Expanding nebulae and their cores

How long do planetary nebulae last? And how bright are they at their
brightest?

As of now, there are no planetary nebulae visible from Earth. The
brightest is 8th magnitude. The reason being that planetary nebulae
are shortlived, thus rare, so all are distant.

Compare with Crab. It is 8th magnitude now. The star is magnitude 16.
It is more distant, and therefore intrinsically brighter, than most
planetary nebulae. It also expands much faster.

It is thought that 200 years ago, in time of Messier, Crab would have
been brighter than now. How bright then?

How bright would Crab have been in 1154? 1064?

When exactly did Crab Nebula pass 6th magnitude?

It is said to have been visible for merely 650 days. Yet at its
brightest, it was magnitude -6.

What was the brightness of Crab back in 1053?

Now, for planetary nebulae - they do not have such short brightness
maxima. How long does the formation of a planetary nebula take?

The most visible white dwarf is Keid B. It is the brightest white
dwarf except Sirius B, and it does not have so bright or so nearby A
star.

Keid A is also dimmer and more distant than Procyon A - but Keid B is
brighter and hotter than Procyon B. The temperature is about 7500 K
for Procyon B, and 13 500 K for Keid B.

Procyon B is about 1,7 milliards of years old. Keid B must be younger.
How old?

What is the distance between Keid A and B? Which of them is closer to
us?

How fast are the moving and accelerating now? What is the minimum and
maximum distance between Keid A and B?

Keid B is about 0,5 solar masses now. It is supposed to have been 1,5
solar masses or so on main sequence.

What was the orbit of Keid A doing while Keid B had a planetary
nebula? What was the orbit like previously?

How would Keid B planetary nebula have looked from inside, like from a
planet near Keid A?

wrote:

How long do planetary nebulae last? And how bright are they at their
brightest?

As of now, there are no planetary nebulae visible from Earth. The
brightest is 8th magnitude. The reason being that planetary nebulae
are shortlived, thus rare, so all are distant.

Compare with Crab. It is 8th magnitude now. The star is magnitude 16.
It is more distant, and therefore intrinsically brighter, than most
planetary nebulae. It also expands much faster.

Well, sure. The Crab Nebula is from a supernova. It's not a planetary
nebula, you know.

--
Erik Max Francis && && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM, Y!M erikmaxfrancis
Freedom is never voluntarily given by the oppressor.
-- Dr. Martin Luther King, Jr.

On Sat, 21 Apr 2007 10:12:38 +0100, chornedsnorkack wrote:

How long do planetary nebulae last? And how bright are they at their
brightest?

Optically 1-30 ky but in X-ray some has been estimated to be 150 ky old.
See :
Sokar N, Planetary nebulae, Scientific American (May) 1992; 266 (5): 36
Astronomy (June) 1993; 21 (6): 18

Planetary nebulae supposedly do not exceed a specific brightness (can't
give you a figure right now). This was once used for measuring the
distance of galaxies outside the local group.

See: Freedman W, Expansion rate and the size of the Universe, Scientific
American (November) 1992; 267 (5): 30


--
gautam

Gautam Majumdar kirjutas:
On Sat, 21 Apr 2007 10:12:38 +0100, chornedsnorkack wrote:

How long do planetary nebulae last? And how bright are they at their
brightest?

Optically 1-30 ky but in X-ray some has been estimated to be 150 ky old.

1000 years?

Then you should expect some to vanish over centuries - and some to
form over centuries or shorter. Do they form?

On Apr 21, 2:12 am, wrote:
Keid A is also dimmer and more distant than Procyon A - but Keid B is
brighter and hotter than Procyon B. The temperature is about 7500 K
for Procyon B, and 13 500 K for Keid B.

13+500 = 513. Liar.

Procyon B is about 1,7 milliards of years old. Keid B must be younger.
How old?

It is /not/ 1+7i "milliards" of anything, ****headed liar!

Keid B is about 0,5 solar masses now. It is supposed to have been 1,5
solar masses or so on main sequence.

liar! cretin!

On Apr 22, 10:53 am, Gautam Majumdar wrote:
See: Freedman W, Expansion rate and the size of the Universe, Scientific
American (November) 1992; 267 (5): 30

Don't còlòniz runons.

On Mon, 23 Apr 2007 17:01:33 +0100, chornedsnorkack wrote:


Gautam Majumdar kirjutas:
On Sat, 21 Apr 2007 10:12:38 +0100, chornedsnorkack wrote:

How long do planetary nebulae last? And how bright are they at their
brightest?

Optically 1-30 ky but in X-ray some has been estimated to be 150 ky
old.

1000 years?

Then you should expect some to vanish over centuries - and some to form
over centuries or shorter. Do they form?

One possibly being watched forming right now - called Sakurai's star. See
this article for details of that star and many other aspects of planetary
nebula.

Weinberger R, Kerber F, Planetary nebulae: understanding the physical and
chemical evolution of a dying star, Science 1997; 276: 1382

--
gautam

Gautam Majumdar kirjutas:
On Mon, 23 Apr 2007 17:01:33 +0100, chornedsnorkack wrote:


Gautam Majumdar kirjutas:
On Sat, 21 Apr 2007 10:12:38 +0100, chornedsnorkack wrote:

How long do planetary nebulae last? And how bright are they at their
brightest?

Optically 1-30 ky but in X-ray some has been estimated to be 150 ky
old.

1000 years?

Then you should expect some to vanish over centuries - and some to form
over centuries or shorter. Do they form?

One possibly being watched forming right now - called Sakurai's star.

A few other young nebulae:

Stingray Nebula

FG Sagittae

CRL 618

For example, FG Sagittae brightened from 13,7 to 9,1. Then dimmed to
16 or so... I think that at the distance of about 2500 pc, 9,1
represents about absolute magnitude -3, or 1000 times solar luminosity.