[vsnet-chat 2594] Re: VS-Chat 2587,90-92

[Brian Skiff <bas@lowell.edu>]

     Yes, it is still easy in astronomy to ask pretty simple questions for
which there is no answer in the literature, but which can be solved by some
direct observation.
     Although using SIMBAD does require getting an account, one can probably
do nearly as well exploring the literature by searching by object name in
the ADS abstract service:

http://adswww.harvard.edu/ads_abstracts.html

This provides links to scanned journals (more than one or two years old)
and to external catalogues.
     I tend to use the IRAS "colors" (flux ratios in the four bands) as a
diagnostic, but only to the extent of separating stars from nebulae.  Nearly
all IRAS sources where the 12-micron flux is > 1.5x the 25-micron flux, and
usually with _no_ detection at 60- or 100-microns, are some sort of AGB star
(semiregular, Mira, carbon star); an exception is the occasional shell around
an OB star.  Things with peak flux at 60- or 100-microns are "nebulae" of
some sort:  planetary nebulae, HII regions, some cold shells around stars,
and _galaxies_.  Usually galaxies peak at 100mu, except for the ones that
peak at 60mu!  A good example is Maffei I, which peaks at 60mu, and shows
an upper limit only for 100mu.  This is right on the galactic plane, and it
was reported by Sharpless as a galactic nebula (in the 50s), and by Lynds
as a nebula, and by Czernik as an open cluster + nebula...who would have
thought to consider it to be a galaxy?  The point is that the IRAS flux
ratios are ambiguous:  based on those alone it could quite reasonably be
a planetary nebula.  If you had found a cool variable in the neighborhood
and were checking for identifications, however, you could tell right away
that the IRAS source was a "something else" and not associable with the star.

\Brian

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