Research
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Variable stars make up a special category of stars that varies in brightness ove
Variable stars make up a special category of stars that varies in brightness over time. As a freshman, I began working with Dr. Robert Cadmus that looked specifically at a subcategory of variable stars whose changes in brightness are caused by radial pulsations. This brightness variation occurs at a certain frequency and changes in this frequency or the addition of other frequencies may be related to changes in the mode of pulsation in the star. This work attempts to quantify those frequency changes using Fourier analysis.
I have continued to work with Dr. Cadmus on his variable star research throughout my time at Grinnell College. Ongoing projects include analyzing the spectra of variable star RS Cyg over time and automating the process of reducing spectra.
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In the summer of 2012, I worked on extended ultraviolet disk (XUV-disk) galaxies
In the summer of 2012, I worked on extended ultraviolet disk (XUV-disk) galaxies with Dr. Juan Carlos Munoz-Mateos at the NRAO in Charlottesville, VA. Galaxies housing XUV-disks exhibit UV emissions beyond the main body of the galaxy where the old stellar population resides. This region of extended UV emission, containing mainly young stars, is bright in the UV but nearly invisible in the infrared and optical, making it possible to find by comparing galaxy images in the infrared and UV.
Through studying XUV-disks, we can gain a better understanding of both star and galaxy formation. Although XUV-disk galaxies are more gas rich than their non-XUV-disk counterparts, they still have very low gas surface densities in their outer regions compared to those in the inner, star-forming regions of most 'normal' galaxies. This allows us to test whether trends such as the Schmidt-Kennicutt law, an empirical trend relating the star formation rate (SFR) to different gas densities, hold at such low gas densities (Kennicutt, R.C., 1998). This in turn will impose constraints on theories of star formation. Not only is there not very much gas in XUV-disk, but the gas also exhibits very low metallicities (oxygen abundance of ZΘ/10) due to the lack of an older stellar population (Gil de Paz, A. et al.,2008). Thus the conditions in which stars are forming in XUV-disks (low gas densities and almost pristine chemical abundances) are perhaps similar to those in the early universe which we cannot examine directly. Additionally, XUV-disks give us more information about galaxy formation. According to the inside-out theory of disk formation, disks form from near the nucleus out into larger radii as time goes on (see, e.g., Bossier & Prantzos, 1999, Munoz-Mateos, J.C., 2007 and references therein). Following this train of logic, XUV-disks are the places where disk-building is currently taking place. If they can sustain star formation for long enough at a high enough rate, they may significantly impact the future of their host galaxy.
My work revolved around characterizing the stellar mass and star formation rates of the XUV-disks relative to the inner regions of the host galaxy and extrapolating the importance of the XUV-disk for the future growth of the galaxy. I'm currently working on a first author paper based on this work.
Boisser, S. & Prantzos, N., 1999 Monthly Notices. 307, 857
Gil de Paz, A. et al., 2008 Formation and Evolution of Galaxy Disks ASP Conference Series. 396, 197
Kennicut, R.C., 1998. ApJ. 498, 541
Munoz-Mateos, J.C., 2007. ApJ. 658, 1006
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Our own star has a planetary system. That system includes both terrestrial and g
Our own star has a planetary system. That system includes both terrestrial and gas planets as well as two debris disks. The Asteroid Belt and the Kuiper Belt. However, we currently do not know how common this type of stellar system is. In the summer of 2013, I had the opportunity to work with Dr. David Trilling of Northern Arizona University to determine the prevalence of debris disks around M dwarfs.
Debris disks, pieces of planetesimals that have been ground into dust by repeated collisions, can be the result of the planet-forming process or the stirring of planetesimals by migrating planets (Kenyon & Bromely 2004; Ribas, Merin, Ardillam & Buoy 2012; Wyatt 2008). However, these collisions can also result from random interactions between planetesimals in a system without planets (Wyatt 2008). The possible connection between the presence of planets and the presence of a debris disk has led some to use debris disk incidence as an indirect measurement of exoplanet incidence. However, more investigation is required before a correlation between them can be confirmed.
In the years following the first debris detection in 1984 (Aumann et al. 1984), the incidence of debris disks around solar type (main sequence FKG) stars has been found to be ≈16% for cold disks and ≈4% for warm disks (Trilling et al. 2008). However the incidence of debris disks around M dwarfs remains unconstrained. As 75% of the stars in the Milky Way are M dwarfs, this represents a serious gap in knowledge about the nature of our galactic neighborhood and our Sun's place within it.
In this research, we examine two samples of stars: one sample of 1288 M and K dwarfs within 25pc and another sample of 172 M and K dwarf stars younger than ≈300 Myr old and within 25pc in search of 12μm and 22μm excesses in order to constrain the incidence of debris disks around M dwarfs.
Auman, H.H., 1984, ApJ, 278, L23
Kenyon, S.J. & Bromley, B.C., 2004, ApJ, 602, L133
Ribas, A., Merin, B., Ardillam, D.R., & Buoy, H., 2012, A&A, 541, 8
Trilling, D.E. et al., 2008, ApJ, 674, 1086
Wyatt, M., 2008, ARA&A, 46, 1146
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Contact
gallagher.674@osu.edu4009 McPherson Lab140 West 18th AvenueColumbus, OH 43210Phone: 614.292.6925Fax: 614.292.2928