A Living Catalog of Novae in M33

Scope of the Catalog: A comprehensive table of M33 novae going back to the first recorded nova in 1919 was created by W. Pietsch and posted on the Max Planck Institute for Extraterrestrial Physics (MPE) webpage (MPE M33 Catalog). The catalog was last updated on 2021 August 24. My purpose in the following table is to continue the M33 nova catalog, but in an abbreviated form. Eruptions of the recurrent nova M33N 2011-10a (= 2021-08a = 2025-10a), the first confirmed recurrent nova in M33, are shown in red. The four objects flagged in the MPE catalog as not novae (M33N 2014-08a, 2014-11a, 2014-11b and 2018-10a, all red long-period variables) are omitted.

At present, I give the nova name, the JD of the start of the eruption, the equatorial coordinates (J2000), the approximate magnitude near the start of the eruption, the spectroscopic class (where known), notes, and references. Note that the JD and magnitude do not necessarily correspond to maximum light, although in most cases they are close. Magnitudes are the brightest reported; filter codes are pg (photographic), Ha (Hα), w (unfiltered/white light), o (ATLAS orange), and standard band names; ? means no filter information is available. The Type column gives the spectroscopic class, based on the Fe II and He/N classes of Williams (1992), where one has been published, as given in the original references: Fe II; He/N; Fe IIb (broad-lined Fe II); Hybrid (Fe IIb systems displaying broad He and N lines); and Nova (spectroscopically confirmed as a nova, class not given). A question mark indicates an uncertain class, "X or Y" an ambiguous one, and a blank entry means that no class is available. For entries reported after the MPE catalog ends (from 2021-08b onward, except the recurrent-nova eruptions 2021-08a and 2025-10a), I have assigned designations following the MPE/CBAT convention (year-month and letter, in order of discovery within the month) and are not official; the AT name is given in the Notes. 2021-08b is lettered after 2021-08a, which MPE had already assigned to the recurrent nova, although it was found 5 days earlier. AT 2024pwl and AT 2025yal, which are long-period variables rather than novae, are listed under their AT names.

Author: A. W. Shafter (SDSU).

How to cite this catalog: If you use data from this catalog in a publication, please cite it as: Shafter, A. W., A Living Catalog of Novae in M33, https://ashafter.sdsu.edu/m33_nova_table.html (accessed [date]). Data for novae discovered through August 2021 are from the MPE catalog of W. Pietsch (https://www.mpe.mpg.de/~m31novae/opt/m33/M33_table.html), which should also be acknowledged. Where your work relies on the properties of individual novae, please also cite the original references given in the References column. This catalog is made available under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

^*Data through 2021 August are from the MPE M33 Catalog. Last updated 2 November 2026; table maintenance is now being assisted by AI (Claude Opus 5.5).