Studies of Resolved Objects in M31

April 25, 2016, rev 5

This page contains a description of an on-going study of star clusters, HII regions, PNe and individual stars in M31 done with Hectospec on the MMT by Nelson Caldwell and a host of others1.  These papers have been published:

Star Clusters in M31: I. A Catalog and a Study of the Young Clusters
A Star in the M31 Giant Stream: The Highest Negative Stellar Velocity Known
Star Clusters in M31. II. Old Cluster Metallicities and Ages from Hectospec Data
Star Clusters in M31. (III): Old Clusters with Bar Kinematics
Star Clusters in M31. IV. A Comparative Analysis of Absorption Line Indices in Old M31 and Milky Way Clusters
Star Clusters in M31: V. Internal Dynamical Trends: Some Troublesome, Some Reassuring
The Metallicity Profile of M31 from Spectroscopy of Hundreds of H II Regions and PNe
Star Clusters in M31. VI. Evidence for Self-enrichment in Old M31 Clusters from Integrated Spectroscopy
First detection and characterization of symbiotic stars in M31
Star Clusters in M31: VII. Global Kinematics and Metallicity Subpopulations of the Globular Clusters

At this web site, you will find the new M31 cluster catalog and links to the spectra, and images, both ground based and HST. 


caldwell here at

1Including but not limited to : Nelson Caldwell, Heather Morrison, Paul Harding, Jim Rose, Ricardo Schiavon, Genevieve Graves, Jeff Kreissler, Joanna Mikolajewska, Michael M. Shara, Jay Strader, Aaron Romanowsky, Nathan Sanders, E. Athanassoula.

Clusters and stars in the revised Hectospec M31 catalog
Just star clusters in M31
Old star clusters, ordered by Name, with searchable coords
Old star clusters, ordered by estimated mass
Old star clusters, ordered by estimated metallicity
Young star clusters, ordered by estimated mass
Young star clusters, ordered by estimated age
Stars in the M31 catalog
PNe in M31
HII regions in M31
Symbiotic stars in M31


The spectra are in jpg format currently. Click on the postage stamp for full resolution. These (aside of a few problem cases that are obvious - young clusters with red continua) have been flux calibrated, deredshifted (actually deblueshifted) and dereddened. These plots show only the blue part of the spectrum. The data was smoothed before plotting.

Postage stamp images of selected Objects in M31

These images come from three sources: the digitized Palomar survey, the Local Group Survey of Massey et al. 2006, AJ, 131, 2478, HST (ACS or WFPC2), and Spitzer (thanks to Dr Pauline Barmby for the last). For each object in these lists, the following are shown:
The HST images are not complete, and in some cases what is shown is merely one image out of a sequence, because the HST archive hasn't yet combined those images.  Those will contain annoying cosmic ray hits.  Each web page contains a list of objects to the left, ordered as stated. The images will appear to the right after clicking. The names used are those from the RBC, and basic information appears next to the images (type, velocity, V magnitude, comments).  "Type" is explained in the catalog notes (see link below).

The WCS on the HST images is not always good, so sometimes the target will be offcenter in the HST images. The images all have N at the top, East to the left (which is not true for the images in Paper I - oops!).

I have made great use of these images to clean up the cluster catalog, but that job is not complete.  If anyone else takes the time to look through these and notes a discrepant type, please feel free to advise me so that I can make changes to the catalog.

Note that objects with an "x" suffix were initially thought to be the object (usually the real object is a few arcsecs away), and were observed with Hectospec before the mistake was realized. These are nearly all stars. The real object is also listed in the catalog (e.g. B088Dx is a bright star, near the old cluster B088D).


Here is a tab delimited catalog containing the physical information about the young clusters discussed in Caldwell et al. 2009. This table is also more uptodate than the published catalog. It is ordered by estimated mass.
M31 Hectospec young cluster catalog
Here is the tab delimited catalog containing the physical information about the old clusters discussed in Caldwell et al. 2011, with some more recent additions. It is ordered by RA.
M31 Hectospec old cluster catalog

Here is the machine readable table containing the physical information about the old clusters discussed in Caldwell & Romanowsky 2016, ordered by RA.
M31 Old Cluster Catalog from CR 2016