J/MNRAS/366/1096 Kinematic distance ambiguity (Busfield+, 2006)
Resolving the kinematic distance ambiguity of southern massive young stellar
object candidates.
Busfield A.L., Purcell C.R., Hoare M.G., Lumsden S.L., Moore T.J.T.,
Oudmaijer R.D.
<Mon. Not. R. Astron. Soc., 366, 1096-1117 (2006)>
=2006MNRAS.366.1096B 2006MNRAS.366.1096B
ADC_Keywords: YSOs ; Stars, distances ; H I data
Keywords: ISM: kinematics and dynamics - Galaxy: structure
Abstract:
We investigate the use of HI data to resolve the near/far ambiguity
in kinematic distances of massive young stellar object (MYSO)
candidates. Kinematic distances were obtained from 13CO 1-0 (and
N2H+) spectral-line observations with the Mopra Telescope towards
94 candidates selected from the Red MSX Source (RMS) survey in the
fourth Galactic quadrant (282°<l<350°). HI data from the
Southern Galactic Plane Survey (SGPS) were used in conjunction with
the HI self-absorption (SA) technique to determine the near or far
distance. We resolved the kinematic distance ambiguity to 70 per cent
of the sources. We can also simultaneously solve for any multiple
line-of-sight component sources. We discuss the advantages and
disadvantages of this technique in comparison with other methods, and
also perform confidence checks on the reliability of using the HI SA
technique.
Description:
The 13CO 1-0 observations were carried out in the periods of 2002
August and 2003 July, using the Mopra 22-m millimetre-wave telescope
of the Australia Telescope National Facility (ATNF).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 81 209 13CO 1-0 kinematic parameters of MSX sources
with a distance ambiguity.
tablea2.dat 67 10 13CO 1-0 kinematic parameters of MSX sources
geometrically solved with no distance ambiguity
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See also:
V/114 : MSX6C Infrared Point Source Catalog (Egan+ 2003)
Byte-by-byte Description of file: tablea?.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- MSX MSX object name in Galactic coordinates
18 A1 --- n_MSX [a] Note on MSX (1)
21 I1 --- m_MSX [1/9]? Weaker line-of-sight components
23- 28 F6.1 km/s Vlsr LSR velocity of the 13CO component(s), or
central N2H+ maser line
31- 33 F3.1 kpc Dnear ?=- Calculated near distance (2) (6)
34 A1 --- n_Dnear [*] * when correct distance solved (3)
36- 38 F3.1 kpc e_Dnear ? rms uncertainty on Dnear
when correct distance solved
40- 43 F4.1 kpc Dfar ?=- Calculated far distance (2)
44 A1 --- n_Dfar [*] * when correct distance solved
46- 48 F3.1 kpc e_Dfar ? rms uncertainty on Dfar
when correct distance solved
50- 55 F6.1 pc z ?=- Scale-height to the Galactic centre
57- 60 F4.1 kpc Rgc Distance to the Galactic centre
62- 63 A2 --- R (FN ?) Adopted distance (6) (4)
65- 81 A17 --- Notes Notes (5)
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Note (1): a: N_2 H^+ maser line being used instead of 13CO line.
Note (2): Calculated near and far distances using the standard Galactic
rotation parameters (R0=8.5kpc, {THETA}0=220km/s) of
Brand & Blitz (1993, Cat. J/A+A/275/67)
Note (3): Correct distance if the kinematic distance ambiguity can be solved.
Note (4): Adopted distance when compared to the HI data as follows:
N = near distance
F = far distance
N? = most probable solution to slightly questionable spectra.
An N? generally represents a dip in HI is present, but much less
than 15-20 or is complicated via velocity structure in 13CO.
F? = most probable solution to slightly questionable spectra.
An F? generally represents a dip may be present in HI but could
be attributed to noise, or is shifted from the 13CO peak position.
? = still unsolved distance ambiguity.
Note (5): Any line-profile problems are briefly noted in this column as:
=> SA/off-beam/double sources have potential absorption at the
chosen velocity component due to SA, off-beam objects, or could
be considered to have double-peaked profiles.
=> Strongest? represents a questionable strongest/best component line
within the spectra which may or may not be the true potential
MYSO from the MSX images.
=> Ambiguous sources are those which still cannot be solved with this
method
=> Structure indicates the line profile is not a typical Gaussian.
=> n/a (not analysed) for all objects of tablea2
Note (6): In tablea2, as these objects are geometrically solved, there are no
near-distance solutions given, and R ="-".
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 25-Sep-2006