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Return-Path: <atel@astronomerstelegram.org> Delivered-To: stefano@bicar.it Received: by mail.planetcloud-host.com (Postfix, from userid 99) id 1E4C2146CE; Sat, 28 Feb 2026 08:09:00 +0100 (CET) X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on mail.planetcloud-host.com X-Spam-Level: * X-Spam-Status: No, score=1.7 required=5.0 tests=RCVD_IN_DNSWL_BLOCKED, RCVD_IN_VALIDITY_RPBL_BLOCKED,RCVD_IN_VALIDITY_SAFE_BLOCKED,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=disabled version=3.4.0 Received-SPF: Pass (sender SPF authorized) identity=mailfrom; client-ip=174.142.199.243; helo=server.astronomerstelegram.org; envelope-from=atel@astronomerstelegram.org; receiver=stefano@bicar.it Received: from server.astronomerstelegram.org (astronomerstelegram.org [174.142.199.243]) by mail.planetcloud-host.com (Postfix) with ESMTP id D098C14472 for <stefano@bicar.it>; Sat, 28 Feb 2026 08:08:15 +0100 (CET) Received: from server.astronomerstelegram.org (localhost [127.0.0.1]) by server.astronomerstelegram.org (Postfix) with ESMTP id E802E288078D for <stefano@bicar.it>; Sat, 28 Feb 2026 02:08:14 -0500 (EST) To: stefano@bicar.it From: atel@astronomerstelegram.org Subject: ATel 17702, 17703, 17704 Message-Id: <20260228070814.E802E288078D@server.astronomerstelegram.org> Date: Sat, 28 Feb 2026 02:08:14 -0500 (EST) ------------------------------------------------------------------------------ The Astronomer's Telegram is free to read, free to publish, free to use. Thanks to the support of our patrons, we can continue to keep it free. https://www.patreon.com/astronomerstel ------------------------------------------------------------------------------ The Astronomer's Telegram http://www.astronomerstelegram.org ------------------------------------------------------------------------------ Posted: Within the last 24 hours ============================================================================== ATEL #17702 ATEL #17702 Title: Rapid decline in brightness of the red nova remnant V838 Mon Author: V. P. Goranskij (SAI, Moscow University; SAO RAS), S. Yu. Shugarov (AI, Slovak Academy of Sciences; SAI, Moscow University), E. A. Barsukova, V. V. Komarov (SAO RAS), A. M. Tatarnikov, G. E. Nikishev, N. P. Ikonnikova (SAI, Moscow University) Queries: bars@sao.ru Posted: 27 Feb 2026; 17:32 UT Subjects:Binary, Nova, Star, Transient, Variables We report a rapid decline in the brightness of the red nova remnant V838 Mon following its light maximum around September 25, 2025 (B = 15.03, V = 12.75, RC = 10.70, IC = 8.48 mag). On 2026 Feb 20.832 UT, the magnitudes decreased to B = 16.29, V = 14.10, RC = 11.78, IC = 9.05 mag. The mean fading rate over the past two months is 0.011 ± 0.001 mag over a day in filter V. Photometry was obtained with 0.5–1-m telescopes. Optical spectra secured on 2025 Dec 06.052 UT and 2026 Feb 19.00 UT with the SAO 1-m and SAI 2.5-m telescopes correspond to an M5-type supergiant with strong TiO molecular bands and Hα emission. The progenitor of V838 Mon was identified as a binary system composed of two B3V-type stars; the more luminous component underwent a red nova outburst in 2002 (ATel #803, #964, #966, #1821, #1996, and #2211; Astrophys. Bull., vol.75, 325, 2020). By 2007, the less luminous component became engulfed by the expanding envelope. Since then, the remnant has evolved as an M-type supergiant with a hot B3V companion embedded within a common envelope. Since 2015, we have detected quasi-periodic variability in the IC band with a characteristic period of about six months. The amplitude of this variability has steadily increased and extends toward shorter wavelengths. We suggest that these brightness variations are associated with the formation of a hot region on the surface of the common envelope above the embedded companion and possible contraction of the envelope. The observed fading is consistent with the passage of this hot region toward the limb and onto the far side of the common envelope due to orbital motion. Around February 23, 2026, the decline ceased, possibly indicating that the hot region had fully rotated out of view. The largest brightness decrease occurred at shorter wavelengths. Link to light curves and spectra included. V838 Mon light curves in IC and V filters, and optical spectra : http://www.sao.ru/hq/bars/V838Mon/v838-VIspec.png ------------------------------------------------------------------------------ Password Certification: Barsukova E.A. (bars@sao.ru) https://www.astronomerstelegram.org/?read=17702 ============================================================================== ATEL #17703 ATEL #17703 Title: AT 2026epw: Discovery of a possible nova from Vera C. Rubin Observatory Author: Anirudh Salgundi (UNC), Igor Andreoni (UNC), Akash Anumarlapudi (UNC), James Freeburn (UNC), Theophile du Laz (Caltech), Michael Coughlin (UMN), V. Ashley Villar (Harvard), Eric Burns (LSU), Jonathan Carney (UNC), Mansi Kasliwal (Caltech). Queries: anirudhs@unc.edu Posted: 27 Feb 2026; 21:00 UT Subjects:Optical, Nova, Transient We report the discovery of a possible Nova found in the Vera C. Rubin Observatory commissioning alert stream via the Babamul broker (du Laz et al., 2025). The transient AT 2026epw (Object ID: LSST-AP-DS-170046106280394867) is located at RA: 185.49089 deg (12h21m57.8s, J2000) deg and Dec: 8.6600 deg (+08d39m26.0s, J2000). The discovery magnitudes are given below: | Band | MJD | Magnitude | Error | |--------|-------------|-------------|-------------------| | i | 61094.19440 | 23.02 | 0.15 | | g | 61094.20301 | 23.13 | 0.08 | | r | 61094.21535 | 22.95 | 0.08 | Visual inspection suggests that the transient is 54.2’’ offset from the host galaxy UGC 07424. The host galaxy is at 25.1 Mpc (Kent et al., 2008), and at this distance, the projected separation of the transient from the host nucleus is 3.31 kpc. The photometry acquired during the first detection epochs (around MJD 61094.19) yields absolute magnitudes of M_g = -8.9, M_r = -9.0, and M_i = -9.0. Further, the source shows a fading rate of 0.54 mag/day in r-band, 0.64 mag/day in g-band, and 0.42 mag/day in i-band. The lack of reddening disfavours a kilonova or an afterglow scenario. Given the photometric evolution and absolute magnitude, we suggest this is a classical nova candidate. Babamul link to the source: https://babamul.caltech.edu/objects/LSST/170046106280394867 The Babamul alerts broker and BOOM software infrastructure (du Laz et al. 2026) is co-developed by the California Institute of Technology and the University of Minnesota. This work acknowledges support from the National Science Foundation through AST Award No. 2432476 (PI Kasliwal; co-PI Coughlin) and leverages experience from the Zwicky Transient Facility (co-PIs Graham and Kasliwal). ------------------------------------------------------------------------------ Password Certification: Akash Anumarlapudi (akasha@unc.edu) https://www.astronomerstelegram.org/?read=17703 ============================================================================== ATEL #17704 ATEL #17704 Title: Fermi J1820-1648: SMA Detection of Bright Millimeter Emission Author: Anna Ho (Cornell), Mark Gurwell, Garrett K. Keating (CfA), Kishalay De (Columbia/CCA), Laura Chomiuk (MSU) Queries: annayqho@cornell.edu Posted: 27 Feb 2026; 22:05 UT Subjects:Millimeter, Nova We observed the classical nova Fermi J1820-1648 (ATel #17688, #17698, #17699, #17700) with the Submillimeter Array (SMA) on 27 February 2026 UT. The SMA realtime quicklook pipeline POLARIS showed the source was detected with high SNR even as the observations were continuing. After observations, data were processed and imaged with the COMPASS calibration pipeline, and a clear point source was detected at the position of the nova, with a flux density of 12.66 +/- 0.73 mJy (SNR 17) at 230 GHz. Gains were calibrated using NRAO530, passband was calibrated using 3C279, flux was calibrated using MWC349A, the total integration time on the target was 2.43 hours, and the SMA was operating with 7 antennas. Further observations are planned. We thank the SMA staff for scheduling and conducting the observation. ------------------------------------------------------------------------------ Password Certification: Anna Ho (ayh24@cornell.edu) https://www.astronomerstelegram.org/?read=17704 ============================================================================== ============================================================================== This is an automatically-generated notice. You can remove yourself permanently from receiving both the Daily Email Digest and Instant Email Notices from The Astronomer's Telegram by following this link: https://www.astronomerstelegram.org?unsubscribe&confirmation=a803d34e7ea924f9a4142bac00763549&address=stefano@bicar.it
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