J/ApJ/720/1055 VBLA observations of W51 Main/South (Sato+, 2010)
Trigonometric parallax of W51 Main/South.
Sato M., Reid M.J., Brunthaler A., Menten K.M.
<Astrophys. J., 720, 1055-1065 (2010)>
=2010ApJ...720.1055S 2010ApJ...720.1055S
ADC_Keywords: Masers ; Proper motions ; H II regions ; VLBI
Keywords: astrometry - Galaxy: fundamental parameters -
Galaxy: kinematics and dynamics - Galaxy: structure -
ISM: individual objects (W51) - masers
Abstract:
We report measurement of the trigonometric parallax of W51 Main/South
using the Very Long Baseline Array. We measure a value of
0.185±0.010mas corresponding to a distance of 5.41+0.31-0.28kpc.
W51 Main/South is a well-known massive star-forming region near the
tangent point of the Sagittarius spiral arm of the Milky Way. Our
distance to W51 yields an estimate of the distance to the Galactic
center of R0=8.3±0.46(statistical)±1.0(systematic)kpc by
simple geometry. Combining the parallax and proper motion measurements
for W51, we obtained the full-space motion of this massive
star-forming region. We find W51 is in a nearly circular orbit about
the Galactic center. The H2O masers used for our parallax
measurements trace four powerful bipolar outflows within a 0.4pc size
region, some of which are associated with dusty molecular hot cores
and/or hyper- or ultra-compact HII regions.
Description:
Prior to the VLBA parallax observations, we used the NRAO Very Large
Array (VLA; program AR677) in the most extended A configuration on
2008 September 28 to find background extragalactic sources as position
references near the target H2O maser sources.
The Very Long Baseline Array (VLBA) observations of W51 Main/South
were scheduled on 2008 October 22, 2009 April 27 and 30, and 2009
October 20 under program BR134.
Objects:
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RA (2000) DE Designation(s)
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19 23 43.87 +14 30 29.5 W51 Main/South = NAME W 51 SOUTH
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 68 37 H2O maser feature motions in W51 Main/South
table4.dat 64 123 Maser spot motions in W51 Main/South
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See also:
J/ApJS/191/232 : CO survey of W51 molecular cloud (Bieging+, 2010)
J/ApJ/706/83 : Embedded YSO candidates in W51 (Kang+, 2009)
J/A+A/473/177 : A search for pre-biotic molecules (Wirstrom+, 2007)
J/MNRAS/353/1025 : JHK photometry of 4 W51 star clusters (Nanda+, 2004)
J/A+A/368/845 : Arcetri Catalog of H2O maser sources. Update. (Valdettaro+,
2001)
J/A+A/358/257 : Molecular clouds SO and CS obs. II. (Nilsson+, 2000)
J/ApJ/463/205 : CS and NH3 Survey of H2O Maser Emission (Anglada+ 1996)
J/A+AS/101/153 : Galactic H2O masers (Palagi+ 1993)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Reg Region identification (1)
7- 8 I2 --- ID [1/37] Maser feature number
10- 14 F5.1 km/s Vlsr LSR velocity
16- 20 F5.1 Jy Tb Brightness temperature in units of Jy/beam (2)
22- 27 F6.3 arcsec x0 X position relative to feature 32 (3)
29- 33 F5.3 arcsec e_x0 Uncertainty in x0
35- 40 F6.3 arcsec y0 Y position relative to feature 32 (3)
42- 46 F5.3 arcsec e_y0 Uncertainty in y0
48- 52 F5.2 mas/yr pmx Proper motion along X (4)
54- 57 F4.2 mas/yr e_pmx Uncertainty in pmx
59- 63 F5.2 mas/yr pmy Proper motion along Y (4)
65- 68 F4.2 mas/yr e_pmy Uncertainty in pmy
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Note (1): Region as follows:
e2-NW = hyper-compact (HC) or ultra-compact (UC) HII region W51e2-NW
e2-E = HC or UC HII region W51e2-E (Shi et al. 2010ApJ...710..843S 2010ApJ...710..843S,
2010ApJ...718L.181S 2010ApJ...718L.181S)
e8 = HC or UC HII region W51e8 (Zhang & Ho 1997ApJ...488..241Z 1997ApJ...488..241Z)
u = "u" region: without detected millimeter or centimeter continuum
emission
See section 3.2 and Figure 2 for further explanations.
Note (2): The brightness (Tb) of each maser feature gives the maximum value
of all spots of the feature from all four epochs (at 22GHz)
Note (3): The positional offsets of x0, y0 relative to feature 32 are those
fitted for the mid-observation year of 2009.318 (i.e., average year
of all four epochs).
Note (4): x ad y denote eastward and northward directions, respectively. A
proper motion of 1mas/yr corresponds to 25.6km/s at a distance of
5.41kpc.
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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- 2 I2 --- ID [1/37] Maser spot IDs in different velocity
channels in each feature (as in table 3)
4 I1 --- Num [1/7] IDs of the component spots in different
velocity channels for each feature
6- 10 F5.1 km/s Vlsr Local Standard of Rest Velocity
12- 16 F5.1 Jy Tb Brightness temperature in units of Jy/beam
18- 23 F6.3 arcsec x0 X position relative to feature 32 spot number 3
25- 29 F5.3 arcsec e_x0 Uncertainty in x0
31- 36 F6.3 arcsec y0 Y position relative to feature 32 spot number 3
38- 42 F5.3 arcsec e_y0 Uncertainty in y0
44- 48 F5.2 mas/yr pmx Proper motion along X
50- 53 F4.2 mas/yr e_pmx Uncertainty in pmx
55- 59 F5.2 mas/yr pmy Proper motion along Y
61- 64 F4.2 mas/yr e_pmy Uncertainty in pmy
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 28-Jun-2012