Day 191 Monday 6th October 2014 M83, PGC 724525 and PGC 48132, NGC 2301 and NGC 5457.

 The weather is improving but the Moon is full and there are extremely high winds which make it difficult to observe here in Spain so I have abandoned the possibility for the moment. Hopefully when the Moon has gone the skies will be clear. 

I used the T30 telescope in Siding Spring to take an image of M83(above). This is a 300 second image of one of my favourite objects.

There are a couple of small galaxies visible on this image - here is a close up. There are a couple more that I have yet to identify.

and also used telescope T30 to image the open cluster NGC 2301

I used T11 in New Mexico to take a 600 second image of NGC 5457

Day 190 Sunday 5th October - Problems with Cloud.

Still no observing due to cloud but I need to inform anyone reading this of a different cloud problem.

I originally went for the cloud option offered by Currys but that just slowed my laptop until I could hardly use it (yes another one) and I could not get it to work. I cancelled that and went for a different service.

I now subscribe to JustCloud and went for the "Unlimited" option. Beware anyone thinking of doing this. The service is only unlimited until you hit a "fair usage dynamic limit"!

Then they stop you from adding any content until you subscribe as a business - sorry - home office user!!

Is it me? Am I missing something here?

Can we now legally use words in advertising that can be redefined by small print?

Following my email saying I thought I had the unlimited option - here is their reply. I leave it to you to decide whether it is a good option to use JustCloud - I am going for a personal cloud storage device and cancelling JustCloud.

Hi Len,

Thank you for your email.

I am sorry to inform you that a temporary hold has been placed on your account which will prevent any further backup.

Regrettably this is due to a breach of our terms and conditions and specifically our Fair Usage Policy.

14. Termination and Fair Use Policy

If you have purchased a Just Cloud Product or Service that is inappropriate for your actual usage, Just Cloud may require you to switch to an appropriate Just Cloud Product or Service which may result in your having to pay Just Cloud additional fees for use of the appropriate product or to terminate your purchased Just Cloud Products or Services and refund, on a prorated basis, any fees paid you may have paid on the unused portion of your Just Cloud subscription. We monitor the usage of our heaviest Unlimited account users, a dynamic margin is calculated based upon averages which, should a user fall into, we may require them to cease backup or move onto a business account.

(www.justcloud.com/terms)

---

Put basically, your account has reached our fair usage dynamic limit. This dynamic limit is calculated by taking the average backup space used of our highest users who have uploaded 100mb or less in the last 30 days. Essentially these are Unlimited users who have finished their backup and the bulk of their data, that they chose the Unlimited Plan for, is uploaded. Regrettably your account has exceeded this dynamic limit by 50GB.

I appreciate this will come as an inconvenience, allow me to explain the options available to you as of now:

1) To continue backing up we recommend upgrading to a Just Cloud Home Office plan, you will find this plan suits your backup needs much better as a heavy user. You can view more about what this plan will offer here:www.justcloud.com/business If you choose to upgrade, any funds you have outstanding on your current plan will of course go towards the upgrade, here is the link to make the upgrade: http://secure.justcloud.com/bizupgrade
2) If you do not wish to backup anything further you can continue on your current plan and access your backed up files as normal.
3) If you wish to delete some files and folders to free up space this will remove the temporary hold.
4) If you want to cancel the account we will issue a pro rata refund for the unused time on the account.

I thank you in advance for your co-operation on this matter. Please let me know how you wish to proceed. 

Kind regards,

Lauren Pollock
Tier 1 Technical Support
JustCloud
http://www.justcloud.com

Day 189 Saturday 4th October 2014 Effects of the lightning strike

I spent the day assessing the damage from the lightning strike. 

The laptop that I used to control all of the equipment had stopped communicating. The ports were dead. I was able to charge it by using the charger from the charger for my other laptop although the plug only fitted loosely - but it did the job. It had a higher current rating than the "dead" charger 

I set the laptop to rebot in safe mode to see if I could see what the problem was. When it rebooted it went through a text sequence on the screen asking me if I wanted to open windows normally, with networking or in safe mode. Whichever option I choose it goes into safe mode and the screen goes black. Going into "safe" mode killed the laptop completely - I cannot use it. Checking the internet for black screen solutions convinced me that you are getting advice in most cases from people who have no idea about computers at all. Going to Microsoft puts you into looped problem solving that has never worked once for me.  Another laptop death I think! I always store data on an external drive and have most of the laptop content stored on my cloud service.

I spent quite a while setting up the other laptop with drivers for the various bits of kit and also changed to my other 30m powered cable that I normally use with my CGEM and Canon 40D. 

At the end of the day:

The telescope is fine - I can connect and control it 

The camera and filter wheel are fine - I can connect and take images.

The focuser will not connect. I have set up ASCOM and the TCF-Si drivers but I can only see as far as the USB to Serial Cable - the software cannot detect the focuser as though it is not there.

There has not been a single clear night recently although the days have improved.

I suspect that the input circuits to the focuser have been damaged by the lightning. This is an excellent piece of kit that is also very expensive and needs to be ordered from the US. Just in case it is a driver problem I have contacted the US manufacturer and am waiting for a reply. If it does not work I do have a manual Crayford focuser that I will need to use instead.

Day 188 Friday 3rd October Lightning strike. Is my equipment damaged?

This is the first day when it appears that we will not be having storms or lightning. On Monday during one of the many lightning storms I was having dinner at about 8pm and there was an extremely loud crack that made me jump about a foot out of my chair - it sounded as though the lightning had struck within the room. All the power in the house went out.

Today - with the possibility of a clear night I tried to set up the equipment ready to observe, The telescope switched on fine - responding to the hand controller as usual and slewing to home with 2 button presses as normal.

Back at the computer in the house however it was a different matter - when I plugged in the USB cable to the port - I did not get the usual bing-bong. I tried my wireless mouse - no bing-bong. None of the ports were working. I googled the problem as usual finding a range of solutions none of which worked. Then the laptop told me that it was low on power and switched itself off - even though it was plugged in. I soon realised that the power supply had failed. I tested the powered USB cable to the telescope on my other laptop - and saw that it was not working. A strange coincidence of three failures at the same time. Maybe not - I think the lightning "strike" caused a surge which blew the laptop power supply and the 30m powered cable  connected to its own electronics and to the laptop ports causing them to blow. I think the telescope , camera and focuser which all connect to that same powered cable through a hub are OK but will not know until I set the sotfware and drivers up on my other laptop - tomorrow's job. I think somebody up there is not in favour of me discovering a supernova!! Maybe I am missing a simpler solution but have not spotted it yet.

Day 187 Thursday 2nd October 2014 Cepheid Variable CF Cas Calculation of its apparent Magnitude and Colour Inde

NGC 7790 contains three Cepheid Variables as shown in the AAVSO Chart. CE Cas A and B are variable elements of the same double star and very close so not within my equipment's ability to separate them to measure their magnitude. This paper "CE Cas a, CE Cas b, and CF Cas in NGC 7790" by J. Smak in 1966 looked at all three variables. This paper followed by Allan Sandage et al. in 1969.

This is my image in VPhot with the target, comparison and check stars shown and an expanded view of CF Cas

 This is the result of the untransformed photometry

 

 I repeated the photometry with the B image of NGC 7790 and obtained a B magnitude of B = 11.598

So B - V = 0.409.

I will continue with this star in future blogs.

Day 186 Wednesday 1st October 2014 Transforming the QX Cas photometry.

Back to the variable star QX Cas in the open cluster NGC 7790 from Monday. I now need to transform Monday's result. For that I need to look also at the image taken through a B filter.

 Here are the results

So using these results and the previous V filter values from Monday in an Excel spreadsheet 

I get the transformed value of V = 10.201

The Variable Star Reference Index has the following data concerning QX Cas

My tests this week of photometry of variable stars are based on single images, I need to use multiple images in practice for values that would be submitted to the AAVSO or the BAA Variable Star Section. I also need to ensure comprehensive reduction and a careful choice of comparison stars.

Day 185 Tuesday 30th September 2014 Photometry of LP Cam in NGC 1502

I used telescope T21 in New Mexico to take B and V images of the open cluster NGC 1502. The images were 90 second exposures. [I intend to transform the measured magnitude of a variable star in the field so I needed V and B images to be able to apply the transformation coefficients that are supplied by itelescope.com.]

This is the cluster using a B filter

 This is the cluster using a V filter

 

This is the V image of NGC 1502 loaded into VPhot. 

 I aim to obtain the current magnitude of the variable star LP Cam and have designated a comparison star and check star as shown. BD+61 675 is the comparison star which has a V magnitude of 9.62 and Tycho 4068:1471 is the check star with a V magnitude of 11.15 from the Tycho catalogue. 

The comparison star had some close neighbours - this is how I positioned the annuli. The central circle takes in just the star and the nearby stars are all positioned in the gap. The outer annulus only includes sky background which is subtracted from the signal in the inner circle (based on the same sky signal per pixel) to give just the flux from the star. The central circle is the same radius of 10 pixels (essential that they are the same) as the other two stars concerned but the outer annulus varies as shown - the scale is different for each image with a common 10 pixel central circle radius.

   

This is the photometry report

So the untransformed V magnitude of the target is 11.168

Day 184 Monday 29th September 2014 QX Cas is suspected of ceasing its variability - I investigate by measuring its current magnitude.

Cloudy weather continues - no observing so I am continuing with the photometry work from yesterday.

Having obtained Transformation Coefficients for my photometry I need to go through the process of applying these to a photometric measurement which I will do today and the transformation later in the week.

 The cluster that I used in yesterday's calculations include a variable star QX Cas. I will use this as a trial of my setup. Here it is on the image of NGC 7790. I downloaded its position from the General Catalogue of Variable Stars (GCVS) within VPhot on the AAVSO site. 

I need a comparison star and a check star so I downloaded the set of comparison stars for this field from VPhot and specified one as the comparison star (blue) and set one to be the check star (red).

The signal and sky circles need to be adjusted to avoid interfering stars as much as possible. This is the result once the aperture, gap and sky annulus have been set.

This is a close up of QX Cas showing pixel values representing the number of photons hitting each pixel within the 30 second exposure time. The numbers on the right show how the pixel values are counted.

 The number of pixels representing the star is 97 - this includes the pixels in the red "ring".

The total pixel value count is 258671 plus 6573 from the ring giving a total value of 265244. 

VPhot does this calculation for you - you don't need to count the pixels and value as I have done - just this once!

VPhot does a similar calculation for the pixels in the sky (outer ring) annulus and summarises all of this in a table as below.

 

 The Sky Annulus statistics give a median value of 192 counts (ADU) for each pixel in the annulus. 

This is used to estimate the sky background count within the aperture.

Sky background = number of pixels in aperture X median sky count = 97 X 192 = 18624

This has to be subtracted from the aperture count to give the star count.

Star (signal) count = 265244 - 18624 = 246620 = I representing Intensity.

The simple process above is often represented as an equation

which makes it seem more complex than it is!!

 So this represents how much light  the star collected in 30 seconds but has to be represented as a magnitude.

The instrumental magnitude m is given by I = - 2.5Log (I/t)

where t is the exposure time in seconds

Dividing I by t gives 246620/30 = 8220.67

Getting the log (base 10) of this gives 3.91491

and multipling by -2.5 gives -9.873 which is the instrumental V magnitude of QX Cas

I see that this corresponds to the IM in the table - thank goodness!

So QX Cas has an IM of -9.873 but this needs to be compared with the I of the comparison star

VPhot calculates a figure of -7.866

The difference in magnitudes is -1.917 

The given V magnitude of the comparison star is 12.117 

The difference in magnitude is added to this to give the measured magnitude of QX Cas which is 10.200

The check star has a given magnitude of 12.452. It was measured at 12.449 - near enough to confirm a good result for QX Cas.

The 10.2 value for QX Cas is untransformed so different equipment could give a different result.

QX Cas is an eclipsing binary and has a period of about 6 days and varies in magnitude between 10.19 at brightest to 10.7 acording to the general documentation  - but this paper informs me that it no longer has eclipses probably caused by a tertiary companion changing its orbital inclination.The value I obtained is the maximum brightness quoted which would be the permanent magnitude if eclipses have ceased in which case it is no longer a variable star.

Arne Henden the top variable star expert had this to say recently about QX Cas:

"That time of year (late September) is good for Cygnus and Cassiopeia.  I like QX Cas, up near NGC 7790.  It is a 10th magnitude blue binary.  In the 1960's, it had a 0.5mag eclipse, but there is a third body in the system and for several decades, no hint of an eclipse has been present.  However, I'd like to get a good light curve about once/year to keep an eye on the system - if the eclipses went away, then they should be back some day!  That would be a simple target to do.  With enough field to cover NGC7790, you also pick up several other variables for free, such as the cepheid variable CF Cas, so even if QX Cas is constant, you have plenty of other things to analyze.

QX Cas has a 6-day period; the NGC7790 cepheids are around 5 days; there are some delta scuti stars in the cluster with periods of a few hours.  So any cadence works.  If you picked a cadence that was optimal for the binary, then the usual rule of thumb is about 100 points per cycle, or an observation every 1.4 hours - that is, you don't have to sit on the field.  However, it sounded like you wanted to set your telescope up and leave it alone, in which case a higher cadence won't hurt (and resolves other variables in the same field).

The problem with a 6d period is that it is impossible to see the daylight half of the light curve.  You have to wait until the 0.00471d builds up to 0.471 days, or about 100 cycles (600 days).  So you can cover one half of the light curve really good this year, and then wait until next year to cover the other half (or find a friend in China to get the other half of the light curve now!).  So it is a good background project - get 6 night's worth of photometry and call it good for the year.

Yes, the objective is to catch an eclipse.  If the eclipse "season" is just starting, the depth may be very shallow, so high precision is the rule - which is one reason why you might want higher cadence and then average several datasets together.

For objects like QX Cas, where an eclipse has not been seen in 50 years, don't trust any ephemeris.  However, for most binary stars, a good rule of thumb is that the eclipse takes about 1/10 of the period; your 13 hours matches the 0.6days from that guideline, and so it would only take one more observer and 6 consecutive clear nights to cover enough of the cycle to rule out any eclipse."

There are three Cepheid Variables in NGC 7790 so I intend to have a look at these when time permits!

Day 183 Sunday 28th September 2014. Using NGC 7790 images to find Transform values for my photometry setup

Still bad weather - cloudy - no observing today.

The negative V image of NGC 7790 (taken last Tuesday on my C14) uploaded to VPhot is shown below

There is a standard chart for this field

These standard V stars are superimposed on the VPhot negative image

Getting a photometric solution with no target will list all of the stars circled in terms of their instrumental V magnitudes. The red magnitude values can be ignored. The signal to noise ratio is significant. The Air Mass indicates how high the object is in the sky - the lower the better.

 

 
 

 

 Without going into the details the same process is used for the B image producing a table of B instrumental magnitudes for the same stars.

I used Excel to produce graphs as follows based on the data from the B and V lists of instrumental magnitudes.I did not use all of the stars and excluded those with lower signal to noise ratios.

 I produced the graph on the left (above) from the instrumental magnitudes determined from my B and V images and the standard B and V magnitudes for the stars. Plotting b-v against B-V shows the difference between standard values and values that my equipment will produce, allowing a "fiddle factor", sorry Transformation Coefficient to be introduced in future photometric measurements, The graph on the right is produced automatically by a downloadable AAVSO programme based on my results. The Transform Coefficient Tbv which is the inverse slope of the graph is 1.067.

 

 These charts show how the measured b and B values differ depending upon the colour of the star - the slope of the graph providing another correcting factor - thus one is called Tb and has a value of 0.099 for my equipment. If there was no change with colour then the line would be horizontal.

Similarly for Tv giving a value of 0.025 for my photometric arrangement.

Comet Siding Spring, Photometry references and NGC 7790 images for determining Transforms.

It is wet in Spain so I used T30 (at Siding Spring) in Australia today to image Comet Siding Spring.

On Tuesday last I imaged NGC 7790 which is one of the recommended star clusters for identifying the transformation coefficents for photometry specific to a telescope and photometric system. I have a number of references for photometry and variable stars being a member of the BAA Variable Star Section , the AAVSO and have the following books as references:

1. A Practical Guide to Lightcurve Photometry and Analysis by Brian D. Warner - you need to be careful there are two Brian Warners - both involved in photometry! (Neither is Marilyn Manson who is actually another Brian Warner) Published by Springer 2006

Brian has made a You Tube video explaining what he does.

2. David Levy's Guide to Variable Stars.  David Levy 2005 Published by Cambridge University Press

I attended a talk by David some years ago which was very well received - this video is about him.

3. Understanding Variable Stars John R. Percy 2007 Cambridge University Press

Last year he won the AAVSO Education Prize.

4.  Observing Variable Stars, Novae and Supernovae. Gerald North 2004 Cambridge University Press.

I came across this ebook by Gerald - I have the real thing in my astronomy library somewhere!

Back to NGC 7790. Here are the B and V images I obtained with my C14+SBIG

 

To be continued...