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Making time-series observations

LCO's global distribution of telescopes is ideal for obtaining time-series data. However the dynamic nature of the scheduler can make it tricky to successfully observe long blocks.

Observing terms

Here is an explanation of some of the terms used in the LCO Observing Portal, which we will use in the discussion below.

Exposure count: The number of exposures performed consecutively without any time gaps. Taken together, a group of exposures is often called an observing block. Reasons for taking multiple exposures might be for averaging them together to remove cosmic rays, or changing the filter between exposures.

Cadence: A special type of request that creates multiple individual requests, each containing their own observing block. The time gap between the individual requests is set by the period.

Period: The time gap between the individual requests spawned by your cadence request. For example, if your observing window (set by your start and end time) is 24 hours, and you choose a period of 6 hours, then a single cadence request should create 3 or 4 individual requests.

Jitter: The time flexibility of your individual request windows. For example, let’s say you submit a cadence request with a period of 6 hours, and a jitter of 2 hours. This will create individual requests centred at every 6 hours, with their start and end times +/-1 hour from those centers.

Exposure Count or Cadence?

There are 2 ways to make a series of sequential observations, with "Exposure Count" or "Cadence". When creating an observing request you should decide which is the best suited to your observing campaign.

Use Exposure Count if:

  • your observations need to follow immediately on from one another (or have less than a couple of minutes gap)
  • your target is changing rapidly e.g. an exoplanet transit, rotating asteroid, binary stars

Use Cadence if:

  • your observations have gaps of more than 10 minutes between them
  • your target is changing on a long timescale, e.g. supernova expansion, microlensing exoplanet
  • you want to monitor a target every few hours/days/weeks

For more detailed tips on using these two methods follow the links below:

> Using Exposure Count for short period time-series

> Using Cadence for longer period time-series