[AZ-Observing] Re: [amastro] query about SN's in general
- From: "Richard Harshaw" <rharshaw2@xxxxxxx>
- To: <az-observing@xxxxxxxxxxxxx>, <amastro@xxxxxxxxxxxxxxx>, <haclist@xxxxxxxxxxxxxxx>, <taaaforum@xxxxxxxxxxxxxxx>
- Date: Sat, 27 Aug 2011 08:02:26 -0700
I wonder if the SN rate can be estimated from models of stellar evolution?
For instance, there are about 1,500 to 2,000 known planetaries in the Milky
Way (and I assume that allows for those that are obscured by foreground
material???). We know the planetary phase of a <3 Solar mass star is a
rather short span (~100,000 years I have read). Given the presence of about
200 billion solar type stars in the Milky Way and the average life span of,
say, 10 billion years, it should be possible to predict the number of PNs at
any one time using a Gaussian distribution? I would not be surprised if
that number came up to around 2,000.
Same thing could be tried for the SN frequency. How many of the 200 billion
stars in a typical Milky Way class galaxy are large enough to make
supernovae? What is the lifetime of these stars relative to their masses?
It should be fairly easy from this to estimate the SN frequency rate. Maybe
this is what has lead to the 1 per 300 years (one I have read) to 1 per 100
years, and so on?
Does anyone in the professional readership of these lists know?
Richard Harshaw
Cave Creek, Arizona
Brilliant Sky Observatory
-----Original Message-----
From: az-observing-bounce@xxxxxxxxxxxxx
[mailto:az-observing-bounce@xxxxxxxxxxxxx] On Behalf Of Wayne (aka Mr.
Galaxy)
Sent: Friday, August 26, 2011 11:53 PM
To: amastro@xxxxxxxxxxxxxxx; az-observing@xxxxxxxxxxxxx;
haclist@xxxxxxxxxxxxxxx; taaaforum@xxxxxxxxxxxxxxx
Cc: dpatchick@xxxxxxxxxxxxxx
Subject: [AZ-Observing] Re: [amastro] query about SN's in general
Benson, AZ 85602
hm ph: 520-586-2244 As usual, good references, Brian. I usually quote a rate
of about 1 SN per 100 years in a galaxy the size of our Milky Way as a very
rough estimate. Astrophysicists use sparse statistics to calculate the SN
rate. I don't know the mathematical rationalization for this technique, but
would think that the numbers just aren't large enough to make more than a
good guess. Anyway we need more eyes on the sky to improve those numbers!
Just for grins I just went outside tonight to see whether the area around
M101 would still be accessible from my location. As luck would have it, the
Big Dipper was still quite visible and the handle was about 10 degrees above
the horizon. Earlier we had a good monsoonal deluge for about 30 minutes so
the skies were scrubbed fairly clean. However, the humidity was still fairly
high and there were still a few lingering clouds in the WNW and the glow of
Tucson in that direction was a nuisance. I was not able to see M101 in my
finder sc
ope but I knew the area pretty well and pointed close to it. To my
surprise I was able to see M101's nucleus readily in my 13-inch and, sure
enough, I could see the new SN easily about 4' SSW of the galaxy's nucleus.
There is an approximately magn 12 foreground star about 1' NNE of the
nucleus. If you draw a line from that star through the nucleus and extend
that line about 4 times you'll come across another star that is about the
same brightness (at least tonight at 11pm local AZ time); that second star
is the new SN. It lies between two foreground stars that are about magn 13
and difficult under the conditions I had to observe. I would say the SN
should be visible in a 4-inch reflector if you have good dark skies. So it
looks like good friend and fellow SN discoverer, Dana Patchick, got his wish
for the M101 SN to be visible in his telescope this weekend! Two nice SNe in
two prominent Messier galaxies in the past few months, what a treat! Enjoy.
Make sure you look at some
of the images that are sure to appear in David Bishop's informative Bright
Supernovae website: http://www.rochesterastronomy.org/supernova.html
Clear skies,
Wayne (aka Mr. Galaxy)
---------- Original Message ----------
From: Brian Skiff <bas@xxxxxxxxxx>
To: amastro@xxxxxxxxxxxxxxx
Subject: Re: [amastro] query about SN's in general
Date: Fri, 26 Aug 2011 18:19:08 -0700
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none;"> </span></p> <!--~-|**|PrettyHtmlStartT|**|-~--><div
id="ygrp-mlmsg" style="position: relative;"><div id="ygrp-msg"
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id="ygrp-text"><p><br>On Fri, 2011-08-26 at 21:49 +0000, GN wrote:<br>>
Jeezes the supernovae in the local group are like waiting for buses in NYC:
they always arrive in bunches. M51 and now M101. <br>> <br>Of course
neither M51 or M101 are in the Local Group, but lots<br>farther away, but
maybe you might consider anything closer than,<br>say, 10 Mpc to be pretty
nearby.<br><br>> The M101 SN makes me wonder: in any ONE galaxy, about
how often would we expect (on average) a supernova? Every ten years? Every
hundred? ...thousand?<br>> <br>> Obviously the way to find supernovae
is to examine galaxies by the bucketful. But to have them popping out like
popcorn kernels f
rom local face on Messiers, that's really something. My guess is that
face-on galaxies give better detection probability than edge on.<br>>
<br>> Or maybe it's a local group financial meltdown and the SNs are the
hardcore resistors who won't put up with stellar foreclosure. <br><br>Have a
look at papers on the subject by Sidney van den Bergh,<br>such as one based
on Bob Evans' visual supernova hunt of about 800<br>Shapley-Ames
galaxies:<br><br>Revised supernova rates in Shapley-Ames galaxies<br><br><a
href="http://adsabs.harvard.edu/abs/1989ApJ...345..752E";>http://adsabs.harva
rd.edu/abs/1989ApJ...345..752E</a><br><br>See also Evans' brief
summary-of-a-summary, which may have the<br>bottom line you're looking
for:<br><br><a
href="http://adsabs.harvard.edu/abs/1992JAVSO..21...52E";>http://adsabs.harva
rd.edu/abs/1992JAVSO..21...52E</a><br><br>...and yet another follow-up using
Evans' visual survey results:<br><br><a
href="http://adsabs.harvard.edu/abs/1999A&A...351..45
9C">http://adsabs.harvard.edu/abs/1999A&A...351..459C</a><br><br>\\Brian
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