IGR J19552+0044: A new asynchronous short period polar
Filling the gap between intermediate and ordinary polars⋆
1 Universidad Nacional Autónoma de México, Instituto de Astronomia, Unidad Academica en Ensenada, 22860 Baja California, Mexico
2 Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
3 Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755, USA
4 South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape Town, South Africa
5 Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
6 New York University Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates
7 Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111 Valparaíso, Chile
8 Center for Backyard Astrophysics (CBA), Backyard, UK
9 Departamento de Ciencias Integradas, Facultad de Ciencias Experimentales, Universidad de Huelva, 21071 Huelva, Spain
10 Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
11 Department of Physics and Astronomy, University of North Carolina at Greensboro, Greensboro, NC 27402-6170, USA
Received: 7 June 2017
Accepted: 14 August 2017
Context. Based on XMM-Newton X-ray observations IGR J19552+0044 appears to be either a pre-polar or an asynchronous polar.
Aims. We conducted follow-up optical observations to identify the sources and periods of variability precisely and to classify this X-ray source correctly.
Methods. Extensive multicolor photometric and medium- to high-resolution spectroscopy observations were performed and period search codes were applied to sort out the complex variability of the object.
Results. We found firm evidence of discording spectroscopic (81.29 ± 0.01 m) and photometric (83.599 ± 0.002 m) periods that we ascribe to the white dwarf (WD) spin period and binary orbital period, respectively. This confirms that IGR J19552+0044 is an asynchronous polar. Wavelength dependent variability and its continuously changing shape point at a cyclotron emission from a magnetic WD with a relatively low magnetic field below 20 MG.
Conclusions. The difference between the WD spin period and the binary orbital period proves that IGR J19552+0044 is a polar with the largest known degree of asynchronism (0.97 or 3%).
Key words: accretion, accretion disks / stars: magnetic field / binaries: close
Photometric and spectroscopic observational data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/608/A36
© ESO, 2017