March 14, 1997

Hi All--

Here's what I think our plan should be for the March FCRAO observing run.

Our goal is to make a plot like this:

Only, our axes will be straighter, and real data will be involved. Paola and I guessed about which molecules will trace which line width/size regimes, but we should be close.

The first core we'll attack is TMC-1C (see coordinate table at end of this document). We already have a good NH₃ map, and an OH map. The OH probably traces an even lower density (larger scale) than the C¹⁸O, but I didn't draw it in my sketch (sorry!). In the "Maps" section of the notebook, you'll find the map of TMC-1C in N₂H⁺ that Paola made at FCRAO. It was made as a single footprint, observed for 15 minutes, and Paola thinks we should just re-do it, for the sake of convenience & consistency. In the "Proposals" section, you'll find maps of TMC-1C in OH and NH₃, as a figure in the IRAM proposal.

After TMC-1C, I think we should move on to either L1512 or L1251A. L1512 has the advantage of being small and boringly-shaped (round), and Paola's already made a Nyquist sampled N₂H⁺ map of it (see the "Maps" section). L1251A is larger, and we already have N₂H⁺, NH₃, and C¹⁸O maps of it. I guess we should go for L1512 first, since this is officially "Taurus" time, and we can save L1251 for time in April?

With all that information in-hand, I think we should do the following for each core we observe:

1. Do 1 footprint each in C¹⁸O, C¹⁷O, H¹³CO⁺ and N₂H⁺, C³⁴S(2-1) (unless a good map already exists for the map in question) with integration times of 15 minutes/pointing for the "easy" or "medium" tracers and 30 minutes/pointing for the "faint " tracers, according to Paola's estimates below:
2. Evaluate how long it will take to map each of these tracers to the half-power contour, for the cases of Nyquist sampling and beam sampling. The Nyquist sampling is a higher priority for the tracers where the maps seem most compact (see expectations on graph above).
3. Proceed with maps to the half-power contour of each tracer... but--if possible, pick one high-density tracer (e.g. N₂H⁺ or C³⁴S (2-1)) to use to look for the bend in the "Type 4" line width-size relation. (That means we'd have to integrate down to ~10% contour or even lower.)
4. Decide whether to pursue the "Type 4" possibility mentioned above for more than one tracer.

Move on to the next core and do essentially the same thing, taking care not to duplicate tracers already observed (see above).

The N₂H⁺ frequency-switching scheme for a 10 MHz BW is shown here.

Coordinates and offsets to the peak position for all the sources are given in Paola's N₂H⁺ summary table, N2Hplusmaps.ps. Be careful to use the "TMC-1C" entry, and none of it's variants. Same goes for L1251A. The LSR velocities are 5.2 km/s for TMC-1C, ~4 km/s for L1512, and -4.3 km/s for L1251A.

As mentioned above, I've put maps of these sources in the "sources" section of the notebook.

Alyssa