Before the Bar: The Hidden Bulge of the Milky Way
Final Report Abstract
In the few months of work on this project, more telescope time was secured and the observations were taken using two different telescopes and instruments: AAOmega spectrograph on the Anglo-Australian 4m Telescope (AAT) and M2FS spectrograph on the Magellan 6.5m telescope. Using the AAT, the observations extended the observations of the bulge RR Lyrae stars to twice the area that was previously surveyed. Kunder made the configuration files to observe 4 new 2 degree fields using AAOmega on the AAT, doubling the number of RR Lyrae stars that previously had spectroscopy. The observing strategy was to target 900 RRL in four fields reaching to l = −7 and l = +7, so that the observations now reach to the outer edge of the bulge. By selecting stars reaching the edge of the bulge, the vertical extent of the classical bulge is probed, and a larger number of fields observed are important to constrain bulge formation scenarios. Using M2FS, Kunder made configuration files to target ~200 RR Lyrae stars in 6 different fields in the bulge with high resolution. The field of view of M2FS is smaller than AAOmega, so fewer RR Lyrae stars could be observed. However, the resolution is higher, with R~22,000, so a more accurate abundance analysis with these stars could potentially be carried out. We were not able to use the M2FS observations after all. The signal-to-noise was not adequate to isolate the individual elemental lines. We can not increase the exposure time, however, as RR Lyrae stars are pulsating stars, and so their spectra varies as their temperature and gravity vary over their pulsation cycle. We will try again to get M2FS observations, but this time use a different wavelength range which the spectrograph is more sensitive to, so we hope to then have the desired signal-to-noise for elemental abundances. Focusing on the Galactic bulge, we discovered that a number of globular cluster stars are being dissolved in the field of the bulge. This result was published and the American Astronomical Society in 2018 made a press release (https://www.stmartin.edu/news-events/news/saint-martins-physics-faculty-memberandrea-kunder-phd-and-team-use-gaia-confirm). The most exciting part of this project is combing our observations with the new observations from Gaia space satellite. Only this combination provides 6 dimensional space and position information, which gives the sharpest image yet on the distribution of RR Lyrae stars throughout the bulge.
Publications
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“Spectroscopic confirmation of the low-latitude object FSR 1716 as an old globular cluster” 2017, A&A, 605, 128
Koch, A., Kunder, A., Wojno, J.
