* Astronomy

Members Login
Post Info TOPIC: M22


L

Posts: 131433
Date:
M22
Permalink  
 


Messier 22 (also M22, Melotte 208, ESO 523-SC4, NGC 6656 and GCl 99) is a magnitude +5.1 globular star cluster located 10600 ±1000 light-years away in the constellation Sagittarius.
Messier 22 is the brightest globular cluster visible from mid-northern latitudes.
M22 contains 32 variable stars and a young planetary nebula associated with IRAS 18333-2357.

The cluster was discovered by German amateur astronomer Johann Abraham Ihle at Leipzig, on the 26th August 1665 while observing Saturn in Sagittarius. 
The cluster was observed by French astronomer Charles Messier on the 5th June 1764, and included in his catalogue of comet-like objects, and notes that the object was already present in the English Celestial Atlas, by John Bevis.

Right Ascension 18h 36m 23.94s, Declination -23° 54' 17.1"

NGC 6656

M22 is very unusual in that it is one of only four globulars (the others being M15, NGC 6441 and Palomar 6) that are known to contain a planetary nebula. It was discovered using the IRAS satellite by Fred Gillett et al.,in 1986 as a pointlike source (IRAS 18333-2357) and subsequently identified as a planetary nebula in 1989 by Gillett et al.
Read more



__________________


L

Posts: 131433
Date:
Messier 22
Permalink  
 


M22 was one of the first globulars to be discovered on August 26, 1665 by Abraham Ihle and it was included in Charles Messier's catalogue of comet-like objects on June 5, 1764.
Read more



__________________


L

Posts: 131433
Date:
RE: M22
Permalink  
 


Title: Fluorine variations in the globular cluster NGC 6656 (M22): implications for internal enrichment timescales
Authors: Valentina D'Orazi, Sara Lucatello, Maria Lugaro, Raffaele G. Gratton, George Angelou, Angela Bragaglia, Eugenio Carretta, Alan Alves-Brito, Inese I. Ivans, Thomas Masseron, Alessio Mucciarelli

Observed chemical (anti)correlations in proton-capture elements among globular cluster stars are presently recognised as the signature of self-enrichment from now extinct, previous generations of stars. This defines the multiple population scenario. Since fluorine is also affected by proton captures, determining its abundance in globular clusters provides new and complementary clues regarding the nature of these previous generations, and supplies strong observational constraints to the chemical enrichment timescales. In this paper we present our results on near-infrared CRIRES spectroscopic observations of six cool giant stars in NGC 6656 (M22): the main objective is to derive the F content and its internal variation in this peculiar cluster, which exhibits significant changes in both light and heavy element abundances. We detected F variations across our sample beyond the measurement uncertainties and found that the F abundances are positively correlated with O and anticorrelated with Na, as expected according to the multiple population framework. Furthermore, our observations reveal an increase in the F content between the two different sub-groups, s-process rich and s-process poor, hosted within M22. The comparison with theoretical models suggests that asymptotic giant stars with masses between 4-5 solar masses are responsible for the observed chemical pattern, confirming evidence from previous works: the difference in age between the two sub-components in M22 must be not larger than a few hundreds Myr.

Read more (99kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Surprising Black-Hole Discovery Changes Picture of Globular Star Clusters

An unexpected discovery by astronomers using the National Science Foundation's Karl G. Jansky Very Large Array (VLA) is forcing scientists to rethink their understanding of the environment in globular star clusters, tight-knit collections containing hundreds of thousands of stars.
Read more

Black hole surprise in ancient star cluster

Astronomers have made the unexpected discovery of two black holes inside an ancient cluster of stars in our galaxy, the Milky Way.
The research, published today in the prestigious journal Nature, describes the detection of two black holes that are about 10 to 20 times heavier than our Sun in the globular cluster named M22.

Read more



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Two stellar-mass black holes in the globular cluster M22
Authors: Jay Strader (Michigan State), Laura Chomiuk (NRAO/Michigan State), Thomas Maccarone (Southampton), James Miller-Jones (ICRAR-Curtin), Anil Seth (Utah)

Hundreds of stellar-mass black holes likely form in a typical globular star cluster, with all but one predicted to be ejected through dynamical interactions. Some observational support for this idea is provided by the lack of X-ray-emitting binary stars comprising one black hole and one other star ("black-hole/X-ray binaries") in Milky Way globular clusters, even though many neutron-star/X-ray binaries are known. Although a few black holes have been seen in globular clusters around other galaxies, the masses of these cannot be determined, and some may be intermediate-mass black holes that form through exotic mechanisms. Here we report the presence of two flat-spectrum radio sources in the Milky Way globular cluster M22, and we argue that these objects are black holes of stellar mass (each ~ 10-20 times more massive than the Sun) that are accreting matter. We find a high ratio of radio-to-X-ray flux for these black holes, consistent with the larger predicted masses of black holes in globular clusters compared to those outside. The identification of two black holes in one cluster shows that the ejection of black holes is not as efficient as predicted by most models, and we argue that M22 may contain a total population of ~ 5-100 black holes. The large core radius of M22 could arise from heating produced by the black holes.

Read more (3456kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Two stellar-mass black holes in the globular cluster M22
Authors: Jay Strader, Laura Chomiuk, Thomas J. Maccarone, James C. A. Miller-Jones & Anil C. Seth

Hundreds of stellar-mass black holes probably form in a typical globular star cluster, with all but one predicted to be ejected through dynamical interactions. Some observational support for this idea is provided by the lack of X-ray-emitting binary stars comprising one black hole and one other star ('black-hole/X-ray binaries') in Milky Way globular clusters, even though many neutron-star/X-ray binaries are known. Although a few black holes have been seen in globular clusters around other galaxies, the masses of these cannot be determined, and some may be intermediate-mass black holes that form through exotic mechanisms. Here we report the presence of two flat-spectrum radio sources in the Milky Way globular cluster M22, and we argue that these objects are black holes of stellar mass (each ~10-20 times more massive than the Sun) that are accreting matter. We find a high ratio of radio-to-X-ray flux for these black holes, consistent with the larger predicted masses of black holes in globular clusters compared to those outside. The identification of two black holes in one cluster shows that ejection of black holes is not as efficient as predicted by most models, and we argue that M22 may contain a total population of ~5-100 black holes. The large core radius of M22 could arise from heating produced by the black holes

Source



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: CNO and F abundances in the globular cluster M22 (NGC 6656)
Authors: Alan Alves-Brito, David Yong, Jorge Meléndez, Sergio Vásquez, Amanda I. Karakas

Recent studies have confirmed the long standing suspicion that M22 shares a metallicity spread and complex chemical enrichment history similar to that observed in Omega Cen. M22 is among the most massive Galactic globular clusters and its colour-magnitude diagram and chemical abundances reveal the existence of sub-populations. To further constrain the chemical diversity of M22, necessary to interpret its nucleosynthetic history, we seek to measure relative abundance ratios of key elements (carbon, nitrogen, oxygen, and fluorine) best studied, or only available, using high-resolution spectra at infrared wavelengths. High-resolution (R = 50,000) and high S/N infrared spectra were acquired of nine red giant stars with Phoenix at the Gemini-South telescope. Chemical abundances were calculated through a standard 1D local thermodynamic equilibrium analysis using Kurucz model atmospheres. We derive [Fe/H] = -1.87 to -1.44, confirming at infrared wavelengths that M22 does present a [Fe/H] spread. We also find large C and N abundance spreads, which confirm previous results in the literature but based on a smaller sample. Our results show a spread in A(C+N+O) of ~ 0.7 dex. Similar to mono-metallic GCs, M22 presents a strong [Na/Fe]-[O/Fe] anticorrelation as derived from Na and CO lines in the K band. For the first time we recover F abundances in M22 and find that it exhibits a 0.6 dex variation. We find tentative evidence for a flatter A(F)-A(O) relation compared to higher metallicity GCs. Our study confirms and expands upon the chemical diversity seen in this complex stellar system. All elements studied to date show large abundance spreads which require contributions from both massive and low mass stars.

Read more (985kb, PDF)



__________________


L

Posts: 131433
Date:
NGC 6656
Permalink  
 


Mundane dark matter may lurk in starry clusters

Pawel Pietrukowicz of Warsaw University in Poland and colleagues have spotted a tiny star in the globular cluster M22 acting as a lens for a background star. At just 0.18 times the sun's mass, it is the smallest star ever seen in a globular cluster. Because its effects on the larger star were seen after just 10 weeks of observations, the team says there are probably many more like it in the cluster, perhaps even enough to account for all the dark matter needed to hold the cluster together. The work will appear in The Astrophysical Journal Letters.
Read more 



__________________


L

Posts: 131433
Date:
RE: M22
Permalink  
 


Scientists detect low mass, faint star

Together with a Polish-Chilean team of researchers, Philippe Jetzer, a Swiss astrophysicist from the University of Zurich has now detected a low-mass star in globular cluster M22 for the first time.
The star was "seen" using a strange gravitational effect called microlensing.
Until now, it was merely assumed that low-mass and therefore extremely faint stars must exist, but even the most modern telescopes find them almost impossible to detect.

Read more 



__________________


L

Posts: 131433
Date:
M22 low-mass star
Permalink  
 


First low-mass star detected in globular cluster

Even the most powerful high-tech telescopes are barely able to record remote low-mass and thus faint stars. Together with researchers from Poland and Chile, an astrophysicist from the University of Zurich has now detected a low-mass star in globular cluster M22 for the first time through microlensing. The result indicates that the overall mass of globular clusters might well be explained without enigmatic dark matter.
Until now, it was merely assumed that low-mass and therefore extremely faint stars must exist. However, in view of the vast distances and weak luminosity of low-mass stars, even the most modern telescopes fail. Together with a Polish-Chilean team of researchers, Swiss astrophysicist Philippe Jetzer from the University of Zurich has now detected the first low-mass star in the globular cluster M22 indirectly. As their recent article accepted in Astrophysical Journal Letters reveals, it involves a dwarf star that has less than a fifth of the mass of our sun and is 3.2 kiloparsecs from it (one kiloparsec corresponding to 3,210 light years).
The evidence, which enables the mass to be determined highly accurately, is based upon so-called gravitational microlensing and requires the highest technical standards available. The measurements were carried out on the ESO VLT 8-meter telescope with adaptive optics at the Paranal Observatory in Chile.

Read more



__________________
1 2  >  Last»  | Page of 2  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard