXor pre-MS star. Dust continuum and the (J = 2 - 1) $^{12}$CO, $^{13}$CO, C$^{18}$O molecular emission lines were observed to characterize the V1647 Ori circumstellar disc and any large scale molecular features present. We detect continuum emission from the circumstellar disc and determine a radius r = 40 au, inclination i = 17$^{\circ}$$^{+6}_{-9}$ and total disc mass of M$_{\mathrm{disk}}$ of ~0.1 M$_{\odot}$. We do not identify any disc structures associated with nearby companions, massive planets or fragmentation. The molecular cloud environment surrounding V1647 Ori is both structured and complex. We confirm the presence of an excavated cavity north of V1647 Ori and have identified dense material at the base of the optical reflection nebula (McNeil's Nebula) that is actively shaping its surrounding environment. Two distinct outflows have been detected with dynamical ages of ~11,700 and 17,200 years. These outflows are misaligned suggesting disc precession over ~5500 years as a result of anisotropic accretion events is responsible. The collimated outflows exhibit velocities of ~2 km s$^{-1}$, similar in velocity to that of other FUor objects presented in this series but significantly slower than previous observations and model predictions. The V1647 Ori system is seemingly connected by an "arm" of material to a large unresolved structure located ~20$"$ to the west. The complex environment surrounding V1647 Ori suggests it is in the early stages of star formation which may relate to its classification as both an FUor and EXor type object.Comment: 18 pages, 14 figures, 4 tables; accepted for publication in MNRA

The ALMA Early Science View of FUor/EXor Objects - V. Continuum Disc Masses and Sizes

Low-mass stars build a significant fraction of their total mass during short outbursts of enhanced accretion known as FUor and EXor outbursts. FUor objects are characterized by a sudden brightening of ∼5 mag at visible wavelengths within 1 yr and remain bright for decades. EXor objects have lower amplitude outbursts on shorter time-scales. Here we discuss a 1.3 mm Atacama Large Millimeter/submillimeter Array (ALMA) mini-survey of eight outbursting sources (three FUors, four EXors, and the borderline object V1647 Ori) in the Orion Molecular Cloud. While previous papers in this series discuss the remarkable molecular outflows observed in the three FUor objects and V1647 Ori, here we focus on the continuum data and the differences and similarities between the FUor and EXor populations. We find that FUor discs are significantly more massive (∼80–600 MJup) than the EXor objects (∼0.5–40 MJup). We also report that the EXor sources lack the prominent outflows seen in the FUor population. Even though our sample is small, the large differences in disc masses and outflow activity suggest that the two types of objects represent different evolutionary stages. The FUor sources seem to be rather compact (Rc \u3c 20–40 au) and to have a smaller characteristic radius for a given disc mass when compared to T Tauri stars. V1118 Ori, the only known close binary system in our sample, is shown to host a disc around each one of the stellar components. The disc around HBC 494 is asymmetric, hinting at a structure in the outer disc or the presence of a second disc

How to Constrain Your M Dwarf. II. The Mass–Luminosity–Metallicity Relation from 0.075 to 0.70 Solar Masse

The mass-luminosity relation for late-type stars has long been a critical tool for estimating stellar masses. However, there is growing need for both a higher-precision relation and a better understanding of systematic effects (e.g., metallicity). Here we present an empirical relationship between Mks and mass spanning $0.075M_\odot<M<0.70M_\odot$. The relation is derived from 62 nearby binaries, whose orbits we determine using a combination of Keck/NIRC2 imaging, archival adaptive optics data, and literature astrometry. From their orbital parameters, we determine the total mass of each system, with a precision better than 1% in the best cases. We use these total masses, in combination with resolved Ks magnitudes and system parallaxes, to calibrate the mass-Mks relation. The result can be used to determine masses of single stars with a precision of 2-3%, which we confirm by a comparison to dynamical masses from the literature. The precision is limited by scatter around the best-fit relation beyond mass uncertainties, perhaps driven by intrinsic variation in the mass-Mks relation or underestimated measurement errors. We find the effect of [Fe/H] on the mass-Mks relation is likely negligible for metallicities in the Solar neighborhood (0.0+/-2.2% change in mass per dex change in [Fe/H]). This weak effect is consistent with predictions from the Dartmouth Stellar Evolution Database, but inconsistent with those from MESA Isochrones and Stellar Tracks. A sample of binaries with a wider range of abundances will be required to discern the importance of metallicity in extreme populations (e.g., in the Galactic Halo or thick disk).Comment: Published in ApJ/AAS Journals. Comments welcome. Code for computing mass posteriors from Ks+distance at https://github.com/awmann/M_-M_K

How to Constrain Your M Dwarf. II. the Mass-Luminosity-Metallicity Relation from 0.075 to 0.70 Solar Masses

The mass–luminosity relation for late-type stars has long been a critical tool for estimating stellar masses. However, there is growing need for both a higher-precision relation and a better understanding of systematic effects (e.g., metallicity). Here we present an empirical relationship between MKS and M* spanning 0.075 Me < M* < 0.70 Me. The relation is derived from 62 nearby binaries, whose orbits we determine using a combination of Keck/NIRC2 imaging, archival adaptive optics data, and literature astrometry. From their orbital parameters, we determine the total mass of each system, with a precision better than 1% in the best cases. We use these total masses, in combination with resolved KS magnitudes and system parallaxes, to calibrate the MKS–M* relation. The resulting posteriors can be used to determine masses of single stars with a precision of 2%–3%, which we confirm by testing the relation on stars with individual dynamical masses from the literature. The precision is limited by scatter around the best-fit relation beyond measured M* uncertainties, perhaps driven by intrinsic variation in the MKS–M* relation or underestimated uncertainties in the input parallaxes. We find that the effect of [Fe/H] on the MKS–M* relation is likely negligible for metallicities in the solar neighborhood (0.0% ± 2.2% change in mass per dex change in [Fe/H]). This weak effect is consistent with predictions from the Dartmouth Stellar Evolution Database, but inconsistent with those from MESA Isochrones and Stellar Tracks (at 5σ). A sample of binaries with a wider range of abundances will be required to discern the importance of metallicity in extreme populations (e.g., in the Galactic halo or thick disk).A.W.M. was supported through Hubble Fellowship grant 51364 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. T.J.D. acknowledges research support from Gemini Observatory. This work was supported by a NASA Keck PI Data Award (award nos. 1554237, 1544189, 1535910, and 1521162), administered by the NASA Exoplanet Science Institut