Nature of the Progenitor of ASASSN-18uk

ATel #12029; Bruce McCollum (AU), Seppo Laine (Caltech/IPAC)
on 10 Sep 2018; 23:38 UT
Credential Certification: Bruce McCollum (mccollub@cua.edu)

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We report SED fitting of catalog data to the progenitor of ASASSN-18uk (AT 2018fxl) which was recently reported to be in outburst by Brimacombe et al. (ATel # 12018). The object has not been discussed in the literature apart from catalogs. Catalogs report magnitudes in U, B, V, Gaia G, R, I, Y, J, Ks, Spitzer bandpasses at 3.6, 4.5, and 5.8 microns, and WISE bandpasses at 3.35 and 4.6 microns along with WISE upper limits at 12 and 22 microns.

We fitted the SED from the catalog magnitudes to the BT-NextGen set of stellar models (Allard et al. 2012, IAUS, 282, 235). We allowed Av to vary as a free parameter from 0.1 to 1, the temperature to vary from 800 K to 10,000 K, the log g to vary from -0.5 to 6, and the metallicity to vary from -4 to 0.5. We also used the Gaia catalog estimated distance (~7200 +/- 1300 pc).

A good fit was obtained using a star having the following parameters: Teff = 4150 +/- 150 K, Av = 0.195, log g = 0.5, and metallicity = -1.4 +/- 0.40. It is seen that there is no infrared excess in the near-IR, while the upper limits at longer wavelengths provide a weak limit on any strong IR excess in that regime. The SED and model comparison plot is available at http://spider.ipac.caltech.edu/staff/seppo/asassn-18uk/fast.bfit.phot_2.png

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 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 VOSA, developed under the Spanish Virtual Observatory project supported from the Spanish MINECO through grant AyA2017-84089. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This work presents results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement (MLA). The Gaia mission website is https://www.cosmos.esa.int/gaia. The Gaia archive website is https://archives.esac.esa.int/gaia. We also wish to acknowledge the Magellanic Clouds Photometric Survey (Zaritsky et al. 2004, AJ, 128, 1606), which created the catalog from which we obtained U, B, and V magnitudes for the fitting.