Friday, November 26, 2010

Carbon Stars, cold weather and other notes...

Thanksgiving has brought very cold temperatures to the Lost Pleiad Observatory.  Thanksgiving day saw a high temperature of 56 degrees, the lowest high temperature since the mid 1970's!  Last night was quite cold with temperatures dropping below freezing for the first time this winter.  Overall, this low pressure system has created fairly poor seeing conditions...however, holidays mean lots of free time to observe as well as markedly reduced light pollution from Tucson.

Last night, I decided to do some observing with my TEC 140 prior to moon rise.  I was rewarded with some of the darkest skies I have seen in the observatory in a long, long time.  Not only were businesses around town closed, but there must have been no one on the roads as the light dome over Tucson was perhaps 25% of its usual brightness, maybe less.  Two observations from last night are worth reporting here.  First, I wanted to find a nice Carbon Star that I could use while leading programs at the Mount Lemmon Sky Center.  Carbon stars are late-type giant stars whose atmospheres contain more carbon than oxygen.  The chemical reactions that take place in the upper layers of the star result in increasing production of carbon compounds, surrounding the star with a "shell" of carbon dust.  This leads to a ruby red like appearance at the eyepiece.  While there are hundreds of these stars known, some of the more famous ones are Mu Cephei, R Leporis, and T Lyrae.  I have been showing T Lyrae during programs, and R Leporis is not quite high enough in the sky yet to utilize.  Mu Cephei is too bright and most observers see it as simply a bit more orange than Betelgeuse in Orion.

If you are interested in observing some of these stellar gems, I'd suggest you visit this webpage which contains a list of carbon stars brighter than visual magnitude 8.5.  The image to the left is of a carbon star in the constellation Canes Venatici and was created by Greg Parker and Noel Carboni of the New Forest Observatory.  I decided to have a go at S Cephei, a long period Mira type variable star.  It's listed as magnitude 7.5  - 12.9 and has a period of 487 days.  Mira type variables are characterized (among other things) by very red colors and are in very late stages of stellar evolution.  These stars will eventually shed their outer layers and become planetary nebula.  S Cephei is currently around magnitude 9 - 9.5 and fading.  It appeared as a brilliant gemstone like red in the eyepiece and will be a very useful example of a carbon star in my programs.

The second Thanksgiving observation I'd like to share is that of NGC 253, the Sculptor Galaxy.  I have observed this object many times in just about every telescope I have owned.  It is a very large spiral galaxy in an intense star birth phase.  It is remarkable in the eyepiece as it reveals extremely complex dust lanes throughout.  Recently I observed it through the 32" Schulman telescope at the Mount Lemmon Sky Center, and was treated to more detail than I could ever capture with pencil and paper.  I wondered how it would look in my 140mm refractor, and last night was perfect for this as the constellation rides low in the south, where typically the light pollution is at its greatest from my location.  I made the sketch below at 75x with a 13mm eyepiece.  To the right of my sketch is an image of this galaxy, taken from the Mount Lemmon Sky Center (south is up in the image, down in my sketch).

Copyright Adam Block/Mount Lemmon SkyCenter/University of Arizona

Finally, speaking of the Mount Lemmon Sky Center, todays Astronomy Picture of the Day features NGC 2024, the Flame Nebula as imaged by my colleague Adam Block at the Mount Lemmon Sky Center.  This is the first MLSC image chosen by the APOD folks since the installation of the 32" Schulman telescope...check it out!

1 comment:

  1. Although it is the brightest, reddest, naked-eye star in the sky, Mu Cephei is NOT in fact a Carbon star.
    Greg Parker