Long Term Evolution of Surface Features on the Red Supergiant AZ Cyg
- Creators
- Norris, Ryan P.
- Baron, Fabien R.
- Monnier, John D.
- Paladini, Claudia
- Anderson, Matthew D.
- Martinez, Arturo O.
- Schaefer, Gail H.
- Che, Xiao
- Chiavassa, Andrea
- Connelley, Michael S.
- Farrington, Christopher D.
- Gies, Douglas R.
- Kiss, László L.
- Lester, John B.
- Montargès, Miguel
- Neilson, Hilding R.
- Majoinen, Olli
- Pedretti, Ettore
- Ridgway, Stephen T.
- Roettenbacher, Rachael M.
- Scott, Nicholas J.
- Sturmann, Judit
- Sturmann, Laszlo
- Thureau, Nathalie
- Vargas, Norman
- Brummelaar, Theo A. Ten
Description
We present H-band interferometric observations of the red supergiant (RSG) AZ Cyg made with the Michigan Infra-Red Combiner (MIRC) at the six-telescope Center for High Angular Resolution Astronomy (CHARA) Array. The observations span 5 years (2011-2016), offering insight into the short and long-term evolution of surface features on RSGs. Using a spectrum of AZ Cyg obtained with SpeX on the NASA InfraRed Telescope Facility (IRTF) and synthetic spectra calculated from spherical MARCS, spherical PHOENIX, and SAtlas model atmospheres, we derive $T_{\text{eff}}$ is between $3972 K$ and $4000 K$ and $\log~g$ between $-0.50$ and $0.00$, depending on the stellar model used. Using fits to the squared visibility and Gaia parallaxes we measure its average radius $R=911^{+57}_{-50}~R_{\odot}$. Reconstructions of the stellar surface using our model-independent imaging codes SQUEEZE and OITOOLS.jl show a complex surface with small bright features that appear to vary on a timescale of less than one year and larger features that persist for more than one year. 1D power spectra of these images suggest a characteristic size of $0.52-0.69~R_{\star}$ for the larger, long lived features. This is close to the values of $0.51-0.53~R_{\star}$ derived from 3D RHD models of stellar surfaces. We conclude that interferometric imaging of this star is in line with predictions of 3D RHD models but that short-term imaging is needed to more stringently test predictions of convection in RSGs.
Abstract
31 pages, 8 tables, 14 figures, accepted to ApJ
Abstract
International audience
Additional details
- URL
- https://hal.archives-ouvertes.fr/hal-03367843
- URN
- urn:oai:HAL:hal-03367843v1
- Origin repository
- UNICA