VERA Status Report
Mizusawa VLBI Observatory,
National Astronomical Observatory of Japan
18 April, 2016

Contents
1 Introduction

3

2 System

3

2.1

Array

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

2.2

Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5

2.2.1

Aperture Eﬃciency . . . . . . . . . . . . . . . . . . . . . . . . .

6

2.2.2

Beam Pattern and Size . . . . . . . . . . . . . . . . . . . . . . .

9

2.2.3

Pointing Accuracy . . . . . . . . . . . . . . . . . . . . . . . . .

10

2.2.4

Sky Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13

2.3

Receivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

14

2.4

Digital signal process . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15

2.5

Recorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

18

2.6

Correlators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

18

2.7

Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

18

2.7.1

Delay and Bandpass Calibration . . . . . . . . . . . . . . . . . .

18

2.7.2

Gain Calibration . . . . . . . . . . . . . . . . . . . . . . . . . .

20

2.7.3

Phase Calibration . . . . . . . . . . . . . . . . . . . . . . . . . .

20

2.8

C-band Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

20

2.9

Geodetic Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . .

20

3 Observing Proposal

22

3.1

Proposal Submission . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22

3.2

Observation Mode

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22

3.3

Angular Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22

3.4

Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

23

1

3.5

Astrometric Observation . . . . . . . . . . . . . . . . . . . . . . . . . .

24

3.6

Calibrator Information . . . . . . . . . . . . . . . . . . . . . . . . . . .

24

3.7

Nobeyama 45-m and Kashima 34-m Telescopes . . . . . . . . . . . . . .

24

3.8

Date Archive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

25

4 Observation and Data Reduction

27

4.1

Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

27

4.2

Observation and correlation . . . . . . . . . . . . . . . . . . . . . . . .

27

4.3

Data Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

27

4.4

Further Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

28

2

1

Introduction

This document summarizes the current observational capabilities of VERA (VLBI Exploration of Radio Astrometry), which is operated by National Astronomical Observatory of Japan (NAOJ). VERA is a Japanese VLBI array to explore the 3-dimensional
structure of the Milky Way Galaxy based on high-precision astrometry of Galactic
maser sources. VERA array consists of four stations located at Mizusawa, Iriki, Ogasawara, and Ishigaki-jima with baseline ranges from 1000 km to 2300 km (see, figure 1).
The construction of VERA array was completed in 2002, and it is under regular operation since the fall of 2003. VERA was opened to international users in the 22 GHz band
(K band) and the 43 GHz band (Q band) from 2009. And also, VERA was opened in
the 6.7 GHz band (C band) as a shared-risk observation from 2011. This document
is intended to give astronomers necessary information for proposing observations with
VERA.

120 ˚
50 ˚

130˚

150 ˚
50 ˚

140˚

40 ˚

40 ˚

Mizusawa(VERAMZSW)

7

km

m

Iriki
(VERAIRIK)

125

1k

Ogasawara(VERAOGSW)

10

Figure 1: Array configurationof VERA.

30 ˚

m

19

km

30 ˚

22

70

1337 kkm

6121827 km

Ishigaki(VERAISGK)
20 ˚
120 ˚
130˚

2

140˚

20 ˚
150 ˚

SystemMost unique aspect of VERA is “dual-beam” telescope, which can simultaneously observe nearby two sources. While single-beam VLBI significantly suﬀers from fluctuationof atmosphere, dual-beam observations with VERA eﬀectively cancel out the atmospheric fluctuations, and then VERA can measure relative positions of target sources
to reference sources with higher accuracy based on the ‘phase-referencing’ technique.

3

2.1

Array

VERA array consists of 4 antenna site in Mizusawa, Iriki, Ogasawara, and Ishigakijima, with 6 baselines (see, figure 1). The maximum baseline length is 2270-km between
Mizusawa and Ishigaki-jima, and the minimum baseline length is 1019-km between Iriki
and Ishigaki-jima. The maximum angular resolution expected from the baseline lengthis about 1.2 mas for K band (22 GHz) and about 0.6 mas for Q band (43 GHz). The
geographic locations of each VERA antenna in the coordinate system of epoch 2009.0
are summarized in table 1. Figures 2 show examples of uv plane coverage.
The coordinates and averaged velocities of VERA sites in Table 1 are predicted value
at the epoch of January 01, 2015. Reference frame of these coordinates is ITRF2008.
The rates of the coordinates of Mizusawa, Iriki, Ogasawara and Ishigaki-jima are theaverage value of change of the coordinates from January 01, 2014 to December 31, 2014.
The 2011 oﬀ the Pacific coast of Tohoku Earthquake (Mj=9.0) brought the co-seismic
large step and non-linear post-seismic movement to the coordinates of Mizusawa. Coseismic steps of the coordinates of Mizusawa are dX=-2.0297m, dY=-1.4111m and
dZ=-1.0758m. The creeping continues still now, though decreased. The changes ofcoordinates by the post-seismic creeping are dX=-0.8574m, dY=-0.5387m and dZ=0.2398m in total from March, 12, 2011 to Jan, 01, 2015.
Table 1: Geographic locations and motions of each VERA antenna
Site
Mizusawa
Iriki
Ogasawara
IshigakiEastLongitude[◦ ′ ′′ ]141 07 57.31
130 26 23.60
142 12 59.80
124 10 15.59

North
Latitude[◦ ′ ′′ ]39 08 00.68
31 44 52.43
27 05 30.49
24 24 43.82

Ellipsoidal
Height
[m]
116.4
573.6
273.1
65.1

Altitude
[m]
75.6
541.6
222.9
38.5

Site
X (m)
Y (m)
Z (m)
IVS2a
IVS8b
CDPc
Mizusawa–3857244.6425 3108782.9988 4003899.1960
Vm
VERAMZSW
7362
Iriki–3521719.8241 4132174.6271 3336994.1240
Vr
VERAIRIK
7364
Ogasawara –4491068.5536 3481545.0831 2887399.7333
Vo
VERAOGSW
7363
Ishigaki–3263995.1565 4808056.3118 2619948.7878
Vs
VERAISGK7365
a
IVS 2-characters code, b IVS 8-characters code, c CDP (NASA Crustal Dynamics Project) code
Site
∆X (m/yr) ∆Y (m/yr)∆Z (m/yr)Mizusawa–0.0887–0.0489–0.0047
Iriki–0.0210–0.0088–0.0151
Ogasawara
0.02660.02750.0084Ishigaki–0.03930.0004–0.0486
The epoch of the coordinates is January, 01, 2015
Average speed was obtained from the VLBI data from January 01, 2014 to January 01, 2015.

Post seismic movements of Mizusawa are very complex. Internal error of coordinatesof Mizusawa by polynomial fitting is 5-6mm. But, in a solution, a several centimeters
diﬀerences arise for every fitting with the increase in geodetic observation data. It is
judged that these diﬀerences are the uncertainly of the coordinates of Mizusawa.

4

UV plot (MIZ-IRK-OGA-ISG, Dec= 20)
3000

2000

2000

1000

1000

V (km)V (km)

UV plot (MIZ-IRK-OGA-ISG, Dec= 60)
3000

0

0

-1000

-1000

-2000

-2000

-3000
-3000

-2000

-1000

0
U (km)

1000

2000

-3000
-3000

3000

-2000

-1000

0
U (km)

1000

2000

3000

UV plot (MIZ-IRK-OGA-ISG, Dec= -20)
3000

2000

V (km)

1000

0

-1000

-2000

-3000
-3000

-2000

-1000

0
U (km)

1000

2000

3000

Figure 2: UV coverage (±3000 km) expected with VERA four antennas from an
observation over elevation of 20◦ . Each panel show UV coverage for the declination of60◦ (top left), 20◦ (top right), and –20◦ (bottom).

2.2

Antennas

All the telescopes of VERA have the same design, being a Cassegrain-type antenna
on AZ-EL mount. Each telescope has a 20-m diameter dish with a focal length of
6-m, with a sub-reflector of 2.6-m diameter. The dual-beam receiver systems for 22
and 43 GHz are installed at the Cassegrain focus. Two receivers are set up on the
Stewart-mount platforms, which are sustained by steerable six arms, and with such
systems one can simultaneously observe two adjacent objects with a separation angle
between 0.32 and 2.2 (2.18 for 43 GHz) deg. The whole receiver systems are set up on
the field rotator (FR), and the FR rotate to track the apparent motion of objects dueto the earth rotation. Table 2 summarizes the ranges of elevation (EL), azimuth (AZ)
and field rotator angle (FR) with their driving speeds and accelerations. The examplesof duration time which requires to set a separation angle between two receiver on
the Stewart-mount platforms are summarized in table 3 . In the case of single beamobserving mode, one of two beams is placed at the antenna vertex (separation oﬀset of
0 deg).
Table 2: Driving Performance of VERA 20-m Antennas
Driving axis Driving range Max. driving speed Max. driving acceleration
AZ1–90◦ ∼450◦
2.1◦ /sec
2.1◦ /sec2
◦
◦
◦
EL
5 ∼85
2.1 /sec
2.1◦ /sec2
2
◦
◦
◦
FR
–270 ∼270
3.1 /sec
3.1◦ /sec2
1◦◦
The north is 0 and the east is 90 .
2
FR is 0◦ when Beam-1 is at the sky side and Beam-2 is at the ground side,
and CW is positive when an antenna is seen from a target source.

5

Table 3: Moving Time of Two Receiver System
Stating separation
0.32◦
0.32◦
0.32◦
0.32◦
0.32◦

2.2.1

End separation
0.5◦
1.0◦
1.5◦
2.0◦
2.2◦

Duration time
11 sec30 sec55 sec86 sec98 secAperture Eﬃciency

The aperture eﬃciency of each VERA antenna is about 45–50% in the K-band andabout 35–50% in the Q-band. (see table 4 and figure 3). These measurements werebased on the observations of Jupiter assuming that the brightness temperature of
Jupiter is 160 K in both the K band and the Q band. The latest measurements
were done in 2015 February. The aperture eﬃciencies are not significantly changed
compared with previous measurements.
Table 4: The Latest Results of Aperture Eﬃciency Measurements of the VERA 20 m
Antennas
Site

Band

Date

ηA
(%)
MIZ
Q
Dec. 07, 2014 45.2±1.6
QJan. 16, 2015 46.9±1.0
QJan. 23, 2015 46.1±1.0
IRKQ
Jan. 12, 2015 39.4±0.9
QJan. 15, 2015 41.1±0.5
QJan. 22, 2015 42.7±0.6
QFeb. 14, 2015 41.6±0.9
OGAQ
Feb. 18, 2015 40.4±1.7
ISG
Q
Dec. 06, 2014 44.4±0.9
QJan. 16, 2015 44.2±1.4
MIZ
K
Feb. 14, 2015 49.2±1.9
KFeb. 15, 2015 46.3±1.5
IRKK
Feb. 18, 2015 45.5±1.3
OGAK
Feb. 18, 2015 46.2±2.0
ISG
K
Feb. 14, 2015 47.3±1.7
KFeb. 15, 2015 47.0±1.5aAssumed apparent diameter for Jupiter.

HPBW(arcsec)76.8±6.4
78.0±3.3
74.0±2.277.1±1.779.9±2.773.9±1.0
72.4±1.275.2±3.274.0±2.876.3±2.2
147.0±7.6139.9±5.1139.9±4.6
154.6±5.8142.8±3.2145.1±4.5

Num. of
Scans
8
16
16
18
14
12
11
13
9
17
9
9
19
12
14
16

Elevation
(deg)
64-66
63-66
59-67
69-74
68-74
63-74
45-66
48-70
64-79
65-81
54-67
55-67
52-72
63-80
43-68
44-69

θb
(arcsec)
39.2
43.0
43.0
43.0
43.0
43.0
43.5
43.5
39.2
43.0
43.5
43.5
43.5
43.5
43.5
43.5

The elevation dependence of aperture eﬃciency for VERA antenna was also measured from the observation toward maser sources. Figure 4 show the relations between
the elevation and the aperture eﬃciency measured for Iriki station. The aperture efficiency in low elevation of ≤ 20 deg decreases slightly, but this decrease is less thanabout 10%. Concerning this elevation dependence, the observing data FITS file include a gain curve table (GC table), which is AIPS readable, in order to calibrate thedependence when the data reduction.
The aperture eﬃciency was also measured at various separation angle of dual-beams
in order to evaluate the dependence of aperture eﬃciency on dual-beam separation angle. Figure 5 show the relations between the beam separation angle and the apertureeﬃciency measured for Iriki antenna. It appears that the aperture eﬃciency decreases
slightly as the separation angle increases. For the calibration of the separation an6

60

Q band55
Efficiency [%]

50
45
40
35
30
25
20
60

-2007
Feb 2008
Jun 16 2008
Jun 17 2008
Oct 9-10 2009
Nov 13-14 2009
Dec 08-09 2009
Jul 22-31 2011
Aug 10-26 2011
Jan 07-09 2012
Jan 30 2012

Feb 27 2012
Mar 13 2012
Jun 27 2012
Dec 26-29 2012
Jan 04-07 2013
Feb 05-19 2013
Mar 12-13 2013
Sep-Nov 2013
Nov-Dec 2013
Feb 2014
Dec 2014-Fev 2015

K band55
Efficiency [%]

50
45
40
35
30
25
20

-2007
Feb 2008
Jun 16 2008
Oct 15 2009
Dec 09 2009
Jul 22-31 2011
Aug 10-26 2011
Jan 07-09 2012
Jan 30 2012
Feb 22 2012
Mar 13 2012
Jan 04-07 2013
Feb 05-20 2013
Mar 11 2013
Sep-Nov 2013
Nov-Dec 2013
Feb 2014
Fev 2015

MIZ

IRK

OGA

ISG

Figure 3: History of the aperture eﬃciency measurements for the VERA antennas.

gle dependence, a gain curve table (GC table) which includes the separation angle
dependence of the aperture eﬃciency is attached to the observed data FITS file.

7

K band

Efficiency

Efficiency

1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0

10

20

30

40
50
EL [deg]

60

70

80

1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0

90

Q band

0

10

20

30

40
50
EL [deg]

60

70

80

90

1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0

K bandEfficiency

Efficiency

Figure 4: The elevation dependence of the aperture eﬃciency in the K band (on Feb
8, 2005; right) and the Q band (on Feb 12, 2005; left) for Iriki antenna. The eﬃciency
is relative value to the measurement at EL = 50◦ .

0

0.25

0.5

0.75

1
1.25
SA [deg]

1.5

1.75

2

2.25

1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0

Q band

0

0.25

0.5

0.75

1
1.25
SA [deg]

1.5

1.75

2

2.25

Figure 5: The dependence of the aperture eﬃciency on the separation angle between
dual-beams in the K band (on Mar 4, 2004; right) and the Q band (on Mar 5, 2004; left)
for Iriki antenna. The eﬃciency of vertical axis is relative value to the measurement
at the separation angle of 0◦ . The curved line indicates the quartic polynomial fitting.

8

2.2.2

Beam Pattern and Size

Figure 6 show the beam patterns in the K band. The side-lobe level is less than about–15 dB, except for the relatively high side-lobe level of about –10 dB for the separation
angle of 2.0 deg at Ogasawara station. The side-lobe of the beam patterns have an
asymmetric shape, but the main beam have a symmetric Gaussian shape without
dependence on separation angle. The measured beam sizes (HPBW) in the K bandand the Q band based on the data of the pointing calibration are also summarized intable 4. The main beam sizes show no dependence on the dual-beam separation angle.

PLot file version 1 created 07-AUG-2003 18:54:17
CONT: W49N 8.0 KM/S BEAM2.MAP-IT.2

400

300

200

ARC SEC

100

0

-100

-200

-300

-400

400
300
200
100
0
-100
ARC SEC
Center at RA 19 10 13.476 DEC 09 06 14.29
Cont peak flux = 1.5787E+04 K km/s
Levs = 1.579E+02 * (0.100, 0.300, 0.500, 1, 3, 5,
10, 30, 50, 100)

-200

-300

-400

PLot file version 1 created 12-SEP-2003 00:37:55
W49N 8.0 KM/S O280905.MAP-IT.1

400

300

200

100
ARC SEC

Figure 6: The beam patterns of
Beam-A in the K band. Top andbottom panels were the results forthe separation angle of 0◦ at Iriki,
and for the separation angle of 2.0◦
at Ogasawara, respectively. These
are derived from the mapping observation of strong H2 O maser toward
W49N, which can be assumed as apoint source, with grid spacing of 75′′ .

0

-100

-200

-300

-400

400
300
200
100
0
-100
ARC SEC
Center at RA 19 10 13.476 DEC 09 06 14.29
Peak flux = 6.3418E+03 K km/s
Levs = 6.342E+01 * (0.100, 0.300, 0.500, 1, 3, 5,
10, 30, 50, 100)

9

-200

-300

-400

-500

2.2.3

Pointing Accuracy

In each VERA antenna, observations to check a pointing accuracy were carried out,
and the pointing oﬀset were calibrated. Pointing oﬀsets for all sky direction were
measured based on five-point scans in the azimuth and elevation direction using strong
maser sources with known positions. Observed pointing oﬀsets were parameterized withthe models described in the equation (1) and (2), and are now corrected to improve
the pointing accuracy. In the equations (1) and (2), A1 -A8 are standard pointing
instrumental parameters for AZ-EL mounting telescope, and A9 -A12 are parameterswhich are introduced to describe higher order eﬀects.

δAz = A1 sin(Az) sin(El) − A2 cos(Az) sin(El) + A3 sin(El) + A4 cos(El) + A5 +A9 sin(2Az) sin(El) − A10 cos(2Az) sin(El) +A11 sin(2Az) cos(El) − A12 cos(2Az) cos(El)(1)
δEl = A1 cos(Az) + A2 sin(Az) + A6 + A7 cos(El) + A8 sin(El) +A9 cos(2Az) − A10 sin(2Az)(2)
The pointing accuracy of each VERA antenna, after the correction of the pointing
instrumental error, are summarized in the table 5. Figure 7 shows examples of theresidual pointing oﬀsets in the Q band. The pointing residuals of the Mizusawa antenna
after the earthquake on March 11 2011 have been checked carefully, and we found no
significant/serious eﬀect on the pointing accuracy due to the earthquake.
Table 5: Pointing Accuracy of VERA 20-m Antennas
Site

Band

Date

σAZ
σEL
Num. of(arcsec) (arcsec)
Scan
IRK
Q
Feb. 14 2015
5.270
5.115
173
ISG
Q
Jan. 16 2015
5.265
6.305
152
MIZ
Q
Jan. 23 2015
5.553
6.083
189
OGA Q
Feb. 16 2015
4.865
6.847
182
Note; σAZ and σEL represent the standard deviation of
the pointing measurements in AZ and EL, respectively.
The pointing measurements were carried out only in the Q band.

10

100

EL Offset(observed) [arcsec]

40
20
0
-20
-40
-60

60
40
20
0
-20
-40
-60

-80

-80

-100

-100
30

60

90 120 150 180 210 240 270 300 330 360
AZ [deg]

100

0

60

20
0
-20
-40
-60

20
0
-20
-40
-60
-80
-100

30

40
50
EL [deg]60

70

EL offset
AZ=0 deg
AZ=30 deg
AZ=60 deg

40

-100
20

90 120 150 180 210 240 270 300 330 360
AZ [deg]

60

-80
10

60

80

40

0

30

100

AZ offset
AZ=30 deg
AZ=60 deg
AZ=90 deg

80

EL offset
EL=10 deg
EL=40 deg
EL=80 deg

80

EL Offset(observed) [arcsec]

AZ Offset(observed) [arcsec]

60

0

AZ Offset(observed) [arcsec]

100

AZ offset
EL=15 deg
EL=45 deg
EL=75 deg

80

80

90

0

10

240

270

20

30

40
50
EL [deg]

60

70

80

90

90

80

70

EL [deg]

60

50

40

30

20

10

0
0

30

60

90

120

150

180
AZ [deg]

210

300

330

360

Figure 7: Examples of pointing residuals for the Iriki antenna in the Q band (43 GHz).
Top and middle panels show relations of the azimuth and elevation, respectively, withthe pointing residuals in azimuth (left) and elevation (right). Bottom panel shows
positions on celestial sphere of the objects which were observed in the pointing measurement.

11

30

30

20

20

EL Offset(residual) [arcsec]

AZ Offset(residual) [arcsec]

For dual-beam observations with large separation angle, there is an additional pointing oﬀset with ∼ 15 arcsec that shows sinusoidal variations with FR angle, as shownin figure 8. This pointing error is not fully calibrated.

10
0
-10
-20
-30
-200

-150

-100

-50

0

50

100

150

10
0
-10
-20
-30
-200

200

-150

-100

-50

30

30

20

20

10
0
-10
-20
-30
-200

-150

-100

-50

0

0

50

100

150

200

50

100

150

200

FR [deg]

EL Offset(residual) [arcsec]

AZ Offset(residual) [arcsec]

FR [deg]

50

100

150

10
0
-10
-20
-30
-200

200

FR [deg]

-150

-100

-50

0
FR [deg]

Figure 8: Pointing oﬀset of Beam-A against dual-beam separation angle in the K bandat Iriki station. Red cross indicate the tracking error with the dual-beam oﬀset, andgreen cross indicate the tracking error without the dual-beam oﬀset (Beam-A is placedat the antenna vertex). These panels show dependency on the field rotator angle(FR) of the azimuth oﬀset (left panel ) and the elevation oﬀset (right panel ). Top andbottom panels show the relations for the separation angle of 1.0 deg (on the observationof W3OH) and 2.0 deg (on the observation of W49N), respectively.

12

2.2.4

Sky Line

Figure 9 show a skyline for the VERA antenna site. While mechanically-possible EL
driving range is from 5 to 85 deg, due to the sky line eﬀect, the lowest observableelevation is as high as 20 deg depending on the stations and the directions. Observers
are requested to take care of the skyline eﬀect if low declination sources are to beobserved.

25

25

Mizusawa

Iriki
20
EL [degree]

EL [degree]

20

15

10

5

15

10

5

0

0
0

30

60

90 120 150 180 210 240 270 300 330 360
AZ [degree]

0

25

60

90 120 150 180 210 240 270 300 330 360
AZ [degree]

25

Ogasawara

Ishigaki20

20
EL [degree]

EL [degree]

30

15

10

5

15

10

5

0

0
0

30

60

90 120 150 180 210 240 270 300 330 360
AZ [degree]

0

30

60

90 120 150 180 210 240 270 300 330 360
AZ [degree]

Figure 9: Sky Line for each VERA antenna. The azimuth of 0 deg is the north.
Mechanically-possible EL range is from 5 deg to 85 deg.

13

2.3

Receivers

Each VERA antenna has the receivers for 5 bands, which are S, C, X, K, and Q bands.
For the common use in 2016B, the K band (22 GHz), the Q band (43 GHz) and the C
band (6.7 GHz) are open for observing. The information about the C band is describedin session 2.8. The low-noise HEMT amplifiers in the K and Q bands are enclosed in
the cryogenic dewar, which is cooled down to 20 K, to reduce the thermal noise. The
range of observable frequency and the typical receiver noise temperature (TRX ) at eachband are summarized in the table 6 and figure 10.
Table 6: Receivers

Frequency Range
TRX aPolarization
[GHz]
[K]
K
21.5-23.8
30-50
LCP
Q
42.5-44.5
40-60b ,70-90c
LCPa
Receiver noise temperatureb
Receiver noise temperature for beam-A receiverb
Receiver noise temperature for beam-B receiver
Band[July 2014]
50

50

K-band #1

K-band #2

40

Trx [K]

Trx [K]

40
30
20
10

30
20
10

0
21

22

23

0
21

24

22

RF [GHz]100
90

Q-band #1

80
70
60

Q-band #2

80
70
60

50

50

40
30
42

40
30
42

43

24

RF [GHz]Trx [K]

Trx [K]

100
90

23

44

45

43

44

45

RF [GHz]RF [GHz]

Figure 10: Receiver noise temperature for each VERA antenna. Top and bottom panels
show measurements in the K and Q bands, and left and right panels show those in thereceiver #1 for beam-A and #2 for beam-B, respectively. Horizontal axis indicate a
RF (radio frequency) at which TRX is measured.

After the radio frequency (RF) signals from astronomical objects are amplified by
the receivers, the RF signals are mixed with standard frequency signal generated in
the first local oscillator to down-convert the RF to an intermediate frequency (IF) of
4.7 GHz–7 GHz. The first local frequencies are fixed at 16.8 GHz in the K band and14

at 37.5 GHz in the Q band. The IF signals are then mixed down again to the baseband frequency of 0–512 MHz. The frequency of second local oscillator is tunablewith a possible frequency range between 4 GHz and 7 GHz. The correction of the
Doppler eﬀect due to the earth rotation is carried out in the correlation process after
the observation. Therefore, basically the second local oscillator frequency is kept to beconstant during the observation. Figure 11 shows a flow diagram of these signals for
the VERA.
K: 21.5 - 23.8 GHz
Q: 42.5 - 44.5 GHz
IF: 4.7 - 7 GHz

Base Band:
0 - 512 MHz

1st Local
K: 16.8 GHz
Q: 37.5 GHz

2nd Local
4 - 7 GHz

RecorderDigital Filter

A/D Converter

Receiver #1

Receiver #2

Figure 11: Flow diagram of signals from receiver to recorder for VERA.

2.4

Digital signal process

A/D (analog-digital) samplers convert the analog base band outputs (0–512 MHz ×
2 beams) to digital form. The A/D converters carry out the digitization of 2-bit
sampling with the bandwidth of 512 MHz and the data rate is 2048 Mbps for eachbeam.
Since the total data recording rate is limited to 1024 Mbps (see the next section),
only part of the sampled data can be recorded onto magnetic tape. The data rate
reduction is done by digital filter system, with which one can flexibly choose number
and width of recording frequency bands. Observers can select modes of the digital filter
listed in the table 7 and table 8. In VERA7Q mode in the table 7, two transitions (v=1
& 2) of SiO maser in the Q band with the Beam-A can be simultaneously recorded.
VERA7C and VERA4S are modes for single-beam observations, such as C-band or
imaging of continuum sources, etc.

15

Table 7: Digital Filter Mode for VERA
Num. CHa

VERA1

Rate
(Mbps)1024

VERA1S

1024

2

VERA7

1024

16

VERA10

1024

16

Mode

a

2

Total number of channels
Channel numbereSide Band (LSB/USB)c

BW/CHb(MHz)
128

Freq. ranged Side Bande
(MHz)
1
A
256 - 384U2B
256 - 384U128
1
A128 - 256L
2A
256 - 384U
16
1
A
256 - 272U
2B
128 - 144U
3B
144 - 160L
4B
160 - 176U
5B
176 - 192L
6
B
192 - 208U
7B
208 - 224L
8B
224 - 240U
9B
240 - 256L
10B
256 - 272U
11B
272 - 288L
12B
288 - 304U
13B
304 - 320L
14
B
320 - 336U
15B
336 - 352L
16
B
352 - 368U
16
1
A
256 - 272U
2B
256 - 272U
3A
272 - 288L4B
272 - 288L5A
288 - 304U
6B
288 - 304U
7A
304 - 320L
8B
304 - 320L
9A
320 - 336U
10B
320 - 336U
11A
336 - 352L
12B
336 - 352L
13A
352 - 368U
14B
352 - 368U
15A
368 - 384L
16
B
368 - 384
Lb
Bandwidth per channel in MHzd
Filtered frequency range in the base band (MHz)

16

CHc

Beam

Table 8: Digital Filter Mode for VERA : continued
Num. CHa

VERA7Q

Rate(Mbps)1024

VERA7C

1024

16

VERA4S

1024

8

Mode

a

Total number of channels
Channel numbereSide Band (LSB/USB)c

16

BW/CHb
(MHz)
16

Freq. ranged Side Bande
(MHz)
1
A
48 - 64L
2
B
48 - 64L
3B
64 - 80U
4
B
96 - 112U
5B
128 - 144U
6
B
160 - 176U
7B
192 - 208U
8B
224 - 240U
9A
352 - 368U
10B
256 - 272U
11B
288 - 304U
12B
320 - 336U
13B
352 - 368U
14B
384 - 400U
15B
416 - 432U
16B
448 - 464U
16
1
A
0 - 16U
2
A
32 - 48U
3
A
64 - 80U
4
A
96 - 112U
5A
128 - 144U
6
A
160 - 176U
7A
192 - 208U
8A
224 - 240U
9A
256 - 272U
10A
288 - 304U
11A
320 - 336U
12A
352 - 368U
13
A
384 - 400U
14A
416 - 432U
15A
448 - 464U
16A
480 - 496U
32
1
A
128 - 160U
2A
160 - 192L
3
A
192 - 224U
4A
224 - 256L
5A
256 - 288U
6A
288 - 320L
7A
320 - 352U
8A
352 - 384
Lb
Bandwidth per channel in MHzd
Filtered frequency range in the base band (MHz)

17

CHc

Beam

2.5

Recorders

VERA is using a hard-disk recording system called OCTADISK which can record withthe rate of 1 Gbps.

2.6

Correlators

The correlation processes are carried out by the software correlator located at NAOJ
Mizusawa campus. In a default correlation, the maximum number of spectral point perantenna are 2048 points across all channels of 2-beams data and the time resolution isusually set to be 1 second. But higher spectral resolution and higher time resolution
are available by the software correlator upon requests. Please contact with vera-prop@ nao.ac.jp, if you require correlating with special parameters.

2.7

Calibration

2.7.1

Delay and Bandpass Calibration

The time synchronization for each antenna is kept within 0.1 µsec using GPS andhigh stability frequency standard provided by the hydrogen maser. To correct for
clock parameter oﬀsets with better accuracy, bright continuum sources with accuratelyknown positions should be observed at usually every 60–90 mins during observations.
The calibration of frequency characteristic (bandpass calibration) can be also done
based on the observation of bright continuum source.
The bandpass characters of the base band in frequency could cause some CH-to-CH
amplitude oﬀset in the visibility output depending on the digital filter mode. The
frequency dependence of the visibility amplitude at K and Q bands are shown in figure 12 and 13. Diﬀerences of the dependence between 2011 and 2012 are less than
10%. External text files for GC tables are available to calibrate such CH-to-CH amplitude oﬀsets for VERA7 mode at K and Q band, VERA7MM mode at K band, andVERA7SIO2 (same as VERA7Q) mode at Q band. This calibration is essential totreat each CH data independently as in the case of multi-CH mapping, or to obtain
the accurate amplitude value from the visibility data across the all CHs. Please accessto the website and download the calibration files in table 9. Then please import thecalibration file using the AIPS task “TBIN”.
Table 9: Information for calibration of CH-to-CH amplitude oﬀset
URL
File for VERA7
File for VERA7MM
File for VERA7SIO2

in preparation, please ask "vera-prop @ nao.ac.jp"
GCTAB VERA7 K2009
GCTAB VERA7 Q2009GCTAB VERA7MM K2009
GCTAB VERA7SIO2 Q200918

MizusawaOgasawara
1.1

1.0

1.0

0.9

0.9

Relative Amplitude to the maximum value of amplitude

Relative Amplitude to the maximum value of amplitude

1.1

0.8
0.7
0.6
0.5

0.4

0.8
0.7
0.6
0.5

0.4

0.3

0.3

0.2

0.2

0.1

0.1

0.00

16

32

48

64

80

0.00

96 112 128 144 160 176 192 208 224 240 256 272 288 304 320 336 352 368 384 400 416 432 448 464 480 496 512

Base Band [MHz]

16

32

48

64

80

Iriki
1.1

1.0

1.0

0.9

0.9

Relative Amplitude to the maximum value of amplitude

Relative Amplitude to the maximum value of amplitude

Base Band [MHz]Ishigaki

1.1

0.8
0.7
0.6
0.5

0.4

0.8
0.7
0.6
0.5

0.4

0.3

0.3

0.2

0.2

0.1

0.1

0.00

96 112 128 144 160 176 192 208 224 240 256 272 288 304 320 336 352 368 384 400 416 432 448 464 480 496 512

16

32

48

64

80

0.00

96 112 128 144 160 176 192 208 224 240 256 272 288 304 320 336 352 368 384 400 416 432 448 464 480 496 512

Base Band [MHz]

16

32

48

64

80

96 112 128 144 160 176 192 208 224 240 256 272 288 304 320 336 352 368 384 400 416 432 448 464 480 496 512

Base Band [MHz]Figure 12: The frequency dependence of the baseband at K band seen for each VERA
antenna; (top-left) Mizusawa, (top-right) Ogasawara, (bottom-left) Iriki, and (bottomright) Ishigaki.

Mizusawa

Ogasawara
1.1

1.0

1.0

0.9

0.9

Relative Amplitude to the maximum value of amplitude

Relative Amplitude to the maximum value of amplitude

1.1

0.8
0.7
0.6
0.5

0.4

0.8
0.7
0.6
0.5

0.4

0.3

0.3

0.2

0.2

0.1

0.1

0.00

16

32

48

64

80

0.00

96 112 128 144 160 176 192 208 224 240 256 272 288 304 320 336 352 368 384 400 416 432 448 464 480 496 512

Base Band [MHz]

16

32

48

64

80

Iriki
1.1

1.0

1.0

0.9

0.9

Relative Amplitude to the maximum value of amplitude

Relative Amplitude to the maximum value of amplitude

Base Band [MHz]Ishigaki

1.1

0.8
0.7
0.6
0.5

0.4

0.8
0.7
0.6
0.5

0.4

0.3

0.3

0.2

0.2

0.1

0.1

0.00

96 112 128 144 160 176 192 208 224 240 256 272 288 304 320 336 352 368 384 400 416 432 448 464 480 496 512

16

32

48

64

80

0.00

96 112 128 144 160 176 192 208 224 240 256 272 288 304 320 336 352 368 384 400 416 432 448 464 480 496 512

Base Band [MHz]

16

32

48

64

80

96 112 128 144 160 176 192 208 224 240 256 272 288 304 320 336 352 368 384 400 416 432 448 464 480 496 512

Base Band [MHz]Figure 13: The frequency dependence of the baseband at Q band seen for each VERA
antenna; (top-left) Mizusawa, (top-right) Ogasawara, (bottom-left) Iriki, and (bottomright) Ishigaki.

19

2.7.2Gain Calibration

Each VERA antenna has the chopper wheel of the hot load (black body at the room
temperature), and the system noise temperature can be obtained by measuring theratio of the sky power to the hot load power (so-called R-Sky method). The hot load
measurement can be made before/after any scan. Also, the sky power is continuously
monitored during scans, so that one can trace the variation of system noise temperature.
2.7.3

Phase Calibration

To calibrate the instrumental phase error by caused the path length diﬀerence in dualbeams, four artificial noise sources (NS) are installed on the feedome base (above themain reflector). During observations, the artificial noise (reflected by sub-reflector)
is injected to dual-beam receivers and correlated on real-time to calculate the phase
diﬀerence between dual-beams. Typical phase residuals of the dual-beam calibration
system are 0.2 mm for using one NS and 0.12 mm for using four NSs. Dual-beam phasecalibration data are also attached to the observed data in a readable format with AIPS.

2.8

C-band Information

Antenna eﬃciency at C-band was estimated to be 50-55 % depending on the stations.
The frequency range of C-band receiver is 6.5 - 7.0 GHz. Typical system temperature isaround 130 K toward the zenith, and optical depth is around 0.03-0.05 under relatively
good conditions. Beam size at 6.6 GHz is around 9 arcmin, and the pointing at C bandis expected to be suﬃciently high, as pointing model is based on measurements usinga shaper beam at 22 GHz. Diﬀerent from the case of K-band and Q-band, VERA
20-m telescope has only one C-band receiver, therefore only a single-beam observation
is available.

2.9

Geodetic Measurement

Geodetic observations are performed as part of the VERA project observations to derive
accurate antenna coordinates. The geodetic VLBI observations for VERA are carriedout in the S/X bands (2 GHz/8 GHz) and also in the K band (22 GHz). The S/Xbands are used in the domestic experiments with the Geographical Survey Instituteof Japan and the international experiments called IVS-T2. On the other hand, the Kband is used in the VERA internal experiments. We obtain higher accuracy results in
the K band compared with the S/X bands. The most up-to-date geodetic parameters
are derived through geodetic analyses.
Non-linear post seismic movement of Mizusawa after the 2011 oﬀ the Pacific coast of
Tohoku Earthquake continues. The position and velocity of Mizusawa is continuously
monitored by GPS. The coordinates in the table 1 are provisional and will be revisedwith accumulation of geodetic data by GPS and VLBI.
In order to maintain the antenna position accuracy, the VERA project has threekinds of geodetic observations. The first is participation in JADE (JApanese Dynamic
Earth observation by VLBI) organized by GSI (Geographical Survey Institute) and
IVS-T2 session in order to link the VERA coordinates to the ITRF2008 (Interna20

tional Terrestrial Reference Frame 2008). Basically Mizusawa station participate in
JADE nearly every month. Based on the observations for ten years, the 3-dimensional
positions and velocities of Mizusawa station till March 09, 2011 is determined withaccuracies of 7-9 mm and about 1 mm/yr in ITRF2008 coordinate system. But theuncertainty of several centimeters exists in the position on and after March 11, 2011.
The second kind of geodetic observations is monitoring of baseline vectors between
VERA stations by internal geodetic VLBI observations. Geodetic positions of VERA
antennas relative to Mizusawa antenna are measured from geodetic VLBI observations
every two weeks. From polygonal fitting of the ten-year geodetic results, the relative
positions and velocities are obtained in the precisions of 1-2 mm and 0.8-1 mm/yr till
March 09, 2011.

21

3

Observing Proposal

For this observing season (August 15th, 2016 to January 15th, 2017), the K and Q
bands dual-beam mode are opened to international users. Also, the C band singlebeam mode is opened tentatively in this season. Total observing time up to 200 hrs
per year will be available for the common-use observing time. The observation with 6
elements array (VERA + Nobeyama 45-m and Kashima 34-m) is available for the Kband and the observation with VERA + Nobeyama 45-m is available for the Q bands( the Q-band observation with Kashima 34-m is not available in this season). The
observing time of the combined array is 100 hrs per year at maximum.

3.1

Proposal Submission

Observing proposals for VERA are invited for the observing period from August 15th,
2016 to January 15th, 2017. The application deadline is on “June 1st 2016” for thisseason. Proposals will be reviewed by referees, and observing time is scheduled by the
VERA Time Allocating Committee of the NAOJ on the basis of the scientific meritsof the proposed research. As for the proposal submission, details can be found at the
VERA homepage,
http://veraserver.mtk.nao.ac.jp/restricted/index-e.html.
Any questions on proposal submission should be sent to “vera-prop @ nao.ac.jp”.
If an applicant wants to have a collaborator from the VERA group member for extensive support, the VERA group can arrange the collaborator (after the acceptance ofproposal).

3.2

Observation Mode

The K band (22 GHz) and the Q band (43 GHz) single/dual-beam mode, and the Cband single-beam mode are available. In addition to VERA four antennas, Nobeyama
45-m and Kashima 34-m are available for the K-band and Nobeyama 45-m is available
for the Q band. However, note that the Nobeyama 45-m and Kashima 34-m data could
be correlated with only one beam data among VERA 2 beams.
The recording rate of 1 Gbps is used in the observation by only VERA. The observation by VERA + Nobeyama 45-m / Kashima 34-m is made by 2-Gbps recording
rate as a shared-risk observation.

3.3

Angular Resolution

The expected angular resolutions for the K band (22 GHz) and the Q band (43 GHz)
are about 1.2 mas and about 0.6 mas, respectively. The synthesized beam size strongly
depend on UV coverage, and could be larger than the values mentioned above because the baselines projected on UV plane become shorter than the distance between
antennas.

22

3.4

Sensitivity

When a target source is observed, a noise level σbl for each baseline can be expressedas√Tsys,1 Tsys,2
2k
√
σbl =
,
(3)
√
η Ae1 Ae2 2Bτ
where k is Boltzmann constant, η is quantization eﬃciency (∼ 0.88), Tsys is system noise
temperature, Ae is antenna eﬀective aperture area which include aperture eﬃciency,
B is the bandwidth, and τ is on-source integration time. Note that for an integration
time beyond 3 min (in the K band), the noise level expected by equation (3) cannot be
attained because of the coherence loss due to the atmospheric fluctuation. Thus, forfinding fringe within a coherence time, the integration time τ cannot be longer than 3minutes. When a continuum source is observed with the digital filter mode of ‘VERA1’
under moderate weather condition, the noise level estimated by the equation (3) is
σbl =23 mJy, assuming that aperture eﬃciency ηA ∼ 50%, B = 128 MHz, τ = 120 sec,
and Tsys = 200 K. Thus the minimum flux which can be detected for each baseline is
160 mJy for S/N = 7. For VLBI observations, signal-to-noise ratio (S/N ) of at least
5 and usually 7 is generally required for finding fringes. On the other hand, when amaser source is observed with the ‘VERA7’ mode under above conditions, the noiselevel is σbl =1.5 Jy, assuming that B = 31.25 KHz (512 spectral channels with 16 MHz
bandwidth) for the VERA7 mode. Thus the minimum detectable flux for each baseline
is 10.2 Jy for S/N = 7. A noise level for each parameter is also expressed as follows,σbl = 23 ×(

Tsys,1200 K)1/2 (

Tsys,2
200 K)1/2 (B
128 M Hz)−1/2 (

τ120 sec

)−1/2

mJy.

(4)

On the dual-beam observation, a continuum source or a maser source which isbrighter than the above baseline sensitivity should be observed as reference sourceby one of the two beams. If the users observe a source which is weaker than theabove sensitivity limit, it is necessary to carry out long time integration with phasereferencing to brighter√ sources. After successful phase-referencing, signal-to-noise ratio
is improved as ∝ τ .

500

500
K-bandQ-band
400

300

300
T [K]

T [K]

400

200

200

100

100

0

May 2004

Sep

Jan 2005

May

0

Sep

Date

May 2004

Sep

Jan 2005

May

Sep

Date

Figure 14: The receiver noise temperature (blue crosses) and the system noise temperature (red open circles) at the zenith in the K band and the Q band with the Mizusawa
antenna.

23

Figure 14 show the receiver noise temperature and the system noise temperature at
the zenith for the K and Q bands, at Mizusawa station. Here the receiver temperatureincludes the temperature increase due to the feedome loss and the spill-over eﬀect. In
Mizusawa, typical system temperature in the K band is Tsys = 150 K in fine weatherof winter season, but sometimes rises above Tsys = 300 K in summer season. The
system temperature at Iriki station shows a similar tendency to that in Mizusawa. In
Ogasawara and Ishigaki-jima, typical system temperature is similar to that for summer
in Mizusawa site, with typical optical depth of τ0 = 0.2 ∼ 0.3. The typical systemtemperature in the Q band in Mizusawa is Tsys = 250 K in fine weather of winterseason, and Tsys = 300 − 400 K in summer season. The typical system temperature in
Ogasawara and Ishigaki-jima in the Q band is larger than that in Mizusawa also.

3.5

Astrometric Observation

In an astrometric observation, the observation using dual-beams is recommended. Also,
it is strongly recommended to observe pair sources with small separation angle (i.e.,less than 1 deg) at high elevation. This will reduce the position errors caused by theresiduals in atmospheric zenith delay, which is diﬃcult to predict accurately (e.g., see
Reid & Honma 2014). Generally, users are encouraged to carefully carry out data
reduction in consultation with a contact person in the VERA project group.
After the huge earthquake on 11 March 2011, the crustal motion at Mizusawa station is still unstable and may not be simply approximated by linear
motion, and this could degrade the astrometric accuracy.

3.6

Calibrator Information

The VLBA calibrator survey of the National Radio Astronomy Observatory (NRAO) isvery useful to search for a continuum source which can be used as a reference source tocarry out the delay, bandpass, and phase calibrations. The source list of this calibrator
survey can be found at the following VLBA homepage,
http://www.vlba.nrao.edu/astro/calib/index.shtml.
The calibrator source for phase-referencing should be brighter than the detection limit
described in the previous section. For delay calibrations and bandpass calibrations,calibrators with 1 Jy or brighter are recommended.
Regarding H2 O maser source list, “the Arcetri Catalog of H2 O maser sources”(Valdettaro et al. 2001, A&A, 368, 845) is very useful. However, we note that theflux of H2 O maser source is highly variable, and also that it is probable that the correlated flux is significantly lower than that in the catalogued flux because of resolving-out
problem with long baselines. We also note that a positional accuracy of a few arcsec
is usually needed for correlation process, but some of the maser sources in the catalog
have larger position uncertainty.

3.7

Nobeyama 45-m and Kashima 34-m Telescopes

The array with the six antennas including Nobeyama 45-m telescope at Nobeyama
Radio Observatory (NRO), NAOJ, and Kashima 34-m telescope at Kashima Space24

Research Center, National Institute of Information and Communications Technology(NICT), is also available for the K band (22 GHz), but for the Q band (43 GHz) only
the Nobeyama 45-m is available in this season.
The observable period for the Nobeyama 45-m telescope is planned to be from
December to May, but it may change due to the progress of its maintenance. The
Kashima 34-m telescope is not available during its maintenance season usually from
August to October. The maintenance season of the Kashima 34-m will change every
year. The user can see at the following homepage about the performance of bothantennas,
http://www.nro.nao.ac.jp/~nro45mrt/html/prop/index-e.html
http://www2.nict.go.jp/aeri/sts/stmg/34m/plan/plan34m.html.
Both telescopes can not attend to VERA observations in their maintenanceperiod, therefore, the array in which the attendances of the Nobeyama 45m telescope and/or the Kashima 34-m telescope are essential is unsuitable
for a monitoring observation. Whether these antennas are joined in the
proposed observation or not is judged by Time Allocating Committee of
VERA and NRO based on a scientific merit of observing proposal andavailability of observing time.
Table 10: Performance of Nobeyama 45-m and Kashima 34-m Telescope
Antenna

NRO 45-m
NICT 34-m
K bandQ bandK bandQ bandAperture diameter
45 m
34 m
Frequency (GHz)20.0–25.0
42–44
21.8–23.8 42.3–44.9
Beam size (arcsec)
73
39
96
51
Aperture eﬃciency (%)
66
48
57
20
Tsys (K)a100
150–300
160
350
EL driving range (deg)
12–80
7–88
a
Typical system noise temperature in good condition.

3.8

Date Archive

The users who proposed the observations will have an exclusive access the data for 18
months after the correlation. After that period, all the observed data in the VERA
common-use observation will be released as archive data. Thereafter, archived data will
be available to any user upon request. This policy is applied to each observation, even
if the proposed observation is comprised of multi-epoch observations in this season.

25

UV plot (MIZ-IRK-OGA-ISG-NOB-KAS, Dec= 20)
3000

2000

2000

1000

1000

V (km)V (km)

UV plot (MIZ-IRK-OGA-ISG-NOB-KAS, Dec= 60)
3000

0

0

-1000

-1000

-2000

-2000

-3000
-3000

-2000

-1000

0

1000

2000

-3000
-3000

3000

-2000

-1000

U (km)

0

1000

2000

3000

U (km)
UV plot (MIZ-IRK-OGA-ISG-NOB-KAS, Dec= -20)
3000

2000

V (km)

1000

0

-1000

-2000

-3000
-3000

-2000

-1000

0
U (km)

1000

2000

3000

Figure 15: UV coverage expected with the array of the six antennas, VERA fourantennas, NRO 45-m, and NICT 34-m telescopes, from an observation over elevationof 20◦ . Each panel show UV coverage for the declination of 60◦ (top left), 20◦ (topright), and –20◦ (bottom).

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4

Observation and Data Reduction

4.1

Preparation

After the acceptance of proposals, users are requested to prepare the observing schedule
file before the observation date. The observer is encouraged to consult a contact personin the VERA project group (which will be assigned after the proposal acceptance) toprepare the schedule file under the support of the contact person.

4.2

Observation and correlation

VERA group take full responsibility for observation and correlation process, and thus
basically proposers will not be asked to take part in observations or correlations. Afterthe observation and the correlation, the correlated data can be downloaded throughan internet in the FITS format. Because the raw data will be erased within 2 months
after the correlation, the user should contact the VERA group member within that
period if the user needs re-correlation or correlation under diﬀerent settings (e.g., with
diﬀerent tracking position).

4.3

Data Reduction

At present, the users are encouraged to reduce the data using the AIPS. The observation
data and calibration data will be provided to the users in a format which AIPS canread.
• As for the amplitude calibration, the VERA’s correlation data in FITS format
have the system temperature measured by the R-sky method and the information(gain-curve table) of the dependence of aperture eﬃciency on antenna elevationand separation of dual-beam. If the user wants a weather information, the informations of the temperature, pressure, and humidity during the observation canbe provided.
• The calibration data for the dual-beam instrumental phase is provided to theusers as text file which can be read as the SN table of AIPS. This text file can beimported using the task “TBIN” of AIPS, and its calibration solution (SN) canbe used for updating the calibration gain factor (CL) table using the AIPS task
CLCAL .
• A-priori delay calculation at correlation is not accurate enough for astrometricmeasurements, and this will be corrected for later with delay-recalculation toolsthat have higher precision. Basically these corrections will be made before thedata are sent to proposers. Please ask a contact person in the VERA projectgroup to check the status of delay recalculation in your data when you receive
the data.
In case of questions or problems, users are encouraged to ask the contact person in the
VERA group for supports. Also, please check the VERA homepage, where the latest
information about data reduction will be shown.

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4.4

Further Information

The users can contact any staﬀ member of the VERA by E-mail (see table 11).
Table 11: Contact Persons
Name
K. M. Shibata
T. JikeT. Hirota
M. Honma

E-mail address
k.m.shibata@nao.ac.jp
takaaki.jike@nao.ac.jp
tomoya.hirota@nao.ac.jp
mareki.honma@nao.ac.jp

Related Instrument
Operation, Schedule management, Antenna site in general
Geodetic measurement
Performance for each antenna
Phase calibration, Data analysis

Some documents for the VERA, including user guides and proposal application
forms, are accessible on the VERA homepage:
http://veraserver.mtk.nao.ac.jp/index.html.

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