sci19014 — Announcement

New Feature Added to the HCV Explorer: Visualisation of HLA Cutout Images

23 December 2019

María Arévalo, Raúl Gutiérrez, Javier Durán, Jesús Salgado, Deborah Baines, Bruno Merín, Guido de Marchi, Paule Sonnentrucker and Antonella Nota

The Hubble Catalog of Variables (HCV) is the first full, homogeneous, catalog of variable sources found in the Hubble Source Catalog (HSC) and built out of publicly available images obtained with the WFPC2, ACS and WFC3 instruments on board the HST. As reported in September's newsletter, the HCV was developed over four years by a team of astronomers at the National Observatory of Athens, led by Alceste Bonanos and sponsored by ESA in collaboration with STScI. The HCV is the deepest catalog of variables available. It includes variable stars in our Galaxy and nearby galaxies, as well as transients and variable active galactic nuclei. In total, the HCV includes 84 428 candidate variable sources (out of 3.7 million HSC sources that were searched for variability) with V ≤ 27 mag; for 11 115 of them the variability is detected in more than one filter. The data points in a light curve range from 5 to 120, the time baseline ranges from under a day to over 15 years, and ∼ 8% of variables have amplitudes in excess of 1 mag.

The HCV Explorer, released to the public together with the HCV on 24 September 2019, is a web visualisation tool that can be used to explore the HCV. It offers interactive and connected plotting of the HCV catalog on the sky, in light curves, in plots and in a results table. Developed by the ESAC Science Data Centre (ESDC), this tool aims to aid exploration of the catalog and enhance data discovery.

An augmented version of the HCV Explorer was released on 13 December 2019 to include the visualisation of image cutouts around the selected source from the original Hubble Legacy Archive (HLA) images used to create the catalogue. Inspection of the original HLA images for each light curve point in the HCV catalog is important in order to verify visually that there are no artifacts that could potentially have affected the automatic HCV pipeline classification of candidate variables (see Bonanos et al., 2019 for a description). The tool uses the HLA cutout service from STScI. The cutout images are displayed in the interface when hovering over, or selecting, a point in a light curve. After selecting the cutouts, three cutout images are displayed: the brightest point in the light curve, the faintest point in the light curve and the currently selected point. Access to the corresponding HLA observation in the European HST Archive is provided, so users can access all the details for the HLA observation (original HLA image, science data files, HSC sources contained in the observation and link to proposals and available related publications). Cutout images are also displayed before the light curve data is downloaded by a user.


Maria Arevalo Sanchez
Software Engineer, ESAC Science Data Centre
Madrid, Spain

Antonella Nota
ESA HST Project Scientist, STScI
Baltimore, USA

About the Announcement



Screenshot of the Hubble Catalog of Variables Tool
Screenshot of the Hubble Catalog of Variables Tool

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