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5h 4h30m 4h Riqht Ascension a

4h38m30s Right Ascension a

4h38m30s Right Ascension a

Figure 1.12 The dense core TMC-1C, as traced by the 1.3 cm line of NH3.

The relative isolation of the young stars in Taurus-Auriga, together with the proximity of the region, have allowed more detailed study of individual stellar formation than in Orion. In particular, molecular transitions sensitive to higher densities than CO have been used effectively to examine the region's dense cores. Figure 1.12 is a radio map of TMC-1C, one of several subcondensations within TMC-1. The observations here were made in the 1.3 cm line of NH3, which traces gas number densities near 104 cm-3. In central density, linear extent, and total mass, the Taurus-Auriga dense cores are similar to most of those traced by CS in Orion, but no very massive fragments are detected.

The dense core shown in Figure 1.12 does not contain a young star, but over half of those observed in NH3 have infrared point sources in their central regions. These embedded objects represent an earlier evolutionary stage than the visible T Tauri stars. Interestingly, most of these infrared stars are associated with molecular outflows. Figure 1.13 is a CO map of the dark cloud L1551, which the reader may locate in Figure 1.9. The striking bipolar lobes represent cloud gas being dragged to great distances from the central infrared source, which in this case is an embedded binary pair known collectively as IRS 5. These stars, with a total luminosity of less than 30 Lq, have a combined mass under 2 Mq. In contrast, a high-mass star or group of stars is creating the outflow in the Orion BN-KL region. Discovered in 1980, the L1551/IRS 5 system was the first detected low-mass outflow, of which hundreds are now known. Indeed, the high frequency of outflow observations probably indicates that every star turns on a powerful wind before it is optically visible.

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