FU Orionis! (Lake Sonoma 22 Feb)

by Steve Gottlieb

We had a large, enthusiastic turnout Saturday night at Lake Sonoma (Grey Pine Flat) with good sky transparency and seeing along with very comfortable temperatures -- couldn't ask for more from a February evening.

One of the highlights of the evening for me was FU Orionis. FU is the prototype of a class of variables similar to young T Tauri stars and are generally found within bright or dark nebulae. In this case, FU is centered in a faint, reflection nebula Cederblad 59. Cederblad 59 is itself centered in a Barnard dark nebula, B35! More on FU Orionis can be found in Burnham's although the information may be somewhat dated now.

Ced 59 05 45 22.4 +09 04 11 Size 3x2

17.5": this is a faint, cometary nebula surrounding reddish FU Orionis. Appears as a very low surface brightness halo, ~2' diameter around a 10.5-11 mag star. A couple of mag 10.5 stars ~13' SW provide a good reference to compare for scattered light around similar stars. It was evident that the glow around FU was real, although there was no structure. FU is situated with a large, mostly starless dark cloud B35.

Barnard 35 05 45 30.7 +09 04.0 Size 20x10

17.5": B35 appears as a large, 20'x10' darker region containing FU Orionis. Shows up best at low power (100x with 20 Nagler or 64x with 31 Nagler) as a large, slightly darker oval region, extended 2:1 E-W. The edge of the dark nebula is fairly sharply defined against the richer milky way background glow of the surrounding fields. A few brighter mag 11 stars are at the northern edge of B35.

Jane Houston was so taken with the view of FU Orionis, that she was inspired to track down FU Monocerotis, which was on the chart of the Uranometria she was working on! It was that kind of night.