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Astron. Astrophys. 347, 473-477 (1999)

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The peculiar M giant HD 154791

Optical counterpart of the X-ray source 4U1700+24 *

S. Gaudenzi 1 and V.F. Polcaro 2

1 Istituto Astronomico dell'Università "La Sapienza", Via G.M. Lancisi 29, I-00161 Roma, Italy
2 Istituto di Astrofisica Spaziale, CNR, Area della Ricerca di Roma Tor Vergata, V. Fosso del Cavaliere snc, I-00133 Roma, Italy

Received 15 January 1999 / Accepted 14 April 1999


HD 154791 is the only optical counterpart of an hard X-ray source (4U1700+24) with an apparently normal M giant spectrum. We present here new high S/N spectroscopic observations of this interesting and poorly studied object, pointing out a number of peculiarities never noticed before; therefore we derive a possible scenario involving a wide binary system, where an old, slowly rotating, neutron star is weekly interacting with its late optical companion. We foresee that this system could evolve, in a short time, into a normal LMXB.

Key words: line: identification – stars: evolution – stars: individual: HD 154791 – stars: late-type – stars: neutron – X-rays: stars

* Based on data collected at the Loiano Observatory

Send offprint requests to: V.F. Polcaro (polcaro@ saturn.ias.fra.cnr.it)

© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999