SMA Yellow Hypergiant HR8752 Project

Accepted and Observed SMA Proposal: Link

Yellow Hypergiant

Yellow Hypergiants are massive star with extremely extended atmosphere. They have initial mass about 20 to 60 solar masses, and will loss about half of the mass. They are located in the region called the Yellow Void in the HR diagram. Yellow Hypergiants are extremely unstable, and have huge luminosity variations. Yellow hypergiant stars are also extremely rare. There are only around 15 known candidates in the Milky Way.

Yellow Hypergiant HR8752 (V509 Cassiopeiae)

Figure 1. Size Comparison between HR8752 (V509 Cas) and other stars. (Pic source = link)

Not so much is known for the inner structure of the HR8752, a yellow hypergiant star. Recent studies showed a double peak profile for the [Ca II] lines,which clearly indicates a disk like structure (eg. Aret et al. 2016,arXiv:1611.06044). The disk structure indicates a change in a mass loss behavior from spherical to axis-symmetrical, corresponding to the increase of temperature through the Yellow Void.

With SMA observations, the inner disk structure can be resolved, providing the opportunity to confirm the existence of a disk and hence observing the inner disk structure. Ultimately, the goal is to further estimate the mass loss of HR8752 during this short-lived phases of enhanced mass loss. The estimation of mass loss rate from integrated CO intensity map would give us a deeper understanding of AGB stars.

Recently, I become the PI (Principal Investigator) of the project “End in sight: Detection of the disk like structure in the Yellow Hypergiant HR8752”. Leading a group of 2, we submitted the SMA filler proposal with Prof. Lai Shi-Ping (NTHU) as our supervisor, and the proposal was accepted by the SMA committee and observed this summer. Starting this semester, we will be able to confirm whether or not a disk exists around HR8752.

Supervisor: Prof. Lai Shi-Ping (NTHU)

Collaborator (Co-PI): Yuejia Zhai (1st year master student in U. Leiden, Holland)

Updated 2017.11.26. Chenghan Hsieh