Archiving occultation light curves Dave Herald Historically lunar

Archiving occultation light curves Dave Herald

• Historically, lunar occultations were observed visually, and were treated as binary events – except for when a binary star was involved. • Fading caused by stellar diameter or Fresnel diffraction were treated as an annoyance rather than something to measure

• In the late 1900’s, considerable interest in discovering double stars from lunar occultations. Many stars were claimed to be close double stars as a result of a visual observer recording an event as non-instantaneous. Modern video recordings of occultations of such stars show the absence of any companion in over 70% of observations many visual occultation ‘discoveries’ were caused by Fresnel diffraction &/or stellar diameter

• Video recording occultations started becoming common around 2000. Now-a-days ‘everyone’ uses video; almost no observations are made visually. • However convenient tools to analyse recordings did not exist in 2000 – the videos were analysed by manually stepping through frame-by-frame. Some people converted each video frame to a FITS image, to measure with conventional astronomical software

• Limovie was released in June 2005. It revolutionised the measurement of videos, generating a light curve that could be easily viewed analysed • A similar tool, Tangra, was released in 2009 Tangra was focussed more on asteroidal occultations than Lunar occultations. • With GPS time stamps video-inserted, possible to easily measure occultation light curves with a 35 msec resolution in time.

• For 10 years we have been measuring light curves on a routine basis. • Ready access to light curves is important for: – detecting double stars – Analysing ‘gradual’ light curves to distinguish between stellar diameter and Fresnel diffraction – Analysis of K 2 observations of that star

• Our reporting and data retention processes are still based on the traditional on/off nature of an occultation event. • We have been slow to recognise the value of, and retain, the data inherently present in an occultation light curve.

i. The Vizie. R astronomical data archiving system is very supportive of us archiving our light curves ii. Light curves can be used to detect double stars, or put a limit on the parameters of a possible double star iii. For large bright stars (eg Antares, Aldebaran), possibilities of measuring brightness variation across the stellar disk iv. The K 2 extension of the Kepler spacecraft mission – our light curves can be important to the analysis of the K 2 observations

Challenges/tasks • decide what data needs to be collected. The light curve needs to be accompanied by all the data needed to interpret the light curve. Eg – Date – Light curve sample duration – star ID – lunar librations & limb slope – observing location – observer identification

• It must be easy to gather the required data – Kazuhisa has added functionality in Limovie to ‘copy’ the light curve data to the clipboard so taht it can be pasted into a reporting tool – Tangra already allows the light curve data to be ‘copied’ – Occult now includes basic functionality to prepare a light curve report as part of the Lunar Occultation observations editor, and from the Minor Planet observations tab of Occult

• It must be easy for observers to send their reports – Occult has implemented one approach. However it assumes the user can use Occult to send emails – The approach involves emailing reports (which are zipped for emailing). Would it be better to upload reports? Would uploading increase risks of being swamped by SPAM?

• Must be easy to consolidate reports – Detect duplicate reports of an event – even when the time period, time resolution, or star identification, differs – Arrange the data in a way that facilitates access – Create indexes to access the data by various star identifications or other parameters – Include the K 2 identification where appropriate, revising as new K 2 fields are established.

• Must be easy to create a version to mount on Vizie. R • Need to establish a data file format that meets Vizier. R, Occult, and user requirements • Make the file available as an Occult download, for querying within Occult? • Establish a nominal interval between updates of the file (monthly? 3 -monthly? yearly? )

• Need to have a suitable data format – Need to allow for easy expansion of data fields in the future – Needs to meet Vizie. R requirements

Summary • Archiving our observed light curves is an important and logical extension of our data recording • It is important that the process be as simple as possible for everyone involved • It will take some time to get a decent system operational • Hopefully everyone will appreciate the value of archiving their observational data, and be patient with the implementation of a suitable tool.