Possible New Variable Star Detected by COIAS
ATel #17472; K. Ando (Okayama U. Sci.), S. Urakawa (JSGA), H. Maehara (NAOJ / NINS), K. Ito (Diver-X Inc.), J. Zhang (Walton International School, Xuzhou)
on 4 Nov 2025; 03:35 UT
Credential Certification: Kazuko Ando (kazuko.ando02@gmail.com)
Subjects: Infra-Red, Optical, Star, Transient, Variables
The COIAS Project is a citizen science initiative using public data from the Subaru Telescope's Hyper Suprime-Cam (HSC) to search for Solar System minor bodies.
During this search, amateur astronomer Jiashuo Zhang reported a potential variable star.
The COIAS team confirmed the variability using additional HSC archival images.
The specifications of the HSC instrument and details of its data releases are described in (Miyazaki et al. 2018, PASJ 70) and (Aihara et al. 2019, PASJ 71), respectively.
The source is located at:
- RA (J2000, ICRS) = 01:08:32.78
- Dec (J2000, ICRS) = +02:34:19.5
Archival COIAS photometry (2015–2020) is listed below:
| Date (UT) |
Filter |
Mag |
Mag_err |
| 2015-10-10T08:27:31.719 | r | 19.699 | 0.003 |
| 2015-10-14T07:58:46.541 | g | 21.066 | 0.008 |
| 2017-08-16T11:50:21.153 | y | 16.856 | 0.001 |
| 2017-08-29T12:59:18.409 | y | 16.865 | 0.001 |
| 2017-09-13T10:18:04.098 | y | 16.865 | 0.001 |
| 2018-11-15T10:21:44.596 | z | 17.199 | 0.002 |
| 2018-12-03T09:35:38.982 | z | 17.191 | 0.001 |
| 2019-01-09T07:08:19.452 | z | 17.192 | 0.001 |
| 2019-10-27T08:56:16.419 | i2 | 18.770 | 0.002 |
| 2019-10-27T12:29:17.396 | i2 | 17.892 | 0.001 |
| 2019-11-02T08:08:29.319 | i2 | 18.350 | 0.001 |
| 2019-11-28T05:07:54.897 | g | 21.043 | 0.007 |
| 2019-11-28T09:19:09.945 | g | 21.061 | 0.011 |
| 2019-11-28T10:35:52.292 | g | 18.772 | 0.001 |
| 2020-01-19T05:09:01.318 | g | 21.048 | 0.009 |
We found a significant brightening of ~2.3 mag within 1.3 hours from the g-band data on 2019 November 28.
All other measurements are broadly consistent with PS-1, SDSS, and DES catalog magnitudes.
Cross-matching with known catalogs shows that the nearest Gaia DR3 source is Gaia DR3 2538725722370046464, located only ~0.3″ from the COIAS position.
Its proper motion (μ ≈ 18 mas/yr) and parallax (π ≈ 1.88 mas, corresponding to d ≈ 0.53 kpc) indicate that the COIAS and Gaia positions are consistent within the expected uncertainties, including proper motion.
The apparent magnitude measured by COIAS (g ≈ 21) corresponds to an absolute magnitude of Mg ≈ 12.4 at the Gaia distance (d ≈ 0.53 kpc), consistent with that expected for an M-dwarf.
These results suggest that the COIAS-detected variability is consistent with a stellar flare originating from this M dwarf. Further follow-up observations are encouraged to better characterize its variability and flaring properties. Since this variability was identified from archival Subaru/HSC images obtained in 2019, it would also be valuable to examine other archival data from nearby epochs (e.g., from other observatories) to search for additional flaring episodes.
If you want to contact us, please send an e-mail to kazuko.ando02@gmail.com.
