Power-law Initial Mass Function Research Articles

COMPARISON OF ALPHA-ELEMENT-ENHANCED SIMPLE STELLAR POPULATION MODELS WITH MILKY WAY GLOBULAR CLUSTERS

We present simple stellar population (SSP) models with scaled-solar and alpha-element enhanced abundances. The SSP models are based on the Dartmouth Stellar Evolution Database, our library of synthetic stellar spectra, and a detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity. In order to test the relative importance of a variety of SSP model ingredients, we compare our SSP models with integrated spectra of 41 Milky Way Globular Clusters (MWGCs) from Schiavon et al. (2005). Using the Mg b and Ca4227 indices, we confirm that Mg and Ca are enhanced by about +0.4 and +0.2 dex, respectively, in agreement with results from high resolution spectra of individual stars in MWGCs. Balmer lines, particularly Hgamma and Hdelta, of MWGCs are reproduced by our alpha-enhanced SSP models not only because of the combination of isochrone and spectral effects but also because of our reasonable HB treatment. Moreover, it is shown that the Mg abundance significantly influences Balmer and iron line indices. Finally, the investigation of power-law initial mass function (IMF) variations suggests that an IMF much shallower than Salpeter is unrealistic because the Balmer lines are too strong on the metal-poor side to be compatible with observations.

Extragalactic constraints on the initial mass function

The local stellar mass density is observed to be significantly lower than the value obtained from integrating the cosmic star formation history (SFH), assuming that all the stars formed with a Salpeter initial mass function (IMF). Even other favoured IMFs, more successful in reconciling the observed z= 0 stellar mass density with that inferred from the SFH, have difficulties in reproducing the stellar mass density observed at higher redshift. In this study, we investigate to what extent this discrepancy can be alleviated for any universal power-law IMF. We find that an IMF with a high-mass slope shallower (2.15) than the Salpeter slope (2.35) reconciles the observed stellar mass density with the cosmic SFH, but only at low redshifts. At higher redshifts z > 0.5, we find that the observed stellar mass densities are systematically lower than predicted from the cosmic SFH, for any universal power-law IMF.

Lifetimes of tidally limited star clusters with different radii

Abstract We study the escape rate of stars, , from clusters with different radii on circular orbits in a tidal field using analytical predictions and direct N-body simulations. We find that depends on the ratio , where rh is the half-mass radius and rJ the radius of the zero-velocity surface around the cluster. For , the ‘tidal regime’, there is almost no dependence of on . To first order this is because the fraction of escapers per half-mass relaxation time, trh, scales approximately as , which cancels out the r3/2h term in trh. For , the ‘isolated regime’, scales as . The dissolution time-scale, tdis, falls in three regimes. Clusters that start with their initial , in the tidal regime dissolve completely in this regime and their tdis is, therefore, insensitive to the initial rh. Our model predicts that has to be 10−20–10−10 for clusters to dissolve completely in the isolated regime. This means that realistic clusters that start with always expand to the tidal regime before final dissolution. Their tdis has a shallower dependence on than what would be expected when tdis is a constant times trh. For realistic values of , the lifetime varies by less than a factor of 1.5 due to changes in . This implies that the ‘survival’ or ‘vital’ diagram for globular clusters should allow for more small clusters to survive. We note that with our result it is impossible to explain the universal peaked mass function of globular cluster systems by dynamical evolution from a power-law initial mass function, since the peak will be at lower masses in the outer parts of galaxies. Our results finally show that in the tidal regime tdis scales as N0.65/ω, with ω the angular frequency of the cluster in the host galaxy.

An alternative method to study star cluster disruption

Many embedded star clusters do not evolve into long-lived bound clusters. The most popular explanation for this infant mortality of young clusters is the expulsion of natal gas by stellar winds and supernovae, which leaves up to 90% of them unbound. A cluster disruption model has recently been proposed in which this mass- independent disruption of clusters proceeds for another Gyr after gas expulsion. In this scenario, the survival chances of massive clusters are much smaller than in the traditional mass-dependent disruption models. The most common way to study cluster disruption is to use the cluster age distribution, which, however, can be heavily affected by incompleteness. To avoid this, we introduce a new method, based on size-of-sample effects, namely the relation between the most massive cluster, M_max, and the age range sampled. Assuming that clusters are sampled from a power-law initial mass function, with index -2 and that the cluster formation rate is constant, M_max scales with the age range sampled, such that the slope in a log(M_max) vs. log(age) plot is equal to unity. This slope decreases if mass-independent disruption is included. For 90% mass-independent cluster disruption per age dex, the predicted slope is zero. For the solar neighbourhood, SMC, LMC, M33, and M83, based on ages and masses taken from the literature, we find slopes consistent with the expected size-of-sample correlations for the first 100 Myr, hence ruling out the 90% mass-independent cluster disruption scenario. For M51, however, the increase of log(M_max) with log(age) is slightly shallower and for the Antennae galaxies it is flat. This simple method shows that the formation and/or disruption of clusters in the Antennae must have been very different from that of the other galaxies studied here, so it should not be taken as a representative case.

The poorly constrained cluster disruption time-scale in the Large Magellanic Cloud

We use Monte Carlo simulations, combined with homogeneously determined age and mass distributions, based on multiwavelength photometry, to constrain the cluster formation history and the rate of bound cluster disruption in the Large Magellanic Cloud (LMC) star cluster system. We evolve synthetic star cluster systems formed with a power-law initial cluster mass function (ICMF) of spectral index a = -2 assuming different cluster disruption time-scales. For each of these cluster disruption time-scales, we derive the corresponding cluster formation rate (CFR) required to reproduce the observed cluster age distribution. We then compare, in a 'Poissonian' Χ 2 sense, model mass distributions and model two-dimensional distributions in log(mass) versus log(age) space of the detected surviving clusters to the observations. Because of the bright detection limit (M lim V ≃ -4.7 mag) above which the observed cluster sample is complete, one cannot constrain the characteristic cluster disruption time-scale for a 104 M ⊙ cluster, t dis 4 [where the disruption time-scale depends on cluster mass as t dis = t dis 4 (M cl /10 4 M ⊙ )ν, with γ ≃ 0.62], to better than a lower limit, t dis 4 > 1 Gyr. We conclude that the CFR has been increasing steadily from 0.3 clusters Myr -1 5 Gyr ago to a present rate of (20-30) clusters Myr -1 for clusters spanning a mass range of ∼100-10 7 M ⊙ . For older ages, the derived CFR depends sensitively on our assumption of the underlying CMF shape. If we assume a universal Gaussian ICMF, then the CFR has increased steadily over a Hubble time from ∼1 cluster Gyr -1 15 Gyr ago to its present value. On the other hand, if the ICMF has always been a power law with a slope close to a = -2, the CFR exhibits a minimum some 5 Gyr ago, which we tentatively identify with the well-known age gap in the LMC's cluster age distribution.

The Nucleosynthesis of26Al and60Fe in Solar Metallicity Stars Extending in Mass from 11 to 120M⊙: The Hydrostatic and Explosive Contributions

We present the 26Al and 60Fe yields produced by a generation of solar metallicity stars ranging in mass between 11 and 120 M☉. We discuss the production sites of these γ-ray emitters and quantify the relative contributions of the various components. We provide the contributions of the wind, the C convective shell, and the explosive Ne/C burning to the total 26Al yield together with the contributions of the He convective shell, the C convective shell, and the explosive Ne/C burning to the 60Fe yield. We conclude that, at variance with current beliefs, 26Al is mainly produced by the explosive C/Ne burning over most of the mass interval analyzed here, while 60Fe is mainly produced by the C convective shell and the He convective shell. By means of these yields we try to reproduce two quite strong observational constraints related to the abundances of these nuclei in the interstellar medium, i.e., the number of γ1.8 photons per Lyman continuum photon, RGxL, and the 60Fe/26Al γ-ray line flux ratio. RGxL is found to be roughly constant along the Galactic plane (and of the order of 1.25 × 10-11), while the 60Fe/26Al ratio has been recently measured by both RHESSI (0.17 ± 0.05) and SPI (INTEGRAL) (0.11 ± 0.03). We can quite successfully fit simultaneously both ratios for a quite large range of exponents of the power-law initial mass function. We also address the fit to γ2 Velorum, and we find that a quite large range of initial masses, at least from 40 to 60 M☉, do eject an amount of 26Al (through the wind) compatible with the current upper limit quoted for this W-R star: such a result removes a long-standing discrepancy between the models and the observational data.

On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions

Based on the CCD observations of remote young open clusters NGC 2383, NGC 2384, NGC 4103, NGC 4755, NGC 7510 and Hogg 15, we constructed their observed luminosity functions (LFs). The observed LFs are corrected for field star contamination determined with the help of galactic star count model. In the case of Hogg 15 and NGC 2383 we also considered the additional contamination from neighbouring clusters NGC 4609 and NGC 2384 respectively. These corrections provided the realistic pattern of cluster LF in the vicinity of the MS turn on point and at fainter magnitudes, revealed the so called H-feature arising due to transition of the Pre-MS phase to MS, which is dependent on the cluster age. The theoretical LFs were constructed representing a cluster population model with continuous star formation for a short time scale and a power law Initial Mass Function (IMF) and these were fitted to the observed LF. As a result we are able to determine for each cluster a set of parameters, describing cluster population (the age, duration of star formation, IMF slope and percentage of field star contamination). It was found that in spite of the non-monotonic behaviour of observed LFs, cluster IMFs can be described as the power law functions with slopes similar to Salpeter's value. The present MS turn on cluster ages are several times lower than those derived from the fitting of theoretical isochrones to the turn off region of the upper Main Sequences.

Constraints on a Universal Stellar Initial Mass Function from Ultraviolet to Near‐Infrared Galaxy Luminosity Densities

We obtain constraints on the slope of a universal stellar initial mass function (IMF) over a range of cosmic star-formation histories (SFH) using z=0.1 luminosity densities in the range from 0.2 to 2.2 microns. The age-IMF degeneracy of integrated spectra of stellar populations can be broken for the Universe as a whole by using direct measurements of (relative) cosmic SFH from high-redshift observations. These have only marginal dependence on uncertainties in the IMF, whereas, fitting to local luminosity densities depends strongly on both cosmic SFH and the IMF. We fit to these measurements using population synthesis and find the best-fit IMF power-law slope to be Gamma=1.15+-0.2 (0.5 < M/M_solar < 120). This slope is in good agreement with the Salpeter IMF slope (Gamma=1.35). A strong upper limit of Gamma<1.7 is obtained which effectively rules out the Scalo IMF due to its too low fraction of high-mass stars. This upper limit is at the 99.7% confidence level if we assume a closed-box chemical evolution scenario and 95% if we assume constant solar metallicity. Fitting to the H-alpha line luminosity density, we obtain a best-fit IMF slope in good agreement with that derived from broadband measurements. Marginalizing over cosmic SFH and IMF slope, we obtain (95% conf. ranges, h=1): omega_stars = 1.1-2.0 E-3 for the stellar mass density; rho_sfr = 0.7-4.1 E-2 M_solar/yr/Mpc^3 for the star-formation rate density, and; rho_L = 1.2-1.7 E+35 W/Mpc^3 for the bolometric, attenuated, stellar, luminosity density (0.09-5 microns). Comparing this total stellar emission with an estimate of the total dust emission implies a relatively modest average attenuation in the UV (<=1 magnitude at 0.2 microns).

Effects of the Dissolution of Low-Concentration Globular Clusters on the Evolution of Globular Cluster Systems

We investigate the role of dissolution of low-concentration clusters due to mass loss through stellar evolution on the evolution of the properties of globular cluster systems (GCSs) in elliptical galaxies. Our simulations show that, for an initial mass-concentration relationship based on that inferred from Galactic globular clusters, dissolution of low-concentration clusters leads to the disruption of a large number of clusters. A power-law initial globular cluster system mass function (GCMF) similar to that observed in young cluster systems in merging galaxies is transformed by this dissolution into a bell-shaped GCMF with a mean mass similar to that of old GCSs for all the galaxies investigated. Two-body relaxation and dynamical friction, which are also included in our simulations, subsequently lead to an additional significant evolution and disruption of the population of clusters. As shown previously, when these processes act on a bell-shaped GCMF with a mean mass similar to that of old GCSs, they do not significantly alter the value of the mean mass. The final GCMFs are bell-shaped with similar peaks at different radii within galaxies and between different galaxies, in agreement with current observations.

Hydrodynamical simulations of a cloud of interacting gas fragments

We present a full hydrodynamical investigation of a system of self-contained, interacting gas ‘cloudlets’. Calculations are performed using smoothed particle hydrodynamics, and cloudlets are allowed to collide, dissipate kinetic energy, merge and undergo local gravitational collapse. The numerical feasibility of such a technique is explored, and the resolution requirements examined. We examine the effect of the collision time and the velocity field on the time-scale for evolution of the system, and we show that almost all star formation will be confined to dense regions much smaller than the entire cloud. We also investigate the possibility, discussed by various authors, that such a system could lead to a power-law initial mass function by a process of repeated cloudlet coagulation, finding that in fact the inter-cloudlet collisions occur at too high a Mach number for merging to play an important part.

Automatic observation rendering (AMORE)

A new method, AMORE – based on a genetic algorithm optimizer, is presented for the automated study of colour-magnitude diagrams. The method combines several stellar population synthesis tools developed in the last decade by or in collaboration with the Padova group. Our method is able to recover, within the uncertainties, the parameters – distance, extinction, age, metallicity, index of a power-law initial mass function and the index of an exponential star formation rate – from a reference synthetic stellar population. No a priori information is inserted to recover the parameters, which is done simultaneously and not one at a time. Examples are given to demonstrate and to better understand biases in the results, if one of the input parameters is deliberately set fixed to a non-optimum value.

TIDAL TAILS OF GLOBULAR CLUSTERS

We present N-body simulations of globular clusters including gravitational field of the Galaxy, in order to study effects of tidal field systematically on the shape of outer parts of globular clusters using NBODY6. The Galaxy is assumed to be composed of central bulge and outer halo. We mvestigate the cluster of multi-mass models with a power-law initial mass function (IMF) starting with different initial masses, initial number of particles, different slopes of the IMF and different orbits of the cluster. We have examined the general evolution of the clusters, the shape of outer parts of the clusters, density profiles and the direction of tidal tails. The density profiles appear to become somewhat shallower just outside the tidal boundary consistent with some observed data. The position angle of the tidal tall depends on the location in the Galaxy as well as the direction of the motion of. clusters. We found that the clusters become more elongated at the apogalacticon than at the pengalacticon. The tidal tails may be used to trace the orbital paths of globular clusters.

Binary stars and the fundamental initial mass function

We have carried out Monte Carlo simulations in which we generate a random pairing of objects drawn from a pre-assumed single-star power-law initial mass function (IMF), which we call the fundamental IMF. We show how the mass functions of primary stars and secondary stars and the mass function of the total mass of systems (if we could resolve them) differ from the underlying fundamental IMF for different slopes of this IMF. We also compare our results with the observed IMF, the binary frequency and the binary mass-ratio distributions for field stars and conclude that the fundamental IMF of subsolar mass stars could be steeper than is currently believed. In other words, the low-mass turn-over of the observed (‘apparent’) IMF could be spurious, if the main-sequence binary fraction of field stars is close to 100 per cent (perhaps owing to invisible companions).

Evolution of globular cluster systems in elliptical galaxies -- II. Power-law initial mass function

We have studied the evolution of globular cluster systems (GCS) in elliptical galaxies with a power-law initial GCS mass function (GCMF) ($f(M) \propto M^{-\alpha}$) similar to that predicted by some theoretical studies of globular clusters formation and to that of young cluster systems observed in merging galaxies. We have carried out a survey over a large number of different host galaxies and we have considered different values for the index, $\alpha$, of the initial power-law GCMF ($\alpha=1.5,1.8,2.0$); we show the dependence of the main GCS final properties (mean mass and dispersion of the final GCMF, fraction of surviving clusters, radial gradient of the GCMF parameters) on the structure of the host galaxy and on the slope of the initial GCMF. For a subsample of host galaxies with values of effective masses and radii equal to those determined using observational data for a number of giant, normal and dwarf galaxies our results show that the relation between the final GCMF properties and those of the host galaxies as well as the dependence of the final GCMF parameters on the galactocentric distance within individual galaxies differ from those observed in old GCS: the values of the final GCS mean mass are in general smaller (4.2 < log M_final < 5.0) than those observed and the galaxy-to-galaxy dispersion of logM_final is larger than that reported by observational analyses. The results are compared with those of a companion paper in which we investigated the evolution of GCS with a log-normal initial GCMF and in which the final GCS properties were perfectly consistent with observations.

Modeling a High‐Mass Turn‐Down in the Stellar Initial Mass Function

Statistical sampling from the stellar initial mass function (IMF) for all star-forming regions in the Galaxy would lead to the prediction of ~1000 Msun stars unless there is a rapid turn-down in the IMF beyond several hundred solar masses. Such a turndown is not necessary for dense clusters because the number of stars sampled is always too small. Here we explore several mechanisms for an upper mass cutoff, including an exponential decline of the star formation probability after a turbulent crossing time. The results are in good agreement with the observed IMF over the entire stellar mass range, and they give a gradual turn down compared to the Salpeter function above ~100 Msun for normal thermal Jeans mass, M_J. The upper mass turn down should scale with M_J in different environments. A problem with the models is that they cannot give both the observed power-law IMF out to the high-mass sampling limit in dense clusters, as well as the observed lack of supermassive stars in whole galaxy disks. Either there is a sharper upper-mass cutoff in the IMF, perhaps from self-limitation, or the IMF is different for dense clusters than for the majority of star formation that occurs at lower density. Dense clusters seem to have an overabundance of massive stars relative to the average IMF in a galaxy.

Constraints on the Space Density of Methane Dwarfs and the Substellar Mass Function from a Deep Near-Infrared Survey.

We report preliminary results of a deep near-infrared search for methane-absorbing brown dwarfs; almost 5 yr after the discovery of Gl 229b, there are only a few confirmed examples of this type of object. New J-band, wide-field images, combined with preexisting R-band observations, allow efficient identification of candidates by their extreme (R-J) colors. Follow-up measurements with custom filters can then confirm objects with methane absorption. To date, we have surveyed a total of 11.4 deg2 to J approximately 20.5 and R approximately 25. Follow-up CH4 filter observations of promising candidates in one-fourth of these fields have turned up no methane-absorbing brown dwarfs. With 90% confidence, this implies that the space density of objects similar to Gl 229b is less than 0.012 pc-3. These calculations account for the vertical structure of the Galaxy, which can be important for sensitive measurements. Combining published theoretical atmospheric models with our observations sets an upper limit of alpha</=0.8 for the exponent of the initial mass function power law in this domain.

On the effects of dynamical evolution on the initial mass function of globular clusters

In this paper we show the results of a large set of N-body simulations modelling the evolution of globular clusters driven by relaxation,stellar evolution,disk shocking and including the effects of the tidal field of the Galaxy. We investigate the evolution of multi-mass models with a power-law initial mass function (IMF) starting with different initial masses, concentrations, slopes of the IMF and located at different galactocentric distances. We show to what extent the effects of the various evolutionary processes alter the shape of the IMF and to what extent these changes depend on the position of the cluster in the Galaxy. Both the changes in the global mass function and in the local one (measured at different distances from the cluster center) are investigated showing whether and where the local mass function keeps memory of the IMF and where it provides a good indication of the current global mass function. The evolution of the population of white dwarfs is also followed in detail and we supply an estimate of the fraction of the current value of the total mass expected to be in white dwarfs depending on the main initial conditions for the cluster (mass and position in the Galaxy).Simple analytical expression by which it is possible to calculate the main quantities of interest (total mass, fraction of white dwarfs, slope of the mass function) at any time t for a larger number of different initial conditions than those investigated numerically have been derived.

Measurement of the Elemental Abundances in Four Rich Clusters of Galaxies. II. The Initial Mass Function and Mass Loss in Elliptical Galaxies, Enrichment, and Energetics in the ICM

view Abstract Citations (128) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Measurement of the Elemental Abundances in Four Rich Clusters of Galaxies. II. The Initial Mass Function and Mass Loss in Elliptical Galaxies, Enrichment, and Energetics in the ICM Loewenstein, M. ; Mushotzky, R. F. Abstract We compare observations from the Advanced Satellite for Cosmology and Astrophysics of abundances in the intracluster media in four clusters, as reported by Mushotzky and coworkers, with calculations of enrichment by protogalactic supernova-driven winds in a simple stellar population with a power-law initial mass function. Using the most recently calculated yields from Type II supernovae, we find that we can account for the total observed amounts of iron, oxygen, and silicon if the initial mass function is significantly flatter than the Salpeter function. Some discrepancies with other elements are indicated. Model-independent implications for the origin and heating of the intracluster medium and for the energetics of protoelliptical galaxies are discussed. Publication: The Astrophysical Journal Pub Date: August 1996 DOI: 10.1086/177542 Bibcode: 1996ApJ...466..695L Keywords: GALAXIES: ELLIPTICAL AND LENTICULAR; CD; GALAXIES: ABUNDANCES; GALAXIES: LUMINOSITY FUNCTION; MASS FUNCTION; GALAXIES: INTERGALACTIC MEDIUM full text sources ADS | data products SIMBAD (6) NED (4) HEASARC (1) Related Materials (1) Part 1: 1996ApJ...466..686M

Proto--Brown Dwarfs. I. Methods and Results for High-Latitude Clouds

view Abstract Citations (31) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Proto--Brown Dwarfs. I. Methods and Results for High-Latitude Clouds Pound, Marc W. ; Blitz, Leo Abstract We describe a method for finding substellar-mass self-gravitating clumps ("proto-brown dwarfs") in nearby molecular clouds, using millimeter-wave telescopes. This method represents a novel approach to looking for brown dwarfs and, for the nearest molecular clouds, has a greater mass sensitivity than traditional methods. We describe how the method can distinguish between various functional forms of the low-mass (<0.2 Msun) stellar initial mass function, which is currently poorly constrained. We present results of a search for proto-brown dwarfs in high galactic latitude molecular clouds. The clouds have relatively low densities [n(H2) ≲ 104 cm-3], are at an average distance of 100 pc, and are apparently not forming stars. We find little unambiguous evidence for self-gravitating objects of any mass in them, although there are clearly clumps with masses as low as 3 MJupiter. We find two clumps in MBM 12(=L1457), the nearest molecular cloud to the sun, which have luminous masses within a factor of 3 of that needed to be gravitationally bound. One of these has a dense core which appears to be in hydrostatic equilibrium. If so, then it is the first known self-gravitating core in a high-latitude cloud. The mean pressure in the clumps is P/k = 2.9 × 105 K cm-3, at least one order of magnitude higher than the general ISM pressure. We therefore conclude that either the clumps are transient structures in regions of typical ISM pressure, or the clouds themselves are short-lived objects in overpressured regions. In the latter case, the clouds will disperse in less than about 106 yr. The search for pro to-brown dwarfs is being expanded to include known star-forming regions in the Ophiuchus and Taurus complexes. The results in Ophiuchus and Taurus will tightly constrain the functional form of the stellar initial mass function at very low masses regardless of whether or not any proto-brown dwarfs are found. The present results already exclude a single power-law initial mass function with index ≳2. Publication: The Astrophysical Journal Pub Date: November 1993 DOI: 10.1086/173394 Bibcode: 1993ApJ...418..328P Keywords: ISM: CLOUDS; ISM: INDIVIDUAL ALPHANUMERIC: L1257; ISM: STRUCTURE; RADIO CONTINUUM: STARS; STARS: LOW-MASS; BROWN DWARFS full text sources ADS | data products SIMBAD (14) Related Materials (2) Erratum: 1995ApJ...444..487P Part 2: 1995ApJ...444..270P

Mass-to-light ratios for globular clusters. II - The low-concentration clusters NGC 288, NGC 5466, and M55 (NGC 6809)

view Abstract Citations (57) References (89) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Mass-to-Light Ratios for Globular Clusters. II. The Low-Concentration Clusters NGC 288, NGC 5466, and M55 (NGC 6809) Pryor, Carlton ; McClure, Robert D. ; Fletcher, J. M. ; Hesser, James E. Abstract Radial velocities accurate to about 1 km/s are measured for 20-30 stars in each of the three low-concentration globular clusters NGC 288, NGC 5466, and M55 in order to calculate the velocity dispersions and mass-to-light ratios (MLRs) for these clusters, which are used to investigate their stellar populations. Single- and multicomponent King models are adapted to the present velocity data and to surface-brightness profiles taken from the literature. The MLRs of NGC 288, NGC 5466, and M55 do not differ significantly from one another or from those of the cluster population as a whole. The MLR of NGC 288 is lower than would be expected for a cluster that had a power law initial mass function as shallow as the observed present-day main-sequence mass function. Models with initial mass functions consisting of two power law segments fit NGC 288 best when 50 to 70 percent of the cluster mass is in stellar remnants. Publication: The Astronomical Journal Pub Date: September 1991 DOI: 10.1086/115929 Bibcode: 1991AJ....102.1026P Keywords: Globular Clusters; Mass To Light Ratios; Stellar Evolution; Stellar Mass; Astronomical Models; Radial Velocity; Astrophysics; CLUSTERS: GLOBULAR; RADIAL VELOCITIES full text sources ADS | data products SIMBAD (82) Related Materials (2) Part 1: 1989AJ.....98..596P Part 3: 1994AJ....107.1397P