Lake Sonoma 2/22/03: observing MSA-227

by Jane Houston Jones

I opened the Millennium Star Atlas to page 227, and set the good book on the shelf of my painter's ladder at Lake Sonoma last night 2/22/03.

I had a particular project on this page so the page itself became my observing list for the night. That particular project will be a report in itself. I liked having only one reference to work from. Each MSA page covers an area 5.4 by 7.4 degrees. On a map of the world, France would fit in this space. :-)

First the sun set, then after astronomical twilight, the zodiacal light leaped into view. This wide triangular cone of glow requires a dark site with good transparency to spot. You may have seen it and thought you were seeing twilight since they both occur in the same area of the sky.

My first target was also home base for most of my starhops on page 227 of MSA. The Rosette Nebula, NGC2244, 2237-2239 - a showpiece object in both my 80mm Short Tube 80 finder with a OIII filter in the 25mm eyepiece, as well as in the 31 Nagler with OIII, and even naked eye, holding the filter to my eye. Only a portion of the whole nebula was visible in the 65x view through the 31 mm Nagler. Most everyone who was interested came over for a look. I spent an hour looking at the detail in the Rosette. The open cluster, NGC2244 is comprised of hot blue stars which emit ultraviolet light that knocks electrons away from hydrogen atoms. When the electrons fall back, they emit the red light which distinctively defines the glow of all emission nebulae. It is easy to see, appearing large as the full moon. The naked eye can see the cluster in a transparent sky like we had last night.

Hubble's Variable Nebula, NGC2261 - the variable star R Monocerotis is the infrared source of the nebula, which is only one half of the bi-polar outflow of this star. The core and nebula are highly variable on a timescale of a few months or more. The star is buried in a pocket of dust 200 AU across. The inner disk surrounding R Mon is about the size of our own planetary system. I wonder if there are planets forming there?

Plaskett's Star, HD47129 - the most massive binary star ever discovered. Situated 50 million miles apart or about half the earth/sun distance, the companion orbits every 14 days. Comprised of two O stars, the total mass of the system is that of 100 suns. Plaskett's star is likely a part of NGC2244 - the central cluster of the Rosette Nebula. Mag 6, visible in binoculars one degree north of the Rosette Nebula

NGC2264 and S Monocerotis - The region around the 4.7 magnitude type O star S Monocerotis is a fascinating mixture of red fluorescent hydrogen and dark, obscuring dust lanes. Some dust patches are close enough to bright stars to reflect light from them. Some of the wispy tendrils of nebulosity are Herbig-Haro objects, jets of matter ejected from newly-formed stars still hidden within the nebula. About 250 stars have been recognised as members of NGC 2264 which is 2700 light years distant. At the eyepiece, we see the mag 3.9 Christmas Tree cluster with S Mon as the tree trunk. The cluster is surrounded by emission nebula and under excellent transparent skies, the elusive Cone Nebula may be visible. But not to the observers at Lake Sonoma. Some of us did, however, see some of the wispy Herbig-Haro objects visible as horizontal streaks in the nebulae below S Monocerotis.

Trumpler 5 - makes a triangle with Hubble's Variable Nebula, S Mon and nebulosity. Tr 5 is an faint open cluster, 125 million years old.

NGC2236, mag 11.09 open cluster looked like a snail, an upside down curl of 50 stars with two pairs of brighter stars, which I could imagine were the snails antennae and ugg, slime trail. Several people came over for a look at this one. Nice!

NGC2251 and NGC2254 are bisected by a line of bright stars reminiscent of the Coathanger asterism, Collinder 399. If you have Millenium Star Atlas, check out page 227 to see what I mean. I kept bumping into the line of stars, so it was easy to differentiate larger mag 7.3 NGC2251 from smaller mag 9.7 NGC2254. NGC 2254 is 2.2 degrees south of the Christmas Tree cluster. Much smaller NGC 2254 is a degree south of this.

Collinder 106, home of Plaskett's star, its brightest member is 2 degrres north of NGC 2252, another open cluster

FU stars - yes I am talking FU Orionis objects. These are young Sun-like stars which are temporarily acrreting material at rapid rates from their surrounding disks of gas and dust. They brighten by a hundred times, stay bright for a century and fade again. The are a violent subclass of T Tauri stars. Each protostar probably goes through this sequence many times before the accretion disk and surrounding cloud are dispersed. Steve Gottleib was showing FU Orionis in his telescope. I had a FU star on my page 227 project too. I resisted the urge to say something silly, observing being a very unsilly hobby. But I called everyone over to see my FU too. :-) FU Monocerotis, that is. There are only ten FU Orionis objects known, and we had seen two of them at Lake Sonoma. Both of them were reddish and surrounded with a very faint nebulosity. FU Orionis was the AAVSO variable star of the month Feb 2002.

T, RW, RW, SV, CV, SW, BE and AX Monocerotis were other interesting stars I checked off on Page 227 last night.

NGC2259, NGC2252, CR111, IC448, CR97, CR96, CR92, CR104, CR107, CR110 Do22, IC2169 were other open clusters in this part of the Winter Milky Way I observed and checked off.

To end the night, I aimed at M-42 using the O-III 31mm Nagler combo, and invited anyone over who wasn't already tired of this object. I noticed Hydra and tried to add one to my Hickson project. I easily found Abell 1060/Hickson 48. I could see a few faint smudges here, mag 13.2 IC2597 and I suspected 48B a small round smudge with my old 9 Nagler for 222x.

A few galaxies were all I wanted to look at last night. I really enjoyed visiting the suburbs of our own Milky Way Galaxy as described on page 227 and adjacent pages of the Millenium Star Atlas.

Millenium Star Atlas info:

DateFebruary 22, 2003, 2002 6:45 p.m.- midnight
LocationLone Rock Flat, Lake Sonoma, California
Lat/Long38 42' 54.7" , 123 02' 43.7"
Altitude900 ft.
Instrument17.5-inch f/4.5 LITEBOX reflector
Ocularsmostly 16 mm Nagler for 125 power, 82 degrees apparant f.o.v
Seeingvery good, very steady deteriorating after 10:00 p.m.
TransparencyLM 6.2 using LM Area 3: 23-Theta-Beta-U Ma, 16 stars at 8:00 p.m. but transparancy deteriorated after 10:00 p.m. Temps 65 degrees at dusk, 41 degrees at midnight, humidity from low 70's to "high" aka "wet" at midnight when we packed up.