Beginners’ guide to using the SSON robotic telescopes (to obtain images for comet astrometry and photometry)

 

Updated 2017 June 26

 

Contents

 

1.0. Introduction

 

The British Astronomical Association’s Robotic Telescope Project uses the Sierra Stars Observatory Network’s telescopes located in the USA (Gemini) and Australia (Warrumbungle). BAA members, or members of affiliated, societies may submit projects for approval and, if so approved, 50% of the requested telescope time will be credited to the observer’s SSON account. Application forms may be obtained from http://www.britastro.org/robotscope/images/robotscope-sson.pdf A successful example is shown in Section 5 below.

 

For those wishing to submit observations to the Minor Planet Center the Observatory Codes for the various telescopes are;

 

Telescope

MPC Code

UI Gemini 0.51m

857

Warrumbungle 0.51m

Q65

 

This tutorial works through the planning for, telescope request for and downloading of images of comet 71P/Clark input on 2017 July 24.

 

2.0. Planning

 

2.1. Where am I looking ?

 

The first task is to identify the area of sky visible for the date and time of the planned observation. One of the simplest ways of doing this is to purchase a planisphere for the latitude of the robotic telescope. For Warrumbungle I use a Philip’s planisphere for latitude 35° South. An alternative is to use the sky chart on the Heavens Above website The chart for the above date is shown in Figure 1.

 

Figure 1. Heavens Above chart, North up, for the Warrumbungle location at midnight on 2017 July 24/25

 

2.2. Which comets are available for imaging?

 

Suitable comets can be determined a planetarium program such as Megastar. More options are explained on the Known comets – observations planning tools and methods page

 

2.2.1 Megastar

 

Prior to plotting comet tracks it is advisable to download the latest orbital elements from http://www.minorplanetcenter.net/iau/Ephemerides/Comets/Soft12Cmt.txt

These should be saved in the Megastar folder as comet.txt. In addition to plotting the comet’s track it is advisable to plot that of the Moon to ensure it is not too close (>30º separation is advisable). Figure 3 shows the track of the comet for 5 days starting on 2014 July 24/25 at 0 hrs UT. Comets for a specific location, date and time and faint magnitude limit can also be plotted.

 

Figure 3. Megastar track of comet 71P/Clark (South up)

 

2.2.3 ‘Light pollution’

 

Proximity to the Moon, a planet or a bright star can adversely affect the quality of the images. For the Moon it is advisable to ensure that the comet is at least 30 degrees away and probably the same distance for a bright star or planet. An example is shown In Figure 4 where the comet was separated from Jupiter (mag -1.9) by just less than 7 degrees. Comet 67P is approximately 1/3rd up from the bottom of the image and just to the left of Jupiter’s ‘tail’.

 

0067p_20151113_1226_dymock

Figure 4. Comet 67P close to Jupiter

 

3.0 Imaging

 

3.1 Determining exposure time

 

The exposure time must be set to avoid both trailing and over exposure of the comet. To determine the correct time both the comets nuclear magnitude (m2) and motion must be determined. The nuclear magnitude is obtained from JPL Horizons website which gives both total (T-mag), m1, and nuclear (N-mag), m2 and the motion from the Minor Planet Center Minor Planet and Comet Ephemeris Service.

 

The JPL Horizons input page is shown in Figure 5. The various options are selected by clicking on change for the required line(s).

 

Figure 5. JPL Horizons input.

 

Click Get Ephemeris to get the data shown in Figure 6. The nuclear magnitude (N-mag) is given as 15.3 (approx.).

 

Figure 6. JPL Horizons output for comet 71P

 

On the MPC Minor Planet and Comet Ephemeris Service page enter;

Comet designation – 71P

Ephemeris start date – 2017 06 24

Number of dates to output – 5

Ephemeris interval – 1

Ephemeris units – select days

Observatory code – Q65

Format for elements output – select MPC 8-line

Select Get ephemerides/HTML page to obtain the data shown in Figure 7

 

Figure 7. MPC Minor Planet and comet Ephemeris Service output.

 

From Figure 6 the nuclear magnitude is given as 15.3 and from Figure 7, the motion is approx. 0.5 arcsecs/min. Figure 8 was derived from experience of using the SSON telescopes. When using the Warrumbungle telescope multiply the exposure time obtained from Figure 8 (which is for the Gemini telescope) by a factor of 1.5.

 

The reason for the difference in total mag (m1 for MPC and T-mag for JPL) is under investigation.

 

Figure 8. Exposure times for imaging with the SSON telescopes.

 

The formula for determining the maximum exposure time (Tmax) to avoid trailing is;

Tmax = 60x(image scale in arcsecs/pixel)/(motion in arcsecs/min)

 

For Warrumbungle the image scale is 0.54 arcsecs/pixel and therefore 1.1 binned 2x2 and the Gemini image scale is 0.8 arcsecs/pixel binned 1x1.

 

From Figure 8 the exposure time for a mag 15 comet, to avoid over exposure, is 60x1.5=90 secs for the Warrumbungle telescope and the maximum exposure time to avoid trailing is 60x1.1/0.48=147 secs.

 

To avoid both over exposure and trailing the lesser of the two values is chosen i.e. 90 secs. Several short exposure images can be obtained which limits trailing but improves the Signal to Noise Ratio (SNR).

 

3.2 SSON imaging request

 

Log in on the SSON home page, Figure 9, (having first registered and purchased credits more of which in section 4 below)

 

Figure 9. SSON Home page

 

There are five steps to scheduling a job starting with selecting ‘Create Schedule’;

 

Step 1 Object

- on the Observation Request Form click on ‘Select an Object from the Object Catalog’, Figure 10

            - select ‘Moving Objects’

            - select ‘Moving Objects Catalogue’/Current Comets

            - enter 71P in  the box ‘Enter Asteroid or Comet Name Search Criteria, the click on ‘Go’

            - select comet 71P/Clark from the list (Figure 11). You will be taken back to the Observation Request Form and the selected comet will

   appear in the Object Name box

 

Figure 10. Observation Request Form

 

Figure 11. Stationary and Moving Objects Catalogs (part)

 

Step 2 Title, Figure 12.

            - Enter Title of your choosing and Observer name. In this example, Comet observations and Roger Dymock.

 

Figure 12. Observation Request Form with Title and Observer boxes completed

 

Step 3 Date and Time (optional – I do not use this)

            - if not used then job will run as soon as possible (it is advisable to check the position of the comet and moon if job is not run for several

              days)

            - if used and the job is not run on input time and day then you need to cancel and reschedule the job

 

Step 4 Telescope/Filters, Figure 13

            - select telescope (Warrumbungle 20”)

            - select filter (clear)

            - enter exposure time (90 secs – from magnitude and motion))

            - input number of times to run this series (5)

            - input time delay between series - 10 mins). A delay between images allows time for the comet to, hopefully, move away from any

              interfering star. If the comet is near the horizon perhaps a smaller delay might be appropriate.

 

Figure 13. Telescope/Filters

 

Step 5 Submit,

            - on the Observation Request Form the credits issued and used are listed, Figure 14

            - select ‘Submit Schedule’

            - then Run another job or View Job List

 

Figure 14. Submit form

 

3.3 Confirmation of job

 

Email(s) will be sent to you sent itemising each job and further emails will be sent after each job is run – examples below. It is worth checking the emails to make sure what you have asked for is correctly listed.

 

SSON Job scheduled on Telescope 6; 71P/Clark

User: rogerdymock

Job ID: 45564

Title: Comet observations

Observers: Roger Dymock

Object Name: 71P/Clark

Catalog:     Moving Objects Catalog 

Epoch:

Filters: C

Duration: 90

Time to repeat series: 5

Total Images: 5

Telescope: 6

UTC Date: N/A

You will receive another email when your job is completed.

Thanks for doing business with SSON!

 

You will receive another email when your job is completed.
 

Job 45564 is available in your SSON ftp account

Telescope: 6-Warrumbungle 20"

Job title: Comet observations

Object Name: 71P/Clark

Duration String: 90

Filter String: C

Times To Repeat Series: 5

Please delete files after you download them. We delete images from our ftp server 3 weeks after the date they were created. Thanks for your business.

 

If any images are missing or of poor quality (cloud or trailed for example) immediately advise SSON and the credits used will be refunded (I have never known this not to be the case – feather in SSON’s cap)

 

4.0. Retrieving images

 

Calibrated images are available from Exavault (the account is set up when you register with SSON) as follows;

- log in to Exavault, Figure 15, which takes you to a list of your images available for download, Figure 16. Note that these are earlier images as

  those relating to this example had not been completed when this tutorial was written.

 

Figure 15. Exavault login

 

- select images for download (zip) – the ‘Download All’ button will change to Download Selected if selection is used. With the Chrome browser you have the option of defining the Download location on your PC – presumably other browsers offer the same facility.

 

Figure 16. List of images with those due to be downloaded selected

 

- delete previously downloaded images by selecting and using the Delete button (I recommend downloading before deleting previously

  downloaded images as I have managed to delete the latest ones before downloading them on one occasion).

 

Example images are shown in Section 6 below.

 

4.0 Other SSON facilities

 

4.1. About/Pricing

 

You only pay for imaging time. Rates are shown in Figure 17

            - cost is $100 per hour

            - $1.67 for a 60 sec image

            - approved BAA project 50% therefore $0.83 for a 60 sec image

 

Figure 17. SSON rates

 

4.2. Purchasing time tab

 

Login, select the Purchase Time tab and complete the form, Figure 18.

 

Figure 18. Purchasing Imaging Time on Sierra Stars Telescopes

 

4.3. Account tab

 

This feature shows your credit history and allows you to manage your own credits.

 

4.4. Telescope tab

 

Each telescope and current weather for its location is described under this tab.

 

4.5. About tab

 

How to use SSON telescopes, etc. is described here.

 

5.0. Example project

 

BAA Robotic Telescope Proposal 

 

Name of Project:       Comet outbursts

 

Observer Name:        Roger Dymock

 

Observer Contact Email Address: 

 

Objectives: 

To monitor comets subject to outbursts in order to improve our understanding of such phenomena.

 

Target Object:

Comets were chosen based on those mentioned in Richard Miles’s presentation at the BAA Ordinary meeting held in December 2014 and a subsequent exchange of emails. They are; 17P, 29P, 52P, 174P and C/2012 X1.

 

In addition targets of opportunity as advised, for example, on the Comets mailing list.

 

Planned observations (2014):

17P                  1 Jun – 1 Nov              (23 wks)

29P                  1 Feb – 1 Aug             (27 wks)

52P                  1 Feb – 1 Jul                (23 wks)

174P                1 May – 1 Aug            (14 wks)

C/2012 X1      1 Feb – 1 Mar              (5 wks)

 

Comets to be imaged weekly (weather and Moon permitting).

 

Select Telescope:

0.6-m f/10 (Sierra Stars Observation Network)

Total Observing Time in minutes:

Plan is to obtain 5 unfiltered images during each week each comet is observable. Exposure times will vary (from say 30 secs to 120 secs) depending on brightness (to obtain reasonable SNR) and motion (to prevent trailing of image) of comet. For the purposes of this project 60 sec exposures are assumed.

Estimated subsidised cost to applicant:     

Assuming each comet can be imaged each week during the periods listed above;

5 x 60 sec images per week for 92 weeks = 460 mins

1 minute observing time on the SSON telescope costs $1.67.

460 mins exposure time costs $768.20 = £471.29 at £1 = $1.63 (Exchange rate 2014 January 15)

Cost to applicant = 50% of  £471.19 = £235.64

 

Cost assumes comet can be observed on schedule which is not always possible due to poor weather, moon interference, etc. In such cases additional observations of the listed comets and targets of opportunity may be made on ‘good’ nights. Any unused credits can of course be reclaimed by the BAA.

Use to which the images will be put:

Results (data and images) have been, and will continue to be, sent to;

·         The British Astronomical Association’s Comet Section (comet observations are published in annual reports in the Journal of the BAA and the ‘Comet’s Tail’ newsletter)

  The Comet Observation Database (COBS) at http://www.cobs.si This database logs both CCD and visual observations allowing immediate access to measurements and enabling comparisons between both types to be made.

·         The BAA’s Robotic Telescope Project co-ordinator for publication on the RTP website

·         The Astronomer (Guy Hurst collects the observations and forwards them to Jonathan Shanklin)

·         The Minor Planet Center (Published in Minor Planet Electronic Circulars ‘Observations of comets’ on a regular basis)

·         Spanish Group (published more or less immediately on their website at http://astrosurf.com/cometas-obs/)

 

6.0 Example images

 

Some comets are quite faint, some are bright and sometimes you catch an unusual grouping.

 

0174p_20140628_1004_dymock

 

2012K1_20140428_0728_dymock

 

2009P1_20111029_0301_2_dymock

 

SSSB trio

Contents