Trigonometric Distance to IRAS 20056+3350:
Massive Star Forming Region onthe Solar Circle
Ross Burns - Kagoshima-U. D2
T. Handa, T. Nagayama, T. Omodaka, A. Nakagawa,
H. Nakanishi, M. Hayashi, M. Shizugami

Conclusions• Distance and proper motion:
D = 4.69 ± 0.62 kpc.
(μα cos δ, μδ) = (−2.62 ± 0.33, −5.65 ± 0.52)mas/yr.

• IRAS 20056+3350 is on the Solar circle
at the tip of the Local Arm.
• IRAS 20056+3350 is a HMSFR(M★ ≥ 16 M).
• Galactic angular rotation (special geometry)Ω0 = 29.75 ± 2.29 km/s/kpc.

Ω0Conclusions

Problems• Distance and proper motion:
Maser elongation
D = 4.69 ± 0.62 kpc.
(μα cos δ, μδ) = (−2.62 ± 0.33, −5.65 ± 0.52)mas/yr.

Only one lobe traced by masers• IRAS 20056+3350 is on the Solar circle
at the tip of the Local Arm. How can we show that IRAS 20056+3350
is on the Solar circle?
• IRAS 20056+3350 is a HMSFR(M★ ≥ 16 M). How can we prove it is a HMSFR?
• Galactic angular rotation (special geometry)Ω0 = 29.75 ± 2.29 km/s/kpc. Is this value reasonable?

#1 Trigonometric distance of theIRAS 20056+3350 SFR

#1 Trigonometric distanceΧ2=1R.A.

Error floor:
0.227mas

Dec.

Error floor:0.050mas

D = 4.69 ± 0.62 kpc.
• Observations: 7 epochs with VERA (Dual-beam mode)• Total: 4 spots Parallax: 2 spots• Data reduction: AIPS
• R.A. bad fittingWhy?

#1 Trigonometric distance:
Maser structure• Maser elongated in
R.A. direction.
time• Emission smearing.

Can we evaluate themaser structure effect?

#1 Trigonometric distance:
Maser structure effecttime

separation

OurReality
VLBI images

In the absence ofacceleration spot
separation should
be linear vs time.

time
2D Gaussian fitsaffected by maser
structure

Deviation from a linear
fit indicates bad
astrometric accuracy

#1 Trigonometric distance:
Maser structure effect
R.A.
Std. dev. = 0.190 mas

Dec.
Std. dev. = 0.040 mas

#1 Trigonometric distance:
Maser structure effectParallax fitting

Error floors:
R.A. direction: 0.227
Dec. direction: 0.050

Maser structure errorParallax fitting of Dec
offsets more reliable

Std.dev to linear fits:
R.A. direction: 0.190
Dec. direction: 0.040

Maser structure is a significant error in our VERA observations

#2 IRAS 20056+3350 on the Solar circle,
at the tip of the Local Arm.

#2 IRAS 20056+3350:
Solar circle, tip of the Local Arm
Solar circle
Using R0 = 8.05
kpc*
we calculate
R★ = 7.91 kpc

Local Arm
3 models:• Branch• Major arm• SpurR★ ≈ R0

VLSR = 9 km/s**
Figure: Reid, M. J., et al. 2014, ApJ, 783, 130
Xu, Y., et al. 2013, ApJ, 769, 15*Honma, M., et al. 2012, PASJ, 64, 136**Jenness, T., et al. 1995, MNRAS, 276, 1024

#3 Physical nature of theIRAS 20056+3350 SFR

#3 IRAS 20056+3350 is a HMSFR:
Wood. & Churchwell., 1989, ApJ, 340, 265
Archive data
Re-evaluated archive data:
L = 24247L

M★ = 16 M



MH2 = 1200 MLine of sight outflow ✜✜ Original data: Casoli, F., et al. 1986, A&A, 169, 281✜ Original data: Zhang, Q., et al. 2005, ApJ, 625, 864

#3 IRAS 20056+3350 is a HMSFR:
Spectral energy distribution
Photometry data:•UKIDSS (J, H, K)•

AKARI IRC (9,18 μm)•

WISE (3.4, 4.6, 12, 22 μm)•IRAS (12, 24, 60, 100 μm)•JCMT (450, 850 μm)

SED model
L = 24500 L
M★ = 18.4 M
Menv = 3300 M
Inclination = 18°(near line-of-sight)
SED fitting software: Robitaille, T. P., et al., 2007, ApJS, 169, 328

#3 IRAS 20056+3350 is a HMSFR:
Spectral energy distribution

Archive data:
L = 24247 L
M★ = 16 M
MH2 = 1200 M
Line-of-sight outflow≈

SED model
L = 24500 L
M★ = 18.4 M
Menv = 3300 M
Inclination = 18°

Consistency
is reassuring

#4 Galactic angular rotationof the LSR, Ω0

#4 Galactic angular rotation of the LSR, Ω0Zhang, Q., et al. 2005, ApJ, 625, 864

Observed masers:
VLSR > 9 km/s
(velocity of cloud)Only measured motionsof 3 maser spots
However, masers traceblue lobe of theoutflow.

#4 Galactic angular rotation of the LSR, Ω0Assumption:
Maser proper motions w.r.t driving source --> smalli.e. the largest velocity components isalong the line-of-sightApproximation:
Group motion of masers --> reasonableapproximation of source proper motion

#4 Galactic angular rotation of the LSR, Ω0• D = 4.69 ± 0.62 kpc.
• IRAS 20056+3350 is on the Solar circle• Proper motion:(μα cos δ, μδ) = (−2.62 ± 0.33, −5.65 ± 0.52) mas/yr.
• VLSR = 9 ± 1 km/s
Using Equation 1. from Nagayama et al. 2011, PASJ, 63, 23

VERA observations of IRAS 20056+3350 give:Ω0 = 29.75 ± 2.29 km/s/kpc.

#4 Galactic angular rotation of the LSR, Ω0
Values of Ω0: tangent point
and Solar circle SFRs
(special geometry)
IRAS 20056+3350:
Ω0 = 29.75 ± 2.29 km/s/kpc.
Consistent with other SFRs
At tangent points
and Solar circle
Burns, R. A., Yamaguchi, Y., Handa, T., et al. 2014, accepted for PASJ, arXiv:1404.5506

Conclusions

Problems Solutions• Distance and proper motion:
Maser elongation
D = 4.69 ± 0.62 kpc.

Use Dec offsets(μα cos δ, μδ) = (−2.62 ± 0.33, −5.65 ± 0.52)mas/yr.

Only one lobe traced by masers
Line-of-sight inclination• IRAS 20056+3350 is on the Solar circle
at the tip of the Local Arm. How can we show that IRAS 20056+3350
is on the Solar circle?
R★ ≈ R0, VLSR = 9 km/s
• IRAS 20056+3350 is a HMSFR(M★ ≥ 16 M). How can we prove it is a HMSFR?
Archive data <-> SED model• Galactic angular rotation (special geometry)Ω0 = 29.75 ± 2.29 km/s/kpc. Is this value reasonable?
Consistent with tangent point
and Solar circle SFRs

Ω0Thank you for listening