VERA Status Report
VERA Observatory,
National Astronomical Observatory of Japan
4 November 2008

Contents
1 Introduction

3

2 System

3

2.1

Array

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

4

2.2

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

4

2.2.1

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

5

2.2.2

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

7

2.2.3

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

9

2.2.4

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

13

2.3

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

14

2.4

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

15

2.5

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

17

2.6

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

17

2.7

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

17

2.7.1

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

17

2.7.2

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

17

2.7.3

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

18

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

18

2.8

3 Observing Proposal

19

3.1

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

19

3.2

Observation Mode

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

19

3.3

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

19

3.4

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

19

3.5

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

21

1

3.6

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

21

3.7

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

21

3.8

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

22

4 Observation and Data Reduction

24

4.1

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

24

4.2

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

24

4.3

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

24

4.4

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

25

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 open to international users in the 22 GHz band
(K band) from 2007, and, from 2009, the 43 GHz band (Q band) is opened as wellas the 22 GHz band, also. This document is intended to give astronomers necessary
information for proposing observations with VERA.

120 ˚
50 ˚

130˚

150 ˚
50 ˚

140˚

40 ˚

40 ˚

Mizusawa(VERAMZSW)

67

km

m

Iriki
(VERAIRIK)

125

1k

Ogasawara(VERAOGSW)

10

Figure 1: Array conﬁgurationof VERA.

30 ˚

m

19

km

30 ˚

22

70

1337 kkm

121827 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 2007.0
are summarized in table 1. Figures 2 show examples of uv plane coverage.
The strong earthquake of magnitude 7.2 occurred close by Mizusawa antenna siteon the 14th of June, 2008 (so called the Iwate-Miyagi Nairiku Earthquake in 2008).
This earthquake yields oﬀset in the coordinates of Mizusawa. Our preliminary analyses
result shows co-seismic 85-90 mm westward, a few mm southward and 10-20 mm downward motions. Those motion is consistent with the fault model of this earthquake. A
slight post-seismic eastward motion is also observed. A mechanical damage to the antenna was not discernible on our investigation after the earthquake. Some parametersof the Mizusawa antenna after the earthquake did not change signiﬁcantly from that
before the earthquake as noted in the following section. The coordinates of Mizusawa
in table 1 are at the epoch of 2007.0 and are not corrected the oﬀset yielded by theearthquake.
Table 1: Geographic locations and motions of each VERA antenna
Site
Mizusawa
Iriki
Ogasawara
IshigakiEastLongitude[◦ ′ ′′ ]141 07 57.20
130 26 23.60
142 12 59.81
124 10 15.58

North
Latitude[◦ ′ ′′ ]39 08 00.73
31 44 52.44
27 05 30.49
24 24 43.83

Ellipsoidal
Elevation
[m]
116.5
573.5
273.1
65.0

Elevation
[m]
75.7
541.5
222.9
38.4

Site
X (m)
Y (m)
Z (m)
IVS2a
IVS8b
CDPc
Mizusawad –3857241.83594 3108784.84704 4003900.53359
Vm
VERAMZSW
7362
Iriki–3521719.63253 4132174.70575 3336994.21445
Vr
VERAIRIK
7364
Ogasawara –4491068.76374 3481544.88226 2887399.60606
Vo
VERAOGSW
7363
Ishigaki–3263994.80474 4808056.33311 2619949.13926
Vs
VERAISGK7365
a
IVS 2-characters code, b IVS 8-characters code, c CDP (NASA Crustal Dynamics Project) coded
The coordinates oﬀsets of Mizusawa antenna due to the earthquake on June 14, 2008 were
dx=0.0584, dy=0.0590, dz=–0.0090 (m).
Site
∆X (m/yr) ∆Y (m/yr)
Mizusawa
0.00095
0.01237
Iriki–0.02153–0.00315
Ogasawara
0.02678
0.03126
Ishigaki–0.03695
0.00412The coordinate system of epoch 2007.0

2.2∆Z (m/yr)–0.00477–0.01497
0.01047–0.04618

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 are installed at
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).
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 deg. The
whole receiver systems are set up on the ﬁeld rotator (FR), and the FR rotate to track
the apparent motion of objects due to the earth rotation. Table 2 summarizes theranges of elevation (EL), azimuth (AZ) and ﬁeld rotator angle (FR) with their driving
speeds and accelerations. In the case of single beam observing 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.

2.2.1

Aperture 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 3 and ﬁgure 3). These measurements were5

based 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 aperture eﬃciency of
the Mizusawa antenna after the earthquake in June 2008 did not change signiﬁcantly
from that before the earthquake (see ﬁgure 3).
Table 3: Aperture Eﬃciency of the VERA 20 m Antennas
Site

Band

Date

ηA
(%)
MIZ
K
Jun. 16, 2008 49.5±3.9
KFeb. 19, 2008 51.5±2.4
IRKK
Apr. 13, 2006 45.2±1.9
OGAK
Feb. 20, 2008 47.6±8.5
ISG
K
Feb. 19, 2008 46.1±7.0
MIZ
Q
Jun. 16, 2008 46.1±5.6
QFeb. 18, 2008 42.3±5.0
IRKQ
Apr. 13, 2006 40.8±2.1
OGA
Q
Feb. 21, 2008 37.8±7.2
ISG
Q
Feb. 20, 2008 47.1±4.9aAssumed apparent diameter for Jupiter.

60
55

Num. of
Scans
9
25
8
18
21
7
13
8
20
18

60

~2007
Feb 2008
Jun 2008

K band

50

50

45

45

40
35

θa
(arcsec)
44.9
32.5
42.5
32.5
32.5
44.9
32.5
42.5
32.5
32.5

40
35

30

30

25

25

20

Elevation
(deg)
28-29
28-28
41-42
25-37
23-43
29-22
25-28
36-40
31-40
35-43

~2007
Feb 2008
Jun 2008

Q band55

Efficiency [%]Efficiency [%]HPBW(arcsec)
177.4±14.7160.5±6.4
150.4±10.2
148.3±18.9156.4±18.9
96.0±14.3
71.1±5.679.9±6.1
71.6±9.3
78.2±6.4

20
MIZ

IRK

OGA

ISG

MIZ

IRK

OGA

ISG

Figure 3: History of the aperture eﬃciency measurements for the VERA antennas.
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 angle 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.
6

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

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

EL [deg]

40

50

60

70

80

90

EL [deg]

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

1.5

1.75

2

2.25

SA [deg]

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

1.5

1.75

2

2.25

SA [deg]

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.

2.2.2

Beam Pattern and Size

Figure 6 show the beam patterns in the K band. The side-lobe level is less thanabout –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 shapewithout dependence on separation angle. The measured beam sizes (HPBW) in the Kband and the Q band based on the data of the pointing calibration are summarized intable 4. The main beam sizes show no dependence on the dual-beam separation angle.

7

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

-500

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)

-200

-300

-400

Table 4: Beam Size of VERA 20-m Antennas
Site

Band

HPBW[AZ]
HPBW[EL](arcsec)(arcsec)
MIZ
K
147.93 ± 7.96
151.35 ± 9.73
IRKK
152.79 ± 9.56 153.93 ± 10.11
OGA
K
148.41 ± 9.49 150.34 ± 11.12
ISG
K
149.30 ± 11.84 151.27 ± 14.13
MIZ
Q
73.49 ± 6.86
76.96 ± 8.09
IRK
Q
77.91 ± 6.75
76.68 ± 7.66
OGA
Q
75.42 ± 5.91
75.87 ± 8.20
ISG
Q
74.83 ± 9.33
73.60 ± 10.52
Each error indicates a standard deviation (1σ).

8Num. ofdata point
596
674
619
697
292
1171
476
224

Date
Mar. 2006
Nov.-Dec. 2005
Feb.-Mar. 2006
Mar. 2006
Feb.-Mar. 2006
Jan.-Mar. 2006
Feb. 2006
Mar. 2006

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 and ﬁgure 8 show theresidual pointing oﬀsets in the K and Q bands, respectively. The pointing residuals of
the Mizusawa antenna after the earthquake in June 2008 dose not have signiﬁcantly
diﬀerent tendency from that before the earthquake.
Table 5: Pointing Accuracy of VERA 20-m Antennas
Site

Band

Date

σAZ
σEL
Num. of(arcsec) (arcsec)
Scan
MIZ
K
Jun.16 2008
9.1
14.2
132
K
Feb.19 2008
7.7
12.0
358
IRK
K
Feb.20 2008
6.9
11.2
212
OGA K
Feb.20 2008
8.0
16.0
150
ISG
K
Feb.19 2008
9.9
10.6
147
MIZ
Q
Jun.16 2008
6.8
13.9
145
Q
Feb.19 2008
5.8
12.1
120
IRK
Q
Feb.18 2008
6.3
7.3
208
OGA Q
Feb.19 2008
4.9
7.9
263
ISG
Q
Feb.20 2008
7.8
8.2
204
Note; σAZ and σEL represent the standard deviation of
the pointing measurements in AZ and EL, respectively.

9

100

60
40
20
0
-20
-40
-60

60
40
20
0
-20
-40
-60

-80

-80

-100

-100
0

30

60

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

100

0

30

60

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

100

K:08/06/16
K:08/02/19
K:07/04/25

80

K:08/06/16
K:08/02/19
K:07/04/25

80

60

EL Offset(obs) [arcsec]

AZ Offset(obs) [arcsec]

K:08/06/16
K:08/02/19
K:07/04/25

80
EL Offset(obs) [arcsec]

AZ Offset(obs) [arcsec]

100

K:08/06/16
K:08/02/19
K:07/04/25

80

40
20
0
-20
-40
-60

60
40
20
0
-20
-40
-60

-80

-80

-100

-100
0

10

20

30

40
50
EL [deg]

60

70

80

90

0

10

20

30

40
50
EL [deg]

60

70

80

90

90
K:08/06/16
K:08/02/19
K:07/04/25

80

70

EL [deg]

60

50

40

30

20

10

0
0

30

60

90

120

150

180
AZ [deg]

210

240

270

300

330

360

Figure 7: Pointing residuals for the Mizusawa antenna in the K band (22 GHz). Top
and middle panels show relations of the azimuth and elevation, respectively, with thepointing residuals in azimuth (left) and elevation (right). Bottom panel shows positions
on celestial sphere of the objects which were observed in the pointing measurement.

10

100

60
40
20
0
-20
-40
-60

60
40
20
0
-20
-40
-60

-80

-80

-100

-100
0

30

60

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

100

0

30

60

90 120 150 180 210 240 270 300 330 360
AZ [deg]100

Q:08/06/16
Q:08/02/19
Q:07/04/23

80

Q:08/06/16
Q:08/02/19
Q:07/04/23

80

60

EL Offset(obs) [arcsec]

AZ Offset(obs) [arcsec]

Q:08/06/16
Q:08/02/19
Q:07/04/23

80
EL Offset(obs) [arcsec]

AZ Offset(obs) [arcsec]

100

Q:08/06/16
Q:08/02/19
Q:07/04/23

80

40
20
0
-20
-40
-60

60
40
20
0
-20
-40
-60

-80

-80

-100

-100
0

10

20

30

40
50
EL [deg]

60

70

80

90

0

90

10

20

30

40
50
EL [deg]

60

70

80

90

Q:08/06/16
Q:08/02/19
Q:07/04/23

80
70

EL [deg]

60
50
40
30
20
10
0
0

30

60

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

Figure 8: Pointing residuals for the Mizusawa antenna in the Q band (43 GHz).

11

30

20

20

10
0
-10
-20
-30
-200

AZ Offset(residual) [arcsec]

EL Offset(residual) [arcsec]

30

-150

-100

-50

0
50
FR [deg]

100

150

10
0
-10
-20
-30
-200

200

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 9. This pointing error is not fully calibrated.

10
0
-10
-20
-30
-200

-150

-100

-50

0
50
FR [deg]

100

150

-100

-50

0
50
FR [deg]

100

150

200

-150

-100

-50

0
50
FR [deg]

100

150

200

10
0
-10
-20
-30
-200

200

-150

Figure 9: 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 10 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

0

30

60

AZ [degree]

AZ [degree]

25

25

Ogasawara

Ishigaki20

20
EL [degree]

EL [degree]

90 120 150 180 210 240 270 300 330 360

15

10

5

15

10

5

0

0
0

30

60

90 120 150 180 210 240 270 300 330 360

0AZ [degree]30

60

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

Figure 10: 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 4 bands, which are S, X, K, and Q bands.
For the common use in 2009, the K band (22 GHz) and the Q band (43 GHz) are open
for observing. 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 11.
Table 6: Receivers

Frequency Range TRX a
[GHz]
[K]
K
21.5-23.8
30-50
Q
42.5-44.5
70-90aReceiver noise temperature
Band

60.0

Trx [K]

50.0

Polarization
LCP
LCP

K-band

MIZ
IRK
OGA
ISG

40.0
30.0
20.0
10.0
0.0
4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

fIF [GHz]

120.0

Trx [K]

100.0

Q-band

MIZ
IRK
OGA
ISG

80.0
60.0
40.0
20.0
0.0
4.0

5.0

6.0

7.0

8.0

fIF [GHz]

Figure 11: Receiver noise temperature for each VERA antenna. Top and bottom panels
show measurements in the K and Q bands, respectively. Horizontal axis indicate a
IF (intermediate frequency) at which TRX is measured. To convert it to RF (radio
frequency), add 16.8 GHz in the K band and 37.5 GHz in the Q band to the IF
frequency.

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 andat 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 tunable
14

with 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 12 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 12: 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 digitalﬁlter listed in the table 7. 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.
For the DIR-100M system, any two CH in VERA7, VERA10, and VERA7Q can be
simultaneously recorded.

15

Table 7: Digital Filter Mode for VERA
Num. CHa

VERA1

Rate
(Mbps)
1024

VERA7

1024

16

VERA101024

16

VERA7Q

1024

16

Mode

a

Total number of channels
Channel numbereSide Band (LSB/USB)c2

BW/CHb(MHz)
128

Freq. ranged Side Bande
(MHz)
1
A
256 - 384U2B
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 - 384L
16
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 - 464
UbBandwidth per channel in MHzd
Filtered frequency range in the base band (MHz)

16

CHc

Beam

2.5

Recorders

VERA has two types of high speed magnetic tape recorders. These data recording systems are the DIR-1000M developed for the VSOP (VLBI Space Observatory Program),and the DIR-2000 which is newly developed for the VERA. The recording speed of eachrecorder is 128 Mbps in the DIR-1000M system and 1024 Mbps in the DIR-2000 system. Because of 2-bit sampling, the total bandwidths are 32 MHz in the DIR-1000M
system and 256 MHz in the DIR-2000 system. The recording time per roll of tape are
2 hrs in the DIR-1000M system and 80 mins in the DIR-2000 system.

2.6

Correlators

The correlation processes is carried out by the FX correlator located at NAOJ Mitaka
campus. The correlator system is originally developed for VSOP, and is modiﬁed for
VERA’s dual-beam observation. The maximum number of antenna station that can becorrelated at the same time is 5 for the DIR-2000 system, and 10 stations for the DIR1000M system. Thus, the correlator can process at once the data recored by DIR-2000
with VERA four station, or the data recored by DIR-1000M with VERA, Nobeyama
45-m telescope, and Kashima 34-m telescope. The correlator cannot process ‘mixed’
correlation between the data recorded by DIR-1000M and those by DIR-2000. In thecorrelator output, the maximum number of spectral point per antenna are 1024 points
across all channels for DIR-1000M, and 2048 points across all channels of 2-beams for
DIR-2000. The time resolution of the correlator output is usually set to be 1 second,
but the high time resolution (down to 25 milliseconds) is also available upon requests(though the total amount of output data becomes larger).

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.
2.7.2

Gain 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.

17

2.7.3Phase Calibration

To calibrate the instrumental phase error 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

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 mainly in the domestic VLBI experiments with Geographical Survey
Institute of Japan. On the other hand, the K band is used in the VERA internal
experiments. We obtain higher accuracy results in the K band compared with theS/X bands. The most up-to-date geodetic parameters are derived through geodetic
analyses. The results of the geodetic measurement are summarized in tables 1. The
epoch of the coordinates is at 2007.0.
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) in order
to link the VERA coordinates to the ITRF2000 (International Terrestrial Reference
Frame 2000). Basically Mizusawa station participate in JADE nearly every month.
Based on the observations for four years, the 3-dimensional positions and velocities ofMizusawa station are determined with accuracies of 7-9 mm and about 1 mm/yr in
ITRF2000 coordinate system. The second kind of geodetic observations is monitoringof baseline vectors between VERA stations by internal geodetic VLBI observations.
Geodetic positions of VERA antennas relative to Mizusawa antenna are measured fromgeodetic VLBI observations every two weeks. From simple linear-ﬁtting of the two-year
geodetic results, the relative positions and velocities are obtained at the precisions of
1-2 mm and 0.8-1 mm/yr. The third kind is continuous GPS observations at the VERA
sites for interpolating VLBI geodetic positions. Daily positions can be determined from
24 hour GPS data. The GPS observations are also used to estimate tropospheric zenith
delay of each VERA site routinely. The time resolution of delay estimates is 5 minutes.

18

3

Observing Proposal

For this observing season (January to December 2009, except June to July 2009 formaintenance), the K and Q bands dual-beam mode are opened to international users.
Total observing time up to 400 hrs will be available for the common-use observing
time. The observation with 6 elements array (VERA + Nobeyama 45-m and Kashima34-m) is also available, with observing time of 100 hrs at maximum. In this season,
the observable period for the Nobeyama 45-m telescope is planned to be in February,
March, and April 2009 due to its maintenance. Also the Kashima 34-m telescope could
not join VERA during its maintenance season, usually from August to October.

3.1

Proposal Submission

Observing proposals for VERA are invited for the observing period from January 2009
to December 2009. The application deadline is on “December 1st, 2008” 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 “veraprop@miz.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

From this year’s common-use, both the K band (22 GHz) and the Q band (43 GHz)
single/dual-beam mode are available. The observation using the six antenna included
Nobeyama 45-m and Kashima 34-m in addition to VERA four antennas is also available. However, note that the observation with Nobeyama 45-m and Kashima 34-m
should be done in single-beam mode.

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.

3.4

Sensitivity

When a target source is observed, a noise level σbl for each baseline can be expressedas√Tsys,1 Tsys,2
2k
√
,
(3)
σbl =
√
η Ae1 Ae2 2Bτ
19

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,(

Tsys,1σbl = 23 ×
200 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

Q-bandK-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 13: 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.
Figure 13 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
20

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 with DIR-2000 recordersystem is recommended because of higher sensitivity than that with DIR-1000M system. 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 causedby the residuals in atmospheric zenith delay, which is diﬃcult to predict accurately.
Generally, users are encouraged to carefully carry out data reduction in consultation
with a contact person in the VERA project group.

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 smaller than that the catalog 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 Space
Research Center, National Institute of Information and Communications Technology(NICT), is also available. In this season, the observable period for the Nobeyama 45-m
telescope is planned to be in February, March, and April 2009 due to its maintenance.
The Kashima 34-m telescope is not available during its maintenance season usuallyfrom 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/index-e.html
http://www2.nict.go.jp/w/w114/stsi/34m/antenna-34m/index.html.
21

Whether these antennas are joined in the proposed observation or not is judged byTime Allocating Committee of VERA and NRO based on a scientiﬁc merit of observing proposal and availability of observing time. Note that the recorder systems
at Nobeyama 45-m and Kashima 34-m are only DIR-1000 (with recording speed of
128 Mbps).
Table 8: 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
35–50
22.0–24.0 42.3–44.9
Beam size (arcsec)
73
38
96
50
Aperture eﬃciency (%)
63
60
40
28
Tsys (K)a100
150–200
141
350
EL driving range (deg)
12–80
7–88
Recorder system
DIR-1000
DIR-1000a
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.

22

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
U (km)

1000

2000

-3000
-3000

3000

-2000

-1000

0
U (km)

1000

2000

3000

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 14: 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).

23

4

Observation and Data Reduction

4.1

Preparation

After the acceptance of proposals, users are requested to prepare the observing scheduleﬁle 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 will be sent to the user in
the FITS format by DVD disks. Because the raw data on the magnetic tapes will beerased within 3 months, 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 the data is calibrated using thetask “CLCAL” of AIPS.
• 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.

24

4.4

Further Information

The users can contact any staﬀ member of the VERA by E-mail (see table 9).
Table 9: Contact Persons
Name
H. Kobayashi
N. Kawaguchi
O. Kameya
K. Shibata
Y. TamuraT. Hirota
M. Honma

E-mail address
hideyuki.kobayashi@nao.ac.jp
kawagu.nori@nao.ac.jp
kameya@miz.nao.ac.jp
k.m.shibata@nao.ac.jp
tamura@miz.nao.ac.jp
tomoya.hirota@nao.ac.jp
mareki.honma@nao.ac.jp

Related Instrument
Project Director, Antenna, Correlator
Total systems, Receiver, Digital instrument
Antenna site in general
Operation, Schedule management
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.

25