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Spectral Type of the Probable Optical Counterpart to the x-ray Pulsar 4U1901+03

ATel #12560; B. McCollum (American U.), S. Laine (Caltech/IPAC)
on 8 Mar 2019; 02:20 UT
Credential Certification: Bruce McCollum (mccollub@cua.edu)

Subjects: Binary, Pulsar

We performed SED fitting of catalog photometry of the object which is suggested by Strader et al. (ATel #12554) to be the probable quiescent optical counterpart to the X-ray pulsar 4U 1901+03 (ATel # 12514, #12515, #12519). We used photometry from 2MASS, UKIDSS, WISE, and Pan-STARSS. We fitted the SED to the BT-Settl model grid of Allard et al. 2012 (RSPTA, 370, 2765A). The Av was varied as a free parameter from 7 to 11, similar the estimate of Strader et al. (ATel # 12554) but with a wider range, using a standard Galactic extinction curve with R = 3.1. The Teff was varied as a free parameter in 100 K increments from 5000 K to 25,000 K.

A good fit was obtained with the following stellar parameters: Teff = 11,600 +/-100 K, Av = 9.2, and log g = 3 +/- 0.25, corresponding to a B8/9 IV star. The fitting makes no assumption or conclusion regarding distance, but the spectral type and high luminosity are consistent with a large distance and early spectral type as suggested by Strader et al. (ATel #12554).

The SED and model comparison plot is posted at http://web.ipac.caltech.edu/staff/seppo/plots/4U-1901-SEDfit.png

Because it is not obvious on the scale of the plot, we note that the fitting suggests a flux excess of ~50% in the WISE W2 (4.6 um) and ~20% in WISE W1 (3.4 um) bands relative to the model SED. The W1 and W2 flux uncertainties are ~3%, smaller than the plot symbols.

This publication makes use of data products from the Two Micron All Sky Survey, 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 publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This work is based in part on data obtained as part of the UKIRT Infrared Deep Sky Survey. This publication makes use of VOSA, developed under the Spanish Virtual Observatory project supported from the Spanish MINECO through grant AyA2017-84089. This work uses data from the Pan-STARRS1 survey. This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France.