[Mesa-users] ARC Online Seminar by Don VandenBerg

Falk Herwig fherwig at uvic.ca
Fri Feb 10 16:52:37 UTC 2023

Dear MESA users,
The University of Victoria Astronomy Research Centre<https://uvic.ca/arc> hosts a seminar by Don VandenBerg with online option. This talk, see below (time is Pacific Standard Time), may be interesting to some of you. It is based on a new paper by Don. For those who don’t know Don’s work, he has a reputation with many as an expert in constructing carefully calibrated isochrones for globular clusters.

Best wishes, Falk.

SEMINAR (Hybrid): Dr. Don VandenBerg, University of Victoria, will give a seminar entitled “Constraints on the Properties of Globular Clusters from Their Horizontal Branch Stars” on Monday, February 13 at 2:00 p.m. PST in ECS 130 and online via Zoom (https://uvic.zoom.us/j/81762773445?pwd=dkdGUDZhbU82Z2c0MXhxbTZUSkdBdz09).

Abstract: Zero-age horizontal branch (ZAHB) stellar models, coupled with ultraviolet photometry from the recent Hubble Space Telescope Wide-Field Camera 3 (WFC3) survey by Piotto et al., provide important constraints on the apparent distance moduli and reddenings of globular clusters (GCs), and thereby on their ages. The WFC3 observations, in particular, make it possible to derive the relative distance moduli of second-parameter clusters (those with similar metallicities but very different HB morphologies) to quite high precision. To ascertain whether age is the primary second parameter (after metallicity) in controlling the distribution of HB stars in GCs, new results will be presented for the second-parameter cluster pairs M3, M13 and NGC 288, NGC 362. To check the distance scale that is inferred from ZAHB models, distance moduli are derived from fits of GC main sequences to local Pop. II dwarfs with very accurate and precise Gaia parallaxes. Although there appears to be rather good agreement if such fits are performed on a V-I,V diagram, there are some perplexing inconsistencies when the B-V,V diagram is considered. A possible solution to this dilemma is that local subdwarfs have high abundances of carbon (i.e., [C/Fe] > 0.0). This will be discussed, along with some tantalizing evidence for such overabundances in in some GCs.

Dr Falk Herwig, Professor
Dept of Physics & Astronomy
University of Victoria

Email: fherwig at uvic.ca
Tel: +1 (250) 721-7743
Twitter: @fherwig

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