CH Lines Research Articles

Simultaneous high speed PIV and CH PLIF using R-branch excitation in the C2Σ+-X2Π (0,0) band

Simultaneous particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) utilizing R-branch transitions in the C-X (0,0) band were performed at a 10-kHz repetition-rate in a turbulent premixed flame. The CH lines at 310.690 nm (from the R-branch of the C-X band) used here have greater efficiency than A-X and B-X transitions, which allows for high-framerate imaging with low laser pulse energy. Most importantly, the simultaneous imaging of both CH PLIF and PIV is enabled by the use of a custom edge filter, which blocks scattering at the laser wavelength (below ∼311 nm) while efficiently transmitting fluorescence at longer wavelengths. The Hi-Pilot Bunsen burner operated with a turbulent Reynolds number of 7900 was used to demonstrate simultaneous PIV and CH PLIF utilizing this filtered detection scheme. Instances where pockets of products were observed well upstream of the mean flame brush are found to be the result of out-of-plane motion of the flame sheet. Such instances can lead to ambiguous results when interpreting the thickness of reaction layers. However, the temporally resolved nature of the present diagnostics facilitate the identification and proper treatment of such situations. The strategy demonstrated here can yield important information in the study of turbulent flames by providing temporally resolved flame dynamics in terms of flame sheet visualization and velocity fields.

THz spectroscopy of [formula omitted]CH+, 13CH+, and [formula omitted]CD+: A combined Dunham analysis of Terahertz lines and [formula omitted] transitions

The THz rotational lines of CH+ and its isotopologues have been observed in the range of 0.9–2.6 THz with JPL frequency multiplication chains. They were analyzed together with the known A1Π-X1Σ+ band system data by using the Dunham formulation and the conventional vibration–rotation energy formula. The Λ-doubling in 1Π states was reexamined, and the doubling or shifts were found to be different for the e- and f-parity levels. In this investigation, the e- and f-parity states were treated as two separate states. The major molecular constants were determined accurately for these two states separately, and were compared with the values obtained previously.

Unveiling the chemistry of interstellar CH

Context. The methylidyne radical CH is commonly used as a proxy for molecular hydrogen in the cold, neutral phase of the interstellar medium. The optical spectroscopy of CH is limited by interstellar extinction, whereas far-infrared observations provide an integral view through the Galaxy. While the HF ground state absorption, another H2 proxy in diffuse gas, frequently suffers from saturation, CH remains transparent both in spiral-arm crossings and high-mass star forming regions, turning this light hydride into a universal surrogate for H2. However, in slow shocks and in regions dissipating turbulence its abundance is expected to be enhanced by an endothermic production path, and the idea of a “canonical” CH abundance needs to be addressed. Aim. The N = 2 ← 1 ground state transition of CH at λ149 μm has become accessible to high-resolution spectroscopy thanks to the German Receiver for Astronomy at Terahertz Frequencies (GREAT) aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Its unsaturated absorption and the absence of emission from the star forming regions makes it an ideal candidate for the determination of column densities with a minimum of assumptions. Here we present an analysis of four sightlines towards distant Galactic star forming regions, whose hot cores emit a strong far-infrared dust continuum serving as background signal. Moreover, if combined with the sub-millimeter line of CH at λ560 μm , environments forming massive stars can be analyzed. For this we present a case study on the “proto-Trapezium” cluster W3 IRS5. Methods. While we confirm the global correlation between the column densities of HF and those of CH, both in arm and interarm regions, clear signposts of an over-abundance of CH are observed towards lower densities. However, a significant correlation between the column densities of CH and HF remains. A characterization of the hot cores in the W3 IRS5 proto-cluster and its envelope demonstrates that the sub-millimeter/far-infrared lines of CH reliably trace not only diffuse but also dense, molecular gas. Results. In diffuse gas, at lower densities a quiescent ion-neutral chemistry alone cannot account for the observed abundance of CH. Unlike the production of HF, for CH+ and CH, vortices forming in turbulent, diffuse gas may be the setting for an enhanced production path. However, CH remains a valuable tracer for molecular gas in environments reaching from diffuse clouds to sites of high-mass star formation.

Stringent upper limit of CH4 on Mars based on SOFIA/EXES observations

Discovery of CH4 in the Martian atmosphere has led to much discussion since it could be a signature of biological and/or geological activities on Mars. However, the presence of CH4 and its temporal and spatial variations are still under discussion because of the large uncertainties embedded in the previous observations. We performed sensitive measurements of Martian CH4 by using the Echelon-Cross-Echelle Spectrograph (EXES) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) on 16 March 2016, which corresponds to summer (Ls = 123.2∘) in the northern hemisphere on Mars. The high altitude of SOFIA (~13.7 km) enables us to significantly reduce the effects of terrestrial atmosphere. Thanks to this, SOFIA/EXES improves our chances of detecting Martian CH4 lines because it reduces the impact of telluric CH4 on Martian CH4, and allows us to use CH4 lines in the 7.5 μm band which has less contamination. However, our results show no unambiguous detection of Martian CH4. The Martian disk was spatially resolved into 3 × 3 areas, and the upper limits on the CH4 volume mixing ratio range from 1 to 9 ppb across the Martian atmosphere, which is significantly less than detections in several other studies. These results emphasize that release of CH4 on Mars is sporadic and/or localized if the process is present.

The benchmark halo giant HD 122563: CNO abundances revisited with three-dimensional hydrodynamic model stellar atmospheres

We present an abundance analysis of the low-metallicity benchmark red giant star HD 122563 based on realistic, state-of-the-art, high-resolution, three-dimensional (3D) model stellar atmospheres including non-grey radiative transfer through opacity binning with four, twelve, and 48 bins. The 48-bin 3D simulation reaches temperatures lower by ~ 300 - 500 K than the corresponding 1D model in the upper atmosphere. Small variations in the opacity binning, adopted line opacities, or chemical mixture can cool the photospheric layers by a further ~ 100 - 300 K and alter the effective temperature by ~ 100 K. A 3D local thermodynamic equilibrium (LTE) spectroscopic analysis of Fe I and Fe II lines gives discrepant results in terms of derived Fe abundance, which we ascribe to non-LTE effects and systematic errors on the stellar parameters. We also determine C, N, and O abundances by simultaneously fitting CH, OH, NH, and CN molecular bands and lines in the ultraviolet, visible, and infrared. We find a small positive 3D-1D abundance correction for carbon (+0.03 dex) and negative ones for nitrogen (-0.07 dex) and oxygen (-0.34 dex). From the analysis of the [O I] line at 6300.3 {\AA}, we derive a significantly higher oxygen abundance than from molecular lines (+0.46 dex in 3D and +0.15 dex in 1D). We rule out important OH photodissociation effects as possible explanation for the discrepancy and note that lowering the surface gravity would reduce the oxygen abundance difference between molecular and atomic indicators.

A comparative study of the effect of varied reaction environments on a swirl stabilized flame geometry via optical measurements

The present work is a part of a larger experimental campaign which examines the behaviour of various fuels on a swirl stabilized flame burner configuration. Overall, detailed speciation measurements and temperature measurements were combined with optical measurements. The work presented here concerns the part of the experimental campaign which deals with the optical characteristics of the examined flames. The work adds to the growing database of experimental measurements assessing engine-relevant reaction environments which shift from traditional ones in order to meet pollutant emission regulations and efficiency standards. Here, the oxidation of several commonly used fuel and fuel surrogates that are subjected to the addition of a bio-derived fuel additive (dimethyl ether) and emulated exhaust gas recirculation (EGR) is studied in a laboratory-scale swirl stabilized burner. The natural flame chemiluminescence has been exploited to selectively measure line of sight CH∗ and OH∗ profiles for combinations of these fuels and reaction environments. As a result, the geometry and intensity of the reaction and oxidation zones have been parametrically evaluated for a sizable number of initial conditions. From an analysis of the collected data, a chemical uniqueness in methane and propane flames has been found along with a change in flame topology as a function reactant temperature and dilution with inert gases, while the flames were virtually unaffected by all other variations in reaction conditions. This insensitivity provides confidence in the use of tailored in-cylinder fluid dynamic/chemical interactions to extend engine operating conditions to otherwise difficult regimes.

Diamond films and particles growth in hydrogen microwave plasma with graphite solid precursor: Optical emission spectroscopy study

We report on growth of diamond particles on graphite sheets and continuous films on Si substrates in a hydrogen microwave plasma using a graphite solid precursor. The special feature of the process is that no methane is added in the CVD reactor, instead, the diamond growth is realized by forming CHx radicals and other carbon species by the graphite etching with atomic hydrogen. The diamond particles deposited on the graphite substrates with very poor adhesion, can be easily collected, thus the approach allows a production of CVD diamond grit. The grit with ~10μm “diameter” was characterized with SEM, Raman spectroscopy and a dynamic laser scattering. Optical emission spectra (OES) of the plasma in the course of the graphite etching/diamond deposition single process were systematically studied, and a quantitative analogy with conventional growth in CH4-H2 mixtures was derived. The graphite etch rate up to 150μm/h was measured, but found to monotonically decrease with the process time, as monitored for more than 10h. A correlation of OES intensities of CH and C2 lines with the measured graphite etch rate is established. The graphite/H2 system for diamond growth is attractive as a high local flux of hydrocarbon species can be formed in proximity of the substrate.

ALMA imaging of C2H emission in the disk of NGC 1068

We study the feedback of star formation and nuclear activity on the chemistry of molecular gas in NGC1068, a nearby (D=14Mpc) Seyfert 2 barred galaxy, by analyzing if the abundances of key molecular species like ethynyl (C2H), a classical tracer of PDR, change in the different environments of the disk of the galaxy. We have used ALMA to map the emission of the hyperfine multiplet of C2H(N=1-0) and its underlying continuum emission in the central r~35"(2.5kpc)-region of the disk of NGC1068 with a spatial resolution 1.0"x0.7"(50-70pc). We have developed a set of time-dependent chemical models to determine the origin of the C2H gas. A sizeable fraction of the total C2H line emission is detected from the r~1.3kpc starburst (SB) ring. However, the brightest C2H emission originates from a r~200pc off-centered circumnuclear disk (CND), where evidence of a molecular outflow has been previously found in other molecular tracers imaged by ALMA. We also detect significant emission that connects the CND with the outer disk. We derived the fractional abundances of C2H (X(C2H)) assuming LTE conditions. Our estimates range from X(C2H)~a few 10^-8 in the SB ring up to X(C2H)~ a few 10^-7 in the outflow region. PDR models that incorporate gas-grain chemistry are able to account for X(C2H) in the SB ring for moderately dense (n(H2)>10^4 cm^-3) and moderately UV-irradiated gas (UV-field<10xDraine field) in a steady-state regime. However, the high fractional abundances estimated for C2H in the outflow region can only be reached at very early times (T< 10^2-10^3 yr) in models of UV/X-ray irradiated dense gas (n(H2)>10^4-10^5) cm^-3). We interpret that the transient conditions required to fit the high values of X(C2H) in the outflow are likely due to UV/X-ray irradiated non-dissociative shocks associated with the highly turbulent interface between the outflow and the molecular gas in NGC1068.

Wavelength-stabilization-based photoacoustic spectroscopy for methane detection

A compact and portable photoacoustic gas sensor was developed for sensitive methane (CH4) detection at 1.6 µm using a software-based wavelength stabilization scheme. A transmission-type photoacoustic cell was connected in series with a reference gas cell to measure the photoacoustic signal and the reference gas absorption for wavelength stabilization simultaneously. The central wavelength of the diode laser was locked to the target CH4 line with a fluctuation of less than 10.6 MHz using a digital proportional–integral–derivative controller. The CH4 sensor was designed to be insensitive to the incoherent external acoustic noise by the cumulative average of the demodulated photoacoustic signal by a digital lock-in amplifier. With an incident laser power of 6 mW, our CH4 sensor achieved a minimum detection limit of 11.5 ppm at 10 s response time and an excellent linearity (R2 = 0.9999) in the concentration range of 400–6300 ppm.

The effect of hydrogen addition in argon-acetylene plasma on the structure of amorphous carbon films

Amorphous carbon films were formed on nickel/silicon (100) substrates by plasma jet chemical vapor deposition (PJCVD). The carbon films were deposited at atmospheric pressure using an argon-acetylene and argon-hydrogen-acetylene plasma. The plasma composition was analyzed by optical emission spectroscopy (OES). The results indicated that the dominant species in the argon-acetylene and argon-hydrogen-acetylene plasmas were the CH radical and C2 particles. The emission intensities of CH and C2 lines depended on the hydrogen amount in plasma and the distance. Scanning electron microscopy analysis demonstrated that the surface roughness of the coatings decreased with the addition of hydrogen and the increase of distance from 5mm to 7mm. The oxygen concentration increased with the increase of the deposition distance. The Raman spectroscopy results indicated that the addition of the hydrogen in the argon-acetylene plasma lead to the formation of nano-crystalline graphite films at 5mm distance. The increase of the distance from 5mm up to 7mm stipulated the formation of multiphase SiC/carbon films when the argon-hydrogen-acetylene ratios were 100:2.4:1 and 100:1.2:1.

Plasma reactor for deposition of carbon nanowalls at atmospheric pressure

In this study a novel plasma reactor for deposition of carbon nanowalls at atmospheric pressure is constructed and characterized. A low power microwave discharge is used as a plasma source and working gas of Ar/H2/CH4 gas mixture. The substrate is heated by plasma flame and its temperature is in the range 600-700 C. The chemical composition of the plasma and the gas mixture effect on the concentration of the various particles in the plasma is investigated by optical emission spectroscopy. The emission spectrum of the plasma jet in Ar/H2/CH4 mixture shows the presence of carbon (Swan band) and an intensive line of CH (388 nm), which are necessary species for deposition of carbon nanostructures. Additional voltage in the range from -20 V to -100 V is applied in order to ensure the vertical growth of graphene walls. Results of deposited carbon nanostructures on metal substrate are shown.

An experimental study on discharge characteristics in a pulsed-dc atmospheric pressure CH3OH/Ar plasma jet

Recently, C/H/Ar plasma discharges found enormous potential and possibility in carbonaceous compounds conversion and production. In this work, a pulsed-dc CH3OH/Ar plasma jet generated at atmospheric pressure is investigated by means of optical and electrical diagnosis concerning the variation of its basic parameters, absolute concentration of OH radicals, and plasma temperature with different CH3OH/Ar volume ratios, in the core region of discharge with needle-to-ring electrode configuration. The voltage–current characteristics are also measured at different CH3OH/Ar ratios. Laser-induced fluorescence (LIF) results here show that only small amounts of added methanol vapor to argon plasma (about 0.05% CH3OH/Ar volume ratio) is favorable for the production of OH radicals. The optical emission lines of CH, CN, and C2 radicals have been detected in the CH3OH/Ar plasma. And, the plasma temperatures increase with successive amount of added methanol vapor to the growth plasma. Moreover, qualitative discussions are presented regarding the mechanisms for methanol dissociation and effect of the CH3OH component on the Ar plasma discharge at atmospheric pressure.

Mid-infrared dual-gas sensor for simultaneous detection of methane and ethane using a single continuous-wave interband cascade laser.

A continuous-wave (CW) interband cascade laser (ICL) based mid-infrared sensor system was demonstrated for simultaneous detection of atmospheric methane (CH4) and ethane (C2H6). A 3.337 µm CW ICL with an emitting wavenumber range of 2996.0-3001.5 cm-1 was used to simultaneously target two absorption lines, C2H6 at 2996.88 cm-1 and CH4 at 2999.06 cm-1, respectively. The sensor performance was first evaluated for single-gas detection by only targeting the absorption line of one gas species. Allan deviations of 11.2 parts per billion in volume (ppbv) for CH4 and 1.86 ppbv for C2H6 with an averaging time of 3.4 s were achieved for the detection of these two gases. Dual-gas detection was realized by using a long-term scan signal to target both CH4 and C2H6 lines. The Allan deviations increased slightly to 17.4 ppbv for CH4 and 2.4 ppbv for C2H6 with an averaging time of 4.6 s due to laser temperature and power drift caused by long-term wavelength scanning. Measurements for both indoor and outdoor concentration changes of CH4 and C2H6 were conducted. The reported single ICL based dual-gas sensor system has the advantages of reduced size and cost compared to two separate sensor systems.

Water in star-forming regions withHerschel(WISH)

Hydrides are simple compounds containing one or a few hydrogen atoms bonded to a heavier atom. They are fundamental precursor molecules in cosmic chemistry and many hydride ions have become observable in high quality for the first time thanks to the Herschel Space Observatory. Ionized hydrides, such as CH+ and OH+, and also HCO+ that affect the chemistry of molecules such as water, provide complementary information on irradiation by far UV (FUV) or X-rays and gas temperature. The targeted lines of CH+, OH+, H2O+, C+ and CH are detected mostly in blue-shifted absorption. H3O+ and SH+ are detected in emission and only toward some high-mass objects. The observed line parameters and correlations suggest two different origins, related to gas entrained by the outflows and to the circumstellar envelope. The column density ratios of CH+/OH+ are estimated from chemical slab models, assuming that the H2 density is given by the specific density model of each object at the beam radius. For the low-mass YSOs the observed ratio can be reproduced for an FUV flux of 2-400 times the ISRF at the location of the molecules. In two high-mass objects, the UV flux is 20-200 times the ISRF derived from absorption lines, and 300-600 ISRF using emission lines. If the FUV flux required for low-mass objects originates at the central protostar, a substantial FUV luminosity, up to 1.5 L_sun, is required. There is no molecular evidence for X-ray induced chemistry in the low-mass objects on the observed scales of a few 1000 AU. For high-mass regions, the FUV flux required to produce the observed molecular ratios is smaller than the unattenuated flux expected from the central object(s) at the Herschel beam radius. This is consistent with an FUV flux reduced by circumstellar extinction or by bloating of the protostar.

MOLECULAR LINE FORMATION IN THE EXTREMELY METAL-POOR STAR BD+44° 493

Molecular absorption lines of OH (99 lines) and CH (105 lines) are measured for the carbon-enhanced metal-poor star BD+44 493 with [Fe/H]=-3.8. The abundances of oxygen and carbon determined from individual lines based on an 1D-LTE analysis exhibit significant dependence on excitation potentials of the lines; d log e/d chi ~ -0.15 - -0.2 dex/eV, where e and chi are elemental abundances from individual spectral lines and their excitation potentials, respectively. The dependence is not explained by the uncertainties of stellar parameters, but suggests that the atmosphere of this object possesses a cool layer that is not reproduced by the 1D model atmosphere. This result agrees with the predictions by 3D model calculations. Although absorption lines of neutral iron exhibit similar trend, it is much weaker than found in molecular lines and that predicted by 3D LTE models.

Carbon abundances of reference late-type stars from 1D analysis of atomic C i and molecular CH lines

A comprehensive model atom was constructed for C i using the most up-to-date atomic data. We evaluated non-local thermodynamical equilibrium (NLTE) line formation for neutral carbon in classical one-dimensional (1D) models representing atmospheres of late-type stars, where carbon abundance varies from the solar value down to [C/H] = −3. NLTE leads to stronger C i lines compared with their local thermodynamical equilibrium (LTE) strength and negative NLTE abundance corrections, ΔNLTE. The deviations from LTE are large for the strong lines in the infrared (IR), with ΔNLTE = −0.10 to −0.45 dex, depending on stellar parameters, and minor for the weak lines in the visible spectral range, with |ΔNLTE| ≤ 0.03 dex. The NLTE abundance corrections were found to be dependent on the carbon abundance in the model. As the first application of the treated model atom, carbon NLTE abundances were determined for the Sun and eight late-type stars with well-determined stellar parameters that cover the −2.56 ≤ [Fe/H] ≤ −1.02 metallicity range. Consistent abundances from the visible and IR lines were found for the Sun and the most metal-rich star of our sample, when applying a scaling factor of SH = 0.3 to the Drawinian rates of C+H collisions. Carbon abundances were also derived from the molecular CH lines and agree with those from the atomic C i lines for each star. We present the NLTE abundance corrections for lines of C i in the grid of model atmospheres applicable to carbon-enhanced (CEMP) stars.

CH in stellar atmospheres: an extensive linelist

The advent of high-resolution spectrographs and detailed stellar atmosphere modelling has strengthened the need for accurate molecular data. Carbon-enhanced metal-poor (CEMP) stars spectra are interesting objects with which to study transitions from the CH molecule. We combine programs for spectral analysis of molecules and stellar-radiative transfer codes to build an extensive CH linelist, including predissociation broadening as well as newly identified levels. We show examples of strong predissociation CH lines in CEMP stars, and we stress the important role played by the CH features in the Bond-Neff feature depressing the spectra of barium stars by as much as 0.2 magnitudes in the $\lambda=$3000 -- 5500 \AA\ range. Because of the extreme thermodynamic conditions prevailing in stellar atmospheres (compared to the laboratory), molecular transitions with high energy levels can be observed. Stellar spectra can thus be used to constrain and improve molecular data.

Correlation between optical emission spectra and the process parameters of a 915 MHz microwave plasma CVD reactor used for depositing polycrystalline diamond coatings

In this paper, the hydrogen and hydrogen-methane mixed plasma have been generated inside a 33 cm diameter quartz bell jar with a low power (9 KW) and lower frequency 915 MHz microwave plasma chemical vapor deposition system. The reactor is being used for growing polycrystalline diamond (PCD) over large area (100 mm). The generated plasma is diagnosed by in situ optical emission spectroscopy method with wave length ranging from 200 to 900 nm. The effects of microwave power, chamber pressure and gas concentration on plasma characteristics have been studied in this work. Within the optical range, Balmer H α , H β , C2swan band and CH lines have been detected at the wavelengths of 655.95, 485.7, 515.82 and 430.17 nm, respectively. It has been observed that for hydrogen plasma, the amount of transition from hydrogen atom inner shell 3 to 2 (H α ) is almost constant with increasing microwave (MW) power (from 2000 to 2800 W) and pressure (from 15 to 30 Torr) initially, after that it increases with further increase of MW power and pressure, whereas, the transition from 4 to 2 (H β ) is slowly increased with increasing MW power and pressure. For hydrogen-methane plasma, intensities of C2 swan band, i.e., the transitions from D3π g to A3π μ energy levels, are also increased with the increasing microwave power and reactor pressure. It has been observed that the radicals present in the plasma are affected by variation of different reactor parameters like pressure, MW power, CH4 concentration, etc.

FIRST EXTRAGALACTIC DETECTION OF SUBMILLIMETER CH ROTATIONAL LINES FROM THEHERSCHEL SPACE OBSERVATORY

We present the first extragalactic detections of several CH rotational transitions in the far-infrared (FIR) in four nearby galaxies: NGC 1068, Arp 220, M 82 and NGC 253 using the \textit{Herschel Space Observatory}. The CH lines in all four galaxies are a factor of 2 - 4 brighter than the adjacent HCN and HCO+ J = 6-5 lines (also detected in the same spectra). In the star formation dominated galaxies, M 82, NGC 253 and Arp 220, the CH/CO abundance ratio is low (1e-5), implying that the CH is primarily arising in diffuse and translucent gas where the chemistry is driven by UV radiation as found in the Milky Way ISM. In NGC 1068, which has a luminous AGN, the CH/CO ratio is an order of magnitude higher suggesting that CH formation is driven by an X-ray dominated region. Our XDR models show that both the CH and CO abundances in NGC 1068 can be explained by an XDR-driven chemistry for gas densities and molecular hydrogen column densities that are well constrained by the CO observations. We conclude that the CH/CO ratio may a good indicator of the presence of AGN in galaxies. We also discuss the feasibility of detecting CH in intermediate- to high-z galaxies with ALMA.

Iron and neutron-capture element abundance variations in the globular cluster M2 (NGC 7089)★

We present CN and CH indices and CaII triplet metallicities for 34 giant stars and chemical abundances for 33 elements in 14 giants in the globular cluster M2. Assuming the program stars are cluster members, our analysis reveals (i) an extreme variation in CN and CH line strengths, (ii) a metallicity dispersion with a dominant peak at [Fe/H] = -1.7 and smaller peaks at -1.5 and -1.0, (iii) star-to-star abundance variations and correlations for the light elements O, Na, Al and Si and (iv) a large (and possibly bimodal) distribution in the abundances of all elements produced mainly via the s-process in solar system material. Following Roederer et al. (2011), we define two groups of stars, "r+s" and "r-only", and subtract the average abundances of the latter from the former group to obtain a "s-process residual". This s-process residual is remarkably similar to that found in M22 and in M4 despite the range in metallicity covered by these three systems. With recent studies identifying a double subgiant branch in M2 and a dispersion in Sr and Ba abundances, our spectroscopic analysis confirms that this globular cluster has experienced a complex formation history with similarities to M22, NGC 1851 and omega Centauri.