On the self-enrichment scenario of galactic globular clusters: Constraints on the IMF

Galactic globular cluster (GC) stars exhibit abundance patterns which are not shared by their field counterparts, In the framework of the widely accepted "self-enrichment" scenario for GCs, we present a new method to derive the Initial Mass Function (IMF) of the polluter stars, by using the observed O/Na abundance distribution. We focus on NGC 2808, a GC for which the largest sample of O and Na abundance determinations is presently available. We consider two classes of possible "culprits" : massive Asymptotic Giant Branch (AGB) stars (4-9 Msun) and winds of massive stars (WMS) in the mass range 10-100 Msun. We obtain upper limits for the slope of the IMF (assumed to be given by a power-law) of the stars initially more massive than the present turnoff mass. We also derive lower limits for the amount of stellar residues. We find that the polluter IMF had to be much flatter than presently observed IMFs in stellar clusters, in agreement with the results of two other methods for GC IMF determination. Additionaly, we find that the present mass of the GC should be totally dominated by stellar remnants if the polluters were AGB stars, but not so in the case of WMS. We critically analyse the advantages and shortcomings of each potential polluter class, and we find the WMS scenario more attractive.Comment: 18 pages, 9 figures, accepted in Astronomy and Astrophysic

Globular cluster abundances: the imprint of first-generation massive stars

Galactic globular cluster (GC) stars exhibit abundance patterns that are not shared by their field counterparts, namely the well-documented O-Na, C-N and Mg-Al anticorrelations. Recent observations provide compelling evidence that these abundance anomalies were already present in the intracluster gas from which the presently observed stars formed. The current explanation is that the gas was polluted very early in the history of the GC by material processed through H burning at high temperatures and then lost by stars more massive than the long-lived stars we still observe today. However the ‘polluters' have not yet been unambiguously identified. Most studies have focused on asymptotic giant brach stars, but rotating massive stars present an interesting alternative. Here, we critically analyse the pros and cons of both potential stellar polluters. We discuss the constraints that the observational data provide on stellar nucleosynthesis and hydrodynamics, as well as on the formation and early evolution of very massive star cluster

Deep inside low-mass stars

Low-mass stars exhibit, at all stages of their evolution, the signatures of complex physical processes that require challenging modeling beyond standard stellar theory. In this review, we recall the most striking observational evidences that probe the interaction and interdependence of various transport processes of chemicals and angular momentum in these objects. We then focus on the impact of atomic diffusion, large scale mixing due to rotation, and internal gravity waves on stellar properties on the main sequence and slightly beyon

Light elements as diagnostics on the structure and evolution of low-mass stars

Low-mass stars exhibit, at all stages of their evolution, the signatures of complex physical processes that require challenging modelling beyond standard stellar theory. In this review, we focus on lithium depletion in low-mass stars. After disecting the Li dip, we discuss how large scale mixing due to rotation and internal gravity waves may interact to explain this feature. We also briefly discuss the impact that is expected on Population II star

Thermohaline mixing in stars and the long-standing 3He problem

Thermohaline mixing has been recently identified as the dominating process that governs the photospheric composition of low-mass bright giant stars (Charbonnel & Zahn 2007). Here we present the predictions of stellar models computed with the code STAREVOL taking into account this mechanism together with rotational mixing and atomic diffusion. We compare our theorical predictions with recent observations and discuss how the corresponding yields for 3He are compatible with the observed behaviour of this light element in our Galax

A new perspective on globular clusters, their initial mass function and their contribution to the stellar halo and the cosmic reionization

We examine various implications from a dynamical and chemical model of globular clusters (GCs), which successfully reproduces the observed abundance patterns and the multiple populations of stars in these systems assuming chemical enrichment from fast-rotating massive stars. Using the model of Decressin et al., we determine the ratio between the observed, present-day mass of GCs and their initial stellar mass as a function of the stellar initial mass function (IMF). We also compute the mass of low-mass stars ejected and the amount of hydrogen ionizing photons emitted by the proto-GCs. Typically, we find that the initial masses of GCs must be ∼8-10 times (or up to 25 times, if second-generation stars also escape from GCs) larger than the present-day stellar mass. The present-day Galactic GC population must then have contributed to approximately 5-8 per cent (10-20 per cent) of the low-mass stars in the Galactic halo. We also show that the detection of second-generation stars in the Galactic halo, recently announced by different groups, provides a new constraint on the GC IMF (GCIMF). These observations appear to rule out a power-law GCIMF, whereas they are compatible with a lognormal one. Finally, the high initial masses also imply that GCs must have emitted a large amount of ionizing photons in the early Universe. Our results reopen the question on the IMF of GCs and reinforce earlier conclusions that old GCs could have represented a significant contribution to reionize the intergalactic medium at high redshif