Central Bureau for Astronomical Telegrams
IAUC 7293: HDE 245770
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Circular No. 7293
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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HDE 245770
F. Giovannelli, Istituto di Astrofisica Spaziale, CNR, Rome;
L. Sabau-Graziati, Division de Ciencias del Espacio, INTA, Madrid;
S. Bernabei, Osservatorio Astronomico di Bologna; and S. Galleti,
Dipartimento di Astronomia, Universita di Bologna, write: "Low-
resolution spectrosopy [Delta(lambda) about 0.66 nm] of HDE 245770
(the optical counterpart of the x-ray pulsar A0535+26; e.g., IAUC
3167, 3655, 5746; Giovannelli and Sabau-Graziati 1992, Space Sci.
Rev. 59, 1) made on Oct. 8 with the 1.5-m Loiano telescope reveals
H-alpha in emission with EW about -0.5 nm. Also, He I lines
(587.6, 667.8, and 706.5 nm) are seen in emission and show
doublings separated by about 1.5 nm. H-beta is in weak absorption
(EW about +0.017 nm). H-gamma and H-delta are seen in absorption
(EW about +0.16 and +0.30 nm, respectively). This result clearly
shows the resumption of optical activity after a period from early
1996 to early 1999 in which a depletion of the circumstellar disk
was clearly seen (Piccioni et al. 1999, IAU Coll. No. 175,
Alicante, Spain). For instance, H-alpha was in absorption on 1998
Nov. 11 and 12 with EW about +0.04 and +0.05 nm, respectively.
Also H-beta, H-gamma, and H-delta were in absorption on 1998 Nov. 9
with EW = +0.19, +0.28, and +0.34 nm, respectively. Photometry of
HDE 245770 performed on 1999 Oct. 9 and 11 gives B = 9.78 +/- 0.04
and 9.77 +/- 0.04, respectively. The historical B lightcurve has
in the past 15 yr shown a continuous trend toward lower luminosity
(starting from a stable mag of about 9.5 during the mid-1970s to
the mid-1980s, and fading to mag about 10), but this trend is now
reversing. As a consequence of this behavior, we expect the x-ray
pulsar companion A0535+26 to have a normal x-ray outburst
(following the classification of Giovannelli and Sabau-Graziati,
ibid.) of intensity about 0.1 Crab on 1999 Dec. 27-31. Optical
indicators (e.g., H-gamma, usually in absorption, will enhance to
fill the continuum or even show emission; optical UBVRI flare of
intensity about 0.1 mag) will precede the x-ray outburst by about
7-10 days. This prediction is based on RXTE data
(http://space.mit.edu/XTE/asmlc/ASM.htlm) and on the orbital period
of the system (110.8 days, from the best-fit multi-year optical
data of Giovannelli's group and others; see Guarnieri et al. and de
Martino et al. 1985, in Multifrequency Behaviour of Galactic
Accreting Sources, pp. 310 and 326; and Priedhorsky and Terrell
1983, Nature 303, 681, who derived a period of 111.0 +/- 0.4 days
from VELA-5B data, related to x-ray quiescent emission from
A0535+26)."
(C) Copyright 1999 CBAT
1999 October 29 (7293) Daniel W. E. Green
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