Planning, Scheduling and Running an Experiment. Aletha de Witt AVN-Newton Fund/DARA 2018 Observational & Technical Training HartRAO

Transcription

1 Planning, Scheduling and Running an Experiment Aletha de Witt AVN-Newton Fund/DARA 2018 Observational & Technical Training HartRAO.

2 Planning & Scheduling observations Science Goal - You want to observe some object/s in the radio You have developed some scientific goal/s - astronomy (continuum/spectral line/astrometry/pulsar timing ) - astrometry & geodesy - something else. Target source/s & instruments - You have a target source/s - what is the best instrument to use - single-dish - connected array - VLBI Calibrator / Reference sources

3 Planning & Scheduling observations e.g. an AGN source Timing resolution: - Single-dish telescopes in general do not spatially resolve the radio source and so provide a measure of the total radio flux density. - Radio telescopes are able to monitor both rapid flares and slow changes in flux Very high spatial resolution: - Very Long Baseline Interferometry (VLBI) provides the highest angular resolution possible of any observational technique => often better than milliarcseconds. - VLBI monitoring provides the only direct measure of relativistic motion in AGN jets. - VLBI makes identification of the location and extend of emission regions possible at a level of detail not available with any other observational technique.

4 Planning & Scheduling observations

5 NGC5128 / Centaurus A PKS Planning & Scheduling observations

6 Example: Target source Radio Galaxy 3C 120: The jet in radio galaxy 3C 120. Units of RA and Dec are milli-arcsec. (Ref: More examples: Mike Garret Lecture notes media=radio_astronomy_course_description:sensitivityv2.pdf

7 Science goal Map the jet structure for comparison with earlier epochs of data at 15 GHz. In order to have decent uv coverage, you decide on 8 hrs of on source time. What peak signal to noise can you reach? The peak flux is Jy, as given in the figure.

8 Instrument Don t forget to take into account: - Resolution - Frequency/bandwidth to use - Sensitivity needed (bandwidth + time, use exposure time calculators) - Observability - Instrument configuration

9 Instrument Don t forget to take into account: - Resolution - Frequency/bandwidth to use - Sensitivity needed (bandwidth + time, use exposure time calculators) - Observability - Instrument configuration

10 Instrument

11 Resolution Angular Resolution θ = 1.22 λ/d -> D = longest baseline Largest Angular Scale θ = 1.22 λ/d -> D =shortest baseline. The size of the source means that VLBI is necessary to resolve the structure of the jet. Therefore either e-merlin or the VLBA should be used

12 Frequency The VLBA has a receiver for 15 GHz while e-merlin does not, therefore the VLBA is the correct instrument.

13 Sensitivity B = 2h 3 c 2 1 e h /kt 1 [W m 2 Hz 1 sr 1 ] T sys = T Bcmb + T A + T at + T wv + T g + T R [K] h << kt, B = 2kT 2 [W m 2 Hz 1 sr 1 ] T B = B 2 /2k [K] S = 2kT s 2 [W m 2 Hz 2 ]

14 Sensitivity B = 2h 3 c 2 1 e h /kt 1 [W m 2 Hz 1 sr 1 ] T sys = T Bcmb + T A + T at + T wv + T g + T R [K] h << kt, B = 2kT 2 [W m 2 Hz 1 sr 1 ] T B = B 2 /2k [K] S = 2kT s 2 [W m 2 Hz 2 ]

15 HartRAO 26m Telescope Technical details:

16 Sensitivity

17 Observability

18 Observability

19 Observability

20 Planning & Scheduling observations Writing a proposal - Making a schedule - Sched, Sked, VieVS

21 Planning & Scheduling observations Example from Michael: supernova SN2014C for 2016 Oct Nov GHz observations of supernova SN2014C - Our goals were to measure the expansion velocity - and see structure (shell?) of SN2014c - Supernova was about 20 mjy (we knew this from VLA observations) - It was ~2.5 yr old, and we expected it to be about 1~2 mas across. - We also wanted astrometry, we want to see whether it is symmetric - 8 hours gave us good SNR and UV-coverage as well - Wanted both resolution + sensitivity (not that bright)

22 Planning & Scheduling observations Observed (with VLBA + EF + Y27): - fringe-finder (very strong, compact source) - calibrator - SN2014C at 8.4 GHz (nod back & forth many times) We also observed sometimes a second calibrator, to have a check on the astrometry, since the calibrator might appear to move a bit Examples of schedules files (e.g. vex file)

23 Geodetic & Astrometric Programmes IVS homepage (geodesy & astrometry)

24 Planning & Scheduling observations Student Reports - notes - Follow the guidelines - Plagiarism - copy/paste - Grammar, spelling mistakes (e.g. a name in capital letters) - If unsure use short sentences - Logical flow or poor logical coherence, overview and summary or conclusion - Paragraphs - Use of non-scientific language - Abbreviations not explained e.g. African VLBI Network (AVN) - Figure captions and image credit - Incorrect statements - Misleading statements e.g. it was believed vs it may be possible - Topic or subject - text must be relevant - Ordering of dates or events - Do not repeat sentences - repeat ideas if they are important - Vague - e.g. higher than standard. what is standard

25 Planning & Scheduling observations Student Reports - notes - References and referencing Wrong reference, Reference not in text or vice versa Reference detail incorrect Website links instead of reference Reference style inconsistent Non-relevant references Stay on topic - you only have 2 pages!! sell your idea/s make it interesting and to the point use references remember that the reviewer may not be an expert on the topic! Winning statement!

26 Thank You Contact Details Aletha de Witt Image credit: Ani Vermeulen, NASSP student 2014