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.

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

• DMLMC = 18.48 ± 0.13• DMCOMA = 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

•DMCOMA – DMLMC ~ 16

Sebo & Rawson (2002)

Persson et al. (2004)

LTAO

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).

DMCOMA = 34.64±0.25

dCOMA ~ 108 pc → α = 5 mas → r ~ 2 pc

That’s all