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IAUC 6200: C/1995 O1; RX J1802.1+1804

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                                                  Circular No. 6200
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
Phone 617-495-7244/7440/7444 (for emergency use only)

     M. Hicks, Lunar and Planetary Laboratory, reports the following JHK
photometry, obtained on July 27 with the 1.8-m telescope at the Lowell
Observatory's Anderson Mesa Station, using the OSIRIS infrared system
in imaging mode.  Synthetic apertures of diameter 12", 18" and 24" were
applied to obtain the following magnitudes: J(12) = 12.22 +/- 0.07,
J(18) = 12.02 +/- 0.07, J(24) = 11.87 +/- 0.09; H(12) = 11.93 +/- 0.02,
H(18) = 11.66 +/- 0.03, H(24) = 11.51 +/- 0.12; K(12) = 11.86 +/- 0.05,
K(18) = 11.56 +/- 0.05, K(24) = 11.37 +/- 0.07.  No color differences
with respect to aperture size were found, and the J-H and J-K magnitudes
are consistent with the solar spectrum, suggesting optically dominant
grain size greater than or equal to 1-2 microns, typical for comets.

RX J1802.1+1804
     J. Greiner, Max-Planck-Institute for Extraterrestrial Physics;
R. Remillard, Center for Space Research, Massachusetts Institute of
Technology; and C. Motch, Strasbourg Observatory, report in response
to IAUC 6195: "The new AM Her system RX J1802.1+1804 was discovered
in ROSAT data as a highly variable and soft x-ray source.  Follow-up
pointed observations revealed a periodic flux modulation with the
ephemeris T(HJD) = 2448907.26986597 + 0.078498(115)E and including
a sharp and nearly complete eclipse of the x-ray emission.  The x-ray
spectrum averaged over the full period is dominated by soft emission
below 0.5 keV.  A blackbody plus a thermal bremsstrahlung model
with a fixed temperature of 10 keV results in kT_bb = 30 +/- 20 eV.
The mean unabsorbed blackbody flux (excluding the eclipse) is 8**10-11
erg cm-2 s-1 in the ROSAT band--the number given on IAUC 6195 is wrong--and
and the ratio of soft (blackbody) to hard (bremsstrahlung) photon flux
(integrated over 0.1-2.4 keV) is 100.  RX J1802.1+1804 is optically
identified with an object of V = 15.  The optical spectrum is typical
for a high-excitation cataclysmic variable with strong emission lines
of H, He I and He II.  Phase-resolved spectroscopy shows a strong
velocity wave, giving a best-fit period of 1.8841 +/- 0.0017 hr.
Photometric observations have revealed 0.1-mag variations, but no eclipse.
The evidence of an x-ray eclipse without a corresponding optical
eclipse implies that the x-ray-emitting region is confined to a small
region on the white-dwarf surface.  These and more details have been
presented at the Abano-Terme Conference on Cataclysmic Variables and
Related Objects in June 1994; preprints are available on request from

1995 August 3                  (6200)              Brian G. Marsden

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