2005/01/31 by Adrienne M. Juett, Deepto Chakrabarty · 5 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1086/430633
published as Astrophys.J. 627 (2005) 926-932 · 8 pages, 3 figures, accepted for publication to the Astrophysical Journal
arxiv created 2005/03/30 · openalex publication_date 2005/07/06 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
We present high-resolution spectroscopy of the neutron star/low-mass X-ray binaries (LMXBs) 4U 1850-087 and 4U 0513-40 as part of our continuing study of known and candidate ultracompact binaries. The LMXB 4U 1850-087 is one of four systems in which we had previously inferred an unusual Ne/O ratio in the absorption along the line of sight, most likely from material local to the binaries. However, our recent Chandra X-Ray Observatory LETGS spectrum of 4U 1850-087 finds a Ne/O ratio by number of 0.22 ± 0.05, smaller than previously measured and consistent with the expected interstellar value. We propose that variations in the Ne/O ratio due to source variability, as previously observed in these sources, can explain the difference between the low- and high-resolution spectral results for 4U 1850-087. Our XMM-Newton RGS observation of 4U 0513-40 also shows no unusual abundance ratios in the absorption along the line of sight. We also present spectral results from a third candidate ultracompact binary, 4U 1822-000, whose spectrum is well fit by an absorbed power-law + blackbody model with absorption consistent with the expected interstellar value. Finally, we present the nondetection of a fourth candidate ultracompact binary, 4U 1905+000, with an upper limit on the source luminosity of <1 × 10 32 ergs s -1 . Using archival data, we show that the source has entered an extended quiescent state.