Flux and color variations of the doubly imaged quasar UM673^⋆,⋆⋆

¹ Département d’Astrophysique, Géophysique et Océanographie, Bât. B5C, Sart Tilman, Université de Liège, 4000 Liège 1, Belgium
e-mail: ricci@astro.ulg.ac.be
² Main Astronomical Observatory, Academy of Sciences of Ukraine, Zabolotnoho 27, 03680 Kyiv, Ukraine
³ Centro de Astro-Ingeniería, Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago, Chile
⁴ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁵ Dipartimento di Fisica “E.R. Caianiello”, Università degli Studi di Salerno, via Ponte Don Melillo, 84085 Fisciano (SA), Italy
⁶ Instituto Nazionale di Fisica Nucleare, Sezione di Napoli, Italy
⁷ SUPA, University of St Andrews, School of Physics & Astronomy, North Haugh, St Andrews, KY16 9SS, UK
⁸ Deutsches SOFIA Institut, Universitaet Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany
⁹ Istituto Internazionale per gli Alti Studi Scientifici (IIASS), Vietri Sul Mare (SA), Italy
¹⁰ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
¹¹ Department of Physics & Astronomy, Aarhus University, Ny Munkegade, 8000 Aarhus C, Denmark
¹² Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, 2100 Copenhagen Ø, Denmark
¹³ KASI – Korea Astronomy and Space Science Institute, 776 Daedukdae-ro, Yuseong-gu, Daejeon 305-348, Republic of Korea
¹⁴ National Space Institute, Technical University of Denmark, 2800 Lyngby, Denmark
¹⁵ Astronomisches Rechen-Institut, Zentrum für Astronomie, Universität Heidelberg, Mönchhofstraße 12–14, 69120 Heidelberg, Germany
¹⁶ Dipartimento di Ingegneria, Università del Sannio, Corso Garibaldi 107, 82100 Benevento, Italy
¹⁷ Bellatrix Astronomical Observatory, Center for Backyard Astrophysics, Ceccano (FR), Italy
¹⁸ Physics Department, Sharif University of Technology, Tehran, Iran
¹⁹ European Southern Observatory, Casilla 19001, Santiago 19, Chile
²⁰ Max Planck Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
²¹ Astrophysics Group, Keele University, Newcastle-under Lyme, ST5 5BG, UK
²² Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
²³ INAF, Osservatorio Astronomico di Brera, 23807 Merate, Italy
²⁴ SOFIA Science Center, NASA Ames Research Center, Mail Stop N211-3, Moffett Field CA 94035, USA
²⁵ Centre for Starand Planet Formation, Geological Museum, Øster Voldgade 5, 1350 Copenhagen, Denmark .
²⁶ Jodrell Bank Centre for Astrophyics, University of Manchester, UK
²⁷ Alsubai’s Establishment for Scientific Studies, Qatar
²⁸ Space Telescope Science Institute (STScI), USA
²⁹ Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, Ontario N2L 2Y5, Canada
³⁰ INAF/Istituto di Astrofisica Spaziale e Fisica Cosmica, Bologna, via Gobetti 101, 40129 Bologna, Italy
³¹ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, Ensenada, B.C. 22800, Mexico
³² Departamento de Ciencias Físicas, Universidad Andrés Bello, Av. República 252, Santiago, Chile

Received: 28 December 2011
Accepted: 31 January 2013

Abstract

Aims. With the aim of characterizing the flux and color variations of the multiple components of the gravitationally lensed quasar UM673 as a function of time, we have performed multiepoch and multiband photometric observations with the Danish telescope at the La Silla Observatory.

Methods. The observations were carried out in the VRi spectral bands during four seasons (2008–2011). We reduced the data using the point spread function photometric technique as well as aperture photometry.

Results. Our results show for the brightest lensed component some significant decrease in flux between the first two seasons (+ 0.09/+ 0.11/+ 0.05 mag) and a subsequent increase during the following ones (− 0.11/− 0.11/− 0.10 mag) in the V/R/i spectral bands, respectively. Comparing our results with previous studies, we find smaller color variations between these seasons as compared with previous ones. We also separate the contribution of the lensing galaxy from that of the fainter and close lensed component.