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Topic: Globular Cluster NGC 6397

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	Star Clusters
		Clusters are so old that any star higher than a G or F-class will have already evolved off the main sequence.
		The globular cluster 47 Tuc from the ground-based AAT and the HST.
		As globular clusters are generally much older than open clusters their colour-magnitude diagrams show more evolved stars.
	outreach.atnf.csiro.au /education/senior/astrophysics/stellarevolution_clusters.html (1264 words)

	Blue Stragglers in Globular Clusters
		Globular clusters are located in galactic halos, of which the Milky Way may have from 180 to 200, or more.
		The globular's core includes exotic objects such as milli-second pulsars, which are neutron stars that are rotating extremely rapidly (between 100 to nearly 1,000 times a second) as if they have the rotational energy of formerly two objects that recently merged.
		Rex A. Saffer of Villanova University and colleagues have found a blue stragger in globular cluster NGC 6397 to be three times as massive as any ordinary star in that cluster, which they and other astronomers believe must have formed from a collisional merger (Sepinsky et al, 2000; and more information and images at APOD).
	www.solstation.com /x-objects/bluestrag.htm (1152 words)

	SurfWax: News, Reviews and Articles On Globular Cluster
		Globular clusters are deficient in heavier elements, because they formed so early in the universe that heavier elements had not been cooked up in abundance in the nuclear furnaces of stars.
		Globular clusters in our own galaxy are one of the more easily viewed cosmic beasts, requiring only a small telescope or good binoculars and a dark sky.
		And, as NGC 6397 is one of the globular clusters closest to the Earth (approximately 7,500 light years away), it was possible to explore its motions in best...
	astronomy.surfwax.com /files/Globular_Cluster_Astronomy.html (2063 words)

	Globular Drawings (Site not responding. Last check: 2007-10-19)
		To illustrate just how big globular clusters are, picture this: The Rosette Nebula is a massive agglomeration of gas and dust that spans across 130 light years of space.
		NGC 362 is located just north of the Small Magellanic Cloud, and is usually overlooked because of that object's brightness and 47 Tuc's dominance.
		This globular is very bright in the eyepiece, and a marvel in medium and large apertures.
	www.belmontnc.4dw.net /globulars.htm (4671 words)

	[56.09] The Recent Disk Passage of the Globular Cluster NGC 6397 (Site not responding. Last check: 2007-10-19)
		NGC 6397 is a nearby (~2.2 kpc) core-collapsed globular cluster, currently about 0.5 kpc from the Galactic plane.
		Proper motions of several hundred stars in the field of NGC 6397 derived from thirty plates spanning 97 years show that the cluster is moving away from the disk.
		At its current Z velocity, the cluster would have passed through the disk 4.7 Myr ago, an upper limit as the gravitational attraction of the disk must have slowed it.
	www.aas.org /publications/baas/v33n4/aas199/356.htm (225 words)

	[No title] (Site not responding. Last check: 2007-10-19)
		Left A ground-based sky survey photograph of the globular cluster NGC 6397, one of the nearest and densest agglomerations of stars to Earth.
		The cluster is located 7,200 light-years away in the southern constellation Ara, and is one of 150 such objects which orbit our Milky Way Galaxy.
		Globular clusters are ideal laboratories for studying the formation and evolution of stars.
	jersey.uoregon.edu /~imamura/209/may10/DarkMatC.txt (221 words)

	Beyond The NGC
		The constellation Ara the altar, lying as it does between the contrasting wonders of galactic Scorpius and extragalactic Centaurus, is indeed an appropriate place to behold the wonders of the early winter sky.
		Its chief deity would doubtless be the giant globular cluster NGC 6397, about twice the diameter of its poor cousin-near-the-meridian, M 13.
		NGC 6215A has not been seen despite the closest scrutiny by a number of prominent ASNSW co-observers, at both Ilford and Mt White.
	www.asnsw.com /articles/bngc/bngc18.htm (805 words)

	Hubble Heritage
		Four types of stars reside within the center of the globular cluster NGC 6397.
		These stars may be very-low-mass white dwarfs, formed in the cores of giant stars whose evolution is somehow interrupted by a stellar collision or an interaction with a binary companion.
		In this Chandra true-color X-Ray image the bright white sources (and the blue source on the right most edge) are cataclysmic variables, while the bright yellow source to lower center is a thermally emitting neutron star, in a quiescent low-mass x-ray binary.
	heritage.stsci.edu /2003/21/supplemental.html (346 words)

	APOD: 2003 August 8 - Blue Stragglers in NGC 6397 (Site not responding. Last check: 2007-10-19)
		Explanation: In our neck of the Galaxy stars are too far apart to be in danger of colliding, but in the dense cores of globular star clusters star collisions may be relatively common.
		Pictured is the central region of NGC 6397, a globular cluster about 6,000 light-years distant, whose
		However, spectroscopic data show that the indicated stars, descriptively dubbed blue stragglers, are clearly main sequence stars which are too blue and too massive to still be there.
	antwrp.gsfc.nasa.gov /apod/ap030808.html (218 words)

	welcome to the astronomy news world: How old is the Milky Way?
		Stars belonging to a globular cluster were born together, from the same cloud and at the same time.
		The longer the time that passed between the formation of the first stars (or, more correctly, their quick demise in supernovae explosions) and the formation of the globular cluster stars, the higher was the Beryllium content in the interstellar medium from which they were formed.
		In fact, the technical problem to overcome is three-fold: First, all globular clusters are quite far away and as the stars to be measured are intrinsically faint, they appear quite faint in the sky.
	astronewsenglish.blogspot.com /2004/08/how-old-is-milky-way.html (1722 words)

	Harvard-Smithsonian Center for Astrophysics: Publications and Public Affairs (Site not responding. Last check: 2007-10-19)
		The new type of stars, tentatively identified as "low-mass white dwarfs," were seen in the globular cluster NGC 6397, a massive collection of stars about 6,000 light years from Earth.
		This cluster is already known to contain two classes of stars thought to have been formed by extreme stellar interactions.
		"Globular clusters have long been used to study the evolution of single stars because they contain large numbers of stars with the same age, chemical abundance, and distance from the Earth," adds Edmonds.
	cfa-www.harvard.edu /cfa/ep/pressrel/pedmonds.html (889 words)

	Globular Star Clusters
		Globular clusters are gravitationally bound concentrations of approximately ten thousand to one million stars, spread over a volume of several tens to about 200 light years in diameter.
		Globular clusters typically contain a number of variable stars, in particular RR Lyrae stars which were once called "Cluster Variables" because of their abundance in globulars.
		It is perhaps a bit surprising that almost all globular clusters seem to be of about the same age; there seems to be a physical reason that they all formed in a short period of time in the history of the universe, and this period was apparently long ago when the galaxies were young.
	www.seds.org /messier/glob.html (1933 words)

	How Old is the Milky Way ? (ESO Press Release 20/04)
		The age of the stars in NGC 6397, as determined by means of stellar evolution models, is 13,400 ± 800 million years.
		Captions: ESO PR Photo 23b/04 identifies the two stars in the globular cluster NGC 6397 for which spectra were obtained with the UVES spectrometer on the VLT (at the centre of the fields shown).
		However, it is not a member of a cluster and its age is by far not as well known as that of the cluster stars.
	www.eso.org /outreach/press-rel/pr-2004/pr-20-04.html (2166 words)

	Main-Sequence Binary Stars in the Core of NGC 6397
		Globular clusters also offer great promise for the study of binary stars (and halo binaries in particular) as such, with the possibility of more uniform samples of binaries than are available in the field.
		Then, the expected position of each star in the epoch 2 images was determined by transforming its epoch 1 position according to the most general linear transformation, minimizing the total square deviation of the transformed positions of its 25 nearest neighbor stars from their actual epoch 2 positions.
		Most notably, in the only other study of MS binaries in the core of a dense cluster (that we know of), Rubenstein and Bailyn (1997) have estimated the binary frequency in the core of NGC 6752 to be in the range 15% to 38%.
	www.physics.sfsu.edu /~abolton/poster.html (2297 words)

	Westfield State College - Dept. of Physical Science - NGC 6231 Poster (Rees) (Site not responding. Last check: 2007-10-19)
		A proper motion study of the globular cluster NGC 6397 (Rees et al., in preparation) found that the cluster passed through the Galactic disk less than 5 Myr ago.
		We have used various measurements of the absolute proper motion and radial velocity of the young open cluster NGC 6231 (often considered the core of the Sco OB1 association) from the literature to derive its three-dimensional space velocity and find that it would have been near NGC 6397's impact point at that time.
		Age determinations for NGC 6231 in the literature are consistent with its formation at the time of or soon after the NGC 6397 disk crossing.
	www.physci.wsc.ma.edu /dept/aas.html (202 words)

	pr-20-99.html
		This means that the precise distance determination to a globular cluster, from a comparison of its WD stars to more nearby WDs with well-known masses and distances, will now be possible, provided the individual properties of the cluster WDs are well determined from such spectroscopic observations [2].
		NGC 6397 are believed to be the oldest stellar aggregates in our Galaxy.
		NGC 6397 passed through and their spectra could be registered simultaneously.
	www.eso.org /outreach/press-rel/pr-1999/pr-20-99.html (1717 words)

	APOD: 2002 February 20 - Oddities of Star Cluster NGC 6397 (Site not responding. Last check: 2007-10-19)
		Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
		This star, a member of globular cluster NGC 6397, is noteworthy not just because it blinks, but because it blinks so fast and because its companion star is so atypical.
		Other collisions near the center of NGC 6397 are thought to have produced other oddities -- blue straggler stars.
	antwrp.gsfc.nasa.gov /apod/ap020220.html (139 words)

	APOD Search Results for "globular cluster" (Site not responding. Last check: 2007-10-19)
		Globular star clusters like M55 roam the halo of our Milky Way Galaxy as gravitationally bound populations of stars known to be much older than stellar groups found in the galactic disk.
		NGC 604 was so large, however, it could form enough stars to make a globular cluster.
		Globular clusters only 40 millions of years old can still be found in the neighboring LMC galaxy, though, but perhaps none so unusual as NGC 1850.
	www.star.ucl.ac.uk /cgi-bin/apod_search?globular+cluster (9697 words)

	ESA - New Science website - First view of a newborn millisecond pulsar? (Site not responding. Last check: 2007-10-19)
		The artist's impression shows the pulsar (seen in blue with two radiation beams) and its bloated red companion star in the globular cluster NGC 6397.
		Scientists believe that the best explanation for seeing a bloated red star instead of a 'quiet' white dwarf in the system is that the pulsar only recently has been spun up to its current rotation speed of 274 times per second by the gases transferred by the red star.
		The cluster is home to a highly unusual system consisting of a fast spinning pulsar and a bloated red companion star.
	www.esa.int /esaMI/SPCS/ESAU80VTYWC_3.html (327 words)

	Long NGC 6231 distance
		We submit that NGC 6397 may have had the opportunity to trigger the formation of NGC 6231, and Wallin et al.
		To determine if this case is really winnable, the large uncertainties in the locations of NGC 6397 and NGC 6231 at the time of the crime need to be better constrained.
		In the meantime, determinations of the Galactic orbits of the clusters could be used to constrain how close they came in the past, but care should be taken to avoid model-dependent errors due to any particular choice of Galactic potential.
	www.physci.wsc.ma.edu /dept/aasrees/ngc6231aasposter.htm (2085 words)

	NGC 6397 (Site not responding. Last check: 2007-10-19)
		Globular cluster NGC 6397 (= Lacaille III.11 = Dunlop 366 = Bennett 98), class IX, in Ara
		This conspicuous globular is one of the two nearest to us (the other one is M4); currently it seems that M4 is a bit closer: M4 is at about 6,800 and NGC 6397 at 7,200 light years, but the uncertainty is large enough that the sequence may change..
		NGC 6397 is one of the at least 20 globulars of our Milky Way Galaxy which have undergone a core collapse, i.e.
	www.seds.org /messier/xtra/ngc/n6397.html (223 words)

	Beryllium in turnoff stars of NGC 6397: Early Galaxy spallation, cosmochronology and cluster formation
		We present the first detection of beryllium in two turnoff stars of the old, metal-poor globular cluster NGC 6397.
		With this method, we estimate that the cluster formed 0.2-0.3 Gyr after the onset of star formation in the Galaxy, in excellent agreement with the age derived from main sequence fitting.
		Our beryllium results, together with the N, O, and Li abundances, provide insights on the formation of this globular cluster, showing that any CNO processing of the gas must have occurred in the protocluster cloud before the formation of the stars we observe now.
	www.edpsciences.org /articles/aa/abs/2004/41/aa1254/aa1254.html (267 words)

	SPACE.com -- Hubble Finds Possible Evidence for Stellar Theory
		This Hubble Space Telescope image shows the globular cluster NGC 6397 in constellation Ara, which is located near the celestial south pole.
		The team conducted several observations of the pulsar-companion system, which resides in the stellar globular cluster NGC 6397, with the aid of the Hubble Space Telescope and the Australian Parkes Observatory radio telescope.
		The scientists realized their observations were unique when they found a millisecond pulsar partnered to a star whose radius was 100 times greater than a white dwarf, and five times greater than a normal star of similar mass.
	www.space.com /scienceastronomy/astronomy/newborn_pulsar_020213.html (560 words)

	Astronomy - Globular cluster NGC 6397 -
		NGC 6397, located 7,200 light-years away in the southern constellation Ara, is one of the nearest globular star clusters.
		Globular clusters, so named for their spheroidal appearance, hold clues about the onset of star formation in our galaxy.
		Recent work suggests that NGC 6397 was born just a few hundred million years after the Milky Way's first stars formed.
	www.astronomy.com /asy/default.aspx?c=a&id=2388 (250 words)

	CASE PUBLICATIONS (Site not responding. Last check: 2007-10-19)
		Kaluzny, J., "CCD photometry of variable stars in the globular cluster NGC 288", 1996, Astron.
		Kaluzny, J. photometry of variable stars in the field of the globular cluster NGC 6397", 1997, Astron.
		Kaluzny, J., Wysocka, A., Stanek, K.Z., W. Krzeminski, W. CCD Photometry of the Globular Cluster 47 Tuc", Acta Astron., Acta Astron.
	www.camk.edu.pl /case/case-publ.html (600 words)

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