sci15008 — Announcement

Hubble Catalogue of Variables

21 October 2015

The Hubble Catalogue of Variables is a three-year project funded by the European Space Agency (ESA), which was recently launched at the National Observatory of Athens, Greece. The goal is to produce a catalogue of variable sources chosen from the 30 million sources in the Hubble Source Catalog (HSC), validate those candidates and make them available in a catalogue.

Over its 25 years of operation, Hubble has visited some regions of the sky multiple times, providing an opportunity to conduct a systematic search for variable objects among the sources in the HSC. The Hubble Catalogue of Variables (HCV) is expected to contain one of the largest collections of variable point sources and extended objects available, spanning a long time baseline up to 25 years, and reaching unprecedented magnitude depths.

The HSC provides the backbone for the HCV project. It combines source lists generated from around 10 000 individual Hubble visits into a single master catalogue. This is done by computing astrometric corrections for each Hubble image based on reference stars from Pan-STARRS, the 2MASS, and SDSS catalogues within the field of view and known distortion patterns for the instruments onboard Hubble. The astrometrically corrected lists are matched using a technique suggested by Budavari & Lubow (2012). The first version of the HSC (Whitmore et al., submitted) was released in February 2015 and contains photometry for 30 million sources, based on images obtained with the WFPC2, ACS/WFC, WFC3/UVIS and WFC3/IR cameras.

The task undertaken by the HCV team is to define an algorithm that will detect and validate a candidate variable star within the HSC. As the Hubble data were collected with different instruments, filters and observing strategies, the photometric accuracy and data quality varies greatly across the HSC, making the detection of variable objects non-trivial. The team is developing algorithms to reliably detect a broad range of light-curve features and variability types, combining several methods to eliminate outliers and reliably detect changes in brightness.

The HCV will be ingested into the MAST and the eHST in the spring of 2018. The HCV pipeline will be deployed at STScI, and will have the capability to produce new, updated versions of the HCV following future releases of the HSC. Stay tuned!

Contacts

Antonella Nota
ESA HST Project Scientist, STScI
Email: hubblenewseurope@stsci.edu

Alceste Bonanos
HCV Project Scientist, National Observatory of Athens, Greece
Email: bonanos@noa.gr