Here is a gzipped,tar full-resolution version of our recent Andromeda VI paper including the extended data tables for the photometry of the variable stars. A postscript file of the paper can be seen here.
Here is the poster presented at the 199th Meeting of the American Astronomical Society displaying our results for the variable star survey of And VI. (Note: The results have been updated in the Pritzl et al. 2002 paper.)
The Galactic dwarf spheroidals have been shown to have diverse star formation histories and stellar populations. This is reflected in the galaxy's variable star population. Various variable star surveys of the Galactic dwarf spheroidals have shown that the RR Lyrae populations, while similar to those found in Galactic globular clusters, have some different mean properties. It is the goal of this study to survey the M31 dwarf spheroidal companions in order to analyze the underlying stellar populations of those galaxies and to see how they compare with what we know of the Galactic dwarf spheroidals and globular clusters.
Do to the small number of observations and the manner by which they were taken, we devised a way to find the best periods and calibrate the data using light curve analysis programs for variable stars created by Andrew Layden. (See Pritzl et al. 2002 for a full description of the reductions.)
In our discussion of the anomalous Cepheids in Andromeda VI, we decided to reanalyze the properties of these stars in general. In order to do this, we searched the literature for all known anomalous Cepheids and ran their photometry through the light curve analysis programs as noted above. Given the distance modulus and reddening of the system from which each of the anomalous Cepheid derived, we were able to calculate the absolute magnitudes from each star. As a result, we found that there was a clear division between the fundamental and first-overtone mode anomalous Cepheids in the period versus absolute magnitude plot. We found that the period-luminosity relations for each mode were not parallel, as was discussed by Nemec, Nemec, & Lutz (1994). We also found that when the anomalous Cepheids were plotted in a period-amplitude diagram, while most of the fundamental mode anomalous Cepheids lie at longer periods for a given amplitude when compared to the first-overtone ones, the division between the two modes isn't as clearly defined at shorter periods.
From the Andromeda VI RR Lyrae, we see that they lie close to Oosterhoff type I Galactic globular clusters in a period-amplitude diagram. The mean period of the fundamental mode, RRab, stars is 0.588 days. This is slightly longer than the typical Oosterhoff type I cluster, but it consistent with what is seen in the Galactic dwarf spheroidal galaxies. It also follows the general trend of the mean period of the RRab stars increasing with decreasing metallicity. We found the mean V magnitude of the RR Lyrae to be 25.29 +/- 0.03 mag, resulting in a distance of 815 +/- 25 kpc on the Lee, Demarque, & Zinn (1990) distance scale. This is consistent with the distance derived by Armandroff, Jacoby, & Davies (1999) using the I magnitude of the tip of the red giant branch. Finally, we were able to make use of an equations created by Alcock et al. (2000) which relates the metallicity of a RRab star to its period and V-band amplitude to calculate the [Fe/H] for each RRab star. While the uncertainty per star is 0.31 from the equation, we found the mean [Fe/H] from the RRab stars in Andromeda VI to be -1.58 dex. This matches exactly with what was found by Armandroff, Jacoby, & Davies (1999) from the red giant branch mean V-I color (<[Fe/H]> = -1.58 +/- 0.20).
Please see Pritzl et al. 2002 for a more detailed discussion on the Andromeda VI variable star survey.
Andromeda I:
Results forthcoming.
Andromeda II:
Results forthcoming.
Andromeda III:
Results forthcoming.
Alcock, C., et al. 2000
"
The MACHO Project 9 Million Star Color-Magnitude Diagram of the Large Magellanic Cloud"
AJ, 119, 2194
Armandroff, T.E., Davies, J.E., & Jacoby, G.H. 1998
"
A Survey for Low Surface Brightness Galaxies around M31. II. The Newly Discovered Dwarf Andromeda V"
AJ, 116, 2287
Armandroff, T.E., Jacoby, G.H., & Davies, J.E. 1999
"
A Survey for Low Surface Brightness Galaxies around M31. II. The Newly Discovered Dwarf Andromeda VI"
AJ, 118, 1220
DaCosta, G.S., Armandroff, T.E., & Caldwell, N. 2002
"
The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda III"
AJ, in press (astro-ph/0204109)
DaCosta, G.S., Armandroff, T.E., Caldwell, N., & Sweitzer, P. 1996
"
The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda I"
AJ, 112, 2576
DaCosta, G.S., Armandroff, T.E., Caldwell, N., & Sweitzer, P. 2000
"
The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda II"
AJ, 119, 705
Ibata, R.A., Gilmore, G., & Irwin, M.J. 1994
A Dwarf Satellite Galaxy in Sagittarius
Nature, 370, 194
Lee, Y.-W., Demarque, P., & Zinn, R. 1990
"
The Horizontal-Branch Stars in Globular Clusters. I. The Period-Shift Effect, the Luminosity of the Horizontal Branch, and the Age-Metallicity Relation"
ApJ, 350, 155
Nemec, J.M., Nemec, A.F.L., & Lutz, T.E. 1994
"
Period-Luminosity-Metallicity Relations, Pulsation Modes, Absolute Magnitudes, and Distances for Population II Variable Stars"
AJ, 108, 222
Pritzl, B.J., Armandroff, T.E., Jacoby, G.H., & Da Costa, G.S. 2002
"
The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda VI"
AJ, in press (astro-ph/0205361)
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