1. PI Total time #CoIs, team Silvia Pedicelli 22h (ELT 42m) G. Bono (OAR); P. Francois (Observatoire de Paris- Meudon); M. Groenewegen (Katholieke Universiteit Leuven); C.D. Laney (South African Astronomical Observatory); B. Lemasle (Universitè de Picardie); M. Mottini (University of Washington); F. Primas (ESO); J. Pritchard (ESO); M. Romaniello (ESO). ELT: A significant stepping-stone for improving the cosmic distances The main aim of this experiment is to improve cosmic distances using primary distance indicators (Classical Cepheids, tip of RGB). ELT will provide the unique opportunity to identify large samples of these objects in the Coma galaxy clusters.

2. Scientific Rationale Cepheids are one of the most important standard candles used for distance determination in the Universe. Pros: Easy to recognise by their variability Their evolutionary and pulsational properties are well-known Are quite common in young stellar systems Cons: time-series data Bright but not enough..... Run A: 4 images (I and K band) takes every 3 days (total 16 images in 4 nights) for two selected spiral galaxies of the Coma Cluster. Run B: 2 images (K band) of selected Cepheds in spiral galaxy of Coma Cluster. Immediate Objective → ELT can solve these problems

3. DM LMC = 18.48 ± 0.13 DM COMA = 34.64 ± 0.25 In LMC → P = 10 → I ~ 14 In COMA → P = 10 → I ~ 30 In LMC → P = 10 → K ~ 13 In COMA → P = 10 → K ~ 29 ELT Justification DM COMA – DM LMC ~ 16 Sebo & Rawson (2002) Persson et al. (2004)

4. LTAO AO K band52.2 µm6hImaging-B I & K50.8 µm16hImaging-A NotesPixelλT.ModeMPRun - +28.5˚ Dec. S/N > 3296h-CepheidsB S/N > 53016h13hComaA NotesMagToTR.A.TargetRun Legacy Value: These data will provide a pristine determination of the Hubble constant only based on primary distance indicators. They can also be used to calibrate secondary distance indicators (SNIa, GCLF, Tully-Fisher relation). DM COMA = 34.64±0.25 d COMA ~ 10 8 pc → α = 5 mas → r ~ 2 pc

5. That’s all