Blog Post 30, WS 9.2, Introduction to the Radio Lab

In the coming weeks, AY17 will be using the millimeter-wave telescope at the Harvard College Observatory to observe the velocities of Giant Molecular Clouds (GMC's) throughout our galaxy.

GMC's are large clusters of Gas and Dust in our galaxy that bit the galactic center (just like everything else).  They are uniquely suited to our lab objective because they emit light in the Radio spectrum due to emissions from Carbon Monoxide molecules.  This frequency (115.271 GHz) is a very convenient frequency because it is much higher than radio stations and telecommunications, but not high enough to be affected by infrared radiation or visible light.  Thus, we can observe during the day.

Our ultimate goal with the lab is to determine a rotation curve for the Milky Way galaxy.  We we do this using the following method:

We will observe a series of clusters along a similar line of sight.  By measuring the doppler shift in their emission lines, we will determine their velocities.  In doing so, we will be able to have data for orbital velocities of a range of objects in the Milky Way, allowing us to create a rotation curve.

A few quick questions and answers for the lab:

- What is going to be the typical integration time per point? 

To achieve a SNR of 10 or more, we will need o do some math.

\[\tau=\frac{SNR^2 T_{sys}^2}{T_A^2 \Delta \nu}=\frac{10^2 \times (500K)^2}{(3K)^2 \times 0.5 MHz}=\boxed{5.6 sec}\]

- Over what range of longitude do you plan to observe? The Lab Handout claims that we will observe in the Gallatic longitude range of 10 degrees to 70 degrees, although most of our targets will be in a similar line of sight.

- How many (l,b) positions do you plan to observe? We have 4 targets, so we will observe at 4 positions.

- Will all your target positions be above 30° when you plan to observe them? Since we are observing around noon, our targets will be visible.

- At what LST are you going to start observing? At what EST? We are going to be observing around 12:00 Noon EST, and about 15:30 LST.

- Are you going to position switch or frequency switch to “flat field” the spectrum?

To flat field, we will position switch the spectrum because a frequency switch would cause us to get a flat field for the wrong observational wavelength.