Science Highlight: The Nuclei of Arp 220 as seen in the most sensitive VLBI images yet!
|
Документ взят из кэша поисковой машины. Адрес
оригинального документа
: http://www.naic.edu/~astro/aovlbi/
Дата изменения: Unknown Дата индексирования: Thu Feb 27 22:21:40 2014 Кодировка: Поисковые слова: южная атлантическая аномалия |
Science Highlight: The Nuclei of Arp 220 as seen in the most sensitive VLBI images yet!
First 2Gbps scinece observation at Arecibo using Mark5C & RDBEs (PFB mode)
The 305-m Arecibo radio telescope became part of the VLBI network in
late 1990s as part of the
HALCA
mission of the Japanese VSOP
project. In 2001, the Arecibo Observatory received its hybrid VLBA-MARK IV
(VLBA4) data acquisition system, and currently NAIC commits Arecibo to
support VLBI observing up to a maximum of 4% of the 305-m's observing time.
The VLBA4 system enables Arecibo to become part of the VLBI networks in
both the US and Europe. Moreover, its size and
geographic location
makes it a valuable addition in global VLBI experiments.
For a concise introduction to the 305-m Arecibo radio telescope,
please see Arecibo Observatory's
Guide For New Users.
Arecibo is available for observations with the VLBA , the HSA (VLBA, phased VLA, GBT, Arecibo, and Effelsberg), the EVN, and global networks. Any proposer wishing to include the Arecibo Telescope in their VLBI observations should submit their proposals as usual for the VLBA, the HSA, the EVN, or Global networks, rather than to Arecibo. In all proposals, special justification for the use of Arecibo should be included.
Observations with ad-hoc arrays will also be considered, but in this case proposals should be submitted to Arecibo as specified at AO Proposals. It is the proposers' responsibility to ensure that telescope time be granted by the other observing facilities involved. For general information on proposing for observing time, telescope schedule, observing software, etc., click on the Observing (general) link on the side menu, or on Observing in the bottom link bar.
If you have included Arecibo in your VLBI observation, please list the Arecibo Telescope as one of the antennas used, and include the following lines in the acknowledgements in your published work.
The Arecibo Observatory is operated by SRI International under a cooperative agreement with the National Science Foundation (AST-1100968), and in alliance with Ana G. Mц©ndez-Universidad Metropolitana, and the Universities Space Research Association.
Arecibo can participate in a VLBI run at frequencies between P and X bands. Arecibo Receivers' web page provides the details of the frequency ranges and the performance parameters of the various receivers.
Arecibo Telescope's tracking time depends on the declination of the source itself. The following table gives an estimate of the tracking time for various declination values.
| Declination (deg) | -1 | 0 | 5 | 10 | 15 | 20 | 25 | 30 | 35 | 38 |
| Tracking Time (h:mm) | 0:30 | 0:58 | 2:18 | 2:27 | 2:42 | 2:46 | 2:40 | 2:20 | 1:35 | 0:10 |
To obtain tracking time values for other declinations, you may either use the web based srcTimes program of Arecibo, or the VLBI scheduling program SCHED.
The inclusion of the 305-m Arecibo radio telescope can dramatically boost the sensitivity of VLBI observations, even with its limited source tracking time. It should also be noted that Arecibo-Saint Croix baseline is one of the shortest and most sensitive baselines in any VLBI observation. The EVN Calculator could be used to estimate the sensitivity of a VLBI observation.
Using the SCHED program, Arecibo could be included in your observe file as any other telescope taking part in the VLBI observations. Currently, all VLBI observations carried out in Arecibo are recorded on Mark 5A disk units.
Arecibo can participate in phased-referenced VLBI observations. Due to the slower slew rates of the Arecibo telescope compared to other stations, we recommend a phase calibrator within a degree or so from the target source. Previous experiments showed that calibrators with a 100 mJy flux density could successfully be used as phase reference sources.
Because Arecibo's gain is both azimuth and zenith angle dependent, and AIPS cannot handle such a function, we provide the users with the SEFD values. With Gain=1, these could be used as Tsys for a priori amplitude calibration in the AIPS task ANTAB (please see the ANTAB explain file in AIPS for more information on the format of the required text file). Recently, Arecibo's amplitude calibration is being incorporated into the VLBI data sets correlated in Socorro, removing the need to run ANTAB in AIPS. The document Tsys measurements for VLBI at Arecibo provides more details on the amplitude calibration procedure.
People involved in VLBI related work at the Arecibo Observatory are: Tapasi Ghosh, Arun Venkataraman, Chris Salter, and Emmanuel Momjian. You may email us at vlbi-grp (append @naic.edu).
