Central Bureau for Astronomical Telegrams
IAUC 5278: N Her 1991; EDITORIAL NOTICE
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Read IAUC 5279
Circular No. 5278
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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
MARSDEN or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
NOVA HERCULIS 1991
P. Predehl, J. H. M. M. Schmitt and J. Trumper, Max-Planck-
Institut fur Extraterrestrische Physik; T. J. O'Brien, H. M. Lloyd and
M. F. Bode, Lancashire Polytechnic; and M. G. Watson and K. A. Pounds,
Leicester University, communicate: "This nova was observed with the
XRT/PSPC of ROSAT on Mar. 30.46 UT, five days after discovery (IAUC
5222). A total of 194 counts were detected within the observation time
of 1235 s, yielding a countrate of 0.16 +/- 0.01 cts/s. According to
its spectrum, the source seems to be highly absorbed with a low-energy
cutoff at approximately 1 keV. This constitutes the first x-ray
detection of a classical nova at or near maximum. Previous observations
of classical novae at this stage with SAS 3, Ariel V and EXOSAT have
only resulted in upper limits on their x-ray flux. The region of the
nova was already observed in the ROSAT all-sky survey during 1990 Sept.
25-28. The data indicate that there was no source present at this
position with an upper limit of approximately 0.01 cts/s."
EDITORIAL NOTICE
As originally discussed on IAUC 3844, plans are now well advanced
to replace the 1950.0 standard equinox by the 2000.0 equinox for
observations, orbits and ephemerides of comets and minor planets. IAU
Commission 20 has recommended that the change (specifically from the
FK4/B1950.0 system to the FK5/J2000.0 system) be made at the beginning
of 1992. Detailed information concerning the conversion and a timetable
for the change were given on MPC 17473-17476 on 1991 Jan. 30.
Specifically, it can be noted that the 1992 editions of the Efemeridy
Malykh Planet and the International Comet Quarterly Handbook are
utilizing J2000.0, and that limited J2000.0 orbital data appear already
in the 1991 May 28 MPCs. The IAU Circulars will follow the lead of the
Minor Planet Circulars in this respect, and this will mean in essence
that the J2000.0 system will be introduced here about six months from
now, after the Nov. 21 MPCs have been prepared. For a limited time we
shall be prepared to make the appropriate conversions to the
observations reported to us, and as November approaches observers must
be particularly careful correctly to indicate which system they are
utilizing. In the case of the Computer Service, the change will occur
closer to the end of the year. Observers of novae, supernovae, etc.,
are advised that there are as yet no plans to abandon the 1950.0 equinox
for non-solar system objects.
1991 May 26 (5278) Brian G. Marsden
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