Simultaneous multi-frequency observations of variables, non-variable, and candidate variable sources are a valuable data for Astronomy. Astronomers interested in simultaneous observations with Planck will find here the necessary data and information for planning their activity.
Planck surveys twice the full sky over a 15 months period, and its first all-sky survey has started on August 13th 2009. From its orbit around L2, Planck observes the sky by continuously scanning nearly great circles on the celestial sphere, and periodically shifting the spin axis to remain anti-Sun throughout the year. The Figure below is an illustration of Planck's surveying strategy. The telescope field-of-view rotates at 1 rpm, while its spins axis regularly moves, about 2 arcmin/hour in ecliptic longitude, to remain anti-Sun.
The Planck's telescope focuses radiation from the sky onto its focal plane, which is shared by two instruments: The Low Frequency Instrument (LFI), an array of radiometers covering three frequency bands from 30 to 70 GHz, and the High Frequency Instrument (HFI), an array of bolometers covering six frequency bands from 100 to 857 GHz. A layout of its focal plane on the sky is displayed bellow.
Even though CMB anisotropies are Planck's main target, its capabilities are also suitable for observations of cold objects, as well as those with bright free-free radiation from ionized gas. Planck will detect galactic and extragalactic objects such as HII regions, cold cores in molecular clouds, flat-spectrum radio sources (like blazars) at low frequencies, and redshifted galaxies (whose dust emission peaks in the high frequencies). An all-sky catalogue of compact and point sources, extracted from Planck's data, will be released to the scientific community approximately 10 months after the first full sky survey is finished, in time for the first post-launch call for Herschel observing proposals. This Planck scientific product, named the Early Release Compact Source Catalogue (ERCSC), will provide useful information about galactic and extragalactic sources, and it will be the first all-sky catalogue at sub-mm wavelengths.
Planck's pointing data and documents
The necessary information to plan a simultaneous observations with Planck, and predict when an object will be observable, is provided by the following data:
The Planned Pointing List (PPL), which contains a sequence of pointings for the Planck's spin axis covering about one month period of the survey.
By combining the position of the spin axis at every pointing (as provided by the PPL) with the angle of each receiver with respect to the spin axis (as provided by the SIAM) it is possible to identify the region of the sky swept by each aligned set of Planck receivers. A source will be observable by a Planck receiver if it is within a beam unit strip during the full rotation of the satellite around its spin axis. For periods not yet covered by the PPL, one should use the LTPPL instead.
An animation of the Planck sky coverage based on LTPPL data, with a NASA/WMAP image as a background, has been produced by Chris North, Cardiff University, and it is available on a video sharing website.
Note: The PPL and LTPPL are planning files, and the actual executed pointings may differ from their contents. The actual executed pointings may differ from the pointings in the PPL but it is not expected that we will see large differences between planned and executed pointings although that cannot be completely ruled out; the corresponding accuracy of the LTPPL is lower because of the longer look-forward timescale. The SIAM contains best knowledge which will evolve through the lifetime of Planck. Currently, the relative placement of the beams is known to a fraction of the smallest beam size, i.e. of order 2 arcminutes. Its absolute location with respect to the spin axis will change during the mission and is currently provided with an accuracy of about 30 arcminutes. The current SIAM is based on ground measurements. As calibrations sources cross the focal plane the accuracy of this information will improve and the SIAM will be updated.
The Planck On-Flight Forecaster (POFF)
The Planck On-Flight Forecaster (POFF) is a tool that reads the PPL and SIAM data and predicts when a user-provided list of positions in the sky will be observable by the Planck receivers (Massardi & Burigana 2009). The POFF is successfully used to plan simultaneous observation of known objects within the Planck collaboration, and it is now available for external observers.
Note: The POFF is not an official Planck product, but it is produced on a best-effort basis by individual members of the Planck collaboration.
To know more
For more details, please, refer to the following work:
The above information should be sufficient to determine where Planck will be pointing at any given time. Further questions or requests for specific information may be directed to e-mail a request, quoting Simultaneous observations with Planck in the subject.