Electronic Telegram No. 5530
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
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Prepared using the Tamkin Foundation Computer Network


RW AURIGAE A
     C. M. Lisse (Applied Physical Laboratory, Johns Hopkins University),
M. L. Sitko (Space Science Institute), and G. M. Engh (NASA Infrared Telescope
Facility) report finding a marked change in the brightness and spectral
character of RW Aur A (R.A. = 5h07m49s.57, Decl. = +30d24'05".2, equinox
J2000.0) from about one hour of observations around 2025 Mar. 17.23 UT using
with the NASA 3.2-m Infrared Telescope Facility (+ SpeX instrument) at Mauna
Kea, HI, USA.  The A component of this T-Tauri binary system is now
photometrically the fainter of the two objects, with its 0.7- to 1.3-micron
flux dropping to about 0.1 that of its previous levels (cf. Lisse et al. 2022,
Ap.J. 928, 189).  The hot CO gas bands at 2.2-2.4 microns have disappeared,
and its numerous atomic and ionic emission lines are highly diminished by an
order of magnitude.  The longer-wavelength flux at 3-5 microns, purportedly
from the system's accretion disk, is little affected.  These findings are
coincident with AAVSO reports of an optical lightcurve showing a drop of
about 2 magnitudes in the system's brightness commencing in Feb. 2025.
     E. O. Waagen, American Association of Variable Star Observers (AAVSO),
writes that irregular fadings occurred in 2010, 2014, 2016, and 2024, with
a possible fading in late 1937.  The 2024 fading began in Dec. and is still
underway as of 2025 Mar. 21.  Recent visual magnitude estimates:  Mar.
19.897 UT, 13.0 (M. Kohl, Duernten, Switzerland); 20.792, 12.8 (W. Kriebel,
Schierling/Walkenstetten, Germany).  Recent photoelectric V magnitudes:
Mar. 19.791, 12.49 (J.-F. Hambsch, Mol, Belgium); 20.064, 12.62 (T. Haugh,
Valparaiso, FL, USA); 20.752, 12.59 (T. Tordai, Budapest, Hungary).
RW Aur is a binary in which both components (A and B) are classical T-Tau
variables.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2025 CBAT
2025 March 21                    (CBET 5530)              Daniel W. E. Green