Relative motion of A1 (blue) with respect to A2 (red) overlaid on the
ALMA continuum observation. The visual impression that A1 orbits around
A2 is confirmed through a detailed analysis of the motion of the
proto-stars over a 30-year period. © MPE
High-resolution observations of a young star forming system clearly
unveil a pair of proto-stars at their earliest stages of evolution
deeply embedded within the source IRAS 16293-2422 in the Ophiuchus
molecular cloud. The team led by the Max Planck Institute for
Extraterrestrial Physics used the ALMA interferometer not only to pin
down the source configuration, but also to measure the gas and stellar
kinematics, determining the mass of the young binary. The two close
proto-stars are somewhat heavier than previously thought and they
revolve around each other once in about 400 years.
The system called IRAS 16293-2422 is one of the brightest
star-forming regions in our neighborhood. It is located in the Ophiuchus
molecular cloud at a distance of about 460 light-years and has been
widely studied, also because it shows strong emission of numerous
complex organic molecules, building blocks of pre-biotic species.
However, until now the detailed configuration of the region was unclear,
with observations at different wavelengths showing multiple compact
sources at slightly different locations. This confusion was due to the
large amount of material in front of the nascent proto-stars, expected
at these earliest stages of formation.
An international team of astronomers led by the Max Planck Institute
for Extraterrestrial Physics (MPE) has now obtained high-resolution
radio observations with the ALMA interferometer, which clearly reveals
two compact sources A1 and A2 in addition to the well-known proto-star B
(see Fig. 1). “Our observations confirm the location of the two close
proto-stars and reveal that each is surrounded by a very small dust
disk. Both, in turn, are in turn embedded in a large amount of material
showing complex patterns” remarks María José Maureira from MPE, the lead
author of the study.
The source A1 has a mass of a bit less than 1 solar mass and is
embedded in a small dust disk about the size of the asteroid belt; the
source A2 has a mass of about 1.4 solar masses and is embedded in a
somewhat larger disk (see
Fig. 2). Interestingly, this disk around A2 also appears at an angle
compared to the overall orientation of the larger cloud structure, while
the disk around the source B – at a much larger distance – is seen
face-on, indicating a rather chaotic formation history.
In addition to direct imaging of the dust emission, the team also
obtained information on the motion of the gas around the stars through
observations of spectral lines of organic molecules, which well trace
the high-density region surrounding the discovered binary system. This
allowed them to get an independent mass measurement and to confirm that
A1 and A2 form a bound pair.
Combining their latest observations with data collected over the past
30 years, the team found that the two stars orbit each other once every
360 years at a distance similar to the extent of Pluto’s orbit, where
the orbit is tilted by about 60° (see Fig. 3). “This is the first time
that we were able to derive the full orbital parameters of a binary
system at this early stage of star formation,” points out Jaime Pineda
from MPE, who contributed to the modelling.
“With these results we are finally able to dive into one of the most
embedded and youngest proto-stellar systems, unveiling its dynamical
structure and complex morphology, where we clearly see filamentary
material connecting the circumstellar disks to the surrounding region
and likely to the cirbumbinary disk. The small disks are probably still
being fed and growing!” emphasizes Paola Caselli, director at MPE and
head of the Center for Astrochemical Studies. “This was only possible
thanks to the great sensitivity of ALMA and the observations of
molecules which uniquely trace these dense regions. Molecules send us
signals at very specific frequencies, and, following changes of such
frequencies across the region (due to internal motions) one can
reconstruct the complex kinematics of the system. This is the power of
astrochemistry.”
Source: Max Planck Institute for Extraterrestrial Physics (MPE)
Original publication
1. Maria Jose Maureira, Jaime E. Pineda, Dominique M. Segura-Cox, Paola Caselli, Leonardo Testi, Giuseppe Lodato, Laurent Loinard, Antonio Hernandez-Gomez
Orbital and mass constraints of the young binary system IRAS 16293-2422 A
Accepted for publication in ApJ
Source
