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Hello, I studied astronomy and physics at the University of Arizona. In my free time I take pictures, play chess, and learn about Galileo. For a movie of the wedding to my beautiful wife Mayra, click here.
"For he hath given me the true knowledge of the things that are: to know the disposition of the whole world, and the virtues of the elements, the beginning, and ending, and midst of the times, the alterations of their courses, and the changes of seasons, the revolutions of the year, and the dispositions of the stars, the natures of living creatures, and rage of wild beasts, the force of winds, and reasonings of men, the diversities of plants, and the virtues of roots, and all such things as are hid and not foreseen, I have learned: for wisdom, which is the worker of all things, taught me. For in her is the spirit of understanding: holy, one, manifold, subtile, eloquent, active, undefiled, sure, sweet, loving that which is good, quick, which nothing hindereth, beneficent, gentle, kind, steadfast, assured, secure, having all power, overseeing all things, and containing all spirits, intelligible, pure, subtile." —Wisdom of Solomon 7:17-23
"La più sublime, la più nobile tra le Fisiche scienze ella è senza dubbio l'Astronomia. L'uomo s'innalza per mezzo di essa come al di sopra di se medesimo, e giunge a conoscere la causa dei fenomeni più straordinari." ("The most sublime, the most noble among the Physical sciences is without doubt Astronomy. Man raises himself through being beyond himself and arrives at understanding the cause of the most extraordinary phenomena.") —Giacomo Leopardi, Storia dell'Astronomia
T Tauri stars are young, nascent, sunlike stars which often have circumstellar disks of gas and dust revolving around them. It is not known, however, how long the gas persists in circumstellar disks before it accretes onto the T Tauri star or perhaps becomes locked up in newly formed gaseous planets. To assess the gas disk lifetime of T Tauri stars, we observed the $^{12}\mathrm{CO~}J=2-1$ rotational transition emission line of two T Tauri stars with the Heinrich Hertz Sub-Millimeter Telescope (HHT) on Mt. Graham, Arizona. We did not detect any gas around our two sources, RX J0432 and the circum-binary disk of St 34. The upper limits of these two objects are shown in the plot of stellar age versus circumstellar disk mass. Also plotted are circumstellar gas disk masses of other T Tauri stars.
Super Star Clusters (SSCs) are massive, dense star formation regions where generally $\ge10^4$ nascent O7.5 stars ionize a cocoon of gas and dust. Due to the large amounts of obscuring gas and dust, SSCs are only observable in the IR or radio. IR detects the warm poly-aromatic hydrocarbons (PAHs) while radio detects thermal free-free emission due to the Lyman continuum flux of the embedded O stars. Measuring the thermal luminosity $L_\mathrm{thermal}$ at a frequency $\nu$ and assuming an HII temperature of $10^4\mathrm{~K}$, one can put a lower limit on the Lyman continuum flux $Q_\mathrm{Lyc}$. Since an O7.5 star has a Lyman continuum of $Q_\mathrm{Lyc}=1.0\times10^{49}\mathrm{~s}^{-1}$, we can estimate how many stars are embedded in a SSC. To detect thermal free-free emission, we observed 27 galaxies in the northern and southern hemispheres with the Australia Telescope Compact Array (ATCA) and Very Large Array (VLA) radio telescopes at 3.5 cm and 6.2 cm and at 1.3 cm and 3.6 cm, respectively. We use the spectral index $\alpha$, where $S_\nu \propto \nu^\alpha$, to determine if a source is thermal, which we define as $\alpha>0.2$. Only 9 of the 27 galaxies selected based upon their likelihood of harboring nascent star formation actually showed evidence of thermal emission. This suggests that SSCs form quickly.
An IMF $\xi(m)$ describes how many zero age main sequence (ZAMS) stars $\xi$ of a given mass $m$ form per unit volume. For stars greater than the sun's mass ($>1\mathrm{~M}_\odot=1.988\times10^{30}\mathrm{~kg}$), the IMF is nearly the same in all star clusters, i.e., it is nearly independent of the physical conditions of a particular star formation environment. It follows a power-law developed by Edwin Salpeter in the '50s: \[ \frac{d\xi(m)}{dm}\propto m^{-\alpha}, \] where $\alpha$ is a constant roughly equal to $2.35$. For stars with masses $<1\mathrm{~M}_\odot$, the IMF is not so well-determined. It is unknown whether the IMF peaks, presumably somewhere around $\sim0.1\mathrm{~M}_\odot$, or whether it flattens off toward low masses or even increases. To investigate this question, we ran Monte Carlo simulations of clusters with various IMFs and analyzed the distribution of the ratio \[ \frac{N(0.08-0.1)}{N(0.03-0.08)}, \] where $N(a-b)$ represents the number of stars with a mass in the range $[a,b]$. We then compared the distribution of these ratios for 7 observed clusters (top panel) to the theoretical distributions (bottom panel) with a $\chi^2$ test. The theoretical distributions arise from clusters obeying Salpeter IMFs with different slopes $\alpha$ in the low mass regime. The solid line represents the distribution of clusters obeying a Chabrier IMF. We were able to constrain strongly that the brown dwarf or sub-stellar IMF does turn over.