Astronomy

 

Above is the view from RLM hall, where the Astronomy Department of the University of Texas at Austin is located.  Spectroscopy is an important tool for astronomers because it allows the study of the nature of the light observed from distant targets.  Below are two images of a spectrum through a toy spectrometer, and an image of me and a TV remote control.  The upper-most image is a spectrum of a hot light bulb demonstrating the visible area of the electromagnetic spectrum.  The image in the middle is a (barely perceptible) spectrum of an infrared remote control, pictured in my hand in the lower-most photo.  Remote controls apparently work using infrared LEDs.  You can hook up the LED to an oscilloscope and see the different signals, I’ve done it.  Infrared light is also used in night vision goggles- since humans radiate primarily in the (thermal) infrared, these devices pick out humans even when it is dark out. 


My research primarily uses infrared spectra and photometry from the Spitzer Space Telescope  and other astronomical observatories to study disks around low mass stars, brown dwarfs, and sub-brown dwarfs.

Infrared light visible to an off-the-shelf digital camera. You can do this at home, try it!

Spectrum of remote control

Spectrometer entrance slit

There are three main advantages of using Spitzer’s infrared spectrograph to study Brown Dwarf disks:

  1. 1)Infrared light goes through dust in star forming regions more easily than visible light, i.e. it suffers less extinction.

  2. 2)Brown Dwarfs and their disks have temperatures that emit most of their radiation in the near infrared

  3. 3)Some of the infrared portion of the spectrum observed by Spitzer is absorbed in Earth’s atmosphere, and is therefore detectable only from the “vacuum” of space

The technique used to identify disks is to observe the Spectral Energy Distribution (SED) of an astronomical light source in a previously identified star forming cloud, like the one pictured in the above Spitzer Space Telescope image.  For objects devoid of disks, the observed SED is predicted to be approximately a single component black body of temperature, T, similar to the stellar photosphere’s effective temperature.


For objects with disks or dusty envelopes, the SEDs are expected to exhibit a multicomponent SED including the omnipresent, albeit dust-reddened, stellar photosphere, and one or more components from passively irradiated portions of the disk at different temperatures. 


Below is a NASA graphic that demonstrates the concept of a two component SED.  The plot is logarithmic on both axes, a graphical display technique typical in astronomical data presentation.