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J/ApJ/393/149 W49N H2O maser outflow: distance and kinematics (Gwinn+, 1992)
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Distance and kinematics of the W49N H2O maser outflow
Gwinn C.R., Moran J.M., Reid M.J.
<Astrophys. J. 393, 149 (1992)>
=1992ApJ...393..149G (SIMBAD/NED BibCode)
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ADC_Keywords: H II regions; Masers; Positional data; Radial velocities
Keywords: Galaxy: kinematics and dynamics - ISM: individual (W49) -
ISM: jets and outflows - ISM: molecules - masers
Description:
Study of the motions of 105 H2O maser features clustered around a newly
formed star in W49N yields the kinematics of the gas flow, the distance to
the source, and the spatial scale of the Milky Way. We find that the maser
outflow is bipolar, with an opening angle of ~60deg and an inclination of
~40deg to the line of sight. The expansion has a constant velocity of
~18 km/s out to a radius of 0.1pc, beyond which the outflow velocity
increases to greater than 200 km/s. This increase may be due to interaction
with ambient material. A rotation is also present; this rotation is nearly
perpendicular to the outflow axis. The rotation may be due to ram pressure
from ambient material; rotation of the ring of H II regions described by
Welch et al. could produce such nonradial motion.
Comparison of Doppler velocities and proper motions yields a distance
of 11.4+/-1.2 kpc for the maser cluster. Combining this with a kinematic
distance for W49N from Galactic rotation, we obtain a value of R0, the
distance to the Galactic center, of 8.1+/-1.1 kpc.
Objects:
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RA (2000) DE Designation(s)
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19 10 13.2 +09 06 12 W 49N
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 61 105 Positions and Velocities of 105 Maser Features
(Flux columns dropped)
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Table 1: Epochs and stations of observations
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Epoch UT Span Stations (1)
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1 1980 Dec 11, 13:00 Dec 12, 1:00 EKGYO
2 1981 Mar 1, 6:0O Mar 1, 19:00 EKGYO
3 1981 Dec 1, 13:00 Dec 2, 19:00 TKGYO
4 1982 Mar 6, 8:00 Mar 6, 20:00 TKGYO
5 1982 Jun 5, 7:00 June 5, 14:00 TKGYO
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Note (1): E: 100 m antenna near Bonn, FRG, of the Max-Planck-Institut
fur Ratioastronomie;
T: 26 m antenna near Onsala, Sweden, of the Onsala Space Observatory;
K: 37 m antenna in Westford, MA of the Northeast Radio Observatory
Corporation;
G: 43 m antenna in Green Bank, WV, of the National Radio Astronomy
Observatory;
Y: One 25 m antenna element of the Very Large Array near Socorro, NM,
of the National Radio Astronomy;
O: 40 m antenna near Big Pine, CA, of the California Institute of
Technology.
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Table2: Doppler velocity ranges observed
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Switch Center velocity Velocity range
Cycle Code (km/s) (km/s)
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A 4 -160.5 -174.0 -147.0
A 3 -129.0 -142.5 -115.5
A 2 -43.5 -57.0 -30.0
A,B 1 -5.0 -18.5 8.5
B 2 18.5 5.0 32.0
B 3 135.0 121.5 148.5
B 4 156.0 142.5 169.5
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Table 3: Reference spots
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Epoch Spectral LSR Doppler Flux Position relative to
channel velocity density -0.8 km/s spot
(switch X=D{alpha}cos{delta} Y=D{delta}
A/B 1) km/s Jy arcsecond arcsecond
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1 37 -1.62 5518 0.000052 -0.000240
2 10 5.96 15616 -0.566165 -0.183691
3 17 3.99 1258 -0.530793 -0.018768
4 86 -15.38 12578 -0.562751 -0.178752
5 34 -0.78 34218 0.000000 0.000000
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Maser Maser number
5- 11 F7.4 arcsec Xpos X position
13- 19 F7.4 arcsec Ypos Y position
22- 27 F6.1 km/s VX Velocity X component along R.A. (1)
29- 32 F4.1 km/s e_VX Error on VX
36- 40 F5.1 km/s VY Velocity Y component along Dec. (1)
42- 45 F4.1 km/s e_VY Error on VY
48- 53 F6.1 km/s VZ Velocity Z component along line of sight (1)
55- 58 F4.1 km/s e_VZ Error on VZ (2)
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Note (1): Quoted error for Vx, Vy is rms of proper motions for multichannel
features (Delta(VZ)>0.6km/s) or standard error from fit for
single-channel features (Delta(VZ)=0.6 km/s)
Note (2): Quoted error for VZ, Delta(VZ), is the range of Doppler velocity
VZ, over which the feature was detected
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Historical Notes: Keypunched at CDS
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(End) James Marcout, Simona Mei [CDS] 10-Aug-1995