The	  inverse	  phase-­‐referencing	  method	  of	  reducing	  VERA	  data	  using	  AIPS	  POPS	

VERARoss	  Burns	  –	  D2,	  Kagoshima	  U.	  

Most	  of	  VERA’s	  data	  is	  reduced	  using	  the	  phase-­‐referencing	  technique	  by	  using	  a	  con@nuum	  (QSO)	  source	  to	  solve	  for	  phase	  ﬂuctua@ons	  in	  the	  sky	  –	  these	  solu@ons	  are	  used	  to	  ‘phase-­‐reference’	  the	  maser	  data.	  When	  there	  are	  no	  strong	  reference	  QSOs	  available	  within	  2.2°	  we	  can	  only	  use	  a	  weak	  (≤	  40	  mJy)	  QSO.	  In	  this	  case	  the	  phase	  solu@ons	  have	  a	  low	  signal	  to	  noise	  ra@o	  (SNR).	  Low	  quality	  phase	  solu@ons	  for	  the	  QSO	  gives	  low	  quality	  maser	  maps	  –	  therefore	  we	  are	  limited	  by	  the	  available	  reference	  sources.	  	  In	  this	  work	  I	  demonstrate	  the	  inverse-­‐phase	  referencing	  reduc@on	  method	  which	  is	  sensi@ve	  to	  weak	  QSOs.	  Therefore,	  by	  using	  this	  method	  we	  are	  not	  so	  strongly	  limited	  in	  our	  choice	  of	  reference	  sources.	  	  I	  plan	  to	  provide	  a	  working	  POPS	  script,	  and	  I	  encourage	  other	  VERA	  users	  to	  prac@ce	  this	  technique.	  

B-­‐beam	  A-­‐beam	  FITLD	  	  +	  combine	  15th	  IF	  FITLD	  Reference	  QSO	  #1	  Some	  VEDA	  results	  for	  S235AB	  J0533+3451	  Amplitude	  calibra@on	  	  +	  Bandpass	  Amplitude	  calibra@on	  	  +	  Bandpass	  CVEL	  Apply	  UVW	  table	  (B-­‐Apply2B)	  Delay	  and	  Phase	  FRING	  on	  bright	  calibrator	  (e.g.	  3C84)	  SNCOR	  (IF	  9)	  Phase-­‐referencing	  is	  diﬃcult	  because	  the	  QSO	  is	  weak	  (≤	  40	  mJy	  in	  AIPS).	  The	  quality	  of	  the	  maser	  results	  are	  not	  good	  enough	  for	  measuring	  annual	  parallax.	  

TACOP	  

#2	  Results	  using	  inverse	  phase-­‐referencing	  GREY: S235 IPOL S235.MOM1.1
CONT: S235 IPOL S235.MOM0.1-64-62

Apply	  UVW	  table	  (A-­‐Apply2A)	  -60

We	  use	  the	  FRING	  solu@on	  of	  the	  bright	  maser	  to	  reference	  the	  QSO	  AND	  to	  make	  self-­‐calibrated	  maser	  image.	  Therefore	  we	  can	  get	  the	  astrometric	  posi@ons	  of	  ALL	  self-­‐
calibrated	  masers.	  	  Self-­‐calibrated	  =>	  Phase-­‐referenced	  -58

10SPLIT	  Reference	  QSO	  (e.g.	  J0533+3451)	  Dual-­‐beam	  calibra@on	  (PLUS.1111)	  H2O	  Masers	  in	  S235AB	  (w.r.t	  reference	  maser)	  86FRING	  Maser	  TACOP	  4

IMAGR	  CONT: J0533+34 IPOL 22217.992 MHZ J0533+34.ICL001.2-25

MilliArc seconds

Phase	  solu@ons	  of	  reference	  maser	  20-2

MilliArc seconds-30-4IMAGR	  -35-6-40-8J0533+3451	  -45-1015

1050
MilliArc seconds
Center at RA 05 33 12.76510000 DEC 34 51 30.3370000
Cont peak flux = 1.2907E-02 JY/BEAM
Levs = 1.298E-03 * (-3, 3, 5, 7, 9, 11, 13, 15,17)1020-2-4
MilliArc seconds
Center at RA 05 40 53.42000000 DEC 35 41 48.8000000
Grey scale flux range= -65.13 -57.53 Kilo M/SCont peak flux = 2.3029E+04 JY/B*M/S
Levs = 5.000E+02 * (1, 2, 4, 8, 16, 32)-5864-6-8

Typical	  referenced	  images	  of	  the	  QSO	  were	  of	  15-­‐20	  mJy	  and	  SNR	  >	  10	  In the case of S235AB, the data reduction was not possible using the normal phase-referencing technique for most epochs because of the weak QSO.
Also, the multi-epoch results from VEDA reductions are not consistent with eachother. It is not possible to measure the parallax of masers in S235AB
using the normal data reduction procedures.
By using the inverse phase-referencing method I detected ≥7 maser features in each epoch. About 3 maser features were detected in at least 6 epochs
and are suitable for parallax fitting. About 10 features are detected in more than 3 epochs and can be used to measure the absolute proper motion. 	

In total, about 50 phase-referenced maser spots were found in each epoch at SNR > 5, and the QSO was detected with a typical SNR of > 10. 	

= 0.825s/am
560.0 ± 0.065
528.0 mas=/trecnu %8( cDpk=61.211
90.0 ±±10.096
12.1 =kpc
D (8% uncertainty)
Plot file version 1 created 22-SEP-2014 03:48:51Parallax	  ﬁFng	  for	  S235AB	  (preliminary)	  16144 8 6 6 8 4)R.A.
sam(offset
tesffo(mas).A.R

Phas deg

10.5
022-1-2

2013
YearFelli,	  M.,	  et	  al.	  2004,	  A&A,	  420,	  553	  21-1.5

2012

The	  mo@on	  of	  the	  maser	  is	  consistent	  with	  the	  blue-­‐shihed	  ouilow	  in	  S235AB.	  

23-0.5-2.5

200
150
100
500-50-100-150
24

Ampl Jy18

1.5

Offset (mas)Offset (mas)Decl. offset (mas)209	  epochs	  π	  =	  0.76	  ±	  0.06	  mas	  D	  =	  1.31	  ±	  0.11	  kpc	  22 20
181602141281 108661
4241 0)sam( tesffo .lceD0222)sam( tesffO

02816141
2101
8642
0

S235 r14070A A.CVEL.2
Freq = 22.2260 GHz, Bw = 16.000 MH Calibrated with CL # 6 and BP # 1 (BP mode 1)

1918172012

2013
Year

2014

The	  results	  of	  parallax	  ﬁeng	  for	  1	  maser	  feature	  in	  S235AB;	  Le#	  image	  is	  the	  sky-­‐plane	  mo@on	  of	  the	  maser,	  	  	  	  	  	  	  	  	  middle	  image	  shows	  the	  oﬀset	  vs	  @me	  in	  (grey)	  Dec.	  and	  (black)	  R.A.,	  right	  image	  is	  the	  oﬀsets	  in	  RA	  and	  Dec.	  	  	   	  aher	  subtrac@ng	  the	  proper	  mo@on	  component.	  

Masers	  associated	  with	  the	  blue	  lobe.	  

20

16
15

Masers	  associated	  with	  the	  parent	  cloud.	  
IF 1(LL)20

0-20

Scalar averaged cross-power spectrum
Timerange: 00/04:48:01 to 00/12:53:00-40-60KM/S (LSR)
Several baselines averaged-80-100