|1- Haghi, H., Hoseini-Rad, S. M., Hasani Zonoozi, A., H. W. Küpper, A., "The effect of primordial mass segregation on the size scale of globular clusters ", MNRAS, 444, 3699-3708 , (2014).|
We use direct N-body calculations to investigate the impact of primordial mass segregation on the size scale and mass-loss rate of star clusters in a galactic tidal field. We run a set of simulations of clusters with varying degrees of primordial mass segregation at various galactocentric radii and show that, in primordially segregated clusters, the early, impulsive mass-loss from stellar evolution of the most massive stars in the innermost regions of the cluster leads to a stronger expansion than for initially non-segregated clusters. Therefore, models in stronger tidal fields dissolve faster due to an enhanced flux of stars over the tidal boundary. Throughout their lifetimes, the segregated clusters are more extended by a factor of about 2, suggesting that (at least) some of the very extended globular clusters in the outer halo of the Milky Way may have been born with primordial mass segregation. We finally derive a relation between star–cluster dissolution time, Tdiss, and galactocentric radius, RG, and show how it depends on the degree of primordial mass segregation.
|2- Hasani Zonoozi, A., Haghi, H., H. W. Küpper, A., Baumgardt, H., J. Frank, M., Kroupa, P., "Direct N-body simulations of globular clusters – II. Palomar 4", MNRAS, 440, 3172-3183 , (2014).|
We use direct N-body calculations to study the evolution of the unusually extended outer halo globular cluster Palomar 4 (Pal 4) over its entire lifetime in order to reproduce its observed mass, half-light radius, velocity dispersion and mass function slope at different radii. We find that models evolving on circular orbits, and starting from a non-mass segregated, canonical initial mass function (IMF) can reproduce neither Pal 4s overall mass function slope nor the observed amount of mass segregation. Including either primordial mass segregation or initially flattened IMFs does not reproduce the observed amount of mass segregation and mass function flattening simultaneously. Unresolved binaries cannot reconcile this discrepancy either. We find that only models with both a flattened IMF and primordial segregation are able to fit the observations. The initial (i.e. after gas expulsion) mass and half-mass radius of Pal 4 in this case are about 57 000 M⊙ and 10 pc, respectively. This configuration is more extended than most globular clusters we observe, showing that the conditions under which Pal 4 formed must have been significantly different from that of the majority of globular clusters. We discuss possible scenarios for such an unusual configuration of Pal 4 in its early years.
|3- Derakhshani , K., Haghi, H., "ERRATUM: THE MOND EXTERNAL FIELD EFFECT ON THE DYNAMICS OF THE GLOBULAR CLUSTERS:
GENERAL CONSIDERATIONS AND APPLICATION TO NGC 2419 (ApJ , 783, 48) ", ApJ , 785, 166-, (2014). (Comment- Hosein Haghi’s name was left off the author list in the original article.
The abstract of the original article (ApJ , 783, 48) can be found as follows)|
In this paper, we investigate the external field effect in the context of the MOdified Newtonian Dynamics (MOND) on the surface brightness and velocity dispersion profiles of globular clusters (GCs). Using N-MODY, which is an N-body simulation code with a MOND potential solver, we show that the general effect of the external field for diffuse clusters, which obey MOND in most of their parts, is that it pushes the dynamics toward the Newtonian regime. On the other hand, for more compact clusters, which are essentially Newtonian in their inner parts, the external field is effective mainly in the outer parts of compact clusters. As a case study, we then choose the remote Galactic GC NGC 2419. By varying the cluster mass, half-light radius, and mass-to-light ratio, we aim to find a model that will reproduce the observational data most effectively, using N-MODY. We find that even if we take the Galactic external field into account, a Newtonian Plummer sphere represents the observational data better than MOND to an order of magnitude in terms of the total χ2 of surface brightness and velocity dispersion.
|4- Haghi, H., Ghasemi, H., Zhao, H. S., "Evaluation of New MOND Interpolating Function
with Rotation Curves of Galaxies", Iranian Journal of Astronomy and Astrophysics, 1: (1), 43-56, (2013).|
The rotation curves of a sample of 46 low- and high-surface brightness galaxies are considered in the context of Milgrom's modi_ed dynamics (MOND) to test a new interpolating function proposed by Zhao et al. (2010)  and compare with the results of simple interpolating function. The predicted rotation curves are calculated from the total baryonic matter based on the B-band surface photometry, and the observed distribution of neutral hydrogen, in which the one adjustable parameter is the stellar mass-to-light ratio. The predicted rotation curves generally agree with the observed curves for both interpolating functions. We show that the _tted M=L in the B-band correlates with B-V color in the sense expected from what we know about stellar population synthesis models. Moreover, the mass-to-light ratios of MOND with new interpolating function is in consistent with scaled Salpeter's initial mass function of the SPS scheme, while those of MOND with simple interpolating function favor Kroupa IMF.
|5- Frank, M. J., Hilker, M., Baumgardt, H., Côté, P., Haghi, H., Küpper, A. H. W., Djorgovski, S. G., "The velocity dispersion and mass function of the outer halo globular cluster Palomar 4", Mon. Not. R. Astron. Soc, 423, 2917-2932 , (2012).|
We obtained precise line-of-sight radial velocities of 23 member stars of the remote halo globular cluster Palomar 4 (Pal 4) using the High Resolution Echelle Spectrograph (HIRES) at the Keck I telescope. We also measured the mass function of the cluster down to a limiting magnitude of V~28 mag using archival HST/WFPC2 imaging. We derived the cluster's surface brightness profile based on the WFPC2 data and on broad-band imaging with the Low-Resolution Imaging Spectrometer (LRIS) at the Keck II telescope. We find a mean cluster velocity of 72.55+/-0.22 km/s and a velocity dispersion of 0.87+/-0.18 km/s. The global mass function of the cluster, in the mass range 0.55<=M<=0.85 M_solar, is shallower than a Kroupa mass function and the cluster is significantly depleted in low-mass stars in its center compared to its outskirts. Since the relaxation time of Pal 4 is of the order of a Hubble time, this points to primordial mass segregation in this cluster. Extrapolating the measured mass function towards lower-mass stars and including the contribution of compact remnants, we derive a total cluster mass of 29800 M_solar. For this mass, the measured velocity dispersion is consistent with the expectations of Newtonian dynamics and below the prediction of Modified Newtonian Dynamics (MOND). Pal 4 adds to the growing body of evidence that the dynamics of star clusters in the outer Galactic halo can hardly be explained by MOND.
|1- Haghi, H., "The remote Galactic globular clusters as a tool to test
gravity models and direct N-body simulation", Dynamics and kinetic theory of
self-gravitating systems, IHP Gravasco Trimester, Paris, (2013).|
|2- Haghi, H., "How primordial mass segregation can increase the size scale
of the star clusters", Vlasov-Poisson : the numerical approach and its limits, IHP Gravasco Trimester, Paris, (2013).|
|3- Haghi, H., "Direct N-body simulations of globular clusters", 1st Doha International Astronomy Conference, Doha, Qatar, (2013).|
|4- Haghi, H., "Distant star clusters of the Milky Way in MOND ", Modified gravity approach to dark sector, Strasbourg, France, (2010).|
|5- Haghi, H., "Testing Fundamental Physics with Distant star Clusters", Tidal Dwarf Galaxies, Physics Centre Bad-Honnef, Germany, (2009).|