MS 1603.6+2600 : a unique low-luminosity X-ray binary ?
Abstract
The evolutionary stage of the eclipsing binary system MS 1603.6+2600 (P = 112.5 min) is discussed and its observed properties reviewed. Three possible Low Mass X-ray Binary (LMXB) evolutionary sequences are discussed. In the first alternative MS 1603.6+2600 has a hydrogen rich secondary and evaporation is uneffective in the period gap. It is evolving along either the CV - like (non-degenerate) or the hydrogen- degenerate sequence. In the CV - like hydrogen non-degenerate sequence the mass accretion rate is relatively high (1O-10 Msun/y) leading to a burster phenomenon with the recurrence time between 10-20 hours.
In the second alternative MS 1603.6+2600 has a hydrogen rich secondary and is in a stage after incomplete evaporation (due to hard pulsar radiation) in the period gap. It is evolving along the hydrogen - degenerate sequence. In the degenerate case the eclipsing millisecond binary pulsar PSR 1744-24A (P = 1.8 h) could be a progenitor of MS 1603.6+2600. In the third alternative MS 1603.6+2600 has a helium rich secondary evolving through the 2h-3h period gap (as a LMXB and without evaporation) towards ultra-short orbital periods. In this evolutionary picture MS 1603.6+2600 could be a progenitor of MXB 1916-05 and should appear as an X-ray transient with the recurrence period of several years. If MS 1603 is a CV system then the last alternative (the system with helium rich secondary) may be applied to explain the observed relative strengths of the helium lines compared to the hydrogen ones (Morris et al. 1990). Determination of the orbital period derivative and further X-ray spectral and optical observations could make the choice between the different alternatives.- Publication:
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Astronomy and Astrophysics
- Pub Date:
- October 1993
- Bibcode:
- 1993A&A...277..483E
- Keywords:
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- stars: binaries: close - stars: evolution - stars: individual: MS 1603.6+2600 - catalysmic variables - X-rays: stars