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IAUC 5329: ER Vul; N Mus 1991

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                                                  Circular No. 5329
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM     EASYLINK 62794505

     D. H. Bradstreet and E. F. Guinan write: "The highly
chromospherically-active, detached eclipsing binary ER Vul (G1 V+G2 V;
P = 0.7 day) is scheduled to be observed continuously with the IUE
satellite during Sept. 26-28.  ER Vul is an important binary because
the physical characteristics of the stars (mass, temperature and
radius) are nearly identical to the those of the sun, except that the
stars rotate nearly 40 times faster and have extremely high levels of
chromospheric and coronal activity.  We are proposing an intensive,
worldwide campaign to conduct a multifrequency study of this
important binary.  Simultaneous photometry, spectroscopy, polarimetry
and radio observations will be crucial in establishing the sites of
active regions and starspots on the stars and to determine the nature
of frequent flarelike events seen in its visible-band lightcurves.
For those interested in photoelectric photometry, the suggested
comparison and check stars are SAO 89378 and SAO 89413, respectively.
For more information please contact us at Villanova University
(telephone 215-645-4823, telefax 215-645-7889, e-mail GUINAN@VUVAXCOM)."

     R. Sunyaev, E. Churazov, M. C. Schmitz-Fraysse and A. Goldwurm,
on behalf of the GRANAT team, report: "Telescopes ART-P and SIGMA
observed the source GRS 1124-684 on Aug. 14-15.  The flux in the
4-30-keV ART-P band was about 35 mCrab, little more than half the
value measured on May 31 (IAUC 5310) during the previous GRANAT
observations, while the flux in the SIGMA 35-200 keV band remained
approximately at the same level (about 90 mCrab), indicating
significant hardening of the x-ray spectrum (i.e., the ratio of flux
below and above 30 keV).  The composite 4-200-keV spectrum has a
complicated shape and can not be described by any simple model.  The
formally applied power law approximation in the 4-200 keV band
requires a photon index of about 1.6, while data above 35 keV are more
consistent with photon index about 2.2.  No significant variability of
the source flux has been detected, in either ART-P or SIGMA data.  The
source luminosity was estimated as (9.0 +/- 0.4) * 10**34, (1.10 +/-
0.13) * 10**35 and (6.8 +/- 1.8) * 10**34 erg/s in the 6-30, 30-100
and 100-200 keV bands (assuming a distance of 1 kpc), respectively.
The observed behavior of GRS 1124-68 is inconsistent with the
exponential decay commonly accepted for x-ray novae."

1991 August 27                 (5329)              Brian G. Marsden

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