A disk-based dynamical mass estimate for the young binary AK Sco

I. Czekala*, S. M. Andrews, E. L. N. Jensen, K. G. Stassun, G. Torres, D. J. Wilner

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We present spatially and spectrally resolved Atacama Large Millimeter / submillimeter Array (ALMA) observations of gas and dust in the disk orbiting the pre-main sequence (pre-MS) binary AK Sco. By forward-modeling the disk velocity field traced by CO J = 2–1 line emission, we infer the mass of the central binary, M* = 2.49 ± 0.10 M⊙, a new dynamical measurement that is independent of stellar evolutionary models. Assuming the disk and binary are co-planar within ∼2°, this disk-based binary mass measurement is in excellent agreement with constraints from radial velocity monitoring of the combined stellar spectra. These ALMA results are also compared with the standard approach of estimating masses from the location of the binary in the Hertzsprung–Russell diagram, using several common pre-MS model grids. These models predict stellar masses that are marginally consistent with our dynamical measurement (at ∼2σ), but are systematically high (by ∼10%). These same models consistently predict an age of 18 ± 1 Myr for AK Sco, in line with its membership in the Upper Centaurus–Lupus association but surprisingly old for it to still host a gas-rich disk. As ALMA accumulates comparable data for large samples of pre-MS stars, the methodology employed here to extract a dynamical mass from the disk rotation curve should prove extraordinarily useful for efforts to characterize the fundamental parameters of early stellar evolution.
Original languageEnglish
Article number154
Number of pages8
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 15 Jun 2015


  • Protoplanetary disks
  • Stars: fundamental parameters
  • Stars: individual: AK Sco
  • Stars: pre-main sequence


Dive into the research topics of 'A disk-based dynamical mass estimate for the young binary AK Sco'. Together they form a unique fingerprint.

Cite this