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A stellar youngster

Z Canis Majoris is a young stellar object, one of the "Orion variables".  The Orion variable classification got its name because the Orion region is so full of active and recent star formation that many of the young, eruptive variables are found there.  Since these stars are eruptive, they're usually classified as Irregular or "I", and since many are also found in regions with nebulae, they also have an "N" for nebular attached.  There are a number of subclasses of stars in this category, including perhaps the most famous, "INT" -- T Tauri stars.  The specific classification given to Z CMa is "INA", which in plain text is simply "irregular, nebular variable, with early spectral type" (Z CMa has a spectral type of B8 -- slightly hotter than Vega which is an A0).

Z CMa is an example of a star that bears watching for years and decades.  The AAVSO has visual data starting around 1928 and continues through the present. One of the most striking things about the light curve is the decades-long, parabolic change in mean light, slowly brightening from magnitude 10 in the early 1940s, rising to magnitude 9 by the late 1960s, and then falling back down to magnitude 10 by the mid 1990s.  Since then, the light curve has been punctuated by a number of short, high-amplitude outbursts -- one of which is going on right now.  If you're a visual observer, this is an interesting one for your long-term program, and CCD observers who can do calibrated, transformed multicolor photometry might find it interesting to follow the light and color changes over time.

We recently issued a Special Notice (#232) on Z CMa after AAVSO observer John Bortle pointed out that the star has apparently reached another bright maximum above magnitude 8.  It will be interesting to follow this star over the coming months.  It will probably be interesting to follow it over the coming decades, too!

Another AAVSO observer, Steve O'Connor, sent me this photograph of the field taken on 2011 January 27.  Z CMa is the pale yellow-white star at the center of the field, and a comparison of the image with a D-scale chart makes it clear that it's much brighter than the "86" comp to the southeast.  This is a good time of year to observe Z CMa, so give it a try if you have room for it in your observing schedule!

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484