VSOP Data Archive System
Satoko Sawada-Satoh1,2 , Yasuhiro Murata1 , Zhi-Qiang Shen1,3 , Philip G. Edwards1 Hisashi Hirabayashi1 , Manabu Watanabe1,4 ,Masaru Watanabe1,4 , Hajime Baba1 , and Fumiaki Nagase1 ;1 ISAS, Japan, 2 NAO, Japan, 3 ASIAA, Taiwan, 4 NASDA, Japan,
Email (SSS): satoko@vsop.isas.ac.jp
Abstract
We present the new VSOP data archive system installedon the Data ARchive and Transmission System (DARTS)at ISAS. The current test archive for VSOP visibility data
started in June 2002, and about 50 datasets are available now(http://www.darts.isas.ac.jp).
1 Introduction
The VLBI Space Observatory Programme (VSOP) led by
ISAS is the ﬁrst space VLBI mission (e.g. Hirabayashi et al.
2000). VSOP has carried out more than 700 observations sincethe HALCA spacecraft was launched in February 1997. Until
now, because correlation of VSOP data was accomplished bythree diﬀerent correlators, VSOP data were distributed andadministered at three diﬀerent sites (table 1).
In order to make it possible to search and display the status of any VSOP observation, we have developed a VSOP
data archive system and installed it on DARTS (e.g. Miuraet al. 2000) at ISAS. It also opens the way to retrieve theobservational data (typically about 1 Gbyte) via ftp after development of high-performance network.

Correlator
MitakaSocorroPenticton

InstituteNAO, Japan
NRAO, USA
DRAO, Canada

2.2 The query form
The query form allows the users to access and search the master list of observations by object name and coordinate (ﬁgure 2). Additionally, observation date, PI’s name and observation category can be used as searching items. VSOP has
three observation categories, General Observing Time (GOT),Survey and Test. GOT program means proposal-based observations. The survey program involves mission-led observationsof AGNs, many of which are not in GOT proposals. Test observations is for checking all elements of the VSOP system.

Format
VSOP
VLBA/MkIV
S2

Table 1: Three correlators used for VSOP

2 VSOP data query and status display
2.1 DARTS system
DARTS is a scientiﬁc database to provide access for general
researchers to observational data obtained by the scientiﬁcsatellites of ISAS. DARTS has a WWW interface, and users
can access the Astrophysics query form from the top page of
DARTS (ﬁgure 1). Now, the interface for Astrophysics data
selection are shared by the VSOP data, and X-ray data fromtwo satellites, ASCA and Italian BeppoSAX.

Figure 2: Astrophysics query form. Further searches arealso available, clicking the bottom-left box “FURTHERSEARCH”,
2.3 Search result
After the search is ﬁnished, a list of datasets which matchthe given conditions is displayed for each satellite in a tabularformat. Users might ﬁnd several VSOP datasets with sameobservation code in the list (ﬁgure 3), because VSOP data arecreated by a correlation process in which various segments of
the observation may be correlated separately.
Clicking the right most column in the table in ﬁgure 3, allows detailed information for the observation to be seen (ﬁgure 4). Users can transfer the data to their local devices or to
the analysis server. All VSOP data are provided in the FITS
format required by reduction softwares like the NRAO AIPS
package (e.g. Fomalont 1981) and Difmap (e.g. Shepherd etal. 1994).
3 Information for data reduction
We provide useful infomation for users who are not familiar with data reduction of VLBI. Our web page, VSOP DataReduction (http://www.vsop.isas.ac.jp/obs/Reduction.html)
shows information, including documentations of the NRAO
AIPS and Difmap, calibration data for each VLBI station,and correction data for the Penticton correlator at DRAO.

Figure 1: The top page of DARTS. VSOP data is categorized
as “HALCA data” in Astrophysics data selection on the page.
(http://www.darts.isas.ac.jp)

4 Future work
Currently, all VSOP archive data available are visibilities inFITS format without any calibration or fringe-ﬁtting. In thefuture, we are planning to archive images and visibilities after
the calibration and fringe-ﬁtting have been carried out. This
makes it possible to implement eﬀective and eﬃcient support
to users, especially those with little experience. Also, thiswould make the size of the archive data much smaller (1–100Figure 3: Searching result. The datasets “vt145-1” and “vt145-2” are obtained from the same single observation “vt145”, but
made by diﬀerent correlation procceses.

Mbyte), which makes it easy to retrieve data using an on-line
archive system.

Figure 4: Observation information for each observation. In
the table, “grt” means Ground Radio Telescope (GRT), andGRTs are listed using GRT codes. Explanation of GRT codesis available in http://www.vsop.isas.ac.jp/obs/GRTcal.html
Acknowledgements
We thank the staﬀ of the VSOP correlator group at NAO
Mitaka of Japan, NRAO Array Operation Center of USA andDRAO of Canada for their contributions.
References
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