scholarly journals ON THE PROBLEM OF THE SPECIFIC FREQUENCY OF GLOBULAR CLUSTERS

2021 ◽  
pp. 137-142
Author(s):  
Ikram Uralbaevich Tadjibaev
Keyword(s):  
Observational Data ◽  
Globular Clusters ◽  
Spiral Galaxies ◽  
Empirical Relationship ◽  
Flux Ratio ◽  
Quadratic Function ◽  
Absolute Magnitude ◽  
Host Galaxy ◽  
Specific Frequency ◽  
The Absolute

In the article, on the basis of observational data the problems of the specific frequency of globular clusters are studied. Possible relationships between them and the absolute stellar magnitude of their host galaxy are considered, where the observational data published in the literature were presented. It should be noted that before us the relationship between the specific frequency and the absolute magnitude is shown as exponential functions. An empirical relationship between the specific frequency and the absolute value of the host galaxy were obtained and showed that the dependence of the specific frequency on the absolute magnitude is not linear, but has a quadratic function. It is also shown that the specific frequency determines the number of globular clusters in a given galaxy relative to our Galaxy. Also in the article, based on the results of studies of the specific frequency, some discussions are presented related to the origin and evolution of globular clusters. The results obtained show that the ratios of the specific frequency to the luminosity of the host galaxy are different. Variations in the specific frequency of elliptical galaxies are associated with variations in the mass-to-luminous flux ratio. This may be due to the fact that the number of globular clusters in spiral galaxies per unit of luminosity of the halo and not of the entire galaxy. Analysis of the observational data shows that the values of the specific frequency of spiral galaxies are 5–6 times less than that of giant elliptical ones. As a result of the results of studies of the specific frequency of the globular clusters, unsolved problems are listed and possible solutions are shown. It is noted that the problem posed will be solved even more accurately if it is considered by the types of galaxies

The range of UV upturn strengths in early-type galaxies can be caused by dissolved metal-rich Globular Clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 112-116
Author(s):  
Paul Goudfrooij
Keyword(s):  
Globular Clusters ◽  
Dynamical Evolution ◽  
Virgo Cluster ◽  
Host Galaxy ◽  
Early Type ◽  
Luminosity Functions ◽  
Central Regions ◽  
Specific Frequency ◽  
Uv Upturn

AbstractI summarize the scenario by Goudfrooij (2018) in which the bulk of the ultraviolet (UV) upturn of giant early-type galaxies (ETGs) is due to helium-rich stellar populations that formed in massive metal-rich globular clusters (GCs) and subsequently dissolved in the strong tidal field in the central regions of the massive host galaxy. These massive GCs are assumed to show UV upturns similar to those observed recently in M87, the central galaxy in the Virgo cluster of galaxies. Data taken from the literature reveals a strong correlation between the strength of the UV upturn and the specific frequency of metal-rich GCs in ETGs. Adopting a Schechter function parametrization of GC mass functions, simulations of long-term dynamical evolution of GC systems show that this correlation can be explained by variations in the characteristic truncation mass Mc such that Mc increases with ETG luminosity in a way that is consistent with observed GC luminosity functions in ETGs. These findings suggest that the nature of the UV upturn in ETGs and the variation of its strength among ETGs are causally related to that of helium-rich populations in massive GCs, rather than intrinsic properties of field stars in ETGs.

scholarly journals The Absolute Magnitudes of RR Lyrae Stars and the Age of the Galaxy

1989 ◽  
Vol 111 ◽  
pp. 121-140
Author(s):  
Allan Sandage
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
Cluster System ◽  
Apparent Magnitude ◽  
Rr Lyrae ◽  
Globular Cluster System ◽  
The Absolute ◽  
Absolute Magnitudes

AbstractIt is shown that the intrinsic spread in the absolute magnitudes of the RR Lyrae variables in a given globular cluster can reach 0.5 magnitudes at a given period or at a given color, due to luminosity evolution away from the zero age horizontal (ZAHB). The size of this intrinsic luminosity spread is largest in clusters of the highest metallicity.The absolute magnitude of the ZAHB itself also differs from cluster to cluster as a function of metallicity, being brightest in clusters of the lowest metallicity. Three independent methods of calibrating the ZAHB RR Lyrae luminosities each show a strong variation of MV(RR) with [Fe/H]. The pulsation equation of P<ρ>0.5 = Q(M,Te, L) used with the observed periods, temperatures, and masses of field and of cluster RR Lyraes gives the very steep luminosity-metallicity dependence of dMv(RR)/d[Fe/H] = 0.42. Main sequence fitting of the color-magnitude diagrams of clusters which have modern main-sequence photometry gives a confirming steep slope of 0.39. A summary of Baade-Wesselink MV(RR) values for field stars determined in four independent recent studies also shows a luminosity-metallicity dependence, but less steep with a slope of dMV(RR)/d[Fe/H] = 0.21.Observations show that the magnitude difference between the main sequence turn-off point and the ZAHB in a number of well observed globular clusters is independent of [Fe/H], and has a stable value of dV = 3.54 with a disperion of only 0.1 magnitudes. Using this fact, the absolute magnitude of the main sequence turn-off is determined in any given globular cluster from the observed apparent magnitude of the ZAHB by adopting any particular MV(RR) = f([Fe/H]) calibration.Ages of the clusters are shown to vary with [Fe/H] by amounts that depend upon the slopes of the MV(RR) = f([Fe/H]) calibrations. The calibrations show that there would be a steep dependence of the age on [Fe/H] if MV(RR) does not depend on [Fe/H]. No dependence of age on metallicity exists if the RR Lyrae luminosities depend on [Fe/H] as dMV(RR)/d[Fe/H] = 0.37. If Oxygen is not enhanced as [Fe/H] decreases, the absolute average age of the globular cluster system is 16 Gyr, independent of [Fe/H], using the steep MV(RR)/[Fe/H] calibration that is favored. If Oxygen is enhanced by [O/Fe] = – 0.14 [Fe/H] + 0.40 for [Fe/H] < –1.0, as suggested from the observations of field subdwarfs, then the age of the globular cluster system decreases to 13 Gyr, again independent of [Fe/H], if the RR Lyrae ZAHB luminosities have a metallicity dependence of dMV(RR)/d[Fe/H] = 0.37.

scholarly journals 1.12. Structure of the inner galactic disk and the bulge - first results

1998 ◽  
Vol 184 ◽  
pp. 39-40
Author(s):  
S. Feltzing
Keyword(s):  
Observational Data ◽  
Globular Clusters ◽  
Spiral Galaxies ◽  
Galactic Disk ◽  
Galactic Bulge ◽  
Very Old ◽  
Difficult Question ◽  
First Results ◽  
Observational Status

Is there an age and/or a metallicity gradient in the Bulge? This is a notoriously difficult question because of the well known age-metallicity-distance degeneracy in colour magnitude diagrams (CMD) as well as the severe crowding and large reddening towards the Galactic Bulge. The current observational data on the bulge in our galaxy and bulges in other spiral galaxies point in disparate directions, that is evidence for both early (e.g. existence of very old halo and bulge globular clusters) and late formation (e.g. Sgr dSph and bar instabilities) can be found as well as the existence and non-existence of metallicity gradients (for a review of the observational status see Wyse, Gilmore & Franx 1997). We here present the CMDs for two fields, Baade's window and SGR-I, Fig.1c and d. Both these regions have low extinction. To determine the age and metallicity for these stars we compare the CMDs with CMDs of globular clusters, also observed with WFPC2, of known metallicity and age, Fig.1a and b. This method enables us to work entirely in the in-flight magnitude system of WFPC2 and there is no need for transformations to standard colours and magnitudes, something which is not straight forward for WFPC2 passbands.

scholarly journals Metallicity Distributions in Extragalactic Globular Cluster Systems: Constraints on Globular Cluster and Galaxy Formation

1998 ◽  
Vol 11 (1) ◽  
pp. 82-85
Author(s):  
Jean P. Brodie
Keyword(s):  
Galaxy Formation ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Spiral Galaxies ◽  
Elliptical Galaxy ◽  
Elliptical Galaxies ◽  
Imaging Data ◽  
Merger Process ◽  
Specific Frequency ◽  
Multi Phase

The merger model for elliptical galaxy formation has received increasing attention since it was first suggested by Toomre & Toomre (1972). Van den Bergh (1984) pointed out a problem with the idea that elliptical galaxies were formed by simply combining two, or more, spiral galaxies. He noted that the specific frequency (SN, number of globular clusters per unit galaxy light) is systematically lower for spirals than for ellipticals. Schweizer (1987) suggested that globular clusters (GCs) might be expected to form in the merger process, thereby alleviating or possibly eliminating the SN problem. Ashman & Zepf (1992) developed this idea into a merger model for GC formation with testable predictions. We recently examined this model in the light of new HST and ground-based imaging data on the blue and red sub-populations of GCs in elliptical galaxies (Forbes, Brodie & Grillmair 1997). We concluded that the merger model for GC formation has serious problems, particularly in explaining the characteristics of GCs in giant elliptical galaxies with high SN. A multi-phase collapse scenario was suggested as more consistent with the available evidence.

The Luminosity-Metallicity Relation for RR Lyrae Stars and its Implications for the Astronomical Distance Scale

1989 ◽  
Vol 111 ◽  
pp. 255-255
Author(s):  
G. Clementini ◽  
C. Cacciari
Keyword(s):  
Globular Clusters ◽  
Galactic Center ◽  
Absolute Magnitude ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Visual Magnitude ◽  
Phase Range ◽  
The Absolute ◽  
Lyrae Stars ◽  
Magnitude Difference

AbstractThe surface brightness version of the Baade-Wesselink method, has been applied to 7 field RR Lyrae stars with metallicity ranging from [Fe/H]= −0.2 to −1.5. V magnitudes, V-R and V-I colors and CORAVEL radial velocities were used, and the analysis was performed over a restricted phase range in order to avoid the complications caused by the pulsating atmospheres. The combination with previous results of the B-W method, which used comparable criteria (Jones, Carney, & Latham, 1988, preprint; Jameson, Fernley, & Longmore 1987, in press M.N.R.A.S; Cohen & Gordon 1987, Ap.J., 318, 215) leads to the following relation between the absolute luminosity and metallicity:Mv = (1.0 ± 0.05) + (0.17 ± 0.05) [Fe/H]This relation is in very good agreement with the preliminary results found by Liu and Janes (this volume). The application of the above relation to the RR Lyraes in M31 and the Magellanic Clouds leads to distance moduli of (m–M)o= 24.21 ± 0.20 for M31, (m–M)o = 18.26 ± 0.20 for the LMC, and (m–M)o =18.85 ± 0.20 for the SMC, and the distance to the galactic center turns out to be approximately 7.2 kpc. From the absolute magnitude of the RR Lyraes and adopting a constant visual magnitude difference between the RR Lyraes and the turn-off ΔV = 3.55 (Buonanno 1986, Mem.S.A.It., 57, 333), we estimate ages of 18.8 and 15.7 Gyr for globular clusters of metallicity [Fe/H] = −2.2 (e.g. M92) and [Fe/H] = −0.8 (e.g. 47 Tuc) respectively, using the age-turnoff luminosity relation derived by Sandage (1982, Ap.J., 252, 553) or 20.9 and 16.9 Gyr using Buonanno’s relation.

scholarly journals The Luminosities of Horizontal Branches and RR Lyrae Stars in Globular Clusters

2004 ◽  
Vol 193 ◽  
pp. 525-529 ◽  
Author(s):  
D.H. McNamara ◽  
M.B. Rose ◽  
P.J. Brown ◽  
D.I. Ketcheson ◽  
J.E. Maxwell ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Absolute Magnitude ◽  
Apparent Magnitude ◽  
Rr Lyrae Stars ◽  
Blue Stragglers ◽  
Rr Lyrae ◽  
The Absolute ◽  
The Difference ◽  
Absolute Magnitudes ◽  
Lyrae Stars

AbstractWe have utilized the latest stellar models of the Y2 (Yonsei-Yale) collaborators and color-magnitude diagrams of globular clusters to infer ages and absolute magnitudes of their horizontal branches (HB). The intrinsic (B – V) color indices of the turn-offs, of the globular clusters were used to find ages. For 47 clusters that appear to be coeval (within ±0.7 Gyr), we find an average age of 12.5 Gyr. We adopt this age and infer the absolute magnitudes of the turn-offs, from the clusters [Fe/H] values. The absolute magnitude of the horizontal branches or RR Lyrae stars are then determined from the difference between the apparent magnitudes of the horizontal branches (or RR Lyrae stars) and the apparent magnitude of the turn-offs, VTO. We conclude: 1) The slope of the MV(HB), [Fe/H] relation is ~0.3 for clusters with [Fe/H] values between —0.5 to —1.5. The relation has zero slope for [Fe/H] values smaller than −1.5. 2) For [Fe/H] < -1.3, the MV(HB) or MV values of RRLyrae stars are not only a function of [Fe/H], but the horizontal-branch type in the sense that the clusters with the blue horizontal branches have more luminous horizontal branches than clusters with red horizontal branches. The same results are found by inferring the luminosities of the HBs from pulsating blue stragglers.

scholarly journals A stellar census in globular clusters with MUSE

2020 ◽  
Vol 635 ◽  
pp. A114 ◽  
Author(s):  
Tim-Oliver Husser ◽  
Marilyn Latour ◽  
Jarle Brinchmann ◽  
Stefan Dreizler ◽  
Benjamin Giesers ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Near Infrared ◽  
Quadratic Function ◽  
Absolute Magnitude ◽  
Type I ◽  
Type Ii ◽  
Single Star ◽  
Link Type ◽  
Different Populations ◽  
Red Giant

Aims. We use the spectra of more than 30 000 red giant branch (RGB) stars in 25 globular clusters (GC), obtained within the MUSE survey of Galactic globular clusters, to calibrate the Ca II triplet metallicity relation and derive metallicities for all individual stars. We investigate the overall metallicity distributions as well as those of the different populations within each cluster. Methods. The Ca II triplet in the near-infrared at 8498, 8542, and 8662 Å is visible in stars with spectral types between F and M and can be used to determine their metallicities. In this work, we calibrate the relation using average cluster metallicities from literature and MUSE spectra, and extend it below the horizontal branch – a cutoff that has traditionally been made to avoid a non-linear relation – using a quadratic function. In addition to the classic relation based on V − VHB, we also present calibrations based on absolute magnitude and luminosity. The obtained relations were used to calculate metallicities for all the stars in the sample and to derive metallicity distributions for different populations within a cluster, which have been separated using so-called “chromosome maps” based on HST photometry. Results. We show that despite the relatively low spectral resolution of MUSE (R = 1900 − 3700) we can derive single star metallicities with a mean statistical intra-cluster uncertainty of ∼0.12 dex. We present metallicity distributions for the RGB stars in 25 GCs and investigate the different metallicities of the populations P3 (and higher) in so-called metal-complex or Type II clusters, finding metallicity variations in all of them. We also detected unexpected metallicity variations in the Type I cluster NGC 2808 and confirm the Type II status of NGC 7078.

scholarly journals Luminosity functions of globular clusters in five nearby spiral galaxies using HST/ACS images

2021 ◽  
Author(s):  
Luis Lomelí-Núñez ◽  
Y D Mayya ◽  
L H Rodríguez-Merino ◽  
P A Ovando ◽  
D Rosa-González
Keyword(s):  
Globular Clusters ◽  
Luminosity Function ◽  
Spiral Galaxies ◽  
Hubble Space Telescope ◽  
Luminosity Functions ◽  
Radial Density Distribution ◽  
Specific Frequency ◽  
Exponential Power ◽  
Turn Over ◽  
Poor Population

Abstract We here present the luminosity function (LF) of globular clusters (GCs) in five nearby spiral galaxies using the samples of GC candidates selected in Hubble Space Telescope mosaic images in F435W, F555W and F814W filters. Our search, which surpasses the fractional area covered by all previous searches in these galaxies, has resulted in the detection of 158 GC candidates in M81, 1123 in M101, 226 in NGC 4258, 293 in M51 and 173 in NGC 628. The LFs constructed from this dataset, after correcting for relatively small contamination from reddened young clusters, are lognormal in nature, which was hitherto established only for the Milky Way (MW) and Andromeda among spiral galaxies. The magnitude at the turn-over (TO) corresponds to MV0(TO)=-7.41±0.14 in four of the galaxies with Hubble types Sc or earlier, in excellent agreement with MV(TO) = −7.40 ± 0.10 for the MW. The TO magnitude is equivalent to a mass of ∼3 × 105 M⊙ for an old, metal-poor population. MV0(TO) is fainter by ∼1.16 magnitude for the fifth galaxy, M 101, which is of Hubble type Scd. The TO dependence on Hubble type implies that the GCs in early-type spirals are classical GCs, which have a universal TO, whereas the GC population in late-type galaxies is dominated by old disk clusters, which are in general less massive. The radial density distribution of GCs in our sample galaxies follows the Sérsic function with exponential power-law indices, and effective radii of 4.0–9.5 kpc. GCs in the sample galaxies have a mean specific frequency of 1.10 ± 0.24, after correcting for magnitude and radial incompleteness factors

scholarly journals Constraints on Galaxy Formation from Extragalactic Globular Clusters

2002 ◽  
Vol 187 ◽  
pp. 175-184
Author(s):  
Jean P. Brodie
Keyword(s):  
Galaxy Formation ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Spiral Galaxies ◽  
Elliptical Galaxy ◽  
Cluster Formation ◽  
Elliptical Galaxies ◽  
Merger Process ◽  
Specific Frequency

The merger model for elliptical galaxy formation has received increasing attention since it was first suggested by Toomre & Toomre (1972). Van den Bergh (1984) pointed out a problem with the idea that elliptical galaxies were formed by simply combining two, or more, spiral galaxies. He noted that the specific frequency (SN, number of globular clusters per unit galaxy light) is systematically lower for spirals than for ellipticals. Schweizer (1987) suggested that globular clusters might be expected to form in the merger process, thereby alleviating or possibly eliminating the SN problem. Ashman & Zepf (1992) developed this idea into a merger model for globular cluster formation with testable predictions.

Discovery, Observational Data and the Orbit of the Amor Group Asteroid 2010 BT3

2012 ◽  
Vol 21 (3) ◽  
Author(s):  
K. Černis ◽  
J. Zdanavičius ◽  
I. Wlodarczyk ◽  
E. Stonkutė
Keyword(s):  
Observational Data ◽  
Absolute Magnitude ◽  
Apparent Brightness ◽  
Photometric Observations ◽  
The Absolute ◽  
Near Earth Objects

AbstractA project devoted to astrometric and photometric observations of asteroids at the Molėtai Observatory is described. One of its most important results is the discovery of the asteroid 2010 BT3 belonging to the Amor group of the near-Earth objects. The results of astrometric and photometric observations of the asteroid are presented. The brightness variations of the asteroid are found to be about 0.2 mag in R. The orbit of the asteroid was computed from 96 observations. This orbit, combined with the apparent brightness, gives the absolute magnitude 21.34 mag and the diameter between 160 m and 360 m, taking albedos of S-type and C-type asteroids, respectively.

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