arXiv subjects

Augusto Damineli

Publications and source records attributed to Augusto Damineli.

At least 37 records · Page 2Linked to original sources

arXiv2019

ATLASGAL-selected high-mass clumps in the inner Galaxy. VII. Characterisation of mid-J CO emission

High-mass stars are formed within massive molecular clumps, where a large number of stars form close together. The evolution of the clumps with different masses and luminosities is mainly regulated by its high-mass stellar content and the formation of such objects is still not well understood. In this work, we characterise the mid-J CO emission in a statistical sample of 99 clumps (Top100) selected from the ATLASGAL survey that are representative of the Galactic proto-cluster population. High-spatial resolution APEX-CHAMP+ maps of the CO(6-5) and CO(7-6) transitions were obtained and combined with additional single-pointing APEX-FLASH+ spectra of the CO(4-3) line. We study the correlations of the CO line luminosities and profiles for the three CO transitions with the clump properties and investigate if and how they change as a function of the evolution. All sources were detected above 3-$σ$ in all three CO transitions and most of the sources exhibit broad CO emission likely associated with molecular outflows. We found that the extension of the mid-J CO emission is correlated with the size of the dust emission traced by the Herschel-PACS 70 $μ$m maps. The CO line luminosity is correlated with the luminosity and mass of the clumps. However, it does not correlate with the L/M ratio. The dependency of the CO luminosity with the properties of the clumps is steeper for higher-J transitions. Our data seem to exclude that this trend is biased by self-absorption features in the CO emission, but rather suggest that different J transitions arise from different regions of the inner envelope. Moreover, high-mass clumps show similar trends in CO luminosity as lower mass clumps, but are systematically offset towards larger values, suggesting that higher column density and/or temperature (of unresolved) CO emitters are found inside high-mass clumps.

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arXiv2019

Distinguishing Circumstellar from Stellar Photometric Variability in Eta Carinae

The interacting binary Eta Carinae remains one of the most enigmatic massive stars in our Galaxy despite over four centuries of observations. In this work, its light curve from the ultraviolet to the near-infrared is analysed using spatially resolved HST observations and intense monitoring at the La Plata Observatory, combined with previously published photometry. We have developed a method to separate the central stellar object in the ground-based images using HST photometry and applying it to the more numerous ground-based data, which supports the hypothesis that the central source is brightening faster than the almost-constant Homunculus. After detrending from long-term brightening, the light curve shows periodic orbital modulation ($ΔV$ $\sim$ 0.6 mag) attributed to the wind-wind collision cavity as it sweeps around the primary star and it shows variable projected area to our line-of-sight. Two quasi-periodic components with time scales of 2-3 and 8-10 yr and low amplitude, $ΔV$ $<$ 0.2 mag, are superimposed on the brightening light-curve, being the only stellar component of variability found, which indicates minimal stellar instability. Moreover, the light curve analysis shows no evidence of `shell ejections' at periastron. We propose that the long-term brightening of the stellar core is due to the dissipation of a dusty clump in front of the central star, which works like a natural coronagraph. Thus, the central stars appear to be more stable than previously thought since the dominant variability originates from a changing circumstellar medium. We predict that the brightening phase, due mainly to dust dissipation, will be completed around 2032 $\pm$ 4 yr, when the star will be brighter than in the 1600's by up to $ΔV$ $\sim$ 1 mag.

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arXiv2018

BRITE-Constellation reveals evidence for pulsations in the enigmatic binary $η$ Carinae

$η$ Car is a massive, eccentric binary with a rich observational history. We obtained the first high-cadence, high-precision light curves with the BRITE-Constellation nanosatellites over 6 months in 2016 and 6 months in 2017. The light curve is contaminated by several sources including the Homunculus nebula and neighboring stars, including the eclipsing binary CPD$-$59$^\circ$2628. However, we found two coherent oscillations in the light curve. These may represent pulsations that are not yet understood but we postulate that they are related to tidally excited oscillations of $η$ Car's primary star, and would be similar to those detected in lower-mass eccentric binaries. In particular, one frequency was previously detected by van Genderen et al. and Sterken et al. through the time period of 1974 to 1995 through timing measurements of photometric maxima. Thus, this frequency seems to have been detected for nearly four decades, indicating that it has been stable in frequency over this time span. These pulsations could help provide the first direct constraints on the fundamental parameters of the primary star if confirmed and refined with future observations.

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arXiv2017

HS 2231+2441: an HW Vir system composed by a low-mass white dwarf and a brown dwarf

HW Vir systems are rare evolved eclipsing binaries composed by a hot compact star and a low-mass main-sequence star in a close orbit. These systems provide a direct way to measure the fundamental properties, e.g. masses and radii, of their components, hence they are crucial to study the formation of sdB stars and low-mass white dwarfs, the common-envelope phase, and the pre-phase of cataclysmic variables. Here we present a detailed study of HS 2231+2441, an HW Vir type system, by analysing BVR$_C$I$_C$ photometry and phase-resolved optical spectroscopy. The spectra of this system, which are dominated by the primary component features, were fitted using NLTE models providing effective temperature Teff = 28500$\pm$500 K, surface gravity log g = 5.40$\pm$0.05 cm s$^{-2}$, and helium abundance log(n(He)/n(H)) = -2.52$\pm$0.07. Geometrical orbit and physical parameters were derived by modelling simultaneously the photometric and spectroscopic data using the Wilson-Devinney code. We derive two possible solutions for HS 2231+2441 that provide component's masses: M$_1$ = 0.19 M$_{\odot}$ and M$_2$ = 0.036 M$_{\odot}$ or M$_1$ = 0.288 M$_{\odot}$ and M$_2$ = 0.046 M$_{\odot}$. Considering the possible evolutionary channels to form a compact hot star, the primary of HS 2231+2441 probably evolved through the red-giant branch scenario and does not have a helium-burning core, which is consistent with a low-mass white dwarf. Both solutions are consistent with a brown dwarf as the secondary.

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arXiv2016

The fossil wind structures of Eta Carinae: changes across on 5.54-year cycle

Eta Carinae, the closest, active, massive binary containing a highly unstable LBV, exhibits expanding, compressed wind shells, seen in emission, that are spatially and spectrally resolved by \hst/\stis. Starting in June 2009, these structures were mapped across its 5.54-year, highly elliptical, binary orbit to follow temporal changes in the light of [Fe~III] 4659Å and [Fe~II] 4815Å. The emissions trace portions of fossil wind-shells, that were formed by wind-wind interactions across each cycle. Over the high-ionization state, dense arcs, photo-ionized by far ultraviolet radiation from the hot secondary, are seen in [Fe~III]. Other arcs, ionized by mid-ultraviolet radiation from the primary star, are seen in [Fe II]. The [Fe III] structures tend to be interior to [Fe II] structures that trace extensive, less disturbed primary wind. During the brief periastron passage when the secondary plunges deep into the primary's extremely dense wind, on the far side of primary star, high-ionization [Fe III] structures fade and reappear in [Fe II]. Multiple fossil wind-structures were traced across the 5.7-year monitoring interval. The strong similarity of the expanding [Fe II] shells suggests that the wind and photo-ionization properties of the massive binary have not changed substantially from one orbit to the next over the past several orbital cycles. These observations trace structures that can be used to test three-dimensional hydrodynamical and radiative-transfer models of massive, interacting winds. They also provide a baseline for following future changes in Eta Carinae, especially of its winds and photoionization properties.

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arXiv2016

Extinction law in the range 0.4-4.8 $μ$m and the 8620 $Å$ DIB towards the stellar cluster Westerlund 1

The young stellar cluster Westerlund 1 (Wd 1: $l$=339.6$^\circ$, b=$-$0.4$^\circ$) is one of the most massive in the local Universe, but accurate parameters are pending on better determination of its extinction and distance. Based on our photometry and data collected from other sources, we have derived a reddening law for the cluster line-of-sight representative of the Galactic Plane (-5$^\circ<$b$<$+5$^\circ$) in the window 0.4-4.8 $μ$m: The power law exponent $α$=2.13$\pm$0.08 is much steeper than those published a decade ago (1.6-1.8) and our index $R_V$=2.50$\pm$0.04 also differs from them, but in very good agreement with recent works based on deep surveys in the inner Galaxy. As a consequence, the total extinction $A_{Ks}$=0.74$ \pm $0.08 ($A_V$=11.40$ \pm$ 2.40) is substantially smaller than previous results(0.91-1.13), part of which ($A_{Ks}$=0.63 or $A_V$=9.66) is from the ISM. The extinction in front of the cluster spans a range of $ΔA_V\sim$8.7\,mag with a gradient increasing from SW to NE across the cluster face, following the same general trend of warm dust distribution. The map of the $J-Ks$ colour index also shows a trend of reddening in this direction. We measured the equivalent width of the diffuse interstellar band at 8620 $Å$ (the "GAIA DIB") for Wd 1 cluster members and derived the relation $A_{Ks}$=0.612 $EW$ $-$ 0.191 $EW^2$. This extends the Munari et al. (2008) relation, valid for $E_{B-V}$ $<$ 1, to the non-linear regime ($A_V$ $>$ 4).

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arXiv2016

To $v_\infty$ and beyond! The He I absorption variability across the 2014.6 periastron passage of $η$ Carinae

We have monitored the massive binary star $η$ Carinae with the CTIO/SMARTS 1.5~m telescope and CHIRON spectrograph from the previous apastron passage of the system through the recent 2014.6 periastron passage. Our monitoring has resulted in a large, homogeneous data set with an unprecedented time-sampling, spectral resolving power, and signal-to-noise. This allowed us to investigate temporal variability previously unexplored in the system and discover a kinematic structure in the P Cygni absorption troughs of neutral helium wind lines. The features observed occurred prior to the periastron passage and are seen as we look through the trailing arm of the wind-wind collision shock cone. We show that the bulk of the variability is repeatable across the last five periastron passages, and that the absorption occurs in the inner 230 AU of the system. In addition, we found an additional, high-velocity absorption component super-imposed on the P Cygni absorption troughs that has been previously un-observed in these lines, but which bears resemblance to the observations of the He~I $λ$10830 Å feature across previous cycles. Through a comparison of the current smoothed particle hydrodynamical simulations, we show that the observed variations are likely caused by instabilities in the wind-wind collision region in our line-of-sight, coupled with stochastic variability related to clumping in the winds.

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arXiv2016

Mid Infrared View of the High Mass Star Formation Region W51A

In this paper we present the results of a mid infrared study of G49.5-0.4, or W51A, part of the massive starbirth complex W51. Combining public data from the $Spitzer$ IRAC camera, and Gemini mid infrared camera T-ReCS at 7.73, 9.69, 12.33 and 24.56 \micron, with spatial resolution of $\sim$0.5\arcsec, we have identified the mid infrared counterparts of 8 ultracompact HII regions, showing that two radio sources are deeply embedded in molecular clouds and another is a cloud of ionized gas. From the T-ReCS data we have unveiled the central core of W51 region, revealing massive young stellar candidates. We modeled the spectral energy distribution of the detected sources suggesting the embedded objects are sources with spectral types ranging from B3 to O5, but the majority of the fits indicate stellar objects with B1 spectral types. We also present an extinction map of IRS~2, showing that a region with lower extinction corresponds to the region where a proposed jet of gas has impacted the foreground cloud. From this map, we also derived the total extinction towards the enigmatic source IRS~2E, which amounts to $\sim$60 magnitudes in the $V$ band. We calculated the color temperature due to thermal emission of the circumstellar dust of the detected sources; the temperatures are in the interval of $\sim$100 -- 150 K, which corresponds to the emission of dust located at 0.1 pc from the central source. Finally, we show a possible mid infrared counterpart of a detected source at mm wavelengths that was found by \cite{zap08,zap09} to be a massive young stellar object undergoing a high accretion rate.

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arXiv2015

A Survey of Extended H$_2$ Emission from Massive YSOs

We present the results from a survey, designed to investigate the accretion process of massive young stellar objects (MYSOs) through near infrared narrow band imaging using the H$_2$ $ν$=1-0 S(1) transition filter. A sample of 353 Massive Young Stellar Object (MYSO) candidates was selected from the Red MSX Source survey using photometric criteria at longer wavelengths (infrared and submillimeter) and chosen with positions throughout the Galactic Plane. Our survey was carried out at the SOAR Telescope in Chile and CFHT in Hawaii covering both hemispheres. The data reveal that extended H$_2$ emission is a good tracer of outflow activity, which is a signpost of accretion process on young massive stars. Almost half of the sample exhibit extended H$_2$ emission and 74 sources (21\%) have polar morphology, suggesting collimated outflows. The polar-like structures are more likely to appear on radio-quiet sources, indicating these structures occur during the pre-UCHII phase. We also found an important fraction of sources associated with fluorescent H$_2$ diffuse emission that could be due to a more evolved phase. The images also indicate only $\sim$23\% (80) of the sample is associated with extant (young) stellar clusters. These results support the scenario in which massive stars are formed by accretion disks, since the merging of low mass stars would not produce outflow structures.

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arXiv2014

X-ray Emission from Eta Carinae near Periastron in 2009 I: A Two State Solution

X-ray emission from the supermassive binary system Eta Carinae declines sharply around periastron. This X-ray minimum has two distinct phases - the lowest flux phase in the first ~3 weeks and a brighter phase thereafter. In 2009, the Chandra X-ray Observatory monitored the first phase five times and found the lowest observed flux at ~1.9e-12 ergs cm-2 s-1 (3-8 keV). The spectral shape changed such that the hard band above ~4 keV dropped quickly at the beginning and the soft band flux gradually decreased to its lowest observed value in ~2 weeks. The hard band spectrum had begun to recover by that time. This spectral variation suggests that the shocked gas producing the hottest X-ray gas near the apex of the wind-wind collision (WWC) is blocked behind the dense inner wind of the primary star, which later occults slightly cooler gas downstream. Shocked gas previously produced by the system at earlier orbital phases is suggested to produce the faint residual X-ray emission seen when the emission near the apex is completely blocked by the primary wind. The brighter phase is probably caused by the re-appearance of the WWC plasma, whose emissivity significantly declined during the occultation. We interpret this to mean that the X-ray minimum is produced by a hybrid mechanism of an occultation and a decline in emissivity of the WWC shock.

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arXiv2011

On the nature of the prototype LBV AG Carinae II. Witnessing a massive star evolving close to the Eddington and bistability limits

We show that the significantly different effective temperatures (Teff) achieved by the luminous blue variable AG Carinae during the consecutive visual minima of 1985-1990 (Teff= 22,800 K) and 2000-2001 (Teff=17,000 K) place the star on different sides of the bistability limit, which occurs in line-driven stellar winds around Teff ~ 21,000 K. Decisive evidence is provided by huge changes in the optical depth of the Lyman continuum in the inner wind as Teff changes during the S Dor cycle. These changes cause different Fe ionization structures in the inner wind. The bistability mechanism is also related to the different wind parameters during visual minima: the wind terminal velocity was 2-3 times higher and the mass-loss rate roughly two times smaller in 1985-1990 than in 2000-2003. We obtain a projected rotational velocity of 220 +- 50 km/s during 1985-1990 which, combined with the high luminosity (L=1.5x10^6 Lsun), puts AG Car extremely close to the Eddington limit modified by rotation (Omega-Gamma limit): for an inclination angle of 90 deg, Gamma_Omega > 1.0 for M< 60 Msun. Based on evolutionary models and mass budget, we obtain an initial mass of ~ 100 Msun and a current mass of 60-70 Msun for AG Car. Therefore, AG Car is close to, if not at, the Omega-Gamma limit during visual minimum. Assuming M=70 Msun, we find that Gamma_Omega decreases from 0.93 to 0.72 as AG Car expands toward visual maximum, suggesting that the star is not above the Eddington limit during maximum phases.

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arXiv2010

Detection of high-velocity material from the wind-wind collision zone of Eta Carinae across the 2009.0 periastron passage

We report near-IR spectroscopic observations of the Eta Carinae massive binary system during 2008-2009 using VLT/CRIRES. We detect a strong, broad absorption wing in He I 10833 extending up to -1900 km/s across the 2009.0 spectroscopic event. Archival HST/STIS ultraviolet and optical data shows a similar high-velocity absorption (up to -2100 km/s) in the UV resonance lines of Si IV 1394, 1403 across the 2003.5 event. UV lines from low-ionization species, such as Si II 1527, 1533 and C II 1334, 1335, show absorption up to -1200 km/s, indicating that the absorption with v from -1200 to -2100 km/s originates in a region markedly faster and more ionized than the nominal wind of the primary star. Observations obtained at the OPD/LNA during the last 4 spectroscopic cycles (1989-2009) also display high-velocity absorption in He I 10833 during periastron. Based on the OPD/LNA dataset, we determine that material with v < -900 km/s is present in the phase range 0.976 < phi < 1.023 of the spectroscopic cycle, but absent in spectra taken at phi < 0.947 and phi > 1.049. Therefore, we constrain the duration of the high-velocity absorption to be 95 to 206 days (or 0.047 to 0.102 in phase). We suggest that the high-velocity absorption originates from shocked gas in the wind-wind collision zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. Using 3-D hydrodynamical simulations of the wind-wind collision zone, we find that the dense high-velocity gas is in the line-of-sight to the primary star only if the binary system is oriented in the sky so that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of omega ~ 240 to 270 degrees. We study a possible tilt of the orbital plane relative to the Homunculus equatorial plane and conclude that our data are broadly consistent with orbital inclinations in the range i=40 to 60 degrees.

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arXiv2009

Eta Carinae in the Context of the Most Massive Stars

Eta Car, with its historical outbursts, visible ejecta and massive, variable winds, continues to challenge both observers and modelers. In just the past five years over 100 papers have been published on this fascinating object. We now know it to be a massive binary system with a 5.54-year period. In January 2009, Eta Car underwent one of its periodic low-states, associated with periastron passage of the two massive stars. This event was monitored by an intensive multi-wavelength campaign ranging from gamma-rays to radio. A large amount of data was collected to test a number of evolving models including 3-D models of the massive interacting winds. August 2009 was an excellent time for observers and theorists to come together and review the accumulated studies, as have occurred in four meetings since 1998 devoted to Eta Car. Indeed, Eta Car behaved both predictably and unpredictably during this most recent periastron, spurring timely discussions. Coincidently, WR140 also passed through periastron in early 2009. It, too, is a intensively studied massive interacting binary. Comparison of its properties, as well as the properties of other massive stars, with those of Eta Car is very instructive. These well-known examples of evolved massive binary systems provide many clues as to the fate of the most massive stars. What are the effects of the interacting winds, of individual stellar rotation, and of the circumstellar material on what we see as hypernovae/supernovae? We hope to learn.

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arXiv2009

Bona-fide, strong-variable galactic Luminous Blue Variable stars are fast rotators: detection of a high rotational velocity in HR Carinae

We report optical observations of the Luminous Blue Variable (LBV) HR Carinae which show that the star has reached a visual minimum phase in 2009. More importantly, we detected absorptions due to Si IV 4088-4116 Angstroms. To match their observed line profiles from 2009 May, a high rotational velocity of vrot=150 +- 20 km/s is needed (assuming an inclination angle of 30 degrees), implying that HR Car rotates at ~0.88 +- 0.2 of its critical velocity for break-up (vcrit). Our results suggest that fast rotation is typical in all strong-variable, bona-fide galactic LBVs, which present S Dor-type variability. Strong-variable LBVs are located in a well-defined region of the HR diagram during visual minimum (the "LBV minimum instability strip"). We suggest this region corresponds to where vcrit is reached. To the left of this strip, a forbidden zone with vrot/vcrit>1 is present, explaining why no LBVs are detected in this zone. Since dormant/ex LBVs like P Cygni and HD 168625 have low vrot, we propose that LBVs can be separated in two groups: fast-rotating, strong-variable stars showing S-Dor cycles (such as AG Car and HR Car) and slow-rotating stars with much less variability (such as P Cygni and HD 168625). We speculate that SN progenitors which had S-Dor cycles before exploding (such as in SN 2001ig, SN 2003bg, and SN 2005gj) could have been fast rotators. We suggest that the potential difficulty of fast-rotating Galactic LBVs to lose angular momentum is an additional evidence that such stars could explode during the LBV phase.

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arXiv2009

On the nature of the prototype LBV AG Carinae I. Fundamental parameters during visual minimum phases and changes in the bolometric luminosity during the S-Dor cycle

We present a detailed spectroscopic analysis of the luminous blue variable AG Carinae during the last two visual minimum phases of its S-Dor cycle (1985-1990 and 2000-2003). The analysis reveals an overabundance of He, N, and Na, and a depletion of H, C, and O, on the surface of AG Car, indicating the presence of CNO-processed material. Furthermore, the ratio N/O is higher on the stellar surface than in the nebula. We found that the minimum phases of AG Car are not equal to each other, since we derived a noticeable difference between the maximum effective temperature achieved during 1985-1990 (22,800 K) and 2000-2001 (17,000 K). While the wind terminal velocity was 300 km/s in 1985-1990, it was as low as 105 km/s in 2001. The mass-loss rate, however, was lower from 1985-1990 (1.5 x 10^(-5) Msun/yr) than from 2000-2001 (3.7 x 10^(-5) Msun/yr). We found that the wind of AG Car is significantly clumped (f=0.10 - 0.25) and that clumps must be formed deep in the wind. We derived a bolometric luminosity of 1.5 x 10^6 Lsun during both minimum phases which, contrary to the common assumption, decreases to 1.0 x 10^6 Lsun as the star moves towards maximum flux in the V band. Assuming that the decrease in the bolometric luminosity of AG Car is due to the energy used to expand the outer layers of the star (Lamers 1995), we found that the expanding layers contain roughly 0.6 - 2 Msun. Such an amount of mass is an order of magnitude lower than the nebular mass around AG Car, but is comparable to the nebular mass found around lower-luminosity LBVs and to that of the Little Homunculus of Eta Car. If such a large amount of mass is indeed involved in the S Dor-type variability, we speculate that such instability could be a failed Giant Eruption, with several solar masses never becoming unbound from the star.(abridged)

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arXiv2007

X-ray Spectral Variation of Eta Carinae through the 2003 X-ray Minimum

We report the results of an X-ray observing campaign on the massive, evolved star Eta Carinae, concentrating on the 2003 X-ray minimum as seen by the XMM-Newton observatory. These are the first spatially-resolved X-ray monitoring observations of the stellar X-ray spectrum during the minimum. The hard X-ray emission, believed to be associated with the collision of Eta Carinae's wind with the wind from a massive companion star, varied strongly in flux on timescales of days, but not significantly on timescales of hours. The lowest X-ray flux in the 2-10 keV band seen by XMM-Newton was only 0.7% of the maximum seen by RXTE just before the X-ray minimum. The slope of the X-ray continuum above 5 keV did not vary in any observation, which suggests that the electron temperature of the hottest plasma associated with the stellar source did not vary significantly at any phase. Through the minimum, the absorption to the stellar source increased by a factor of 5-10 to NH ~3-4E23 cm-2. The thermal Fe XXV emission line showed significant excesses on both the red and blue sides of the line outside the minimum and exhibited an extreme red excess during the minimum. The Fe fluorescence line at 6.4 keV increased in equivalent width from 100 eV outside the minimum to 200 eV during the minimum. From these observed features, we discuss two possible causes of the X-ray minimum; the eclipse of the X-ray plasma and an intrinsic fading of the X-ray emissivity. The drop in the colliding wind X-ray emission also revealed the presence of an additional X-ray component which exhibited no variation on timescales of weeks to years. This component may be produced by the collision of high speed outflows at v \~1000-2000 km s-1 from Eta Carinae with ambient gas within a few thousand AU from the star.

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arXiv2002

NGC 3576 IRS 1 in the Mid Infrared

We present the results of high-resolution mid-infrared observations of the source NGC 3576 IRS 1. Near diffraction-limited images were taken at the Gemini South Observatory through OSCIR's filters N, 7.9, 9.8, 12.5 and IHW18. The source IRS 1 was resolved into 3 sources for the first time at mid-infrared wavelengths. For each source we constructed the SED from 1.25 to 18 microns, as well the color temperature and the spatial distribution of the dust in the region. The optical depth of the silicate absorption feature at 9.8 microns is presented also.

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arXiv2001

Massive Star Birth in the Inner Galaxy: Obscured Massive Star Clusters

The current census of, and stellar population in, massive Galactic star clusters is reviewed. In particular, we concentrate on a recent survey of obscured Galactic Giant H II (GHII) regions and the associated stellar clusters embedded in them. The regions have been selected as the most luminous radio continuum sources, and as such the stellar clusters appear to be among the youngest massive clusters in the Galaxy. The emergent stellar populations are further studied through near infrared spectroscopy of the brighter members. We also discuss the massive stellar clusters within 50 pc of the Galactic center (GC), comparing their known properties to those found in the GHII region survey. It is suggested that the somewhat younger clusters associated with the GHII regions are more suited to measuring the initial mass function in massive star clusters. Narrow band images in the central pc of the GC are presented which identify the young stellar sequence associated with the evolved He I emission line stars.

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