Red stars in NGC 884

As has been pointed out elsewhere, open clusters are considered to be
relatively young with stars of blue and white. So what's the deal with the
high population of red stars in NGC 884 (one of the clusters in the double
cluster). I've seen red stars in other open clusters, like the bright core
star of M37.

Is there a relationship between red (carbon?) stars and planetary nebulae?
Are all carbon stars potentially remnants of planetary nebulae? If so, maybe
the central star of the planetary nebula in M46, will appear red in the
future, having blown off some of its shell. Sort of a premature aging.

Are all red stars carbon stars?

Curious,
Stephen

Stephen Paul wrote:

As has been pointed out elsewhere, open clusters are considered to be
relatively young with stars of blue and white. So what's the deal with the
high population of red stars in NGC 884 (one of the clusters in the double
cluster). I've seen red stars in other open clusters, like the bright core
star of M37.

There can be a few red giant stars in open clusters. This is a key to
actually getting the age of these groups, as the more red giants they have,
the older they tend to be. Most of the stars in NGC 884 are younger lower to
moderate-mass stars, but the cluster is just old enough that the most massive
stars which were formed early in the cluster's history will have evolved off
the main sequence to become red giants (or in some cases, red supergiants).
The more massive the star, the faster its evolution goes, so with a relatively
high-mass star, it can become a red giant while its less massive neighbors are
still puttering along nicely on the main sequence. Some open clusters are
very old (like M67 or NGC 188 for example), so they can contain a lot of red
giants and very few (if any) blue stars.

Is there a relationship between red (carbon?) stars and planetary nebulae?

Well, not immediately. Eventually, red giants may give rise to planetary
nebulae as their outer atmospheres become unstable and their cores collapse,
but you will find very few red stars at the cores of most planetary nebulae.
Most of these central stars are hot pre-white dwarf stars. Carbon stars are
usually just cool giants with a lot of Carbon compounds showing up in their
spectra (which tends to make them redder due to the Carbon compound absorption
bands).

Are all red stars carbon stars?

No, red dwarfs and some red giants are not Carbon stars, but the very reddest
stars you will see in a telescope will often tend to be Carbon stars. I like
V Aquilae, TX Piscium, and R Leporis as probably the reddest stars I have ever
seen. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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"Stephen Paul" wrote in message ...

As has been pointed out elsewhere, open clusters are considered to be
relatively young with stars of blue and white. So what's the deal with the
high population of red stars in NGC 884 (one of the clusters in the double
cluster). I've seen red stars in other open clusters, like the bright core
star of M37.

Well, that varies a lot depending on the cluster. Some clusters, like
the Pleiades, are genuinely young, and still haven't evolved any red
giants worth speaking of. Most open clusters are old enough so that a
few of the stars -- the brightest and most massive, which burn fastest --
have evolved into red giants. Most often, you find those at or near
the center of the cluster, because heavy stars tend to "sink" due to
orbital dynamics, while light stars tend to rise -- and eventually
"evaporate". M37 is an excellent example; it has a single red star
almost dead center which is about a magnitude brighter than any of
the cluster's other stars.

Although open clusters are young compared to globulars, some of them
have ages that are significant fractions of the universe's age, like
M67, which is around 5 billion years old.

In general, you can tell young clusters by the preponderance of blue
stars. Blue stars (O and B) burn out in times ranging from 1 million
years to 100 million years, so any cluster with them has to be young.
Also, young clusters tend to be dominated by a handful of very bright
stars -- the Pleiades or M36 being good examples. Old open clusters
look more like globulars, with dozens or hundreds of stars only one
or two magnitudes fainter than the brightest star. That is because
the most massive stars have already gone through their main-sequence
lives and their red-giant lives, and are now white dwarfs or neutron
stars, emitting very little light.

- Tony Flanders

Many thanks to you and David.

Stephen Paulwrote



Is there a relationship between red (carbon?) stars and planetary nebulae?
Are all carbon stars potentially remnants of planetary nebulae? If so, maybe
the central star of the planetary nebula in M46, will appear red in the
future, having blown off some of its shell. Sort of a premature aging.

It's the other way around, to some degree. Red stars must be
very cool. The only very cool stars we can see at the distance
of any open cluster are red giant stars. These stars have run
out of hydrogen in their core, and are fusing helium their
cores (or about to fuse helium, or just finished fusing helium).
The outer layers of the stars puff out to tens or hundreds of times
their size during the hydrogen-fusing stage, growing much cooler
and redder. In a small fraction of these red giants, carbon
atoms which are formed in the core are transported to the
envelope, making carbon stars.

Because the outer layers of the atmosphere are so far from the
center of the star --- where most of the mass lies --- they are
held only weakly by the gravity of the star. Instabilities
in the atmosphere cause many red giants to develop pulsations;
in some cases, the motions grow until the outer layers are blown
clear off the star and float into space, making planetary
nebulae.

So, actually, some carbon stars may turn into planetary
nebulae.

Are all red stars carbon stars?

No, very few.


Michael Richmond

"Stephen Paul" wrote in message ...
So what's the deal with the high population of red stars in NGC
884
(one of the clusters in the double cluster).

The reddened M class supergaint stars you speak of can be seen in
online color photographs of the two components of the Perseus Double
cluster - NGC884 (the chi Persei cluster) and NGC869 (the h Persei
cluster), all accessed in 2/2004, e.g. -

Mike Halderman's photos:
http://www.mrh.org/20021115-05.html
http://www.mrh.org/39-10.html

Jerry Xiaojin Zhu's photos:
http://www-cgi.cs.cmu.edu/~zhuxj/ast...ngc884869.html

Bruce Glagola's photos:
http://www.glagola.darkhorizons.org/...my/double.html

A Webda online color-magnitude (C-M) diagram for open cluster's NGC
884 (the chi Persei cluster) and NGC 869 (the h Persei cluster) also
shows the outlier reddened stars.
http://obswww.unige.ch/webda/cgi-bin...gc0884+NGC+884
http://obswww.unige.ch/webda/cgi-bin...gc0884+NGC+869

Some articles that can be read online at the NASA astronomical
database site (ADS) discuss these M class supergaints. Hopefully, I
have correctly interperted their content.

---------------------
Wildey, Robert L. 1964. The Stellar Content of H and Chi
Persei-Cluster and Association. ApJ S8:439 (1964)
NASA ADS link:
http://adsabs.harvard.edu/cgi-bin/bi...%2E8%2E%2E439W

Wildey (1964) provides a more detailed raw C-M diagram for the chi
Persei Cluster (NGC884). Wildey at Fig. 17, page 489. He also shows
a schematic of the key C-M diagram components. Fig. 20 at 492. His
key conclusion, at pages 496-497, is that there were three star
formation events at 7, 17 and 60 million years ago in NGC884. They
are evidenced by three bright star sequences seen in his color
magnitude schematic, Figure 20, above absolute magnitude -4.0. Wildey
concluded that the supergaint helium burning M class stars represent
the aged and early-formed supergaints from a first star formation
event 60 million years ago.

---------------------
Schild, Rudolph. 1967. Ages and Structures of Stars in the H and Chi
Persei Association. ApJ 148:449
NASA ADS link:
http://adsabs.harvard.edu/cgi-bin/np...p;db_key=A ST

Schild (1967) provides a schematic diagram of the 2D structure of h
and chi Persei clusters in parsecs distances. Schild at 456. Schild
concluded that the first star formation event which created the large
O Stars in nucleus of the h Persei cluster (NGC869) occured about 6.5
million years ago. Those stars spread out uniformly out between the h
and c Persei clusters. About 11.5 million years ago, a previous
stellar formation event created the nucleus of the chi Persei cluster
and the older (reddened M) supergaints near the core of chi Persei
cluster. Unlike Wildey, Schild felt that the larger M class stars
dispersed outside the core of chi Persei (NGC884) were not part of the
cluster, but were members of the general Perseus Arm. "At the same
time [11.5 million years ago], star formation may have taken place
over much more extensive reaches of the Perseus arm, and many of the
[reddened M] supergaints seen in the direction of the outer group [the
area between h and chi Persei clusters] cannot be ambigously
identified with the assocation." Schild at 456-457. Schild did not
feel there was a third creation event at 60 million years ago, as
discussed by Wildey.

--------------------
Slesnick, C.L. et al. 2002. The Star Formation History and Mass
Function of the Double Cluster h and chi Persei
ApJ 576(2):880-893
NASA ADS link:
http://adsabs.harvard.edu/cgi-bin/np...p;db_key=A ST

I have not read this newest article that showed up the NASA ADS index.
You would have to go a university library to obtain a copy.

I've seen red stars in other open clusters, like the bright core star of M37. Is there
a relationship between red (carbon?) stars and planetary nebulae?

Assuming this is one question, I believe the relationship between
open clusters and red stars primarily is age. The older the cluster,
the more stars have exhausted burning their hydrogren and have
progressed to the helium burning phase. Most open clusters are
created in the galactic plane. Their stars are gravitationally bound.
They tend to be young objects (less than 60 million years old)
composed of white-blue stars because tidal forces in the galactic
plane tend to "tear" them apart as they grow older. The kinematic
energy of the cluster's members also cause the clusters to "evolve"
into ungravitational bound moving groups - like the Hyades moving
group or the Usra Major moving group. Eventually, the kinematic
motions of the cluster's members "evaporate" all of its stars into the
"average" motion of the surrounding galactic plane. Molecular clouds
create new clusters; the cycle continues.

Occasionally, an open cluster will be created at, or will be thrown
into, the high latitudes above the galactic plane. Such clusters can
escape the ravages of galactic tidal forces and "live" to "age" into
an an older and redder open cluster. Open cluster M44 at galactic
latitude +32° is 790 million years old. M44 is currently overhead in
the winter sky, and is the best optical example, IMHO. It is one of
the reddest and oldest open clusters. It's redden faintnest also
makes M44 harder for beginner's to find. M41 at about galactic
latitude -10° is another example.

M44, Beehive Cluster in Cancer
J0840.4+1940 oc G205.92+32.48 oc
Age: 790M Distance: 160 pc
http://seds.lpl.arizona.edu/messier/m/m044.html

M41 OC in Canis Major
J0646.9-2044 oc G231.09-10.25 oc
Age: 290M Distance: 705 pc
http://seds.lpl.arizona.edu/messier/m/m041.html

Hope this answers your question. Thanks for pointing out these red
gaints around NGC884; I had seen them, but had not given them much
thought. Looking up the answer to your question gave me much more
insight into the prominent summer-autumn Double Perseus cluster.

Regards - Kurt

Stephen Paul wrote:
As has been pointed out elsewhere, open clusters are considered to be
relatively young with stars of blue and white. So what's the deal with the
high population of red stars in NGC 884 (one of the clusters in the double
cluster). I've seen red stars in other open clusters, like the bright core
star of M37.

You might be interested in the following paper on the Double Cluster red
supergiants that I published in the Journal of the British Astronomical
Association a few years ago:

http://www.tristram.uklinux.net/vari...le-cluster.pdf

Unfortunately, the photo on the first page got left-right inverted
during the publication process.

Tristram

--
http://www.tristram.uklinux.net

Tristram Brelstaff wrote in message ...
You might be interested in the following paper on the Double Cluster red
supergiants that I published in the Journal of the British Astronomical
Association a few years ago: snip

Great article. I really enjoyed it. I have always used Ptolemy's
Cluster M7 with the Double Cluster as contrasting examples of a near
cluster and two distant clusters in the summer sky. I did not realize
that the Double Cluster also contained examples of distant M
supergaints, that can be contrasted with near supergaint Anatares in
the summer sky or Mira in the autumn sky.

I have always been interested in putting together a tour list of
optical Perseus Arm tracers. The Humphreys 1970 article (ApJ 160:1149
6/1970), cited in your J. Br. Astron. Assoc. 106:5 1996 article gave
me another useful list of M supergaint tracers in Perseus Arm OB
Assocations.

Do you have any recommendations for any articles provided such a list.
I have been working with the list of optical spiral arm tracers in
Table I of Kimeswenger, An Optical Spiral Arm Beyond the Perseus arm,
Astron. Astrophys. 209:51 (1989).

Regards, Kurt

"PrisNo6" wrote in message
om...

Hope this answers your question. Thanks for pointing out these red
gaints around NGC884; I had seen them, but had not given them much
thought.

Thanks for the data. I was just poking around the sky with my 12.5" Meade
Starfinder Dob when I turned to the Double Cluster and saw a string of red
stars. It wasn't long before I saw that there was actually a large
population.

I like red stars, especially carbon stars. Also the concept of density and
rotational velocity in a neutron star is a mind boggling.

Speaking of carbon stars, I was poking around in the area of the Rosette
Nebula (could have been way off too) when I stumbled across a _very_ red
star. Any guesses, that I might be able to go back and look for it again?

Stephen Paul

Stephen Paul nous a écrit :


Speaking of carbon stars, I was poking around in the area of the
Rosette Nebula (could have been way off too) when I stumbled across a
_very_ red star. Any guesses, that I might be able to go back and
look for it again?

The nearest red stars are :
HR2308 (6h25m +14°43') spectral type N0 in Orion,
and R Cmi (07h 08m +10°01') spectral type SC5 in Canis Minor.
R Cmi must be a very red star, according to its spectral type.
A bit further, there is also TU Gem (6h10' +26°01') spectral type N3.

--
Norbert. (no X for the answer)
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