Digging deeper into the dense Galactic globular cluster Terzan 5 with electron-multiplying CCDs

Variable star detection and new discoveries^★

¹ Millennium Institute of Astrophysics MAS, Nuncio Monsenor Sotero Sanz 100, Of. 104, Providencia, Santiago, Chile
² Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
³ Centre for Exoplanet Science, SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
⁴ Centre for Electronic Imaging, Department of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
⁵ Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
⁶ Centre for ExoLife Sciences, Niels Bohr Institute, University of Copenhagen, Øster Voldgade 5, 1350 Copenhagen, Denmark
⁷ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
⁸ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg (ZAH), 69120 Heidelberg, Germany
⁹ Centro de Astronomía, Universidad de Antofagasta, Avenida Angamos 601, Antofagasta 1270300, Chile
¹⁰ Department of Physics, Isfahan University of Technology, Isfahan 84156-83111, Iran
¹¹ Instituto de Astronomia y Ciencias Planetarias, Universidad de Atacama, Copayapu 485, Copiapo, Chile
¹² University of Southern Denmark, Department of Physics, Chemistry and Pharmacy, SDU-Galaxy, Campusvej 55, 5230 Odense M, Denmark
¹³ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen, Denmark
¹⁴ Dipartimento di Fisica “E.R. Caianiello”, Università di Salerno, Via Giovanni Paolo II 132, 84084, Fisciano, Italy
¹⁵ Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Napoli, Italy
¹⁶ Universität Hamburg, Faculty of Mathematics, Informatics and Natural Sciences, Department of Earth Sciences, Meteorological Institute, Bundesstraße 55, 20146 Hamburg, Germany
¹⁷ Astronomy Research Center, Research Institute of Basic Sciences, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea
¹⁸ European Southern Observatory (ESO), Alonso de Córdova 3107, Vitacura, Santiago, Chile
¹⁹ Instituto de Astrofísica e Ciências do Espaço, Departamento de Física, Universidade de Coimbra, 3040-004 Coimbra, Portugal
²⁰ Departamento de Matemática y Física Aplicadas, Facultad de Ingeniería, Universidad Católica de la Santísima Concepción, Alonso de Rivera 2850, Concepción, Chile
²¹ Department of Physics, Sharif University of Technology, PO Box 11155-9161, Tehran, Iran

Received: 8 July 2023
Accepted: 26 June 2024

Abstract

Context. High frame-rate imaging was employed to mitigate the effects of atmospheric turbulence (seeing) in observations of globular cluster Terzan 5.

Aims. High-precision time-series photometry with the highest angular resolution so far has been obtained for the crowded central region of Terzan 5. Observations were carried out using ground-based telescopes, implementing ways to avoid saturation of the brightest stars in the field observed.

Methods. The Electron-Multiplying Charge Coupled Device (EMCCD) camera installed at the Danish 1.54 m telescope at the ESO La Silla Observatory was used to produce thousands of short-exposure time images (ten images per second), which were stacked to produce the normal-exposure-time images (minutes). We employed difference image analysis in the stacked images to produce high-precision photometry using the DanDIA pipeline.

Results. We analyzed the light curves of 1670 stars with 242 epochs in the crowded central region of Terzan 5 in order to statistically detect variable stars in the field observed. We present a possible visual counterpart outburst at the position of the pulsar J1748-2446N, and the visual counterpart light curve of the low-mass X-ray binary CX 3. Additionally, we present the discovery of four semiregular variables. We also present updated ephemerides and properties of the only RR Lyrae star previously known in the field covered by our observations in Terzan 5. Finally, we report a significant displacement of two sources by ~0.62 and 0.59 arcsec with respect to their positions in previous images available in the literature.