Spectral Type of the Unusual Dimming Star ASASSN-V J190917.06+182837.36

ATel #13111; B. McCollum (American Univ.), S. Laine (Caltech/IPAC)
on 15 Sep 2019; 21:37 UT
Credential Certification: Bruce McCollum (mccollub@cua.edu)

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We performed SED fitting of ASASSN-V J190917.06+182837.36 which Way et al. (2019, ATel #13106) reported to show an unusual dimming episode. We used archival photometry from Gaia, 2MASS, and WISE. The fitting was done against the BT-Settl-CIFIST stellar model grid (Baraffe et al. 2015, A&A, 577A, 42B). The Teff was allowed to vary as a free parameter from 1500 K to 7000 K. The Av was allowed to vary from 1.0 to 3.0 assuming a standard Galactic extinction law.

A good fit was obtained for an object having Teff = 6000 +/- 149 K and Av = 2.10 +/- 0.12. Based on the SED fit and the Gaia distance of approximately 1320 +/- 80 pc (Bailer-Jones et al. 2018, AJ, 156, 58), the object's bolometric luminosity is 61 +/- 13 solar luminosities.

The expected Av from ISM extinction in that direction at that distance is ~ Av = 1.5 +/- 0.1, using the 3-D Galactic extinction map of Green et al. 2019 (submitted; astro-ph). Thus the best fit implies that there is a substantial amount of circumstellar reddening. If the fitting is performed with the value of Av forced to be 1.5 +/- 0.1, the chi-squared value increases by about 35% because the IR photometry and Gaia photometry do not then match the same dereddened model SED well.

The fact that a good fit with no outliers was obtained despite combining data which represent three epochs spread over ~20 years is consistent with the observation by Way et al. (2019) that the dimming episodes appear to be infrequent (at least ~3 years if periodic).

This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. 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 publication makes use of VOSA, developed under the Spanish Virtual Observatory project supported by the Spanish MINECO through grant AyA2017-84089. VOSA has been partially updated by using funding from the European Union's Horizon 2020 Research and Innovation Programme, under Grant Agreement no. 776403 (EXOPLANETS-A).