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PESSTO Survey Strategy

As the ESO approved time was stretched out over 5 years, we must either reduce the density of our observing runs (and still cover 12 months of every year), or reduce the annual survey period and keep the cadence and spectroscopic density coverage the same. The Survey Director recommends that the we reduce the annual survey period to approximately 9 months (actually 9 lunations) and schedule 10N per lunation broken into three runs of 4N, 3N and 3N.

In each calendar year PESSTO runs 1 Jan - 31 May and 1 Sept - 31 Dec i.e. it skips the three months June - August.

Advantages
  • matches the search period for LaSilla/QUEST. SkyMapper runs all year
  • Avoids the Galactic centre season
  • Avoids the Chilean winter (which is the reason for LaSilla/QUEST avoiding these months)
Disadvantages
  • PTF runs through June - August, and stops Dec-Feb (but long term future of PTF beyond end of 2012 is not clear)
  • Possibly easier to get observers June-Aug, rather than Nov-Jan (due to teaching etc)
  • Nights are shorter in Chilean summer

Overall, the main consideration has to be a direct coordination with the two southern surveys (given the uncertain futures of PTF and PS1 beyond 2012-2013) and optimising the number of likely clear nights together with young target selection. Hence the suggestion of 9 months (removing June - August).

In each of 9 lunations the following observing strategy, where one "Run" consists of three separate sub-runs :
  • 4 nights around dark moon (Run A ; EFOSC2 only)
  • gap of 5 nights
  • 3 nights (moon is a few days before first quarter, approx 10% illumination, ~2hrs above horizon) - Run B (2N EFOSC2 ; 1N SOFI)
  • gap of 5 nights
  • 3 nights mostly bright time (moon is 75% illuminated, a few days before full moon) - Run C (2N EFOSC2 ; 1N SOFI)
Example of the three sub-runs during a lunation (Mar/Apr 2012 taken as an example) - see here for higher resolution pdf version : Lunation-Strategy.pdf

Observing management strategy:

Clearly, providing coverage with experienced observers for 90 nights per year is a significant challenge. This requires the commitment of institutions to provide the manpower to cover the observing runs and data reduction. We are proposing the following strategy.
  • Each run within a lunation 4ON/5OFF/3ON/5OFF/3ON is to be be covered by 2 observers who travel to Chile. The first is the lead observer, an experienced observer of postdoc level or above. The other is a student, who must have had some previous observing experience (i.e. should not be a complete novice). Previous NTT experience is not specifically required. We will request funds from ESO to cover the costs of these two observers (and this meets the normal ESO rules) . If institutes would like to send a third observer as a student, for training, then the PESSTO team will encourage that subject to agreement from ESO. The third observer funding would not then be covered by ESO.
  • The experienced (lead) observer should stay for at least the first run of 4 nights, during which time he or she should ensure that the student is trained and comfortable to run the remaining two 3night runs by themselves.
  • When the lead observer departs after the 4night run, the trained student then takes over the role of lead observer for the remaining two 3night runs (the purpose of the third observer would be to train as many students as possible giving a larger pool of experienced student observers).
  • The 2 observers in Chile MUST be supported by a data reduction team in Europe (or equivalent home institute). This must be a minimum of one named person who will carry out the data reduction during the lunation. The requirements are listed below in the Data reduction Strategy Section. It is the responsibility of each institute to ensure that the observing team and the data reduction team are functional and meet the requirements laid out here.
  • We define the "Observing Team" as the NTT observers together with the data reducers in Europe (or other home institute).

Target alert and OB preparation

The observing team are responsible for coordination with the Target and Alert Team to define and prepare the night plan and the instrument OBs. We will run the observing time in Queue mode fashion, with the OBs normally being defined XX days before each run starts. However we want to ensure that rapid response can occur and we will instigate our own ToO mode - targets can be supplied by the Target and Alert Team directly to the observers and can request immediate observation. e.g. if surveys are producing targets rapidly enough that fast transients can be identified on the same night, then we will allow our own ToO type of over-ride.

Data reduction strategy:

Specific requirements and responsibilities :
  • The Observing Team (which includes the data reducers) must provide reduced spectra within 12hrs of the night being completed i.e. during the european daytime following a Chilean night. These can be preliminary reductions, but must be wavelength and flux calibrated (as a minimum) and be reasonable quality reductions.
  • The data reducers must also provide a preliminary assessment of the spectra and spectral types (e.g. through SNID, Gelato, superfit etc).
  • These spectra, and the information must be made available to the collaboration (and the public, by definition) immediately, by uploading to the ETABASE system
  • A full and complete reduction of the spectra must occur within 7 days of the end of the lunation. Full and complete reduction means that the extraction, wavelength calibration, flux calibration and telluric removal have been completed as best can be achieved (it does not mean photometrically fluxed spectra).
  • All reduced data must be uploaded to the ETABASE archive system to replace the preliminary, fast reductions.

outstanding questions on data reduction strategy

NTT pipeline
Subpages (1): NTT Pipeline
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David Young,
14 Dec 2012, 01:41
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