Testing methods of accurate low frequency astrometry for ... · Gabor Orosz (PI), Hiroshi Imai,...
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2.0º 0.7º 3.5º 2.9º (in-beam) Gabor Orosz (PI), Hiroshi Imai, Richard Dodson, Maria Rioja, Akiharu Nakagawa, Ross Burns, Dieter Engels, Sandra Etoka, Yoshiharu Asaki, Hiroyuki Nakanishi, Sandor Frey Department of Physics and Astronomy, Kagoshima University, Kagoshima, Japan Contact: [email protected] Testing methods of accurate low frequency astrometry for hydroxyl masers Engels et al 2015, arXiv:1503.04674 van Langevelde et al 1990, A&A 239, 193 Peterson et al 2011, ApJ 737, 104 Nakagawa et al 2014, PASJ 66, 101 Reid et al 2014, ApJ 783, 130 Whitelock et al 2000, MNRAS 319, 728 van Langevelde et al 2000, A&A 357, 945 Vlemmings et al 2003, A&A 407, 213 Vlemmings et al 2007, A&A 472, 547 Rioja et al 2009, PoS 014, arXiv:0909.4590 Dodson et al 2013, AJ 145, 147 Asaki et al 2007, PASJ 59, 397 This research has made use of the Very Long Baseline Array. I would like to acknowledge RadioNET, STEPS, the JSPS Bilateral Programs, Kagoshima University and Monbukagakusho:MEXT for financial support, and the help of my colleagues and friends. 2015.07.06-10. OH 138.0+7.2 VLBI astrometry of 1612 MHz OH masers VLBI astrometry can be used to measure the accurate positions of masers relative to quasars (calibrators). However, at low frequencies the dispersive ionosphere degrades the accuracy, introducing a large systematic error. We can try to correct for this error by using an in-beam calibrator and several secondary calibrators, to measure short-term dynamic variations and the two-dimensional phase gradient around the maser. With precise astrometry of hydroxyl masers around OH/IR stars, we can determine the parallax and proper motion of these sources. OH astrometry can be used to study the shells of these heavily enshrouded and massive AGBs, evaluate and calibrate other distance methods and prepare new techniques for the SKA. (For prior results in OH astrometry, see van Langevelde et al 2000, Vlemmings et al 2003, 2007.) TUFQT ¯ μ Dec = -0.46 ± 0.30 mas/yr ¯ μ RA =0.24 ± 0.08 mas/yr d =5.6 +4.4 -1.8 kpc measurements have an additional systematic error of ~0.15 mas (not shown by error bars) ⇡ =0.18 ± 0.08 mas -0.5 -0.4 -0.3 -0.2 -0.1 0 0 0.1 0.2 0.3 R.A. offset [mas] direction of Galactic Plane proper motion μ α μ δ ー7 ー8 ー9 ー8.5 ー7.5 Log P 2.5 2.6 2.7 2.55 2.65 2.45 VERA (weighted) T Lep RR Aql R Cas U Her SY Scl S CrB RX Boo R Aqr S Crt W Hya VLBI (weighted) VERA (unweighted) Whitelock et al.2008 3.15 – 4 – 3 – 5 – 6 – 10 2.6 (PLR) –9.7 –5.2 –3.9 –3.2 M K = -3.51 log P +1.37 parallactic distance ~ 5.6 kpc kinematic distance ~ 3.1 kpc phase-lag distance ~ 2.2 kpc Reid et al 2014 (gal. const.) Engels et al 2015 2 MASS magnitudes J (16.77) H (12.17) K (8.55) M K log P –8.8 –7.6 –6.8 (8.3 kpc) Correction for extinction: (J - K ) 0 =1.85 mag ) A k ⇠ 3.7 mag ) K 0 ⇠ 4.9 mag Whitelock et al 2000 Nakagawa et al 2014 Engels et al 2015 The measured annual parallax is a preliminary result (only in-beam) and is estimated to still have uncorrected ionospheric errors of ~0.15 mas (cf. Asaki et al 2007). The parallax of the OH/IR star can be used to study the higher-end part of the period-luminosity relationship of Mira variables, or to evaluate less direct distance estimators (e.g. phase-lag or kinematic). The 1612 MHz maser spectrum and integrated flux variation of our target OH/IR star is measured with the Nancay Radio Telescope (D. Engels and S. Etoka, Nancay 1612 MHz monitoring of OH/IR stars, Engels et al 2015). van Langevelde et al 1990 1.6 ionosphere (nighttime) ionosphere (daytime) troposphere Δ⌧ / ΔTECU ⌫ 2 Peterson et al 2011 0 0.1 0.2 0.3 0.4 0.5 0.6 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Dec. offset [mas] R.A. offset [mas] 0 2 4 6 8 10 12 0 2 4 6 8 10 φ obs = φ geo + φ atm + φ str + φ pos + φ inst + φ therm +2⇡ n φ iono,✓ + φ iono,t + φ trop,✓ + φ trop,t atmospheric phase ambiguity geometric structural positional instrumental thermal dynamic troposphere static troposphere dynamic ionosphere static ionosphere ✓ 10 3 ◆ = 120 ∆φ Imaging the same maser spot with all the various 3 antenna subarrays in the VLBA (a total of 120). The ~0.5 mas spread in position is likely due to residual phase errors (from ionosphere, maser structure, thermal noise). Even after the GPS based corrections the effect of ∆TEC dominates the phase error budget. Multiple calibrators allow the determination of ∆TEC across the field and the removal of this limitation on astrometric accuracy (MultiView, Rioja et al 2009, Dodson et al 2013). 1.6 GHz
Transcript of Testing methods of accurate low frequency astrometry for ... · Gabor Orosz (PI), Hiroshi Imai,...
2.0º 0.7º
3.5º
2.9º
(in-beam)
Gabor Orosz (PI), Hiroshi Imai, Richard Dodson, Maria Rioja, Akiharu Nakagawa, Ross Burns, Dieter Engels, Sandra Etoka, Yoshiharu Asaki, Hiroyuki Nakanishi, Sandor Frey
Department of Physics and Astronomy, Kagoshima University, Kagoshima, JapanContact: [email protected]
Testing methods of accurate low frequency astrometry for hydroxyl masers
Engels et al 2015, arXiv:1503.04674van Langevelde et al 1990, A&A 239, 193Peterson et al 2011, ApJ 737, 104Nakagawa et al 2014, PASJ 66, 101Reid et al 2014, ApJ 783, 130Whitelock et al 2000, MNRAS 319, 728
van Langevelde et al 2000, A&A 357, 945Vlemmings et al 2003, A&A 407, 213Vlemmings et al 2007, A&A 472, 547Rioja et al 2009, PoS 014, arXiv:0909.4590Dodson et al 2013, AJ 145, 147Asaki et al 2007, PASJ 59, 397
This research has made use of the Very Long Baseline Array. I would like to acknowledge RadioNET, STEPS, the JSPS Bilateral Programs, Kagoshima University and Monbukagakusho:MEXT for financial support, and the help of my colleagues and friends.
2015.07.06-10.
OH 138.0+7.2 VLBI astrometry of 1612 MHz OH masers
VLBI astrometry can be used to measure the accurate positions of masers relative to quasars (calibrators). However, at low frequencies the dispersive ionosphere degrades the accuracy, introducing a large systematic error. We can try to correct for this error by using an in-beam calibrator and several secondary calibrators, to measure short-term dynamic variations and the two-dimensional phase gradient around the maser. With precise astrometry of hydroxyl masers around OH/IR stars, we can determine the parallax and proper motion of these sources. OH astrometry can be used to study the shells of these heavily enshrouded and massive AGBs, evaluate and calibrate other distance methods and prepare new techniques for the SKA.(For prior results in OH astrometry, see van Langevelde et al 2000, Vlemmings et al 2003, 2007.)
µ̄Dec = �0.46± 0.30 mas/yr
µ̄RA = 0.24± 0.08 mas/yr
d = 5.6+4.4�1.8 kpc
measurements have an additional systematic error of ~0.15 mas (not shown by error bars)
⇡ = 0.18± 0.08 mas
-0.5
-0.4
-0.3
-0.2
-0.1
0
0 0.1 0.2 0.3
Dec
. offs
et [m
as]
R.A. offset [mas]
dire
ctio
n of
Gal
actic
Pla
ne p
rope
r m
otio
n
µα
µδ
MK
ー7
ー8
ー9
ー8.5
ー7.5
Log P2.5 2.6 2.72.55 2.652.45
VERA (weighted)
T Lep
RR Aql
R Cas
U Her
SY Scl
S CrB
RX Boo
R AqrS Crt
W Hya
VLBI (weighted)VERA (unweighted)
Whitelock et al.2008
3.15
– 4
– 3
– 5
– 6
– 10
2.6
(PLR) –9.7
–5.2
–3.9
–3.2
MK=
�3
.51 log
P +
1
.37
parallactic distance ~ 5.6 kpc
kinematic distance ~ 3.1 kpc
phase-lag distance ~ 2.2 kpc
Reid et al 2014 (gal. const.)
Engels et al 2015
2 MASS magnitudesJ (16.77)H (12.17)K (8.55)
MK
log P
–8.8
–7.6
–6.8
(8.3 kpc)
Correction for extinction:(J �K)0 = 1.85 mag
) Ak ⇠ 3.7 mag
) K0 ⇠ 4.9 magWhitelock et al 2000
Nakagawa et al 2014
Engels et al 2015
The measured annual parallax is a preliminary result (only in-beam) and is estimated to still have uncorrected ionospheric errors of ~0.15 mas (cf. Asaki et al 2007). The parallax of the OH/IR star can be used to study the higher-end part of the period-luminosity relationship of Mira variables, or to evaluate less direct distance estimators (e.g. phase-lag or kinematic).
The 1612 MHz maser spectrum and integrated flux variation of our target OH/IR star is measured with the Nancay Radio Telescope (D. Engels and S. Etoka, Nancay 1612 MHz monitoring of OH/IR stars, Engels et al 2015).
van Langevelde et al 1990
1.6
ionosphere (nighttime)ionosphere (daytime)
troposphere
�⌧ / �TECU
⌫2
Peterson et al 2011
0 0.1 0.2 0.3 0.4 0.5 0.6 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Dec
. offs
et [m
as]
R.A. offset [mas]
0
2
4
6
8
10
12
0 2 4 6 8 10
12
14
16
�obs
= �geo
+ �atm
+ �str
+ �pos
+ �inst
+ �therm
+ 2⇡n
�iono,✓
+ �iono,t
+ �trop,✓
+ �trop,t
atmospheric
phase ambiguitygeometric structural
positional
instrumental
thermal
dynamic troposphere
static troposphere
dynamic ionosphere
static ionosphere
✓10
3
◆= 120
∆φ
Imaging the same maser spot with all the various 3 antenna subarrays in the VLBA (a total of 120). The ~0.5 mas spread in position is likely due to residual phase errors (from ionosphere, maser structure, thermal noise).
Even after the GPS based corrections the effect of ∆TEC dominates the phase error budget. Multiple calibrators allow the determination of ∆TEC across the field and the removal of this limitation on astrometric accuracy (MultiView, Rioja et al 2009, Dodson et al 2013).
1.6
GH
z
