ASI Workshop- Roma, March 25, 2009
Probing the nature of Stellar Populations in Globular Clusters 1. Results from the Project granted by ASI in the 2007 Call Supporto Analisi dati - Cosmologia delle strutture Formate 2. The HST Large Programme UV light from old stellar populations : 177 orbits to a Large Programme with an Italian leadership
GALACTIC GLOBULAR CLUSTERS old SSP (?) many stars ASTRO ARCHEOLOGY TRACERS of the structure & formation history of the Galaxy ASTRO TEMPLATE LABORATORY for theoretical models of stellar evolution & TEMPLATES to study Galaxies ASTRO DYNAMICS LABORATORY for stellar dynamics environment SE
Probing the nature of Stellar Populations in Globular Clusters Project granted by ASI with 76 Keu in the 2007 Call Supporto Analisi dati - Cosmologia delle strutture Formate RUs: Bologna (Ferraro) and Padua (Piotto) More than 280 hours of Observing time with HST & SPITZER in the period 2004-2007 10 approved projects on hot issues in SPs studies the mass loss problem multiple populations in GCs dynamical effect on stellar evolution
Mass Loss and SP integrated Colors 0.51M o 0.7 M o MASS LOSS in RGB 0.8 Mo Impact on: HB morphology UV excess of Ellipticals Stellar evolution models
0.51M o 0.7 M o MASS LOSS in RGB Mass Loss and SP integrated Colors 0.8 Mo 0.51M o 0.7 M o MASS LOSS in RGB 0.8 Mo 0.51M o 0.7 M o 0.8 Mo
Piotto et al (2002)
MASS LOSS IN POPULATION II GIANTS 26hr of IRAC@Spitzer deep mapping of 17 GGCs spanning the entire range of metallicity and HB morphology
MASS LOSS IN POPULATION II GIANTS nearir J,H,K Obs (photospheric parameters) + mid-ir 3.6,4.5,5.8,8 µm (dust emission) [K-8], [K-6], etc color indices ==> circumstellar dust excess INDICATOR The first-empirical ML relation for Pop II giants Properties of the mass-loss process The emerging scenario little dependence on Z, Z higher ML in blue HB clusters
MASS LOSS IN POPULATION II GIANTS NGC6388 NGC6441 Dust-excess stars almost 800 stars! 600 stars! 10% with dust excess Origlia et al (2009, in preparation)
Observational evidence of multiple stellar populations in star clusters
Multiple main sequence in Omega Centauri A triple MS from ACS/HST multiepoch data. Cluster members selected by proper motions. Bedin et al. in preparation cluster stars
The most unexpected discovery in Omega Centauri multiple MS 17x12=204 hours i.t. at VLT The blue MS is more metal rich than the redder one BlueMS: [Fe/H]=-1.27 RedMS: [Fe/H]=-1.56 Piotto et al. (2005, ApJ, 621,777)
The only possible explanation The blue MS is populated by a second generation of strongly He enriched (Y~0.40) stars 1.4x10 5 solar masses of fresh helium are embedded in the second generation of stars
The triple main sequence in NGC 2808 From ACS/HST data The MS of NGC 2808 splits in three separate branches TO Piotto et al. 2007, ApJ, 661, L35 Overabundances of helium (Y~0.30, Y~0.40) can reproduce the two bluest main sequences. The TO-SGB regions are so narrow that any difference in age between the three groups must be significantly smaller than 1 Gyr
The HST Large Programme UV light from old stellar populations Granted time: 177 orbits in Cycle16 Supplemental PI: F.R. Ferraro (UNIBO) Co-I: Lanzoni, Dalessandro, Mucciarelli, Miocchi (UNIBO) Origlia, FusiPecci, Buzzoni, Cacciari (INAF) Valenti (ESO), Beccari (ESA) Rood (UVA,USA), O Connell (UVA,USA), Sigurdsson (UVPen,USA), Schiavon (GEMINI,USA) Italian leadership + Italian major partecipation (60%) Cycle 16 Supp oversubscription: 16!!!!!
UV sensitivity, high resolution HST systematic studies of hot SPs in the core of high density GGCs
The HST Large Programme UV light from old stellar populations Aim: far/mid UV observations of 45 GGCs WFPC2 Filters: F170W, F225W, F336W, F555W ACS/SBC Filter: F150LP Expected data-base: more than 700 images are planned This will be the largest UV survey of old stellar clusters ever obtained Scientific Goal: properly sample the HOT stellar populations in OLD stellar systems (effect of dynamics on stellar evolution, origin of the UV excess, multi-population along the HB, etc)
Dalessandro et al (2008)
The dynamical history of the cluster is imprinted into the BSS radial distribution
CONCLUSIONS The italian scientific community working on SPs in GCs is very active and it has reached level of internationally recognized excellence in the field of the observations from the space. We MUST maintain this advantage by fully exploiting the recent successes (this means a prompt analysis of the data, the possibility of attracting brilliant foreign PhDs, funding for travels and attending international conferences, etc) We need the ASI support for this. Suggestions: Guarantee grant support for obs.. time from satellites (for instance in the case of HST, NASA has adopted a formula: 6K$ per each assigned orbit in GO proposals weight for the percentage of US participation in the project) Encouraging grants for approved proposals with Italian leadership