TY - JOUR
T1 - Warm water deuterium fractionation in IRAS 16293-2422
T2 - the high-resolution ALMA and SMA view
AU - Persson, Magnus Vilhelm
AU - Jørgensen, Jes Kristian
AU - van Dishoeck, E. F.
PY - 2013/1/1
Y1 - 2013/1/1
N2 - Context. Measuring the water deuterium fractionation in the inner warm
regions of low-mass protostars has so far been hampered by poor angular
resolution obtainable with single-dish ground- and space-based
telescopes. Observations of water isotopologues using (sub)millimeter
wavelength interferometers have the potential to shed light on this
matter. Aims: To measure the water deuterium fractionation in the
warm gas of the deeply-embedded protostellar binary IRAS 16293-2422. Methods: Observations toward IRAS 16293-2422 of the 53,2 -
44,1 transition of H218O at 692.07914
GHz from Atacama Large Millimeter/submillimeter Array (ALMA) as well as
the 31,3 - 22,0 of H218O at
203.40752 GHz and the 31,2 - 22,1 transition of
HDO at 225.89672 GHz from the Submillimeter Array (SMA) are presented.
Results: The 692 GHz H218O line is seen
toward both components of the binary protostar. Toward one of the
components, "source B", the line is seen in absorption toward the
continuum, slightly red-shifted from the systemic velocity, whereas
emission is seen off-source at the systemic velocity. Toward the other
component, "source A", the two HDO and H218O lines
are detected as well with the SMA. From the H218O
transitions the excitation temperature is estimated at 124 ± 12
K. The calculated HDO/H2O ratio is (9.2 ± 2.6) ×
10-4 - significantly lower than previous estimates in the
warm gas close to the source. It is also lower by a factor of ~5 than
the ratio deduced in the outer envelope. Conclusions: Our
observations reveal the physical and chemical structure of water vapor
close to the protostars on solar-system scales. The red-shifted
absorption detected toward source B is indicative of infall. The
excitation temperature is consistent with the picture of water ice
evaporation close to the protostar. The low HDO/H2O ratio
deduced here suggests that the differences between the inner regions of
the protostars and the Earth's oceans and comets are smaller than
previously thought.
Appendix A is available in electronic form at http://www.aanda.org
AB - Context. Measuring the water deuterium fractionation in the inner warm
regions of low-mass protostars has so far been hampered by poor angular
resolution obtainable with single-dish ground- and space-based
telescopes. Observations of water isotopologues using (sub)millimeter
wavelength interferometers have the potential to shed light on this
matter. Aims: To measure the water deuterium fractionation in the
warm gas of the deeply-embedded protostellar binary IRAS 16293-2422. Methods: Observations toward IRAS 16293-2422 of the 53,2 -
44,1 transition of H218O at 692.07914
GHz from Atacama Large Millimeter/submillimeter Array (ALMA) as well as
the 31,3 - 22,0 of H218O at
203.40752 GHz and the 31,2 - 22,1 transition of
HDO at 225.89672 GHz from the Submillimeter Array (SMA) are presented.
Results: The 692 GHz H218O line is seen
toward both components of the binary protostar. Toward one of the
components, "source B", the line is seen in absorption toward the
continuum, slightly red-shifted from the systemic velocity, whereas
emission is seen off-source at the systemic velocity. Toward the other
component, "source A", the two HDO and H218O lines
are detected as well with the SMA. From the H218O
transitions the excitation temperature is estimated at 124 ± 12
K. The calculated HDO/H2O ratio is (9.2 ± 2.6) ×
10-4 - significantly lower than previous estimates in the
warm gas close to the source. It is also lower by a factor of ~5 than
the ratio deduced in the outer envelope. Conclusions: Our
observations reveal the physical and chemical structure of water vapor
close to the protostars on solar-system scales. The red-shifted
absorption detected toward source B is indicative of infall. The
excitation temperature is consistent with the picture of water ice
evaporation close to the protostar. The low HDO/H2O ratio
deduced here suggests that the differences between the inner regions of
the protostars and the Earth's oceans and comets are smaller than
previously thought.
Appendix A is available in electronic form at http://www.aanda.org
U2 - 10.1051/0004-6361/201220638
DO - 10.1051/0004-6361/201220638
M3 - Letter
VL - 549
JO - Astronomy & Astrophysics
JF - Astronomy & Astrophysics
SN - 0004-6361
M1 - L3
ER -