SOAR spectroscopic classification of Gaia21esm and Gaia21eqn as highly reddened classical novae
ATel #15001; A. Kawash, E. Aydi (MSU), P. Velez (OB Observatory, SSO), L. Chomiuk, J. Strader, K. V. Sokolovsky (MSU)
on 26 Oct 2021; 16:13 UT
Credential Certification: Adam Kawash (kawashad@msu.edu)
Subjects: Optical, Nova, Transient
We report on spectroscopic follow up of Gaia21esm and Gaia21eqn. Both transients were reported as hostless red transients in the Galactic plane by Gaia Photometric Science Alerts (GSA) making them classical nova candidates. Gaia appears to be the only transient reporting survey to have detected them. We obtained low resolution spectra with the Goodman spectrograph (Clemens et al. 2004, SPIE, 5492, 331) on the 4.1m SOAR telescope on 2021-10-26.0, and both spectra are consistent with that of classical nova eruptions. These are the 16th and 17th Galactic novae to be spectroscopically confirmed in 2021, the highest number confirmed in a single year on record. We discuss each individual nova below.
Gaia21esm was first detected by Gaia on 2021-09-20 at G = 13.8 mag and then again on 2021-10-16 at G = 16.3 mag. Because GSA requires transients to be detected in both fields of view (Hodgkin et al. 2021 A&A, 652, A76), it was not reported as a new transient until after the second detection. The low resolution Gaia BP/RP spectrum shows a red continuum with apparent emission lines. The SOAR spectrum shows a red continuum with strong emission lines of H I and O I. Halpha is characterized by a FWHM of around 2000 km/s. The overall spectrum is that of a highly reddened classical nova, after optical peak.
Gaia21eqn has only been detected on 2021-10-06 at G = 13.9 in both fields of view. The low resolution Gaia spectrum also shows a red continuum with possible emission lines. The field is nearing Solar conjunction, making follow up observations of this transient difficult. We obtained 600s R- and I-band images of the field with a Sky90 refractor on 2021-10-22. The low altitude of 21 deg. made reliable photometry difficult to measure, but we estimate a brightness of R = 19.7 +/- 1.9 mag and I = 14.7 +/- 0.1 mag, consistent with a highly reddened transient that has likely faded since the last Gaia observation. The SOAR spectrum also shows a red continuum with strong emission lines of H I and O I and a Halpha FWHM of around 2300 km/s. The overall spectrum is also that of a highly reddened classical nova, after the optical peak.
We would like to thank SOAR observing assistant Carlos Corco for help with these difficult low altitude observations. This ATel is based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministerio da Ciencia, Tecnologia, Inovacoes e Comunicacoes do Brasil (MCTIC/LNA), the U.S. National Science Foundation's National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU). We also acknowledge ESA Gaia, DPAC and the Photometric Science Alerts Team (http://gsaweb.ast.cam.ac.uk/alerts).
