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Deep co-added sky from Catalina Sky Survey images

Singhal, Akshat and Bhalerao, Varun and Mahabal, Ashish A. and Vaghmare, Kaustubh and Jagade, Santosh and Kulkarni, Sumeet and Vibhute, Ajay and Kembhavi, Ajit K. and Drake, Andrew J. and Djorgovski, S. George and Graham, Matthew J. and Donalek, Ciro and Christensen, Eric and Larson, Stephen and Beshore, Edward C. (2021) Deep co-added sky from Catalina Sky Survey images. Monthly Notices of the Royal Astronomical Society, 507 (4). pp. 4983-4996. ISSN 0035-8711. doi:10.1093/mnras/stab2246.

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A number of synoptic sky surveys are underway or being planned. Typically, they are done with small telescopes and relatively short exposure times. A search for transient or variable sources involves comparison with deeper baseline images, ideally obtained through the same telescope and camera. With that in mind, we have stacked images from the 0.68 m Schmidt telescope on Mt. Bigelow taken over 10 yr as part of the Catalina Sky Survey. In order to generate deep reference images for the Catalina Real-time Transient Survey (CRTS), close to 0.8 million images over 8000 fields and covering over 27 000 sq. deg have gone into the deep stack that goes up to 3 mag deeper than individual images. CRTS system does not use a filter in imaging; hence, there is no standard passband in which the optical magnitude is measured. We estimate depth by comparing these wide-band unfiltered co-added images with images in the g band and find that the image depth ranges from 22.0 to 24.2 across the sky, with a 200-image stack attaining an equivalent AB magnitude sensitivity of 22.8. We compared various state-of-the-art software packages for co-adding astronomical images and have used SWARP for the stacking. We describe here the details of the process adopted. This methodology may be useful in other panoramic imaging applications, and to other surveys as well. The stacked images are available through a server at Inter-University Centre for Astronomy and Astrophysics.

Item Type:Article
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URLURL TypeDescription Paper ItemCo-add images and weight files ItemAdditional material
Singhal, Akshat0000-0003-1275-1904
Bhalerao, Varun0000-0002-6112-7609
Mahabal, Ashish A.0000-0003-2242-0244
Vaghmare, Kaustubh0000-0003-4525-1172
Vibhute, Ajay0000-0003-1501-6972
Kembhavi, Ajit K.0000-0003-0598-4152
Djorgovski, S. George0000-0002-0603-3087
Graham, Matthew J.0000-0002-3168-0139
Larson, Stephen0000-0001-6643-6032
Additional Information:© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2021 July 24. Received 2021 July 24; in original form 2020 August 4. Published: 10 August 2021. We thank, Bruce Berriman, John Good, Frank Masci, Steve Hartung, and Simon Krugoff for their guidance. We also thank CSS, CRTS, IUCAA, Indo-US Science and Technology Forum (IUSSTF), and National Science Foundation (NSF) for the excellent support. The Catalina Sky Survey is funded by a grant from the National Aeronautics and Space Administration’s Near-Earth Object Observations programme. The CRTS web service at IUCAA was partly developed under the Virtual Observatory program funded by the Ministry of Communication and Information Technology of the Government of India and the Data Driven Initiatives program funded by the National Knowledge Network. This work is based in part on data products produced at Terapix available at the Canadian Astronomy Data Centre as part of the Canada–France–Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. Ashish A. Mahabal (AAM), Andrew J. Drake, Ciro Donalek, Matthew J. Graham (MJG), and S. George Djorgovski (SGD) were supported in part by the NSF grants AST-0909182, AST-1313422, AST-1413600, and AST-1518308, and the Ajax Foundation. AAM, MJG, and SGD were also supported by IUSSTF. We also thank ClassACT: Indo-US centre for astronomical object and feature characterization and classification. This research made use of MONTAGE. It is funded by the National Science Foundation under Grant Number ACI-1440620, and was previously funded by the National Aeronautics and Space Administration’s (NASA) Earth Science Technology Office, Computation Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of Technology. This work was done during the tenure of Akshat Singhal and Varun Bhalerao in Inter-University Centre for Astronomy and Astrophysics. Data Availability: All the final co-add images and weight files are available at Additional material such as configuration files, scripts for processing bulk images, log files, etc. is available at The raw data underlying this article will be shared on reasonable request to the corresponding author.
Group:Astronomy Department
Funding AgencyGrant Number
Ministry of Communication and Information Technology (India)UNSPECIFIED
National Knowledge NetworkUNSPECIFIED
Ajax FoundationUNSPECIFIED
Indo-US Science and Technology ForumUNSPECIFIED
Subject Keywords:surveys – stars: general – transients – imaging – techniques: image processing
Issue or Number:4
Record Number:CaltechAUTHORS:20211027-160410998
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Official Citation:Akshat Singhal, Varun Bhalerao, Ashish A Mahabal, Kaustubh Vaghmare, Santosh Jagade, Sumeet Kulkarni, Ajay Vibhute, Ajit K Kembhavi, Andrew J Drake, S George Djorgovski, Matthew J Graham, Ciro Donalek, Eric Christensen, Stephen Larson, Edward C Beshore, Deep co-added sky from Catalina Sky Survey images, Monthly Notices of the Royal Astronomical Society, Volume 507, Issue 4, November 2021, Pages 4983–4996,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111656
Deposited By: Tony Diaz
Deposited On:28 Oct 2021 21:24
Last Modified:28 Oct 2021 21:24

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