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 M K S and M * spanning 0.075M < M * < 0.70M . 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 K S magnitudes and system parallaxes, to calibrate the M K S -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 M K S -M * relation or underestimated uncertainties in the input parallaxes. We find that the effect of [Fe/H] on the M K S -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 snow-line is the region of a protoplanetary disk at which a major volatile, such as water or carbon monoxide, reaches its condensation temperature. Snowlines play a crucial role in disk evolution by promoting the rapid growth of icecovered grains 1−6 . Signatures of the carbon monoxide snow-line (at temperatures of around 20 kelvin) have recently been imaged with in the disks surrounding the pre-main-sequence stars TW Hydra 7−9 and HD163296 [3,10] , at distances of about 30 astronomical units (au) from the star. But the water snow-line of a protoplanetary disk (at temperatures of more than 100 kelvin) has not hitherto been seen, as it generally lies very close to the star (less than 5 au away for solartype stars 11 ). Water-ice is important because it regulates the efficiency of dust and planetesimal coagulation 5 , and the formation of comets, ice giants and the cores of gas giants 12 . Here we report ALMA images at 0.03-arcsec resolution (12 au) of the protoplanetary disk around V883 Ori, a protostar of 1.3 solar masses that is undergoing an outburst in luminosity arising from a temporary increase in the accretion rate 13 . We find an intensity break corresponding to an abrupt change in the optical depth at about 42 au, where the elevated disk temperature approaches the condensation point of water, from which we conclude that the outburst has moved the water snow-line. The spectral behaviour across the snow-line confirms recent model predictions 14 : dust fragmentation and the inhibition of grain growth at higher temperatures results in soaring grain number densities and optical depths. As most planetary systems are expected to experience outbursts caused by accretion during their formation [15,16] our results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation. V883Ori is an FU Ori object identified as such by [17] from followup spectroscopy of deeply embedded sources from the Infrared Astronomical Satellite (IRAS). It is located in the Orion Nebula Cluster, which has a distance of 414±7 pc [18] . It has a disk mass of 0.3 M and a bolometric luminosity of 400 L [19] . We have obtained 230 GHz/1.3 mm (band-6) observations of V883 Ori using the Atacama Large Millimeter/submillimeter Array (ALMA) in four different array configurations with baselines ranging from 14 m to 12.6 km, which were taken in ALMA Cycle-2 and Cycle-3. These new ALMA observations include continuum and the 12 CO, 13 CO, and C 18 O J = 2 -1 spectral lines. We use the C 18 O gas line to investigate the dynamics of the system at 0.2 (90 au) resolution and the continuum data to constrain the physical properties of the dust in the V883 Ori disk at 0.03 (12 au) resolution. In Figure 1 (top panel) we show our Cycle-3 continuum image at 0.03 resolution, the highest resolution ever obtained for a FU Ori object at millimeter wavelengths. We find that the V883 Ori disk has a two-region morphology, with a very bright inner disk (r ∼ 0.1 , 42 au) and a much more tenuous outer dis...

We introduce the Ophiuchus DIsc Survey Employing ALMA (ODISEA), a project aiming to study the entire population of Spitzer -selected protoplanetary discs in the Ophiuchus Molecular Cloud (∼300 objects) from both millimeter continuum and CO isotopologues data. Here we present 1.3 mm/230 GHz continuum images of 147 targets at 0.2 (28 au) resolution and a typical rms of 0.15 mJy. We detect a total of 133 discs, including the individual components of 11 binary systems and 1 triple system. Fifty-three of these discs are spatially resolved. We find clear substructures (inner cavities, rings, gaps, and/or spiral arms) in 8 of the sources and hints of such structures in another 4 discs. We construct the disc luminosity function for our targets and perform comparisons to other regions. A simple conversion between flux and dust mass (adopting standard assumptions) indicates that all discs detected at 1.3 mm are massive enough to form one or more rocky planets. In contrast, only ∼50 discs (∼1/3 of the sample) have enough mass in the form of dust to form the canonical 10 M ⊕ core needed to trigger runaway gas accretion and the formation of gas giant planets, although the total mass of solids already incorporated into bodies larger than cm scales is mostly unconstrained. The distribution in continuum disc sizes in our sample is heavily weighted towards compact discs: most detected discs have radii < 15 au, while only 23 discs (∼15% of the targets) have radii > 30 au.

As protostars evolve from optically faint / infrared bright (Class I) sources to optically bright / infrared faint (Class II) the solid material in their surrounding disks accumulates into planetesimals and protoplanets. The nearby, young Ophiuchus star-forming region contains hundreds of protostars in a range of evolutionary states. Using the Atacama Large Millimeter Array to observe their millimeter continuum emission, we have measured masses of, or placed strong upper limits on, the dust content of 279 disks. The masses follow a log-normal distribution with a clear trend of decreasing mass from less to more evolved protostellar infrared class. The (logarithmic) mean Class I disk mass, M = 3.8 M ⊕ , is about 5 times greater than the mean Class II disk mass, but the dispersion in each class is so high, σ log M 0.8−1, that there is a large overlap between the two distributions. The disk mass distribution of flat-spectrum protostars lies in between Classes I and II. In addition, three Class III sources with little to no infrared excess are detected with low disk masses, M 0.3 M ⊕ . Despite the clear trend of decreasing disk mass with protostellar evolutionary state in this region, a comparison with surveys of Class II disks in other regions shows that masses do not decrease monotonically with age. This suggests that the cloud-scale environment may determine the initial disk mass scale or that there is substantial dust regeneration after 1 Myr.