TY - JOUR
T1 - Is CGCS 5926 a symbiotic X-ray binary?
AU - Masetti, N.
AU - Munari, U.
AU - Henden, A. A.
AU - Page, K. L.
AU - Osborne, J. P.
AU - Starrfield, Sumner
N1 - Funding Information:
We are grateful to the following people for their assistance in the acquisition of the optical spectra of CGCS 5926: Alessandro Siviero (Asiago), Gianni Cetrulo and Antonio Englaro (La Polse di Cougnes), Alberto Milani (Campo de’ Fiori), and Silvia Galleti and Roberto Gualandi (Loiano). We also thank Mauro Dadina and Isabella Pagano for discussions, and the anonymous referee for useful remarks which helped us to improve the quality of this paper. This research has made use of the ASI Science Data Center Multimission Archive; it also used the NASA Astrophysics Data System Abstract Service and the NASA/IPAC Infrared Science Archive, which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This publication made use of data products from the Two Micron All Sky Survey (2MASS), which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has also made extensive use of the SIMBAD and VIZIER databases operated at CDS, Strasbourg, France. N.M. acknowledges financial contribution from the ASI-INAF agreement No. I/009/10/0. K.L.P. and J.P.O. acknowledge the support of the UK Space Agency. S.S. acknowledges partial support from NSF and NASA grants to ASU.
PY - 2011
Y1 - 2011
N2 - We report on multiwavelength (X-ray to optical) follow-up observations of the carbon star CGCS 5926. These were motivated by the fact that this star is positionally coincident with a faint X-ray emitting object belonging to the ROSAT catalog of sources, thus suggesting a possible symbiotic X-ray binary (SyXB) nature for it. Our spectrophotometric optical data confirm the giant carbon star nature of the object and allow us to classify its spectral type as C(6,2). This classification places CGCS 5926 at a distance of ∼5 kpc from Earth. BVRCIC photometry of the star shows that it displays a variability of ∼0.3 mag on timescales of months, with the star getting bluer when its brightness increases. Our photometric data indicate a periodicity of 151 days, which we explain as due to radial pulsations of CGCS 5926 on the basis of its global characteristics. The source is not detected at X-rays with Swift/XRT down to a 0.3-10 keV band luminosity of ≈ 3 × 1032 erg s-1. This nondetection is apparently in contrast with the ROSAT data; however we show that, even if the probability that CGCS 5926 can be a SyXB appears quite low, the present information does not completely rule out such a possibility, while it makes other interpretations even more unlikely if we assume that the ROSAT detection was real. This issue might thus be settled by future, more sensitive, observations at high energies.
AB - We report on multiwavelength (X-ray to optical) follow-up observations of the carbon star CGCS 5926. These were motivated by the fact that this star is positionally coincident with a faint X-ray emitting object belonging to the ROSAT catalog of sources, thus suggesting a possible symbiotic X-ray binary (SyXB) nature for it. Our spectrophotometric optical data confirm the giant carbon star nature of the object and allow us to classify its spectral type as C(6,2). This classification places CGCS 5926 at a distance of ∼5 kpc from Earth. BVRCIC photometry of the star shows that it displays a variability of ∼0.3 mag on timescales of months, with the star getting bluer when its brightness increases. Our photometric data indicate a periodicity of 151 days, which we explain as due to radial pulsations of CGCS 5926 on the basis of its global characteristics. The source is not detected at X-rays with Swift/XRT down to a 0.3-10 keV band luminosity of ≈ 3 × 1032 erg s-1. This nondetection is apparently in contrast with the ROSAT data; however we show that, even if the probability that CGCS 5926 can be a SyXB appears quite low, the present information does not completely rule out such a possibility, while it makes other interpretations even more unlikely if we assume that the ROSAT detection was real. This issue might thus be settled by future, more sensitive, observations at high energies.
KW - stars: AGB and post-AGB
KW - stars: carbon
KW - stars: individual: CGCS 5926
KW - techniques: spectroscopic
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U2 - 10.1051/0004-6361/201117260
DO - 10.1051/0004-6361/201117260
M3 - Article
AN - SCOPUS:80053934292
SN - 0004-6361
VL - 534
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A89
ER -