SOAR spectroscopic follow-up of the Galactic optical transient TCP J15244460-6059200

ATel #15473; E. Aydi, K. V. Sokolovsky, J. Strader, L. Chomiuk, A. Kawash (MSU), and Andrew Pearce (AAVSO)
on 26 Jun 2022; 09:34 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Elias Aydi (aydielia@msu.edu)

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We report on spectroscopic follow up of the optical transient TCP J15244460-6059200 which was discovered by Andrew Pearce, Nedlands, Western Australia, on UT 2022-06-25.48 at an unfiltered magnitude of 10.7. The discoverer reports that the transient was not visible on three frames taken on 2022-06-22.52 and 2022-06-24.47, meaning that the transient is less than a day old. The latest data from the All-Sky Automated Survey for SNe (ASAS-SN, Shappee et al. 2014, ApJ, 788, 48) show that the transient peaked at g-magnitude = 10.9 and has declined by 1.4 mag in one day (see light curve link below). The transient matches a Gaia source (ID #5875610751015084544), with a mean G-magnitude = 13.75, implying an outburst magnitude of less than 3 magnitudes. Archival data from the SkyMapper Southern Sky Survey of the candidate match reports the following photometry: g = 13.9, r = 13.7, and i = 13.6.

On 2022-06-26.21 we obtained a low-resolution spectrum using the Goodman spectrograph (Clemens et al. 2004, SPIE, 5492, 331) on the 4.1 m SOAR telescope, covering a wavelength range of 4000-7800 A. The spectrum shows a red continuum with broad and strong emission lines of H I, He I, and O I. The lines show a broad emission base with a narrower emission core. Halpha has a FWZI larger than 10,000 km/s. The spectrum resembles that of a very fast classical nova after optical peak. The low amplitude of the transient raises questions about its nature and the possible progenitor match. TCP J15244460-6059200 could be an unusually low-amplitude, ultra-fast nova or a more exotic phenomenon. There is a slight chance that the actual progenitor system is much fainter and coincides with the bright (~14 mag) match, which would explain the unusually low-amplitude of the transient. Follow-up observations are encouraged in all bands.

We used SOAR images to measure the position of the nova with respect to UCAC3 stars in the field:

 
15:24:47.63 -60:59:47.3 +/-0.2" J2000 

Preliminary photometry using an ensemble of APASS stars results in the following values:

 
2459756.74489 g=11.8 
2459756.74480 r=10.8 
2459756.74549 i=10.4 

The magnitude measurement uncertainty is dominated by the uncertainty in zero-point calibration and is expected to be smaller than 0.1mag.

The ASAS-SN sky-patrol light curve (Kochanek et al. 2017, PASP, 129, 4502): https://asas-sn.osu.edu/sky-patrol/coordinate/85994024-ab1f-4750-a978-343c6047d476

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).