PDF superior Variable stars in the fornax dsph galaxy I The globular cluster fornax 4

Variable stars in the fornax dsph galaxy  I  The globular cluster fornax 4

Variable stars in the fornax dsph galaxy I The globular cluster fornax 4

significant terms only ( Poretti 2001). Visual inspection of the intranight light curves was also performed. After having com- pared the results, only candidate variable stars confirmed by both methods have been accepted (29 stars in total). Our time series extends over three consecutive nights in 2003, four nights in 2004, and one further night in 2005 (see Table 1). Variable stars with periods of several days or longer would not be detectable in the data set of each individual year, since the long period will show effects only on longer timescales. Such long-period variable stars, if present, would manifest themselves as stars having different magnitudes in the three years of our survey; since we have only 4 or 5 epochs, they would appear as periodic variable stars with a prominent low-frequency peak in the power spectra. Indeed, we do not have such candidates in our sample. At the same extent, non- periodic variable stars with a timescale of 1 Y 5 days will manifest themselves as periodic variable stars, since any periodogram will find a (false) period when a nonperiodic variable is sampled at 4 or 5 epochs only. Irregular, rapid-variable stars are of course un- detectable, but they are also not very probable. In conclusion, it is rather unlikely that we have missed any such long-period var- iable stars in For 4, if any are present.
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THE ACS FORNAX CLUSTER SURVEY  IX  THE COLOR MAGNITUDE RELATION OF GLOBULAR CLUSTER SYSTEMS

THE ACS FORNAX CLUSTER SURVEY IX THE COLOR MAGNITUDE RELATION OF GLOBULAR CLUSTER SYSTEMS

the FCS, (3) GCs belonging to high-mass galaxies, and (4) GCs belonging to low-mass galaxies. The vertical dashed lines in each panel mark the color expected for the blue and red populations based on the relation between the host galaxy magnitude and peak colors presented in Peng et al. (2006). Filled circles indicate the KMM fitting results, corresponding to the means obtained from adopting two different initial guesses (indicated by asterisks; see Section 3.1 for more details). The number of luminosity bins is 25, except for NGC 1399, where 10 luminosity bins were adopted. The solid blue and red lines indicate linear least-square fits to the KMM peak positions. The long-dashed line at intermediate colors denotes the dividing point between the blue and red peaks (i.e., the color where both blue and red peaks contribute 50% to the number counts) derived from the KMM fits. The open triangles indicate the median color of GCs blueward and redward of the dividing line. The dotted line is a fit to the median colors. For both the CMD of NGC 1399 and that of the FCS high-mass sample, we also show least-squares fits to the median colors blueward and redward of a magnitude-independent dividing line. This dividing line is given by the mean color of the long-dashed line between the brightest magnitude bin and M z = − 8.1 mag.
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New variable stars in the globular cluster NGC 5694

New variable stars in the globular cluster NGC 5694

the 1.3m telescope, comprising a total of 41, 43, and 44 images in B, V , and I, respec- tively. The second dataset was obtained in the course of 4 nights, between June 30 and July 23, 2007, with the 0.9m telescope, comprising a total of 5 images per filter. The third dataset was again obtained in the course of 4 nights, between January 10 and 14, 2010, with the 1.0m telescope, comprising a total of 6 images per filter.

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The Globular Cluster NGC 5286  II  Variable Stars

The Globular Cluster NGC 5286 II Variable Stars

The position of the cluster in a metallicity versus HB- type diagram is displayed in Figure 6. Here HB type L ≡ (B − R)/(B + V + R), where B , R , V are the numbers of blue, red, and variable (RR Lyrae-type) HB stars, respectively; this quantity was derived for NGC 5286 in Paper I. As discussed by Catelan (2009), Oosterhoff-intermediate GCs, such as found in several GCs associated with the dwarf satellite galaxies of the Milky Way, tend to cluster inside the triangular-shaped region marked in this diagram—whereas Galactic GCs somehow are not found in this same region, thus giving rise to the Oosterhoff dichotomy in the Galaxy. In this same plane, OoI clusters tend to fall to the left (i.e., redder HB types) of the triangular-shaped region, whereas OoII objects are more commonly found to its right. NGC 5286 falls rather close to the Oosterhoff-intermediate region in this plane, but its position is indeed still consistent with OoII status (see also Figure 8 in Catelan 2009).
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The ACS Fornax Cluster survey  I  Introduction to the survey and data reduction procedures

The ACS Fornax Cluster survey I Introduction to the survey and data reduction procedures

As a first attempt to solve the problem, a new set of PSFs was constructed using k 1000 stars in fields located in the out- skirts of the Galactic GC 47 Tucanae ( programs GO-10048 and GO-10375). We determined three different PSFs using obser- vations taken in 2004 September, 2004 December, and 2005 February. By doing so, we generated an empirical PSF for each galaxy that was determined no more than two months from the ACSFCS observations. This procedure was motivated by the fact that, on 2004 December 20, HST underwent a secondary mirror adjustment (which the observatory is regularly subjected to in order to correct systematic changes in the relative position of the primary and secondary mirrors). In this particular case, the secondary mirror was moved by 4.16 m, a sizable displace- ment that certainly changed the focus and affected the PSF ( Krist 2003). Although the empirically derived PSFs clearly reveal the postmovement PSF to show a more compact core, a redetermi- nation of the GC sizes showed that these new PSFs did not solve the anomalous sizes found in the g band. Nevertheless, the new PSFs do constitute an improvement over the single PSF ap- proach adopted for the ACSVCS ( both in terms of time sam- pling and number of stars used to construct the PSF), so we kept them for the analysis of all galaxies that do not show an anom- alous size difference. For galaxies that were observed after 2004
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VARIABLE STARS IN THE GLOBULAR CLUSTER NGC 2808

VARIABLE STARS IN THE GLOBULAR CLUSTER NGC 2808

The variables all occupy the area of the PA diagram where the M3 RRL as well as where other Oosterhoff I RRLs have been shown to reside (e.g., Clement & Shelton 1999). The position of a star in this diagram can be affected by the presence of the Blazhko effect (e.g., Cacciari et al. 2005), and as discussed above, almost all the RR Lyrae variables presented here show signs of this phenomenon. Because the light curves presented here have a large number of observations, it is straightforward to determine the amplitudes using the average light curves of the Blazhko stars. Nevertheless, a visual determination of the change in amplitude in each Blazhko RR0 is obtained and shown as a symmetric error bar in the figure. The change from the average light curve amplitude to the maximum Blazhko amplitude ranges from ∼0.1 to 0.4 mag. Even when taking the amplitude variation due to the Blazhko cycle into account, the variables are all of OoI type. We note that our assumption of a symmetric Blazhko amplitude change may overestimate the lower amplitude value, as exhibited for example by the shortest- period RR Lyrae variable V23. The light curve of V23 does not seem to show amplitudes that fall to zero at some points; its error bar reaching to almost zero is an artifact of assuming symmetric error bars. Such an overestimate would not change our conclusion that all the variables are OoI-type.
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A detailed census of variable stars in the globular cluster NGC 6333 (M9) from CCD differential photometry

A detailed census of variable stars in the globular cluster NGC 6333 (M9) from CCD differential photometry

Recently our team has performed CCD photometry of several globular clusters by employing the DIA technique to produce precise time series photometry of individual stars down to V ∼ 19.5 mag. The DIA photometry has proven to be a very useful tool in obtaining high-quality light curves of known variables, and for discovering and classifying new variables (e.g. Arellano Ferro et al. 2011; Bramich et al. 2011; Kains et al. 2012; Figuera Jaimes et al. 2013; and references therein), where previous CCD photomet- ric studies have not detected stellar variability, particularly in the crowded central regions of the clusters. Thus, in this paper we report the analysis of new time series photometry of NGC 6333 in the V and I filters. In Section 2, we describe the observations and data reductions. In Section 3, the problem of the differential reddening in the cluster field of view (FOV) is addressed and the approach we used to correct it is described. Section 4 contains a detailed discussion on the approach to the identification of new variables and their classification. In Section 5, we apply Fourier light-curve
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The Globular Cluster NGC 6402 (M14)  II  Variable Stars

The Globular Cluster NGC 6402 (M14) II Variable Stars

clear differences in mass and kinematics, compared to GCs without EHBs. They speculate that this difference may point to an extragalactic origin of GCs with EHBs; in particular, they might be former nuclei of dwarf galaxies that were dis- rupted as they were accreted by the Milky Way, or genuine GCs formed in the outskirts of the “building blocks” that were later accreted to the Galaxy’s halo. In this sense, Gao et al. (2007) also studied the possible origin of halo GCs from past accretion events. Searching for GCs sharing both specific en- ergy and angular momentum and that lie on the same orbital plane, as expected if they have a common origin, they found five possible ghost streams that may be associated to merging events, with M14 being a member of one of these streams. In- terestingly, NGC 6864 (M75), an EHB cluster with a possible OoInt classification (Corwin et al. 2003; Scott et al. 2006), is also a suggested member of the same stream. The remaining cluster in this ghost stream, NGC 6535, has only two reported variables (Liller & Clement 1977), one of them correspond- ing to an RRab star with a period of P = 0.5884 d (i.e., close to the middle of the “Oosterhoff gap” in Fig. 8), and the other being a short-period RRc. Judging from their magnitudes, however, both of these stars are likely field stars in the back- ground of the cluster (Liller 1980; Sarajedini 1994). Interest- ingly, several of the GCs belonging to other ghost streams in Gao et al. (2007) had previously been suggested to have an extragalactic origin.
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THE VARIABLE STAR POPULATION OF THE GLOBULAR CLUSTER B514 IN THE ANDROMEDA GALAXY

THE VARIABLE STAR POPULATION OF THE GLOBULAR CLUSTER B514 IN THE ANDROMEDA GALAXY

We have identified and obtained periods and light curves for 82 RRab stars and 7 RRc stars in the GC B514 of the Andromeda galaxy. The average period of the B514 RRab stars for which we have complete and reliable light curves and their location on the period–amplitude diagram indicate likely OoI- type characteristics (see the right side of Figure 4), however, the cluster’s low metallicity is more typical of an OoII type. Thus, B514 seems to follow a different rule than what is found in the MW, where metal-poor ([Fe/H] −1.7) GCs containing RR Lyrae stars have Oosterhoff II type. This may suggest that B514 is indeed a somewhat peculiar cluster, as indicated by independent evidence of some similarity with peculiar clusters in the MW such as ω Cen, M54, and NGC2419 (Federici et al. 2007). Alternatively, we are seeing an indication that the M31 GCs have different RR Lyrae pulsation characteristics than that seen in the main body of the MW GCs. A more detailed analysis will be done based on the entire sample of M31 clusters observed in our Cycle 15 program, and the results will be presented in a forthcoming paper (R. Contreras et al. 2010, in preparation).
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Variable stars in the fornax dSph galaxy  III  The globular cluster fornax 5

Variable stars in the fornax dSph galaxy III The globular cluster fornax 5

We have also reconsidered the HB morphology of For 5 by computing the Lee–Zinn parameter (Zinn 1986; Lee 1990; Lee et al. 1990), (B − R)/(B+V + R) (where B, R, and V represent the numbers of blue, red, and variable stars on the HB, respectively) of For 5, based on our photometry and number counts. We have considered only stars with 8 < r < 45 , since we do not have reliable photometry of the Magellan data within 8 . Our results are: R = 8 ± 1, V = 16 ± 1, B = 33 ± 1, and (B − R)/(B+V + R) = 0.44 ± 0.17 in agreement with Buonanno et al. (1998) who derived 0.44 ± 0.09, and slightly smaller than the MG03 values, who find 0.52 ± 0.04 (all chips) and 0.52 ± 0.05 (PC only). According to our (B − R)/(B +V + R) value For 5 locates on the right edge of the distribution of the Oo-Int clusters band in the [Fe/H]-HB type diagram (see Figure 8 in Catelan 2009), for [Fe/H] = −2.20 dex, and on the middle of this band for [Fe/H] = −1.73 dex. We note that the MG03 values would instead place For 5 slightly outside the Oo-Int band for [Fe/H] = −2.20 dex (see Figure 8 of Catelan 2009).
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THE ADVANCED CAMERA FOR SURVEYS FORNAX CLUSTER SURVEY  VII  HALF LIGHT RADII OF GLOBULAR CLUSTERS IN EARLY TYPE GALAXIES

THE ADVANCED CAMERA FOR SURVEYS FORNAX CLUSTER SURVEY VII HALF LIGHT RADII OF GLOBULAR CLUSTERS IN EARLY TYPE GALAXIES

We measure the half-light radii of globular clusters (GCs) in 43 galaxies from the Advanced Camera for Surveys (ACS) Fornax Cluster Survey. We use these data to extend previous work in which the environmental dependen- cies of the half-light radii of GCs in early-type galaxies in the ACS Virgo Cluster Survey were studied, and a corrected mean half-light radius (corrected for the observed environmental trends) was suggested as a reliable distance indicator. This work both increases the sample size for the study of the environmental dependencies, and adds leverage to the study of the corrected half-light radius as a possible distance indicator (since Fornax lies at a larger distance than the Virgo cluster). We study the environmental dependencies of the size of GCs using both a Principal Component Analysis as well as two-dimensional scaling relations. We largely confirm the environmental dependencies shown in Jord´an et al., but find evidence that there is a residual correlation in the mean half-light radius of GC systems with galaxy magnitude, and subtle differences in the other correlations—so there may not be a universal correction for the half-light radii of lower luminosity galaxy GC systems. The main factor determining the size of a GC in an early-type galaxy is the GC color. Red GCs have r h = 2.8 ± 0.3 pc, while blue GCs
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Variable stars in the Quintuplet stellar cluster with the VVV survey

Variable stars in the Quintuplet stellar cluster with the VVV survey

Differential Image Analysis (DIA; Wozniak 2008 and references therein) is a useful technique for variability detection in crowded fields. In this method, a reference image is selected whether as a single epoch from a data set, or as a combination of several images. All other images are transformed to the coordinate system of the also called ‘template’. Then the reference image is convolved by a kernel function, and finally every single epoch of the data set is subtracted from this convolved image (e.g. Alard & Lupton 1998; Alard 2000). Usually the template turns out to be the best seeing image available. However, Huckvale, Kerins & Sale (2014) found that for the particular case of the VVV survey, a better sampled image (i.e. with a poorer seeing) is more suitable as a reference.
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The Next Generation Fornax Survey (NGFS)  II  The Central Dwarf Galaxy Population

The Next Generation Fornax Survey (NGFS) II The Central Dwarf Galaxy Population

Elliptical galaxies are known to fall on a so-called fundamental plane ( FP ) , a tight correlation between effective radius, central velocity dispersion, and the average effective surface brightness within the effective radius ( e.g., Faber & Jackson 1976; Djorgovski & Davis 1987; Dressler et al. 1987; Faber et al. 1987; Bender et al. 1992; Burstein et al. 1997; Gallazzi et al. 2006 ) .  A similar relation was found by Tollerud et al. ( 2011 ) , showing that dispersion-supported galaxies form a one-dimensional fundamental curve in the mass – radius – luminosity space from ultrafaint dwarf spheroidals to giant cluster spheroids.  Since the FP shows very little residual scatter, it implies very similar mass-to-light ratios and suggests a uniform formation process for bright elliptical galaxies. Projecting the FP onto the luminosity versus  surface-brightness plane, Kormendy ( 1985 ) had noted that there seems to be a dichotomy between the scaling relations of bright elliptical galaxies and dwarf galaxies.  This dichotomy can be interpreted as the result of different formation mechanisms for giant ellipticals and dwarf spheroids, but it is still hotly debated in the literature ( e.g., Binggeli 1994; Graham & Guzmán 2003; Ferrarese et al. 2006; Kormendy et al. 2009; Kormendy & Bender 2012 ) .  In order to investigate these possible differences in the formation process of dwarf galaxies in comparison to bright elliptical and spiral galaxies, we plot in Figure 8 the effective radius ( r eff , in units of parsec ) as a function of stellar
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The age structure of globular cluster systems in early type galaxies and its dependence on host galaxy properties

The age structure of globular cluster systems in early type galaxies and its dependence on host galaxy properties

Studies of the M 87 globular cluster system are manifold and led to controversial results. Based on Keck spectroscopy Cohen et al. (1998) found no sign of age differences between the globular clusters. Neither did Jordán et al. (2002), using Strömgren photometry obtained with HST/WFPC2. On the other hand, globular cluster sub-populations with an age di ff erence of 3−6 Gyr were claimed by Kundu et al. (1999). The combined op- tical and near-infrared colors of the globular clusters used in this study and first published by Kissler-Patig et al. (2002) are mostly consistent with an old (≈13 Gyr) population. Nevertheless, a small very red ((V −K) > 3.4) sub-population is found that shows (V − I) colors that are too blue for an old (10−13 Gyr) popula- tion. The interpretation of the age distribution for this sample (see Figs. 5 and 2) is somewhat less conclusive than the one for NGC 1399 (mostly due to the smaller number of objects), but is best interpreted along the same lines: the dominant metal-rich sub-population is old, but there is evidence for a small interme- diate age population as well.
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RR Lyrae Stars in the Globular Cluster NGC 6101

RR Lyrae Stars in the Globular Cluster NGC 6101

Observations of NGC 6101 were taken in the V and I bands by the Faulkes Telescope South over two main seasons: one over August and September 2010 and a further season to help refine the periods in April 2011. Aperture photometry using a 2.8 arcsecond–radius aper- ture was performed through Makali’i software for all measured stars, with the sky estimated from representa- tive patches of dark sky from the largely star-free edges of the images. While point spread function (PSF) photom- etry would have been preferred, we were limited to our choice of methodology due to reasons outlined in Section 4. However, due to the quite diffuse nature of this globular cluster, aperture photometry performed well. The stabil- ity of the comparison star over all observations was found by comparison to a check star, which was found to be E 0.01 mags RMS in both bands (shown in Figure 2). The comparison star used was found to have an apparent magnitude of V ¼ 14.65 0.01 and I ¼ 13.34 0.01 from the photometric solution. V- and I-band magnitudes measured for each RR Lyrae are provided as online sup- plementary material.
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Dynamical versus stellar masses of ultracompact dwarf galaxies in the Fornax cluster star

Dynamical versus stellar masses of ultracompact dwarf galaxies in the Fornax cluster star

The metallicity difference between the spectra and tem- plates used to analyse them may lead to biased velocity dispersion measurements (see Section 1.3.1 in Chilingarian 2006) at least if the analysis is done in the pixel space, thus affecting both NBursts full spectral fitting and fx- cor cross-correlation measurements. The low metallicity of a template star resulting in shallower absorption lines may be compensated by decreasing the velocity dispersion, i.e. smearing absorption lines to a lower degree than it should be in order to match the line depth in the target spectrum being analysed. Then we would expect to see the correlation between UCD metallicities and differences of velocity disper- sion measurements in Mieske et al. (2008) and our present study, which we do not detect at a statistically significant level. This can be explained because the described degener- acy between metallicity and velocity dispersion mostly af- fects the data for targets with velocity dispersions similar to or lower than the instrumental spectral resolution. In our case, most low-σ targets have low metallicities well corre- sponding to those of the ω Cen template stars. On the other hand, massive metal-rich UCDs with relatively high velocity dispersions are bright,hence their spectra have good signal- to-noise ratios reducing the degeneracy effects.
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The ACS Fornax Cluster Survey  V  Measurement and Recalibration of Surface Brightness Fluctuations and a Precise Value of the Fornax Virgo Relative Distance

The ACS Fornax Cluster Survey V Measurement and Recalibration of Surface Brightness Fluctuations and a Precise Value of the Fornax Virgo Relative Distance

The full promise of the optical SBF method was finally brought to fruition with the installation of the Advanced Camera for Surveys (ACS) on board HST. The ACS Wide Field Channel (WFC) samples the point-spread function (PSF) with a resolution comparable to the WFPC2 planetary camera CCD, but over a much larger ∼ 3. 3 × 3. 3 field and with about 5 times the throughput at the wavelengths typically used for SBF analyses. SBF investigations with ACS/WFC in the F814W bandpass (most similar to the I band) include the first studies of large samples of high signal-to-noise radial SBF gradients in early-type galaxies (Cantiello et al. 2005, 2007a), the first optical SBF distance measurements out to ∼100 Mpc or beyond (Biscardi et al. 2008), and a precise distance to a peculiar gas-rich S0 galaxy in the Dorado group (Barber Degraaff et al. 2007). The ACS/WFC has also afforded the first samples of reliable B-band (F435W) SBF measurements beyond the Local Group (Cantiello et al. 2007b), which are useful for stellar population work.
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The Next Generation Fornax Survey (NGFS)  IV  Mass and Age Bimodality of Nuclear Clusters in the Fornax Core Region

The Next Generation Fornax Survey (NGFS) IV Mass and Age Bimodality of Nuclear Clusters in the Fornax Core Region

When comparing the predictions ( CliN and GxeV are similar in this parameter space; dash-dotted lines in Figure 11 ) with Fornax nucleated galaxies, the predicted masses tend to be a factor of a few smaller than the observed ones over the mass range covered by the models ranging from 2 × 10 8 M e to 3 × 10 10 M e . Antonini et al. ( 2015 ) noticed the offset and argue that the underweight of model nuclei is due to the interaction of the nucleus with the central massive BH, which makes the nucleus lose stars faster, in addition to galaxy mergers, where BH binaries form and ef fi ciently eject surrounding stars.  These effects have a greater impact in more massive galaxies than in low-mass dwarfs.  The overall prediction by Antonini et al. ( 2015 ) is that both mechanisms are likely active during nucleus growth and that their relative contribution depends on the star-cluster formation ef fi cien- cy.  These models show that for galaxies less massive than ∼ 3 × 10 11 M e , in situ star formation contributes ∼ 50% of the nucleus mass and becomes more important for more massive galaxies.  This suggests that massive galaxies are more ef fi cient in driving the gas fl ows to the galaxy core regions than are low- mass galaxies.  This gas funneling allows for subsequent star formation to progress to more advanced stages, with implica- tions for the resulting chemical makeup of the stellar populations, which would exhibit lower [α/ Fe ] element ratios.
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Chemical Compositions of Field and Globular Cluster RR Lyrae Stars  I  NGC 3201

Chemical Compositions of Field and Globular Cluster RR Lyrae Stars I NGC 3201

Dating back to Baade ( 1958 ) , RR Lyrae stars ( RRL ) have played a fundamental role as tracers of old ( t > 10 Gyr ) stellar populations. RRLs are ubiquitous, having been identi fi ed both in gas-poor and in gas-rich stellar systems. Moreover, they can be easily identi fi ed, thanks to a particular coupling between pulsation period and shape / amplitude of their optical light curves. Therefore, they have been extensively used to investigate the early formation and the spatial structure of the Galactic bulge ( Pietrukowicz et al. 2015 ) and of the Galactic halo ( Drake et al. 2013; Torrealba et al. 2015 ) . The RRLs in globulars have been widely used not only to constrain the evolutionary properties of old, low-mass, central helium- burning stars, but also to investigate the impact that the intrinsic parameters ( metallicity ) and the environment have on the topology of the instability strip and on their pulsation properties ( Oosterhoff 1939; van Albada & Baker 1973; Caputo 1997; Bono et al. 2007 ) .
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Variations in the lithium abundances of turn off stars in the globular cluster 47 Tucanae

Variations in the lithium abundances of turn off stars in the globular cluster 47 Tucanae

At variance, the GC NGC 6752, which is about a factor of 4 more metal-rich than NGC 6397, displays a strong variation (up to 0.4 dex) in Li abundances among TO stars (Pasquini et al. 2005). These variations, however, do not appear to be random, but are anti-correlated with the variations of sodium and nitro- gen, and correlated with the variations of oxygen, in the same stars. Such variations cannot be produced by diffusion mecha- nisms, since the effect of diffusion would be similar for lithium and sodium. Neither can they arise from mixing occurring in the stars themselves, since the base of the convection zone in such stars attains a temperature of 1.5 MK, which is very far from the region of lithium burning (Piau 2005, private com- munication). Pasquini et al. (2005) suggest that the most likely source of such anomalies are intermediate mass asymptotic giant branch (IM-AGB) stars which have polluted either the material out of which the TO stars were formed, or their atmospheres. The nucleosynthetic signatures of IM-AGB stars are in qualitative
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