Nature of the Optical Counterpart to MASTER OT J155814.41-163017.1

ATel #12076; B. McCollum (American Univ.), S. Laine (Caltech/IPAC)
on 3 Oct 2018; 22:01 UT
Credential Certification: Bruce McCollum (mccollub@cua.edu)

Tweet

We report fitting the SED of archival photometry of counterpart of MASTER OT J155814.41-163017.1 (ATel # 12071) to the BT-NextGen set of model atmospheres (Allard et al., 2009, Phil.Trans.Royal.Ast.Soc.A, 270, 2765).

Measurements flagged as being of good quality are available from Pan-STARRS and SDSS in the ugriz bandpasses. Measurements in those two data sets in comparable bandpasses are mostly within one sigma of each other. The PAN-STARRS data and SDSS data were obtained at different epochs about five years apart. The ugriz magnitudes are all ~21.

In the fitting, the object temperature was allowed to vary from 1000 K to 70,000 K. The Av was allowed to vary as an independent variable from 0.1 to 5. Log g was varied from -0.5 to 6, and the metallicity was varied from -4 to 0.5.

The best fit when assuming no IR excess was obtained from the following parameters: T = 50,000 +/- 968 K, Av = 1.57 +/- 0.30, log g = 2.5 +/- 0.5, and metallicity z = 0. A plot of the model fit and data is available at

http://spider.ipac.caltech.edu/staff/seppo/master_ot_j155814/master-ot-J155814.41-163017-sed.jpg

Our best fit Av assuming a standard Galactic extinction law corresponds to E(B-V) ~ 0.40 to 0.60. According to the three-dimensional Galactic extinction map of Green et al. (2018; MNRAS, 478, 651), the E(B-V) in the direction of MASTER OT J155814.41-163017.1 is ~0.25 for all distances from ~250 pc to 50,000 pc. In addition, there is a slight flux excess relative to the model SED in the i and z bands. Thus the object may have a significant amount of circumstellar extinction in the line of sight.

If we assume for the fitting that the i and z magnitudes are affected by some unspecified excess, the chi-square of the best fit improves from 9.6 to 5.2, and the new best fit is obtained with T = 50,000 +/- 933 K, Av = 1.57 =/- 0.27, log g = 3.5 +/- 0.48, and metallicity = 2.5.

This research has made use of the VizieR catalogue access too, CDS, Strasbourg, France. The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation Grant No. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), the Los Alamos National Laboratory, and the Gordon and Betty Moore Foundation. This publication makes use of VOSA, developed under the Spanish Virtual Observatory project supported from the Spanish MINECO through grant AyA2017-84089. We acknowledge use of the SDSS Data Release 9 (Alam et al. 2015, ApJS, 219, 12).