[vsnet-chat 71] Coordinates for LMC X-Ray sources.

[Mati Morel <morel@ozemail.com.au>]

Dear Readers,
In 1996 I received from Dr. Paul Schmidtke, Arizona State University,
a number of reprints reporting the results of his work on LMC/SMC
X-ray sources, especially Supersoft Sources (SSS). Study of these 
sources is a highly specialized area, involving firstly use of data
form X-ray detecting satellites such as ROSAT. The identification of
optical counterparts is a somewhat painstaking process, using large
telescopes, as the optical ids., are generally faint, at the mag.
19-20 level.  However, a couple of the LMC SSS's have been studied 
in some detail at optical wavelengths, such as CAL 87, which is an
eclipsing binary. It shows short duration, shallow X-Ray eclipses
which coincide in phase with the primary optical minimum. A paper
appears in Pub. Ast. Soc. of the Pacific, 105, 863-866, 1993 August.
A finder chart is given, but no coordinates. The position is
(1950) 5h47m27.0s  -71 10'11". This star is included in the list of
known LMC variables in vol. 5 of the GCVS, as star V4382 (page 69).

Not all X-ray sources in the direction of the Magellanic clouds are
Cloud members. Some are local foreground stars, while some are even
background objects (AGNs - Active Galaxy Nuclei).

Another reprint summarizes LMC SSS's as follows:
<Three of the supersoft X-ray sources in LMC have been identified
with disk-dominated, close binaries whose absolute magnitudes range
between Mv ~ -1.6 and +0.5. We note that the orbital periods for  
these systems are longer than the ones for typical low-mass X-ray
binaries. Two of the systems (CAL 83 and RXJ0513.9-6951) show evidence
of high-velocity outflows or possibly collimated, precessing jets.
Optical counterparts for three systems have not been found, but they
must be considerably fainter than those already identified.
.....(one sentence omitted)..... The nature of the component stars in
the supersoft sources is not yet resolved, but models include white
dwarfs, neutron stars, or black holes as the collapsed star. It seems 
likely that the SSS include several types of systems, and more than
one model may be needed to understand them.>
Source: reprint of paper "Supersoft X-ray Sources in the LMC", pp439-444 in
'Compact Stars in Binaries' (1996, J. van Paradijs et al eds.).

A very useful paper providing positions and finder charts for Magellanic
Cloud X-ray sources appears in Publ. A.S.P. for January 1997.

Cheers,
Mati Morel

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MOREL ASTROGRAPHICS
Stellar Data & Information Centre
c/o M. Morel
6 Blakewell Road,
Thornton  NSW 2322
AUSTRALIA
Tel. /fax : 61 49 662078  E-mail: morel @ozemail.com.au
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